Acute Respiratory Failure

Acute Respiratory Acute Respiratory

FailureFailure

Acute Respiratory FailureAcute Respiratory Failure

• Failure in one or both gas exchange functions: oxygenation and carbon dioxide elimination

• In practice:

PaO2<60mmHg or PaCO2>46mmHg

• Derangements in ABGs and acid-base status

Acute Respiratory FailureAcute Respiratory Failure

• Hypercapnic v Hypoxemic respiratory failure

• ARDS and ALI

Hypercapnic Respiratory FailureHypercapnic Respiratory Failure

(PAO2 - PaO2)

Alveolar Hypoventilation

V/Q abnormality

PI max

increasednormal

Nl VCO2

PaCO2 >46mmHgNot compensation for metabolic alkalosis

CentralHypoventilation

NeuromuscularProblem

VCO2

V/Q Abnormality

HypermetabolismOverfeeding

The Case of Patient RVThe Case of Patient RV

71M s/p L AKA revision.PMH: CAD s/p CABG, COPD on home O2 and CPAP, DM, CVA, atrial fibrillation

PACU: L pleural effusion, hypotension, altered mental status. Sent to ICU for monitoring.

POD#1: RR overnight, intermittently hypoxic.BiPAP 40%: 7.34/65/63/35/+10Preintubation: 7.28/91/81/43


(PAO2 - PaO2)


V/Q abnormality

PI max

increasednormal

Nl VCO2



NeuromuscularProblem

VCO2

V/Q Abnormality




Brainstem respiratory depression Drugs (opiates) Obesity-hypoventilation syndrome

PI max


NeuromuscularDisorder

nlPI max

Critical illness polyneuropathyCritical illness myopathy

HypophosphatemiaMagnesium depletion

Myasthenia gravisGuillain-Barre syndrome


(PAO2 - PaO2)


V/Q abnormality

PI max

increasednormal

Nl VCO2



NeuromuscularDisorder

VCO2

V/Q Abnormality



V/Q abnormalityIncreased Aa gradient

Nl VCO2

VCO2

V/Q Abnormality




Nl VCO2

VCO2

V/Q Abnormality


• Increased dead space ventilation• advanced emphysema• PaCO2 when Vd/Vt >0.5

• Late feature of shunt-type• edema, infiltrates



Nl VCO2

VCO2

V/Q Abnormality


• VCO2 only an issue in pts with ltd ability to eliminate CO2

• Overfeeding with carbohydrates generates more CO2

Hypoxemic Respiratory FailureHypoxemic Respiratory Failure

Is PaCO2 increased?

Hypoventilation (PAO2 - PaO2)?

Hypoventilation alone

Respiratory driveNeuromuscular dz

Hypovent plus another

mechanism

Shunt

Inspired PO2

High altitudeFIO2

(PAO2 - PaO2) No

NoYes

Is low PO2 correctable

with O2?

V/Q mismatch

No Yes

Yes

The Case of Patient ESThe Case of Patient ES

77F s/p MVC. Injuries include multiple L rib fxs, L hemopneumothorax s/p chest tube placement, L iliac wing fx. PMH: atrial arrhythmia, on coumadin. INR>2

HD#1 RR 30s and shallow. Pain a/w breathing deeply.Placed on BiPAP overnight

PID#1BiPAP 80%: 7.45/48/66/32/+10


Is PaCO2 increased?

Hypoventilation (PAO2 - PaO2)?

Hypoventilation alone

Respiratory driveNeuromuscular dz

Hypovent plus another

mechanism

Shunt

Inspired PO2

High altitudeFIO2

(PAO2 - PaO2) No

NoYes

Is low PO2 correctable

with O2?

V/Q mismatch

No Yes

Yes


V/Q mismatch

V/Q mismatch DO2/VO2 Imbalance

PvO2>40mmHg PvO2<40mmHg

DO2: anemia, low COVO2: hypermetabolism


V/Q mismatch

SHUNTV/Q = 0

DEAD SPACEV/Q = ∞

AtelectasisIntraalveolar filling Pneumonia Pulmonary edema

Pulmonary embolusPulmonary vascular dzAirway dz (COPD, asthma)

Intracardiac shuntVascular shunt in lungs

ARDSInterstitial lung dzPulmonary contusion


Acute Respiratory Distress Syndrome

• Severe ALI• B/L radiographic

infiltrates• PaO2/FiO2 <200mmHg

(ALI 201-300mmHg)• No e/o L Atrial P;

PCWP<18



• Develops ~4-48h• Persists days-wks• Diagnosis:

– Distinguish from cardiogenic edema

– History and risk factors

Inflammatory Alveolar Injury


Pro-inflmm cytokines (TNF, IL1,6,8)



Neutrophils - ROIs and proteases damage capillary endothelium and alveolar epithelium


Fluid in interstitium and alveoli




Fluid in interstitium and alveoli

• Impaired gas exchange Compliance PAP





Exudative phase Fibrotic phaseProliferative phase

Diffuse alveolar damage



Direct Lung Injury• Infectious pneumonia• Aspiration, chemical pneumonitis• Pulmonary contusion, penetrating lung injury• Fat emboli• Near-drowning• Inhalation injury• Reperfusion pulmonary edema s/p lung transplant



Indirect Lung Injury• Sepsis• Severe trauma with shock/hypoperfusion• Burns• Massive blood transfusion• Drug overdose: ASA, cocaine, opioids, phenothiazines,

TCAs. • Cardiopulmonary bypass• Acute pancreatitis



Complications• Barotrauma

• Nosocomial pneumonia

• Sedation and paralysis persistent MS depression and neuromuscular weakness



• 861 patients, 10 centers• Randomized• Tidal Vol 12mL/kg PDW,

PlatP<50cmH2O• Tidal Vol 6mL/kg PDW,

PlatP<30cmH2O• NNT 12

• 31% mortality v 39.8%• 65.7% breathing without assistance by day 28 v 55%• Significantly more ventilator-free days• Significantly more days without failure of nonpulmonary

organs/systems

Acute Respiratory Failure

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