Lab Case 32 – Interpretation

1. Her blood gas shows:

Mixed respiratory alkalosis and high anion gap metabolic acidosis, elevated lactate and hypokalaemia. Normal renal function and ketones. Previously healthy female who is tachycardic and hypotensive.

 

Anion gap = 19, expected CO2 = 32 with actual of 24

2. Salicylate toxicity.

Other causes include sepsis (CNS, other), other toxins (metformin, paracetamol).

No renal failure or ketoacidosis

3. Risk assessment:

A young female with clinical signs of severe Salicylate toxicity, likely to be acute, within the last 6-12 hours (due to age, symptoms) as evidenced by acidaemia and  tachypnoea. The dose is likely to be > 300 mg/kg
Normal renal function is reassuring in terms of treatment required.

Rapid deterioration is expected without immediate intervention

In general, Salicylate toxicity:

< 150 mg/kg – mild symptoms

150 – 300 mg/kg – tinnitus, dizziness, respiratory alkalosis

>300 mg/kg – altered mental state, seizures, metabolic acidosis

> 500 mg/kg – fatal if untreated

4. Confirm diagnosis (rule out differential)

a. Resuscitation/ Supportive care – ABC approach, ivi fluids (GI losses, insensible losses), treat hypoglycaemia and seizures

b. Correct acidaemia – NaHCO3 infusion (mix 150 mmol of NaHCO3 in 850 ml of 5% dextrose as infusion or immediate temporizing with 50 mEq bolus of NaHCO3 (repeat as required). Monitor Potassium – will drop further due to shift). Care when intubating – as prolonged loss of respiratory drive will rapidly worsen acidosis and cause cardiac arrest, maintain controlled hyperventilation.

c. Decontamination – 50 g AC up to 8 hours of ingestion, repeat in 2-4 hours. ensure secure airway.

d. Enhanced elimination by:

Urinary alkalinization with NaHCO3 infusion (aim urine pH 7-8)

Haemodialysis

5.

a. Urinary alkalinization not feasible

b. Severe toxicity – ARF, AMS, seizures

c. Salicylate level > 7.2 (chronic >4.4)

d. Salicylate level > 4.4 despite AC, urinary alkalinization

e. Low threshold in elderly or poor urine output despite adequate hydration

 

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