Respiratory Failure Diagnosis and Management K. Weinmeister 1

Respiratory Failure Kenney Weinmeister M.D. Definition • Demand overwhelms the capacity of the system • Hypoxemia: PaO2 < 60 mmHg • Hypercarbia: PaCO2 > 49 mmHg 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) 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 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 Hypercapnic Respiratory Failure • Hypoventilation – Extrapulmonary disorders • Severe V/Q mismatch Extrapulmonary Respiratory Failure • Hypoxemic with normal A-a gradient • Hypercarbic acute or chronic – CNS – PNS – Respiratory muscles – Chest Wall – Pleura – Upper Airways Central Nervous System Causes of Respiratory Failure • • • • • Drugs Hypothyroidism Brainstem injury or tumor Primary alveolar hypoventilation Central sleep apnea 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 Respiratory Muscle Dysfunction • • • • • Muscular dystrophies Myotonic dystrophies Polymyositis Periodic paralysis Electrolyte disorders Chest Wall and Pleural Disorders • • • • • • Kyphoscoliosis Obesity hypoventilation Flail chest Fibrothroax Thoracoplasty Ankylosing spondylitis Upper Airway Obstruction • Acute epiglottitis • Bilateral vocal cord paralysis • Acute laryngeal edema • Tracheal stenosis – Anaphylaxis – Trauma • Tracheomalasia • Foreign body • Tumors aspiration • Retropharyngeal hemorrhage Pulmonary Causes of Respiratory Failure • Lower airway – Asthma, COPD • Parenchymal – Pulm. Edema, infections, interstitial lung dz • Pulmonary vasculature – PE, Primary pulmonary hypertension Options for Ventilation • Noninvasive positive pressure ventilation • Invasive positive pressure ventilation • Negative pressure ventilation Noninvasive Positive Pressure Ventilation • Continuous positive airway pressure – Hypoxemia – Functional airway obstruction • Bilevel positive airway pressure – Hypercarbia – COPD – Neuromuscular or chest wall disorders Invasive Positive Pressure Ventilation • • • • Acute decompensation Fail NIPPV Mechanical Airway obstruction Protect airway Negative Pressure Ventilation • Chronic respiratory failure • Neuromuscular disease • No functional airway obstruction 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