Respiratory acidosis

Background

• acidemia = pH < 7.38
• respiratory acidosis = pCO2 > 42
• Acute respiratory acidosis: Change in pH = 0.008 X (40 - PaCO2)

vs. Chronic respiratory acidosis: Change in pH = 0.003 X (40 - PaCO2)

• determine if another primary acid/base disturbance is occurring
  • calculate AG
  • if HCO3 < 24 + (pCO2-40)/10 x 3(+/-1) then there is a superimposed primary metabolic acidosis
    • for every 10mm increase in pCO2 >40, HCO3expected increases by 2-4mEq (2 if acute/limited time for metabolic compensation, 4 if chronic i.e. COPD)
  • if HCO3 > 24 + (pCO2-40)/10 x 3(+/-1) then suspect primary metabolic alkalosis

Etiology

Hypoventilation - acute vs chronic

Differential Diagnosis

• COPD
• Drugs (Opioid Overdose)
• Chest wall dz
• Pleural dz
• Trauma

Management

Improve alveolar ventilation

1. Bronchodilators
2. CPAP
3. Intubation (esp of pH < 7.25)
   • Do not reduce pH too quickly (>5Hg/h)
     • Can lead to abrupt Hypocalcemia/Hypokalemia

See Also

• Acid-base disorders