A client 2 hours post-appendectomy reports sudden onset of severe abdominal pain, rigid abdomen, and has a temperature of 39.8°C (103.6°F). What does the nurse suspect?

PERITONITIS is inflammation of the peritoneum (the membrane lining the abdominal cavity and covering abdominal organs). In the post-appendectomy context, it suggests either: (1) the appendix perforated at or during surgery; (2) surgical site contamination; (3) anastomotic leak. CLINICAL PRESENTATION: CLASSIC TRIAD: Severe abdominal pain (often described as 'board-like rigidity'); Rigid, board-like abdomen (involuntary guarding — the abdominal wall muscles contract to protect underlying inflamed organs); High fever (39-40°C is typical of significant infection/inflammation); ADDITIONAL SIGNS: Rebound tenderness (pain worsens when examiner quickly releases pressure after palpation); Nausea and vomiting; Decreased or absent bowel sounds; Tachycardia and hypotension as sepsis develops. NURSING PRIORITIES: Notify provider/surgeon IMMEDIATELY — do not delay for any additional assessment; this is a potentially life-threatening surgical emergency; Position: semi-Fowler's (helps localise infection and reduces diaphragm pressure); NPO (nothing by mouth — likely return to OR); IV access and fluid resuscitation; Vital signs continuously; Labs: CBC, BMP, blood cultures, lactate; Prepare for emergent return to operating room. TREATMENT: Surgical exploration and washout; broad-spectrum antibiotics covering gram-negatives and anaerobes.