Respiratory Failure

An inability of the lungs to maintain arterial blood gas (ABG) at normal levels when a subject breathes air at rest
1. Failure for oxgenation
2. Failure for CO2 removal
3. Failure for both
General guideline: PO2 < 60mmHg and/or PCO2 > 50mmHg
Physiological causes
1. Hypoventilation
  1. Upper airway obstruction
    1. Dec. PO2 + Inc. PCO2
  2. Weakness/ paralysis of respiratory muscles
  3. Chest wall injury
2. Alveolar ventilation/ perfusion mismatching
  1. Chronic obstructive lung disease
  2. Restrictive disease
    1. Dec. PO2 + Inc. PCO2/ Normal PCO2
  3. Pneumonia
3. Impaired diffusion
  1. Lung edema
  2. Adult respiratory distress syndrome (Shock lung)
    1. Dec. PO2 + Normal PCO2/ Dec. PCO2
      1. N. PCO2 due to high solubility coefficient of CO2
Types
1. Type I
  1. Gas exchange failure
  2. PO2 < 60mmHg ; PCO2 < 50mmHg
2. Type II
  1. Ventilatory failure
  2. PO2 < 60mmHg ; PCO2 > 50mmHg
Hypoxemia
1. Causes
  1. Hypoventilation
  2. Diffusion impairment
  3. Shunt
    1. Blood passing process X do gas exchange
  4. V/Q mismatching
2. Detection
  1. Cyanosis
  2. Tachycardia
  3. CNS (mental clouding)
  4. PaO2
3. Effects
  1. Tissue hypoxia: Dec. O2 delivery
  2. (CNS, myocardium)
  3. Ceasation of aerobic oxidation
  4. Anaerobic glycolysis
  5. Metabolic acidosis (lactic acid)
4. Physiological changes
  1. Mild (PaO2 60mmHg)
    1. Mental performance impaired
    2. Vision impaired
    3. Mild hyperventilation
  2. Severe (PaO2 < 40mmHg)
    1. CNS (Headache, sleepy, clouding of consciousness)
    2. CVS (Tachycardia, mild hypertension)
    3. Pulmonary (hypertension)
  3. Very severe (PaO2 Dec.)
    1. CNS (Permanent damage)
    2. CVS (Bradycardia, hypotension)
    3. Pulmonary (Severe hypertension)
    4. Renal (Proteinuria)
Hypercapnia
1. Causes
  1. Hypoventilation
  2. V/Q mismatching
  3. Injudicious use of O2 therapy
    1. Hypoxic ventilatory drive abolished --> V dec.
    2. Hypoxic pulmonary vasoconstriction abolished--> worsening of V/Q inequality
    3. i.e. Only giving O2 but not improving ventilation
2. Effects
  1. Moderate hypercapnia
    1. Inc. cerebral blood flow
    2. Headache
      1. More blood--> Inc. cerebral pressure
  2. Severe hypercapnia
    1. Narcotic
    2. Clouding of consciousness
Acidosis
1. Respiratory acidosis (Inc. PCO2)
2. Metabolic acidosis (lactic acid)
  1. Renal compensation: HCO3- retention
Management
1. Treatment for underlying disease
  1. Antibiotic therapy for infection
  2. Specific treatment for neuromuscular disorder
2. Treatment for airway obstruction
  1. Removal of secretion
    1. Encouragement to cough
    2. Aspiration of secretion (brochoscopy)
    3. Prevent viscous secretion by adequate hydration
    4. Drubs to liquefy sputum
  2. Bronchoconstriction
    1. Use of bronchodilators
3. Treatment for hypoxemia
  1. Oxygen therapy (if necessary)
    1. Chronic obstructive disease: 25-30% O2
    2. Shock lung: 60% O2
    3. Effectiveness: evaluated by oximeter: SO2 > 90% = safe
  2. Mechanical ventilation
    1. For neuromuscular disorder
4. Treatment for hypercapnia
  1. Mechanical ventilation

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Respiratory Failure

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	Created by Mandy Ng about 9 years ago