A 65-year-old man is brought to the emergency department by his family due to a 2-day hist… — USMLE Step 2 CK

A 65-year-old man is brought to the emergency department by his family due to a 2-day history of worsening confusion, extreme thirst, and frequent urination. He has a 12-year history of type 2 diabetes mellitus and takes metformin and sitagliptin. He recently recovered from a mild urinary tract infection.

Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate of $112\text{/min}$ , blood pressure of $100/60\text{ mmHg}$ , and respiratory rate of $18\text{/min}$ .

Physical examination reveals dry mucous membranes and poor skin turgor. He is somnolent but arousable.

Laboratory evaluation shows:

Laboratory Test	Result
Serum sodium	$132\text{ mEq/L}$
Serum potassium	$3.1\text{ mEq/L}$
Serum chloride	$98\text{ mEq/L}$
Serum bicarbonate	$22\text{ mEq/L}$
Blood urea nitrogen	$48\text{ mg/dL}$
Serum creatinine	$1.9\text{ mg/dL}$
Serum glucose	$940\text{ mg/dL}$
Serum ketones	Small
Serum osmolality	$350\text{ mOsm/kg H}_2\text{O}$

An intravenous line is established, and rapid fluid resuscitation with $0.9\%$ sodium chloride is initiated. Which of the following is the most appropriate next step in the pharmacological management of this patient?

Addition of intravenous potassium chlorideAnswer
B
Initiation of a continuous intravenous regular insulin infusion
C
Administration of intravenous sodium bicarbonate
D
Switching intravenous fluids to 0.45% sodium chloride
E
Initiation of broad-spectrum intravenous antibiotics

Answer

The correct answer is the addition of intravenous potassium chloride.

This patient is presenting with a hyperosmolar hyperglycemic state (HHS). The initial step in management is aggressive intravenous fluid resuscitation with

0.9\%

normal saline, which has already been initiated. The next critical step is to evaluate the serum potassium level before starting insulin therapy. Patients with HHS typically have massive total body potassium depletion due to profound osmotic diuresis. Insulin administration drives both glucose and potassium into the cells, which can acutely lower serum potassium levels and precipitate life-threatening cardiac arrhythmias and respiratory muscle weakness. According to standardized protocols, if the serum potassium is

< 3.3\text{ mEq/L}

, insulin must be held, and intravenous potassium chloride must be administered (usually

20-30\text{ mEq/hr}

) until the potassium level rises to

\ge 3.3\text{ mEq/L}

. Only then is it safe to initiate an insulin infusion.

Step-by-Step Solution

Analyze the patient's clinical presentation and laboratory results.

The patient has extreme hyperglycemia (

940\text{ mg/dL}

), high serum osmolality (

350\text{ mOsm/kg}

), and altered mental status with minimal ketones/acidosis (bicarbonate

22\text{ mEq/L}

), confirming a diagnosis of hyperosmolar hyperglycemic state (HHS).

Identifying the specific metabolic syndrome is necessary to apply the correct treatment algorithm.

Evaluate the current management and identify the next physiological priority.

Fluid resuscitation with

0.9\%

sodium chloride has appropriately been started. The next priority is addressing the serum potassium level of

3.1\text{ mEq/L}

before giving insulin.

In HHS and DKA, mortality is often driven by metabolic shifts during treatment rather than the hyperglycemia itself.

Apply the treatment algorithm for HHS regarding potassium management.

Because insulin shifts potassium intracellularly, administering insulin when serum potassium is

< 3.3\text{ mEq/L}

will cause severe hypokalemia. Therefore, insulin must be withheld and intravenous potassium chloride administered first.

Preventing life-threatening cardiac arrhythmias and respiratory muscle weakness is the immediate priority.

Key Concept

In the management of hyperosmolar hyperglycemic state (HHS) or diabetic ketoacidosis (DKA), if the serum potassium level is less than 3.3 mEq/L, insulin therapy is strictly contraindicated and must be held until intravenous potassium chloride brings the level above 3.3 mEq/L.

Estimated Time:1m 30s

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