plasma osmolar gap can determine cause of metabolic acidosis
- related: anion gap metabolic acidosis
- tags: #note
The plasma osmolal gap is the difference between the measured and calculated plasma osmolality. The calculated plasma osmolality is determined as follows:
Plasma Osmolality (mOsm/kg H2O) = (2 × Serum Sodium [mEq/L]) + Plasma Glucose (mg/dL)/18 + Blood Urea Nitrogen (mg/dL)/2.8 + EtOH/4.6
A high osmolal gap (>10 mOsm/kg H2O) indicates the presence of unmeasured osmoles such as methanol or ethylene glycol, which are metabolized to organic acids, thereby increasing the anion gap. A high osmolal gap is also seen in pseudohyponatremia, in which plasma osmolality is normal while calculated osmolality is low. The patient's history should guide further testing for unmeasured anions.
Links to this note
- anion gap metabolic acidosis
- ethylene glycol toxicity
- This patient has typical findings of ethylene glycol toxicity, including central nervous system depression, an increased anion gap metabolic acidosis, and an increased plasma osmolar gap can determine cause of metabolic acidosis.