💊 Chapter 126: Salicylate Poisoning

Mixed respiratory alkalosis + metabolic acidosis · Tinnitus, hyperventilation, fever · Done nomogram · Urinary alkalinisation (urine pH >7.5) · Haemodialysis · Severe: CNS depression, pulmonary oedema · Activated charcoal · Oil of wintergreen (methyl salicylate) highly concentrated

🔍 Core Concepts: Salicylate Poisoning

📌 Mechanism
Uncoupling of oxidative phosphorylation → fever, metabolic acidosis. Direct respiratory centre stimulation → respiratory alkalosis (mixed disorder). Increased oxygen demand, hyperventilation, tinnitus.
⚠️ Clinical Features
Mild: nausea, tinnitus, tachypnoea. Moderate: fever, diaphoresis, agitation. Severe: metabolic acidosis, CNS depression, seizures, pulmonary oedema, renal failure.
📊 Done Nomogram
Plot salicylate level (mg/dL) vs time post-ingestion. Level above line indicates toxicity. Not reliable for chronic overdose or >24h.
💊 Urinary Alkalinisation
IV sodium bicarbonate to achieve urine pH >7.5 (traps salicylate, increases excretion 4-fold). Target blood pH 7.50-7.55. Monitor K+ (hypokalaemia reduces efficacy).
🩸 Haemodialysis
Indications: severe metabolic acidosis (pH <7.2), CNS depression, pulmonary oedema, renal failure, level >100 mg/dL (acute) or >60 (chronic).
⚠️ Oil of Wintergreen (Methyl Salicylate)
Extremely concentrated (1 tsp = 7 g aspirin). Small ingestion (1-2 mL) can be fatal. Treat aggressively.

🩺 Stepwise Approach: Salicylate Poisoning

1
ABCs & stabilization
Airway: intubate if CNS depression. Breathing: avoid hyperventilation (already present). Circulation: IV fluids (dehydration common). Activated charcoal 1 g/kg if within 1-2h.
2
Laboratory evaluation
Salicylate level (draw at 2-6h; repeat q2-3h until peak and declining). ABG (mixed respiratory alkalosis + metabolic acidosis). Electrolytes, glucose, BUN/Cr, LFTs.
3
Urinary alkalinisation (if moderate-severe)
IV sodium bicarbonate 1-2 mEq/kg bolus, then 150 mEq/L in D5W at 1.5-2x maintenance. Target urine pH >7.5, blood pH 7.50-7.55. Monitor K+ (add KCl if hypokalaemia).
4
Haemodialysis indications
Severe metabolic acidosis (pH <7.2), CNS depression (seizures, coma), pulmonary oedema, renal failure, salicylate level >100 mg/dL (acute) or >60 (chronic), or failure of alkalinisation.
5
Supportive care
Correct hypoglycaemia. Treat hyperthermia with cooling (antipyretics ineffective). Avoid bicarbonate if no acidosis. Forced diuresis contraindicated (pulmonary oedema risk).
6
Repeat levels
Check salicylate level q2-4h until falling. Sustained-release or enteric-coated may have delayed peak. Monitor for deterioration.