In a patient on postoperative day 4 after surgery for perforated diverticulitis who develops a fever of 38.9 °C, what is the most appropriate immediate investigation: wound inspection for surgical site infection, blood cultures, or chest radiograph?

Postoperative Day 4 Fever After Perforated Diverticulitis Surgery

The most appropriate immediate action is to check the wound for surgical site infection (SSI), as fever on postoperative day 4 following perforated diverticulitis surgery is equally likely to be caused by SSI as any other source, and wound inspection is the most direct, immediate, and non-invasive method to identify a potentially life-threatening complication. 1, 2

Rationale for Prioritizing Wound Inspection

Fever timing is critical in this scenario. Fever occurring at 96 hours (day 4) post-surgery represents a critical transition point where the probability shifts from benign inflammatory response to infectious causes. 1, 2 The systemic inflammatory response from surgery typically resolves within 48-72 hours, making fever at day 4 equally likely to represent surgical site infection as other infectious sources. 1, 3

Why Wound Inspection First

• Immediate availability and diagnostic yield: Wound inspection can be performed at the bedside immediately without delay, transport, or additional resources. 2
• High-risk surgical context: Perforated diverticulitis involves contaminated/dirty surgery with fecal peritonitis, placing this patient at significantly elevated risk for deep SSI and intra-abdominal sepsis. 4, 5
• Critical findings require immediate action: If erythema extends >5 cm from the incision with induration, or if any necrosis is present, immediate intervention is required with opening of the suture line, empiric antibiotics, and dressing changes. 1, 2

Specific Wound Assessment Details

Look for these specific findings during inspection: 1, 2

• Purulent drainage (any amount mandates intervention)
• Spreading erythema (measure extent from incision)
• Induration or firmness extending beyond incision
• Warmth, tenderness, or swelling
• Skin necrosis or ecchymoses
• Fascial dehiscence or "woody" feel suggesting necrotizing infection

Why Blood Cultures Are Secondary (But Still Important)

Blood cultures should be obtained, but only after wound inspection and only if specific criteria are met. 4

Blood cultures are indicated when: 4, 1

• Temperature ≥38.9°C (which this patient has) AND systemic signs beyond isolated fever
• Hemodynamic instability, altered mental status, or signs of bacteremia/sepsis
• After wound inspection if SSI is confirmed or suspected

Important caveat: In patients with complicated intra-abdominal infections who do not have hypotension, tachypnea, or delirium, and there is no concern for antibiotic-resistant organisms, blood cultures are not routinely recommended. 4 However, given this patient's high-risk surgery (perforated diverticulitis), blood cultures should be obtained if the wound shows signs of infection or if systemic signs develop. 4

Blood Culture Technique if Indicated

• Obtain at least two sets (ideally 60 mL total) from different anatomical sites without time interval between them. 4
• If central venous catheter present, obtain simultaneous peripheral and central samples to calculate differential time to positivity. 4, 6

Why Chest X-Ray Is Least Appropriate

Chest radiography is not indicated for isolated fever on day 4 without respiratory symptoms. 4, 1

• Chest X-ray becomes indicated only if respiratory symptoms develop (cough, dyspnea, hypoxemia). 4, 1
• The diagnostic yield of routine chest X-ray for asymptomatic postoperative fever is extremely low. 1
• Atelectasis should be a diagnosis of exclusion, not a default assumption. 1, 3

Algorithmic Approach for This Patient

Step 1: Immediate wound inspection 1, 2

• Remove dressings completely
• Assess for purulent drainage, erythema extent, induration, necrosis
• If positive findings → obtain Gram stain and culture, start empiric antibiotics

Step 2: Assess for systemic signs of severe infection 4

• Hemodynamic instability (hypotension, tachycardia >100)
• Altered mental status
• Respiratory compromise
• If present → obtain blood cultures immediately

Step 3: If wound normal and no severe systemic signs 4

• Consider CT abdomen/pelvis to evaluate for intra-abdominal abscess or anastomotic leak
• Blood cultures may still be reasonable given temperature 38.9°C and high-risk surgery

Step 4: Empiric antibiotics if infection confirmed 1, 2

• For sigmoid resection/GI tract surgery: cephalosporin + metronidazole, levofloxacin + metronidazole, or carbapenem
• Must cover both aerobic and anaerobic bacteria

Critical Pitfalls to Avoid

• Assuming atelectasis without investigation – this is a diagnosis of exclusion. 1, 3
• Starting empiric antibiotics before obtaining cultures – compromises diagnostic accuracy. 3
• Delaying wound inspection – SSI can rapidly progress to necrotizing infection, especially with Enterococcus or fungal contamination from perforated diverticulitis. 5
• Ordering chest X-ray reflexively – wastes resources and delays appropriate evaluation without respiratory symptoms. 1

Red Flags Requiring Immediate Escalation

Immediate surgical consultation required if: 1, 2

• Severe systemic toxicity (hypotension, altered mental status, organ dysfunction)
• Clinical suspicion of necrotizing fasciitis (hard "woody" feel, skin necrosis, gas in tissues)
• Purulent drainage with extensive erythema and induration
• Persistent fever beyond 48-72 hours despite appropriate therapy may indicate inadequate source control requiring re-operation 4, 3

Answer: A) Check wound for SSI is the most appropriate immediate action.