Does Organophosphate Poisoning Cause Metabolic Acidosis?
Yes, organophosphate poisoning definitively causes metabolic acidosis, which serves as both a diagnostic marker and prognostic indicator of severe poisoning. 1, 2, 3
Metabolic Acidosis as a Clinical Feature
Metabolic acidosis develops in organophosphate poisoning through multiple mechanisms:
- Systemic hypoxia from respiratory failure and tissue hypoperfusion leads to lactic acidosis within hours of exposure 4
- Cardiovascular collapse with reduced systemic vascular resistance contributes to tissue ischemia and acidosis 3
- The acidosis occurs even when respiratory function is adequately maintained with mechanical ventilation 3
Prognostic Significance
Acid-base status at presentation predicts mortality risk in a clear hierarchical pattern: no acidosis < metabolic acidosis < respiratory acidosis < mixed acidosis 1
- Patients with metabolic acidosis have a 25% mortality rate, with 75% of deaths due to cardiovascular failure 1
- Patients with respiratory acidosis have a 50% mortality rate, with deaths primarily from respiratory failure 1
- Mixed acidosis carries the highest mortality risk 1
Clinical Presentation and Complications
The metabolic acidosis in organophosphate poisoning is accompanied by:
- Severe dehydration and hypovolemia from hypersecretion of salivary, bronchial, and sweat glands, plus vomiting and diarrhea 4
- Refractory hypotension with maintained cardiac output but severely reduced systemic vascular resistance that does not respond to catecholamines 3
- Acute anuric renal failure in severe cases, requiring hemodialysis 2
- Rhabdomyolysis with myoglobinuria from calcium overload in skeletal muscle, further contributing to acidosis and renal damage 5
Treatment Implications
The presence of metabolic acidosis mandates aggressive treatment:
- Immediate atropine administration (1-2 mg IV for adults, doubled every 5 minutes until atropinization) 5, 6
- Early pralidoxime (2g IV loading dose followed by continuous infusion) 5
- Intravenous albumin and fluid resuscitation to restore blood volume and tissue oxygenation 4
- Benzodiazepines for seizures and agitation 5
- Early endotracheal intubation for life-threatening poisoning 5
Critical Monitoring Parameters
Monitor these laboratory values to detect and manage metabolic acidosis:
- Serial arterial blood gases to assess acid-base status 1
- Lactate levels as a marker of tissue hypoxia 4
- Creatine kinase and potassium for rhabdomyolysis detection 5
- Creatinine for renal function 4
Common pitfall: Do not delay antidote administration while waiting for laboratory confirmation of acidosis—clinical signs of severe poisoning (bronchorrhea, bronchospasm, seizures, bradycardia) require immediate treatment 5