An unresponsive 59-year-old man is transported to the emergency department by ambulance af… — USMLE Step 2 CK

An unresponsive $59$ -year-old man is transported to the emergency department by ambulance after his partner noticed profound confusion, severe weakness, and abdominal pain over the past $48$ hours. He has a known history of locally advanced head and neck squamous cell carcinoma. According to his partner, he has been drinking excessive amounts of water and urinating frequently for the past week, and has not had a bowel movement in $5$ days. Vital signs reveal a heart rate of $115/\text{min}$ and blood pressure of $98/60\text{ mmHg}$ . The patient is afebrile. Physical examination demonstrates notably dry mucous membranes, delayed capillary refill, and generalized hypotonia.

Laboratory evaluation shows:
Serum sodium: $139\text{ mEq/L}$
Serum potassium: $4.1\text{ mEq/L}$
Serum chloride: $104\text{ mEq/L}$
Serum bicarbonate: $25\text{ mEq/L}$
Blood urea nitrogen: $52\text{ mg/dL}$
Serum creatinine: $2.3\text{ mg/dL}$
Serum total calcium: $12.8\text{ mg/dL}$
Serum albumin: $1.5\text{ g/dL}$
Serum phosphorus: $2.0\text{ mg/dL}$

An electrocardiogram demonstrates sinus tachycardia with a shortened QT interval.

What is the most appropriate initial step in the management of this patient?

Intravenous normal saline infusionCevap
B
Intravenous furosemide administration
C
Intravenous zoledronic acid administration
D
Emergent hemodialysis
E
Intravenous broad-spectrum antibiotic therapy

Cevap

Intravenous normal saline infusion

The correct answer is intravenous normal saline infusion. This patient has a corrected serum calcium of

14.8\text{ mg/dL}

(calculated as

\text{Corrected Ca} = 12.8 + 0.8 \times [4.0 - 1.5]

). Severe hypercalcemia (defined as

>14\text{ mg/dL}

) frequently causes a nephrogenic diabetes insipidus-like state by downregulating aquaporin channels in the collecting ducts, resulting in profound polyuria, severe volume depletion, and prerenal acute kidney injury. The initial and most critical step in managing severe hypercalcemia is aggressive volume expansion with isotonic normal saline. This intervention achieves three vital goals: it rapidly restores intravascular volume, it improves the glomerular filtration rate, and it directly enhances the renal excretion of calcium by decreasing proximal tubular calcium reabsorption.

Adım Adım Çözüm

Calculate the corrected serum calcium to accurately assess the severity of hypercalcemia in the setting of hypoalbuminemia.

Using the formula

\text{Corrected Ca} = \text{Total Ca} + 0.8 \times (4.0 - \text{Albumin})

, the value is

12.8 + 0.8 \times (4.0 - 1.5) = 14.8\text{ mg/dL}

Serum calcium is highly protein-bound, primarily to albumin. A low albumin level artificially lowers the measured total calcium, masking the true extent of biologically active ionized calcium.

Identify the pathophysiologic consequences of severe hypercalcemia based on the clinical presentation.

The patient's corrected calcium is

>14\text{ mg/dL}

, which triggers a nephrogenic diabetes insipidus-like state, leading to massive polyuria, volume depletion, and prerenal acute kidney injury.

The clinical presentation of thirst, polyuria, hypotension, and an elevated

\text{BUN}/\text{Creatinine}

ratio confirms severe intravascular volume depletion.

Determine the most appropriate initial pharmacological intervention for hypercalcemic crisis.

The absolute first step is aggressive intravenous volume expansion with isotonic normal saline.

Normal saline rapidly restores intravascular volume, improves the glomerular filtration rate, and significantly enhances the renal excretion of calcium.

Anahtar Kavram

The initial management of severe hypercalcemia (corrected calcium

>14\text{ mg/dL}

) requires aggressive intravenous fluid resuscitation with normal saline to correct the profound volume depletion caused by calcium-induced nephrogenic diabetes insipidus.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru