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Acute Respiratory Failure

Acute Respiratory Failure. Acute 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 Failure.

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Acute Respiratory Failure

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  1. Acute Respiratory Failure

  2. Acute 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

  3. Acute Respiratory Failure • Hypercapnic v Hypoxemic respiratory failure • ARDS and ALI

  4. Hypercapnic Respiratory Failure PaCO2 >46mmHg Not compensation for metabolic alkalosis (PAO2 - PaO2) normal increased Alveolar Hypoventilation V/Q abnormality VCO2 Nl VCO2 PI max Central Hypoventilation Neuromuscular Problem Hypermetabolism Overfeeding V/Q Abnormality

  5. The 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/+10 Preintubation: 7.28/91/81/43

  6. Hypercapnic Respiratory Failure PaCO2 >46mmHg Not compensation for metabolic alkalosis (PAO2 - PaO2) normal increased Alveolar Hypoventilation V/Q abnormality VCO2 Nl VCO2 PI max Central Hypoventilation Neuromuscular Problem Hypermetabolism Overfeeding V/Q Abnormality

  7. Hypercapnic Respiratory Failure Alveolar Hypoventilation nlPI max PI max Central Hypoventilation Neuromuscular Disorder Critical illness polyneuropathy Critical illness myopathy Hypophosphatemia Magnesium depletion Myasthenia gravis Guillain-Barre syndrome Brainstem respiratory depression Drugs (opiates) Obesity-hypoventilation syndrome

  8. Hypercapnic Respiratory Failure PaCO2 >46mmHg Not compensation for metabolic alkalosis (PAO2 - PaO2) normal increased Alveolar Hypoventilation V/Q abnormality VCO2 Nl VCO2 PI max Central Hypoventilation Neuromuscular Disorder Hypermetabolism Overfeeding V/Q Abnormality

  9. Hypercapnic Respiratory Failure V/Q abnormality VCO2 Increased Aa gradient Nl VCO2 Hypermetabolism Overfeeding V/Q Abnormality

  10. Hypercapnic Respiratory Failure V/Q abnormality VCO2 Increased Aa gradient Nl VCO2 Hypermetabolism Overfeeding V/Q Abnormality • Increased dead space ventilation • advanced emphysema • PaCO2 when Vd/Vt >0.5 • Late feature of shunt-type • edema, infiltrates

  11. Hypercapnic Respiratory Failure V/Q abnormality VCO2 Increased Aa gradient Nl VCO2 Hypermetabolism Overfeeding V/Q Abnormality • VCO2 only an issue in pts with ltd ability to eliminate CO2 • Overfeeding with carbohydrates generates more CO2

  12. Is low PO2 correctable with O2? Yes No V/Q mismatch Hypoxemic Respiratory Failure Is PaCO2 increased? Yes No Hypoventilation (PAO2 - PaO2)? Yes No (PAO2 - PaO2) Hypovent plus another mechanism Inspired PO2 Hypoventilation alone High altitude FIO2 Respiratory drive Neuromuscular dz Shunt

  13. The 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#1 BiPAP 80%: 7.45/48/66/32/+10

  14. Is low PO2 correctable with O2? Yes No V/Q mismatch Hypoxemic Respiratory Failure Is PaCO2 increased? Yes No Hypoventilation (PAO2 - PaO2)? Yes No (PAO2 - PaO2) Hypovent plus another mechanism Inspired PO2 Hypoventilation alone High altitude FIO2 Respiratory drive Neuromuscular dz Shunt

  15. Hypoxemic Respiratory Failure V/Q mismatch PvO2<40mmHg PvO2>40mmHg DO2/VO2 Imbalance V/Q mismatch DO2: anemia, low CO VO2: hypermetabolism

  16. Hypoxemic Respiratory Failure V/Q mismatch Atelectasis Intraalveolar filling Pneumonia Pulmonary edema ARDS Interstitial lung dz Pulmonary contusion SHUNT V/Q = 0 DEAD SPACE V/Q = ∞ Pulmonary embolus Pulmonary vascular dz Airway dz (COPD, asthma) Intracardiac shunt Vascular shunt in lungs

  17. Hypoxemic Respiratory Failure V/Q mismatch Atelectasis Intraalveolar filling Pneumonia Pulmonary edema ARDS Interstitial lung dz Pulmonary contusion SHUNT V/Q = 0 DEAD SPACE V/Q = ∞ Pulmonary embolus Pulmonary vascular dz Airway dz (COPD, asthma) Intracardiac shunt Vascular shunt in lungs

  18. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome • Severe ALI • B/L radiographic infiltrates • PaO2/FiO2 <200mmHg (ALI 201-300mmHg) • No e/o L Atrial P; PCWP<18

  19. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome • Develops ~4-48h • Persists days-wks • Diagnosis: • Distinguish from cardiogenic edema • History and risk factors

  20. Inflammatory Alveolar Injury

  21. Inflammatory Alveolar Injury Pro-inflmm cytokines (TNF, IL1,6,8)

  22. Inflammatory Alveolar Injury Pro-inflmm cytokines (TNF, IL1,6,8) Neutrophils - ROIs and proteases damage capillary endothelium and alveolar epithelium

  23. 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

  24. 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 • Impaired gas exchange •  Compliance •  PAP

  25. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome Exudative phase Fibrotic phase Proliferative phase Diffuse alveolar damage

  26. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome 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

  27. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome Indirect Lung Injury • Sepsis • Severe trauma with shock/hypoperfusion • Burns • Massive blood transfusion • Drug overdose: ASA, cocaine, opioids, phenothiazines, TCAs. • Cardiopulmonary bypass • Acute pancreatitis

  28. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome Complications • Barotrauma • Nosocomial pneumonia • Sedation and paralysis  persistent MS depression and neuromuscular weakness

  29. Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome • 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

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