What is the most likely diagnosis for a post-operative patient with fever, tachycardia, tachypnea, and leukocytosis after an elective subtotal colectomy?

Systemic Inflammatory Response Syndrome (SIRS)

This patient has Systemic Inflammatory Response Syndrome (SIRS), not sepsis, because the fever and inflammatory markers at 12 hours post-colectomy represent the expected physiologic response to major surgical trauma rather than infection. 1, 2

Why This is SIRS and Not Sepsis

The patient meets SIRS criteria with 3 out of 4 parameters:

• Temperature 38°C (fever criterion met) 3
• Heart rate 110/min (tachycardia criterion met) 3
• WBC 15 x 10⁹/L (leukocytosis criterion met) 3
• Respiratory rate 18/min (normal, criterion not met) 3

However, fever within the first 48 hours after surgery is typically non-infectious, benign, and self-limiting. 1, 2 Surgery triggers a systemic inflammatory response characterized by neuroendocrine changes including fever, and the magnitude corresponds to the extent of surgical injury—a subtotal colectomy represents major abdominal surgery with significant tissue trauma. 1, 2

Critical Timing Distinction

Surgical site infections rarely occur during the first 48 hours after surgery, with the notable exceptions being group A streptococcal or clostridial infections (which present with severe systemic toxicity, not seen here). 3, 1, 2 The guideline explicitly states that fever during the first 48 hours usually arises from non-infectious causes, whereas fever after 96 hours (day 4) is when infection becomes equally likely. 3, 1

At 12 hours post-operatively, this patient is well within the window where SIRS from surgical trauma is the expected finding. 1, 2

Why Not Sepsis or Severe Sepsis?

During the first 48 hours postoperatively, the diagnosis of sepsis requires the presence of SIRS resulting from a proven infection (e.g., bacteremia, fungemia, or UTI). 3 This patient has no documented infection source, no positive cultures, and no clinical signs beyond the expected inflammatory response to surgery. 3, 1

The patient is hemodynamically stable (BP 110/70 mmHg) without vasopressor requirement, has no organ dysfunction, and shows no signs of severe sepsis such as hypotension, acute renal failure, or multiple organ failure. 3

Clinical Management Approach

For this patient at 12 hours post-colectomy:

• Daily wound inspection looking for purulent drainage, spreading erythema >5 cm from incision, or signs of necrotizing infection 1, 4
• No routine cultures or antibiotics are indicated at this time unless infection signs develop 1, 2
• Observation and supportive care are appropriate, as early benign postoperative fever typically resolves spontaneously within 2-3 days 1
• Reassess if fever persists beyond 72 hours or new symptoms develop, as this shifts probability toward infectious causes 1, 2

Common Pitfall to Avoid

Do not reflexively start antibiotics for fever in the first 48 hours post-surgery without evidence of infection. 1 The clinical criteria for sepsis during this time period should be more stringent because SIRS may result from the stress associated with surgery itself. 3 Unnecessary antibiotic use should be avoided and guided by culture results and clinical judgment. 1

Answer: (D) Systemic inflammatory response syndrome