Regulation In Health Care and Temperature Balance
What is Thermal Balance,Thermal Regulation,Nursing Care and Thermal Assessment,Thermal Regulation Patterns,Temperature Measuring Issues In Nursing,Newer Researches For Clinical Aspects of Thermal Regulation.
What is Thermal Balance
Thermal balance is defined as a thermal “steady state” in which the
loss of body heat is equal to the heat gain. In health, this balance produces a
thermoneutral state, optimal for cellular function.
In humans, this state
averages about 37°C±.05 for internal temperatures and 33.5°C±.05 for skin.
Variations in body temperature respond to both homeostatic and circadian
influences.
Thermal Regulation
Circadian rhythm of core temperature is regulated by a remarkably
stable endogenous “clock” which has helped to make it the most widely used
circadian indicator. Hypothalamic thermoregulatory controls keep internal
temperatures fairly stable, despite environmental changes and the propensity of
heat to escape to cooler regions.
Metabolic and physical activity continually
generates heat, even as it is constantly lost to the cooler environment.
Current theory is that elaborate thermoregulatory control systems maintain
temperatures within the optimal set point range. Compensatory cooling or
warming mechanisms respond to deviations above or below this range.
Temperatures rising above this range evoke vasodilation and sweating, while
falling temperatures cause vasoconstriction, shivering, and increased metabolic
activity.Each physiological response increases or inhibits the transfer of heat
by affecting the thermodynamics of conduction, convection, radiation, and
evaporation.
Vasodilation warms the skin where heat is more easily lost to air,
contact surfaces, or liquids. Vasoconstriction creates a poorly perfused
insulative layer of tissue that conserves heat. In infants, cold exposure
causes metabolic breakdown of brown fat to generate heat. In older children and
adults, the primary means of heat generation is shivering.
Nursing Care and Thermal Assessment
Nurses have recognized the importance of assessing thermal balance
as a vital health indicator for as long as the profession has existed. Body
temperature provides an important vital sign of metabolic, neurological, and
infectious activity.
Circadian rhythms, monthly cycles, and daily body
temperature ranges are assurances of healthy variations. The pregnant mother
provides heat exchange both for herself and the fetus; therefore, high maternal
body temperatures, from fever, hyperthermia, or prolonged “hot tub” use, put
the unborn infant at risk for neurological damage.
Temperature elevations in
the acutely ill and injured may indicate either fever or hyperthermia. Each has
its own dynamics and treatment. Fevers are usually self limiting.
Thermoregulatory control is lost during hyperthermia and requires aggressive
cooling treatment.
Temperatures above 42”C can cause irreversible neural
cellular damage. Conductive cooling blankets, ice packs, and cooling fans are
used to lower core temperatures. In immunosuppression associated with cancer
treatment, fevers may indicate fulminating systemic infection. However, the
immunosuppressed HIV-infected patient may become febrile from high cytokine
levels, without obvious secondary infection.
In both groups, constant
assessment of other indicators is necessary to rule out infection. Situations
that promote heat loss or interfere with heat generations put patients at risk
for hypothermia. The neonatal nurse must be extremely sensitive to the
low-birthweight infant’s need for external heat source.
Unable to shiver, the
neonate expends oxygen to metabolize brown fat and can easily become hypoxic
from cold exposure. Declining metabolic and vasomotor activity makes elders
particularly susceptible to heat loss during surgery, trauma, or outdoor
exposure. Hypothermic states can destabilize thermoregulatory function further,
eventually leading to death.
Thermal Regulation Patterns
Fever patterns were used to detect the onset and progress of
infections since early times. It was recognized that high temperatures could
lead to brain damage, so nurses routinely cooled patients with fever or heat
stroke with ice packs, cooling sponge baths, or circulating fans.
In the 1970s,
nurses used conductive cooling blankets, with refrigerated circulating coolant,
to treat refractory hyperthermia. Sharp gradients between skin and core
temperatures stimulated vigorous and distressful shivering. Interventions to
prevent shivering were among the earliest to be tested by nurses.
Interest in
and awareness of temperature variations became more acute among nurse
researchers when advanced technology in thermometry was introduced to clinical
settings. In the 1970s, thermistor probes in hemodynamic monitoring systems
made pulmonary artery temperatures possible in some critical care settings. As
probes became available for bladder, tympanic membrane, and skin temperatures,
studies of gradients between body regions and measurement sites were common.
Variation in quality and precision of instruments made studies of reliability
and accuracy important. Recognition of malignant hyperthermia, a rare but
lethal genetically-linked disorder occurring when susceptible persons receive
anesthetic agents, led to closer surveillance of peri-operative body
temperature.
This precaution reduced mortality from hyperthermia in this
uncommon condition, but also brought to awareness the high incidence of low
body temperatures in most surgical patients.
Increased survival of preterm
infants in the 1970s created increased concern for thermal balance of
vulnerable infants. Studies of environmental influences, warming devices, and
skin-to-skin contact were made possible by sophisticated continuous skin
temperature monitors.
Temperature Measuring Issues In Nursing
Temperature measurement issues continue to dominate clinical
nursing research, stimulated by commercial development of new technology in
thermometers. There is an on-going program of research in body temperature
measurement by Erickson and colleagues (Erickson, RS, 1999; McKenzie &
Erickson, 1996), who have compared oral, skin, rectal, and tympanic membrane
measurement sites in children and adults.
Findings reassure nurses that oral
measurement provided reliable intermittent thermal assessment in afebrile
patients. While placement site and method of insertion yield statistically
significant differences, they are of less clinical importance.
Erickson’s work
was set apart from other contemporary studies by her appropriate statistical
treatment beyond simple correlations and by meaningful interpretation of device
reliability, accuracy, and linearity. In the past decade, nurse researchers
began drawing inferences from observed relationships between thermal changes
and other variables.
Gradients between skin and core temperatures initiate
thermoregulatory responses (see Shivering). Studies have shown the importance
of thermal gradients and rate of cooling in initiating shivering in a
comparison of cooling blanket temperatures (Caruso, Hadley, Shukla, Frame,
& Khoury, 1992; Sund-Levander & Wahren, 2000).
Nursing research has
also tested methods to alleviate adverse effects of warming and cooling in
patients of all ages. Particularly vulnerable are the preterm infant, the
elderly, and patients recovering from surgery, cardiopulmonary bypass, or
traumatic injury.
Anderson (Anderson, Chiu, et al., 2003) pioneered “kangaroo
care” as a method of maintaining thermal balance in preterm and term infants.
Drawn from perinatal practices of Western Europe, this method uses skin-to-skin
care for infants held against the skin under the mother or father’s clothing.
Self-demand breast-feeding and lactation were promoted by close constant maternal
contact. More recently, the relationships between the infant’s body temperature
and environment, circadian rhythm, and parental co-sleeping have been
investigated (Thomas & Burr, 2002).
Several studies have compared cooling
interventions in febrile adults with similar findings (Caruso et al., 1992;
Henker et al., 2001). Most concluded that antipyretic drugs are as effective as
cooling without inducing distressful shivering. In a controlled trial with
febrile patients with HIV disease, insulating skin against heat loss actually
kept peak febrile temperatures lower (Holtzclaw, 1998).
While numerous small
studies in nursing have tested various products that cool febrile patients or
restore heat loss in perioperative patients, they are often empirical in nature.
By contrast, the investigations mentioned above are theoretically based on
principles of thermodynamics and physiological responses. They seek to explain
mechanisms, predict consequences, and alleviate hazards of altered thermal
balance.
Newer Researches For Clinical Aspects of Thermal-Regulation
Some of the newer areas of research conducted by nurse scientists
related to thermal balance are studies using animal models to demonstrate
effects of exercise on thermoregulatory responses (Rowsey, Metzger, &
Gordon, 2001) and circadian influences on thermoregulation in obesity (Jarosz,
Lennie, Rowsey, & Metzger, 2001).
As more nurses enter fields of genetics,
immunology, and molecular biology, they will play important roles in seeking
origins and mechanism of thermoregulatory responses. New avenues for nursing
research in thermal balance emerge as new situations of vulnerability develop
and measurement techniques are advanced.
At particular risk is the rapidly
growing population of the frail elderly. Declining metabolic rate, lower
vasomotor sensitivity, and diminishing insulation from body fat make this group
vulnerable to extremes in heat or cold. The existence and treatment of
thermoregulatory failure in home bound patients is an area that nursing has not
yet systematically studied.
Improved survival of individuals with neurological,
vasomotor, and endocrine impairments and with extensive burns creates new
situations where thermal balance is altered. Only recently have nurses begun to
investigate relationships between the circadian city of body temperature and
the effectiveness of other therapies.
Study and intervention are needed in
addressing thermal balance, thermal perception, and thermal comfort during a
health alteration variety of life events and