Temperature Monitoring (2) PDF

Tempreature monitoring(2) Dr/ asmaa salama Introduction Body temperature is Temperature is a maintained in a measure of the narrow range that average kinetic permits biochemical energy of a collection enzymatic reactions o...

Tempreature monitoring(2) Dr/ asmaa salama Introduction Body temperature is Temperature is a maintained in a measure of the narrow range that average kinetic permits biochemical energy of a collection enzymatic reactions of particles. necessary for homeostasis to occur. Body temperature actually fluctuates over the course of the day (with an early morning nadir and evening peak) and also varies based on age (lower in older individuals), gender (lower in males), activity level, and site at which it is measured. Mean rectal temperatures are typically in the range of 36.7 to 37.5◦C, and mean axillary temperatures are 35.5 to 37◦C. Heat gain can occur as a result of physiologic (e.g. exercise, shivering), pathologic (e.g. malignant hyperthermia, infection/inflammation), or iatrogenic (e.g. overwarming) processes. Heat is also transferred within the body owing to redistribution from the core to the periphery and surface that occurs with the loss of regulatory mechanisms (e.g. peripheral/cutaneous vasoconstriction) during anesthesia Heat loss from the body occurs in the typically cold operating room environment as a result of several mechanisms.  Radiation ……Heat energy is transferred from higher to lower temperature surfaces by infrared radiation when there is no direct contact between the surfaces,  Conduction……. when there is direct contact between the surfaces.  Convection ……..contributes to heat loss when cool air currents absorb heat energy as they pass.  Finally, evaporation …………..of moisture from skin surfaces and surgically exposed body cavities results in loss of heat energy. Thermometers Early methods of measuring oral or rectal temperature using mercury- or alcohol-filled glass thermometers They have fallen out of favor because of the risks of glass breakage toxic spillage, difficulty reading results slow response time. Thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the Seebeck effect, and this voltage can be interpreted to measure temperature. Thermocouples are widely used as temperature sensors. Thermistors a thermistor This resistance uses a can be semiconductor measured, and that varies in from that, the resistance temperature can based on its be calculated. temperature. Infrared sensors measure the amount of infrared heat energy emitted by an object by radiation, they do not need to be in direct contact with the object. usually designed to measure from either the forehead or the tympanic membrane. The accuracy of forehead infrared thermometers, however, has been shown to be poor in both adult and pediatric populations. Newer models, however, have shown increased accuracy and report temperatures close to that of pulmonary artery catheters. Therefore, use of infrared technology may become more prevalent. Infrared thermomet er Liquid crystal devices Thermotropic liquid crystals have been integrated into disposable plastic strips They typically have a useful range of 34 to 40◦C. The strips may be applied to the forehead when being used to measure core temperature, to the extremities during nerve blocks to monitor the temperature rise associated with a successful block, or to sites of vascular flaps to monitor blood flow indirectly. Monitoring sites Various internal and external body sites are available for temperature monitoring. The suitability of each site depends on the procedure being performed, the equipment available, and the relative need for accuracy Central core temperature Intermediate sites Surface temp Core/central sites Core temperature represents the temperature of highly perfused tissues (e.g. liver, kidneys, heart). Advantages  Generally, these sites (as well as the brain) are in equilibrium with one another, although regional differences may develop transiently or iatrogenically.  These sites are also less influenced by vasomotor thermoregulatory mechanisms (compared with peripheral sites)  and are the sites of most of the vital enzymatic reactions that require strict temperature control. The nasopharynx can be used as an indirect but accurate measure of brain and, under equilibrium conditions, core temperature. Optimal positioning requires placement of the probe past the nares and soft palate. Spontaneous breathing and gas leakage around airway devices may alter measurements at this site. Still, it is the most common site of temperature measurement during anesthesia, at least among European centers studied. The esophagus it is important to have the sensor placed in an optimal position because temperature variations of up to 6◦C have been reported. The coldest temperature occurs where the heart and breath sounds are best heard (presuming the use of a combined thermometer and esophageal stethoscope) and the warmest part is 12 to 16 cm past this point. Continuous gastric suctioning may also reduce measured temperatures at this site. In the absence of rapid infusions of cold fluids or an open thoracic cavity, lower esophageal temperature has been shown to closely approximate brain temperature. The tympanic membrane may be a useful site for central temperature measurement because of its proximity to the internal carotid artery. This location provides a measurement of brain temperature Similarly, it may be useful for cases using deliberate hypothermia for brain protection. pulmonary artery catheter Central temperature can also be measured in the by using a thermistor integrated into a thermodilution cardiac output pulmonary artery catheter. These measurements most accurately reflect core temperature in the absence of topical and systemic cooling during cardiopulmonary bypass. Pulmonary artery temperatures may also be lower than those measured in the nasopharynx and rectum after cardiopulmonary bypass discontinuation. Intermediate sites Intermediate temperature monitoring sites lag behind central temperature monitors in their response to temperature change. Oral (i.e. sublingual) temperatures are typically slightly (0.3◦C) below core temperature and may be further affected by breathing and eating or drinking. rectal temperatures, discrepancies with core temperature are the result of heat-producing bacteria in the rectum, stool insulation, and cooler lower extremity venous return. On the other hand, rectal sensors can be useful indicators of the temperature of poorly perfused tissues. Bladder temperature accuracy depends on the rate of urine flow. When urine flow is low, bladder temperature parallels rectal temperature. At high urine flow rates, bladder temperature agrees with pulmonary artery measurements Peripheral temperature monitoring sites Generally on the skin surface, are subject to numerous environmental and thermoregulatory influences. Although this reduces their accuracy as a monitor of core temperature, the less-invasive nature of monitoring at such sites make it useful in many settings. Skin surface temperatures are lower than core temperatures. The most commonly used skin sites are the forehead and the axilla. With forehead sensors, the difference is consistently 2◦C lower than core temperature measured, making it a reasonable estimate of core temperature after adjusting for this difference. Axillary temperatures are approximately between forehead and core values, and accuracy may be improved by optimal placement of the probe over the axillary artery with the patient’s arm adducted. Digital thermometer Digital sublingual thermometer A temperature probe is placed under the patient's tongue, with the lips closed around the instrument. The patient should not have recently smoked or consumed hot or cold substances. Digital thermometers are recommended over glass thermometers, as they have a disposable probe cover and give results in approximately 10 to 20 seconds, as opposed to 3 to 5 minutes for a glass probe. Digital rectal thermometer They are indicated in children and patients who cannot fully cooperate. A lubricated blunt-tipped thermometer should be inserted approximately 4 to 5 cm into the anal canal at a 20-degree angle from the horizontal, with the patient in a prone position. A rectal temperature reading is the preferred method in patients suspected of hypothermia. A rectal probe and a thermocouple are essential for measuring temperatures as low as 25 C (77 F). Complicati ons very rarely a source of significant complications. complications from placement of temperature probes (or similar instruments): tympanic membrane perforation, epistaxis, esophageal perforation, rectal perforation, and electrical burns. Preexisting pathology of any potential site should prompt consideration of an alternative site. These include esophageal abnormalities (e.g. hiatal hernia, esophageal diverticulum, varices), nasopharyngeal issues (e.g. sinusitis, bleeding diatheses with increased chance of epistaxis), rectal abnormalities, and ear abnormalities (e.g. otitis, tympanostomy). Fever Fever, or pyrexia, is the elevation of an individual's core body temperature above a 'set-point' regulated by the body's thermoregulatory center in the hypothalamus. This increase in the body's 'set-point' temperature is often due to a physiological process brought about by infectious causes or non- infectious causes such as inflammation, malignancy, or autoimmune processes. These processes involve the release of immunological mediators, which trigger the thermoregulatory center of the hypothalamus, leading to an increase in the body's core temperature.  The normal temperature of the human body is approximately 37 degrees Celsius (C), or 98.6 degrees Fahrenheit (F), and varies by about 0.5 C throughout the day. This variation results from normal physiological processes throughout the human body, including metabolic changes, sleep/wake cycles, hormone variability, and changing activity levels. However, in the case of a fever, the increase in the core body temperature is often greater than 0.5 C and is attributed to a fever-inducing substance (pyrogen) Classification Low-grade: 37.3 to 38.0 C (99.1 to 100.4 F) Moderate-grade: 38.1 to 39.0 C (100.6 to 102.2 F) High-grade: 39.1 to 41 C (102.4 to 105.8 F) Hyperthermia: Greater than 41 C (105.8 F) Hyperpyrexia is the term for exceptionally high fever (greater than 41 C), which can occur in patients with severe infections. Hyperpyrexia may also be seen in patients with CNS hemorrhages and is associated with a poor outcome Elevated brain temperature may lead to increased intracranial pressure, ischemic brain injury, exacerbation of cerebral edema, and death. Hyperthermia (Latin for “beyond-heat”), on the other hand, is a sudden and uncontrolled increase in body temperature (even above 41 °C [105.8F] ), due to a failure of the body’s thermoregulatory mechanism. In hyperthermia, the body is unable to lose enough heat to cope with increased production and maintain a normal temperature. Unlike fever, there is no involvement of the hypothalamus, and the hypothalamic set-point remains untouched. Hyperthermia, also known as heat-stroke, is extremely dangerous and is treated as a serious emergency. difference between fever and hyperthermia An important difference between fever and hyperthermia is that in the latter, the increase in temperature isn’t mediated by cytokines (cellular messengers). As a result, hyperthermias do not respond to anti-pyretic drugs, such as Aspirin or Acetaminophen, like fevers do. Heat Exhaustion Heat exhaustion is the most common form of heat- related illness. Patients with heat exhaustion experience flu-like symptoms that include hyperthermia (usually temp 41 oC severe neurologic dysfunction (e.g., delirium, coma, and seizures), severe volume depletion with hypotension, and multiorgan involvement that includes rhabdomyolysis, acute kidney injury, disseminated intravascular coagulopathy (DIC), and marked elevation in serum transaminases, presumably from liver. The inability to produce sweat (anhidrosis) is a typical, but not universal, feature of heat stroke (4).  There are two types of heat stroke: (a) classic heat stroke, which is related to environmental temperatures. (b) exertional heat stroke, which is related to strenuous exercise. Exertional heat stroke tends to be more severe, with a higher incidence of multiorgan dysfunction Management The management of heat stroke includes volume resuscitation and body cooling to reduce the body temperature to 38°C (100.4°F). Hypothermia is defined as a decrease in body temperature below 35°C (95°F), and can be the result of environmental forces (accidental hypo-thermia), a metabolic disorder (secondary hypothermia), or a therapeutic intervention (induced hypothermia).  The hypothalamus regulates body temperature through autonomic mechanisms. This region of the brain receives input from central and peripheral thermal receptors. Muscle tone and basal metabolic rate (BMR) increase initially in response to cold stress. Heat production can double through these mechanisms. Shivering also enhances heat production, increasing metabolism 2 to 5 times the baseline BMR