principles of mechanical ventilation ret 2284 module 3.0 modes of ventilation

Principles of Mechanical Ventilation

RET 2284 Module 3.0 Modes of Ventilation

Modes of Ventilation

Mode Description of a breath type and the timing of

breath delivery Terms or acronyms used to describe the way a

ventilator performs in a particular situation; often invented by physicians, therapists, or manufacturers

Basically there are three breath delivery techniques used with invasive positive pressure ventilation CMV – controlled mode ventilation SIMV – synchronized Spontaneous modes


CMV Continuous Mandatory Ventilation

All breaths are mandatory and can be volume or pressure targeted

Controlled Ventilation – when mandatory breaths are time triggered

Assist/Control Ventilation – when mandatory breaths are either time triggered or patient triggered


CMV Continuous Mandatory Ventilation

Controlled Ventilation – when mandatory breaths are time triggered Mandatory breath – ventilator determines the start

time (time triggered) and/or the volume or pressure target


CMV Controlled Ventilation

Appropriate when a patient can make no effort to breathe or when ventilation must be completely controlled Drugs Cerebral malfunctions Spinal cord injury Phrenic nerve injury Motor nerve paralysis



In other types of patients, controlled ventilation is difficult to use unless the patient is sedated or paralyzed with medications Seizure activity Tetanic contractions Inverses I:E ratio ventilation Patient is fighting (bucking) the ventilator Crushed chest injury – stabilizes the chest Complete rest for the patient



Adequate alarms must be set to safeguard the patient E.g., disconnection

Sensitivity should be set so that when the patient begins to respond, they can receive gas flow from the patient

Do not lock the patient out of the ventilator!


CMV Assist/Control Ventilation

A time or patient triggered CMV mode in which the operator sets a minimum rate, sensitivity level, type of breath (volume or pressure)

The patient can trigger breaths at a faster rate than the set minimum, but only the set volume or pressure is delivered with each breath


CMV Assist/Control Ventilation

Indications Patients requiring full ventilatory support Patients with stable respiratory drive

Advantages Decreases the work of breathing (WOB) Allows patients to regulate respiratory rate Helps maintain a normal PaCO2

Complications Alveolar hyperventilation


CMV Volume Controlled –

CMV Time or patient triggered,

volume targeted, volume cycled ventilation

Graphic (VC-CMV) Time-triggered, constant

flow, volume-targeted ventilation


CMV Volume Controlled –

CMV Time or patient triggered,

volume targeted, volume cycled ventilation

Graphic (VC-CMV) Time-triggered,

descending-flow, volume-targeted ventilation


CMV Pressure Controlled – CMV

PC – CMV (AKA – Pressure control ventilation - PCV)

Time or patient triggered, pressure targeted (limited), time cycled ventilation

The operator sets the length of inspiration (Ti), the pressure level, and the backup rate of ventilation

VT is based on the compliance and resistance of the patient’s lungs, patient effort, and the set pressure



Note inspiratory pause



Note shorter Ti



Airway pressure is limited, which may help guard against barotrauma or volume-associated lung injury Maximum inspiratory pressure set at 30 – 35 cm

H2O Especially helpful in patients with ALI and ARDS

Allows application of extended inspiratory time, which may benefit patients with severe oxygenation problems

Usually reserved for patient who have poor results with a conventional ventilation strategy of volume ventilation



Occasionally, Ti is set longer than TE during PC-CMV; known as Pressure Control Inverse Ratio Ventilation Longer Ti provides better oxygenation to some

patients by increasing mean airway pressure Requires sedation, and in some cases paralysis


IMV and SIMV Intermittent Mandatory Ventilation – IMV

Periodic volume or pressure targeted breaths occur at set interval (time triggering)

Between mandatory breaths, the patient breathes spontaneously at any desired baseline pressure without receiving a mandatory breath Patient can breathe either from a continuous

flow or gas or from a demand valve



Indications Facilitate transition from full ventilatory support

to partial support

Advantages Maintains respiratory muscle strength by

avoiding muscle atrophy Decreases mean airway pressure Facilitates ventilator discontinuation – “weaning”



Complications When used for weaning, may be done too quickly

and cause muscle fatigue Mechanical rate and spontaneous rate may

asynchronous causing “stacking” May cause barotrauma or volutrauma


IMV and SIMV Synchronized IMV

Operates in the same way as IMV except that mandatory breaths are normally patient triggered rather than time triggered (operator set the volume or pressure target)

As in IMV, the patient can breathe spontaneously through the ventilator circuit between mandatory breaths



At a predetermined interval (respiratory rate), which is set by the operator, the ventilator waits for the patient’s next inspiratory effort

When the ventilator senses the effort, the ventilator assists the patient by synchronously delivering a mandatory breath



If the patient fails to initiate ventilation within a predetermined interval, the ventilator provides a mandatory breath at the end of the time period



Indications Facilitate transition from full ventilatory support

to partial support

Advantages Maintains respiratory muscle strength by

avoiding muscle atrophy Decreases mean airway pressure Facilitates ventilator discontinuation – “weaning”



Complications When used for weaning, may be done too quickly

and cause muscle fatigue


Spontaneous Modes Three basic means of providing support

for continuous spontaneous breathing during mechanical ventilation

Spontaneous breathing

CPAP

PSV – Pressure Support Ventilation


Spontaneous Modes Spontaneous breathing

Patients can breathe spontaneously through a ventilator circuit; sometimes called T-Piece Method because it mimics having the patient ET tube connected to a Briggs adapter (T-piece)

Advantage Ventilator can monitor the patient’s breathing and

activate an alarm if something undesirable occurs

Disadvantage May increase patient’s WOB with older ventilators


Spontaneous Modes CPAP

Ventilators can provide CPAP for spontaneously breathing patients Helpful for improving

oxygenation in patients with refractory hypoxemia and a low FRC

CPAP setting is adjusted to provide the best oxygenation with the lowest positive pressure and the lowest FiO2


Spontaneous Modes CPAP

Advantages Ventilator can

monitor the patient’s breathing and activate an alarm if something undesirable occurs


Spontaneous Modes PEEP (Positive End Expiratory Pressure)

“According to its purest definition, the term PEEP is defined as positive pressure at the end of exhalation during either spontaneous breathing or mechanical ventilation. However, use of the term commonly implies that the patient is also receiving mandatory breaths from a ventilator.” (Pilbeam)

PEEP becomes the baseline variable during mechanical ventilation


Spontaneous Modes PEEP

Helps prevent early airway closure and alveolar collapse and the end of expiration by increasing (and normalizing) the functional residual capacity (FRC) of the lungs

Facilitates better oxygenation

NOTE: PEEP is intended to improve oxygenation, not to provide ventilation, which is the movement of air into the lungs followed by exhalation


Spontaneous Modes Pressure Support Ventilation – PSV

Patient triggered, pressure targeted, flow cycled mode of ventilation

Requires a patient with a consistent spontaneous respiratory pattern

The ventilator provides a constant pressure during inspiration once it senses that the patient has made an inspiratory effort


Spontaneous Modes PSV



Indications Spontaneously breathing patients who require

additional ventilatory support to help overcome WOB, CL, Raw Respiratory muscle weakness

Weaning (either by itself or in combination with SIMV)



Advantages Full to partial ventilatory support Augments the patients spontaneous VT

Decreases the patient’s spontaneous respiratory rate

Decreases patient WOB by overcoming the resistance of the artificial airway, vent circuit and demand valves

Allows patient control of TI, I, f and VT



Advantages Set peak pressure Prevents respiratory muscle atrophy Facilitates weaning Improves patient comfort and reduces need for

sedation May be applied in any mode that allows

spontaneous breathing, e.g., VC-SIMV, PC-SIMV



Disadvantages Requires consistent spontaneous ventilation Patients in stand-alone mode should have back-

up ventilation VT variable and dependant on lung

characteristics and synchrony Low exhaled E Fatigue and tachypnea if PS level is set too low


Spontaneous Modes Flow Cycling During PSV

Flow cycling occurs when the ventilator detects a decreasing flow, which represents the end of inspiration

This point is a percentage of peak flow measured during inspiration PB 7200 – 5 L/min Bear 1000 – 25% of peak flow Servo 300 – 5% of peak flow

No single flow-cycle percent is right for all patients


Spontaneous Modes Flow Cycling During

PSV Effect of changes in

termination flow

A: Low percentage (17%)

B: High percentage (57%)

Newer ventilators have an adjustable flow cycle criterion, which can range from 1% - 80%, depending on the ventilator


Spontaneous Modes PSV during SIMV

Spontaneous breaths during SIMV can be supported with PSV (reduces the WOB)

PCV – SIMV with PSV


Spontaneous Modes PSV during SIMV

Spontaneous breaths during SIMV can be supported with PSV

VC – SIMV with PSV



NOTE: During pressure support ventilation (PSV), inspiration ends if the inspiratory time (TI) exceeds a certain value. This most often occurs with a leak in the circuit. For example, a deflated cuff causes a large leak. The flow through the circuit might never drop to the flow cycle criterion required by the ventilator. Therefore, inspiratory flow, if not stopped would continue indefinitely. For this reason, all ventilators that provide pressure support also have a maximum inspiratory time.



Setting the Level of Pressure Support Goal: To provide ventilatory support

Spontaneous tidal volume is 10 – 12 mL/Kg of ideal body weight

Maintain spontaneous respiratory rate <25/min

Goal: To overcome system resistance (ET Tube, circuit, etc.) in the spontaneous or IMV/SIMV mode Set pressure at (PIP – Pplateau) achieved in a

volume breath or at 5 – 10 cm H2O



Exercise: Using the PIP and the PPlateau from the pressure waveform below, recommend a pressure support setting for this patient (patient is in VC-SIMV mode)

35

25

Answer: 10 cm H2O


Spontaneous Modes PSV - The results of your work

35 cm H2O

10 cm H2O


Spontaneous Modes Bilevel Positive Airway Pressure (BiPAP)

An offshoot of PEEP/CPAP therapy Most often used in NPPV AKA

Bilevel CPAP Bilevel PEEP Bilevel Pressure Support Bilevel Pressure Assist Bilevel Positive Pressure Bilevel Airway Pressure



Commonly patient triggered but can be time triggered, pressure targeted, flow or time cycled

The operator sets two pressure levels IPAP (Inspiratory Positive Airway Pressure)

IPAP is always set higher than EPAP Augments VT and improves ventilation

EPAP (Expiratory Positive Airway Pressure) Prevents early airway closure and alveolar collapse

at the end of expiration by increasing (and normalizing) the functional residual capacity (FRC) of the lungs

Facilitates better oxygenation



The operator sets two pressure levels IPAP EPAP

NOTE: The pressure difference between IPAP and EPAP is pressure support


Questions?

principles of mechanical ventilation ret 2284 module 3.0 modes of ventilation

Documents

modes of ventilation

time cycled ventilation

patient slide

e ratio ventilation

patient triggered slide

patient triggered cmv

volume targeted

breath slide