Emergency medical services bring a 47-year-old mechanic to the hospital after he was found deeply lethargic in his workshop. His coworkers report that he had been working alone on a vehicle's cooling system and seemed disoriented before collapsing. On presentation, his temperature is (), blood pressure is mmHg, pulse is /min, and respiratory rate is /min. Physical examination reveals an unarousable patient with deep, rapid breathing. Arterial blood gas analysis on room air shows a pH of 7.21, of 24 mmHg, and of 95 mmHg.
Laboratory evaluation reveals the following:
| Parameter | Value |
|---|---|
| Sodium | mEq/L |
| Potassium | mEq/L |
| Chloride | mEq/L |
| Bicarbonate | mEq/L |
| Blood urea nitrogen | mg/dL |
| Creatinine | mg/dL |
| Glucose | mg/dL |
| Measured serum osmolality | mOsm/kg |
Based on the provided laboratory results, what is the patient's calculated serum osmolar gap in mOsm/kg ?
Answer: 40 mOsm/kg H2O
Answer
40
The correct answer is 40. The serum osmolar gap is defined as the difference between the directly measured serum osmolality and the calculated serum osmolality. The formula for calculated serum osmolality in conventional units (mg/dL) is: . Using the patient's values, this is computed as mOsm/kg . The measured osmolality is 334 mOsm/kg . Subtracting the calculated value from the measured value yields an osmolar gap of mOsm/kg . A normal osmolar gap is typically less than 10 to 15 mOsm/kg . In a patient with central nervous system depression, high anion gap metabolic acidosis, and exposure to automotive fluids, a markedly elevated osmolar gap strongly suggests intoxication with an unmeasured osmotically active alcohol, such as ethylene glycol (antifreeze).
Step-by-Step Solution
Key Concept
Calculation and interpretation of the serum osmolar gap in toxic alcohol ingestion.