Part of the TeachMe Series

Post-Operative Pyrexia

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Last updated: June 3, 2018
Revisions: 13

Last updated: June 3, 2018
Revisions: 13

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Pyrexia (fever) refers to a raised body temperature, typically greater than 37.5c. It is common in surgical patients, either due to the underlying disease process or as a post-operative complication.

Whilst infection is regularly the suspected cause, other conditions must be considered when approaching the surgical patient with pyrexia (Fig. 1).

In this article, we shall look at the aetiology, investigations and management of pyrexia in the post-operative surgical patient.



The most common cause of pyrexia in the post-operative patient is infection. The specific post-operative day on which the fever develops may indicate the source of the infection:

  • Day 1-2 – consider a respiratory source
  • Day 3-5 – consider a urinary tract source
  • Day 5-7 – consider a surgical site infection or abscess/collection formation
  • Any day post-operatively – consider infected IV lines or central lines as a source

The investigation of the infection source should also be tailored to the patient. For example, in a patient who has undergone a bowel resection, post-anastomotic leak is an important differential to be considered and should be investigated as a matter of urgency.

Other Causes of Pyrexia

Other causes of post-operative pyrexia include:

  • Iatrogenic – which may include a drug-induced reaction (e.g. antibiotics or anaesthetic agents) or from a transfusion reaction.
  • Venous thromboembolism – although rare, a PE or DVT can cause a low grade fever without any other overt clinical features
  • Secondary to prosthetic implantation – with any foreign body, for example after an AAA repair, a low-grade fever may be evident
  • Pyrexia of Unknown Origin
Fig 1 - The 5 Ws of Post-Operative Pyrexia

Figure 1 – The 5 Ws of post-operative pyrexia. Infectious sources in the post-operative period predominately originate from the lung (“wind”, days 1-2), urinary tract (“water”, days 3-5) and surgical site infections or abscess formation (“wound”, days 5-7).

Pyrexia of Unknown Origin

Pyrexia of Unknown Origin (PUO) is defined as a recurrent fever (>38oc) persisting for >3wks without an obvious cause, despite >1wk of inpatient investigation.

Causes of PUO include infection of unknown source (30%), malignancy (classically B-symptoms from lymphoma, 30%), connective tissue diseases or vasculitis (30%) and drug reactions.

Clinical Features

The underlying source of the pyrexia will largely determine the clinical presentation of the patient. Importantly, if the patient appears unwell and needs urgent resuscitation and management, start an A to E approach as necessary and only attempt to identify the source of infection once the patient is stable.

If no obvious source is apparent, enquire about specific systems symptoms, such as urinary frequency, urgency, or dysuria, productive cough or dyspnoea, haemoptysis, chest or calf pain, or wound or IV line tenderness or discharge.

On initial examination, examine for signs of pulmonary infection, IV line infections, wound infections, and calf tenderness. If post-operative, also examine for specific complications from the operation (e.g. signs of peritonism in anastomotic leak).


septic screen is essential in investigating the surgical patient with pyrexia. In most cases, the source is obvious and your screen can be tailored accordingly, yet in a less clear presentation a wider screen is indicated. It can include:

  • Blood tests– FBC, CRP, U&Es.
  • Urine dipstick
  • Cultures– blood, urine, sputum, and wound swab
  • Imaging– Chest X-ray

If the source cannot be identified through the septic screen, more detailed investigations may be required, such as a CT scan for any suspected anastomotic leak or Doppler US for suspected DVT.

Fig 2 - A CXR showing left lower zone consolidation

Figure 2 – A chest x-ray showing left lower zone consolidation.


Any identified infection should be treated empirically with antibiotics, pending sensitivity results. Empirical antibiotic regimes will vary depending on local sensitivities – therefore follow your local hospital guidance. Example empirical treatments are given in Table 1. If the patient is septic, start immediate management for sepsis.

If no infectious cause can be identified, do not start empirical antibiotics. First look for non-infectious causes and consult a senior colleague and a microbiologist for further advice.

Additional support can be provided via anti-pyrexials and analgesia. It is important to ensure the patient remains hydrated; observations should be increased and a fluid balance started

A low threshold of suspicion should be present for suspected sepsis. Any new rise in temperature whilst on antibiotics should prompt repeating the septic screen (and investigating other potential causes than infection). Any concerns should warrant an early senior review.

Infection Source

Empirical Antibiotic Regime

Lower Respiratory Tract Co-Amoxiclav 625mg PO TDS for 5 days
Lower Urinary Tract

Upper Urinary Tract

Trimethoprim 200mg PO BD for 3 days

Co-Amoxiclav 625mg PO TDS for 14 days

Surgical Site or Cellulitis Flucloxacillin 500mg PO QDS for 5 days
IV line

(Central Line)

Flucloxacillin 500mg PO QDS for 5 days

(Vancomycin, levels requires close monitoring, follow local guidelines for dosing)

Intra-Abdominal Cefuroxime 1.5g IV TDS + Metronidazole 500mg TDS IV
Septic Arthritis Flucloxacillin 2g IV QDS
Unknown source Cefuroxime 1.5g IV TDS + Metronidazole 500mg TDS IV + Gentamycin 5mg/kg STAT

Table 1 – Example empirical regimens per infection source.

Key Points

  • Ensure to take an A to E approach for all cases of pyrexia in the surgical patient
  • Consider the time since operation and details of the procedure to help focus your investigations
  • Not all cases of pyrexia are due to infection