A 41-year-old man is brought to the emergency department by ambulance after being found obtunded in an alleyway. Medical records indicate a history of severe alcohol use disorder and major depressive disorder. Vital signs are temperature 36.1°C (97.0°F), blood pressure 105/65 mm Hg, pulse 112/min, and respirations 24/min. Physical examination shows a somnolent man who arouses only to painful stimuli. Pupils are equal and reactive. Cardiopulmonary examination is unremarkable.
Laboratory results are as follows:
| Test | Result | Reference Range |
|---|---|---|
| Sodium | 138 mEq/L | 136-145 mEq/L |
| Potassium | 4.8 mEq/L | 3.5-5.0 mEq/L |
| Chloride | 100 mEq/L | 95-105 mEq/L |
| Bicarbonate | 14 mEq/L | 22-28 mEq/L |
| Blood urea nitrogen | 14 mg/dL | 7-18 mg/dL |
| Creatinine | 1.3 mg/dL | 0.6-1.2 mg/dL |
| Glucose | 90 mg/dL | 70-110 mg/dL |
| Ethanol | 138 mg/dL | 0 mg/dL |
| Serum osmolality (measured) | 345 mOsm/kg H2O | 275-295 mOsm/kg H2O |
Arterial blood gas analysis on room air reveals:
pH: 7.23
PaCO2: 28 mm Hg
PaO2: 96 mm Hg
Based on the laboratory results provided, calculate the patient's osmolar gap.
Cevap: 29 mOsm/kg H2O
Cevap
29
The osmolar gap is the difference between the directly measured serum osmolality and the calculated serum osmolality. When evaluating a patient for toxic alcohol ingestion, any known ethanol must be included in the calculation to isolate the gap caused specifically by unmeasured toxins like methanol or ethylene glycol. The standard formula using US units (mg/dL) is: Calculated Osmolality = . Using the provided laboratory values, this equals . Subtracting this calculated value from the measured osmolality of 345 yields an osmolar gap of . An osmolar gap greater than 10-15 is generally considered abnormal and highly suggestive of an unmeasured alcohol.
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Anahtar Kavram
Calculation and interpretation of the osmolar gap in the presence of ethanol.