What are the contraindications for forced alkaline diuresis?

Contraindications for Forced Alkaline Diuresis

Forced alkaline diuresis is contraindicated in patients who are losing chloride by vomiting or from continuous gastrointestinal suction, and in patients receiving diuretics known to produce hypochloremic alkalosis. 1

Definition and Mechanism

Forced alkaline diuresis is a treatment regimen that increases poison elimination through the administration of intravenous sodium bicarbonate to produce urine with a pH ≥ 7.5, combined with enhanced urine flow. This technique increases the elimination of certain toxins by ion trapping in the renal tubules.

Absolute Contraindications

1. Chloride-losing conditions:

   • Active vomiting 1
   • Continuous gastrointestinal suction 1
   • Concurrent use of diuretics causing hypochloremic alkalosis 1

2. Renal impairment:

   • Obstructive uropathy 2
   • Significant renal dysfunction 2
   • Acute kidney injury 2

3. Volume status abnormalities:

   • Hypovolemia 2
   • Severe fluid overload with pulmonary edema 2

4. Electrolyte disturbances:

   • Severe hypokalemia 2
   • Hypocalcemia 3
   • Pre-existing metabolic alkalosis 3

Relative Contraindications

1. Cardiovascular conditions:

   • Severe heart failure with reduced ejection fraction 2
   • Hemodynamic instability requiring vasopressors 2

2. Neurological conditions:

   • Intracranial hypertension 2
   • Risk of cerebral edema 4

3. Special populations:

   • Elderly patients with multiple comorbidities 2
   • Patients with liver disease 4

Complications to Monitor

1. Electrolyte imbalances:

   • Hypokalemia (most common) 3
   • Hypocalcemia 3
   • Hypomagnesemia 2

2. Acid-base disturbances:

   • Metabolic alkalosis 3
   • Alkalotic tetany 3

3. Hemodynamic issues:

   • Hypotension 2
   • Volume overload 5

4. Renal complications:

   • Worsening renal function 2
   • Xanthine precipitation in renal tubules (when used with allopurinol) 2

Clinical Decision Algorithm

1. Assess appropriateness of therapy:

   • Determine if the toxin is amenable to alkaline diuresis (e.g., salicylates, phenobarbital, chlorpropamide, 2,4-D, mecoprop) 3, 6
   • Consider alternative elimination methods if available (e.g., multiple-dose activated charcoal for phenobarbital) 3

2. Evaluate for contraindications:

   • Check renal function
   • Assess volume status
   • Review electrolyte panel
   • Evaluate cardiac function

3. If proceeding with therapy:

   • Monitor urine pH (target ≥ 7.5) 3
   • Maintain adequate urine flow (approximately 600 mL/h for certain toxins) 3
   • Supplement potassium to prevent hypokalemia 3
   • Monitor vital signs, fluid balance, and electrolytes frequently

Important Considerations

• The term "forced alkaline diuresis" should be replaced with "urine alkalinization" to emphasize that urine pH manipulation rather than diuresis is the primary objective 3
• For salicylate poisoning, urine alkalinization alone may be more effective and safer than combined forced alkaline diuresis 5
• Hemodialysis is superior to forced alkaline diuresis for severe poisonings and should be considered when criteria are met 3
• The risk-benefit ratio must be carefully assessed, as the procedure can cause significant fluid retention and electrolyte disturbances 5

Forced alkaline diuresis requires careful patient selection and monitoring to avoid potentially serious complications. When contraindications are present, alternative detoxification methods should be considered.