Fever confuses clinicians.
For the clinician, fever indicates an infection (most of the time). Can it tell me what kind of infection and
where it is though? Fever is sometimes associated
with raised heart rate, cool peripheries and general malaise. This picture can be very difficult to discern
from sepsis. Fever therefore presents a
dilemma. If the tachycardia and lethargy
could be simply associated with a febrile moment, do I wait to see if the red
flags resolve when the fever settles? If
that resolution happens (by far the most likely outcome), I have avoided
unnecessary treatment and admission, both of which are at best unpleasant and
inconvenient (at worst they both carry their own small risk of morbidity and
mortality). If it later turns out that
the child was septic (unlikely but always possible), then the delay, intended
to remove the confounder of fever, may have caused harm.
So if fever causes confusion and anxiety, it’s probably a
good thing to be clear about a few things to do with fever. Let’s work through some common questions.
Is fever helpful or necessary in fighting infections?
This is something that is frequently posed: that fever is a
normal feature of an immunological process. It is then suggested that we should not
interfere with it. I’m afraid that this
argument holds little water. Unless
there is good evidence that the height of the fever correlates with better
outcome (and unsurprisingly this is not the case) then we can’t attribute the
death of the microbes to a thermal effect.
Yes, fever may be a part of a process but that doesn’t make it necessary
or desirable. Are fumes a normal outcome
from an engine running? Yes. Would it be great if we could get the same
performance from our engines with less or no fumes? Yes.
Fever is a sign that the immune system is doing something but there is
no good evidence that reducing fever is harmful to the body’s business of
fighting the infection.
Is fever harmful to the brain?
The simple answer is that no, fever itself is not harmful as
long as it is due to a functional immune response. That doesn’t mean that the infection couldn’t
be harmful, but a fever is not harmful in itself as far as we know.
(There is such a thing as malignant pyrexia which has a
high morbidity and mortality rate.
Malignant pyrexia is not a normal physiological response, fever during
an infection is.)
Is fever always significant?
Not always. Sometimes a raised temperature is not even a fever. It can be environmental. Babies in particular are prone to getting hot if overdressed or in a hot room.
If a raised temperature is due to infection, the issue of how determined we should be when we look for a focus is a complicated one. Different circumstances will require different approaches. The history and examination are important but so is the age of the child. Babies have a much higher incidence of sepsis and serious bacterial infections. The threshold for investigation is far lower in a three week old than a three year old.
Consider these two scenarios:
In the first scenario the pre-test probability of significant infection is low as long as there are no special circumstances (returning traveller etc.) but in the second they are far higher.
Does fever cause febrile convulsions?
Not always. Sometimes a raised temperature is not even a fever. It can be environmental. Babies in particular are prone to getting hot if overdressed or in a hot room.
If a raised temperature is due to infection, the issue of how determined we should be when we look for a focus is a complicated one. Different circumstances will require different approaches. The history and examination are important but so is the age of the child. Babies have a much higher incidence of sepsis and serious bacterial infections. The threshold for investigation is far lower in a three week old than a three year old.
Consider these two scenarios:
- A three year old presents with the parent saying that they were really hot at home that morning. They now have a normal temperature. Examination is completely normal and the child looks well. Heart rate and other parameters are all normal.
- A three week old presents with the parent saying that they were really hot at home that morning. They now have a normal temperature. Examination is completely normal and the child looks well. Heart rate and other parameters are all normal.
In the first scenario the pre-test probability of significant infection is low as long as there are no special circumstances (returning traveller etc.) but in the second they are far higher.
Does fever cause febrile convulsions?
Probably not. A
review article (1) previously reported that the available evidence showed that
antipyretic use was not associated with a reduced rate of febrile
convulsions. This is entirely plausible
as two events which repeatedly occur together do not have to be one causing the
other. It makes perfect sense that both the
fever and the fit could be caused by biochemical changes brought about by
either the infection or the body’s response to it.
There was a new paper (2) published in 2018 in which the authors
claimed to have clearly demonstrated that antipyretics reduced the recurrence
rate of febrile convulsion in children who had already had a fit. The recurrence rate of fits during the same
illness was so high in this study as to suggest that either the data was skewed
or that the population was so different to normal as to make the results
difficult to apply to practice. Although
this latest publication did challenge the accepted view that lack of fever
control is not to be blamed for febrile convulsion, many have seen it as a blip
rather than a reason to change their practice.
I remain open minded but still in the “fever does not directly cause the
fit” camp.
Does the height of the fever indicate a more serious
infection?
The answer to this is, “not really.” A fever of 40C is slightly more likely to
indicate a serious bacterial infection (SBI) than a temperature of 38C in an
unwell child. Despite this weak
correlation, height of fever is an unreliable indicator of SBI. Ultimately the decisions and diagnosis should
be made based on other findings. A child
with a fever of 40C, a red throat, red ears and no signs of SBI probably has a viral
URTI. A child with a temperature of 38C
with cough, grunting and focal reduced air entry and coarse crepitation in the
chest is presumed to have pneumonia. The number of the temperature itself
is of little use in making those decisions. Undoubtedly, a high
fever might act as a speed bump to a clinician, making them look twice and
think carefully. That’s no bad
thing. However a higher temperature
shouldn’t mandate a different diagnosis or course of action.
Should we be treating fever in children?
Fever, it seems, is neither harmful nor beneficial. The medicines that we give to children should
in theory be administered with the aim of reducing pain and general malaise. In practice, children who are febrile usually
display signs of feeling unwell. This
means that we end up giving them medication anyway. The reason may be different but the end
result is the same.
If a child is febrile but seems to feel entirely well and
demonstrates no evidence of pain, it seems entirely reasonable to not treat the
fever for the fever’s sake. That
scenario does happen but is reasonably uncommon.
We should probably de-emphasise the role of fever in the
clinical assessment. The presence of
fever is an important piece of information in the acute assessment of a child
but only to trigger a search for a focus.
Once it is known that the child has an infection, the focus should be on
useful discriminators such as appearance, behaviour, duration and pattern of
the illness.
Fever is an important feature of history and
examination. The significance and cause
of the fever is the question which then occupies the clinician’s mind. If the cause and effect of the symptoms are
found to be benign, the fever becomes a detail, not a task. We treat the child not the fever.
Edward Snelson
Doctor who prefers it hot
@sailordoctor
References
Doctor who prefers it hot
@sailordoctor
