1. Respiratory Failure Kenney Weinmeister M.D.

2. Definition Demand overwhelms the capacity of the system Hypoxemia: PaO2 < 60 mmHg Hypercarbia: PaCO2 > 49 mmHg

3. Alveolar-arterial Oxygen Tension Difference PAO2 = FIO2 x atmos. pres. - PaCO2/R PAO2 = 150 - PaCO2/0.8 P(A-a) O2 gradient = 2.5 + 0.21 x age (yr)

4. Duration of Hypercarbia Acute minutes to hours –Acute Change in pH =.008 x change PCO2 Chronic days –Chronic Change in pH =.003 x change PCO2 Mixed –Change in pH is >.003 <.008

5. Hypoxemic Respiratory Failure Hypoventilation –Normal A-a gradient V/Q mismatch –Elevated A-a gradient Significantly improves with !00% oxygen Right to left shunts –Elevated A-a gradient Does not significantly improve with 100% oxygen

6. Hypercapnic Respiratory Failure Hypoventilation –Extrapulmonary disorders Severe V/Q mismatch

7. Extrapulmonary Respiratory Failure Hypoxemic with normal A-a gradient Hypercarbic acute or chronic –CNS –PNS –Respiratory muscles –Chest Wall –Pleura –Upper Airways

8. Central Nervous System Causes of Respiratory Failure Drugs Hypothyroidism Brainstem injury or tumor Primary alveolar hypoventilation Central sleep apnea

9. Peripheral Nervous System Causes of Respiratory Failure Spinal cord Tetanus Strychnine ALS Guillain Barre Synd. Shellfish Bilateral phrenic nerve palsy Diptheria Pseudocholinesterase deficiency Myasthenia Gravis Eaton-Lambert Botulism Organophosphate poisoning

10. Respiratory Muscle Dysfunction Muscular dystrophies Myotonic dystrophies Polymyositis Periodic paralysis Electrolyte disorders

11. Chest Wall and Pleural Disorders Kyphoscoliosis Obesity hypoventilation Flail chest Fibrothroax Thoracoplasty Ankylosing spondylitis

12. Upper Airway Obstruction Acute epiglottitis Acute laryngeal edema –Anaphylaxis –Trauma Foreign body aspiration Retropharyngeal hemorrhage Bilateral vocal cord paralysis Tracheal stenosis Tracheomalasia Tumors

13. Pulmonary Causes of Respiratory Failure Lower airway –Asthma, COPD Parenchymal –Pulm. Edema, infections, interstitial lung dz Pulmonary vasculature –PE, Primary pulmonary hypertension

14. Options for Ventilation Noninvasive positive pressure ventilation Invasive positive pressure ventilation Negative pressure ventilation

15. Noninvasive Positive Pressure Ventilation Continuous positive airway pressure –Hypoxemia –Functional airway obstruction Bilevel positive airway pressure –Hypercarbia –COPD –Neuromuscular or chest wall disorders

16. Invasive Positive Pressure Ventilation Acute decompensation Fail NIPPV Mechanical Airway obstruction Protect airway

17. Negative Pressure Ventilation Chronic respiratory failure Neuromuscular disease No functional airway obstruction

18. Conclusion Differentiate type of respiratory failure –Hypoxemic vs hypercarbia –Hypoventilation vs V/Q mismatch Determine if chronic or acute Most often acute respiratory failure due to V/Q mismatch