A 68-year-old man with a history of type 2 diabetes mellitus is brought to the emergency d… — USMLE Step 2 CK

A 68-year-old man with a history of type 2 diabetes mellitus is brought to the emergency department due to progressively worsening confusion and profound weakness over the past 4 days. He recently recovered from a mild upper respiratory illness. On examination, he is lethargic but arousable. Vital signs show a blood pressure of $92/58\text{ mm Hg}$ , a heart rate of $118/\text{min}$ , and a respiratory rate of $16/\text{min}$ . His mucous membranes are parched, and skin turgor is significantly decreased.

Initial laboratory evaluation reveals:
Serum sodium: $129\text{ mEq/L}$
Serum potassium: $4.4\text{ mEq/L}$
Serum chloride: $95\text{ mEq/L}$
Serum bicarbonate: $22\text{ mEq/L}$
Blood urea nitrogen: $48\text{ mg/dL}$
Serum creatinine: $1.9\text{ mg/dL}$
Serum glucose: $600\text{ mg/dL}$

In order to properly select the composition of intravenous fluids for resuscitation, the patient's true sodium status must be evaluated.

What is the patient's corrected serum sodium concentration in $\text{mEq/L}$ ? (Assume a correction factor of $1.6\text{ mEq/L}$ for each $100\text{ mg/dL}$ increase in glucose above $100\text{ mg/dL}$ ).

Cevap: 137 mEq/L

Cevap

137

In the setting of severe hyperglycemia, the high concentration of glucose in the extracellular fluid creates an osmotic gradient that draws water out of cells. This transcellular fluid shift dilutes the serum sodium concentration, leading to a phenomenon known as translocational hyponatremia. To determine the patient's true sodium status, a correction factor must be applied. The standard correction adds

1.6\text{ mEq/L}

to the measured sodium for every

100\text{ mg/dL}

increase in glucose above a baseline of

100\text{ mg/dL}

. For a glucose level of

600\text{ mg/dL}

, the excess is

500\text{ mg/dL}

. Multiplying

5

1.6

yields a correction of

8\text{ mEq/L}

. Adding this to the measured sodium of

129\text{ mEq/L}

results in a corrected serum sodium of

137\text{ mEq/L}

. This indicates that the patient actually has a normal serum sodium concentration, which is critical for choosing the appropriate intravenous fluid for resuscitation.

Adım Adım Çözüm

Identify the patient's measured serum sodium and serum glucose levels.

Measured Na =

129\text{ mEq/L}

, Glucose =

600\text{ mg/dL}

These are the two variables required to calculate the corrected serum sodium.

Calculate the amount of glucose elevation above the normal baseline of

100\text{ mg/dL}

600 - 100 = 500\text{ mg/dL}

above normal.

The correction factor is only applied to the excess glucose driving the osmotic shift.

Determine the total sodium correction value by applying the given factor.

Correction =

5 \times 1.6 = 8\text{ mEq/L}

For every

100\text{ mg/dL}

of excess glucose, sodium is artificially lowered by

1.6\text{ mEq/L}

Add the correction value to the measured serum sodium.

129 + 8 = 137\text{ mEq/L}

This yields the true serum sodium concentration, guiding appropriate fluid therapy.

Anahtar Kavram

Pseudohyponatremia due to hyperglycemia (translocational hyponatremia)

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

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