Approach to a postoperative fever: Clinical sciences

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Introduction0:00–0:37

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.

ABCDE/Unstable Branch0:37–1:01

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.

Stable Branch1:01–1:21

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.

Immediate Branch1:21–1:41

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.

Surgery-Induced Physiologic Fever1:41–2:10

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.

Acute Transfusion reaction & Acute drug reaction2:10–3:22

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.

Acute Branch3:22–3:48

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.

Postoperative Atelectasis or Pneumonia - wind3:48–4:28

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.

Postoperative UTI - water4:28–5:14

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.

Surgical site infection- wound5:14–6:05

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.

Phlebitis, DVT, or central line infection: - walkiing6:05–7:11

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.
The final W stands for “wonder drugs.” This is known as drug fever, and may develop anytime, but most often presents subacutely after postoperative day 7.

Drug fever & transition to Subacute Branch7:11–7:31

Keep in mind that this is a diagnosis of exclusion, so all the other causes of postoperative fever need to be ruled out first.Alright, let's switch gears and focus on causes of fever during the subacute phase, defined as postoperative weeks 1 to 4.

Subacute branch & Anastomotic leak7:31–8:47

Once again, you’ll need to do a fever workup, but here you’ll also need a more in-depth workup. Two important diagnoses you do not want to miss are anastomotic leak and Clostridium difficile or C.
diff infection. Anastomotic leaks occur when the normal healing process of the resected tissue is hindered.
After abdominal surgery, history might reveal abdominal pain, nausea, vomiting, and bowel changes like constipation or obstipation where the patient can not pass stool or gas.
On exam, you might find abdominal tenderness, distension, signs of peritonitis, or tachycardia. Labs will typically show leukocytosis with left shift on CBC, and electrolyte abnormalities like low magnesium and phosphorus on CMP.
Next, order a CT of the abdomen and pelvis. If the CT shows free fluid or a fluid collection, edema, or inflammation around the anastomotic site, or extravasation of oral contrast, you can diagnose anastomotic leak.
Keep in mind that this can be a surgical emergency. Now, postoperative use of antibiotics can alter the normal GI flora, allowing C.

C. diff infection8:47–9:21

diff bacteria to proliferate and cause infection. In this case, history might reveal watery diarrhea, colicky abdominal pain, and sometimes nausea and vomiting.
On exam, you might find abdominal tenderness and distension with hyperactive bowel sounds. CBC might be normal or show leukocytosis, and CMP may show electrolyte abnormalities.
If you suspect C. diff, make sure to obtain a stool culture to confirm.Finally, fever presenting more than 30 days after surgery is considered delayed.

Delayed phase/Source Unrelated to Surgery9:21–9:59

You should start your evaluation with a fever workup to rule out previous causes like pneumonia, UTI, and central line infections.
However, most fevers during this period are unrelated to surgery and likely caused by community-acquired infections, such as the common cold or upper respiratory tract infections.
Still, there are two important surgery-related causes of fever you do not want to miss: device or prosthesis infection, and fistula formation.
You should consider device or prosthesis infection if the operation involves implantation of a device, like a mesh for hernia repair, or an orthopedic prosthesis for hip replacement, and reports of pain around the implantation site.

Device or Prosthesis infection9:59–10:42

On exam, you might find erythema, edema, and tenderness around the implantation site. You will likely see leukocytosis on CBC, and positive blood cultures if the patient has a vascular graft or prosthetic heart valve.
If you suspect an infected device, order an ultrasound for superficial implants and CT for deep implants. You may see inflammatory changes like edema and fluid collection, or even vegetations around the device on imaging.Lastly, you should suspect fistula formation in patients who underwent high-risk operations, like oncologic resection requiring anastomosis of organs with a lumen, or had postoperative chemoradiation.

Fistula Formation10:42–11:44

You might see foul discharge or bleeding from a visible fistula tract opening accompanied by erythema and tenderness. Keep in mind that fistulas can also be internal, such as a colovesical fistula.
If you suspect a fistula, order an ultrasound or CT to visualize the fistula tract, and send a sample of the discharge for cultures so you can tailor antibiotics.One last high yield fact!
Sometimes postoperative fever and infections can present more rapidly than the typical timeline expected. This can occur when there was contamination during surgery, such as from a break in sterility or a perforated appendicitis; an aggressive pathogen causing the infection, such as necrotizing fasciitis or MRSA; or an undiagnosed systemic infection, like COVID-19.Alright, as a quick recap… Causes of postoperative fever can be grouped based on time of onset.

Recap11:44–12:52

Within the immediate postoperative phase, most common causes are transfusion reaction if the patient received intraoperative blood products, acute drug reaction if they received general anesthetics or antibiotics, or physiologic if all other causes are ruled out.
During the acute phase, causes of fever are represented by the 5 W’s: wind for pulmonary issues like atelectasis or pneumonia, water for UTIs, wound for surgical site infection, walking for vascular causes like DVT, phlebitis or central line infection, and finally wonder drugs, which can also present in the subacute phase.
During this phase, you should also consider anastomotic leaks and C. diff infection.
Lastly, fever in the delayed phase is usually caused by community-acquired infections, but you should also consider device or prosthesis infection if one was used during surgery, and fistula formation for patients who underwent high-risk operations.