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

Effect of a Forced-Air Warming Blanket on Different Parts of the Body on Core Temperature of Patients Undergoing Elective Open Abdominal Surgery: A Randomized Controlled Single-Blind Trial

PURPOSE

This study aimed to determine the effect of a forced-air warming blanket placed on different body parts on the core temperature of patients undergoing elective open abdominal surgery.

DESIGN

Prospective, single-center, randomized, controlled, single-blind trial.

METHODS

A total of 537 patients who underwent open abdominal surgery were randomized into groups A, B, and C and provided with different forced-air warming blankets. Group A was given an upper body blanket, group B a lower body blanket, and group C an underbody blanket. The incidence of intraoperative hypothermia, the time maintaining the core temperature over 36 ℃ before hypothermia, the duration of hypothermia, the rewarming rate, and relevant complications were compared among three groups.

FINDINGS

Intraoperative hypothermia occurred in 51.4% of patients in group B, 37.6% of patients in group A, and 34.1% of patients in group C (P = .002). Maintaining the core temperature above 36 ℃ was longer before hypothermia in groups A and C (log-rank P = .006). In groups A and C, the duration of hypothermia was shorter, the rewarming rate was higher, and the incidence of shivering and postoperative nausea and vomiting were lower, compared to group B.

CONCLUSIONS

In patients undergoing elective open abdominal surgery, a forced-air warming blanket on the upper body part or underbody area decreased intraoperative hypothermia, prolonged the time to maintain the core temperature above 36 ℃ before hypothermia, and could better prevent further hypothermia when the core temperature had decreased below 36 ℃. In addition, it was significantly superior in reducing shivering and postoperative nausea and vomiting in the postanesthesia care unit.

Comparative Efficacy of Six Active Warming Systems for Intraoperative Warming in Adult Patients Undergoing Laparoscopic Surgery: A Systematic Review and Network Meta-Analysis

Intraoperative hypothermia is very common and harmful in adult patients undergoing laparoscopic surgery. A variety of active warming systems has received close attention and has been researched by related scholars. However, the relative efficacy of these systems and which active warming system is preferred for such patients remain unclear. The aim of this study was to compare and rank six active warming systems regarding intraoperative warming efficacy in adult patients undergoing laparoscopic surgery. Following the PRISMA 2020 guidelines, relevant randomized controlled trials (RCTs) on the efficacy of different active warming systems in warming adult patients undergoing laparoscopic surgery were searched from five English databases and three Chinese databases. The quality of the studies was assessed using the Cochrane Risk of Bias tool (RoB2). The outcome was the final intraoperative core temperature. We estimated direct effects by using pairwise meta-analysis, estimated relative effects and ranking with the consistency model to conduct an NetworkMeta-Analysis (NMA). We used GRADE (Grading of Recommendations Assessment, Development, and Evaluation) to assess the certainty of the evidence. Sensitivity analysis was performed to test the robustness of the results. This study is registered with PROSPERO, with number CRD42022309057. In total, 19 RCTs involving 6 active warming systems and comprising 1364 patients were included in this NMA. The NMA once again confirmed the validity of forced-air warming (FAW) systems compared with other active warming systems, and further showed that underbody FAW was associated with more remarkable warming efficacy in different types of FAW systems. NMA was used to perform an exhaustive comparison of the warming efficacy of six active warming systems and indicated that underbody FAW was most likely to be the most effective warming system in adult patients undergoing laparoscopic surgery; however, considering the sparsity of the network, our results should be cautiously interpreted. Furthermore, a large number of high-quality RCTs comparing the warming efficacy of different competitive active warming systems are needed.

Thermal suit connected to a forced-air warming unit for preventing intraoperative hypothermia: A randomised controlled trial

BACKGROUND

Inadvertent intraoperative hypothermia is a common occurrence in surgical patients. A thermal suit is an option for passive insulation. However, active warming is known to be more effective. Therefore, we hypothesised that a forced-air warming (FAW) unit connected to the thermal suit is superior to a commercial FAW blanket and a warming mattress in breast cancer surgery.

METHODS

Forty patients were randomised to this prospective, clinical trial to wear either the thermal suit or conventional hospital clothes under general anaesthesia. The Thermal suit group had a FAW unit set to 38°C and connected to the legs of the suit. The Hospital clothes group had a lower body blanket set to 38°C and a warming mattress set to 37°C. Core temperature was measured with zero-heat-flux sensor. The primary outcome was core temperature on admission to the recovery room.

RESULTS

There was no difference in mean core temperatures at anaesthetic induction (P = .4) or on admission to the recovery room (P = .07). One patient in the Thermal suit group (5%) vs six patients in the Hospital clothes group (32%) suffered from intraoperative hypothermia (P = .04, 95% CI 1.9%-49%). Mean skin temperatures (MSTs) were higher in the Thermal suit group during anaesthesia. No burns or skin irritations were reported. Two patients in the Thermal suit group sweated.

CONCLUSIONS

A thermal suit connected to a FAW unit was not superior to a commercial FAW blanket, although the incidence of intraoperative hypothermia was lower in patients treated with a thermal suit.

Randomised trial comparing forced-air warming to the upper or lower body to prevent hypothermia during thoracoscopic surgery in the lateral decubitus position

BACKGROUND

In the supine position, forced-air warming is more effective on the lower body than on the upper body to prevent intraoperative hypothermia. However, it is unknown in the lateral decubitus position. We thus compared forced-air warming on the upper and lower bodies in the lateral position.

METHODS

Patients (n=123) were randomised to receive forced-air warming on the upper body or lower body during thoracoscopic surgery in the lateral position. We measured the nasopharyngeal temperature at 0, 30, 60, 90, and 120 min after lateral positioning during surgery and the infrared tympanic membrane temperature at 0, 30, 60, 90, and 120 min after surgery. Patients received both upper and lower body warming at a temperature of <35.5°C. The primary outcome was the incidence of intraoperative hypothermia with a temperature of <36.0°C.

RESULTS

Intraoperative hypothermia was less frequent with the upper body warming than with the lower body warming {21/62 vs 35/61, risk ratio [95% confidence interval (CI)] 0.6 (0.4-0.9), P=0.011}. The intraoperative temperature was higher with the upper body warming than with the lower body warming at 30 (P=0.002), 60 (P<0.001), and 90 (P<0.001) min after lateral positioning, and the postoperative temperature was higher at 0 (P<0.001) and 30 (P=0.001) min after surgery. Fewer patients received both upper and lower body warming in the upper body warming group than in the lower body warming group during surgery (1 vs 7, P=0.032).

CONCLUSIONS

Forced-air warming was more effective on the upper body than on the lower body to prevent hypothermia during thoracoscopic surgery in the lateral decubitus position.

CLINICAL TRIAL REGISTRATION

NCT02993666.

Temperature management under general anesthesia: Compulsion or option

Administration of general anesthesia requires continuous monitoring of vital parameters of the body including body temperature. However, temperature continues to be one of the least seriously monitored parameters perioperatively. Inadvertent perioperative hypothermia is a relatively common occurrence with both general and regional anesthesia and can have significant adverse impact on patients' outcome. While guidelines for perioperative temperature management have been proposed, there are no specific guidelines regarding the best site or best modality of temperature monitoring and management intraoperatively. Various warming and cooling devices are available which help maintain perioperative normothermia. This article discusses the physiology of thermoregulation, effects of anesthesia on thermoregulation, various temperature monitoring sites and methods, perioperative warming devices, guidelines for perioperative temperature management and inadvertent temperature complications (hypothermia/hyperthermia) and measures to control it in the operating room.

Research: Testing of a Novel Portable Body Temperature Conditioner Using a Thermal Manikin

A battery-operated active cooling/heating device was developed to maintain thermoregulation of trauma victims in austere environments while awaiting evacuation to a hospital for further treatment. The use of a thermal manikin was adopted for this study in order to simulate load testing and evaluate the performance of this novel portable active cooling/heating device for both continuous (external power source) and battery power. The performance of the portable body temperature conditioner (PBTC) was evaluated through cooling/heating fraction tests to analyze the heat transfer between a thermal manikin and circulating water blanket to show consistent performance while operating under battery power. For the cooling/heating fraction tests, the ambient temperature was set to 15°C ± 1°C (heating) and 30°C ± 1°C (cooling). The PBTC water temperature was set to 37°C for the heating mode tests and 15°C for the cooling mode tests. The results showed consistent performance of the PBTC in terms of cooling/heating capacity while operating under both continuous and battery power. The PBTC functioned as intended and shows promise as a portable warming/cooling device for operation in the field.

Risk Factors for Postoperative Shivering After Oral and Maxillofacial Surgery

PURPOSE

Postoperative shivering is a frequent complication of anesthesia. However, there are few reports about postoperative shivering in oral and maxillofacial surgery. Postoperative shivering in patients after osteotomy was observed from April 2008 to September 2015. This retrospective study investigated the risk factors of postoperative shivering in oral and maxillofacial surgery.

PATIENTS AND METHODS

Anesthesia records of patients who underwent an osteotomy of the maxilla or mandible were checked. A patient's background (gender, age, height, and weight), anesthesia time, operative time, fentanyl, remifentanil, fluid volume, urine volume, blood loss volume, agent for anesthetic maintenance, rectal temperature at the end of surgery, and type of surgery were recorded in addition to the occurrence of postoperative shivering. In the univariate analysis, the Fisher exact test and the χ² test were used, and a multivariable analysis was performed using stepwise logistic regression to determine risk factors of postoperative shivering.

RESULTS

In this study, 233 cases were investigated, and 24 patients (11.5%) had postoperative shivering. The occurrence of postoperative shivering was correlated with blood loss volume (shivering group, 633.9 ± 404.8 mL; nonshivering group, 367.0 ± 312.6 mL; P < .01) and core temperature at the end of surgery (shivering group, 37.2 ± 0.6°C; nonshivering group, 37.5 ± 0.5°C; P < .01). Two variables were associated with postoperative shivering. Rectal temperature at the end of surgery was the highest risk factor (odds ratio = 2.560277; 95% confidence interval, 1.236774-5.327362), and blood loss volume was the next highest risk factor (odds ratio = 0.997733; 95% confidence interval, 0.999-0998).

CONCLUSION

Clinicians should pay attention to postoperative shivering not only in patients with hypothermia but also in patients with substantial blood loss.

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.

Hypothermia Prevention During Surgery: Comparison Between Thermal Mattress And Thermal Blanket


This study aimed to compare the efficiency of the thermal blanket and thermal mattress in the prevention of hypothermia during surgery. Thirty-eight randomized patients were divided into two groups (G1 – thermal blanket and G2 - thermal mattress). The variables studied were: length of surgery, length of stay in the post-anesthetic care unit, period without using the device after thermal induction, transport time from the operating room to post-anesthetic care unit, intraoperative fluid infusion, surgery size, anesthetic technique, age, body mass index, esophageal, axillary and operating room temperature. In G2, length of surgery and starch infusion longer was higher (both p=0.03), but no hypothermia occurred. During the surgical anesthetic procedure, the axillary temperature was higher at 120 minutes (p=0.04), and esophageal temperature was higher at 120 (p=0.002) and 180 minutes (p=0.03) and at the end of the procedure (p=0.002). The thermal mattress was more effective in preventing hypothermia during surgery.

Anaesthetic perioperative management of patients with pancreatic cancer

Pancreatic cancer remains a significant and unresolved therapeutic challenge. Currently, the only curative treatment for pancreatic cancer is surgical resection. Pancreatic surgery represents a technically demanding major abdominal procedure that can occasionally lead to a number of pathophysiological alterations resulting in increased morbidity and mortality. Systemic, rather than surgical complications, cause the majority of deaths. Because patients are increasingly referred to surgery with at advanced ages and because pancreatic surgery is extremely complex, anaesthesiologists and surgeons play a crucial role in preoperative evaluations and diagnoses for surgical intervention. The anaesthetist plays a key role in perioperative management and can significantly influence patient outcome. To optimise overall care, patients should be appropriately referred to tertiary centres, where multidisciplinary teams (surgical, medical, radiation oncologists, gastroenterologists, interventional radiologists and anaesthetists) work together and where close cooperation between surgeons and anaesthesiologists promotes the safe performance of major gastrointestinal surgeries with acceptable morbidity and mortality rates. In this review, we sought to provide simple daily recommendations to the clinicians who manage pancreatic surgery patients to make their work easier and suggest a joint approach between surgeons and anaesthesiologists in daily decision making.

Perioperative Temperature Monitoring and Patient Warming: A Survey Study

OBJECTIVE

Hypothermia is defined as the decrease of core body temperature under 36°C. Hypothermia is observed at a rate of 50-90% in the perioperative period. In our study, we aimed to measure the perception of hypothermia in our country, to evaluate the measures taken by physicians to intercept hypothermia, to determine the frequency and the methods used to monitor body temperature and the techniques used in warming the patients. Another aim was to develop a guideline for preventing perioperative hypothermia.

METHODS

The questionnaire consisted of 26 multiple-choice questions. The time needed to answer the questions was 8-10 minutes.

RESULTS

Of the 1380 individuals, 312 (22.6%) answered the questions in the questionnaire. Of these, 148 (47.4%) declared they were working in university hospitals, 80 (25.6%) in training and research hospitals, 51 (16.4%) in government hospitals and 33 (10.6%) in various private hospitals. Of the 312 individuals, 134 (42.9%) were specialists, 107 (34.3%) were resident physicians, 71 (22.8%) were academics. In addition, 212 (67.9%) reported working in operating rooms, 49 (15.7%) in intensive care units and 42 (13.5%) both in operating rooms and intensive care units. In the answers, there was variation among the hospital types in applications of body temperature monitoring and warming the patient. Another finding was that the individuals had different approaches to the concepts on perioperative hypothermia and its consequences.

CONCLUSION

The perceptions of physicians and the allied health personnel in government and private hospitals should be enhanced by informing them about the passive and active heating systems to prevent hypothermia. Although the situation in university and training and research hospitals seems to be better, defects are still observed in practice. Preparation of a national guideline for prevention of perioperative hypothermia is needed.

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.

Maintenance of core body temperature in anaesthetised pigeons (Columba livia domestica): a comparison of two thermal devices

Active thermal devices are used to prevent hypothermia during anaesthetic procedures. Two thermal devices, one conductive and one convective, were compared for their effect on maintenance of core body temperature (CBT) during 1h of general anaesthesia in pigeons (Columba livia domestica). In a randomised crossover trial, CBT decreased significantly less with the conductive device than when the convective device was used (2.5 ± 0.7°C and 3.8 ± 0.9°C, respectively; P<0.01). Moreover, CBT was maintained above a clinically acceptable level of 38.3°C in 82% of pigeons when the conductive device was selected, compared to 14% of pigeons with the convective device. The use of the conductive device is therefore recommended in preference to the convective device when performing anaesthetic procedures in birds.

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.