Surgical Critical Care: Respiratory Acid-Base Disorders
Respiratory Acidosis
Causes
- Hypoventilation
- Neuromuscular Disease
- Asthma or COPD
- Interstitial Lung Disease
- Opioids
Physiologic Changes
Acuity
- Acute Respiratory Acidosis
- Only Slight Compensation Over Minutes-Hours from Cellular Buffering of Plasma Proteins
- Estimated Changes (For Every 10 mmHg Increase in pCO2 Above 40 mmHg):
- HCO3 Increases 1 mEq/L
- pH Decreases 0.08 Below 7.40
- Chronic Respiratory Acidosis
- Adequate Compensation Over Days-Weeks from Renal Excretion of Acid & Reabsorption of Bicarbonate
- Estimated Changes (For Every 10 mmHg Increase in pCO2 Above 40 mmHg):
- HCO3 Increases 3.5 mEq/L
- pH Decreases 0.03 Below 7.40
Treatment
- Treatment of Underlying Causes
- Correct Hypercapnia Gradually – Rapid Alkalization of CSF Can Cause Seizures
Respiratory Alkalosis
Causes
- Hyperventilation
- Anxiety
- Salicylates (Early)
- Pulmonary Embolism (PE)
Physiologic Changes
Acuity
- Acute Respiratory Alkalosis – High pH Change Due to Slow Renal Compensation
- Chronic Respiratory Alkalosis – Lower pH Change Due to Renal Compensation Over Days-Weeks with Decreased Reabsorption of Bicarbonate
Treatment
- Treatment of Underlying Causes