Fever
in adults a common but much misunderstood entity: A brief Note
Dr KS
Dhillon, FRCS, LLM
Introduction
Anecdotal evidence shows that when a person feels
that he has fever, he treats himself with paracetamol and when he visits his
family doctor for fever, the doctor also prescribes paracetamol. The nurses in
the hospital start tepid sponging of the patient when the temperature is just
over 370C and sometimes they will call the doctor in the middle of
the night for advice on whether to serve paracetamol to the patient. Such
anecdotal experiences raise several questions which beg to be answered.
What
is fever?
Fever, an elevation of body temperature, also known
as hyperthermia, is an important sign of health and disease in medical care of
patients. The detection of normal body temperature or the norm was established
way back in the middle of the 19th century by a German physician
(Wunderlich) when the thermometer was first introduced. Although at that time
the thermometers were not calibrated and axillary temperatures (which were 1.4
to 2.2 degrees higher than that obtained by present digital devices) were
measured, the norm for body temperature was established as a body temperature
of 370C and any temperature of 380 C or more was defined
as fever. Although the present day devices are more accurate and we know that
normal body temperature is a range rather than a fixed number, most medical
practitioners regard a temperature of 370 C as the norm and any
temperature of 380 C or more as fever.
There are variations in the temperatures recorded by
different means at different sites. The core body temperature is accurately
measured via catheters in the pulmonary artery and that is believed to be the
gold standard. However in clinical practice the rectal temperature is believed
to be the gold standard. There are variations in the temperature measured at
the rectum, axilla, mouth and the ear. However the tympanic membrane temperature
measurement by digital devices has become a norm due its convenience and speed
with which the temperature can be taken especially in a busy medical setting.
Review of literature shows that there is no fixed
figure for normal body temperature just as there is no fixed figure for pulse
rate or blood pressure. The temperature will vary with the device used, site of
measurement, age and sex of the individual and the time of day when the
temperature is taken. The temperature is lower in the morning and higher in the
afternoon/evening. The temperature also varies with the menstrual cycle in
females. The temperature is lower in the elderly frail individuals (1).
In a healthy adult (18 to 40 years), studies show
that the oral temperature can range from 35.6o C to 38.20 C
with a mean of 36.80C. The 6am maximum temperature is about 37.20C
and 4pm maximum temperature is about 37.70C with a daily variation
of 0.50C (2). In practice a temperature of 370C is
considered as normal body temperature with a circadian variation of between 0.50C
to 10C (3). Fever is defined as temperature of 38.30C or
more and unless there is other evidence of infection, temperature of below 38.30C
does not need any investigation (3).
What
causes fever?
The hypothalamus regulates the body temperature
based on, the signals received from peripheral cold/warmth receptors via the
peripheral nerves and from the temperature of the blood that surrounds the
neurons in the hypothalamus.
Fever results from the resetting to a higher level
the hypothalamic temperature set point at which the body temperature is
normally maintained. This results in activation of the vasomotor centre which produces
peripheral vasoconstriction leading to shunting of the blood to internal organs
and reduction of heat loss. At this point the patient feels cold and shivering
occurs which generates more heat from muscular activity. When the patient feels
cold he/she takes cover under warm clothes which further leads to a rise in
body temperature. The shift of blood to internal organs increases metabolic
activity which generates more heat especially in the liver. All these chain of
events results in a rise in body temperature till the new hypothalamic set
point is reached and after that the hypothalamus maintains the temperature till
the set point is changed by further change in events within and around the
patient.
The hypothalamic resetting of set point is mediated
by cytokines which are released by monocytes in response to infection or trauma
or other insults to the body. Sympathetic hyperactivity is also known to
increase the production of heat.
What
is the significance of fever?
Elevation of body temperature appears to be an
evolutionary protective response against infection which exists in the animal
kingdom. Elevation of body temperature has been shown to be protective against
infection in animals. When the body temperature rises the immune function
improves with production of antibodies and cytokines, t-cell activation, and
increased neutrophil and monocyte function. A rise in body temperature has been
shown to inhibit streptococcus pneumonia (3).
Studies in humans have found a positive correlation
between high temperatures and improved survival in patients with certain
bacterial infections (3). However in patients with limited cardio-respiratory
reserves, high fever can have deleterious effects because high fever increases
oxygen consumption, increases CO2 production, increases energy expenditure and
increases cardiac output. For every 10C rise in body temperature
there is a 10% increase in oxygen consumption. In patients with CVA and traumatic
brain injury moderate elevation of temperature can worsen the brain damage (3).
Invariably in clinical practice all patients with
fever are treated with antipyretic medications and external cooling to reduce
the temperature to normal. When we know that fever is body’s protective
response to infection, it appears that these attempts to reduce the body
temperature to normal, are illogical. Furthermore bringing the temperature to
normal will prevent the physician from monitoring the response to treatment instituted.
The use antipyretic pharmaceutical agents may cause acute hepatitis, in very
ill patients (especially alcoholics and emaciated patients), and in patients
who have been self-medicating themselves with acetaminophen for chronic pain.
The use of cooling blankets have been shown to be no more effective than the
use of anti-pyretic in bringing down the temperature and these cooling blanket
can produce rebound hyperthermia.
The general recommendations are that fever should
not be treated symptomatically with medication or external cooling except in
patients with brain injury, patients with poor cardio-pulmonary reserve and in
patients with temperatures of more than 400C (3).
Most healthy individuals tolerate temperatures of up
to 40.50C well without ill-effects. Hyperthermia beyond 42.10C
can cause cellular damage affecting the brain, muscles and the heart. It can
cause DIVC, hypoxia, acidosis, hyperkalaemia, coma, fits, arrhythmias, and
hypotension and can sometimes be lethal (4).
There is no evidence to support the routine treatment
of fever even in patients with septic shock. In fact studies of pharmacologic
antipyretics in such patients have failed to show any clinical benefit and some
have even suggested they do more harm (5). A study by Lee et al showed that in
critically ill septic patients, administration of NSAIDs or acetaminophen was independently
associated with 28-day mortality, and there was no association between fever
with mortality (5).
Conclusion
There are no norms for body temperature but most medical
practitioners regard a temperature of 370C with a circadian
variation of between 0.50C to 10C as normal. Fever is
defined as temperature of 38.30C or more. Temperature is an
important vital sign which allows the physician to monitor the response to
treatment. Fever should not be treated symptomatically with medication or
external cooling except in patients with brain injury, patients with poor
cardio-pulmonary reserve and in patients with temperatures of more than 400C.
Most patients tolerate temperatures of up to 40.50C without any
ill-effects. Elevated temperatures are body’s attempt at healing and it would
be paradoxical to bring the temperature to the so called norms. Treating fever
in critically ill septic patients has been associated with mortality.
References
1. Sund-Levander M, Grodzinsky E. Time
for a change to assess and evaluate body temperature in clinical practice. International
Journal of Nursing Practice 2009; 15: 241–249.
2. Mackowiak PA, Wasserman SS, Levine MM. A critical
appraisal of 98.6 degrees F, the upper limit of the normal body temperature,
and other legacies of Carl Reinhold August Wunderlich. JAMA 1992; 268(12):1578.
3. Marik PE. Fever in the ICU. Chest 2000;
117(3):855.
4. Goroll AH, Muller AG (Editors). Primary care
medicine: Office evaluation and management of adult patient. 2009, 6th
edition, Lippincott Williams & Wilkins.
5. Lee BH, Inui D, Suh GY, et al. Fever and
Antipyretic in Critically ill patients Evaluation (FACE) Study Group.; Association
of body temperature and antipyretic treatments with mortality of critically ill
patients with and without sepsis: multi-centered prospective observational
study. Crit Care. 2012; 16(1):R33.
