Fever after surgery

Postoperatively, there may be an increase in temperature due to postaggregation metabolism during surgery. Normally, the temperature normalizes on the 2nd - 3rd p. o. day (Herold 2022).

If there are temperature elevations over this period, especially accompanied by leukocytosis, it should be assumed that the fever has other causes and should be clarified immediately (Herold 2022).

Postoperative fever may occur as:

- 1. reaction to the postaggregation metabolism:

In the first postoperative hours, postaggregation metabolism may result in subfebrile temperatures between 37.5 - 38.0 degrees C or even low-grade fever between 38.1 - 38.5 degrees C (Schwenk 2020). Usually, normalization of body temperature occurs on the 2nd - 3rd day, but sometimes later in children (Schumpelik 2010).

- 2. postoperative complication:

Fever > 38.5 degrees C - especially accompanied by leukocytosis (Herold 2022) - always indicates a complication (Schwenk 2020) and should be clarified immediately (Herold 2022).

During general or visceral surgery, fever occurs in up to 70% of patients as a neuroendocrine stress reaction (Lippert 2017).

After hysterectomies, for example, fever is found in 15 - 38 % of patients p. o. (Kaufmann 2013).

The causes of postoperative fever differ greatly and depend on the time of onset and the level of fever:

- perioperative fever:

- neuroendocrine stress reaction as an expression of an inflammatory event (Schwenk 2020)

- septic surgery

- atelectasis of the lung

- reactions to drugs and blood transfusions

- craniocerebral trauma

- neurosurgical operations

- malignant hyperthermia (Eisoldt 2006)

- fever within the first 2 p. o. days:

- wound infections

- postaggregation metabolism

- (aspiration) pneumonia

- sepsis

- Resorptive fever (Eisoldt 2006)

- Fever after more than 2 days p. o.

- Wound infection

- infection of the CVC

- intraabdominal abscesses

- deep vein thrombosis

- pulmonary embolism

- urinary tract infection

- peritonitis due to anastomosis insufficiency

- cholecystitis (stress gallbladder)

- sinusitis

- colitis

- Pneumonia (Eisoldt 2006)

The hypothalamus controls body temperature. Neurons in the preoptic anterior and posterior hypothalamus receive signals for temperature control from:

- Peripheral nerves (these transmit information from the cold and heat receptors of the skin).

- Blood circulating around the region (Kasper 2015).

Pyrogenic cytokines and exogenous pyrogens can lead to a change in the set point (Smid 2018).

• 1. pyrogenic cytokines (obsolete term: endogenous pyrogens):

These are produced in the body during inflammatory processes (Smid 2018). They include, for example, IL- 1, IL- 6, tumor necrosis factor (TNF), interferons (especially interferon alpha) (Kasper 2015).

Fever occurring in the early postoperative phase is an expression of this inflammatory process. Cytokines are released by the surgically induced tissue damage and lead to an increased body temperature (Sökeland 2007).

• 2. exogenous pyrogens:

These are derived from microbacterial toxins such as gram-positive and gram-negative bacteria as well as viruses, etc.

They play a role in p. o. fever due to complications (Smid 2018).

The cytokines lead to an elevation of the hypothetical set point in the hypothalamus. This activates neurons in the vasomotor center and leads to a reduction in heat loss through the skin via vasoconstriction in the extremities. Shivering may occur at this stage to thereby increase heat production by the muscles. The liver also contributes to heat production, as does putting on warmer clothing, hot water bottle, etc. when shivering. The processes of heat production and heat maintenance continue until the blood flowing through the neurons of the hypothalamus is at the temperature of the new thermostat setting. Once this temperature is reached, the hypothalamus maintains the designated temperature (Kasper 2015).

Postoperative fever in response to postaggregation metabolism does not require further workup.

However, if fever occurs due to postoperative complications, immediate:

- precise inspection of the wound, especially with regard to inflammation parameters and secretion discharge

- palpation and auscultation of the abdomen in cases of abdominal surgery

- Indications of any existing defensive tension

- Auscultation of the lungs

- Checking laboratory parameters (especially C-reactive protein and leukocytes)

- If abnormalities are found, imaging should be used (Schwenk 2019)

Fever due to postoperative complications:

- in particular, C- reactive protein (CrP) and leukocytes should be checked.

Leukocytes usually react more rapidly than CrP to infection. Both leukocytosis and leukopenia should be interpreted as alarm signals (Schwenk 2019).

- Urine examination for indications of a urinary tract infection (Schwenk 2019).

The most common pathogens p. o. fever are:

- staphylococci

- gram-negative enterococci such as E. coli, Klebsiellen

- enterococci

and preferably in intensive care units:

- Pseudomonads

- Fungi (Eisoldt 2006)

- Postoperative shivering

This occurs immediately postoperatively with increasing loss of effect of the anesthetics. It is due to perioperative hypothermia and should not be confused with shivering. It is a physiologic mechanism for heat production. However, in shivering, oxygen demand is increased by approximately 40% (Torossian 2019).

• Symptomatic therapy:

In all patients with fever, symptomatic measures should be taken in the form of:

- adequate substitution of fluids (Runge 2018). Fluid requirements increase by 0.5 - 1.0 l / 24 h for every 1 degree C (Herold 2022).

- Removal of warming blankets and excessive clothing (Weihrauch 2022).

- Antipyretics if necessary

Inhibitors of cyclooxygenase such as paracetamol, ibuprofen or acetylsalicylic acid are particularly suitable in this case

- Non-essential drugs should be discontinued immediately because of the possibility of drug fever (Herold 2022).

- Calf Wrap:

These are always indicated if there is a contraindication to antipyretics. In all other patients with elevation of the temperature set point, it has been shown that calf wraps - as long as the temperature set point is still elevated - are not very effective, actually increase peripheral vasoconstriction and shivering, and are usually subjectively perceived as unpleasant. In studies, the combination of calf wraps and antipyretics was not shown to be superior to antipyretic administration alone (Weihrauch 2022).

Only in cases of hyperthermia without an increase in the temperature set point are calf wraps still indicated (Weihrauch 2022)

Postoperative fever as a reaction to postaggregation metabolism does not require any therapy because it is self-limited.

Postoperative fever as a sign of a complication can be treated symptomatically and / or causally, depending on the cause.

• Chills

If the patient experiences chills, this should typically be interpreted as an indication of a catheter-associated infection, particularly from central venous catheters (CVC) or bladder catheters (Schwenk 2019).

Therefore, all foreign bodies such as probes, drains, central venous catheters, bladder catheters, etc. should be removed as early as possible. Sometimes this is already sufficient as a therapeutic measure. Otherwise, antibiotics are required, taking into account the general condition and risk profile (Schwenk 2019).

Symptomatic therapy of chills consists of administration of opioids and low-dose corticosteroids (Schwenk 2019).

• Acute wound infection

If postoperative fever reveals evidence of acute wound infection due to diagnostic complications, rapid goal-directed intervention or reoperation is required (Schwenk 2019).

• Superficial wound infection

In the vast majority of cases, superficial infections in the surgical area can be adequately treated by removal of suture material, regular irrigation, and dressing changes (Schwenk 2019).

• Postoperative fever of unclear origin

If no cause for the fever can be found during diagnostics, the patient should be treated antipyretically with e.g. metamizole 1 g and close observation (Schwenk 2019).

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