For each set of the following biochemical and arterial blood gas parameters:
Any reasonable scenario accepted that was both biochemically correct AND clinically likely.
Test |
Value |
Normal Adult Range |
Sodium |
145 mmol/L |
135 – 145 |
Potassium |
4.0 mmol/L |
3.2 – 4.5 |
Chloride* |
91 mmol/L |
100 – 110 |
Bicarbonate |
30 mmol/L |
24 – 32 |
pH* |
7.62 |
7.35 – 7.45 |
pCO2* |
30 mmHg (3.9 kPa) |
35 – 45 (4.6 – 5.9) |
Increased anion gap, metabolic alkalosis and respiratory alkalosis.
Clinical scenario – salicylate overdose.
Let us dissect these results systematically.
This is a mixed respiratory and metabolic alkalosis with a raised anion gap. There is only one beast which presents in this way: the salicylate overdose. To be precise, metabolic acidosis and respiratory alkalosis are characteristic of salicylate toxicity, and the metabolic alkalosis is some sort of unrelated sideshow. It is either due to torrential vomiting (which frequently accompanies salicylate intoxication) or due to the forced alkaline diuresis (which is the favoured method of enhancing salicylate clearance). Either way, all three acid-base disturbances are frequently seen together in the suicidal aspirin eater.
This level of discussion is probably sufficient for a question which was probably worth no more than 2 marks in a ten-mark question. These derangements of physiology are discussed in greater detail in the chapter on salicylate overdose from the "Acid-Base Disturbances" section.
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