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CHAPTER 63: Persistent Fever 557

CHAPTER Persistent Fever TEMPERATURE REGULATION AND MEASUREMENT
63 Gretchen Yandle Healthy, nonfasting, resting adults, closely regulate sublingual tem-
perature between 33.2°C and 38.1°C. There is normally a small normal
2
Bennett P. deBoisblanc
diurnal variation in temperature of approximately 0.5°C, which nadirs
around 6 am and peaks around 4 pm. This tight regulation occurs due
3
to continual adjustment of thermogenic and cooling processes. Eating,
exercise, and sleep deprivation increase body temperature while fasting
KEY POINTS reduces it. Technically fever refers to an increase in the natural set point
4
• Fever occurs in more than 50% of patients at some time during their for homeostatic temperature control while hyperthermia refers to an
ICU stay. uncontrolled elevation of body temperature.
Thermoregulation resides within the hypothalamus. While countless
5
• Approximately 50% of fevers are due to noninfectious causes, such exogenous and endogenous pyrogens have been identified, almost all
as drug fevers, surgical trauma, and central nervous system injury. have been shown to stimulate the release of proximal proinflamma-
• A thoughtful evaluation of a fever may reduce costs and lessen the tory cytokines, such as IL-6, IL-8, IL-1β, and TNF, which subsequently
potential risk to the patient. induce the synthesis of prostaglandin E2 (PGE2) within the preoptic
• Extreme elevations of temperature (>41.1°C) are most often not nucleus of the anterior hypothalamus (Fig. 63-1). Binding of PGE2
due to infectious etiologies. shifts the hypothalamic thermostat increasing sympathetic activity,
6
• Heat stroke, serotonin syndrome, neuroleptic malignant syn- inducing shivering, and impairing heat loss. Typically patients with
drome, and malignant hyperthermia are life-threatening causes of fever experience chills until the core body temperature rises to the new
hyperpyrexia that must be immediately recognized and treated in set point.
Body temperature can be measured by several different methods
order to avoid multisystem organ failure and death. and at many different sites. The most common clinically used sites are
• Although fever is associated with adverse outcomes in the ICU, the mouth, axilla, rectum, skin, tympanic membrane, bladder, central
there is no conclusive evidence to support the routine treatment of veins, and pulmonary artery. Under normal circumstances, rectal
fever due to infection in non-brain-injured patients. temperature is approximately 0.5°C higher and axillary temperature
0.1°C lower than sublingual temperature. During critical illness the
2
variability between sites may increase. For example, during open
mouth breathing, sublingual temperature falls relative to tympanic
INTRODUCTION membrane temperature. Likewise, skin temperature can fall relative to
7
1
Fever is a ubiquitous phenomenon in the intensive care unit. core temperature during cardiogenic shock due to a decrease in cuta-
Although fever is a natural response to illness and injury, the occur- neous blood flow. Because of this variability, mouth, skin, and axillary
8
rence of an elevated temperature in a critically ill patient frequently measurements are not recommended for use in critically ill patients.
initiates both a gamut of unfocused diagnostic testing and multiple Often a rectal probe is recommended because it provides accurate and
intravenous infusions of broad-spectrum antibiotics, often without a minimally invasive measurements of core temperature; however, some
critical appraisal of the unique issues of the individual patient. This have suggested that rectal thermometers pose a risk of bacteremia in
9
“one-size-fits-all” approach may not only add unnecessary costs, man- neutropenic patients. Central venous thermistor measurements have
power, and interventions to patient care but may also expose patients long been the gold standard for core temperature measurement, but
to unnecessary risks. However, in selected patients, clinical pathways with the decline in the use of thermodilution pulmonary artery cath-
have the potential both to reduce costs and to improve the appropri- eters, this method is now rarely used. Whatever the chosen method
ateness of treatment, the latter of which may then lead to improved and the chosen site of measurement, both should be documented and
survival. A thorough understanding of the common etiologies of used consistently.
fever is critical to customizing the care of individual patients. In this
chapter, we will review the physiology of temperature regulation, how EPIDEMIOLOGY AND IMPACT OF FEVER
to best measure temperature in the ICU, the epidemiology and the
clinical impact of fever, the differential diagnosis of elevated body Very often fever is the first and only sign of a serious underlying
temperature, common infectious and noninfectious causes of fever, infection while at other times it may simply represent a normal stress
and general guidelines to evaluation and management in hopes to response to critical illness. A consensus task force from the American
provide the reader with a rational approach to the febrile patient in College of Critical Care Medicine and the Infectious Diseases Society
the intensive care unit. of America has defined fever as a single oral temperature of >38.3°C

Fever: from bug to body

O
O OH
HO OH
Bacteria Leukocytes Pyrogenic Hypothalamus PGE 2 Physiologic changes
cytokines (ie, shivering)
(eg, TNF- , that retain heat,
Il-1, IFN-g) leading to a rise
in core body temp
FIGURE 63-1. Schematic of fever pathway.

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