Approach to Fever, by Dr. Eli Freiman.
By the end of this video, the learner
will be able to summarize the clinical basics of fever,
describe the physiology of body temperature regulation
and the pathogenesis of fever, and discuss
the approach to evaluation and management
of a fever in a child.
Introduction.
Body temperature is generally measured
in four different ways--
oral, rectal, axillary and infrared.
Rectal measurement is considered to be the reference
standard for measuring body temperature,
but is contraindicated in neutropenic patients
and is generally avoided in older patients
due to patient discomfort.
Oral temperatures run about 0.6 degrees
Celsius lower and are heavily influenced
by recently ingested liquids and respiratory rate.
Infrared measurements utilize technology
to measure heat produced by either the tympanic membrane
or temporal artery, and are widely
used in the hospital and emergency department setting.
However, data are not conclusive about diagnostic utility.
Axillary measurements are considered
to be the least reliable and often run lower
than rectal temperatures.
The mean normal temperature for adults
is 37 degrees Celsius, while children and infants have
a higher average temperature.
Fever is defined differently in different age groups,
in part, because of the epidemiology
of invasive, bacterial infections.
In children under three months old,
we have a lower temperature threshold
to trigger an infectious workup.
Some institutions choose to call a fever 38 degrees Celsius.
For older children, the temperature
that might trigger an infectious workup
may be higher, like 38.5 or 39 degrees.
Remember however, that fever should only
be a piece of the larger clinical evaluation
when deciding how deeply to investigate a certain patient
presentation.
And lower temperature should not preclude investigation
of an ill-appearing patient.
Patients with specific underlying conditions
that increase the risk of infection such as sickle cell
disease, neutropenia, or HIV, should
be investigated thoroughly with any concerning
elevation in temperature.
Physiology.
Fever is an elevation in body temperature
mediated by hypothalamic pathways
in the central nervous system.
The hypothalamic thermoregulatory center
controls body temperature through three mechanisms.
One-- controlling heat production mainly
in the muscles and liver, two-- controlling heat dissipation
from the skin and lungs, and three--
setting the normal body temperature.
Fever is a physiologic process where the hypothalamus sets
a higher body temperature set point in response to endogenous
signaling.
The body then rebalances heat production and dissipation
to elevate the body temperature to the new set point.
This is why patients with new fevers
often feel cold and experience rigors.
Their current body temperature, although elevated
above true normal, lives below the newly elevated hypothalamic
set point and lead to the subjective feeling of cold.
Pathogenesis.
Peripheral phagocytes release various cytokines in response
to encountered foreign antigens or injury,
including IL-1, IL-6, TNF-alpha, and interferon.
These cytokines then act on the anterior hypothalamus,
resulting in the upregulation of prostaglandins, especially
PGE-2, which results in an increase
in the hypothalamic set point for body temperature.
With a new higher set point, the body increases heat generation
through processes such as increased metabolic rate,
increasing muscle tone or contraction,
and decreasing epidermal heat loss
by modulating skin perfusion.
Combined, these result in higher body temperature
to meet the newly increased hypothalamic set point
and result in clinical fever.
Initial Fever Evaluation.
Initial evaluation of all fevers starts with a thorough history
and physical exam with an emphasis on the adequacy
of cardiopulmonary physiology.
Thorough histories and physical exams
can, with the exception of neonates,
often pinpoint the likely source of fever.
Signs of other underlying diseases should be evaluated.
Remember that response to antipyretic therapy
does not differentiate between viral or bacterial etiologies.
In the pediatric history, important pieces
of information to elicit are, but are not
limited to, headache and photo phobia,
ear tugging or pain, sore throat, neck pain, swelling,
or decreased range of motion, cough and shortness
of breath, costovertebral angle tenderness
or dysuria, focal abdominal pain, vomiting, or diarrhea,
rash, or focal limb or joint pain or swelling.
On exam, be mindful to assess for evidence
of altered perfusion by evaluating
for abnormal vital signs, altered mental status,
mottled skin, or delayed capillary refill.
Patients who are ill-appearing or have unstable vital signs
should have a broad infectious workup, empiric antibiotics,
and be admitted to higher levels of care.
Infants younger than 90 days are at significant risk
for serious bacterial infections,
or SBI, for example, urinary tract infection, bacteremia,
or meningitis, or even disseminated
herpes simplex virus, or HSV infection,
without overt symptoms.
There are specific protocols governing
the evaluation of febrile infants 90 days
of age and younger.
Protocols vary by institution, but generally involve
blood, urine, and cerebrospinal fluid,
or CSF, tests via lumbar puncture
with bacterial cultures.
The youngest infants are also commonly evaluated
for invasive HSV infection, specifically HSV meningitis,
by sending HSV PCR from the CSF.
Decision whether to test for HSV meningitis often
depends on age, specific risk factors,
and whether there is a CSF pleocytosis.
The goal of such evaluations is to identify infants
at risk for SBI and HSV for hospitalization and empiric
antimicrobials.
However, common viral illnesses, such as
respiratory syncytial virus, RSV, or enterovirus
remain the most common cause of fever in infants
under 90 days of age.
Unlike infants less than three months old,
children ages three to 36 months old
are epidemiologically at lower risk
for serious bacterial illness and are
more able to communicate their symptoms.
Children in this age group who, after a thorough history
and physical exam, are well-appearing but do not
have a clear source of fever, are often
identified as having fever without a source, or FWS.
The majority of patients with FWS
have self-limited viral infections
or quickly develop a recognizable source
of bacterial infection.
Fever without a source is different than fever
of unknown origin, or FUO, which is when a fever has been
present for eight or more days.
FUO will not be discussed here.
Types of serious bacterial illness in this age group
include meningitis, periorbital or orbital cellulitis,
septic arthritis, osteomyelitis, UTI, pneumonia,
and skin infections.
Initial evaluation of well-appearing children
between three to 36 months old with FWS
includes urine testing for higher risk patients,
such as girls less than 24 months,
uncircumcised boys less than 12 months,
and circumcised boys less than six months.
Routine laboratory evaluation and empiric therapy
for patients outside of the high-risk age groups
is not recommended.
It is very important that immunization status
is included in the history for these patients.
Patients with FWS who have not been completely immunized
should routinely receive screening blood and urine
infection studies.
Many guidelines recommend empiric antibiotics
in incompletely immunized patients with leukocytosis.
Management of Fever.
As we previously discussed, the first step in treating fever
is determining the cause, as the underlying
etiology will guide management.
Treatment for all of the potential causes of fever
will not be covered in this video.
Instead, we will focus on symptomatic management
of fever.
In otherwise healthy children with minimal symptoms,
treatment of fever with antipyretics is not required.
Despite multiple studies, there is no conclusive evidence
that treating fever, as opposed to the underlying condition,
reduces morbidity or mortality, except in cases
where reducing metabolic demand is important.
The decision to treat fever should be
made on a case-by-case basis.
The benefits of antipyretic therapy
include improvement in the child's discomfort,
a decrease in insensible losses to prevent dehydration,
and analgesia.
Potential downsides include delayed identification
of the underlying etiology, drug toxicity, and allergy.
The most commonly used oral antipyretics
are acetaminophen and ibuprofen.
Antipyretics work in part by blocking prostaglandin
synthesis and restoring the hypothalamic thermoregulatory
set point to normal.
Remember not to use aspirin in children
due to the risk of Reye's syndrome,
except under very specific circumstances.
Sometimes, providers will choose to not use
antipyretics in order to monitor the trajectory and amplitude
of the patient's fever curve.
Thank you for watching this video on approach to fever.