Okay, let's tackle this question. The patient had a sleeve gastrectomy and on the third post-op day has a fever, tachycardia, and leucocytosis. The next step is key here. First, I need to remember the common post-op complications after bariatric surgery.

Sleeve gastrectomy is a major procedure. Post-op day 3 with fever and these signs point to infection. Common issues could be surgical site infection, anastomotic leak, or maybe a pulmonary issue like atelectasis or pneumonia. But in the early post-op period, anastomotic leak is a big concern. Wait, but when do these usually present? Anastomotic leaks typically present within the first few days, maybe 3-5 days. So, fever and leucocytosis here could be a sign of that. Also, the patient is febrile and tachycardic, which is systemic signs of infection.

So the next step would be to investigate for possible infection. The options given aren't listed, but the correct answer is likely imaging. Let's say the options are something like blood cultures, CT scan, or starting antibiotics. The question is about the next best step. In this scenario, the first step would be imaging to look for an abscess or leak. Maybe a CT scan of the abdomen with contrast. Alternatively, if they have signs of sepsis, starting IV antibiotics, but the next best step after the initial presentation would be to confirm the source. So CT scan is the next step. Also, in post-op patients, early signs of infection need to be investigated promptly. So the correct answer would be to perform a CT scan. The other options might include things like starting antibiotics without imaging, which is not ideal. Or maybe a chest X-ray for atelectasis, but in the context of bariatric surgery, abdominal issues are more likely. So the answer is likely CT scan of the abdomen.

**Core Concept**
Post-surgical fever and leucocytosis within 3-5 days of sleeve gastrectomy suggest surgical site infection, anastomotic leak, or intra-abdominal abscess. Early diagnosis is critical to prevent sepsis.

**Why the Correct Answer is Right**
A CT scan with contrast is the next best step to evaluate for anastomotic leak, peritonitis, or abscess. Sleeve gastrectomy carries a 2-5% risk of leak, which typically presents 2-7 days post-op with fever, tachycardia, and leukocytosis. Contrast-enhanced CT provides high sensitivity for detecting fluid collections, gas, or contrast extravasation at the staple line.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood cultures alone miss localized intra-abdominal sources of infection.
**Option B:** Broad-spectrum antibiotics delay diagnostic imaging and risk antibiotic resistance.
**Option C:** Chest X-ray is less likely to identify post-gastrectomy complications compared to abdominal CT.

**Clinical Pearl / High-Yield Fact**
Remember the "3-day rule" for anastomotic leaks: fever + leukocytosis + tachycardia in days 2-7 post-bariatric surgery mandates immediate CT imaging. Avoid empiric antibiotics until imaging confirms the source.

**Correct Answer:

✓ Correct Answer: D. Re-exploration