Vomiting vs Laxatives
- Vomiting = loss of gastric acid → metabolic alkalosis
- Laxatives = loss of bicarbonate-rich intestinal fluid → metabolic acidosis
Vomiting
- Metabolic alkalosis
- Increased H+ loss from stomach acid → Retained HCO3-
- ↓ Cl-
- ↓ Urine Cl- (Kidney tries to retain)
- ↓ K+
- Hypovolemia
Laxative Abuse
- Metabolic acidosis
- ↓ HCO3- → lost in diarrhea
- ↓ Cl-
- ↑ Urine Cl- saline laxatives
- ↓ Urine Cl- stimulant laxatives
- ↓ K+
- Hypovolemia
| Feature | Vomiting | Laxative Abuse |
|---|---|---|
| Primary Acid-Base | Metabolic alkalosis | Metabolic acidosis |
| Serum HCO₃⁻ | ↑ (retained due to acid loss) | ↓ (lost in diarrhea) |
| Serum Cl⁻ | ↓ (hypochloremia) | ↓ (due to GI losses) |
| Serum K⁺ | ↓ (renal loss due to aldosterone) | ↓ (GI losses + secondary hyperaldosteronism) |
| Urine Cl⁻ | ↓ (<20 mEq/L, kidney tries to retain Cl⁻) | ↑ (>20 mEq/L if using saline laxatives) or ↓ with stimulant laxatives |
| Volume Status | Hypovolemic | Hypovolemic |
| Aldosterone | ↑ (volume depletion activates RAAS) | ↑ |