04-Acute 20Respiratory 20Failure 1

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Copyright 2008 Society of Critical Care Medicine

Diagnosis and Management

of Acute Respiratory Failure


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2Copyright 2008 Society of Critical Care Medicine

Objectives

Define and classify acute respiratoryfailure

Describe the pathophysiology andmanifestations of acute respiratoryfailureReview oxygen supplementationstrategies


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Case Study

Elderly man with chronic lungdisease is brought to ED withprogressive dyspnea

Respiratory rate 30/min, moderate

distressUsing accessory muscles, wheezing

What evaluation is needed to determine

if acute respiratory failure exists?

What findings suggest respiratory

failure?


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Case Study

Elderly man with chronic lungdisease is brought to ED withprogressive dyspnea

Respiratory rate 30/min, moderatedistressUsing accessory muscles, wheezing

The patient is likely to have whatform of respiratory failure?


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Forms of RespiratoryFailure

Hypoxemic

Room air PaO25060mm Hg (6.7-8 kPa)

Abnormal PaO2:FiO2ratio

Hypercapnic

PaCO2

50 mm Hg (6.7kPa) with pH


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Case Study

Arterial blood gas: pH 7.32, PaCO2 58mm Hg (7.7 kPa), PaO2 50 mm Hg (6.7kPa) on room air

Chest radiograph: hyperinflation,increased interstitial markings in thelower lobes

Why is this patient hypoxemic?


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Ventilation/perfusion mismatchImpaired gas diffusion

Alveolar hypoventilation

High altitude

Causes of Hypoxemia



Causes of Hypoxemia

O2

CO2

ShuntNormal V/Q Mismatch

Ventilation/perfusion mismatch



Causes of Hypoxemia

Impaired gas diffusionAlveolar hypoventilation

High altitude

Alveolar

hypoventilation

O2CO2

Impaired diffusion

High altitude



Case Study

Arterial blood gas: pH 7.32, PaCO2 58(7.7 kPa) mm Hg, PaO2 50 mm Hg (6.7kPa) on room air

Is the hypoxemia due tohypoventilation and PaCO2 ?

Alveolar-arterial O2 gradient

PAO2 =[FIO2 x (Pb 47)] [1.25 x PaCO2]PAO2 =[0.21 x (760 47)] [1.25 x 58] = 78

Gradient = 78-50 = 28 mm Hg (3.7 kPa)



Case Study

Elderly man with chronic lungdisease with dyspnea, tachypnea,and wheezing

Arterial blood gas: pH 7.32, PaCO2

58mm Hg (7.7 kPa), PaO2 50 mm Hg (6.7kPa) on room air

Why is this patient hypercapnic?



Hypercapnia

Alveolar minute ventilationVA= (VT-VD) f

What causes increaseddead space (VD)?

Hypovolemia

Low cardiac outputPulmonary embolus

High airway pressures



Case Study

Elderly man with chronic lungdisease with dyspnea, tachypneaand wheezing

Arterial blood gas: pH 7.32, PaCO2 58

mm Hg (7.7 kPa), PaO2 50 mm Hg (6.7kPa) on room air

How would you treat the hypoxemia?

Treat the underlying condition

Supplemental oxygen



O2 SupplementationDevices

O2 concentrationHigh

Controlled

Low

FlowHigh

Moderate

Low



Pharmacologic Adjuncts

Inhaled 2-agonists Metered-dose inhaler Nebulizer

Inhaled ipratropium Metered-dose inhaler Nebulizer

Corticosteroids

Antibiotics


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Case Study

Young woman overdosed onantidepressants and alcohol

Respiratory rate 8 breaths/min

Arterial blood gas: pH 7.15, PaCO271 mm Hg (9.5 kPa), PaO2 56 mm Hg(7.5 kPa) on room air

Why is this patient hypoxemic?PAO2 =[0.21 x (760 47)] [1.25 x 71]

= 61


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Case Study

Why is this patient hypercapnic?

How would you treat the hypoxemia?

Young woman overdosed onantidepressants and alcohol

Respiratory rate 8 breaths/min

Arterial blood gas: pH 7.15, PaCO271 mm Hg (9.5 kPa), PaO2 56 mm Hg(7.5 kPa) on room air


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Questions


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Key Points

Acute respiratory failure is classifiedas hypoxic, hypercapnic or mixed

Ventilation/perfusion mismatching isthe most common cause of hypoxic

ARFHypercapnic ARF is due todecreased minute ventilation

O2

supplementation is used to treathypoxemiaPharmacologic adjuncts may beneeded in ARF

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04-Acute 20Respiratory 20Failure 1