Surgery – Post-operative complications.

Post operative clinical scenarios are very high-yield in Surgery on USMLE Step 2CK and USMLE Step 3. Also, useful for COMLEX and Family medicine boards.  Archer USMLE reviews focus extensively on these highyield concepts with evidence based information and Question/ Answer analysis to promote critical thinking.

Here, we will discuss several scenarios in post-operative setting, diagnosis and management. This discussion will be followed by self – assessment questions to reinforce your knowledge and to test your analytical skills in complex scenarios.

One important clue in the diagnosis of certain post operative complications is the timing – the day after which the symptom appeared can offer a big clue towards the underlying complication.

General post-operative complications include post-operative fever, atelectasis, wound infection, embolism and deep vein thrombosis.

The highest incidence of post-operative complications is between 1 and 3 days after the surgery. However, specific complications occur in the following distinct temporal patterns: early post-operative, several days after the operation, throughout the post-operative period, and in the late post-operative period. Let us discuss common scenarios in post-operative period.

1) Post-operative fever : A common problem seen after surgery

The Rule of W mnemonic was initially introduced in 1980s to elucidate the most frequent causes of postoperative fever based on the timing. The original Rule of W lists the most common causes of fever as :  A. Wind (atelectasis) B. Water (urinary tract infection) C. Wound (wound infection) D. Walking (venous thromboembolism) E. Wonder drug (drug induced fever).


In the past, atelectasis was considered to be a frequent cause of postoperative fever. However, significant evidence that followed later on indicated that it’s not a clear cause of fever in post-op setting. As per a study from Roberts and colleagues , when fever was defined as a temperature of 100.4 F or higher, atelectasis was seen only in 47% of patients. Another study by Engoren showed that the incidence of atelectasis increased as the incidence of fever decreased with each successive postoperative day.  This bolsters the idea that atelectasis was associated with neither the presence nor the severity of fever.

The Rule of W has undergone changes and a simplified evidence based pnemonic has been proposed by Dr. Hyder and colleagues.

Revised Rule of W mnemonic for Post-Op fever: 

  1. Waves (ie, electrocardiogram waves – Myocardial infarction)
  2. Wind (pneumonia)
  3. Water (UTI)
  4. Wound (sSSI and dSSI)
  5. Walking (VTE)


Etiology of post-op fever can be identified depending on : a) Time since operation b) Type of surgery c) associated clinical features. The following time scales can help you in arriving at most likely etiology of post-op fever.

First 24 hours : systemic response to surgical trauma and pre-existing infection should be considered. Myocardial infarction should be considered – EKG will be helpful.

24 to 72 hours : Pneumonia most common. Atelectasis is no longer felt to be a cause of post-op fever > 100.4F

3 to 7 days : Pneumonia, Wound infection, UTI, Intraperitoneal sepsis, Sepsis and Anastomotic leak are common causes

7 to 10 days : Deep vein thrombosis ( can start as soon as 5 days post-op and up until 4 to 6 weeks) and Pulmonary embolism

Do a full clinical examination, inspect the wound for infection signs, obtain chest x-ray to rule out atelectasis or pneumonia and check for calf tenderness while evaluating post-operative fever to identify the etiology.

2. Hemorrhage:

Primary hemorrhage: either starting during surgery or following post-operative increase in blood pressure – replace blood loss and may require return to OR to re-explore wound.

If large volumes of blood have been transfused during surgery, you must remember an entities such as “dilutional thrombocytopenia”, “dilutional coagulopathy” and “consumption coagulopathy” .  Large volume blood transfusions more than 5 units can lead to fall in the clotting factors due to dilution and consumption from bleeding/ clotting. Hemorrhage may be exacerbated by consumption coagulopathy. Check CBC, PT, PTT. Transfuse platelets and Fresh frozen plasma with large volume blood transfusions.

If large volumes of blood have been transfused during surgery, you must also remember electrolyte imbalances can occur such as hypocalcemia which can eventually lead to cardiac arrest if severe. Transfused blood contains anticoagulants such as potassium citrate which when given in excess can chelate the calcium in the body causing a drop in free calcium. Look for signs of hypocalcemia. Check calcium level always after massive blood transfusion and replete calcium if low.

Late post-operative haemorrhage occurs several days after surgery and is usually due to infection damaging vessels at the operation site. Treat infection and consider exploratory surgery.

3) Infection : Infectious complications are the main causes of post-operative morbidity in abdominal surgery.

Wound infection: most common form is superficial wound infection occurring within the first week presenting as localised pain, redness and slight discharge usually caused by skin staphylococci.

Cellulitis and abscesses: present in the first week but can occur as late as third post-operative week. Presents with fever and local signs of infection. Cellulitis is treated with antibiotics. In case of abscess, sutures must be removed and wound must be probed. If there is a depper abscess, surgical re-exploration must be performed.Wound must be left open to heal by secondary intention.

Wound sinus : a late infectious complication from a deep chronic abscess that can occur after apparently normal healing. Usually needs re-exploration to remove non-absorbable suture or mesh, which is often the underlying cause.

4) Disordered wound healing : includes Wound dehiscence and Incisional Hernia

Wound dehiscence : A serious complication with mortality up to 30% and occurs at about 7 to 10 days in the post-operative period. Affects about 2% of mid-line laparotomy wounds. Wound dehischence is often heralded by serosanguinous discharge from wound. – if the question mentions a serosanguinous dischargefrom surgical wound in 7-10days post-op always keep this entity in mind.  A defect can be palpated in the wound area. Initial management includes opiate analgesia, sterile dressing to wound, fluid resuscitation and early return to theatre for resuture under general anesthesia.

Incisional hernia :Occurs in 10-15% of abdominal wounds usually appearing within first year but can be delayed by up to 15 years after surgery. Risk factors include obesity, distension and poor muscle tone, wound infection and multiple use of same incision site. Presents as bulge in abdominal wall close to previous wound. Usually asymptomatic but there may be pain, especially if strangulation occurs. Management includes abdominal binders in uncomplicated hernia but surgical repair is needed when where there is pain or strangulation.

5) Urinary Problems :

Urinary retention: common immediate post-operative complication – often tested on the exam. Usually, this is because of post-operative pain and can be treated conservatively with adequate analgesia. If this fails,  catheterization is the next step.

UTI: very common, especially in women, and may not present with typical symptoms. Treat with antibiotics and adequate fluid intake. Also, indwelling catheters left for long duration increases the risk of UTI. If catheter required for more than 2 weeks 90% patients will develop bacteriuria.

Acute Renal Failure : If there is no urinary output or oliguria after surgery, urinary retention should first be considered and a foley catheter must be inserted. After foley insertion, if there is still no urinary output – cosider, acute renal failure as the reason for oliguria or anuria. Acute renal failure can be pre-renal ( hypoperfusion secondary to shock) or renal ( interstitial nephritis secondary to antibitics used or Acute tubular necrosis secondary to rhabdomyolysis or drugs) or post renal secondary to bladder flow obstruction. It is important to identify the etiology so that it can be adequately treated as soon as possible. Follow the guidelines for investigating ARF that are mentioned under our renal lectures.

6) Post-operative delirium : very common and must be differentiated from other causes of delirium such as dehydration, hypoxia, electrolyte imbalance and sepsis. Treat the underlying cause and treat symptoms with haloperidol.

7) Bowel function issues:

Delayed return of bowel function:  post-op ileus is a common problem. Patient may complain of nausea, anorexia and vomiting. Management is conservative – electrolyte repletion, hydration. More prolonged and severe form of post-op ileus is calledadynamic obstruction .  Patient may have vomiting and intolerance to oral intake. It must be distinguished from mechanical obstruction. An obstructive series x-rays can help in differentiating it from mechanical obstruction. A CT scan with oral contrast is very useful if there is suspicion of mechanical obstruction. If it involves large bowel – usually described as ” colonic pseudo-obstruction“. Diagnosed by instant barium enema

Early mechanical obstruction: may be caused by twisted or trapped loop of bowel or adhesions occurring approximately 1 week after surgery.  Treat with nasogastric aspiration plus IV fluids. If progresses despite conservative measures,  requires surgery.

Late mechanical obstruction: adhesions can organise and persist, commonly causing episodes of small bowel obstruction  months or years after initial surgery. Treatment is same  as for early mechanical obstruction.

8) Respiratory complications

Occur in up to 15% of general anaesthetic and major surgery and include:

a) Atelectasis (alveolar collapse):Caused when airways become obstructed, usually by bronchial secretions. Common cause post-operative fever from day 0 to day 2. Symptoms are slow recovery from operations, poor color, mild tachypnea, tachycardia and low-grade fever. Prevention is by pre-and post-operative physiotherapy. In severe cases, positive pressure ventilation may be required

b) Pneumonia: requires antibiotics, physiotherapy. CXR will reveal infiltrate with out volume loss. In atelectasis, the infiltrate is usually accompanied by volume loss in the lung.

c) Aspiration pneumonitis: Sterile inflammation of the lungs due to inhalation of gastric contents.  There is a preceding history of vomiting or regurgitation which is a clue and such symptoms are followed by rapid onset of breathlessness and wheezing. Mortality is nearly 50% and requires urgent treatment with bronchial suction, positive pressure ventilation, prophylactic antibiotics and IV steroids. Antibiotics in aspiration pneumonitis/ suspected aspiration pneumonia should cover both anerobes and gram negatives eg: piperacillin/ tazobactam. Clindamycin alone may be insufficient since it does not have gram negative coverage.

d) Acute Respiratory Distress Syndrome: ( ARDS): presents with rapid, shallow breathing, severe hypoxemia with scattered crepitations but no cough, chest pains or hemoptysis, appearing 24-48 hours after surgery. Occurs in many conditions where there is direct or systemic insult to the lung, e.g. multiple trauma with shock. CXR reveals bilateral diffuse infiltrates in the absence of congestive heart failure. A swan ganz catheter reveals normal PCWP (pulmonary capillary wedge pressure) ( remember that increased PCWP will favor CHF or fluid overload as the cause of acute diffuse CXR infiltrates rather than ARDS) Requires intensive care with mechanical ventilation with positive-end pressure ( HIGH PEEP / LOW TIDAL VOLUME Strategy – refer to our pulmonology lectures for ventilation strategies and strategies for ARDS)

Access ARCHER USMLE Step3 Theory Lectures for Multiple HighYield Concepts

One Response

  1. ATELECTASIS DOES NOT CAUSE FEVER. I would hope USMLE has updated their records by now.

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