Can vomiting cause hyponatremia?

Can Vomiting Cause Hyponatremia?

Yes, vomiting can definitely cause hyponatremia through loss of chloride-rich gastric fluid and subsequent volume depletion, which triggers compensatory mechanisms that affect sodium balance. 1

Mechanism of Hyponatremia from Vomiting

Vomiting leads to hyponatremia through multiple pathophysiologic pathways:

• Direct fluid and electrolyte loss: Vomiting results in loss of chloride-rich gastric fluid, causing both hypochloremia and volume depletion 1
• Volume depletion triggers: The resulting hypovolemia activates compensatory mechanisms including non-osmotic vasopressin (ADH) release, which promotes water retention and dilutes serum sodium 2, 3
• Classification: This creates hypovolemic hyponatremia, where both sodium and water are lost, but proportionally more sodium is depleted 4, 3

Clinical Recognition in Older Adults

When assessing volume depletion from vomiting, look for at least four of these seven specific signs to identify moderate-to-severe depletion: confusion, non-fluent speech, extremity weakness, dry mucous membranes, dry tongue, furrowed tongue, and sunken eyes 5. Additional indicators include decreased venous filling (empty veins) and low blood pressure 5.

Severity Thresholds Requiring Action

The consensus guidelines provide clear triggers for intervention:

• Significant fluid loss from vomiting should trigger sick day medication guidance and electrolyte monitoring 5
• Greater than 4 episodes of vomiting in 12 hours or inability to keep fluids down warrants immediate contact with healthcare providers 5
• Severe symptoms requiring emergency care include reduced consciousness, new confusion, or inability to maintain fluid intake 5

Treatment Approach

For hypovolemic hyponatremia from vomiting, the treatment is volume repletion with isotonic fluids (0.9% normal saline), NOT fluid restriction 5, 4, 3:

• Administer isotonic fluids orally, nasogastrically, subcutaneously, or intravenously depending on severity 5
• Normal saline (154 mEq/L sodium) is the appropriate choice for hypovolemic hyponatremia 4
• Maximum correction rate: Do not exceed 8 mmol/L increase in sodium over 24 hours to prevent osmotic demyelination syndrome 1, 4

Common Clinical Pitfall

A critical mistake is treating vomiting-induced hyponatremia with fluid restriction—this is only appropriate for euvolemic hyponatremia (SIADH), not hypovolemic states 4, 3. Patients with volume depletion from vomiting require volume replacement, as fluid restriction would worsen their condition 5.

Additional Electrolyte Considerations

• Potassium replacement is often necessary concurrently, as vomiting typically causes hypokalemia alongside hyponatremia 1
• Hypochloremia typically resolves with correction of the hyponatremia using chloride-containing solutions like normal saline 1, 6

Case Example from Literature

A documented case demonstrated severe hyponatremia (94 mEq/L) in a patient with nausea, vomiting, and multiple falls, where the hyponatremia was directly attributed to volume loss from vomiting combined with diuretic use and consumption of solute-free water 7. This illustrates how vomiting can contribute to profound sodium disturbances, particularly when combined with other risk factors.