Approach to a postoperative fever: Clinical sciences

Postoperative fever is defined as a systemic body temperature at or above 38 degrees Celsius or 100.4 degrees Fahrenheit within the postoperative period. Causes of postoperative fever include drug or transfusion reaction, infection, and derangements of the normal healing process. Based on the time of onset, postoperative fever is divided into 4 phases: immediate, acute, subacute, and delayed.

Now, the first step in evaluating a patient with postoperative fever is to perform an ABCDE assessment to determine if the patient is stable or unstable. For unstable patients, you must secure the airway, provide supplemental oxygen, establish IV access, start IV fluids if tachycardia and hypotension are present, monitor their vitals, and examine the surgical site.

When it comes to stable patients, the first step is to obtain a history and physical examination, and labs like CBC. In history, you should find out the type of operation performed, date of the operation, and the time of fever onset. CBC is used to establish a baseline and help monitor the response to treatment.

Let's begin with the immediate postoperative period or fever that presents within 24 hours of the operation. While the most common cause of fever during this time is physiologic, it can also be caused by life-threatening causes like an acute transfusion reaction or adverse drug reaction.

First up, physiologic fever frequently occurs after operations that involve high levels of tissue trauma, like burns or multi-trauma exploratory laparotomy. Often, fevers are transient and self-limited, but you should still order a CBC, chest x-ray, and urinalysis to rule out other causes. Because surgery induces a systemic inflammatory response, the patients may have a physiologic fever with mild leukocytosis.

Next, let's move on to dangerous causes of fever in the immediate postoperative period. You should suspect an acute transfusion or drug reaction if the patient has a personal or family history of transfusion reaction or a drug allergy, as well as if the patient received blood products or medications known to cause adverse reactions, such as general anesthetics and IV antibiotics. Physical exam might reveal flushing, skin rash, and sometimes angioedema, respiratory distress, or hypotension. If you suspect acute transfusion or drug reaction, notify the blood bank, send a sample, and check the blood that was given to make sure it’s the correct patient and correct type.

Additionally, order CMP, chest x-ray, urinalysis, and a Coombs test. In a transfusion reaction, labs might show hemolytic anemia, leukopenia, and elevated bilirubin. Chest x-ray usually reveals diffuse bilateral pulmonary infiltrates or edema, while urinalysis is positive for hemoglobinuria, and Coombs test is positive. However, in a drug reaction, all of these tests are normal.

Let’s move on to the acute phase, which occurs within postoperative days 1 to 7. The causes of fever during this period can be summed up by the 5 Ws: wind, water, wound, walking, and wonder drugs. For these patients, you’ll need to do a “fever workup”, which includes a chest x-ray, urinalysis, CBC, and blood cultures.

Alright, let’s talk about “wind” first. Fever within postoperative days 1 and 2 is often related to “wind”, which includes atelectasis or pneumonia. Patients might report dyspnea or cough, while physical exam might reveal increased work of breathing, small breaths, and splinting due to pain, as well as decreased O2 saturation, poor tidal volume on incentive spirometer, and pulmonary crackles on auscultation. CBC can be normal or show leukocytosis. However, chest x-ray will show opacification in one or both of the lower lobes, which indicates atelectasis; or solitary or multiple consolidations, indicating pneumonia.

Next on our list is “water.” Water refers to a postoperative UTI, which typically develops between postoperative days 3 and 5. History might reveal urinary frequency, dysuria, lower abdominal fullness or pain, or an indwelling urinary catheter. On exam, you might find suprapubic tenderness. CBC will show mild leukocytosis. The urine usually appears cloudy, and urinalysis can be positive for nitrites and leukocyte esterase, as well as high WBCs and bacteriuria. Usually, blood cultures are negative, unless the infection has progressed to urosepsis. Finally, if you suspect a UTI, you must order a urine culture to confirm it and tailor the antibiotics.

The third W stands for “wound,” which represents a surgical site infection, or SSI. SSI initially presents around postoperative days 5 to 7 and can be superficial or deep. Superficial SSI can present as pain around the skin incision with erythema, edema, and tenderness on exam. If it has progressed to an abscess, you might palpate a painful and fluctuant mass. Deep SSI can present as abdominal pain if the patient underwent abdominal surgery, for example. Labs may reveal leukocytosis. Now, if you suspect a superficial SSI, order an ultrasound, which could show soft tissue edema or a fluid collection. For deep SSI, order a CT to see if there is edema or fluid collection around the surgical site.

The fourth W stands for walking, which represents vascular causes like DVT, phlebitis, and central line infection, that typically occur around postop day 5 and beyond. History might reveal important risk factors including immobility and prolonged peripheral IV or central line use. On exam, you should suspect DVT if you see painful unilateral limb swelling with erythema. However, phlebitis usually presents as redness and edema limited to the soft tissue at the site of a peripheral IV. The affected vein can sometimes feel like a “firm cord.” Central line infections might have purulent drainage around the insertion site and can often present with signs of sepsis. In DVT and phlebitis, CBC and fever workup can be normal, while with central line infections, you might see leukocytosis and positive blood cultures. Be sure to remove the central venous catheter for line infections. Make sure to order an ultrasound of the affected limb to assess for venous thrombosis to help confirm your diagnosis.