Respiratory Failure

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Respiratory Failure

• Kenney Weinmeister M.D.

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Definition

• Demand overwhelms the capacity of the system
• Hypoxemia PaO2 lt 60 mmHg
• Hypercarbia PaCO2 gt 49 mmHg

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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)

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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 gt.003 lt.008

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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

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Hypercapnic Respiratory Failure

• Hypoventilation
• Extrapulmonary disorders
• Severe V/Q mismatch

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Extrapulmonary Respiratory Failure

• Hypoxemic with normal A-a gradient
• Hypercarbic acute or chronic
• CNS
• PNS
• Respiratory muscles
• Chest Wall
• Pleura
• Upper Airways

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Central Nervous System Causes of Respiratory
Failure

• Drugs
• Hypothyroidism
• Brainstem injury or tumor
• Primary alveolar hypoventilation
• Central sleep apnea

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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

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Respiratory Muscle Dysfunction

• Muscular dystrophies
• Myotonic dystrophies
• Polymyositis
• Periodic paralysis
• Electrolyte disorders

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Chest Wall and Pleural Disorders

• Kyphoscoliosis
• Obesity hypoventilation
• Flail chest
• Fibrothroax
• Thoracoplasty
• Ankylosing spondylitis

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Upper Airway Obstruction

• Acute epiglottitis
• Acute laryngeal edema
• Anaphylaxis
• Trauma
• Foreign body aspiration
• Retropharyngeal hemorrhage

• Bilateral vocal cord paralysis
• Tracheal stenosis
• Tracheomalasia
• Tumors

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Pulmonary Causes of Respiratory Failure

• Lower airway
• Asthma, COPD
• Parenchymal
• Pulm. Edema, infections, interstitial lung dz
• Pulmonary vasculature
• PE, Primary pulmonary hypertension

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Options for Ventilation

• Noninvasive positive pressure ventilation
• Invasive positive pressure ventilation
• Negative pressure ventilation

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Noninvasive Positive Pressure Ventilation

• Continuous positive airway pressure
• Hypoxemia
• Functional airway obstruction
• Bilevel positive airway pressure
• Hypercarbia
• COPD
• Neuromuscular or chest wall disorders

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Invasive Positive Pressure Ventilation

• Acute decompensation
• Fail NIPPV
• Mechanical Airway obstruction
• Protect airway

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Negative Pressure Ventilation

• Chronic respiratory failure
• Neuromuscular disease
• No functional airway obstruction

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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