Assessment of the efficiency of warming devices during neonatal surgery

Introduction of a Warming Bundle to Reduce Hypothermia in Neonatal Surgical Patients

INTRODUCTION

Hypothermia in the neonatal surgical population has been linked with significant morbidity and mortality. Our goal was to decrease intra and postoperative hypothermia.

INTERVENTION

In November 2021, a radiant warmer and hat were included along with standard warming methods prior to the start of General Surgery procedures to minimize episodes of hypothermia.

PRIMARY OUTCOME

Core body temperature was measured pre, intra and post-operatively.

METHODS

Data were prospectively collected from electronic medical records from July 2021 to March 2023. A retrospective analysis was performed. Hypothermia was defined as a temperature <36.5C. Control charts were created to analyze the effect of interventions.

RESULTS

A total of 277 procedures were identified; 226 abdominal procedures, 31 thoracic, 14 skin/soft tissue and 6 anorectal. The median post-natal age was 36.1 weeks (IQR: 33.2-39.2), with a pre-surgical weight of 2.3 kg (IQR: 1.6-3.0) and operative duration of 181 min (IQR: 125-214). Hat and warmer data were unavailable for 59 procedures, both hat and warmer were used for 51 % procedures, hat alone for 29 %, warmer alone for 10 % and neither for 10 % of procedures. Over time there was a significant increase in hat utilization while warmer usage was unchanged. There was a significant increase in the mean lowest intra-operative temperature and decrease in proportion of hypothermic patients intra-operatively and post-operatively.

CONCLUSIONS

The inclusion of a radiant warmer and hat decreased the proportion of hypothermic patients during and after surgery. Further studies are necessary to analyze the impact on surgical outcomes.

LEVEL OF EVIDENCE

III.

Fetal and Neonatal Anesthesia

Anesthesia for fetal and neonatal surgery requires subspecialized knowledge and expertise. Attention to important anatomic, physiologic, and metabolic differences seen in pregnancy and at birth are essential for the optimal care of these patients. Thorough preoperative evaluations tailored intraoperative strategies and careful postoperative management are critical when devising the anesthetic approach for each of these cases.

Combination of warming blanket and prewarmed intravenous infusion is effective for rewarming in infants with postoperative hypothermia in China

BACKGROUND

Postoperative hypothermia in the postanesthesia care unit (PACU) in neonates and infants is a well-known serious complication as it can increase the risk of blood loss, wound infections, and cardiac arrhythmias.

AIM

To identify an effective rewarming method for neonates and infants in China with postoperative hypothermia, an open-label, randomized, and controlled study was performed to compare the effects of three different rewarming methods.

METHODS

Neonates and infants (<1 year) admitted to the PACU after surgery between June 2011 and November 2012 in a local hospital were investigated. Patients diagnosed with hypothermia were randomly divided into three groups and rewarmed with only blanket (blanket group), blanket plus electric blanket (heating blanket group), and blanket plus prewarmed intravenous (i.v.) infusion (warmed infusion group). From the beginning of rewarming, the rectal temperature was recorded every 10 min up to 180 min.

RESULTS

The incidence of postoperative hypothermia in neonates and infants was 5.9%. Patients rewarmed with warming blanket plus prewarmed i.v. infusions showed the shortest rewarming time (67.0 ± 2.6 min, P = 0.02) and highest rewarming efficiency (0.027 ± 0.0008°C·min(-1) , P = 0.039).

CONCLUSIONS

The combination of conventional blanket rewarming and prewarmed i.v. infusion was shown to be an effective rewarming method for hypothermic infants in China.

Peri-operative warming devices: performance and clinical application

Since the adverse consequences of accidental peri-operative hypothermia have been recognised, there has been a rapid expansion in the development of new warming equipment designed to prevent it. This is a review of peri-operative warming devices and a critique of the evidence assessing their performance. Forced-air warming is a common and extensively tested warming modality that outperforms passive insulation and water mattresses, and is at least as effective as resistive heating. More recently developed devices include circulating water garments, which have shown promising results due to their ability to cover large surface areas, and negative pressure devices aimed at improving subcutaneous perfusion for warming. We also discuss the challenge of fluid warming, looking particularly at how devices' performance varies according to flow rate. Our ultimate aim is to provide a guide through the bewildering array of devices on the market so that clinicians can make informed and accurate choices for their particular hospital environment.

Prevention of intraoperative hypothermia in neonates and infants: results of a prospective multicenter observational study with a new forced-air warming system with increased warm air flow

OBJECTIVES

Neonates and infants are at the highest risk of developing perioperative hypothermia. A number of methods to prevent hypothermia during pediatric anesthesia are in use, and despite the fact that conventional forced-air warmers are the most effective devices, they are not always sufficient enough to maintain body temperature. Therefore, recently a new forced-air warming system with an increased warm air flow was introduced to the market.

AIM

The aim of this study was to evaluate this new forced-air warming system in neonates and infants during pediatric anesthesia. We hypothesized that the new blanket alone is sufficient enough to prevent neonates and infants from intraoperative hypothermia.

METHODS

Neonates and infants (body weight <10 kg) were enrolled in this prospective multicenter observational study. After admission to the operating room, the children were placed on the new forced-air warming blanket. Body temperature was measured continuously until admission to the recovery room or pediatric intensive care unit (PICU).

RESULTS

Hundred and nineteen children with a median body weight of 4.1 kg (range: 0.7-9.8) were enrolled and received their intended treatment. Median body temperature at the induction of anesthesia was 36.5 °C (range: 35.3-38.2 °C) and increased with the length of the operation up to 37.8 °C (37.1-38.2 °C) after 180 min. Median body temperature after admission to the recovery room or PICU was 37.2 °C (36.0-38.6 °C) and remained significantly above baseline (P < 0.05).

CONCLUSIONS

The new forced-air warming system as a sole warming device is effective in preventing perioperative hypothermia during pediatric anesthesia in neonates and infants.

A simulation study of gel pillow heat conductance

PURPOSE

The gel-filled pillow is a device used to provide a soft surface to support and cradle an infant's head. Little is known about the thermal conductive properties of this device when used in an open crib. This simulation study evaluated the use of the Squishon 2 gel pillow in an open crib to determine the potential cooling effects on a mannequin infant.

SUBJECTS

This simulation study was conducted on a thermal mannequin.

DESIGN

A descriptive comparative repeated-measures design was employed.

METHODS

A thermal mannequin with the head placed on the gel pillow was used. The energy required to keep the mannequin head at 37 degrees C in 4 conditions was measured. The 4 conditions were as follows: (1) lying in an open crib on a standard mattress (baseline), (2) lying on the gel pillow with the disposable cover from the manufacturer, (3) the head wearing a cap and lying on the gel pillow, and (4) the head without the hat lying on the gel pillow with an insulated cover over the pillow.

MAIN OUTCOME MEASURES

Univariate analysis of variance (ANOVA) revealed significant differences in energy required to maintain the mannequin head at 37 degrees C among the 4 conditions (F3 = 283.23, P = .0001). The hat on head condition was found to decrease energy utilization by an average of 6.36 kcal/d when compared with the head on mattress condition (P = .0001). Extrapolation of energy to maintain mannequin head warmth into potential kilocalories utilized revealed that a potential increase in kilocalories needed to maintain thermoneutrality would be needed.

RESULTS

The most effective way of conserving heat was in the hat on the mannequin head while lying on a gel pillow condition. The use of a gel pillow without a hat or an insulated barrier caused an increase in energy requirements and kilocalorie usage in this mannequin model.

CONCLUSION

The results of this simulation study suggest that use of the gel pillow outside of a thermally controlled environment and in an open crib environment may increase energy use to maintain thermoneutrality. The Squishon 2 gel pillow conducts heat from the mannequin head and may increase kilocalories per day consumption in the preterm infant. Furthermore, the results of the study support previous findings that a hat helps conserve energy.

[Heat exchanges and thermoregulation in the neonate]

The newborn's energy expenditure is used in order of priority for: (i) basic metabolism; (ii) body temperature regulation and (iii) body growth. Thermal regulation is an important part of energy expenditure, especially for low birth-weight infants or preterm newborns. The heat exchanges with the environment are greater in the infant than in the adult, explaining the increased risk of body hypo- or hyperthermia. The newborn infant is a homeotherm, but over a long period of time, he cannot maintain the thermal processes. Further developments are expected to improve the infant's thermal environment, with assessment of the various heat exchange mechanisms by conduction, convection, radiation and evaporation. The quantification of the respective parts of these exchanges would improve nursing care through clinical procedures or equipment used to ensure the control of the optimal thermohygrometric conditions in incubators, especially when the likelihood of excessive body cooling is high. The present review focuses on the various body heat exchange mechanisms, the thermoregulation processes of the newborn, and their implications in clinical usage and limitations in the neonatal intensive care unit.

What determines the efficacy of forced-air warming systems? A manikin evaluation with upper body blankets

BACKGROUND

Forced-air warming has gained acceptance as an effective means to prevent perioperative hypothermia. However, little is known about the influence of air flow and air temperature at the nozzle and the influence of heat distribution in the blankets on the efficacy of these systems.

METHODS

We conducted a manikin study with heat flux transducers using five forced-air warming systems to determine the factors that are responsible for heat transfer from the blanket to the manikin.

RESULTS

There was no relation between air temperature at the nozzle of the power unit and the resulting heat transfer. There was also no relation between the air flow at the nozzle of the power unit and the resulting heat transfer. However, all blankets performed best at high air flows above 19 L/s. The heat exchange coefficient, the mean temperature gradient between the blanket and the manikin correlated positively with the resulting heat transfer and the difference between the minimal and maximal blanket temperature correlated negatively with the resulting heat transfer.

CONCLUSIONS

The efficacy of forced-air warming systems is primarily determined by the blanket. Modern power units provide sufficient heat energy to maximize the ability of the blanket to warm the patient. Optimizing blanket design by optimizing the mean temperature gradient between the blanket and the manikin (or any other surface) with a very homogeneous temperature distribution in the blanket will enable the manufacturers to develop better forced-air warming systems.

The safety and effectiveness of a modified convection heating system for children during anesthesia

BACKGROUND

Convection heating shows most promise in maintaining children's core temperatures under anesthesia. We have previously shown that a modified convection heating technique worked in a mannequin model and sought to establish its safety and effectiveness in a clinical study.

METHODS

Children were recruited who were having elective surgery under general anesthesia lasting >90 min. The children were anesthetized and maintained in a room temperature of 21 degrees C. Warming was performed by a 'Bair Hugger' attached to a heat dissipation box, producing turbulent air from multiple outlet holes on its face. A plastic sheet covered the child, was attached to the top of the box, tucked into the sides of the bed and left open at the head end. Temperatures at various sites (air, skin, and core) were continuously monitored using thermistors connected to a datalogger and laptop. Analysis was performed using Excel.

RESULTS

The study comprised 40 children ranging in age from 2 days to 12.5 years and weigh 2.5-73 kg. Operations were 'peripheral' (e.g. urethroplasty) lasting 90 min to major laparotomy lasting 590 min. Body surface area uncovered was 5-25%. Skin temperatures rose to a maximum of c. 40 degrees C. Core temperatures rose after a 12-min lag by 0.01-0.04 degrees C x min(-1). In children who became hyperthermic, cooling was readily achieved by turning the heating off and leaving the fan running.

CONCLUSIONS

The technique is safe and effective for children throughout the pediatric range. The practice of increasing room temperature above 21 degrees C for elective cases should be abandoned. Continuous monitoring of core temperature is necessary to prevent hyperthermia.