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OPENPediatrics Pediatric Ventilator SimulatorKnowledge Guide

Last Updated May 1, 2020

Table of Contents Background and Setup Individual Settings Asessing Adequacy of Mechanical Ventilation Waveforms Patient Monitoring Ventilator Management and Troubleshooting Inhaled Nitric Oxide COVID-19 Considerations Adult Considerations References and Resources

Pediatric Mechanical Ventilator Knowledge Guide 1

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OPENPEDIATRICS TM

Pediatric Mechanical Ventilator Knowledge Guide 2OPENPEDIATRICS TM

Background and SetupIndications for Mechanical Ventilation

Mechanical ventilation is indicated in those patients who have one or more of the following conditions:• An inability to oxygenate effectively• An inability to ventilate effectively• An inability to protect their airway

These indications may occur as a result of many different underlying diseases, such as pneumonia, bronchiolitis, asthma, apnea, seizure, encephalitis, airway abnormalities, and many others.

Inadequate oxygenation

Hypoxemic respiratory failure occurs as a result of impaired gas exchange and may be the result of many diseases including pneumonia, bronchiolitis, congestive heart failure, asthma, cystic fibrosis, interstitial lung disease, pulmonary fibrosis, and many others. In some diseases such as pneumonia or congestive heart failure, the alveoli may become filled with pus and/or fluid, limiting their ability to effectively exchange oxygen. Additionally, in certain diseases such as pneumonia, areas of lungs may be collapsed or under-recruited, causing ventilation-perfusion mismatching, impairing the ability of these areas to exchange oxygen effectively.

Hypoxemic respiratory failure is manifested as decreased arterial partial pressure of oxygen (PaO2). This is typically defined as:

• PaO2 of less than 60 mmHg (8 kPa)• Oxygenation Index (OI) > 4. OI = (Fraction of Inspired Oxygen (FiO2) x Mean Airway Pressure x

100) / PaO2• PaO2 / FiO2 (PF) ratio < 300

Often, hypoxemic respiratory failure can be treated with oxygen or non-invasive ventilation. However, severe hypoxemic respiratory failure, as in pediatric acute respiratory distress syndrome (PARDS), most often requires invasive mechanical ventilation. Hypoxemia is a major immediate threat to proper organ function and should be treated aggressively.

Inadequate ventilation

Hypercapnic respiratory failure is defined as an elevated partial pressure of CO2 in the arterial blood (PaCO2). The respiratory muscles, chest wall, and the respiratory centers of the brain comprise the respiratory pump. The pump is responsible for maintaining adequate alveolar ventilation and regulating PaCO2. A failure of one or more of these components results in ventilatory failure (PaCO2 > 55 mmHg or 7.3 kPa).

Hypercarbia may occur either because of lung diseases or as a result of neurological, metabolic, or muscular diseases. Lung diseases such as pneumonia, bronchiolitis, or asthma cause inadequate gas exchange resulting in accumulation of CO2 in the blood. Neurological, metabolic or muscular


Ventilation

Ventilation is the process of moving air between the environment and the lungs through inhalation and exhalation. Adequacy of ventilation is measured non-invasively by End Tidal Carbon Dioxide (EtCO2) analysis or invasively by ABG analysis (PaCO2). Minute ventilation is equal to the tidal volume x respiratory rate per minute.

The ventilator can influence ventilation in two primary ways:

1. Varying the tidal volume (Vt) delivered to the patient, which can be either directly set (as in volume controlled ventilation) or measured as a result of the set pressure and lung compliance (as in pressure controlled ventilation)

2. Varying the breath rate

To adjust ventilation on the ventilator, set or adjust the tidal volume to the goal range for the patient, and then once in goal range, adjust the breath rate.

diseases, such as seizures, spinal muscular atrophy, or encephalitis, may cause hypercarbia through an impaired respiratory drive and/or muscular effort, limiting the ability of a patient to generate an adequate respiratory rate and/or tidal volume.

Inability to protect airway

The lower respiratory tract is normally protected from foreign body and fluid aspiration through the intact functioning of the airway reflexes and epiglottis. Some conditions impair function and put the lower airways at risk for injury due to aspiration of oral or gastric contents.

Patients with diseases such as encephalitis, meningitis, intractable seizures, head trauma, brain injury, or diseases causing a Glasgow Coma Score < 8 may be at risk for aspiration, and endotracheal intubation and mechanical ventilation may be required in some of these patients. The use of a cuffed endotracheal tube is recommended to decrease risk of aspiration during mechanical ventilation.

Oxygenation

Oxygenation refers to the process of adding oxygen to the body. Adequacy of oxygenation is measured non-invasively by pulse oximetry measurement (SpO2) or invasively by ABG analysis (PaO2).

The ventilator can influence oxygenation in two primary ways:

1. Varying the amount of oxygen delivered to the patient (FiO2)2. Varying the amount of pressure delivered to the patient which influences alveolar recruitment

(Positive End Expiratory Pressure or PEEP, and Mean Airway Pressure or MAP).

Oxygen in high concentrations can lead to toxicity, and therefore, the goal FiO2 is ≤ 0.3. If a patient requires an FiO2 > 0.3, increasing PEEP and MAP should be considered.


Ventilation

Ventilation is the process of moving air between the environment and the lungs through inhalation and exhalation. Adequacy of ventilation is measured non-invasively by End Tidal Carbon Dioxide (EtCO2) analysis or invasively by ABG analysis (PaCO2). Minute ventilation is equal to the tidal volume x respiratory rate per minute.

The ventilator can influence ventilation in two primary ways:

1. Varying the tidal volume (Vt) delivered to the patient, which can be either directly set (as in volume controlled ventilation) or measured as a result of the set pressure and lung compliance (as in pressure controlled ventilation)

2. Varying the breath rate

To adjust ventilation on the ventilator, set or adjust the tidal volume to the goal range for the patient, and then once in goal range, adjust the breath rate.

Ventilator Device

Prior to using a ventilator, the clinician must ensure that all ventilator components are clean, connected appropriately, and properly functioning.

Gas Source

Most ventilators require highly pressurized oxygen and air sources, typically piped in the wall at fifty pounds per square inch (psi). Some ventilators have air compressors or turbines that don’t require a highly pressurized air source but still require oxygen. An example is the LTV® Ventilator, which is turbine driven, and therefore does not require highly pressurized gas sources. However, an oxygen source is required in order to titrate and deliver an appropriate FiO2.

Power Source

Most modern ventilators are computer-controlled and require electricity to function. They are plugged into a standard electrical outlet. Some (especially older) ventilators are pneumatically powered, and therefore do not require electricity. However, the functionality, especially monitoring, of these ventilators is greatly diminished. Most modern ventilators have batteries that can maintain functionality of the ventilator for 30-90 minutes in the event of a power failure or transport.

Humidifier

Normally, the upper airways (nasal passages, nasopharynx, and larynx) serve to properly condition inhaled gases through filtering, heating and humidifying. Small particles of dust and other particles are filtered and removed from the inhaled breath by hair and the mucociliary system. The air is then heated to body temperature (37°C) and humidified to 100% relative humidity prior to reaching the alveoli in the lungs.


When the upper airways are bypassed, as in endotracheal intubation, inhaled gases must be externally heated and humidified to prevent the airways from drying out and impairing the function of the mucociliary system. The active humidifier on the ventilator provides both heat and humidification of inhaled gases.

Dead Space

Dead space is the inhaled volume that is not involved in gas exchange. Normally, the conducting airways (nasal passages to mainstem bronchi) comprise the majority of dead space volume. Alveoli that are ventilated but do not participate in gas exchange (ventilation without perfusion) also contribute to dead space. Normal dead space volume to tidal volume (Vd/Vt) ratio is 1:2 (or about 20-40%).

When a patient is intubated and mechanically ventilated, the Vd/Vt is affected not only by the conducting airways, but by airway equipment (such as the endotracheal tube (ETT), end tidal CO2 monitoring device, suction catheter, or any other adapter that is located between the ventilator circuit wye and the airway). Conditions such as ARDS, where significant ventilation-perfusion mismatching occurs, are typically associated with a high Vd/Vt.

Pediatric Ventilator Circuit

A ventilator circuit directs inhaled gas from the ventilator to the patient (inspiratory limb), and exhaled gas from the patient to the ventilator (expiratory limb). The ventilator measures the volume and flow of gas entering and leaving the patient’s lungs. The humidifier is attached to the inspiratory limb, and an end-tidal carbon dioxide (EtCO2) detection device may be attached between the ventilator circuit ‘wye’ and the endotracheal tube. Inhaled medications are given through the inspiratory limb. Suctioning is performed directly at the endotracheal tube, at the junction of the inspiratory and expiratory limbs (wye). If there are any leaks in or discontinuity of the ventilator circuit, the ventilator will alert the user through a low pressure alarm.

A pediatric ventilator circuit is smaller in diameter compared to an adult circuit. The more rigid, less compliant circuit tubing decreases compressible volume loss, which otherwise can contribute to the ventilator providing inaccurate volume measurements for infant and pediatric patients.

Patient Size Selection

Most ventilators require the selection of patient size based on the ventilator itself as well as which ventilator circuit is selected. For the purposes of this simulator, we will use the following criteria for patient selection:

• < 5 kg: neonatal• 5-20 kg: pediatric• > 20 kg: adult

Gas Exchange Goals for Healthy Lungs

Patients may be intubated and mechanically ventilated for non-respiratory diseases such as stroke or recovery from surgical procedures. These patients often do not have significant lung disease,


and have relatively good lung compliance. Oxygenation and ventilation goals for these patients are similar to non-intubated healthy individuals.

Goal Tidal Volume (Vt)

Goal tidal volume (Vt) is 5-8 mL/kg for the patient’s ideal body weight (IBW).

Goal pH

Goal pH is 7.35-7.45. Once Vt is in goal, adjust the respiratory rate (RR) as necessary to achieve the goal pH.

Goal PaCO2

Goal PaCO2 is 35-45 mmHg (4.7-6 kPa).

Goal SpO2

Goal SpO2 is > 92% and PaO2 is > 80 mmHg (10.7 kPa). PaO2 is often much higher than this in healthy lungs. As hyperoxia is harmful, the FiO2 and/or PEEP should be weaned as able to minimize oxygen toxicity.

Spontaneous Breathing

Permit spontaneous breathing when possible. This can be accomplished with partial support (Pressure or Volume Synchronized Intermittent Mandatory Ventilation (SIMV) with low mandatory breath rate), or Pressure Support Ventilation (PSV) to promote conditioning of the diaphragm.

Ventilator Settings

Typical ventilator settings for adults with healthy lungs include the following:• Tidal Volume: 5-8 mL/kg• Plateau Pressure: < 30 cmH2O• PEEP: 5-7 cmH2O• FiO2: <0.5• Breath Rate: 12-30 bpm• Inspiratory Time: 0.8-1.4 sec• Trigger Sensitivity: 0.8-3 L/min

Gas Exchange Goals for PARDS

PARDS is defined as hypoxemia and chest imaging findings of new infiltrate(s) consistent with acute pulmonary parenchymal disease, that develop within seven days of a known clinical insult that could cause PARDS, and are not fully explained by cardiac failure or fluid overload.


Goal Vt is 3-6 mL/kg IBW. Low Vt and low pressures minimize harmful stretch injury (volutrauma and barotrauma).


Goal Plateau Pressure

Aim to keep plateau pressure < 28 cmH2O, but slightly higher plateau pressures may be necessary in patients with decreased chest wall compliance (i.e. patients with obesity).

Goal pH

Goal pH is 7.15-7.30 for moderate-severe PARDS. In mild PARDS, more normal gas exchange may be targeted with a goal of 7.25-7.35.

Goal PaCO2

PaCO2 is allowed to rise (permissive hypercapnia) and titrated based on goal pH. This minimizes volutrauma and barotrauma associated with high ventilator pressures and volumes. If Vt is in goal range, titrate breath rate as necessary to achieve goal pH.

Exceptions to permissive hypercapnia and acidosis include intracranial hypertension, severe pulmonary hypertension, cardiovascular instability, severe ventricular dysfunction, and some congenital heart defects. The use of bicarbonate supplementation is not routinely recommended.

Goal SpO2

Goal SpO2 is 92-97% for patients with mild PARDS with PEEP < 10 cmH2O.Goal SpO2 is 88-92% for patients with moderate-severe PARDS with PEEP > 10 cmH2O.Goal FiO2 is ≤ 0.3. If FiO2 > 0.3 is required, consider incremental increase of PEEP to improve lung recruitment. For patients requiring very high PEEP, FiO2 may need to be > 0.3.


Permit spontaneous breathing when appropriate. Patients with PARDS are often unstable and may not tolerate spontaneous breathing in the acute/early phase of the disease. As the patient begins to recover, spontaneous breathing should be encouraged which can improve the distribution of ventilation throughout the lung fields and promote diaphragm conditioning.

Gas Exchange Goals for Neurological Conditions

Patients may be intubated and mechanically ventilated for neurological diseases such as traumatic brain injury. These patients often do not have significant lung disease, and have relatively good lung compliance. However, they often require tight control of PaCO2 to prevent increased cerebral blood flow and edema, as increased PaCO2 can lead to cerebral vasodilation. It is also important to ensure good oxygenation to prevent secondary hypoxic brain injury.


Goal tidal volume (Vt) is 5-8 mL/kg for the patient’s ideal body weight (IBW). If in pressure control mode, adjust the peak pressure (Ppeak) as necessary to achieve this volume range. Ppeak is usually 20-25 cmH2O or less. Low pulmonary pressures will help facilitate adequate cerebral drainage.


Goal pH

Goal pH is 7.35-7.40. Once Vt is in goal, adjust the respiratory rate (RR) as necessary to achieve the goal pH.

Goal PaCO2

Goal PaCO2 is 35-40 mmHg (4.7-5.3 kPa). If a patient is acutely herniating, targeting a PaCO2 of 30 mmHg (4 kPa) may be warranted while initiating definitive treatment.

Goal SpO2

Goal SpO2 is 92-99% to prevent secondary hypoxic injury and minimize risk of oxygen toxicity.

Modes of Ventilation

Most ventilators have a variety of modes from which the clinician must choose to be applied to his or her patients. It is the clinician’s responsibility to choose the most appropriate mode for individual patients. This is often determined by the size and condition of the patient. A mode is characterized by control, phase, and conditional variables. Pressure control ventilation is an example of a ventilator mode during which inspiratory pressure is controlled. This means that tidal volume becomes variable and will depend on the patient’s respiratory system compliance, airway resistance, and spontaneous effort.

Many ventilator modes share common set parameters such as positive end-expiratory pressure (PEEP), respiratory rate, and FiO2. Other set parameters will vary depending on the specified mode.

Mode

Pressure Control Ventilation (PCV)

PCV delivers a clinician-determined inspiratory pressure: peak pressure (Ppeak) for a fixed period of time (inspiratory time) at a predetermined frequency (breath rate). Tidal volume and inspiratory flow are variable in pressure control and will vary depending upon respiratory system compliance, airway resistance and patient respiratory effort. There are different forms of PCV. The primary difference results from how spontaneous respiratory efforts are incorporated into the mode (please see Assist Control and Synchronized Intermittent Mandatory Ventilation below).

Volume Control Ventilation (VCV)

VCV delivers a predetermined volume (or more accurately, a flow rate for a period of time to achieve the set volume). The inspiratory pressure will vary depending on the respiratory system compliance, airway resistance and patient effort. A High Peak Inspiratory Pressure Alarm helps alert clinicians when inspiratory pressures increase to a high level to minimize the risk that injurious pressures are not delivered to the patient. Breath rate, PEEP and FiO2 are also set.


Sub-mode

Assist Control (AC)

Mandatory breaths are synchronized with inspiratory efforts if applicable. Spontaneous efforts above the mandatory breath rate result in the ventilator delivering an additional breath that is identical to the mandatory breath (same pressure and inspiratory time).

Synchronized Intermittent Mandatory Ventilation (SIMV)

Mandatory breaths are synchronized with inspiratory efforts if applicable. Spontaneous efforts above the mandatory rate result in the ventilator delivering an additional breath that is set differently from the mandatory breath (different pressure and inspiratory time). The spontaneous breath is typically a pressure-supported breath which will vary in tidal volume, inspiratory flow, and inspiratory time.

Pressure Support Ventilation (PSV)

PSV is a spontaneous mode of ventilation and requires appropriate patient effort in order to ventilate effectively. All breaths are patient triggered (either by flow or pressure) and patient terminated. The pressure support breath is terminated when the inspiratory flow drops to a predetermined percentage of the peak inspiratory flow detected for that breath. This enables patients to vary not only tidal volume but also inspiratory time. An inspiratory pressure, PEEP, FiO2, cycling, and triggering parameters are set during PSV. Volume, inspiratory flow, inspiratory time, and breath rate are all variable and must be monitored closely.

Continuous Positive Airway Pressure (CPAP)

CPAP is a mode of ventilation that is non-phasic. A constant pressure is applied to the airways during inspiration and expiration. This mode is most frequently applied non-invasively (to alleviate mild respiratory distress, hypoxemia or obstructive sleep apnea) or during invasive ventilation as part of a spontaneous breathing trial in preparation for extubation.


Individual SettingsOxygen Concentration

Definition

FiO2 is the fraction of inspired oxygen delivered to the patient. The FiO2 is a set variable on the ventilator that is often set as either a fraction (0.21-1.0) or a percentage (21-100%).

Physiology

FiO2 is expressed as a percentage and adjusted to maintain a target arterial oxygen saturation. FiO2 ranges > 0.50 for long periods of time are considered toxic levels. Unless contraindicated, patients are usually started on 100% oxygen when initially intubated, and the FiO2 is weaned down once the patient is stabilized on the ventilator.

Patient Example

A patient with pneumonia is receiving FiO2 0.50 with SpO2 99%. FiO2 should be weaned.

Mandatory Breath Rate

Definition

The breath rate is adjusted along with the tidal volume to achieve adequate minute ventilation for the patient to meet ventilation goals. The breath rate is set in number of breaths per minute (bpm or breath/min). Initial rates are set according to age and disease state of the patient. Often the setting of the rate is dependent on whether or not the patient is spontaneously breathing.

PhysiologyTypical respiratory rates for age are set as follows:

Patient’s Weight (kg)

Age (years)

Rate (bpm)

1 <1 25-453 <1 22-405 <1 20-3510 1 20-3016 3 20-3019 5 15-2527 8 15-2535 10 15-2545 12 15-2261 15 12-2070 18 12-20


Remember Minute Ventilation = Respiratory Rate x Vt.

After ensuring Vt is in goal range for the patient, the breath rate may be increased or decreased to adjust ventilation. Increasing the respiratory rate will usually allow more CO2 to be eliminated from the body. Most ventilators allow the patient to take breaths in addition to the mandatory rate set on the ventilator. When increasing the breath rate, make sure to monitor expiratory flow, ensuring that the flow reaches zero before the next breath to limit air trapping.

Patient Example

An intubated toddler may have a set rate in the range of 20-30 bpm.

Peak Inspiratory Pressure

Definition

Peak Inspiratory Pressure (PIP) is the variable that determines the size of the patient’s breath in PCV. Pressure is set in cmH2O and is generally set as a change in pressure from baseline (PEEP) to peak pressure, or delta-pressure (delta-P).

Physiology

Tidal volume is affected by compliance and resistance. Patients with healthy lungs require less pressure to achieve the same tidal volume as compared to patients with sick, non-compliant lungs. PIP is initially set based on how much pressure it takes to visibly move the chest during manual ventilation. PIP is adjusted to achieve the desired tidal volume.

In PCV, the flow rate is variable. Inspiratory flow will remain high until the set PIP is achieved, and then will vary (usually decreasing) throughout the remainder of the breath to maintain the set inspiratory pressure. This results in a square pressure waveform and a decelerating flow waveform. As a result of this flow pattern, the bulk of the tidal volume is delivered during the earlier portion of the breath.

Patient Example

A 4-year-old girl was intubated secondary to status epilepticus. Her initial PIP was set at 15 cmH2O which gives her Vt of 5 mL/kg.

Inspiratory Time

Definition

Inspiratory time is the time over which the Vt is delivered (VCV), or the pressure is maintained (PCV). Inspiratory time is initially set based on the age and pulmonary condition of the patient. In PCV, inspiratory time is set directly in seconds. In VCV, it may be set directly in seconds or indirectly as a result of the peak inspiratory flow and respiratory rate.


Physiology

Typical inspiratory times are as follows:

• Neonatal: 0.3-0.5 seconds• Infant: 0.4-0.8 seconds• Child: 0.6-1.0 seconds• Adult: 0.8-1.4 seconds

The inspiratory time may be shortened or lengthened depending on the disease state of the patient. Inspiratory time may be shortened in obstructive diseases such as asthma or bronchiolitis to allow more time for exhalation, or lengthened in PARDS to improve alveolar recruitment.

Patient Example

A 6-month-old infant with bronchiolitis and air trapping who is ventilated with PCV has an inspiratory time set at 0.4 seconds (low end of infant range) to allow more time for exhalation.

Tidal Volume

Definition

Tidal Volume (Vt) is the amount of gas delivered to the patient per breath. Vt should be set for 5-8 mL/kg in patients with healthy and compliant lungs. A goal Vt for a patient with PARDS should be 3-6 mL/kg. Vt is set in milliliters (mL) and is chosen based on the goal Vt and ideal body weight.

Physiology

In VCV, the ventilator delivers a preset Vt over an inspiratory time. The flow remains constant throughout the inspiratory phase of the breath. Regardless of the compliance or resistance, the preset Vt is delivered.

Patient Example

A 6 kg patient with pneumonia and PARDS has a measured Vt of 44 mL, which is approximately 7.4 mL/kg.

Peak Inspiratory Flow

Definition

Peak inspiratory flow is the highest rate of gas flow delivered to a patient during a breath. It influences how quickly a breath is delivered. In VCV, there are three components to a breath:

• Vt• Inspiratory time• Peak inspiratory flow


Clinicians set two of the variables, and the third is determined automatically. Peak inspiratory flow is set in L/min. Typically, Vt is set first, then inspiratory flow is adjusted to achieve an inspiratory time that is appropriate for the age of the patient.

Physiology

The set flow pattern is typically square (constant flow) or descending ramp (decelerating flow) throughout the inspiratory phase. In patients who are spontaneously breathing, care must be taken to meet the flow demands of the patient. That is, if a patient’s spontaneous peak inspiratory flow demand is 10 L/min, the peak flow on the ventilator should be set to meet or slightly exceed 10 L/min. If flow demands are not met, the patient may develop increased work of breathing or become tachypneic or asynchronous with the ventilator, causing patient discomfort. It is also important to ensure the set inspiratory time is appropriate for the patient size and disease state. Time must be monitored closely, because a breath that is delivered in a very short period of time may result in higher peak inspiratory pressures. A breath delivered over too long a period of time may result in patient discomfort or air trapping.

Patient Example

A 6 kg child with healthy lungs has a Vt set at 48 mL and a desired inspiratory time of 0.6 seconds. The inspiratory flow would need to be approximately 5 L/min with a square waveform to achieve this flow.

Trigger Sensitivity

Definition

The trigger sensitivity refers to the flow or pressure signal which must be detected at the airway by the ventilator to signal a spontaneous breath. If a flow trigger is set, it will be set as a positive number in L/min, and a spontaneous breath is triggered once the patient’s inspiratory flow exceeds the flow trigger threshold. If a pressure trigger is set, it will be set as a negative number in cmH2O, and a spontaneous trigger will be achieved when a negative pressure exceeds the threshold.

Physiology

The trigger sensitivity is set at a level to minimize work and improve patient-ventilator synchrony, but avoid ventilator auto-triggering. If trigger sensitivity is too high (too sensitive), artifactual flow and pressure can inappropriately trigger the ventilator and cause auto-triggering. If the trigger sensitivity is too low (too insensitive), the patient may have to work excessively to trigger a breath, or may not be able to trigger a breath at all. Flow triggering is generally more sensitive.Typical values for trigger sensitivity are:

Flow (L/min)

Pressure (cmH2O)

Infant 0.2-1.0 -1Child 0.5-1.0 -1Adult 0.8-3.0 -2


Troubleshooting

Assess flow and pressure waveforms as well as patient effort. Ensure that the ventilator is not delivering breaths that are not triggered by patient respiratory effort. If so, consider adjusting trigger sensitivity by turning the flow/pressure trigger up (i.e. requiring higher flow or pressure to trigger a breath).

Ensure patient does not have to “work” too hard to get a breath from the ventilator. If so, consider adjusting trigger sensitivity by turning the flow/pressure trigger down (i.e. requiring lower flow or pressure to trigger a breath).

Patient Example

A 3-year-old child was intubated for pneumonia and is recovering and now starting to breathe spontaneously. Her flow trigger is set at 1.0 L/min.

Pressure Support

Definition

Pressure support refers to the amount of pressure applied to spontaneously triggered breaths during synchronized intermittent mandatory ventilation (SIMV) in either pressure or volume control modes. It may also refer to the pure spontaneous breathing mode during which no mandatory breaths are present and all breaths are patient triggered (pressure support ventilation or PSV).

Physiology

Pressure support is patient triggered, pressure limited, and flow cycled. Patient triggered means that the ventilator detects spontaneous effort (based on the set flow or pressure trigger) and initiates a breath in sync with the patient’s effort. Pressure limited refers to the fact that the preset peak pressure is maintained during inspiration. Flow cycled means that the ventilator terminates the inspiration once inspiratory flow falls below a certain predetermined percentage of peak inspiratory flow. Potential benefits include reduced work of breathing and improved patient-ventilator synchrony.

Patient Example

An infant with bronchiolitis is being assessed for extubation readiness. The pressure support level should be set at 10 cmH2O.


Assessing Adequacy of Mechanical VentilationPeak Pressure

Peak pressure is the highest pressure that is achieved when delivering a breath. In pressure control ventilation, the peak pressure is reached in the initial part of the inspiratory time and held for the duration of inspiration. Peak pressure is influenced by airway resistance, and may be increased in conditions such as poor lung compliance, bronchospasm, and secretions.

Tidal Volume

Vt is set directly in VCV.

Vt is variable in PCV. It will depend on the set inspiratory pressure and is influenced by respiratory system compliance, airway resistance and patient respiratory effort. Thus, it is essential to continuously monitor Vt in PCV. Ventilator alarms assist the user in detecting tidal volumes that are too low or too high based on set goals.

Goal Vt is 5-8 mL/kg for a patient with relatively healthy lungs and 3-6 mL/kg for a patient with PARDS.

Tidal volume is displayed in L or mL, or mL/kg.

Minute Ventilation

Minute Ventilation (MV) is the product of respiratory rate and tidal volume (MV = RR x Vt). Optimal MV will vary between patients based on patient size, metabolic demands, and feeding regimen. MV affects PaCO2 on blood gas analysis, and is used to follow ventilation trends over time. MV is displayed in L/min.

On some ventilators, MV is displayed as total and spontaneous MV to assess how much the patient’s spontaneous efforts are contributing to the total MV.

Mean Airway Pressure

Mean Airway Pressure (MAP) represents the area under the curve of the pressure waveform, and is influenced by the peak/plateau pressure, PEEP, RR and inspiratory time. It is increased when any of those variables are increased. Increases in MAP can help with oxygenation by recruiting alveoli.

Plateau Pressure

A plateau pressure requires a special maneuver on the ventilator called an inspiratory hold. It is necessary especially during volume targeted modes to determine the amount of pressure that is transmitted to the lungs. When the inspiratory hold function is activated by the clinician, the ventilator will hold the volume delivered at end inspiration for a period of 3-5 seconds. Pressure throughout the respiratory system equilibrates during the maneuver and the ventilator will display the plateau pressure.


The plateau pressure can be used to calculate static compliance and gauge the safety of the ventilator settings. In general, targeting a plateau pressure < 28 cmH2O is recommended, but slightly higher plateau pressures (29-32 cmH2O) may be necessary in patients with decreased chest wall compliance (i.e. patients with obesity). The inspiratory hold can only be performed on patients who are not spontaneously breathing, as patient efforts during the maneuver will reduce accuracy.

End Expiratory Pressure/Auto-PEEP

End expiratory pressure is an important measurement during mechanical ventilation that is most often used to assess air trapping in the lungs secondary to airway obstruction. End expiratory pressure (or auto-PEEP) is the pressure that exists in the lungs at the end of expiration, just before the start of the next inspiration.

An expiratory hold maneuver, whereby the expiratory valve in the ventilator is temporarily occluded (usually for 0.5-3 seconds) at the end of exhalation, is performed by selecting the expiratory hold option on the ventilator. The pressure in the ventilator circuit is then measured. Depending upon the ventilator used, auto-PEEP will be displayed as either total auto-PEEP (total end expiratory pressure including set PEEP) or delta auto-PEEP (the difference between measured end expiratory pressure during an expiratory hold and set PEEP).

In patients whose ventilator settings are appropriate and when airway obstruction is not present, the total auto-PEEP should equal the set PEEP. If obstruction is present, as in a child with asthma, delta auto-PEEP can be elevated from 1-20 cmH2O.

It is important to note that any spontaneous respirations will adversely affect the accuracy of this maneuver and therefore expiratory hold maneuvers should be performed only on patients who are not spontaneously breathing.

Ventilator Alarms

Ventilator alarms are crucial components to safe delivery of mechanical ventilation. Properly set ventilator alarms alert clinicians to changing patient conditions and acute problems that need attention. Ventilator alarms should be set for every patient and adjusted with changes in the patient’s condition.

When setting alarms, it is important to consider the patient’s disease, acuity, and environment. The following are general recommendations for setting alarms and should be adjusted on an individual basis. Most alarms have a high and low setting which alert clinicians when the values go outside of this range.

Respiratory Rate (RR)• High - Set at double the baseline RR (for example, if a patient’s RR is 30 bpm, set the high RR

alarm to 60 bpm)• Low - Set at half the baseline RR (if a patient’s RR is 30 bpm, set the low RR alarm to 15 bpm)


Minute Ventilation (Ve)• High - Set at double the baseline Ve (for example, if a patient’s Ve is 2.0 L/min, set the high

Vealarm to 4.0 L/min)• Low - Set at half the baseline Ve (if a patient’s Ve is 2.0 L/min, set the low Ve alarm to 1.0 L/min)

Peak Inspiratory Pressure (PIP)• High – Set at 5-10 cmH2O above the set PIP (during PCV) or the baseline monitored PIP (during

VCV) (for example, if a patient’s PIP is 20 cmH2O, set the high PIP alarm to 25-30 cmH2O)• Low – Set midway between the PEEP and the set PIP (during PCV) or baseline monitored PIP

(during VCV) (if a patient’s PIP is 20 cmH2O and PEEP is 5 cmH2O, set the low PIP alarm to 12 cmH2O)

Apnea Interval• Set based on the size of your patient and RR for age (for example, set the apnea interval for

an infant to 10 seconds, and an older child to 20 seconds). If the apnea interval alarms, the ventilator will switch to backup ventilation.


WaveformsOverviewMost ventilators display a variety of waveforms which can aid the clinician in determining the patient’s condition and adequacy of ventilatory support. The pressure, flow, and volume waveforms are the most readily displayed and used. A firm understanding of the ventilator mode and associated ‘normal’ waveforms is necessary to provide safe and effective care. The waveforms shown on the ventilator screen demonstrate normal pressure, flow, and volume waveforms.

Reading the Waveforms

Roll over the terms below to see how they correspond to the ventilator:• Peak Inspiratory Pressure• PEEP• Inspiratory Time• Expiratory Time• Peak Inspiratory Flow• Peak Expiratory Flow• Volume

Pressure• Y-axis - Pressure (cmH2O)• X-axis - Time (seconds)

Flow• Y-axis - Flow (L/min) - Positive is inspiration and negative is expiration• X-axis - Time (seconds)

Volume• Y-axis - Volume (mL)• X-axis - Time (seconds)

PIPInsp. Time Exp. Time

PEEP

Peak Insp. Flow

Peak Exp. Flow

Volume


Pressure Control Ventilation

Waveform Characteristics

Pressure Waveform

Note the square appearance of the pressure waveform. In this mode, pressure is controlled and inspiratory flow is variable. On the waveform, observe that the peak pressure is 27 cmH2O and the PEEP is 7 cmH2O. The inspiratory time can also be determined by calculating the time in which the pressure is above the set PEEP value.

Flow waveform

The inspiratory time is the portion of time during which the flow is positive. The expiratory time is the portion of time in which the flow is negative.

Volume Control Ventilation


Pressure Waveform

Note the descending ramp pattern of the pressure waveform. In this mode, inspiratory flow is controlled and pressure is variable. On the waveform, observe that the peak pressure is 29 cmH2O and the PEEP is 7 cmH2O. The inspiratory time can also be determined by calculating the time in which the pressure is above the set PEEP value.

Flow waveform

The inspiratory time is the portion of time during which the flow is positive. The expiratory time is the portion of time in which the flow is negative.

Pressure Support Ventilation


Pressure Waveform

Note the square appearance of the pressure waveform. Like in PCV, in pressure support ventilation (PSV), pressure is controlled and inspiratory flow is variable. You will also notice in this simulator the waveform is yellow when a breath is triggered by the patient.

Flow waveform

The ventilator cycles into expiration when the inspiratory flow decays to a predetermined proportion of the peak inspiratory flow (in this case, 25% of peak inspiratory flow).


Secretions

Paying close attention to the expiratory portion of the flow waveform, you can observe that the signal has a jagged appearance. This indicates that something is interrupting smooth exhaled gas flow and could represent secretion build up, water in the ventilator circuit or even some rare airway abnormalities.

Patients who are intubated and mechanically ventilated require assistance with pulmonary toilet. These patients are also often sedated, limiting their ability to effectively cough. Thus, suctioning the patient regularly is an important aspect of respiratory management of ventilated patients. However, it is important to remember that suctioning is not a benign procedure and de-recruitment of alveoli can occur, causing hypoxia.

Treatment of secretions involves suctioning the ETT. Indications for suctioning include:• The presence of secretions visible in the ETT or heard on auscultation of the lungs• Suspected secretions with decrease in oxygen saturation or elevated EtCO2 value• Routine suctioning is performed at least every 12 hours in ETT < 4.0 mm diameter to prevent

obstruction

When performing suctioning, it is important to pre-oxygenate the patient with a brief increase in FiO2 to 1.0 to give the patient oxygen reserve and attempt to prevent desaturation with the procedure. This increased FiO2 should continue during and immediately following the procedure until the patient is stable. There is often an increase oxygen button on the ventilator that will transiently increase the FiO2 to 1.0.

Airway Obstruction/Bronchospasm

Paying close attention to the expiratory portion of the flow waveform, you can observe that the flow does not return to 0 L/min before the next breath is initiated. This indicates expiratory obstruction, and can occur secondary to secretion build up, bronchospasm, or kinking of the endotracheal tube.

Patients who are endotracheally intubated and mechanically ventilated may develop bronchospasm, especially if they have a history of reactive airways disease or asthma. Inhaled beta-agonist therapy can be administered to the patient through the ETT to treat bronchospasm. It is important to note that you may have to give a higher dose than usual to your patient, as much of the medication can become stuck to the ETT.


Patient-Ventilator Dyssynchrony

Paying close attention to all three waveforms (particularly the pressure waveform), you can observe that the patient is making inspiratory efforts but is not receiving support from the ventilation in synchrony with these efforts. This may indicate a need to adjust the trigger sensitivity to be more sensitive (less difficult for the patient to trigger a breath) in order to allow the ventilator to deliver support in sync with the patient.

A patient who is intubated and mechanically ventilated will usually require sedation. A patient who is not well sedated may have patient-ventilator dyssynchrony, which can impair gas exchange. Most often, the goal is to have a patient comfortable, yet breathing spontaneously on the ventilator. In patients with severe ALI/ARDS, however, deep sedation and paralysis may be required for effective oxygenation.

Sedation protocols vary by institution, but will often include a sedative agent such as dexmedetomidine (propofol for adult patients), opioids, and/or benzodiazepines. Intermittent intravenous bolus doses or continuous infusions are commonly used. Many centers are trying to limit benzodiazepine use as it can worsen delirium.

Leak

Paying close attention to the volume waveform, you can observe that the expiratory volume does not return to 0 mL. This means that a portion of the inspired breath did not return through the expiratory circuit/valve of the ventilator. This could be caused by a leak around the endotracheal tube, circuit leak, ventilator malfunction, or a pneumothorax actively draining into a chest tube.

Some ventilators will also display both inspiratory and expiratory volume and/or calculate percent leak. If you suspect the lower expiratory volume is due to a leak around the ETT, you can inflate the pilot balloon or add more air to the cuff. If the cuff is fully inflated and the leak is preventing you from delivering ventilator settings that are necessary for the patient, you may need to exchange the ETT for a larger size. Additionally, if the ETT is uncuffed, you may need to exchange for a cuffed ETT, especially if you are trying to deliver a high MAP.


Patient MonitoringPatient Assessment

You can gather a lot of important information about the adequacy of mechanical ventilation and identify any changes in the patient’s condition by examining the patient.


You want to assess whether the patient is initiating effort to breathe. Many ventilators have some designation, such as a color change on the ventilator waveforms, that show whether a breath is patient-initiated or ventilator-initiated. Patients that are spontaneously breathing may have better ventilator synchrony with a mode in which they can control their own rate and inspiratory time, such as SIMV or PSV. In this simulator, ventilator-initiated breaths are red and patient-initiated, or spontaneous, breaths are yellow.

Work of Breathing

Work of breathing refers to the amount of effort a patient is using to breathe. Normally, inspiration is an active process requiring some degree of work, while expiration is passive. Work of breathing may increase with changes in lung compliance, increases in airway resistance (as with secretions or bronchospasm), or inadequate flow rate delivery. Signs of increased work of breathing are tachypnea and the use of accessory muscles.

Chest Excursions

Chest excursion refers to the movement of the chest up and down with each breath. The quality of the movement is a very subjective measure and is often described as diminished, good, or excessive chest movement. Adequate tidal volumes should cause good chest movement. The symmetry of movement between the right and left side is also assessed. An asymmetric chest rise may indicate a pneumothorax.


Breath Sounds

Breath sounds can be heard when auscultating a patient’s chest with a stethoscope. Patients that are mechanically ventilated often have very mechanical sounding breath sounds. It is important to listen for symmetry and for abnormal sounds, such as wheezing, crackles or coarse breath sounds.

Perfusion

Perfusion is an indicator of the adequacy of the delivery of oxygen and blood to the tissues. Poor perfusion may be a sign of inadequate oxygen delivery to the body. Perfusion is assessed by evaluating the patient’s skin color, temperature, and capillary refill time.

Non-Invasive Monitoring

Vital Signs

Vital signs are important to monitor when a patient is being mechanically ventilated, especially if the patient is sedated and/or paralyzed, as it can be a marker for inadequate sedation, ventilation, and/or oxygenation.

Heart Rate

Heart rate is the number of heartbeats per minute. Normal values for heart rates vary based on the age of the patient. Tachycardia is often seen with inadequate sedation, ventilation, and/or oxygenation. Bradycardia in the pediatric patient is rare, but can be observed in severe hypoxemia.

Blood Pressure

Blood pressure measures the arterial pressure of the systemic circulation and is measured in mmHg or kPa. Normal values for blood pressure vary with age. Hypertension is often seen with inadequate sedation and ventilation. Hypotension can be seen in patients that are excessively sedated, hypoxemic, or in shock.

Oxygen Saturation

Oxygen saturation is also referred to as SpO2. It is the amount of oxygen bound to hemoglobin in the blood and is expressed as a percentage of the maximal binding capacity. Normal oxygen saturation is in the range of 95–100%. The oxygen saturation can be measured non-invasively with a pulse oximeter or invasively with an arterial blood gas analysis measurement, and helps to detect inadequate oxygenation.

Respiratory Rate

Respiratory rate is the number of breaths per minute. Normal values for respiratory rates vary based on the age of the patient. Tachypnea is often seen with inadequate sedation, ventilation, and/or oxygenation.


End-tidal Carbon Dioxide

EtCO2 non-invasively measures the carbon dioxide exhaled by the patient during each breath. Detection of EtCO2 can be used to confirm ETT placement following intubation. Additionally, EtCO2 can be used to monitor trends and abrupt changes in ventilation and/or circulation. A normal EtCO2 waveform has 4 components:

Phase 0: Inspiration Phase 1: Dead space ventilation Phase 2: Mixing of dead space and alveolar CO2 Phase 3: Plateau

The value given on an EtCO2 is the plateau value. In normal, healthy humans, the EtCO2 normal value is 35-45 mmHg (4.7-6 kPa), which is 3-5 mmHg (0.4-0.67 kPa) below the arterial value of CO2 (PaCO2). So if the PaCO2 was 40mmHg, the EtCO2 would be 35 - 37 mmHg. Dead space and V/Q mismatching can increase this gradient.

An abrupt decrease in EtCO2 can indicate a sudden loss of cardiac output as occurs in cardiac arrest or a large pulmonary embolism. It could also indicate dislodgment or complete plugging of an ETT or a disconnection of the ventilator circuit. EtCO2 values can be monitored over time to assess how adjustments to the ventilator and/or changing lung physiology are affecting ventilation over time. This decreases the frequency of need for invasive blood gas sampling. Arterial Blood Gas Analysis

Arterial blood gases (ABGs) are sampled either from an arterial puncture or from an indwelling arterial line. When reviewing an ABG, it is important to remember your patient’s ventilation goals. In a patient with PARDS, the goal is a permissive hypercapnia strategy with pH 7.15-7.30. In patients with healthy lungs, the goal is liberalized to pH of 7.35-7.45 with a PaCO2 35-45 mmHg (4.7-6 kPa).

You can use both the EtCO2 monitor and repeat ABG analyses to monitor the adequacy of mechanical ventilation as you make changes to the ventilator or when the patient’s physiology changes. ABG monitoring is particularly helpful in patients with mixed respiratory and metabolic diseases, where the pH is influenced by more than just the PaCO2, and therefore EtCO2 alone may not be sufficient to fully understand the patient’s condition.

In pediatrics, we often draw venous blood gases. Remember that venous blood gases will have a lower pH and higher PaCO2 than an arterial sample drawn at the same time. If the venous sample is a free-flowing, non-tourniqueted sample, the venous pH will be approximately 0.05 points lower than an arterial sample. The PaCO2 will will be approximately 5 mmHg (0.7 kPa) higher than an arterial sample.


Ventilator Management and Troubleshooting

Systematic Approach

When assessing adequacy of ventilation and oxygenation, the clinician needs to evaluate the patient, non-invasive and invasive monitoring, and the ventilator with a systematic approach.

Patient

Assess the patient’s work of breathing and synchrony with the ventilator. If either of these are abnormal, the rest of the evaluation will help you understand what can be optimized to improve the patient’s condition.

Non-Invasive and Invasive Monitoring

Assess the vital signs, paying close attention to heart rate, respiratory rate, SpO2, and EtCO2, which will help you assess adequacy of sedation, ventilation and oxygenation. ABG results demonstrate the effectiveness of the current ventilator settings on your patient’s ventilation and oxygenation.

Ventilator Parameters

The goal is to keep Vt 5-8 mL/kg for healthy lungs and 3-6 mL/kg for patients with PARDS, and to keep plateau pressures < 28 cmH2O (29-32 cmH2O may be acceptable for patient with severe PARDS). If the patient is not spontaneously breathing, the plateau pressure may also be obtained by performing an inspiratory hold maneuver. The goal is to keep PaO2 > 60 mmHg (9.1 kPa).

In VCV, the Vt is set by the clinicians and peak inspiratory pressures (PIP) are monitored. To adjust ventilation, set the Vt to the patient’s goal range and then adjust respiratory rate to achieve goal ventilation while assuring acceptable PIP and making sure the patient fully exhales with each breath.

In PCV, the delta pressure is set by the clinicians and tidal volumes (Vt) are monitored. To adjust ventilation, set the delta pressure as you monitor the measured Vt. Adjust the delta pressure to achieve the patient’s goal Vt range. Once the Vt is in goal range, adjust respiratory rate to achieve goal ventilation while assuring acceptable pressures and making sure the patient fully exhales with each breath.

To adjust oxygenation, wean the FiO2 as able. If FiO2 > 0.3 is required to meet oxygenation goals, increase PEEP and attempt to wean FiO2 as oxygenation improves. If FiO2 is < 0.3, consider weaning FiO2 and/or PEEP.

Ventilation

Hypocarbia is defined as a low partial pressure of CO2 in arterial blood (PaCO2 < 35 mmHg or 4.7 kPa). Hypocarbia can occur when the support from the ventilator is too great. In this case, the clinician must decrease either the tidal volume, breath rate, or a combination of the two in order to reduce the minute ventilation and increase the PaCO2.


Hypercarbia is defined as an elevated partial pressure of CO2 in arterial blood (PaCO2 > 45 mmHg or 6 kPa). In otherwise healthy patients, this may indicate a need to increase the minute ventilation (tidal volume, breath rate, or both) in order to eliminate the excess CO2 and correct the hypercarbia. However, patient condition, other monitored parameters, including pH, degree of lung injury and others are important when considering who requires increased ventilation.

To adjust ventilation, first titrate the ventilator settings to make sure the tidal volume is in the set goal for the patient, and then adjust the breath rate. The breath rate is usually adjusted in increments of 2-4 bpm. You may need to continue to tweak both of these parameters to achieve ventilation goals. This will need to be continuously monitored and adjusted, especially as the patient’s condition changes.

Patient Example

A patient is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. Notice that the tidal volumes are > 7mL/kg, which are not lung protective.

Oxygenation

Hypoxia is defined as a low partial pressure of O2 in arterial blood (PaO2 < 60 mmHg or 8 kPa). Hypoxia can occur when the patient has severe lung disease and/or support from the ventilator is insufficient. In this case, the clinician must increase oxygen delivery (FiO2) and/or alveolar recruitment (PEEP or MAP), or perform airway clearance (remove secretions). It is necessary to monitor ABG values for signs of inadequate oxygen delivery (PaO2 < 60 mmHg or 8 kPa, and/or acidosis not related directly to shock which may be a sign of lactic acid production from inadequate oxygen delivery).

Hyperoxia is defined as an elevation in partial pressure of O2 in arterial blood (PaO2 > 200 mmHg or 26.7 kPa). Clinicians must decrease oxygen delivery (FiO2) and/or alveolar recruitment (PEEP or MAP) to maintain PaO2 in the goal range based on the degree of lung injury. The sicker the patient’s lungs, the lower the PaO2 that is tolerated. For a patient with PARDS, a goal PaO2 is around 60 mmHg (8 kPa).

FiO2 should always be weaned as able to the lowest setting to avoid oxygen toxicity while ensuring adequate oxygenation. If FiO2 > 0.3 is required to meet oxygenation goals, stepwise alveolar recruitment can be achieved by increasing PEEP in increments of 1-2 cmH2O. Then attempt to wean FiO2 as oxygenation improves. You will need to adjust both FiO2 and PEEP to achieve oxygenation goals. Oxygenation will need to be continuously monitored and settings adjusted, especially as the patient’s condition changes. If FiO2 is < 0.4, wean PEEP.

Note: Intermittent increases in FiO2 to 1.0 in response to transient desaturations in children who were born full term may be necessary. Additionally, high FiO2 (> 0.50) is sometimes necessary to maintain adequate oxygenation in children who are severely ill.


Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. Note that the oxygen saturations and PaO2 are greater than necessary for a patient with pneumonia.

Agitation

Sedation is usually required to allow a patient to tolerate intubation and mechanical ventilation. Patients with severe lung disease may require deep sedation and paralysis to tolerate the necessary ventilator settings to ensure adequate oxygenation and ventilation. On the other hand, a patient who is clinically improving and is nearing extubation may only need to be lightly sedated while spontaneously breathing on low ventilator settings.

A patient who is not well sedated may have patient-ventilator dyssynchrony, which can impair gas exchange. Careful ongoing titration of sedatives by physician and/or nurse-driven protocols is critically important to ensure that patients are sedated well enough to tolerate mechanical ventilation while being light enough to spontaneously breathe, if applicable.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. The patient is not adequately sedated. Note the dyssynchrony between the patient and the delivered breaths on the waveforms.

Circuit Disconnect

Occasionally, the ETT and circuit can become disconnected, especially when the patient is agitated. It is important to recognize this quickly as the patient will not be receiving oxygen and will experience alveolar derecruitment.

Circuit disconnect can be noted by observing the circuit disconnect or low pressure alarms on the ventilator, examining the patient and seeing that the circuit and ETT are disconnected, and/or noting a lack of ventilator waveforms or patient generated parameters, such as exhaled tidal volume. Investigating the circuit to make sure it is properly connected is an important component of the DOPE (Dislodgment, Obstruction, Pneumothorax, Equipment) algorithm. The appropriate action is to reconnect the circuit to the patient.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. Note the lack of waveforms and low pressure alarm on the ventilator.


Pneumothorax

When patients are on high ventilator settings, they are at risk for pneumothorax, especially when the patient has injured and inflamed lungs. A pneumothorax can impair oxygenation and ventilation, and cause hemodynamic effects (tachycardia and decreased blood pressure for age), especially when it is under tension (tension pneumothorax). Pneumothorax can be detected by noting tachypnea, lack of breath sounds on one side of the chest, and/or asymmetrical chest rise. Investigating for pneumothorax is one component of the DOPE (Dislodgment, Obstruction, Pneumothorax, Equipment) algorithm. The appropriate maneuver for a clinically significant pneumothorax is to perform needle decompression to remove air from the pleural space, followed by placement of a chest tube. Increasing the FiO2 in the short term will help with oxygenation. Trying to minimize the ventilator settings as much as the patient will tolerate will help decrease the risk of another pneumothorax and may help resolve the air leak.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. Note the hypoxia and asymmetric chest rise when examining the patient. Evaluate the chest x-ray noticing the pneumothorax.

Cardiopulmonary Interactions

When a patient is receiving high positive ventilator pressures, venous return to the heart can be impaired because of the changes in the pressure gradient between the chest and abdomen. This can cause hemodynamic changes (tachycardia and hypotension) related to high intrathoracic pressures. The cardiopulmonary interactions can be especially pronounced in patients with decreased circulating volume. The most appropriate step is to restore effective circulating volume by administering a fluid bolus, improving preload. In some cases, inotropic agents may be indicated.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. The patient’s oxygenation has been worsening and the PEEP was increased resulting in increased MAP. Note the patient has developed tachycardia and hypotension.

Weaning

When a patient develops respiratory failure and requires intubation, sedatives and short acting muscle relaxants are usually administered to ensure patient comfort and optimize intubation. Therefore, immediately following intubation the patient should be placed on a breath rate and volume/pressure settings to completely support ventilation. As the patient recovers and respiratory function begins to return to normal, appropriate ventilator weaning is necessary.

The goals of ventilator weaning are to ensure adequate gas exchange (according to disease specific goals for oxygenation and ventilation), ensure appropriate spontaneous effort (non-distressed spontaneous respiratory effort) and eventually liberate the patient from mechanical ventilation.


Weaning can occur at a variety of speeds and is dependent upon the patient’s underlying condition or recovery from disease. Rapid weaning may be appropriate in a patient who has healthy lungs that was intubated for a procedure. In patients with pulmonary disease (asthma, bronchiolitis, pneumonia, PARDS) it may be more appropriate to wean more slowly.

The goals of ventilation and oxygenation may change as the patient improves. For example, a patient with improving PARDS may have goal Vt that change from 3-6 mL/kg to 5-8 mL/kg. Less pressure is also required to achieve goal Vt as lung condition improves.

Ventilator settings are decreased as lung compliance and oxygenation improves. It is important to closely monitor vital signs, respiratory parameters and blood gas data to ensure ventilator changes are safe and appropriate. Eventually the mode may be changed to a spontaneous mode of ventilation such as PSV.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. The patient’s condition has improved and he requires weaning of settings.

Extubation Readiness Assessment

Once the patient’s disease process that necessitated intubation has resolved, it is important to determine if the patient has recovered enough to tolerate extubation. Trialing the patient on low or physiologic ventilator settings will help to provide this information. It is also necessary to recall what, if any, respiratory support the patient required prior to intubation (i.e. nocturnal BiPAP at baseline), because the patient may be able to be extubated from higher than usual settings if the patient will be supported with additional respiratory support.

An extubation readiness assessment involves simulating the extubation environment by placing the patient on low or physiologic ventilator settings, and monitoring the patient to determine adequate oxygenation and ventilation on the these settings. Extubation readiness assessment varies between institutions, but in this simulator we will use the following parameters:

1. Ensure the patient is spontaneously breathing, and transition to a spontaneous breathing mode (pressure support ventilation or PSV)

2. Ensure the patient is on a low PEEP (5 cmH2O) unless they will be extubated directly to CPAP or BiPAP with a higher PEEP

3. Ensure the patient is on minimal pressure support to overcome resistance in the ETT. This will vary by ETT size as resistance is inversely related to the size of the ETT.

• ETT < 3.5mm ID: PS = 10 cmH2O• ETT 4-4.5mm ID: PS = 8 cmH2O• ETT ≥ 5.0mm ID: PS = 6 cmH2O

4. Ensure the patient is on a low FiO2 (< 0.5)5. Check for an ETT leak to make sure that there is not significant airway edema. Pediatric

patients are at higher risk for increased airway resistance in setting of airway edema (Poiseuille’s law). If there is no air leak at pressures greater than 25 cmH2O, diuretics and or steroids may need to be considered.


Once you place the patient on minimal settings, you will want to monitor the patient’s work of breathing, vital signs (especially RR), EtCO2, and ABG. If after a period of time (some centers use two hours), the patient has adequate oxygenation, ventilation, work of breathing, and vital signs, you may consider extubation.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. The patient has continued to improve and needs to be evaluated if he is ready for extubation.

Extubation

Once a patient has demonstrated adequate oxygenation and ventilation on an extubation readiness assessment, you may want to consider extubation. In addition to ensuring the patient is breathing spontaneously, has appropriate work of breathing and vital signs, and has adequate oxygenation and ventilation on low ventilator settings, you will want to make sure the following parameters are also met:

• The sedation has been optimized for extubation. It is often necessary to decrease or discontinue sedative infusions so that the patient is fully awake for extubation. The protocol for doing so will vary between institution. Generally, if a patient has been on sedatives for a short period of time (i.e. less than five days), you may be able to discontinue sedative infusions. If the patient has received sedatives for longer, you may need to wean the infusions.

• Enteral feeds have been held for extubation. As re-intubation is a possibility, you want to limit the risk of complications, i.e. aspiration. Feeds should be held as per institutional NPO guidelines.

• The patient has a leak around the ETT. Pediatric patients are at higher risk for increased airway resistance in setting of airway edema (Poiseuille’s law) because of their smaller airways as compared to adults. This can lead to upper airway obstruction, increased work of breathing and in severe cases, respiratory failure. Checking for a leak around the ETT involves listening at the patient’s cheek or neck with a stethoscope, administering a manual breath with a ventilation bag with manometer, and determining at which pressure air leaks around the ETT. The goal is to have a leak at 25 cmH2O or less. If there is no leak around the ETT, diuretics and/or steroids may be considered, and extubation may need to be delayed.

Patient Example

An infant is admitted to the ICU and is intubated secondary to respiratory failure from pneumonia. Note his work of breathing, vital signs, ventilation, and oxygenation are in acceptable range. Thus, he has recovered and is ready for extubation.


Inhaled Nitric Oxide

Indications and Delivery

Inhaled nitric oxide (iNO) is a potent, pulmonary specific vasodilator. iNO may also be used for certain cardiac or pulmonary conditions that cause pulmonary hypertension. Additionally, pulmonary hypertension can occur with diseases that cause hypoxic respiratory failure and may respond to iNO such as severe acute respiratory distress syndrome.

iNO is delivered to the patient using a specialized device which injects set amount of nitric oxide into the inspiratory limb of the breathing circuit. Dose ranges generally are 1-20 parts per million (ppm), and are sometimes as high as 40 ppm. The typical starting dose is 20 ppm.

After connecting a patient to iNO, it is important to monitor the patient’s PaO2 and SpO2. Patients that respond to iNO should demonstrate an improvement in oxygenation within 30 minutes or less. Patient Example

A patient with a history of pulmonary hypertension is admitted with pneumonia and has refractory hypoxia. You wish to trial iNO to see if it can improve oxygenation.

Weaning

Decreasing the iNO may be considered when a patient is clinically stable and improved, with improvement in pulmonary hypertension and adequate oxygenation on low FiO2 (usually < 0.4).iNO is typically decreased incrementally: 20 ppm —> 10 ppm —> 5 ppm —> 2.5 ppm —> 1 ppm —> 0 ppm. Weaning must be done carefully as supplemental iNO reduces the exogenous excretion of iNO by the patient.

As you wean, the goal is to have the patient increase intrinsic nitric oxide production by gradually discontinuing iNO. In general, the pulmonary vasculature is more sensitive to weaning at lower concentrations of iNO, hence the slower wean at lower concentrations.

Discontinuing the iNO (turning the iNO off from 1 ppm) may be considered once the PaO2 > 80 mmHg (10.7 kPa), SpO2 > 90% and FiO2 < 0.4. Following discontinuation of iNO, if the patient’s oxygenation decreases and the patient requires an increase in FiO2 by more than 0.1-0.2 (or FiO2 > 0.6) to maintain SpO2, consider restarting at 1 ppm.

Patient Example

A patient with pulmonary hypertension and pneumonia was initiated on iNO with clinical improvement in oxygenation and pulmonary hypertension. His ventilator settings have been weaned and he is ready to begin weaning iNO.


Toxicity

Methemoglobinemia is a form of hemoglobin that has a decreased capacity to carry oxygen to the blood. It forms as a result of a reaction between nitric oxide and hemoglobin. Methemoglobin is measured by co-oximetry which can be performed by most blood gas analyzers.

Normal methemoglobin levels are < 1-2%. When levels of methemoglobin exceed 5-10% of the total hemoglobin, patients can become cyanotic. This condition is referred to as methemoglobinemia.The treatment for symptomatic methemoglobinemia is methylene blue. To reduce the risk of methemoglobinemia, iNO doses > 20 ppm should not be used for extended periods of time and methemoglobin levels should be monitored daily.


COVID-19 Considerations

Introduction

In late 2019, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as the cause of an epidemic acute respiratory illness, Coronavirus Disease 2019 (COVID-19), in Wuhan, China. The virus has since spread rapidly around the world, and was declared a pandemic on March 11, 2020.

The clinical manifestations of COVID-19 include fever, pharyngitis, upper and lower respiratory symptoms. While the majority of cases are mild, progression to acute respiratory distress syndrome (ARDS) is described in up to 15 to 30% of cases. Pneumocytes with viral cytopathic effect and cytokine storm have been described as mechanisms central to the pathophysiology of severe illness caused by COVID-19.

Imaging findings in patients affected by COVID-19 include radiographic evidence of viral pneumonia; in severe cases, CT imaging is notable for patchy ground glass opacities, predominant in the periphery and bases.

The majority of deaths occur among adults aged > 60 years, in particular in individuals with pre-existing comorbidities such as cardiovascular disease, hypertension, chronic respiratory disease, malignancy, and diabetes.

Management

There is limited and evolving guidance of the management of patients with critical illness due to COVID-19, and the care of the patient with COVID-19 is largely supportive.

In general, the recommendations favor conservative fluid resuscitation with balanced crystalloids and the use of norepinephrine as the first-line vasoactive agent.

In treating patients with COVID-19 and acute hypoxemic respiratory failure, it is recommended to titrate oxygen to maintain peripheral oxygen saturation (SpO2) between 92 and 96%, with escalation as indicated to high-flow nasal cannula (HFNC) or noninvasive positive pressure ventilation (NIPPV), recognizing that these interfaces are aerosol-generating and may pose an infection risk to healthcare workers.

For patients with progressive respiratory failure, it is recommended that intubation (an aerosol-generating procedure) occur early, by the most experienced airway provider, and in a negative pressure room with healthcare workers wearing appropriate personal protective equipment.In general, lung-protective (Vt 4-8 mL/kg) and high-PEEP ventilator strategies are recommended, with consideration of neuromuscular blockade and proning for patients with moderate to severe disease. In patients with refractory hypoxic failure despite optimization of ventilation strategies, consideration of inhaled nitric oxide and extracorporeal membrane oxygenation (ECMO) support is warranted.


At present there is insufficient evidence to support the routine use of corticosteroids; in fact, corticosteroids may increase viral shedding. The use of antibiotics in the case of suspected bacterial co-infection, however, is recommended.

While there are multiple ongoing randomized controlled trials looking at the use of antiviral agents (including Remdesivir and lopinavir/ritonavir ), the current available evidence does not support routine use of such agents. Chloroquine or hydroxychloroquine are also under investigation for their potential interference with the virus trafficking and cellular receptors, but are also not recommended for routine use.

Of note, the use of non-steroidal anti-inflammatory agents to treat fever in patients with COVID-19 remains a topic of debate, owing to the potential for up-regulation of expression of the ACE-2 receptors targeted by SARS-CoV-2, and thus acetaminophen for fever control remains the favored approach.


Adult Considerations

Gas Exchange Goals for Healthy Lungs

Adult patients may be intubated and mechanically ventilated for a variety of respiratory and non-respiratory problems.

For patients that are intubated for non-respiratory problems and who have normal lung function, oxygenation and ventilation goals are the same as non-intubated healthy individuals.


Goal Vt is 5-8 mL/kg for the patient’s ideal body weight (IBW).

Goal pH

Goal pH is 7.35-7.45. Once Vt in is goal, adjust breath rate to achieve pH goal.

Goal PaCO2

Goal PaCO2 is 35-45 mmHg (4.7-6 kPa).

Goal PaO2

Goal PaO2 is >80 mmHg (10.7 kPa). PaO2 is often much higher in healthy lungs. Hyperoxia is harmful, so FiO2 should weaned to minimize toxicity.


Permit spontaneous breathing when possible. This can be accomplished with partial support (Pressure or Volume Synchronized Intermittent Mandatory Ventilation (SIMV) with low mandatory breath rate), or Pressure Support Ventilation (PSV) to promote conditioning of the diaphragm.

Ventilator Settings

Typical ventilator settings for adults with healthy lungs include the following:• Tidal Volume: 5-8 mL/kg• Plateau Pressure: < 30 cmH2O (evaluate with inspiratory hold)• PEEP: 5-7 cmH2O• FiO2: < 0.5• Breath Rate: 12-30 bpm• Inspiratory Time: 0.8-1.4 sec• Trigger Sensitivity: 0.8-3 L/min


Gas Exchange Goals for ARDS

Adult guidelines for the management of Acute Respiratory Distress Syndrome (ARDS) vary slightly as compared to PARDS guidelines.

ARDS is a life-threatening condition characterized by a reduction in pulmonary compliance and significant respiratory failure secondary to inflammation of the lung tissue. There are many causes of ARDS including sepsis and pneumonia. ARDS is defined as hypoxemia and chest imaging findings of bilateral infiltrate(s) consistent with acute pulmonary parenchymal disease, that develop within seven days of a known clinical insult that could cause ARDS in a ventilated patient with PEEP ≥ 5 cmH2O, which is not fully explained by cardiac failure or fluid overload.

Mild, moderate, and severe ARDS are defined by the PaO2/FiO2 ratio:• Mild: PaO2/FiO2 = 201 - 300 mmHg (26.7 - 40 kPa)• Moderate: PaO2/FiO2 = 101 - 200 mmHg (13.3 - 26.7 kPa)• Severe: PaO2/FiO2 ≤ 100 mmHg (13.3 kPa)

Optimal ventilation for ARDS includes a lung protective strategy with high PEEP, low tidal volumes, and permissive hypercapnia.


Goal Vt is 6 mL/kg IBW (guidelines support range 4-8mL/kg). Low Vt and low pressures minimize harmful stretch injury (volutrauma and barotrauma).

Goal pH

Goal pH is 7.25-7.35.

Goal PaCO2

PaCO2 is allowed to rise (permissive hypercapnia) and titrated based on goal pH. This minimizes volutrauma and barotrauma associated with high ventilator pressures and volumes. If Vt is in goal range, titrate breath rate as necessary to achieve goal pH. Exceptions to permissive hypercapnia and acidosis include intracranial hypertension, severe pulmonary hypertension, cardiovascular instability, severe ventricular dysfunction, and some congenital heart defects. The use of bicarbonate supplementation is not routinely recommended.

Goal PaO2

Goal PaO2 is often > 60 mmHg (8 kPa). Some patients may tolerate lower oxygenation goals (SpO2 > 88%). If FiO2 > 0.5 is required for adequate oxygenation, consider incremental increase of PEEP to improve lung recruitment.

Prone Positioning

Prone positioning for at least 12 hr/day should be considered for adults with severe ARDS.


Ventilator settings

Typical ventilator parameters for adults with ARDS may include the following:• Tidal Volume: 4-8 mL/kg• Plateau Pressure: < 30 cmH2O (evaluate with inspiratory hold)• PEEP: > 5 cmH2O• FiO2: < 0.5• Breath Rate: 15-35 bpm• Inspiratory Time: 0.7-1.4 sec• Trigger Sensitivity: 0.8-3 L/min

Extubation Readiness Assessment

Once the patient’s disease process that necessitated intubation has resolved, it is important to determine if the patient has recovered enough to tolerate extubation.

An extubation readiness assessment or spontaneous breathing trial involves simulating the extubation environment by placing the patient on low or physiologic ventilator settings. The patient’s breathing rate, work of breathing, tidal volume, and gas exchange is monitored, and helps to determine how likely the patient is to be successfully extubated.

The Rapid Shallow Breathing Index (RSBI) is a tool that can help to predict successful extubation.

RSBI = spontaneous breath rate/Vt in L

In patients that have otherwise met criteria for extubation (see below), a RSBI <105 breaths/min/L predicts a likely successful extubation.

Extubation readiness assessment varies between institutions, but in this simulator we will use the following parameters:

1. Ensure the patient is spontaneously breathing, and transition to a spontaneous breathing mode (pressure support ventilation or PSV)

2. Ensure the patient is on a low PEEP (5 cmH2O) unless they will be extubated directly to CPAP or BiPAP with a higher PEEP

3. Ensure the patient is on minimal pressure support to overcome resistance in the ETT, this is usually 5-6 cmH2O in adults

4. Ensure the patient is on a low FiO2 (< 0.5)5. Ensure the patient has a strong cough and minimal secretions6. Ensure the patient is hemodynamically stable

If after a period of time on minimal settings, (some centers use two hours), you may consider extubation if the patient has adequate work of breathing, gas exchange, and RSBI <105 breaths/min/L.

Alternative strategies to assess extubation readiness in adults may include a T-piece or CPAP trial. These practices can vary between institutions.


Guidelines• Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress

syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference. PCCM. 2015; 16(5):428-39. All rights reserved.

• Fan E, Del Sorbo L, Goligher EC, et al. An Official American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine Clinical Practice Guideline: Mechanical Ventilation in Adult Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2017;195(9):1253–1263.

COVID-19 Resources• CDC COVID-19 Response Team. Severe Outcomes Among Patients with Coronavirus Disease

2019 (COVID-19) - United States, February 12-March 16, 2020. MMWR Morb Mortal Wkly Rep. 2020;69(12):343–346.

• MacLaren G, Fisher D, Brodie D. Preparing for the Most Critically Ill Patients With COVID-19: The Potential Role of Extracorporeal Membrane Oxygenation. JAMA. 2020;10.1001/jama.2020.2342.

• Xu Z, Shi L, Wang Y, et al. Pathological findings of COVID-19 associated with acute respiratory distress syndrome. Lancet Respir Med. 2020;S2213-2600(20)30076-X.

• Ruan Q, Yang K, Wang W, Jiang L, Song J. Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China [published online ahead of print, 2020 Mar 3]. Intensive Care Med. 2020;1–3.

• Shi H, Han X, Jiang N, et al. Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study. Lancet Infect Dis. 2020;20(4):425–434. doi:10.1016/S1473-3099(20)30086-4.

COVID-19 References• Shi H, Han X, Jiang N, et al. Radiological findings from 81 patients with COVID-19 pneumonia in

Wuhan, China: a descriptive study. Lancet Infect Dis. 2020;20(4):425–434.• Alhazzani W, Møller MH, Arabi YM, et al. Surviving Sepsis Campaign: guidelines on the

management of critically ill adults with Coronavirus Disease 2019 (COVID-19) [published online ahead of print, 2020 Mar 28]. Intensive Care Med. 2020;1–34.

• World Health Organization. Clinical management of severe acute respiratory infection (SARI) when COVID-19 disease is suspected. Interim guidance March 13, 2020. https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-(ncov)-infection-is-suspected. CC BY-NC-SA 3.0 IGO.

• Lee N, Allen Chan KC, Hui DS, et al. Effects of early corticosteroid treatment on plasma SARS-associated Coronavirus RNA concentrations in adult patients. J Clin Virol. 2004;31(4):304–309.

References and Resources

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