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Pulmonary Critical Care-------------

The Approach to Acute Respiratory Failure

– By: John J. Beneck MSPA, PA-C

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Objectives

• Understand lung function as it applies to pathological processes including:– Air movement– Diffusion– Circulation– Gas transport

• Understand Acute Respiratory Failure with regard to:– Clinical manifestations– Etiology– Presentation– Diagnosis– Treatment

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Objectives (Cont)

• Understand the role of PPV in the care of respiratory failure

• Introduce various mechanical ventilation modalities and weaning strategies

• Understand ARDS with regard to:– Definition– Presentation– Diagnosis / Differential Diagnosis– Etiology– Complications– Treatment– Prognosis

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Abbreviations

• ARDS-Acute respiratory distress syndrome

• BNP-B type naturetic peptide

• CBC-Complete blood count

• CK-MB-MB fraction of creatinine kinase

• CMP-Complete metabolic panel

• CMV-Continuous mechanical ventilation

• DVT-Deep vein thrombosis

• ED-Emergency department

• F/U-Follow up

• FiO2-Fraction of inspired oxygen

• GI-Gastrointestinal

• Hb-Hemoglobin

• Mg-Magnesium

• MI-Myocardial infarction

• mmHg-Millimeters of mercury

• NIF-Negative inspiratory force

• NPPV-Noninvasive positive pressure ventilation

• PAO2-Partial pressure of oxygen in the alveoli

• PaO2/CO2-Partial pressure of oxygen and CO2 in the arteries

• Patm-Atmospheric pressure

• PH2O-Partial pressure of water vapor

• PCWP-Pulmonary capillary wedge pressure

• PE-Pulmonary embolus

• PNA-Pneumonia

• PPV-Positive pressure ventilation

• R-diffusion coefficient of CO2

• SOB-Short of breath

• VTE-Venous thromboembolism

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Case 1

• 18 year old male in ED with history of anxiety and acute onset of dyspnea and SOB. P: 94, R: 28, BP: 132/78, T: 37.0, SaO2: 99% on room air.

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Case 2

• You are called for a 58 year old female admitted 2 days prior with sepsis. Now with severe SOB. P: 110, R:36, BP: 105/66, T:37.6, SaO2 90% on 4 liter nasal cannula.

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Case 3

• You are called for a 78 year old male admitted 10 hours prior for exacerbation of COPD. He is obtunded and barely rousable. P: 88, R: 6, BP: 146/88, T: 36.8, SaO2 95% on 4 liter nasal cannula. ABG: 7.13 / 103 / 86 / 33 / 93%

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Lung Function

• Oxygenation

• Ventilation

• Dependent on circulation

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Air Movement - Breathing

• Negative intra-thoracic force– The role of the pleura

• Compliance• Airway resistance• Radial traction – dec resistance – pulls on

tubes to make a larger lumen

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Factors Affecting Intra-thoracic Force

• Trauma

• Neuromuscular disease

• Pleural effusion

• Pneumothorax

• Sedation

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Factors Affecting Compliance

• Chest wall compliance– Trauma– Hyper-expansion – gets bigger b/c lungs push it out.

Ribs lever against diaphragm. Dec chest wall compliance

– Pleural changes

• Lung compliance– Interstitial edema– Fibrosis– Air trapping

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Factors Affecting Resistance

• COPD

• Asthma

• Pulmonary edema

• Airway edema

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Après Air Movement(What Comes Next)

• Diffusion in the lungs

• Circulation

• Diffusion in the tissues

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Circulatory Gas Transport

• Pulmonary circulation

• Gas transportability

• Systemic circulation

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Gas Diffusion

• Layers– Surfactant– Alveolar membrane– Interstitial fluid– Capillary membrane– Plasma

• Healthy barrier is 0.5 microns• Different gases behave differently

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Factors Affecting Diffusion

• Type of gas

• Membrane thickness

• Pressure gradient

• Blood flow

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Normal Oxygenation

• It’s all about DIFFUSION

– Confounders

• Other gases: N2, H2O, CO2, trace gases

• Speed of the blood

– Erythrocyte exposure time 0.75 - 0.25 seconds

• Diffusion membrane

• Hemoglobin status

(Rest) (Exercise)

www.anaesthetist.com/icu/organs/lung/lungvol.gif

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Oxygen Cascade

• Inspired oxygen – 160 mmHg• Alveolar oxygen – 100 mmHg• Oxygen in blood – 90 mmHg

– Dissolved in plasma

• Oxygen at tissue (mitochondrial) level 4 - 20 mmHg

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Pulmonary Math

• Alveolar gas equation (short)

– PAO2 = [(P atm - P H2O) x FiO2] - PaCO2 / R

– (760-47) x FiO2(%) – PaCO2 / 0.8

– 713 x 0.21– 40 / 0.8

– 150-50

– Approx 100 mmHg

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A(Alveolar)-a(Arterial) GradientA-a Gradient

• PAO2 – PaO2(P atm – P H2O) x FiO2 - PaCO2 / R - PaO2 (obtained from

ABG)(760-47) x FiO2(%) – PaCO2 / 0.8 – PaO2 713 x 0.21– 40 / 0.8 – PaO2 150– 50 – PaO2 100 – PaO2

*Normal gradient = Age/4+4*In a healthy young adult, this is about 10 mmHg but can change

dramatically with diseases affecting diffusion membrane

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Oxygen in the Blood

• Total O2– Total O2 = (Hb(g/dl) x 1.34 x SaO2) + (PaO2 x 0.003)

= (14 x 1.34 x 0.98) ….… + (90 x 0.003)

=18.4 ml/100ml blood …. + 0.27 ml/100ml blood

Oxygen Bound toHemoglobin

OxygenDissolved inPlasma

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Point for Possible Confusion

• PaO2 and SaO2 are completely different, though interdependent measurements

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Oxyhemoglobin Dissociation Curve

• What moves it to the right?– Lower pH– Higher PaCO2– Higher temp– Higher level of

2,3 BPG• Usually

induced by chronic hypoxemia

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CO2 Transport

• CO2 transport– 23% bound to Hb – Carbaminohemoglobin– 70% as HCO3 – Bicarbonate– 7% dissolved in plasma

• Volatile as H2CO3– H20 + CO2 H2CO3 H+ + HCO3-

– Amount present is unmeasureable due to volatility but proportional to PaCO2

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Normal VentilationAir Movement + Diffusion

• Inspiration– Negative intrathoracic pressure via diaphragm

and intercostal muscles

• Simple diffusion of O2 and CO2• Expiration

– Positive intrathoracic pressure via relaxation of diaphragm and intercostals

– Lung recoil

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Working Together

• V/Q – Ventilation / Perfusion– Matching/mismatching

• Shunting– PNA, pulmonary edema, atelectasis…

• Dead space ventilation– Pulmonary embolism

• Compensatory mechanisms– Pulmonary arteriole constriction

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Acute Respiratory FailureWhere To Start

• Where does the problem lie?– Air movement

• Apnea/Hypopnea

• Airway resistance– Asthma

– Edema

– Lung or chest wall compliance• Restriction/Trauma

• Interstitial fibrosis

• Air trapping

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Acute Respiratory FailureWhere Else…

• Diffusion abnormalities– Interstitial edema/fibrosis– Gradient abnormalities

• Relation to diffusion membrane– (A-a gradient)

• Ambient hypoxemia

– V/Q mismatch• Shunting

• Dead space ventilation

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Acute Respiratory FailureWhere Else…

• Blood flow– Fast flow

• Rest vs. exercise

– Slow flow• HF

• Pulmonary vascular resistance

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Acute Respiratory FailureWhere Else…

• Gas transport– Hemoglobin level

• Anemia

– Oxyhemoglobin dissociation

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Acute Respiratory FailureManifestations

• Hypoxemia

• Hypercapnia (ventilatory failure)

• ABG representation

• Rapid onset, severe V/Q mismatch

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Acute Respiratory Failure Etiology

• Pneumonia• COPD• Sepsis• MI• PE• Pulmonary edema

• Pneumothorax• Lung Path.• Drugs• Shock• Trauma• ARDS

Complication of another condition…

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Acute Respiratory Failure Typical Presentation

• Respiratory distress Respiratory rate

– Use of accessory muscles of respiration

• Scalene m.

• Sternocleidomastoid m.

• Pectoralis Major m.

• Abdominals

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Acute Respiratory Failure Presentation (Cont)

• Coma

• Cyanosis

• Diaphoresis –sweating

• Delirium

• Lethargy (esp. with COPD)– CO2 narcosis / hypoxic drive

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Acute Respiratory Failure Mimics

• Anxiety

• Pain

• Agitation

• Panic attack

• Kussmaul’s breathing

• Cheyne-Stokes breathing – between hypo/hyperventilation

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Acute Respiratory Failure Rapid Diagnostics

• ABG – the way to know

• CXR

– PA/Lat vs. portable

• EKG

• CBC, CMP, Mg, CK-MB, Troponin I

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Acute Respiratory Failure Interventions

• Hypoxemia

– O2 delivery systems

• Nasal cannula/Oxymizer

• Simple mask - not used

• Partial rebreather mask - not used

• Venturi mask

• Non-rebreather mask

• To maintain PaO2 60 or SaO2 90%

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Acute Respiratory Failure Interventions

• Ventilatory support

– BIPAP (NPPV) –non invasive pos pressure –

when we think it will only be for a short time.

– Endotracheal intubation

– Mechanical ventilation (PPV)

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Reasons to Intubate

• Airway obstruction• Airway protection• Secretion management• Unresponsive hypoxemia• Ventilation management

– Acidosis– Apnea– Injury/toxicity

• Anesthesia

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Mechanical Ventilation Modes

• CMV – controlled mechanical ventilation

• A/CMV – assist/control mechanical ventilation

• IMV/SIMV – synchronized intermittent mandatory ventilation

• PSV – pressure support ventilation

• PCV – pressure control ventilation

• PEEP – positive end expiratory pressure

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Consequences of PPV

• Barotrauma• Vent. assoc. lung

injury• Hemodynamic effects• Hemodynamic

monitoring changes• Muscle atrophy

• Impaired mucociliary clearance

• O2 toxicity• GI• Splanchnic / Renal• Cerebral• Auto PEEP

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Consequences of PPV (Cont)

• Auto PEEP

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CMV - Weaning Modalities

• Treat underlying

illness or cause of

respiratory failure to

maximum effect.

• Treat complications.

• Then...

• Wean O2 / PEEP Assist Breaths• Use of PSV• NIF

– At least -20 cmH2O

• F/U ABG

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Acute Lung Injury (ALI)

• “Acute and persistent lung inflammation with increased vascular permeability”

• 3 clinical features:– Bilateral infiltrates– PaO2 / FiO2 ratio 201-300 (room air PaO2

60)• Lower value = worse disease

– No evidence of left atrial pressure• PCWP 18 mmHg or less

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Acute Respiratory Distress Syndrome (ARDS)

• Definition

– “Severe end of the spectrum of “acute lung

injury””

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Acute Respiratory Distress Syndrome

• ALI - worse

• PaO2 / FiO2 ratio 200 or less– Room air PaO2 40

• Diffuse alveolar damage

• Low lung compliance vascular permeability diffusion gradient

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ARDS Presentation

• Initial– Severe Hypoxemia

– Tachypnea / Dyspnea

– Diffuse rales

– Rapid decline and need for mechanical ventilation

• ABG– Acute respiratory alkalosis – so hypoxic that they are

hyperventilationg

– Severe hypoxemia

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ARDS Dx

• Initially resembles CHF or Pulmonary

Edema

• Importance of clinical course

• Swan Ganz catheter

• BNP or NT-Pro BNP

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ARDS Etiology

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ARDS Occurrence

• Approx. 190,600 cases / yr

• 15% ICU pts

• 20% mech vent pts

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ARDS DDx

• Diffuse alveolar hemorrhage

• Acute interstitial pneumonia

• Idiopathic acute eosinophilic pneumonia

• Carcinoma

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ARDS Complications

• Mostly related to CMV– Barotrauma– Nosocomial Pneumonia– Multisystem failure

• DVT – pt not mobile• GI bleed• Malnutrition• Catheter related infections• Drug effects

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ARDS Tx

• O2• Prudent sedation /

paralysis• Analgesia• Diuresis• PPV

• Nutritional support• Glucose control• VTE prophylaxis• GI prophylaxis• Prudent transfusions• Monitor for

nosocomial pneumonia

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ARDS Prognosis

• 25-30% mortality

– Multisystem failure

• Variable outcomes in survivors

– Long term neurocognitive impairment

– Ventilatory impairment resolves

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Remember the Cases?

• 18 year old male in ED with history of anxiety and acute onset of dyspnea and SOB. P: 94, R: 28, BP: 132/78, T: 37.0, SaO2: 99% on room air. Panic attack

• You are called for a 58 year old female admitted 2 days prior with sepsis. Now with severe SOB. P: 110, R:36, BP: 105/66, T:37.6, SaO2 90% on 4 liter nasal cannula. Give more o2, investigate, ddx ARDS

• You are called for a 78 year old male admitted 10 hours prior for exacerbation of COPD. He is obtunded and barely rousable. P: 88, R: 6, BP: 146/88, T: 36.8, SaO2 95% on 4 liter nasal cannula. Partially comp resp acidosis. Went into acute resp failure on acute resp acidosis. Decreased resp drive.ABG: 7.13 / 103 / 86 / 33 / 93%R.O.M.E. ?

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References

• 1. Prchal, J.T. Diagnosis and Treatment of Methemoglobinemia. In UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA, 2006.

• 2. Lyn-Kew, K., Hyzy, R.C. Physiologic and Pathophysiologic Consequences of Positive Pressure Ventilation. In UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA, 2006.

• 3. Hansen-Flaschen, J., Siegel, M.D. Acute Respiratory Distress syndrome: Definition; Epidemiology; Diagnosis; and Etiology. In UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA, 2006.

• 4. Siegel, M.D. Acute Respiratory Distress Syndrome: Pathophysiology; Clinical Manifestations; and Prognosis. In UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA, 2006.

• 5. Siegel, M.D. Supportive Care and Oxygenation in Acute Respiratory Distress Syndrome. In UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA, 2006.

• 6. Lung Function Fundamentals. At www.anaesthetist.com/icu/organs/lung/lungvol.gif accessed 9/09.