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Department of Anesthesiology; Albert Einstein Medical Center; Philadelphia, PA; rothj{at}einstein.edu
To the Editor:
How should we manage the temperature of a febrile patient undergoing surgery? Should we allow the patient's temperature to drift down to normal or should we maintain his/her febrile temperature? According to anecdotal information, many practitioners let the patient's temperature drift down to normal. I argue that in many cases we should maintain the patient's temperature at the elevated, febrile set point. Let's examine several considerations.
The first consideration is whether fever is a harmful byproduct of infection or a host's defense response. If it is a harmful byproduct, then we should actively, or at least permissively, cool the febrile patient. If the fever is the host's defense, then we should try to maintain the patient at the elevated thermoregulatory set point. Although this question may still be unanswered (1), there is clear evidence that fever is a beneficial part of a coordinated defense (2,3). The lines of evidence include evolutionary, correlative, antipyretic, and hyperthermia/hypothermia studies (2). For example, infectious illnesses are of longer duration, and mortality rates increase if the fever is treated (2). Additionally, as the febrile response is highly regulated, it likely has an adaptive role (2).
A second consideration is that fever represents an alteration in the thermoregulatory set point. Unless something occurs during surgery that decreases the elevated set point, the patient will attempt to return to this set point in the postoperative period. Shivering and high metabolic cost in the early postoperative period are likely to be undesirable. Also, there is some risk to administering antipyretic therapy to maintain the lower temperature, and antipyretics may be ineffective (1).
A third consideration is whether maintaining a patient at an elevated temperature increases the metabolic rate. It is estimated that for every 1°C increase in temperature, the metabolic rate increases by up to 13%. This is probably offset to some extent by the decreased metabolic rate during anesthesia. This is significantly less than the potential 500% increase for the postoperative shivering patient (4).
A fourth consideration is that increases in core temperature up to 41°C have never been shown to be harmful per se (5). In contrast, therapeutic hyperthermia with temperatures >42°C has been associated with tissue damage, e.g., fat necrosis.
In some specific instances, a febrile state is clearly harmful. For example, in neurologic injury, carotid endarterectomy, neurosurgery, cardiac surgery, and after cardiac arrest, neurologic injury may be greater in the presence of an increased temperature (6). In pediatric patients, one has to be concerned about febrile seizures (7). Lastly, because heart rate increases as temperature increases, in patients in whom a tachycardia may be harmful (e.g., ischemic disease, valvular heart disease, obstructive cardiomyopathy, etc), decreasing the temperature can assist in treating the tachycardia.
In pregnant patients, one should be concerned about the effect of hyperthermia on the fetus. Temperatures >39°C during the first 10 wk of pregnancy during organogenesis may be associated with a sixfold increased risk of neural tube defect (8). Also, although infections increase the chance of preterm labor, this may be due to the underlying disease causing cytokine release from the amniotic cells rather than the fever per se (9).
In some patients, attempts to lower a patient's temperature may be overcome by the patient's thermal regulatory system (10). Such a futile attempt would just wastefully increase catabolism and oxygen consumption while activating the sympathetic nervous system (11).
There are little data concerning how one should manage the temperature of a febrile patient undergoing surgery (12). At least one text advocates treating the elevated temperature of a febrile patient, provides no justification for doing so, and acknowledges that it may worsen the situation (10). It is possible that the correct decision may be pathogen-specific (1). Until there are outcome studies that answer this question, the individual practitioner should consider the above arguments in managing the temperature of a febrile patient.
REFERENCES
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