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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

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Respiratory failure

Respiratory Failure

Kenney Weinmeister M.D.


Definition
Definition

  • Demand overwhelms the capacity of the system

  • Hypoxemia: PaO2 < 60 mmHg

  • Hypercarbia: PaCO2 > 49 mmHg


Alveolar arterial oxygen tension difference
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
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
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
Hypercapnic Respiratory Failure

  • Hypoventilation

    • Extrapulmonary disorders

  • Severe V/Q mismatch


Extrapulmonary respiratory failure
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
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

Peripheral Nervous System Causes of Respiratory Failure


Respiratory muscle dysfunction
Respiratory Muscle Dysfunction

  • Muscular dystrophies

  • Myotonic dystrophies

  • Polymyositis

  • Periodic paralysis

  • Electrolyte disorders


Chest wall and pleural disorders
Chest Wall and Pleural Disorders

  • Kyphoscoliosis

  • Obesity hypoventilation

  • Flail chest

  • Fibrothroax

  • Thoracoplasty

  • Ankylosing spondylitis


Upper airway obstruction

Acute epiglottitis

Acute laryngeal edema

Anaphylaxis

Trauma

Foreign body aspiration

Retropharyngeal hemorrhage

Bilateral vocal cord paralysis

Tracheal stenosis

Tracheomalasia

Tumors

Upper Airway Obstruction


Pulmonary causes of respiratory failure
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
Options for Ventilation

  • Noninvasive positive pressure ventilation

  • Invasive positive pressure ventilation

  • Negative pressure ventilation


Noninvasive positive 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
Invasive Positive Pressure Ventilation

  • Acute decompensation

  • Fail NIPPV

  • Mechanical Airway obstruction

  • Protect airway


Negative pressure ventilation
Negative Pressure Ventilation

  • Chronic respiratory failure

  • Neuromuscular disease

  • No functional airway obstruction


Conclusion
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


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