Respiratory acidosis

Background

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

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

DDX

1. COPD
2. Drugs (opioids)
3. Chest wall dz
4. Pleural dz
5. Trauma

Treatment

1. Improve alveolar ventilation
   1. Bronchodilators
   2. CPAP
   3. Intubation (esp of pH < 7.25)
      1. Do not reduce pH too quickly (>5Hg/h)
         1. Can lead to abrupt hypocalcemia/hypokalemia

Source

Tintinalli, KAJI 2011