Acute Respiratory Acute Respiratory Failure Failure

Acute Respiratory Failure Failure in one or both gas exchange functions: oxygenation and carbon dioxide elimination In practice: PaO2 46mmHg Derangements in ABGs and acid-base status

Acute Respiratory Failure Hypercapnic v Hypoxemic respiratory failure ARDS and ALI

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome 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)

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

Inflammatory Alveolar Injury Fluid in interstitium and alveoli Pro-inflmm cytokines (TNF, IL1,6,8) Neutrophils - ROIs and proteases damage capillary endothelium and alveolar epithelium

Inflammatory Alveolar Injury Fluid in interstitium and alveoli Impaired gas exchange  Compliance  PAP Pro-inflmm cytokines (TNF, IL1,6,8) Neutrophils - ROIs and proteases damage capillary endothelium and alveolar epithelium

Hypoxemic Respiratory Failure Acute Respiratory Distress Syndrome Exudative phaseFibrotic phase Proliferative phase Diffuse alveolar damage

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

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

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

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