A 72-year-old man is evaluated on postoperative day 2 following an open sigmoid colectomy … — USMLE Step 2 CK

A $72$ -year-old man is evaluated on postoperative day $2$ following an open sigmoid colectomy for recurrent complicated diverticulitis. The patient reports worsening shortness of breath that began this morning. His medical history is significant for chronic obstructive pulmonary disease and essential hypertension. His current medications include inhaled tiotropium and prophylactic subcutaneous enoxaparin. Temperature is $37.9^\circ\text{C}$ ( $100.2^\circ\text{F}$ ), blood pressure is $138/82\text{ mm Hg}$ , pulse is $112/\text{min}$ , and respirations are $24/\text{min}$ . Pulse oximetry shows an oxygen saturation of $88\%$ on room air. Jugular venous pressure is $6\text{ cm H}_2\text{O}$ . Pulmonary auscultation reveals decreased breath sounds at the lung bases bilaterally without crackles or wheezes. Cardiac examination shows a regular tachycardia without murmurs. The surgical incision site is clean, dry, and intact. Arterial blood gas analysis on room air shows:

pH: $7.48$
$pCO_2$ : $30\text{ mm Hg}$
$pO_2$ : $58\text{ mm Hg}$
$HCO_3^-$ : $22\text{ mEq/L}$

A chest radiograph reveals linear opacities at the bilateral lung bases with an unchanged cardiac silhouette and no pleural effusions. Which of the following is the most appropriate next action for this patient?

A
Administer intravenous furosemide
B
Start empiric intravenous piperacillin-tazobactam
Initiate incentive spirometry and early ambulationAnswer
D
Obtain blood cultures, urine cultures, and an abdominal computed tomography scan
E
Apply Winter's formula to assess for a mixed acid-base disorder

Answer

Initiate incentive spirometry and early ambulation

The patient is presenting with postoperative atelectasis, one of the most common pulmonary complications following abdominal surgery. Incisional pain often causes patients to take shallow breaths (splinting), which leads to the collapse of basilar alveoli. This alveolar collapse creates a right-to-left intrapulmonary shunt (V/Q mismatch), resulting in hypoxemia. The hypoxemia triggers reflex tachypnea, which blows off excess carbon dioxide and creates a primary respiratory alkalosis (pH

> 7.45

, low

pCO_2

). Atelectasis also commonly causes a mild, non-infectious inflammatory fever on postoperative days 1 through 3. The chest radiograph showing linear opacities without consolidation confirms the diagnosis. The most effective management is aimed at re-expanding the collapsed alveoli through deep breathing exercises (incentive spirometry), directed coughing, adequate pain control, and early ambulation.

Step-by-Step Solution

Analyze the patient's timeline and vital signs.

The patient is on postoperative day 2 with a low-grade fever, tachypnea, tachycardia, and hypoxemia.

Establishing the postoperative timeline is critical for identifying the most likely cause of fever and respiratory distress.

Evaluate the physical examination and imaging findings.

Examination shows decreased breath sounds at the bases without fluid overload signs. Chest radiograph shows basilar linear opacities.

Linear opacities without focal consolidation or pulmonary edema strongly suggest alveolar collapse (atelectasis).

Interpret the arterial blood gas (ABG) results.

The ABG reveals a pH of 7.48 and a pCO2 of 30 mm Hg, indicating a primary uncompensated respiratory alkalosis.

Hypoxemia from atelectasis drives reflex hyperventilation, leading to the observed respiratory alkalosis.

Determine the appropriate management.

Select non-pharmacologic lung expansion therapies.

Postoperative atelectasis is best managed mechanically through deep breathing exercises (incentive spirometry), adequate pain control, and early mobilization.

Key Concept

Postoperative atelectasis typically presents on days 2-3 with hypoxemia, respiratory alkalosis, and a low-grade fever; it is managed with incentive spirometry and early ambulation.

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