Respiratory Failure

Respiratory Failure

1. An inability of the lungs to maintain arterial blood gas (ABG) at normal levels when a subject breathes air at rest

   • Failure for oxgenation
   • Failure for CO2 removal
   • Failure for both

2. General guideline: PO2 < 60mmHg and/or PCO2 > 50mmHg

3. Physiological causes

   • Hypoventilation
     • Upper airway obstruction
       • Dec. PO2 + Inc. PCO2
     • Weakness/ paralysis of respiratory muscles
     • Chest wall injury
   • Alveolar ventilation/ perfusion mismatching
     • Chronic obstructive lung disease
     • Restrictive disease
       • Dec. PO2 + Inc. PCO2/ Normal PCO2
     • Pneumonia
   • Impaired diffusion
     • Lung edema
     • Adult respiratory distress syndrome (Shock lung)
       • Dec. PO2 + Normal PCO2/ Dec. PCO2
         • N. PCO2 due to high solubility coefficient of CO2

4. Types

   • Type I
     • Gas exchange failure
     • PO2 < 60mmHg ; PCO2 < 50mmHg
   • Type II
     • Ventilatory failure
     • PO2 < 60mmHg ; PCO2 > 50mmHg

5. Hypoxemia

   • Causes
     • Hypoventilation
     • Diffusion impairment
     • Shunt
       • Blood passing process X do gas exchange
     • V/Q mismatching
   • Detection
     • Cyanosis
     • Tachycardia
     • CNS (mental clouding)
     • PaO2
   • Effects
     • Tissue hypoxia: Dec. O2 delivery
     • (CNS, myocardium)
     • Ceasation of aerobic oxidation
     • Anaerobic glycolysis
     • Metabolic acidosis (lactic acid)
   • Physiological changes
     • Mild (PaO2 60mmHg)
       • Mental performance impaired
       • Vision impaired
       • Mild hyperventilation
     • Severe (PaO2 < 40mmHg)
       • CNS (Headache, sleepy, clouding of consciousness)
       • CVS (Tachycardia, mild hypertension)
       • Pulmonary (hypertension)
     • Very severe (PaO2 Dec.)
       • CNS (Permanent damage)
       • CVS (Bradycardia, hypotension)
       • Pulmonary (Severe hypertension)
       • Renal (Proteinuria)

6. Hypercapnia

   • Causes
     • Hypoventilation
     • V/Q mismatching
     • Injudicious use of O2 therapy
       • Hypoxic ventilatory drive abolished --> V dec.
       • Hypoxic pulmonary vasoconstriction abolished--> worsening of V/Q inequality
       • i.e. Only giving O2 but not improving ventilation
   • Effects
     • Moderate hypercapnia
       • Inc. cerebral blood flow
       • Headache
         • More blood--> Inc. cerebral pressure
     • Severe hypercapnia
       • Narcotic
       • Clouding of consciousness

7. Acidosis

   • Respiratory acidosis (Inc. PCO2)
   • Metabolic acidosis (lactic acid)
     • Renal compensation: HCO3- retention

8. Management

   • Treatment for underlying disease
     • Antibiotic therapy for infection
     • Specific treatment for neuromuscular disorder
   • Treatment for airway obstruction
     • Removal of secretion
       • Encouragement to cough
       • Aspiration of secretion (brochoscopy)
       • Prevent viscous secretion by adequate hydration
       • Drubs to liquefy sputum
     • Bronchoconstriction
       • Use of bronchodilators
   • Treatment for hypoxemia
     • Oxygen therapy (if necessary)
       • Chronic obstructive disease: 25-30% O2
       • Shock lung: 60% O2
       • Effectiveness: evaluated by oximeter: SO2 > 90% = safe
     • Mechanical ventilation
       • For neuromuscular disorder
   • Treatment for hypercapnia
     • Mechanical ventilation