An unresponsive 74-year-old woman is brought to the emergency department by emergency medical services after being found on the floor of her apartment by her daughter. The daughter notes that the patient had been increasingly disoriented and complaining of excessive thirst and urination over the past week.
Past medical history: Type 2 diabetes mellitus, hypertension, hyperlipidemia.
Vital signs:
- Temperature: 37.0°C (98.6°F)
- Blood pressure: 92/58 mm Hg
- Heart rate: 118/min
- Respirations: 16/min
Physical examination shows an obtunded patient with dry mucous membranes, decreased skin turgor, and a delayed capillary refill of 4 seconds.
Laboratory studies:
| Test | Result | Reference Range |
|---|---|---|
| Sodium | 130 mEq/L | 136-145 mEq/L |
| Potassium | 4.5 mEq/L | 3.5-5.0 mEq/L |
| Chloride | 92 mEq/L | 98-106 mEq/L |
| Bicarbonate | 24 mEq/L | 22-28 mEq/L |
| Blood urea nitrogen (BUN) | 84 mg/dL | 7-18 mg/dL |
| Creatinine | 2.1 mg/dL | 0.6-1.2 mg/dL |
| Glucose | 900 mg/dL | 70-110 mg/dL |
What is this patient's calculated serum osmolality in mOsm/kg?
Answer: 340 mOsm/kg
Answer
340
The patient's calculated serum osmolality is determined using the standard formula: . Substituting the patient's laboratory values yields , which equals mOsm/kg. This significantly elevated value is consistent with Hyperosmolar Hyperglycemic State (HHS), which often presents with extreme hyperglycemia, high serum osmolality, and profound dehydration.
Step-by-Step Solution
Key Concept
The calculated serum osmolality requires converting glucose and BUN to mmol/L. The formula is .