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BACKGROUND: Core temperature measurements are an important component of perioperative patient monitoring. It is fairly easy to obtain core temperature measurements invasively in anesthetized patients. However, such measurements are more difficult to obtain noninvasively in awake patients. Recently, a new version of a temporal artery thermometer for noninvasive core temperature measurements (TemporalScannerTM TAT-5000) was introduced with accuracy and precision advertised as being comparable to invasive core temperature measurements. In this study, we sought to determine if this new thermometer is an acceptable substitute for invasive bladder temperature measurement. METHODS: In 35 patients undergoing neurosurgical interventions and 35 patients in the neurosurgical intensive care unit, measurements from the temporal artery thermometer were compared with those from a bladder thermometer. Four measurements were obtained from each patient.
RESULTS: Overall 280 measurement pairs were obtained. The mean bias between the methods was 0.07°C ± 0.79°C; the limits of agreement were CONCLUSIONS: The results of this study do not support the use of temporal artery thermometry for perioperative core temperature monitoring; the temporal artery thermometer does not provide information that is an adequate substitute for core temperature measurement by a bladder thermometer.
Core temperature measurement is an important component of perioperative patient monitoring, as both core hypothermia (1–3) and core hyperthermia (4–8) have significant implications for the surgical patient. Accurate core temperature measurements can be obtained from several locations including the distal esophagus, rectum, bladder, and pulmonary artery, among others. Obtaining these core temperature measurements in the anesthetized and tracheally intubated patient is fairly easy, yet for unanesthetized patients, many core temperature measurement methods are either too invasive or simply not feasible. In the neurosurgical intensive care unit (ICU), patients are often unanesthetized to enable close neurological monitoring. Core temperature monitoring can also be difficult in patients with neuraxial anesthesia. However, these patients are as likely as patients with general anesthesia to become hypothermic, and so proper temperature monitoring is no less important (9). There is a similar need for a fast and accurate yet noninvasive core temperature monitoring system in pediatric care, where rectal thermometry is still considered the "gold standard" of temperature measurement. There are several noninvasive methods for core temperature measurements and they have proven to be of limited value: Axillary methods (10–13), aural canal infrared thermometers (14–17), and liquid crystal forehead thermometers (18) are not accurate enough for clinical purposes; both axillary and aural canal thermometers have a low sensitivity for detecting fever in comparison to standard core temperature measurement methods (16). Likewise, in pediatric patients, supralingual thermometry with pacifier thermometers cannot replace rectal thermometry (19). A new type of infrared temporal artery thermometer has recently been developed (TemporalScannerTM TAT-5000, Exergen, Boston, MA) with the goal of providing a more accurate noninvasive measure of core temperature. This new device records skin temperature on the area over the temporal artery at a rate up to 1000 measurements per second. The highest temperature is registered, and core temperature is calculated using a proprietary algorithm that compensates for ambient temperature. Previous versions of this thermometer have been tested in several, predominantly pediatric, studies. These studies have shown the temporal thermometer to be more accurate than aural infrared thermometers (20), and useful as a screening method for clinically important fever in children (21–23), yet it was not recommended for routine clinical use and deemed too inaccurate to replace standard invasive temperature measurements (19,22–24). However, the new version of the thermometer, TAT-5000, claims to be as accurate and precise as invasive core temperature thermometry because of improvements in the hardware and the user guidelines. We tested the TAT-5000 temporal artery thermometer in a neurosurgical patient population, which has a high risk for fever (25). Specifically, we compared the TAT-5000 temporal artery thermometer with a bladder thermometer (26) and assessed the sensitivity and specificity of the temporal artery thermometer for detecting hypothermia and fever. The goal of the study was to determine if the temporal artery thermometer agreed closely enough with bladder temperature measurements to be a useful substitute in the perioperative and the intensive care setting.
Written informed consent was obtained from all participating patients after the protocol was approved by the IRB of the Medical University of Vienna. We studied 35 patients scheduled for open cranial or spinal surgery during their procedures and 35 patients in the neurosurgical ICU. Patients studied during surgery were not studied again if admitted to the neurosurgical ICU. All patients were 18- to 80-yr old. Morphometric and demographic patient characteristics were initially recorded. Patients were managed according to the discretion of the responsible anesthesiologist. All temporal artery thermometer measurements were conducted by one experienced anesthesiologist trained to use the device. A bladder temperature sensor (accuracy ±0.2°C) incorporated into a urinary drainage catheter (Smiths-Medical, London, United Kingdom) (26,27) was inserted after arrival to the neurosurgical operating room (OR) or to the neurosurgical ICU, respectively. Temporal temperatures were recorded in the OR at four times: 1) at arrival in the OR; 2) 30 minutes after anesthetic induction; 3) at the end of surgery; and 4) 30 minutes after arrival in the postanesthesia care unit. In the neurosurgical ICU, temperature was recorded four times at 1-h intervals. From each OR- and ICU-patient, four measurements were acquired (280 measurements overall).
Temporal artery measurements were performed according to the TAT-5000 manual: The patients hair was brushed aside if necessary, and the probe was positioned on the center of the patients forehead. The measurement button was depressed, and the measurement was performed sliding from the center midline across the forehead to the hairline. With the button still depressed, the probe was lifted from the forehead and the region behind the earlobe was scanned, as recommended, to exclude falsely low temperature readings caused by evaporative cooling due to forehead sweating. Then, the button was released and the temperature recorded. The duration of this procedure was Thermal management in the neurosurgical OR consisted of forced air warming (Bair HuggerTM, Arizant, MN). In the neurosurgical ICU, treatment for fever was performed according to a routine protocol, which included the administration of metamizol and forced air cooling (PolarAirTM, Arizant, MN). Our primary outcome was the agreement in temperature reading between the established method (bladder temperature) and the temporal artery thermometer. Our secondary outcome was sensitivity and specificity for fever and hypothermia. Fever was defined as core temperature >37.8°C, and hypothermia was defined as core temperature <35.5°C. A priori the acceptable limits of agreement were chosen to be ±0.5°C. These limits can be considered clinically relevant, as a change of >0.5°C exceeds the usual temperature cycle variations in humans (28) and has been used in similar, previous studies (24,29).
Statistical Analysis Data were analyzed using MedCalc (MedCalc Corporation, Belgium) for Bland-Altman and ROC-curve analysis; for other analysis, SPSS (SPSS, Chicago, IL) was used.
Seventy patients were enrolled in the study: 35 in the neurosurgical OR and 35 in the neurosurgical ICU. All enrolled patients completed the study and four measurements were obtained from each patient. Demographic and morphometric variables, use of BairHuggerTM or PolarAirTM and diagnosis of fever or hypothermia are displayed in Table 1. Neurosurgical interventions included open cranial tumor surgery, aneurysm clipping surgery, and spinal surgery. Patients in the neurosurgical ICU were studied only if they consented before surgery. Overall 280 measurement pairs were obtained.
Method Comparison
Repeatability The TAT-5000 thermometers sensitivity for the detection of fever and for the detection of hypothermia is displayed in Table 3. The area under the ROC curve for detection of fever >37.8°C was 0.95 (95% CI: 0.92–0.98; Fig. 2); the area under the ROC curve for detection of hypothermia <35.5°C was 0.71 (95% CI: 0.66–0.77; Fig. 3).
This study demonstrates that the TAT-5000 temporal artery thermometer does not provide information that is an adequate substitute for core temperature measurement by a bladder thermometer. In an environment such as perioperative neurosurgical care, where precise temperature measurements are important, the temporal artery thermometer cannot be recommended. We defined a clinically acceptable bias of ±0.5°C, as this range is within the range of normal circadian body temperature variations (28,32) and is also consistent with the bias found when comparing different standard core temperature measurement sites (33,34). The limits of agreement between bladder and temporal artery thermometry were more than twice this clinically acceptable range (Table 2). Sensitivity for detecting low-grade fever was acceptable only for fever screening purposes (Table 3). Sensitivity for detecting hypothermia was very poor (Table 3). As inadvertent perioperative hypothermia is not uncommon and has been shown to be associated with numerous comorbidities (1–3), this result is of particular importance. In contrast to previous studies, forehead sweating had no significant influence on the performance of the temporal artery thermometer (24). This may have been due to the improved user guidelines mandating a measurement behind the earlobe, where there is less evaporative cooling. This is the first report comparing the new TAT-5000 temporal artery thermometer to bladder thermometry in a perioperative and intensive care setting. Several studies have evaluated consumer and professional models of temporal artery thermometers manufactured by Exergen, primarily in a pediatric setting. In these studies, the temporal artery thermometer was compared to standard core temperature measurement sites: bladder temperature, pulmonary artery temperature, rectal temperature, axillary temperature, and aural infrared temperature. The temporal artery thermometer proved to surpass axillary and aural infrared thermometers, and was found to be sufficiently accurate to serve as a screening method for high rectal fever in a pediatric population. All of the following studies tested previous versions of the TAT-5000: Suleman et al. (24) compared the temporal thermometer in a fairly small sample size with pulmonary artery catheters and bladder catheters; the performance of the thermometer was very poor and a sensitivity of 0% for fever was measured in adults. Greenes and Fleisher (20) found an adequate sensitivity for the temporal artery thermometer only for patients with high rectal fever and recommended it solely as a better alternative to the aural infrared thermometer. Schuh et al. (22) found the professional version of the medical-grade temporal artery thermometer to be an effective screening method, yet it was not able to replace rectal thermometry. In a recent study, Hebbar et al. (23) does not recommend the temporal artery thermometer as a replacement for invasive core temperature measurements, yet judges it to be more reliable and applicable than axillary temperature measurements. In accordance with these studies, we are not able to recommend the use of the new temporal artery thermometer as a substitute for standard core temperature measurements because of its inadequate agreement with bladder temperature, its poor performance for detecting mild hyper- and hypothermia, and its wide range of repeatability error. A limitation of our study is the use of bladder temperature to measure core temperature. It is not an undisputed core temperature measurement site, and pulmonary artery temperature measurements would certainly have been preferable, yet they were generally considered too invasive in our patients. The inaccuracies caused by this core temperature measurement site may have contributed somewhat to the study results. Furthermore, Greenes and Fleisher (35) found that rectal temperature measurements lag behind those measured at the temporal artery. It can therefore not be excluded that a similar temperature lag further contributed to a deterioration of our temporal artery thermometer results. Another limitation is that although four measurements were obtained in one patient, these measurements were treated as independent measurements. For method comparison, two subsequent temporal artery measurements were averaged; discrepancies between the thermometry methods might have been even greater if only a single temporal artery measurement had been performed. The range of bladder temperature in our patients was narrow. It included only a few patients with high fever or moderate-to-deep hypothermic temperatures. Thus, statements about the performance of the temporal artery thermometer under febrile conditions or during moderate or deep hypothermia are not possible. Finally, 74% of the study patients had some kind of cranial surgery. It is not known to what extent a surgical cranial intervention influences temporal artery flow and the temperature of the skin over the temporal artery. In conclusion, screening for fever and measurement of core temperature, when other more invasive measurement methods are not feasible, may be applications for the temporal artery thermometer. However, the new version of the temporal artery thermometer, Temporal Scanner TAT-5000, cannot replace more invasive temperature monitoring systems when highly reproducible core temperature measurements are required.
The authors thank Nancy Alsip, PhD, for editing this manuscript. Her salary is paid by the Outcomes Research Institute of the University of Louisville, Louisville, Kentucky.
Accepted for publication June 18, 2007. Presented, in part, at the Euroanesthesia-Congress, Vienna, 2005. None of the authors has a personal financial interest related to this work. Reprints will not be available from the author.
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