Intraoperative temperature regulation in children using a liquid-warming garment

Abstract

Purpose

Children undergoing operative intervention while induced under general anesthesia are at risk for experiencing a significant decrease in core body temperature that can lead to adverse systemic effects. Given that the head contributes an estimated 18% of a child’s body surface area, we theorized that a liquid-warming garment applied to the head could control a pediatric patient’s core body temperature during surgical procedures.

Methods

Patients undergoing elective, non-cranial, general surgical procedures were enrolled in the study. A head garment with an embedded network of tubing was placed on the patient. The garment connected to a computer-controlled water bath that managed the temperature of the water in the tubing through a feedback mechanism.

Results

Ten patients with ages ranging from 1 day to 3 years (mean age 10.5 months) were enrolled in this study. The average procedure length was 82.5 min. The mean core body temperature throughout the procedure for all-comers was 36.5 ± 0.9 °C with an overall mean difference in maximum and minimum temperatures of 1.32 ± 1.1 °C.

Conclusion

A liquid-warming garment applied to the head of pediatric surgical patients is an innovative and relatively low-cost means to regulate and to maintain the ideal core body temperature of patients undergoing surgical procedures.

Introduction

Close monitoring and regulation of a patient’s body temperature are key components of proper care during operative intervention under general anesthesia. Of particular concern is a decrease in core body temperature or hypothermia. This state has adverse implications for almost every organ system [1], Notably, for the surgical patient, hypothermia leads to coagulopathy due to decreasing the activity of the enzymes of the coagulation cascade as well as inducing platelet dysfunction [1,2], Therein, hypothermia is also part of the lethal triad of shock and trauma along with acidosis and coagulopathy.

Adequate intraoperative thermoregulation becomes even more of an imperative in the pediatric population in whom mature mechanisms of independent temperature modulation based on ATP production have not been fully established [1, 3]. This is particularly true for neonates due to limited hair, minimal adipose deposition, greater insensible losses through immature skin, and high total body surface area (TBSA) to body mass [2, 3]. In addition, nonshivering thermogenesis—a key means of heat production in neonates—increases metabolism and oxygen consumption. Similarly, neonates also lack sufficient cooling mechanisms, such as sweating, which makes hyperthermia a risk.

Background

Initially, multi-disciplinary researchers at our institution developed a physiologically based liquid cooling/warming garment (LCWG) for the National Aeronautics and Space Administration (NASA) based on the most efficient body areas for heat transfer [4, 5]. This LCWG relies on conductive heat exchange to control body temperature. The warming garment developed for the present study is an offshoot off this research. Given the importance of temperature control in our pediatric population, our interest was piqued to evaluate the use of this technology for our patients as well. It is known that warming 10–20% of body surface area can maintain the core body temperature in adults who were not under general anesthesia [4], As the head contributes an estimated 18% of a child’s TBSA, we theorized that an LCWG applied to the head could adequately control a pediatric patient’s core body temperature during surgical procedures.

Methods

The Institutional Review Board of the University of Minnesota granted approval for this prospective case series. Through convenience sampling, we enrolled ten pediatric patients undergoing elective, non-cranial, general surgical procedures at the University of Minnesota Masonic Medical Center in the years 2004–2006. Informed consent was obtained from the guardians of all individual participants included in the study. Information regarding the patient age, patient gender, procedure, and operating surgeon was documented.

The LCWG utilized for the study was a form-fitting head garment, which resembled a child’s winter hat (Fig. 1). It had an embedded network of tubing; the internal diameter of the tubing was 4 mm. The garment connected to a computer-controlled water bath that managed the temperature of the water in the tubing. The garment was warmed to a maximum of 45 °C with a feedback mechanism that would respond appropriately to keep the core body temperature to 37 °C.

Fig. 1.

LCWG used for the study. Photograph used with permission of the guardian

The LCWG was placed on the patient’s head upon arrival to the operating room and removed at the conclusion of the case. Core body temperature was monitored using an esophageal and/or rectal thermometer in addition to the monitoring of at least one peripheral site, such as the axilla or the forehead. The baseline temperatures of the patient and the water bath were recorded followed by the notation of the temperatures every 5 min. The length of the procedure was also documented. After data compilation was complete, trends were analyzed with descriptive statistics of the continuous, interval data, including minimum, maximum, and mean core body temperatures for each patient. Special attention was given to the difference between the maximum and minimum temperatures for each patient as this helped to evaluate the precision of the LCWG.

Results

Ten patients were enrolled from September 2004 to November 2006 (Table 1). Their ages ranged from 1 day to 3 years (mean age 10.5 months). 80% of the procedures (n = 8) were abdominal/pelvic, and the remaining 20% were thoracic. The average procedure length was 82.5 min with a range of 25–180 min. The ratio of male-to-female patients was 1:1.

Table 1.

Characteristics and results for patients using the LCWG

Patient	Sex	Age	Procedure	Procedure lengtha	Mean temperatureb	Maximum temperatureb	Minimum temperatureb	Difference (max-min)c
1	Female	2 months	Laparoscopic soave	180	34.5	36.0	32.0	4.0
2	Female	2 weeks	Posterior sagittal anorectoplasty	105	36.6	36.8	36.3	0.5
3	Female	9 months	Ileostomy takedown	100	36.3	37.4	35.6	1.8
4	Female	31 months	Peritoneal dialysis catheter insertion	30	37.0	37.3	36.8	0.5
5	Male	15 months	Ostomy creation	75	36.7	37.0	36.4	0.6
6	Male	1 day	Repair of diaphragmatic hernia	110	38.0	38.4	37.3	1.1
7	Male	5 months	Plication of left diaphragm, gastrostomy tube placement	130	37.0	37.8	36.4	1.4
8	Male	2 months	Inguinal hernia repair, circumcision	45	36.4	36.6	36.3	0.3
9	Male	1 month	Inguinal hernia repair	25	36.0	36.3	35.4	0.9
10	Female	40 months	Umbilical hernia repair	25	36.0	36.5	34.4	2.1
Mean				82.5	36.5	37.0	35.7	1.32

The first procedure listed for each patient was considered the primary procedure

^aProcedure length is reported in minutes

^bTemperatures are reported as °C

^cThe difference between the maximum and minimum temperatures

The mean core body temperature throughout the procedure for all-comers was 36.5 ± 0.90 °C with a range of mean temperatures from 34.5 to 38.0 °C. The overall mean difference in maximum and minimum temperatures was 1.32 ± 1.1 °C (range 0.5–4.0 °C) (Fig. 2). Two patients had a temperature less than 36.0 °C at the beginning of the case; the baseline core temperature of one patient (patient 5) was not recorded, however, the first recorded temperature was 36.9 °C. Figure 3 displays the temperature trend for a representative patient.

Fig. 2.

Difference in maximum and minimum temperature for each patient

Fig. 3.

Trend of temperatures throughout the case for patient 7

The water bath was turned off due a persistently low temperature in one patient (patient 1). Treatment with a warming blanket was initiated with improvement in the patient’s temperature. In two patients (patients 3 and 10), it was noted that the LCWG was too small. Patient 10 was also documented to have a significant amount of hair on her head. There were no instances of any adverse events in this study, including any thermal injury to the scalp.

Discussion

There have been a number of innovative approaches to the regulation of temperature in the pediatric surgical patient, and many of these techniques have focused on head garments. A cotton head wrap lined with Mylar was tested in a pilot study of infants being rewarmed after cardiopulmonary bypass at Boston Children’s Hospital [6]. Slightly higher median temperatures upon departure from the operating room and upon arrival to the intensive care unit were noted compared to the control population, however, the differences were not statistically significant. Trevisanuto et al. found polyethylene caps provided comparable temperature control in preterm infants as a polyethylene occlusive skin wrap applied to the whole body except the head [7].

In the global arena, settings and countries with limited resources necessitate low cost yet effective interventions. A group from the University of Padua has proposed a protocol to study the use of woolen caps in addition to kangaroo mother care to sustain normothermia in low-birth-weight infants in low-resource settings [8]. A meta-analysis was conducted by Oatley et al. to assess the application of plastic coverings, such as plastic bags to the body of neonates immediately after birth as a means to reduce the incidence of hypothermia, mortality, and morbidity [9]. They reported a 21–58% reduction in the rate of hypothermia, however, there was no evidence of reduced morbidity and mortality.

Our design of a liquid-based garment was inspired by the work of other researchers within our institution who were developing similar garments for astronautical use [4, 5]. Their work focused primarily on the areas of the human body most efficient at facilitating heat transfer. In consideration of a pediatric population, it was a natural step to recognize the heads of children as an optimal site given the relatively large surface area represented by the pediatric head. Motta et al. studied the temperature of pediatric patients after cardiopulmonary bypass while using a warming garment based on circulating water that was placed essentially on all sites not involved in the operative field [10]. Compared to a control group, the study group utilizing the warming garment had higher temperatures during the post-operative period monitored by the study; the differences were statistically significant for the majority of the time.

Our experience with an LCWG placed on the head of our pediatric surgical patients was promising. Patient 1 was an outlier in that there was a 4.0 °C temperature difference between the minimum and maximum temperatures, and the device eventually was shut off. As this was our first studied patient, this result may be due to our relative inexperience with the device. If this patient is removed from analysis, the mean temperature difference for all-comers drops from 1.32 °C to 1.02 ± 0.63 °C. We did not experience adverse outcomes, such as thermal injuries or device malfunction.

There are limitations to this study. The sample size was small, and our initial results may not be reproducible. In addition, larger, randomized trials are warranted to establish superiority to existing therapies, such as forced air-warming devices.

There are multiple potential applications for an LCWG. It has proved beneficial in the pediatric post-cardiopulmonary bypass population as discussed above. Furthermore, although admittedly more complicated than plastic bags or wool caps, the technology is simple and has potential applications for settings with minimal resources. In addition, a treatment that has been evolving in the recent years is the use of therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy [2, 11], Although not completely elucidated yet, the early results suggest that therapeutic hypothermia can provide an element of neuroprotection for this population, and a LCWG could potentially be applied in this scenario as well.

In conclusion, a liquid cooling/warming garment applied to the head of pediatric surgical patients is an innovative and relatively low-cost means to regulate and to maintain the ideal core body temperature of patients undergoing surgical procedures.