Comparison of two different temperature maintenance strategies during open abdominal surgery: upper body forced-air warming versus whole body water garment

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.

Prevention of Perioperative Hypothermia: A Prospective, Randomized, Controlled Trial of Bair Hugger Versus Inditherm in Patients Undergoing Elective Arthroscopic Shoulder Surgery

PURPOSE

To determine if a clinically significant difference in the core body temperature (CBT) exists between the Bair Hugger (BH) and Inditherm (IT) warming devices in patients undergoing arthroscopic shoulder surgery.

METHODS

This was a parallel, 2-treatment, prospective, randomized, controlled trial conducted in patients undergoing elective arthroscopic shoulder surgery in the beach-chair position using room-temperature irrigation fluid. The BH was used as the indicative forced-air warming device, whereas the IT served as the indicative resistive heating system. By use of a minimal clinically significant difference of 0.6°C and standard deviation of 0.6°C, a power analysis showed that a sample size of 90 patients (45 per group) would be required. Patients fulfilling the inclusion criteria were recruited from the clinics of the senior authors. Anesthetic and surgical protocols were standardized. The intraoperative CBT was recorded every 5 minutes using a nasopharyngeal thermistor probe. Demographic data as well as the volume of irrigation fluid used were also noted.

RESULTS

A steady decline in the CBT was observed in both groups up to 30 minutes after induction of anesthesia. Beyond 30 minutes, the BH group showed a gradual increase in temperature whereas it continued to decline in the IT group. A statistically significant difference in the CBT was observed from 60 minutes onward (P = .025). This difference continued to increase up to 90 minutes (P < .001). At no time was a rise in the CBT observed in the IT group. At completion of the study and surgical procedure, 13 of 47 patients in the BH group and 32 of 44 patients in the IT group had hypothermia (P = .0002).

CONCLUSIONS

The CBT was statistically significantly better with the use of the BH compared with the IT mattress. However, the differences in the CBT did not reach the level of clinical significance of 0.6°C. Far fewer patients in the BH group had hypothermia at the end of surgery. Therefore, this study supports the use of the BH in elective arthroscopic shoulder surgery for the prevention of hypothermia.

LEVEL OF EVIDENCE

Level I.

The influence of body mass index on temperature management during general anaesthesia-A prospective observational study

RATIONALE, AIMS, AND OBJECTIVES

During general anaesthesia, body core temperature is influenced by several factors that are either anaesthesia-related (type and duration of anaesthesia and fluid management), surgery-related (type of surgery and extent of the surgical procedure), or patient-related (age, gender, body weight, and preoperative body core temperature). Interestingly, data concerning body mass index (BMI) and its influence on patients' temperature are sparse. The aim of this study was to evaluate the impact of BMI on body core temperature under general anaesthesia.

METHODS

A single centre, prospective, observational study was conducted at a university hospital. Two cohorts (lower limb surgery and abdominal surgery) were evaluated. Patients were treated according to actual German guidelines for the prevention of hypothermia. Temperature was measured sublingually prior to anaesthesia and during the first 60 minutes of anaesthesia. Each cohort was divided in three subgroups (BMI < 24 kg m^-2 , BMI 25-34.9 kg m^-2 , and BMI > 35 kg m^-2 ) according to body weight.

RESULTS

A total of 206 patients were evaluated. One hundred four underwent lower limb surgery; 102 underwent abdominal surgery. After induction of anaesthesia, temperature dropped in all subgroups, but this decline was more pronounced in patients with lower BMI. Significant differences concerning temperature changes were observed in abdominal surgery between low and high BMI groups. After 60 minutes of anaesthesia, group-dependent temperature differences had levelled out, and relevant differences compared with preoperative temperatures could no longer be observed in any of the groups.

CONCLUSION

Current guidelines provide effective protection against perioperative hypothermia. In the current study, this was true for obese as well as normal weight patients.

Clinical practice guideline. Unintentional perioperative hypothermia

The importance of the safety of our patients in the surgical theatre, has driven many projects. The majority of them aimed at better control and clinical performance; mainly of the variables that intervene or modulate the results of surgical procedures, and have a direct relationship with them. The Spanish Society of Anesthesiology, Critical Care and Therapeutic Pain (SEDAR), maintains a constant concern for a variable that clearly determines the outcomes of our clinical processes, "unintentional hypothermia" that develops in all patients undergoing an anesthetic or surgical procedure. SEDAR has promoted, in collaboration with other scientific Societies and patient Associations, the elaboration of this clinical practice guideline, which aims to answer clinical questions not yet resolved and for which, up to now, there are no documents based in the best scientific evidence available. With GRADE methodology and technical assistance from the Ibero-American Cochrane Collaboration office, this clinical practice guideline presents three recommendations (weak in favor) for active heating methods for the prevention of hypothermia (skin, fluid or gas); three for the prioritization of strategies for the prevention of hypothermia (too weak in favor and one strongly in favor); two of preheating strategies prior to anesthetic induction (both weak in favor); and two for research.

Prevention of laparoscopic surgery induced hypothermia with warmed humidified insufflation: Is the experimental combination of a warming blanket synergistic?

INTRODUCTION

Maintaining normothermia during anesthesia is imperative to provide quality patient care and to prevent adverse outcomes. Prolonged laparoscopic procedures have been identified as a potential risk factor for hypothermia, due to continuous insufflation of cold and dry carbon dioxide. Perioperative hypothermia is associated with increased hospital cost and many complications including; impaired drug metabolism, impaired immune function, cardiac morbidity, shivering, coagulopathy.

METHODS

In this experimental study, four pigs underwent four interventions each, resulting in 16 total trials. Using standardized general anesthesia in a randomized Latin-square sequence the four interventions include: 1. Control group without an administered pneumoperitoneum, 2. Administered standard pneumoperitoneum using 21°C insufflated gas and under-body forced-air warming, 3. Administered pneumoperitoneum with insufflation of warmed/humidified carbon dioxide, 4. Administered pneumoperitoneum with insufflation of warmed/humidified carbon dioxide and under-body forced-air warming. The primary outcome was distal esophageal temperature change 4 hours after trocar insertion.

RESULTS

Four hours after trocar insertion, pigs in the control group lost 2.1 ± 0.4°C; pigs with warmed and humidified insufflation lost 1.8 ± 0.4°C; pigs with forced-air warming group lost 1.3 ± 0.9°C; and pigs exposed to a combination of warmed and humidified insufflation with forced-air warming increased by 0.3 ± 0.2°C.

CONCLUSION

This experimental animal study provides evidence that a combination of warmed and humidified insufflation of carbon dioxide (CO2) in conjunction with forced-air warming is an effective strategy in the prevention of perioperative hypothermia. Further clinical trials investigating humans are therefore indicated.

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.

Normothermia in Arthroplasty

BACKGROUND

Since the initial design of surgical theatres, the thermal environment of the operating suite itself has been an area of concern and robust discussion. In the 1950s, correspondence in the British Medical Journal discussed the most suitable design for a surgeon's cap to prevent sweat from dripping onto the surgical field. These deliberations stimulated questions about the effects of sweat-provoking environments on the efficiency of the surgical team, not to mention the effects on the patient. Although these benefits translate to implant-based orthopedic surgery, they remain poorly understood and, at times, ignored.

METHODS

A review and synthesis of the body of literature on the topic of maintenance of normothermia was performed.

RESULTS

Maintenance of normothermia in orthopedic surgery has been proven to have broad implications from bench top to bedside. Normothermia has been shown to impact everything from nitrogen loss and catabolism after hip fracture surgery to infection rates after elective arthroplasty.

CONCLUSION

Given both the physiologic impact this has on patients, as well as a change in the medicolegal environment around this topic, a general understanding of these concepts should be invaluable to all surgeons.

Effect of peritoneal lavage solution temperature on body temperature in anaesthetised cats and small dogs

A prospective, randomised, non-blinded, clinical study to assess the effect of peritoneal lavage using warmed fluid on body temperature in anesthetised cats and dogs of less than 10 kg body mass undergoing coeliotomy. A standardised anaesthetic protocol was used. Oesophageal and rectal temperatures were measured at various time points. At the end of surgery, group 1 patients (n=10) were lavaged with 200 ml/kg sterile isotonic saline at 34±1°C and group 2 (n=10) at 40±1°C. Groups were similar with respect to age, mass, body condition and surgical incision length. Duration of anaesthesia, surgical procedures and peritoneal lavage was similar between groups. Linear regression showed no significant change in oesophageal temperature during the lavage period for group 1 (P=0.64), but a significant increase for group 2 patients (P<0.0001), with mean temperature changes of -0.5°C (from (36.3°C to 35.9°C) and +0.9°C (from 35.4°C to 36.3°C), respectively. Similar results were found for rectal temperature, with mean changes of -0.5°C and +0.8°C (P=0.922 and 0.045), respectively. The use of isotonic crystalloid solution for peritoneal lavage at a temperature of 40±1°C significantly warms small animal patients, when applied in a clinical setting, compared with lavage solution at 34±1°C.

Meta-analysis: effectiveness of forced-air warming for prevention of perioperative hypothermia in surgical patients

AIM

The aim of this study was to evaluate the effectiveness of forced-air warming for preventing perioperative hypothermia.

BACKGROUND

Perioperative hypothermia commonly occurs in patients receiving anaesthesia during surgeries. However, the effectiveness of warming systems requires verification.

DESIGN

Systematic review incorporating meta-analysis.

DATA SOURCES

We searched OVID, PubMed, Cochrane Library, Medline, CINAHL, CETD and CEPS databases (2001-2015) for randomized controlled trials published in English and Chinese. Outcome measures of interests were body temperature and thermal comfort.

REVIEW METHODS

Cochrane methods, Quality of evidence (GRADE) assessments and Jadad Quality Score were used.

RESULTS

Twenty-nine trials (1875 patients) met inclusion criteria, including seven trials (502 patients) related to thermal comfort. Results showed that: (1) forced-air warming was more effective than passive insulation and circulating-water mattresses; (2) there was no statistically significant difference among forced-air warming, resistive heating blankets, radiant warming systems and circulating-water garments; and (3) that thermal comfort provided by forced-air warming was superior to that of passive insulation, resistive heating blankets and radiant warming systems, but inferior to that of circulating-water mattresses.

CONCLUSIONS

Forced-air warming prevents perioperative hypothermia more effectively than passive insulation and circulating-water mattresses, whereas there is no statistically significant difference in its effectiveness compared with circulating-water garments, resistive heating blankets and radiant warming systems.

Active body surface warming systems for preventing complications caused by inadvertent perioperative hypothermia in adults

BACKGROUND

Inadvertent perioperative hypothermia is a phenomenon that can occur as a result of the suppression of the central mechanisms of temperature regulation due to anaesthesia, and of prolonged exposure of large surfaces of skin to cold temperatures in operating rooms. Inadvertent perioperative hypothermia has been associated with clinical complications such as surgical site infection and wound-healing delay, increased bleeding or cardiovascular events. One of the most frequently used techniques to prevent inadvertent perioperative hypothermia is active body surface warming systems (ABSW), which generate heat mechanically (heating of air, water or gels) that is transferred to the patient via skin contact.

OBJECTIVES

To assess the effectiveness of pre- or intraoperative active body surface warming systems (ABSW), or both, to prevent perioperative complications from unintended hypothermia during surgery in adults.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; Issue 9, 2015); MEDLINE (PubMed) (1964 to October 2015), EMBASE (Ovid) (1980 to October 2015), and CINAHL (Ovid) (1982 to October 2015).

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that compared an ABSW system aimed at maintaining normothermia perioperatively against a control or against any other ABSW system. Eligible studies also had to include relevant clinical outcomes other than measuring temperature alone.

DATA COLLECTION AND ANALYSIS

Several authors, by pairs, screened references and determined eligibility, extracted data, and assessed risks of bias. We resolved disagreements by discussion and consensus, with the collaboration of a third author.

MAIN RESULTS

We included 67 trials with 5438 participants that comprised 79 comparisons. Forty-five RCTs compared ABSW versus control, whereas 18 compared two different types of ABSW, and 10 compared two different techniques to administer the same type of ABSW. Forced-air warming (FAW) was by far the most studied intervention.Trials varied widely regarding whether the interventions were applied alone or in combination with other active (based on a different mechanism of heat transfer) and/or passive methods of maintaining normothermia. The type of participants and surgical interventions, as well as anaesthesia management, co-interventions and the timing of outcome measurement, also varied widely. The risk of bias of included studies was largely unclear due to limitations in the reports. Most studies were open-label, due to the nature of the intervention and the fact that temperature was usually the principal outcome. Nevertheless, given that outcome measurement could have been conducted in a blinded manner, we rated the risk of detection and performance bias as high.The comparison of ABSW versus control showed a reduction in the rate of surgical site infection (risk ratio (RR) 0.36, 95% confidence interval (CI) 0.20 to 0.66; 3 RCTs, 589 participants, low-quality evidence). Only one study at low risk of bias observed a beneficial effect with forced-air warming on major cardiovascular complications (RR 0.22, 95% CI 0.05 to 1.00; 1 RCT with 12 events, 300 participants, low-quality evidence) in people at high cardiovascular risk. We found no beneficial effect for mortality. ABSW also reduced blood loss during surgery but the magnitude of this effect seems to be irrelevant (MD -46.17 mL, 95% CI -82.74 to -9.59; I² = 78%; 20 studies, 1372 participants). The same conclusion applies to total fluids infused during surgery (MD -144.49 mL, 95% CI -221.57 to -67.40; I² = 73%; 24 studies, 1491 participants). These effects did not translate into a significant reduction in the number of participants being transfused or the average amount of blood transfused. ABSW was associated with a reduction in shivering (RR 0.39, 95% CI 0.28 to 0.54; 29 studies, 1922 participants) and in thermal comfort (standardized mean difference (SMD) 0.76, 95% CI 0.29 to 1.24; I² = 77%, 4 trials, 364 participants).For the comparison between different types of ABSW system or modes of administration of a particular type of ABSW, we found no evidence for the superiority of any system in terms of clinical outcomes, except for extending systemic warming to the preoperative period in participants undergoing major abdominal surgery (one study at low risk of bias).There were limited data on adverse effects (the most relevant being thermal burns). While some trials included a narrative report mentioning that no adverse effects were observed, the majority made no reference to it. Nothing so far suggests that ABSW involves a significant risk to patients.

AUTHORS' CONCLUSIONS

Forced-air warming seems to have a beneficial effect in terms of a lower rate of surgical site infection and complications, at least in those undergoing abdominal surgery, compared to not applying any active warming system. It also has a beneficial effect on major cardiovascular complications in people with substantial cardiovascular disease, although the evidence is limited to one study. It also improves patient's comfort, although we found high heterogeneity among trials. While the effect on blood loss is statistically significant, this difference does not translate to a significant reduction in transfusions. Again, we noted high heterogeneity among trials for this outcome. The clinical relevance of blood loss reduction is therefore questionable. The evidence for other types of ABSW is scant, although there is some evidence of a beneficial effect in the same direction on chills/shivering with electric or resistive-based heating systems. Some evidence suggests that extending systemic warming to the preoperative period could be more beneficial than limiting it only to during surgery. Nothing suggests that ABSW systems pose a significant risk to patients.The difficulty in observing a clinically-relevant beneficial effect with ABSW in outcomes other than temperature may be explained by the fact that many studies applied concomitant procedures that are routinely in place as co-interventions to prevent hypothermia, whether passive or active warming systems based in other physiological mechanisms (e.g. irrigation fluid or gas warming), as well as a stricter control of temperature in the context of the study compared with usual practice. These may have had a beneficial effect on the participants in the control group, leading to an underestimation of the net benefit of ABSW.

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.

Active cutaneous warming systems to prevent intraoperative hypothermia: a systematic review

This study analyzed the evidence available in the literature concerning the effectiveness of different active cutaneous warming systems to prevent intraoperative hypothermia. This is a systematic review with primary studies found in the following databases: CINAHL, EMBASE, Cochrane Register of Controlled Trials and Medline. The sample comprised 23 randomized controlled trials. There is evidence in the literature indicating that the circulating water garment system is the most effective in maintaining patient body temperature. These results can support nurses in the decision-making process concerning the implementation of effective measures to maintain normothermia, though the decision of health services concerning which system to choose should also take into account its cost-benefit status given the cost related to the acquisition of such systems.

Core temperatures during major abdominal surgery in patients warmed with new circulating-water garment, forced-air warming, or carbon-fiber resistive-heating system

PURPOSE

It has been reported that recently developed circulating-water garments transfer more heat than a forced-air warming system. The authors evaluated the hypothesis that circulating-water leg wraps combined with a water mattress better maintain intraoperative core temperature ≥36°C than either forced-air warming or carbon-fiber resistive heating during major abdominal surgery.

METHODS

Thirty-six patients undergoing open abdominal surgery were randomly assigned to warming with: (1) circulating-water leg wraps combined with a full-length circulating-water mattress set at 42°C, (2) a lower-body forced-air cover set on high (≈43°C), and (3) a carbon-fiber resistive-heating cover set at 42°C. Patients were anesthetized with general anesthesia combined with continuous epidural analgesia. The primary outcome was intraoperative tympanic-membrane temperature ≥36°C.

RESULTS

In the 2 h after anesthesia induction, core temperature decreased 1.0 ± 0.5°C in the forced-air group, 0.9 ± 0.2°C in the carbon-fiber group, and 0.4 ± 0.4°C in the circulating-water leg wraps and mattress group (P < 0.05 vs. forced-air and carbon-fiber heating). At the end of surgery, core temperature was 0.2 ± 0.7°C above preoperative values in the circulating-water group but remained 0.6 ± 0.9°C less in the forced-air and 0.6 ± 0.4°C less in the carbon-fiber groups (P < 0.05 vs. carbon fiber).

CONCLUSIONS

The combination of circulating-water leg wraps and a mattress better maintain intraoperative core temperature than did forced-air and carbon-fiber warming systems.

Comparing ambient, air-convection, and fluid-convection heating techniques in treating hypothermic burn patients, a clinical RCT

Background

Hypothermia in burns is common and increases morbidity and mortality. Several methods are available to reach and maintain normal core body temperature, but have not yet been evaluated in critical care for burned patients. Our unit's ordinary technique for controlling body temperature (Bair Hugger^®+ radiator ceiling + bed warmer + Hotline^®) has many drawbacks e.g.; slow and the working environment is hampered.

The aim of this study was to compare our ordinary heating technique with newly-developed methods: the Allon™2001 Thermowrap (a temperature regulating water-mattress), and Warmcloud (a temperature regulating air-mattress).

Methods

Ten consecutive burned patients (> 20% total burned surface area and a core temperature < 36.0°C) were included in this prospective, randomised, comparative study. Patients were randomly exposed to 3 heating methods. Each treatment/measuring-cycle lasted for 6 hours. Each heating method was assessed for 2 hours according to a randomised timetable. Core temperature was measured using an indwelling (bladder) thermistor. Paired t-tests were used to assess the significance of differences between the treatments within the patients. ANOVA was used to assess the differences in temperature from the first to the last measurement among all treatments. Three-way ANOVA with the Tukey HSD post hoc test and a repeated measures ANOVA was used in the same manner, but included information about patients and treatment/measuring-cycles to control for potential confounding. Data are presented as mean (SD) and (range). Probabilities of less than 0.05 were accepted as significant.

Results

The mean increase, 1.4 (SD 0.6°C; range 0.6-2.6°C) in core temperature/treatment/measuring-cycle highly significantly favoured the Allon™2001 Thermowrap in contrast to the conventional method 0.2 (0.6)°C (range -1.2 to 1.5°C) and the Warmcloud 0.3 (0.4)°C (range -0.4 to 0.9°C). The procedures for using the Allon™2001 Thermowrap were experienced to be more comfortable and straightforward than the conventional method or the Warmcloud.

Conclusions

The Allon™2001 Thermowrap was more effective than the Warmcloud or the conventional method in controlling patients' temperatures.

Hipotermia no período intra-operatório: é possível evitá-la?

O estudo teve como objetivo identificar as medidas adotadas para a prevenção de hipotermia no período intra-operatório. Trata-se de um estudo com delineamento de pesquisa não experimental, tipo descritivo-exploratório, prospectivo. Para tal elaborou-se um instrumento de coleta de dados, o qual foi submetido à validação aparente e de conteúdo. A amostra foi constituída de 70 pacientes. A medida mais empregada na sala de operação foi o método passivo de aquecimento cutâneo como o uso de lençol de algodão (11,4%) e o enfaixamento dos membros inferiores (14,3%). A utilização de um método ativo de aquecimento cutâneo ocorreu uma única vez (1,4%). Os resultados evidenciados demonstraram a necessidade de implementação de intervenções eficazes para a prevenção da hipotermia e o enfermeiro tem papel importante neste contexto, uma vez que a segurança do paciente e a redução de complicações decorrentes do procedimento anestésico cirúrgico são metas do cuidado de enfermagem.

Forced-air and a novel patient-warming system (vitalHEAT vH2) comparably maintain normothermia during open abdominal surgery

BACKGROUND

The vitalHEAT vH(2) (Dynatherm Medical, Inc., Fremont, California) system transfers heat through a single extremity using a combination of conductive heat (circulating warm water within soft fluid pads) with mild vacuum, which improves both vasodilation and contact between the heating element and the skin surface. We tested the hypothesis that core temperatures were not >0.5°C lower in patients warmed with the vitalHEAT system than with forced air.

METHODS

Patients having general anesthesia for open abdominal surgery were randomly assigned to the circulating-water sleeve on 1 arm (n = 37) or an upper-body forced-air warming cover (n = 34). Patients were eligible to participate when body mass index was 20 to 36 kg/m(2), age was 18 to 75 years, and ASA physical status was 1 to 3. Intraoperative distal esophageal (core) temperatures were recorded. Repeated-measures analysis and 1-tailed t tests were used to assess noninferiority of vitalHEAT to forced air using a noninferiority δ of -0.5°C.

RESULTS

Demographic and morphometric characteristics were similar, as were surgical details. Preoperative core temperatures were similar in each group. Intraoperative core temperatures were also similar with each warming system and were significantly noninferior during the first four hours of surgery. The observed difference in means was never more than about 0.2°C. After 4 hours of surgery, the average temperature was 36.3°C ± 0.6°C (mean ± sd) with the circulating-water sleeve (n = 18) and 36.4°C ± 0.5°C with forced air (n = 20), for a difference (95% confidence interval) of -0.21°C (-0.47, 0.06).

CONCLUSIONS

The 2 systems thus apparently transfer comparable amounts of heat. Both appear suitable for maintaining normothermia even during large and long operations.

A systematic review of the effectiveness of cutaneous warming systems to prevent hypothermia

AIMS

To retrieve and critique recent randomised trials of cutaneous warming systems used to prevent hypothermia in surgical patients during the intraoperative period and to identify gaps in current evidence and make recommendations for future trials.

BACKGROUND

Hypothermia affects up to 70% of anaesthetised surgical patients and is associated with several significant negative health outcomes.

DESIGN

Systematic review using integrative methods.

METHODS

We searched CINAHL, EMBASE, Cochrane Register of Controlled Trials and Medline databases (January 2000-April 2007) for recent reports on randomised controlled trials of cutaneous warming systems used with elective patients during the intraoperative period. Inclusion criteria. We included randomised control trials examining the effects of cutaneous warming systems used intraoperatively on patients aged 18 years or older undergoing non-emergency surgery. Studies published in English, Spanish or Portuguese with a comparison group that consisted of either usual care or active cutaneous warming systems without prewarming were reviewed.

RESULTS

Of 193 papers initially identified, 14 studies met the inclusion criteria. There was moderate evidence to indicate that carbon-fibre blankets and forced-air warming systems are equally effective and that circulating-water garments are most effective for maintaining normothermia during the intraoperative period. Few trials reported costs.

CONCLUSIONS

Carbon-fibre blankets and forced-air warming systems are effective and circulating-water garments may be preferable. Future research should measure the direct and indirect costs associated with competing systems.

RELEVANCE TO CLINICAL PRACTICE

Nurses can use this review to inform their selection of warming interventions in perioperative nursing practice. They can also assess other factors such as nursing workload, staff training and equipment maintenance, which should be incorporated into future research.

Circulating-water garment or the combination of a circulating-water mattress and forced-air cover to maintain core temperature during major upper-abdominal surgery

BACKGROUND

A recent heat-balance study in volunteers suggested that greater efficacy of circulating-water garments (CWGs) results largely from increased heat transfer across the posterior skin surface since heat transfer across the anterior skin surface was similar with circulating-water and forced-air. We thus tested the hypothesis that the combination of a circulating-water mattress (CWM) and forced-air warming prevents core temperature reduction during major abdominal surgery no worse than a CWG does.

METHODS

Fifty adult patients aged between 18 and 85 yr old, undergoing major abdominal surgery, were randomly assigned to intraoperative warming with a combination of forced-air and a CWM or with a CWG (Allon ThermoWrap). Core temperature was measured in the distal oesophagus. Non-inferiority of the CWM to the CWG on change from baseline to median intraoperative temperature was assessed using a one-tailed Student's t-test with an equivalency buffer of -0.5°C.

RESULTS

Data analysis was restricted to 16 CWG and 20 CWM patients who completed the protocol. Core temperature increased in both groups during the initial hours of surgery. We had sufficient evidence (P=0.001), to conclude that the combination of a CWM and forced-air warming was non-inferior to a CWG in preventing temperature reduction, with mean (95% CI) difference in the temperature change between the CWM and the CWG groups (CWM-CWG) of 0.46°C (-0.09°C, 1.00°C).

CONCLUSIONS

The combination of a CWM and forced-air warming is significantly non-inferior in maintaining intraoperative core temperature than a CWG.

TRIAL REGISTRY

This trial has been registered at clinical trials.gov, identifier: NCT 00651898.

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.

Active warming systems to maintain perioperative normothermia in hip replacement surgery: a therapeutic aid or a vector of infection?

Various reliable body heat-regulating systems have been designed and developed with the aim of maintaining an adequate body temperature in the course of major surgery. This is crucial to avoid the onset of potentially severe complications that are especially serious in elderly and debilitated subjects. Among these systems, the Bair Hugger blanket has demonstrated excellent efficacy. However, some reports in the literature have suggested that the use of such devices can increase the risk of nosocomial infections, particularly surgical wound infections. The aim of this study was to assess the risk of contamination of the surgical site correlated to the use of the Bair Hugger blanket during hip replacement surgery. To this end, the level of bacterial contamination of the air in the operating theatre was quantified with and without the use of the Bair Hugger, during the course of 30 total non-cemented hip implants performed in patients with osteoarthritis. Sampling was done both in the empty theatre and during surgical procedures, in different zones around the operating table and on the patient's body surface. Statistical analysis of the results demonstrated that the Bair Hugger system does not pose a real risk for nosocomial infections, whereas it does offer the advantage of preventing the potentially very severe consequences of hypothermia during major orthopaedic surgery. In addition, monitoring patients over the six months following the operation allowed us to exclude a later manifestation of a nosocomial infection.

[Perioperative thermal management]

Perioperative hypothermia can influence clinical outcome negatively. It triples the incidence of adverse myocardial outcomes, significantly increases perioperative blood loss, significantly augments allogenic transfusion requirements, and increases the incidence of surgical wound infections. The major causes are redistribution of heat from the core of the body to the peripheral tissues and a negative heat balance. Adequate thermal management includes preoperative and intraoperative measures. Preoperative measures, e.g., prewarming, enhance heat content of the peripheral tissues, thereby reducing redistribution of heat from the core to the peripheral tissues after induction of anesthesia. Intraoperative measures are active skin surface warming of a large body surface area with conductive or convective warming systems. Intravenous fluids should be warmed when large volumes of more than 500-1000 ml/h are required. The body surfaces that cannot be actively warmed should be insulated. Airway humidification and conductive warming of the back are less efficient.

Thermal management of the patient: where does the patient lose and/or gain temperature?

PURPOSE OF REVIEW

Anesthesia inhibits normal thermoregulatory control, leading to perioperative hypothermia or allowing therapeutic hypothermia. During the last decade many studies have shown the effects of anesthesia on thermoregulation. As a consequence many active warming and cooling devices are available to manipulate patients' core temperature. This review focuses on new findings in the field of temperature management.

RECENT FINDINGS

Thermal management of patients has improved tremendously in recent years. Many outcome studies have shown adverse effects of perioperative hypothermia, as well as beneficial effects of therapeutic hypothermia after out-of-hospital cardiac arrest and brain trauma. However, inducing hypothermia is limited by physiologic thermoregulatory responses. Small reductions in core temperature lead to vasoconstriction and shivering, effectively hindering hypothermia. Thus prevention of vasoconstriction and shivering have become major goals during induction of therapeutic hypothermia. All anesthetics, opioids and sedatives lower the vasoconstriction and shivering threshold, thus allowing hypothermia. However, these drugs have side effects, such as respiratory depression, sedation and nausea. Several drugs, alone or in combination, lower the shivering threshold while causing minimal or no side effects.

SUMMARY

Anesthesia affects thermoregulatory control and leads to perioperative hypothermia. The prevention of perioperative hypothermia improves patient's outcome. Therapeutic hypothermia can be induced and also improves outcome in certain conditions.

The effect of preoperative warming on patients' postoperative temperatures

Many perioperative clinicians encounter difficulty in preventing hypothermia in surgical patients. One intervention to prevent perioperative hypothermia is the use of forced-air warming. Although forced-air warming is used most frequently in the intraoperative area, prewarming patients with forced-air warming systems before induction of anesthesia may be enough to prevent hypothermia throughout the surgical procedure, allowing patients to arrive in the postanesthesia care unit in a normothermic state. A review of the literature on preoperative forced-air warming is provided, and the effect of prewarming on postoperative patient temperatures is discussed.

Water-filled garment warming of infants undergoing open abdominal or thoracic surgery

We have assessed the efficacy of a water-filled garment (ThermoWrap-Allon 2001) to maintain normothermia in small infants during major open abdominal or thoracic surgery. Twenty-two patients were studied in a case-matched comparison of two methods of thermal control intended to maintain core body temperature at 37 degrees C. The standard method involved a warm air mattress with additional insulation. The ThermoWrap garment covered the head, trunk and legs and the water temperature was automatically controlled. Central and peripheral temperatures were recorded every 15 min. Nineteen infants had abdominal and three had thoracic operations. The mean weight was 3.2 kg (range 1.4-7.8 kg). Over time, the core temperature declined with standard care but not with the ThermoWrap. Core temperature was statistically lower in the standard care infants by 30 min after start of surgery. Six infants had a core temperature of less than 35 degrees C with standard care (lowest 33.7 degrees C); the lowest temperature with the ThermoWrap was 35.6 degrees C. Some infants had cold hands with the ThermoWrap. Core temperature is better preserved with the ThermoWrap; extra insulation of exposed arms may be necessary. An important advantage of the ThermoWrap is its ability to control body temperature automatically.

Cerebrospinal Fluid and Plasma Pharmacokinetics of the Cyclooxygenase 2 Inhibitor Rofecoxib in Humans: Single and Multiple Oral Drug Administration

Cerebrospinal fluid (CSF) pharmacokinetics of orally administered cyclooxygenase 2 inhibitors, with single or multiple dosing, is of clinical relevance because it may relate to the analgesic efficacy of these drugs. We enrolled 9 subjects with implanted intrathecal catheters in the study. After 50-mg oral rofecoxib administration, the CSF drug concentration lagged slightly behind the plasma drug concentration. The ratio of the 24-h area under the drug-concentration curve (AUC) in CSF to plasma was 0.142. After daily dosing of rofecoxib 50 mg/d for 9 days, rofecoxib concentrations in plasma and CSF were larger on Day 9 than on Day 1, with the 24-h AUC on Day 9 more than twice the Day 1 AUC for both plasma and CSF. After nine consecutive daily doses of rofecoxib, the AUC(CSF)/AUC(plasma) ratio was 0.159. The important findings of this study are that CSF rofecoxib levels are approximately 15% of plasma levels and that repeated daily dosing more than doubles the AUC in CSF.

The effects of heated and room-temperature abdominal lavage solutions on core body temperature in dogs undergoing celiotomy

To document the magnitude of temperature elevation obtained with heated lavage solutions during abdominal lavage, 18 dogs were lavaged with sterile isotonic saline intraoperatively (i.e., during a celiotomy). In nine dogs, room-temperature saline was used. In the remaining nine dogs, saline heated to 43+/-2 degrees C (110+/-4 degrees F) was used. Esophageal, rectal, and tympanic temperatures were recorded every 60 seconds for 15 minutes after initiation of the lavage. Temperature levels decreased in dogs lavaged with room-temperature saline. Temperature levels increased significantly in dogs lavaged with heated saline after 2 to 6 minutes of lavage, and temperatures continued to increase throughout the 15-minute lavage period.

Nutrient induced thermogenesis during major colorectal excision--a pilot study

OBJECTIVE

Hypothermia may occur during general anaesthesia and is associated with postoperative coagulopathy, ischaemic cardiac events, wound infections and increased metabolic expenditure due to shivering. The purpose of the present pilot study was to determine whether the administration of certain amino acids (Vamin 18) during general anaesthesia could prevent postoperative hypothermia.

PATIENTS AND METHODS

Two groups of patients were studied. The study group comprised 10 patients who underwent complex major colorectal operations. In this group an infusion of 500 mls of Vamin 18 (Fresenius Kabi Ltd) was commenced immediately after induction of anaesthesia but prior to the skin incision. In a control group (n=10) who underwent similar surgical procedures Vamin 18 was not administered. In both groups core body temperature, using an oesophageal probe was recorded during the procedure and recovery period. Ambient theatre and recovery room temperature and other body warming techniques were standardized for all patients. Statistical analysis was performed using t-test for comparison of linear temperature changes at different times during the procedure for both groups of patients.

RESULTS

The body temperature was statistically significantly reduced in both groups at skin incision when compared with temperature prior to induction of anaesthesia. (

STUDY GROUP

mean 0.74 degrees C, SD=0.38, P =<0.001;

CONTROL GROUP

mean 0.54 degrees C, SD=0.43, P=0.003]. The increase in body temperature between the time of skin incision and recovery period was statistically significant (P=0.012) in the study group but not so in the control group (P=0.730).

CONCLUSION

The results of the present pilot study demonstrate that complex colorectal operations are associated with a decrease in body temperature which is most marked immediately after the induction of anaesthesia. The perioperative administration of Vamin 18 appears to increase the rate of recovery of body temperature. The impact of this thermogenic effect on perioperative morbidity and mortality should be studied in a prospective randomised clinical trial.

Conductive Heat Exchange with a Gel-Coated Circulating Water Mattress

The use of forced-air warming is associated with costs for the disposable blankets. As an alternative method, we studied heat transfer with a reusable gel-coated circulating water mattress placed under the back in eight healthy volunteers. Heat flux was measured with six calibrated heat flux transducers. Additionally, mattress temperature, skin temperature, and core temperature were measured. Water temperature was set to 25 degrees C, 30 degrees C, 35 degrees C, and 41 degrees C. Heat transfer was calculated by multiplying heat flux by contact area. Mattress temperature, skin temperature, and heat flux were used to determine the heat exchange coefficient for conduction. Heat flux and water temperature were related by the following equation: heat flux = 10.3 x water temperature - 374 (r(2) = 0.98). The heat exchange coefficient for conduction was 121 W . m(-2) . degrees C(-1). The maximal heat transfer with the gel-coated circulating water mattress was 18.4 +/- 3.3 W. Because of the small effect on the heat balance of the body, a gel-coated circulating water mattress placed only on the back cannot replace a forced-air warming system.

Older people and hypothermia: the role of the anaesthetic nurse

Older clients are at increased risk during surgical intervention because of age-related system changes and comorbid conditions. However, recent advances in surgical and anaesthetic techniques, together with modern monitoring technology and the proliferation of ambulatory surgery, have reduced mortality in older patients undergoing surgery. Nevertheless, inadvertent hypothermia in older clients remains problematic. Therefore, an understanding of specific diseases prevalent in old age, coupled with a comprehensive knowledge of the physiological impact of ageing in all body systems, underpins the role of the anaesthetic nurse.

Effectiveness of a circulating-water warming garment in rewarming after pediatric cardiac surgery using hypothermic cardiopulmonary bypass

OBJECTIVE

To evaluate the effectiveness and safety of the ALLON 2001 microprocessor-based thermoregulation system in pediatric patients undergoing cardiac surgery requiring hypothermic cardiopulmonary bypass compared with the routine thermal care.

DESIGN

Prospective randomized clinical study.

SETTING

Single tertiary academic medical center.

PARTICIPANTS

Infants (0-1 year) who underwent congenital heart surgery requiring hypothermic cardiopulmonary bypass (n = 18). Patients with open wounds and/or patients treated with an investigational drug or device within 30 days of surgery were excluded.

INTERVENTIONS

Randomized use of thermoregulation system (warming garment, n = 9) or routine thermal care (control, n = 9) after separating from cardiopulmonary bypass until the arrival to the pediatric intensive care unit (PICU).

MEASUREMENTS AND MAIN RESULTS

There were no statistically significant differences in the demographic data, cardiopulmonary bypass time, operating room time, incidence of deep hypothermic circulatory arrest, and cooling temperature between the groups. The nasopharyngeal temperature was significantly higher in the warming garment group after separation from cardiopulmonary bypass. Nasopharyngeal temperature at 20 minutes was 36.5 degrees C versus 35.01 degrees C (p = 0.0047), at 40 minutes was 36.98 degrees C versus 35.30 degrees C (p = 0.034), and at admission to the PICU was 36.09 degrees C versus 35.31 degrees C (p = not significant). There was no difference in the core-to-peripheral temperature gradient (nasopharyngeal-to-skin temperature) between the 2 study groups at any time point. No adverse events related to the use of the warming garment thermoregulation system were observed.

CONCLUSION

The investigated thermoregulation system was effective in preventing the after-drop of temperature that occurs after cardiopulmonary bypass in small infants compared with routine warming methods.

Implications of the use of neuromuscular transmission monitoring on immediate postoperative extubation in off-pump coronary artery bypass surgery

BACKGROUND AND OBJECTIVE

When continuous infusions of neuromuscular blocking drugs are administered during lengthy interventions and no routine antagonism of their effects is applied, there is a dramatic incidence of residual curarization. We have examined whether the use of neuromuscular transmission monitoring results in differences in the incidence of postoperative residual curarization, the use of antagonist agents, and the endotracheal extubation rate and outcome after continuous infusion of rocuronium in patients undergoing off-pump coronary artery bypass surgery.

METHODS

Twenty patients were assigned to group 1 (n = 10, non-blinded neuromuscular transmission monitoring) or group 2 (n = 10, blinded neuromuscular transmission monitoring). In group 1, patients were given rocuronium at an infusion rate of 6 microg kg(-1) min(-1). The rate was manually adjusted in order to maintain T1/T0 at 10%. In group 2, a rocuronium infusion was started 30 min after induction of anaesthesia, at a rate of 6 microg kg(-1) min(-1); this rate was left unchanged during surgery. The rocuronium infusion was discontinued on completion of all vascular anastomoses; propofol was stopped at the beginning of closure of the subcutis and pirinitramide (piritramide) 15 mg was administered intravenously. Remifentanil was discontinued at the beginning of skin closure and neostigmine (50 microg kg(-1)) administered at the end of surgery when the train-of-four ratio was < 0.9 in group 1, and routinely in group 2. A 20 min test period for spontaneous ventilation was allowed once surgery had been accomplished. When the train-of-four ratio was > or = 0.9 (group 1), patients were extubated if also breathing spontaneously, fully awake and able to follow commands. When they met the clinical criteria for normal neuromuscular function after induced blockade, patients in group 2 were extubated when fully awake and able to follow commands.

RESULTS

In group 1, the rate of rocuronium infusion required to keep T1/T0 at 10% was 5 +/- 1.9 microg kg(-1) min(-1); this was not significantly different from the fixed rate in group 2 (P = 0.15). One patient in group 2 was excluded. Eight out of 10 and eight out of nine patients in groups 1 and 2, respectively, reached the extubation criteria. Three out of eight, and five out of eight, patients from groups 1 and 2, respectively, were extubated in the operating room. At that time of endotracheal extubation, all three patients from group 1, but only four of the five patients from group 2 had a train-of-four ratio > or = 0.9. In group 2, one patient was reintubated in the intensive care unit. The incidence of pharmacological reversal was high in group 1.

CONCLUSIONS

Although we found no additional benefit of using neuromuscular transmission monitoring, it seems an absolute necessity for safety reasons. Pharmacological antagonism was mandatory. However, in our opinion, it is not wise routinely to perform immediate postoperative extubation in off-pump coronary artery bypass surgery.

Water warming garment versus forced air warming system in prevention of intraoperative hypothermia during liver transplantation: a randomized controlled trial [ISRCTN32154832]

BACKGROUND: The authors compared two strategies for the maintenance of intraoperative normothermia during orthotopic liver transplantation (OLT): the routine forced-air warming system and the newly developed, whole body water garment. METHODS: In this prospective, randomized and open-labelled study, 24 adult patients were enrolled in one of two intraoperative temperature management groups during OLT. The water-garment group (N = 12) received warming with a body temperature (esophageal) set point of 36.8 degrees C. The forced air-warmer group (N = 12) received routine warming therapy using upper- and lower-body forced-air warming system. Body core temperature (primary outcome) was recorded intraoperatively and during the two hours after surgery in both groups. RESULTS: The mean core temperatures during incision, one hour after incision and during the skin closing were significantly higher (p < 0.05, t test with Bonferroni corrections for the individual tests) in the water warmer group compared to the control group (36.7 PlusMinus; 0.1, 36.7 PlusMinus; 0.2, 36.8 PlusMinus; 0.1 vs 36.1 PlusMinus; 0.4, 36.1 PlusMinus; 0.4, 36.07 PlusMinus; 0.4 degrees C, respectively). Moreover, significantly higher core temperatures were observed in the water warmer group than in the control group during the placement of cold liver allograft (36.75 PlusMinus; 0.17 vs 36.09 PlusMinus; 0.38 degrees C, respectively) and during the allograft reperfusion period (36.3 PlusMinus; 0.26 vs 35.52 PlusMinus; 0.42 degrees C, respectively). In addition, the core temperatures immediately after admission to the SICU (36.75 PlusMinus; 0.13 vs 36.22 PlusMinus; 0.3 degrees C, respectively) and at one hr (36.95 PlusMinus; 0.13 vs 36.46 PlusMinus; 0.2 degrees C, respectively) were significantly higher in the water warmer group, compared to the control group, whereas the core temperature did not differ significantly afte two hours in ICU in both groups. CONCLUSIONS: The investigated water warming system results in better maintenance of intraoperative normothermia than routine air forced warming applied to upper- and lower body.