Temperature monitoring and perioperative thermoregulation

Triage assessment in pediatric emergency departments: a national survey

OBJECTIVES

Because of the varying physiological and developmental stages in children, the taking of vital signs and other assessments at triage in an emergency department (ED) can be challenging. The purpose of this study was to examine current triage practices in pediatric EDs in the United States.

METHODS

A mailed survey was sent in August 2006 to the medical directors of the 99 pediatric EDs listed on the National Association of Children's Hospitals and Related Institutions Web site, with follow-up mailing in October 2006 and subsequent phone contact.

RESULTS

Eighty-eight surveys were returned (90% response rate). When asked what assessments are done on all patients at triage, all EDs (100%) obtain pulse rate and respiratory rate, 92% measure temperature, 60% measure blood pressure, 41% measure pulse oximetry, and 13% assess Glasgow Coma Scale. The methods used to measure temperature were widely variable. Multiple methods are used to assess pain: for those aged 0 to 2 years, 44% use a Wong FACES Scale and 48% use a behavioral scale; at 2 to 4 years, most (80%) use the Wong FACES Scale, but in older 10- to 18-year-old patients, most (81%) use a numerical scale. The use of standing orders at triage is variable.

CONCLUSIONS

Despite the important decisions made based on triage assessment in a pediatric ED, there is wide variability in the parameters assessed and the methodology used. Additional research should focus on the validity and reliability of each assessment to determine the best practices.

Non-invasive continuous cerebral temperature monitoring in patients treated with mild therapeutic hypothermia: an observational pilot study

AIM OF THE STUDY

To investigate if body temperature as measured with a prototype of a non-invasive continuous cerebral temperature sensor using the zero-heat-flow method to reflect the oesophageal temperature (core temperature) during mild therapeutic hypothermia after cardiac arrest.

METHODS

In patients over 18 years old with restoration of spontaneous circulation after cardiac arrest, a temperature sensor that uses the zero-heat-flow principle was placed on the forehead during the periods of cooling and re-warming. This temperature was compared to oesophageal temperature as the primary temperature-monitoring site. To assess agreement, we used the Bland-Altman approach and Lin's concordance correlation coefficient.

RESULTS

From September 2008 to April 2009, data from 19 patients were analysed. The median time from restoration of spontaneous circulation until temperature sensor application was 53min (interquartile range, 31; 96). All sensors were removed when a core temperature of 36 degrees C was reached. These measurements were in agreement with oesophageal temperature measurements. No allergic reaction, rash or other irritation occurred on the skin around or under the probes. Bland-Altman results showed a bias of -0.12 degrees C and 95% limits of agreement of -0.59 and +0.36 degrees C. Lin's concordance correlation coefficient was 0.98.

CONCLUSIONS

Body temperature measurements using a non-invasive continuous cerebral temperature sensor prototype that uses the zero-heat-flow method accurately reflected oesophageal temperature measurements during mild therapeutic hypothermia in patients with restoration of spontaneous circulation after cardiac arrest.

Forced-air warming: technology, physical background and practical aspects

PURPOSE OF REVIEW

There is an ever-increasing number of forced-air warming devices available in the market. However, there is also a paucity of studies that have investigated the physical background of these devices, making it difficult to find the most suitable ones.

RECENT FINDINGS

Heat flow produced by power units depends on the air temperature at the nozzle and the airflow. The heat transfer from the blanket to the body surface depends on the heat exchange coefficient, the temperature gradient between the blanket and the body surface and the area that is covered. Additionally, the homogeneity of heat distribution inside the blanket is very important. The lower the temperature difference between the highest and the lowest blanket temperature, the better the performance of the blanket.

SUMMARY

The efficacy of a forced-air warming system is mainly determined by the design of the blankets. A good forced-air warming blanket can easily be detected by measuring the temperature difference between the highest blanket temperature and the lowest blanket temperature. This temperature difference should be as low as possible. Because of the limited efficacy of forced-air warming systems to prevent hypothermia, patients must be prewarmed for 30-60 min even if a forced-air warming system is used during the operation. During the operation, the largest blanket that is possible for the operation should be used.

Resistive-heating or forced-air warming for the prevention of redistribution hypothermia

BACKGROUND

We evaluated the efficacy of resistive-heating or forced-air warming versus no prewarming, applied before induction of anesthesia for prevention of hypothermia.

METHODS

Twenty-seven patients scheduled for laparoscopic colorectal surgery were randomized into 1 of 3 groups: no prewarming; 30 minutes of prewarming with a carbon fiber total body cover at 42 degrees C; or 30 minutes of preoperative forced-air warming at 42 degrees C. The forced-air warming cover excluded the shoulders, ankles, and feet. The prewarming period was exactly 30 minutes. At the 31st minute, a total IV anesthesia technique was initiated, and all patients were actively warmed with a lithotomy blanket. Tympanic and distal esophageal temperatures were measured. Categorical data were analyzed using chi(2) test, and continuous data were analyzed with analysis of variance. P <0.05 was considered statistically significant.

RESULTS

The mean esophageal temperatures differed significantly between the control and the carbon fiber group from 40 to 90 minutes of anesthesia. After 50 minutes of anesthesia, the mean esophageal temperatures in the control, carbon fiber, and forced-air groups were 35.9 degrees C +/- 0.3 degrees C, 36.5 degrees C +/- 0.4 degrees C, and 36.2 degrees C +/- 0.3 degrees C, respectively. No statistically significant difference was found between the forced-air and control groups. After 30 minutes of prewarming with resistive heating, patients had an esophageal temperature that was significantly higher than the control group.

CONCLUSIONS

Prewarming should be considered part of the anesthetic management when patients are at risk for postoperative hypothermia.

Heat loss through the glabrous skin surfaces of heavily insulated, heat-stressed individuals

Insulation reduces heat exchange between a body and the environment. Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss. We have previously reported that cooling the glabrous skin surfaces is effective in alleviating heat stress and that the application of local subatmospheric pressure enhances the effect. In this paper, we compare the effects of cooling multiple glabrous skin surfaces with and without vacuum on thermal recovery in heavily insulated heat-stressed individuals. Esophageal temperatures (T(es)) and heart rates were monitored throughout the trials. Water loss was determined from pre- and post-trial nude weights. Treadmill exercise (5.6 km/h, 9-16% slope, and 25-45 min duration) in a hot environment (41.5 degrees C, 20-30% relative humidity) while wearing insulating pants and jackets was used to induce heat stress (T(es)>or=39 degrees C). For postexercise recovery, the subjects donned additional insulation (a balaclava, winter gloves, and impermeable boot covers) and rested in the hot environment for 60 min. Postexercise cooling treatments included control (no cooling) or the application of a 10 degrees C closed water circulating system to (a) the hand(s) with or without application of a local subatmospheric pressure, (b) the face, (c) the feet, or (d) multiple glabrous skin regions. Following exercise induction of heat stress in heavily insulated subjects, the rate of recovery of T(es) was 0.4+/-0.2 degrees C/h(n=12), but with application of cooling to one hand, the rate was 0.8+/-0.3 degrees C/h(n=12), and with one hand cooling with subatmospheric pressure, the rate was 1.0+/-0.2 degrees C/h(n=12). Cooling alone yielded two responses, one resembling that of cooling with subatmospheric pressure (n=8) and one resembling that of no cooling (n=4). The effect of treating multiple surfaces was additive (no cooling, DeltaT(es)=-0.4+/-0.2 degrees C; one hand, -0.9+/-0.3 degrees C; face, -1.0+/-0.3 degrees C; two hands, -1.3+/-0.1 degrees C; two feet, -1.3+/-0.3 degrees C; and face, feet, and hands, -1.6+/-0.2 degrees C). Cooling treatments had a similar effect on water loss and final resting heart rate. In heat-stressed resting subjects, cooling the glabrous skin regions was effective in lowering T(es). Under this protocol, the application of local subatmospheric pressure did not significantly increase heat transfer per se but, presumably, increased the likelihood of an effect.

Children with infantile neuronal ceroid lipofuscinosis have an increased risk of hypothermia and bradycardia during anesthesia

BACKGROUND

Neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive neurodegenerative diseases characterized by lysosomal accumulation of autofluorescent material in neurons and other cell types. The infantile NCL (INCL) subtype is rare (1 in >100,000 births), the most devastating of childhood subtypes, and is caused by mutations in the gene CLN1, which encodes palmitoyl-protein thioesterase-1.

METHODS

To investigate the incidence of hypothermia and bradycardia during general anesthesia in patients with INCL, we conducted a case-control study to examine the perianesthetic course of patients with INCL and of controls receiving anesthesia for diagnostic studies.

RESULTS

Eight children with INCL (mean age 25 mo [range, 10-32] at first anesthetic) and 25 controls (mean age 44 mo [range, 18-92]) underwent 62 anesthetics for nonsurgical procedures. Patients with INCL had neurologic deficits including developmental delay, myoclonus, and visual impairment. Patients with INCL had lower baseline temperature (36.4 +/- 0.1 vs 36.8 +/- 0.1, INCL versus controls, P < 0.007), and during anesthesia, despite active warming techniques, had significantly more hypothermia (18 vs 0 episodes, P < 0.001) and sinus bradycardia (10 vs 1, P < 0.001) compared with controls. INCL diagnosis was significantly associated with temperature decreases during anesthesia (P < 0.001), whereas age, sex, and duration of anesthesia were not (P = NS).

CONCLUSIONS

We report that patients with INCL have lower baseline body temperature and during general anesthesia, despite rewarming interventions, are at increased risk for hypothermia and bradycardia. This suggests a previously unknown INCL phenotype, impaired thermoregulation. Therefore, when anesthetizing these children, careful monitoring and routine use of warming interventions are warranted.

Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 February 2008 and 31 January 2009 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

A comparative evaluation of humidifier with heated wire breathing circuit under general anesthesia

BACKGROUND

Dry and cold anesthetic gas deteriorates patient's respiratory function and body heat balance. We examined whether a humidifier with heated wire circuit might maintain core temperature and humidity of inspired gas in patient undergoing general anesthesia.

METHODS

We enrolled forty ASA physical status I, II patients under general anesthesia for this study. We allocated the patients randomly into two groups with (experimental group) or without (control group) Humitube(R) anesthesia circuit, which delivered heated and humidified inspired anesthetic gases. We recorded the temperatures and humidity of the inspired gases throughout the surgery.

RESULTS

The temperatures and relative humidity of the inspired gases in experimental group were significantly greater compared to control group (36.2 +/- 0.9degrees C, 89.5 +/- 4.8% vs. 30.4 +/- 1.8degrees C, 37.9 +/- 5.9%, P < 0.05) during anesthesia. The core temperatures in experimental group were significantly greater compared to control group (36.1 +/- 0.3degrees C vs. 35.7 +/- 0.1degrees C, P < 0.05) during anesthesia.

CONCLUSIONS

A humidifier with heated wire system for anesthesia breathing circuit is helpful to maintain core temperature and adequate humidity.

Relative efficiency of two warming devices during laparoscopic cholecystectomy

Intraoperative hypothermia is a known consequence of general anaesthesia. Forced air warming devices are commonly used to prevent hypothermia in anaesthesia, but there are limited data on the use of radiant warming devices. Previous trials comparing the efficacy of forced air and radiant warming devices have reported discordant results. The current study evaluated the efficacy of these devices during elective laparoscopic cholecystectomy, where surgery was expected to last > 60 minutes. Twenty-nine patients were randomised to either a forced air warming device (Warm-touch; group 1, n = 15) or a radiant warming device applied to the face (Sun-touch; group 2, n = 14). All fluids were given via a standardised fluid warmer set at 41 degrees C. Oesophageal temperature was measured every 15 minutes until the end of the procedure. Between-group, over-time temperatures and interaction were analysed using a linear mixed model. Statistical significance was ascribed at P < or = 0.05. The median (range) time of surgery was 90 (60 to 180) minutes. Mean (SD) oesophageal temperatures in the Warm-touch and Sun-touch groups were at 15 minutes 36.2 (0.30) degrees C and 36.2 (0.57) degrees C, and at 90 minutes 36.2 (0.44) degrees C and 35.9 (0.29) degrees C respectively. There was no statistically significant temperature difference between groups (P = 0.69) or over time (P = 0.61), and no interaction between time and treatment group (P = 0.97). Postoperative headache was recorded in four Sun-touch and no Warm-touch patients (P = 0.04). No difference in the efficacy of the Sun-touch warming device compared with the Warm-touch was demonstrated. Operational-mode side-effects may limit the use of the Sun-touch device.