Postoperative Fever

Etiology

The timing strongly influences etiology.

• Underlying conditions (e.g., immunosuppressed patients) may have a reduced inflammatory response or reduced fever while at the same time having a serious infection.
• Differential diagnosis includes infectious (e.g., nosocomial or surgical site infections) and non-infectious (e.g., deep vein thrombosis, pulmonary embolus, myocardial infarction, drug-related, transfusion-related, endocrine-related for example adrenal insufficiency or thyroid storm) causes.
• Fever is more likely to be due to infection as the time interval following surgery increases.
• Fever in patients may have more than one cause at the same time, and infectious and non-infectious causes may coexist.

Epidemiology

Postoperative fever is very common. The exact incidence of postoperative fever is not known, but the numbers are high. Estimates from different surgical procedures reveal that fever occurs early in the postoperative period anywhere from 20% to 90% of patients. In the majority of these cases, the fever usually occurs on the first or second day after surgery and has been linked to benign causes. Postoperative fever is known to occur after all types of surgical procedures, irrespective of the type of anesthesia. The fever also occurs in children and both genders. Postoperative fever can occur after minor surgical procedures but is rare and depends on the type of procedure. Overall, both abdominal and chest procedures result in the highest incidence of postoperative fever.[3][4]

Pathophysiology

Systemic Inflammatory Response Syndrome (SIRS):

Four criteria include:

• Temperature higher than 38 C or less than 36 C
• Heart rate higher than 90 beats per minute
• Respiratory rate greater than 20 per minute
• White blood cell count greater than 12 x 10/L or less than 4 x 10/L

Two of the 4 criteria are needed to identify a patient with SIRS.

Two of the SIRS criteria plus a suspected source of sepsis are required to diagnose sepsis.

• Sepsis plus organ dysfunction is consistent with severe sepsis.
• Severe sepsis plus refractory hypotension (refractory to fluid resuscitation) is consistent with septic shock.

Signs of Organ Dysfunction

• Systolic BP less than 90 mm Hg or mean arterial pressure less than 65 mm Hg.
• Drop in BP greater than 40 mm Hg (especially in hypertensive patients)
• Lactate greater than 2 mmol/L
• Urine output less than 0.5 mg/kg/hr for 2 consecutive hours
• Drop in Glasgow coma scale (GCS) or abbreviated mental test scores

History and Physical

Immediate Fever

Fever occurs immediately after surgery or within hours on postoperative days (POD) 0 or 1.

• Malignant hyperthermia: high-grade fever (greater than 40 C), occurs shortly after inhalational anesthetics or muscle relaxant (e.g., halothane or succinylcholine), may have a family history of death after anesthesia. Laboratory studies will reveal metabolic acidosis and hypercalcemia. If not readily recognized, it can cause cardiac arrest. The treatment is intravenous dantrolene, 100% oxygen, correction of acidosis, cooling blankets, and watching for myoglobinuria.
• Bacteremia: High-grade fever (greater than 40 C) occurring 30 to 40 minutes after the beginning of the procedure (e.g., Urinary tract instrumentation in the presence of infected urine). Management includes blood cultures three times and starting empiric antibiotics.
• Gas gangrene of the wound: High-grade fever (greater than 40 C) occurring after gastrointestinal (GI) surgery due to contamination with Clostridium perfringens; severe wound pain; treat with surgical debridement and antibiotics.
• Febrile non-hemolytic transfusion reaction: Fevers, chills, and malaise 1 to 6 hours after surgery (without hemolysis). Management: Stop transfusion (rule out hemolytic transfusion reaction) and give antipyretics (avoid aspirin in the thrombocytopenic patient).

Acute Fever

Fever occurs in the first week (1 to 7 POD).

• POD 1 to 3: Pyretic response to surgery occurs during the first 48 hours.[5] Diagnostic testing is usually not indicated unless there are associated symptoms. After this time period complete blood count, chest radiograph, urinalysis with culture, blood cultures, and wound cultures are required as first tests in all patients.
• POD 3: Unresolved atelectasis resulting in pneumonia (respiratory symptoms, Chest x-ray with infiltrates or consolidation, sputum culture, empiric antibiotics and modification according to culture result and sensitivity), or development of urinary tract infection (urine analysis and culture, treat with empiric antibiotics and modify according to culture result and sensitivity)
• POD 5: Thrombophlebitis (may be asymptomatic or symptomatic, diagnose with Doppler ultrasound of deep leg and pelvic veins and treat with heparin)
• POD 7: Pulmonary embolism (tachycardia, tachypnea, pleuritic chest pain, ECG with right heart strain pattern (a low central venous pressure goes against diagnosis), arterial blood gas with hypoxemia and hypocapnia, confirm the diagnosis with CT angiogram, and treat with heparin if recurrent pulmonary embolism while anticoagulated with therapeutic INR, Inferior vena cava filter placement is the next step
• POD 7 (5 to 10): Wound infection: Risk increases if the patient is immunocompromised (e.g., diabetic), abdominal wound, duration of surgery greater than 2 hours, or contamination during surgery. Signs include erythema, warmth, tenderness, discharge. Rule out abscess by physical exam plus ultrasound if needed. If an abscess is present, drainage and antibiotics are needed. Prevention is by careful surgical technique and prophylactic antibiotics (e.g., intravenous cefazolin at the time of induction of anesthesia as well as postoperatively if needed)

Subacute Fever

Fever occurs between postoperative weeks 1 and 4.

• POD 10: Deep infection (pelvic or abdominal abscess and if abdominal abscess could be sub-hepatic or sub-phrenic). A digital rectal exam to rule out the pelvic abscess and CT scan to localize intra-abdominal abscess. Treatment includes re-exploration vs. radiological guided percutaneous drainage.
• Drugs: Diagnosis of exclusion includes rash and peripheral eosinophilia

Delayed Fever

Fever after more than 4 weeks.

• Skin and soft tissue infections (SSTI)
• Viral infections

The above differential diagnosis is for causes that are categorized based on timing. However, there are many other causes that may have specific signs on physical exam and occur after specific surgery that are not included in the above differential.

Evaluation

Initial assessment includes general appearance, GCS, and vital signs to determine how sick the patient is.[6][7]

• Airway, Breathing, Circulatory, Disability, Exposure (quick assessment to identify and simultaneously provide appropriate management)
• Check patient notes (the type of procedure, timing of the procedure, intraoperative complications, anesthesia records, patient comorbidities, last ward rounds)
• Check patient Intake and Output (including the type of stools, if the patient with type 7 stools rule out Clostridium difficile enterocolitis)
• Check patient orders (is the patient being treated with antibiotics or not, receiving deep vein thrombosis prophylaxis or not)
• System based assessment (pulmonary, cardiac, gastrointestinal, urinary)
• Sites of infection that are visible (i.e., skin for bedsores, cellulitis, vascular access sites)
• Besides tests, vital signs should be monitored. If the patient is hypotensive, venous blood gas is needed to measure serum lactate. It will guide fluid resuscitation; if the patient is tachycardic, bedside ECG might be important to confirm their rhythm, might rule out myocardial infarction; oxygen saturation 96% to 98% in patients with healthy lungs or 89% to 92% in carbon dioxide retaining patients, for example, COPD patients; monitor blood glucose levels because high blood glucose levels point towards septic response; urinalysis to rule out urinary tract infection
• Blood tests: WBC, CRP especially if trending upward might point towards a septic response, hemoglobin level would point toward the oxygen-carrying capacity of the blood, liver function tests to rule out liver injury, coagulation parameters, and platelets to rule out disseminated intravascular coagulation, renal function to rule out kidney injury or electrolyte abnormalities
• Microbiology: Cultures (blood, urine, wound, and sputum if producing it), if suspecting line sepsis (blood culture from the line, remove the line and send the tip to the lab)
• Imaging: Chest x-ray (prove or rule out pneumonic process), abdominal imaging (ultrasound, CT scan to rule out collections)
• Venous doppler of the legs to rule out deep vein thrombosis

Treatment / Management

Treatment can include oxygen, fluid balance, intravenous fluids, and a urinary catheter, or antibiotics.

• Drugs: antibiotics, analgesia, antiemetics
• Incentive Spirometry
• Venous thromboembolism prophylaxis (low molecular weight heparin and wearing pneumatic stocking)
• Escalation (relay information to a senior health professional and ask for further advice from  infectious disease physician)

Differential Diagnosis

As discussed earlier, the differentials are based on the timing of the fever, among other factors. Some of the important differentials are listed below.

• Pneumonia
• Pulmonary embolus
• Wound infection
• Urinary tract infection
• Transfusion reaction
• Sinusitis

Prognosis

In most patients, postoperative fever is due to a benign cause and resolves spontaneously. Patients with deep vein thrombosis and pulmonary embolism usually have a low-grade fever that resolves within a few days of treatment. The prognosis is worse for patients who have anastomotic leaks or bowel obstruction.

Complications

Failure to diagnose the cause of fever or identify the severity of it can lead the patient into SIRS, sepsis, severe sepsis, or septic shock. This can lead to prolonged hospitalization and even increase the mortality rate.