A 68-year-old man with a history of ischemic cardiomyopathy (left ventricular ejection fra… — USMLE Step 2 CK

A 68-year-old man with a history of ischemic cardiomyopathy (left ventricular ejection fraction 35%), severe chronic obstructive pulmonary disease (COPD), and type 2 diabetes mellitus is evaluated in the intensive care unit. He was admitted 3 days ago for urosepsis after presenting with fever, hypotension, and altered mental status. On admission, he received 4 liters of intravenous normal saline and was started on empiric intravenous vancomycin and cefepime.

Blood cultures from admission grew *Escherichia coli* at 24 hours. Today, sensitivities resulted showing the organism is susceptible to ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole, but resistant to ampicillin.

The patient is now afebrile and his blood pressure has stabilized off vasopressors. However, the nurse reports that he has developed worsening dyspnea over the last 12 hours.

Vital signs are:
Blood pressure: $128/78 \text{ mmHg}$
Heart rate: $102/\text{min}$
Respiratory rate: $26/\text{min}$
$SpO_2$ : $89\%$ on room air

Physical examination reveals an elevated jugular venous pressure of $11 \text{ cm } H_2O$ . Lung auscultation demonstrates bibasilar crackles and scattered expiratory wheezes. There is 2+ bilateral pitting lower extremity edema.

Laboratory results:

Parameter	Value
Serum sodium	$136 \text{ mEq/L}$
Serum potassium	$4.2 \text{ mEq/L}$
Serum chloride	$104 \text{ mEq/L}$
Serum bicarbonate	$12 \text{ mEq/L}$
Blood urea nitrogen	$42 \text{ mg/dL}$
Serum creatinine	$1.9 \text{ mg/dL}$
Thyroid-stimulating hormone (TSH)	$0.2 \ \mu\text{U/mL}$ (Normal: $0.4-4.0 \ \mu\text{U/mL}$ )
Free T4	$0.7 \text{ ng/dL}$ (Normal: $0.8-1.8 \text{ ng/dL}$ )

Arterial blood gas (room air):
pH: $7.27$
$pCO_2$ : $26 \text{ mmHg}$
$pO_2$ : $64 \text{ mmHg}$

Which of the following is the most appropriate next step in management?

Administer intravenous furosemide and change antibiotics to intravenous ceftriaxoneAnswer
B
Administer intravenous methylprednisolone, nebulized bronchodilators, and change antibiotics to intravenous ceftriaxone
C
Initiate noninvasive positive pressure ventilation and administer intravenous sodium bicarbonate
D
Administer intravenous levothyroxine and change antibiotics to intravenous ceftriaxone
E
Administer intravenous furosemide and continue intravenous vancomycin and cefepime

Answer

The most appropriate management is to administer intravenous furosemide to treat the acute decompensated heart failure and de-escalate the antibiotic regimen to intravenous ceftriaxone for targeted treatment of the E. coli bacteremia.

The correct sequence of actions requires synthesizing multiple systemic issues. First, the patient's severe dyspnea, wheezing, and bibasilar crackles following 4 liters of normal saline indicate acute decompensated heart failure (ADHF). Because the patient has underlying COPD, it is critical to rule out a COPD exacerbation. The ABG shows a metabolic acidosis (

HCO_3^-

of 12) with a calculated high anion gap (

136 - 104 - 12 = 20

), typical in resolving sepsis or uremia. Using Winter's formula to determine expected respiratory compensation:

pCO_2 = (1.5 \times 12) + 8 = 26 \pm 2

. Since the measured

pCO_2

is exactly 26 mmHg, there is no superimposed respiratory acidosis. If the patient were having a severe COPD exacerbation causing his current distress, he would have relative CO2 retention. Therefore, the treatment is diuresis (furosemide). Second, the patient has *E. coli* bacteremia susceptible to ceftriaxone. Continuing empiric vancomycin and cefepime violates antibiotic stewardship; therapy must be de-escalated. Finally, the abnormal thyroid labs reflect euthyroid sick syndrome, which requires no treatment.

Step-by-Step Solution

Assess the cause of respiratory distress using the physical exam and arterial blood gas.

The patient has elevated jugular venous pressure, crackles, edema, and a high anion gap metabolic acidosis. Applying Winter's formula (

1.5 \times 12 + 8 = 26 \pm 2

), the expected

pCO_2

perfectly matches the measured

pCO_2

(

26 \text{ mmHg}

This rules out a superimposed respiratory acidosis (which would be expected in a severe COPD exacerbation causing dyspnea) and confirms the dyspnea and wheezing ('cardiac asthma') are due to acute decompensated heart failure from aggressive fluid resuscitation.

Evaluate the current antibiotic regimen against the culture sensitivity data.

The patient is on empiric vancomycin and cefepime, but blood cultures grew *Escherichia coli* susceptible to ceftriaxone.

According to antimicrobial stewardship principles, therapy must be de-escalated to the most targeted, narrow-spectrum effective agent once sensitivities are known.

Interpret the thyroid function tests in the context of critical illness.

The patient has low TSH and low free T4.

In the ICU setting, this pattern is classic for euthyroid sick syndrome (nonthyroidal illness syndrome). Administration of exogenous thyroid hormone is not indicated and can be deleterious.

Key Concept

Management of acute decompensated heart failure (ADHF) in critically ill patients, utilizing Winter's formula to differentiate ADHF from COPD exacerbation, paired with mandatory antibiotic de-escalation.

Estimated Time:3m 0s

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