Tympanic Membrane Temperature Research Articles

Infrared Thermometry of Newborn Infants

An infrared thermometer, the FirstTemp, was tested among newborn infants by comparing tympanic membrane temperature measurements in three operating modes, "Cal-tympanic," "Cal-surface," and "Cor-tympanic," with nearly simultaneous tympanic membrane, rectal, and axillary temperature measurements using other standard methods. The FirstTemp underestimated other measurements of body temperature in the "Cal-tympanic" mode and overestimated them in the "Cor-tympanic" mode. In the "Cal-surface" mode, the First-Temp readings were significantly lower than tympanic membrane temperatures measured with a thermistor probe and electronic thermometer (mean difference 0.2 degrees C) but not significantly different from rectal or axillary temperatures. According to these results, the FirstTemp can be used reliably in the "Cal-surface" mode but not in the "Cal-tympanic" or "Cor-tympanic" mode. Its speed and ease of operation offer significant advantages over traditional clinical methods of temperature measurement.

PROFOUND HYPOTHERMIA (<10°C) COMPARED TO DEEP HYPOTHERMIA (15°C) IMPROVES NEUROLOGIC OUTCOME IN DOGS AFTER 2 HOURS CIRCULATORY ARREST INDUCED TO ENABLE RESUSCITATIVE SURGERY

Deaths from uncontrollable hemorrhage might be prevented by arresting the circulation under protective hypothermia to allow resuscitative surgery to repair these injuries in a bloodless field. We have shown previously that in hemorrhagic shock, circulatory arrest of 60 minutes under deep hypothermia (tympanic membrane temperature, Ttm = 15 degrees C) was the maximum duration of arrest that allowed normal brain recovery. We hypothesize that profound cerebral hypothermia (Ttm less than 10 degrees C) could extend the duration of safe circulatory arrest. In pilot experiments, we found that the cardiopulmonary system did not tolerate arrest at a core (esophageal) temperature (Tes) of less than 10 degrees C. Twenty-two dogs underwent 30-minute hemorrhagic shock (mean arterial pressure 40 mm Hg), rapid cooling by cardiopulmonary bypass (CPB), blood washout to a hematocrit of less than 10%, and circulatory arrest of 2 hours. In deep hypothermia group 1 (n = 10), Ttm was maintained at 15 degrees C during arrest. In profound hypothermia group 2 (n = 12), during cooling with CPB, the head was immersed in ice water, which decreased Ttm to 4 degrees-7 degrees C. The Tes was 10 degrees C in all dogs during arrest. Reperfusion and rewarming were by CPB for 2 hours. Controlled ventilation was to 24 hours, intensive care to 72 hours. In the 20 dogs that followed protocol, best neurologic deficit scores (0% = normal, 100% = brain death) at 24-72 hours were 23% +/- 19% in group 1 and 12% +/- 8% in group 2 (p = 0.15). Overall performance categories and histologic damage scores were significantly better in group 2 (p = 0.04 and p less than 0.001, respectively). We conclude that profound cerebral hypothermia with CPB plus ice water immersion of the head can extend the brain's tolerance of therapeutic circulatory arrest beyond that achieved with deep hypothermia.

The Thermoregulatory Threshold in Infants and Children Anesthetized with Isoflurane and Caudal Bupivacaine

Hypothermia in anesthetized adults provokes centrally mediated, peripheral thermoregulatory vasoconstriction at threshold temperatures approximately 2.5 degrees C below normal. The weight dependence of thermoregulatory vasoconstriction was evaluated in 33 unpremedicated pediatric patients receiving isoflurane/oxygen anesthesia (end-tidal concentrations approximately 0.9%) and caudal anesthesia with bupivacaine. The patients were prospectively assigned to four weight groups (5-10 kg, 10-20 kg, 20-30 kg, and 30-50 kg). Central temperature was measured at the tympanic membrane, and average skin surface temperature was determined from four cutaneous sites; mean body temperature was calculated from central and average skin temperatures. Finger blood flow was determined using laser Doppler flowmetry and forearm-fingertip skin temperature gradients. Significant peripheral vasoconstriction was prospectively defined as a laser Doppler flow index 50% of the value recorded 10 min after induction of anesthesia. Thermoregulatory thresholds were defined as the tympanic membrane or mean body temperatures at which significant vasoconstriction occurred. Vasoconstriction occurred in 32 of the patients at temperatures ranging from 34.4 to 35.3 degrees C. Central and mean body threshold temperatures did not differ among the groups, and were similar to those observed previously in adults. There was a good correlation between laser Doppler flowmetry and forearm-fingertip skin temperature gradients in individual patients.

Thermoregulatory Vasoconstriction Decreases Cutaneous Heat Loss

To determine the extent to which thermoregulatory vasoconstriction decreases heat loss to the environment, we measured regional heat flux, average skin temperature, and tympanic membrane temperature before and after thermoregulatory vasoconstriction in five minimally clothed volunteers maintained in a 30.8 +/- 0.1 degrees C environment. Thermoregulatory vasoconstriction was induced by central venous infusion of cooled fluid. Peripheral cutaneous blood flow was evaluated with venous-occlusion volume plethysmography and skin-surface temperature gradients. Laser Doppler flowmetry was used to measure vasoconstriction in centrally located skin. This model mimics the common clinical situation in which patients in a warm environment are centrally cooled by administration of cold intravenous fluids or by lavage of internal cavities with cold fluids. Tympanic membrane temperature decreased 1.5 +/- 0.3 degrees C in the first 15 min after the cold fluid infusion was started and remained approximately 1 degrees C below control values during the rest of the study. Average skin-surface temperature decreased slowly to approximately 0.7 degrees C below control. Flow in capillaries of centrally distributed skin, determined with laser Doppler flowmetry, decreased only approximately 40%. Total heat flux, and flux from the arms and legs decreased approximately 25% (15.5 +/- 0.3 W). Heat loss from the trunk and head decreased only 17%, whereas, loss from the hands and feet (10.5% of the body surface area) decreased approximately 50%. All measured values decreased significantly following vasoconstriction (P less than 0.01). Therefore, thermoregulatory vasoconstriction in a thermoneutral environment appears to decrease cutaneous loss of metabolic heat approximately 25%.

Skin-Surface Warming

The authors determined the efficacy of four postoperative warming devices by measuring cutaneous and tympanic membrane temperatures, and heat loss/gain using 11 thermocouples and ten thermal flux transducers in five healthy, unanesthetized volunteers. Overall thermal comfort was evaluated at 5-10 min intervals using a 10-cm visual analog scale. The warming devices were: 1) a pair of 250-W infrared heating lamps mounted 71 cm above the abdomen; 2) the Thermal Ceiling MTC XI UL (500 W) set on "high" and mounted 56 cm above the volunteer; 3) a 54-by-145-cm circulating-water blanket set to 40 degrees C placed over the volunteer; and 4) the Bair Hugger forced air warmer with an adult-sized cover set on "low" (approximately 33 degrees C), "medium" (approximately 38 degrees C), and "high" (approximately 43 degrees C). Following a 10-min control period, each device was placed over the volunteer and activated for a 30-min period. All devices were started "cold" and warmed up during the study period. The Bair Hugger set on "medium" decreased heat loss more than each radiant warming device and as much as the circulating-water blanket. All methods reached maximum efficacy within 20 min. Set on "high," the Bair Hugger increased skin-surface temperature more than the circulating-water blanket. The Bair Hugger (all settings) and the water blanket raised skin temperature more than the radiant heaters. The circulating-water blanket was the most effective device for heating an optimally placed transducer on the chest (directly under and parallel to the radiant heat sources, and touching the water and Bair Hugger blankets).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative rewarming trial of gastric versus peritoneal lavage in a hypothermic model

A comparison of gastric lavage versus peritoneal lavage rewarming was studied in a hypothermic rabbit model. The gastric lavage group (n = 5) had a mean rewarming time of 136 ± 25.1 minutes versus the peritoneal lavage group (n = 6) mean rewarming time of 131.7 ± 27.9 minutes ( p = .795). Good correlation was found between tympanic membrane temperature readings and both rectal temperature readings ( r = .69) in gastric lavage group and esophageal temperature readings ( r = .90) in the peritoneal lavage group. Gastric lavage and peritoneal lavage have the same rewarming rates in the present hypothermic model.

Shivering during Epidural Anesthesia

The authors tested the hypothesis that during epidural anesthesia: 1) shivering-like tremor is primarily normal thermoregulatory shivering; 2) hypothermia does not produce a subjective sensation of cold; and 3) injectate temperature does not influence tremor intensity. An epidural catheter was inserted into ten healthy, nonpregnant volunteers randomly assigned to skin-surface warming below the T10 dermatome (warmed group) or no extra warming (unwarmed group). Each volunteer was given two 30-ml epidural injections of 1% lidocaine (16.0 +/- 4.7 degrees C and 40.6 +/- 0.7 degrees C at the catheter tip), in random order separated by at least 3 h. Skin-temperature gradients (forearm-fingertip) and tympanic membrane and average skin temperatures were recorded; significant vasoconstriction was prospectively defined as a gradient greater than or equal to 4 degrees C. Integrated electromyographic (EMG) intensity was recorded from four upper-body muscles. Overall thermal comfort was evaluated using a visual analog scale. Tympanic membrane temperatures decreased significantly in the unwarmed group (n = 6). Tremor occurred following ten of 12 injections in unwarmed volunteers, but only following one of eight injections in the warmed group. Integrated EMG intensity did not differ significantly following epidural injection of warm and cold lidocaine: tremor started when tympanic membrane temperature decreased about 0.5 degrees C and continued until central temperature returned to within 0.5 degrees C of control. Tremor always was preceded by hypothermia and vasoconstriction in the arms. Thermal comfort increased in both groups after epidural injection, with maximal comfort occurring at the lowest tympanic temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of an Infrared Tympanic Membrane Thermometer in Pediatric Patients

Body temperature measurement provides important information for evaluation of pediatric patients. Because of the role that central nervous system thermoreceptors play in temperature homeostasis, accurate measurement at core body sites has long been sought.1 Rectal temperature, often considered the "gold standard" for clinical use, does not correlate well with deep measurements.2,3 Pulmonary artery catheters and deep rectal probes measure core temperature accurately4 but are not practical for clinical use. The tympanic membrane shares the same vascular supply that perfuses the hypothalamus and is an excellent, readily accessible site for core temperature measurement.1 Although indwelling contact-type tympanic membrane temperature probes provide accurate data, patient discomfort and complications such as perforation have restricted their use.4,5

EVALUATION OF A TYMPANIC MEMBRANE THERMOMETER IN AN OUTPATIENT CLINICAL SETTING

Temperature measurement is one of the most commonly performed medical procedures. A study was conducted to evaluate the correlation between temperature measurements obtained by glass-mercury and infrared tympanic membrane thermometers. One hundred two patients completed the study, and the mean difference between the two methods of temperature measurement was -0.311 +/- 0.691 C (95% confidence interval, +1.071 to -1.693 C). The relationship between the two devices as calculated by linear regression analysis is tympanic membrane temperature = 0.74 x oral/rectal temperature + 10.2 (r = .763). In view of the poor correlation found in our study, we cannot recommend automatic substitution of the glass-mercury thermometer with an infrared tympanic membrane device.

Evaluation of a tympanic membrane thermometer in an outpatient clinical setting.

Temperature measurement is one of the most commonly performed medical procedures. A study was conducted to evaluate the correlation between temperature measurements obtained by glass-mercury and infrared tympanic membrane thermometers. One hundred two patients completed the study, and the mean difference between the two methods of temperature measurement was -0.311 +/- 0.691 C (95% confidence interval, +1.071 to -1.693 C). The relationship between the two devices as calculated by linear regression analysis is tympanic membrane temperature = 0.74 x oral/rectal temperature + 10.2 (r = .763). In view of the poor correlation found in our study, we cannot recommend automatic substitution of the glass-mercury thermometer with an infrared tympanic membrane device.

Intraoperative Temperature Monitoring Sites in Infants and Children and the Effect of Inspired Gas Warming on Esophageal Temperature

This study tested the hypotheses that 1) temperatures of "central" sites are similar in infants and children undergoing noncardiac surgery and 2) airway heating and humidification increases distal esophageal temperature. Twenty children were randomly assigned to receive 1) active airway humidification using an airway heater and humidifier set at 37 degrees C (N = 8), 2) passive airway humidification using a heat and moisture exchanger (N = 6), or 3) no airway humidification and/or heating (control, N = 6). There were no statistically significant differences between tympanic membrane, esophageal, rectal, and axillary temperatures. The temperatures of the peripheral skin surface (forearm and fingertip) were significantly lower than tympanic membrane temperature and significantly different from each other. Although esophageal and tympanic membrane temperatures in the entire group were similar, esophageal temperatures in patients receiving active and passive airway humidification were about 0.35 degrees C above tympanic temperatures after induction of anesthesia. In contrast, esophageal temperatures in patients without airway humidification were 0.25 degrees C below tympanic temperatures after induction of anesthesia. Esophageal-tympanic membrane temperature differences in the patients given active and passive humidification differed significantly from the corresponding sum in the control group at all times, but not from each other.

Effect of respiratory rate, respiratory depth, and open versus closed mouth breathing on sublingual temperature

The effect of open mouth breathing, tachypnea, and hyperpnea, either alone or in combination, on sublingual and tympanic membrane temperature in healthy adults was investigated. Seventy-eight subjects maintained randomly assigned breathing patterns for 15 minutes. Temperatures were monitored immediately prior to and for 5 minutes following the breathing protocol. The only statistically significant finding (p less than .01) was a lower sublingual temperature with open mouth breathing. No significant changes in tympanic membrane temperature were seen.

Natural cooling of the brain during outdoor bicycling?

Tympanic membrane temperature (Ttymp) and deep esophageal temperature (Tes) were measured in 8 subjects during normal outdoor bicycling. Metabolic rate (VO2) was determined by the Douglas bag method. Heart rate was sampled continuously. Skin surface temperatures were measured at the forehead, chest and shoulder, and core temperatures in the deep esophagus and at the tympanic membrane using a radio telemetry system. For each outdoor experiment an indoor experiment in a climatic chamber, adjusted to the same air temperature but in still air, was performed. The subjects exercised at the same VO2 as in the outdoor trial on a stationary bicycle ergometer. Measurements were taken with the same equipment as in the outdoor experiments. O2-consumption (l.min-1) and heart rates (beats.min-1) were similar during outdoor and indoor bicycling, averaging 2.38 +/- 0.018 (SE) and 2.26 +/- 0.07, 141 +/- 7 and 147 +/- 8, respectively. During steady state Tes was the same during outdoor and indoor bicycling (37.95 degrees C), while Ttymp was significantly lower during outdoor bicycling. delta (Tes-Ttymp) was 1.25 degrees C during outdoor and 0.5 degrees C during indoor exercise. It is concluded that, if tympanic temperature is lowered by counter-current cooling of its arterial supply, then cooling of the brain may also take place in humans during physical activity under normal outdoor conditions with convective air movements. But the magnitude of a possible brain cooling cannot be deduced from the fall in tympanic temperature.

EFFECTS OF HYPOTHERMIA ON SOMATOSENSORY EVOKED RESPONSES IN MAN

Somatosensory evoked responses after median nerve stimulation were recorded in 21 patients during hypothermic cardiopulmonary bypass. During hypothermia a significant linear correlation (P less than 0.001) was found between evoked potential latency and temperature. Correlation was best for tympanic membrane temperature during cooling and for perfusate temperature (arterial, venous) during rewarming. The increase in latency was more pronounced for middle latency components (N2, N3) and for the early cortical N1 than for the cervical N0 and central conduction time. In all patients N1 was detectable at 26 degrees C, with slightly reduced amplitude. In the rewarming period the changes occurred in the reverse order and pre-bypass values were achieved at normothermia. The slopes of the regression lines were different during cooling and rewarming, when latencies were related to patient (tympanic, nasopharyngeal, rectal) temperature, but identical when arterial or venous blood temperature was used as the reference. No correlation was found between latency and perfusion pressure. We conclude that sophisticated temperature measurement is required to aid the interpretation of evoked responses used during hypothermia.

Die Wirkung von Isofluran und Enfluran auf somatosensorisch evozierte Potentiale nach Stimulation des Nervus medianus

The effects of enflurane and isoflurane on somatosensory evoked potentials (SEP) after median nerve stimulation were studied in 25 healthy adult patients. Cervical and cortical SEP were recorded simultaneously. pCO2 and tympanic membrane temperature were kept constant. Following induction of anaesthesia with thiopentone, fentanyl and succinylcholine SEP were recorded during normoventilation with 100% oxygen and after inhalation of 66.6% nitrous oxide. Isoflurane at inspired concentrations of 0.8, 1.65, 2.5, 3.3% was given to 10 patients at 15 minutes intervals and was reduced after nitrous oxide had been replaced by oxygen. 15 patients received equipotent doses of enflurane (1.1, 2.2, 3.25, 4.3%.) SEP were recorded at the end of each interval. Isoflurane and enflurane caused dose dependent increases in latency of the cortical SEP. This effect was more pronounced with enflurane. Isoflurane reduced amplitude of the primary cortical response more than enflurane, when ventilation was performed with 66.6% nitrous oxide in oxygen. High doses of enflurane in oxygen augmented cortical SEP amplitudes associated with a marked increase in latency. Isoflurance and enflurance anaesthesia slightly altered cervical SEP. Middle latency components of the cortical SEP were progressively diminished with increasing isoflurane or enflurane concentrations. The effect of both agents in terms of delayed latencies and reduced amplitudes should be considered when recordings are performed intraoperatively.

Spectral analysis of the EEG during hypothermic cardiopulmonary bypass.

In 39 patients undergoing aorto-coronary-bypass grafting, spectral analysis of the EEG (compressed spectral array: CSA) and calculation of spectral edge frequency (SEF) were performed. The effects of different temperatures and of perfusion pressure (PP) were analyzed. Predictable patterns were observed. During cooling on cardiopulmonary bypass (CPB), linear regression analysis revealed a close correlation between SEF and tympanic membrane (Tty) or nasopharyngeal temperature (Tnp). During rewarming, a nonlinear correlation between SEF and Tty or Tnp was found. Rectal temperature as well as blood temperature in the arterial or venous line of the oxygenator seemed to be less useful. The independence of SEF and PP was demonstrated during the whole procedure. At the onset of CPB, after correction of the aortic clamp for performance of the aortic anastomosis and after removal of the aortic clamp, bilateral EEG slowing of varying duration occurred in 20 patients. Comparison of mean SEF before and after CPB revealed a difference of about 5 Hz. In no patient were major neurological abnormalities observed postoperatively.

Effects of Drinking Water Temperature on Production Responses in Lactating Holstein Cows in Summer

During late summer, 24 lactating Holstein cows were offered 10 or 28°C (control) drinking water ad libitum at 1400h for 10min to investigate the effects on respiration rates, body temperatures, dry matter intake, and milk production. Experimental design was a 2×3 factorial arrangement of the two drinking water temperatures with .8, 1.1, and 1.4% dietary potassium associated with another experiment. Following 1 wk adjustment and 1 wk standardization, cows were blocked by dry matter intake as a percentage of body weight within parity and randomly assigned to treatments within blocks. Cows were denied access to water from 0900 until 1400h. Respiration rates and rectal temperatures were recorded before and after watering. Tympanic membrane temperatures (8/h) were recorded during the comparison period using 4 cows per water treatment. No interaction occurred between water and potassium. Water at 10°C had a greater cooling effect than 28°C water. No differences were found between treatments in respiration rates and rectal temperatures after drinking water was offered. Chilled drinking water decreased tympanic membrane temperatures, which remained lower longer. Cows that drank 10°C drinking water increased dry matter intake and milk yield.

Fall in deep body temperature by cold gas inhalation at hyperbaric helium-oxygen environments (16 and 31 bar)

Four male volunteers served as subjects for studies under hyperbaric helium-oxygen environments at 16 bar and 31 bar (simulated saturation dive). Tympanic membrane temperature, rectal temperature, ventilatory gas temperature, expiratory volume, respiratory frequency and cardiac frequency were measured during Cold Gas Inhalation (CGI : 20min) and recovery period (20min) in a warm hyperbaric chamber. Dyspnea and fall in deep body temperatures were evident during CGI (inspired gas temperature : 6°C at 31bar, 7°C at 16 bar). The change of tympanic membrane temperature during CGI and recovery period was more definite than rectal temperature. This phenomenon was induced by remarkable direct heat exchange between environment and body core, owing to high heat conductivity and high heat capacity of respiratory gas. Concerning safety and physiological functions of the deep sea diver and human exposed to hyperbaric helium-oxygen environment, not only rectal temperature monitoring is very important but also tympanic membrane temperature monitoring.

Effect of Heated Humidified Gases on Temperature Drop after Cardiopulmonary Bypass

In an attempt to prevent the decrease in nasopharyngeal temperature (NPT) ("afterdrop") after cardiac surgery, 30 patients undergoing hypothermic cardiopulmonary bypass (CPB) were randomly assigned to receive humidified heated inspired gases at 45 degrees C at the proximal end of the endotracheal tube (group I) or dry gases at room temperature (group II), from the time of termination of CPB. All patients received high flow rates on CPB during the rewarming period with the use of vasodilator drugs when necessary. Both groups were comparable with respect to total bypass time, rewarming time, and temperature at termination of CPB. In addition, the NPT was compared with the tympanic membrane temperature (TMT) in group I to assess the validity of the NPT under these conditions. The results indicate that heating and humidifying inspired gases do not prevent afterdrop and do not falsely increase the nasopharyngeal temperature. The reasons for the ineffectiveness of heated humidified gases may include a large heat deficit at termination of CPB despite a normal NPT, and the very small heat content of heated gases. Monitoring the temperature of a site that reflects the heat deficit, and a more complete rewarming during CPB are suggested as a better approach to the prevention of afterdrop.

Tympanic membrane temperature of term and preterm neonates

Deep body temperatures of 70 term and 24 preterm newborn infants were measured at two sites: deep rectum (5 cm beyond the anus) and tympanic membrane. A significant correlation was found between deep rectal and tympanic membrane temperatures in both term and preterm infants. Mean deep rectal and tympanic membrane temperatures in term infants were 37.01°C and 36.83°C, respectively. Mean deep rectal and tympanic membrane temperatures in preterm infants were both 36.69°C.