Passive Warming Methods Research Articles

Benefits of Passive Warming on Surgical Patients Undergoing Regional Anesthetic Procedures

Introduction Perioperative normothermia is vital to reduction of surgical morbidity and mortality and improved surgical patient outcomes. Preoperative patient warming with active or passive warming measures is a key factor to maintaining normothermia throughout the perioperative process. Identification of the problem Potential for development of perioperative hypothermia is associated with use of regional anesthetic procedures (RAPs). Use of active warming during RAP placement is not feasible because of sterility requirements and patient positioning during RAP placement. QI question/Purpose of the study To determine if application of preoperative passive warming methods would maintain body temperature in patients receiving RAPs and contribute to reduced length of stay in PACU at a Level 1 trauma center in Middle Tennessee. Methods After being deemed IRB Exempt, this QI project utilized a convenience sample of 120 patients receiving RAP in conjunction with an elective orthopedic, abdominal, or thoracic surgical procedure. Passive warming trial: 53 patients received warming via thermal insulated surgical cap ($1.54/ea) & activated chemical warmer ($0.54/ea) placed on the inner, upper aspect of one arm. Retrospective review: 67 patients received warming using forced warm air gown ($9.75/ea). All preoperative warming measures remained in place approximately 90 minutes. Tympanic temperature was assessed upon admission, at transfer to OR, after induction of general anesthesia, and upon arrival to PACU. Outcomes/Results No difference in mean temperatures was found between groups post-induction or upon admission to PACU. Additionally, 51.9% of passive group (n = 28) experienced an increase in temperature compared to 48.2% (n = 26) of retrospective group. A statistically significant, positive correlation was found between admission temperature and transfer to OR temperature with age (p = 0.18). Passive group averaged 13.5-minute shorter PACU LOS. Discussions Passive warming affords the RAP population opportunity to receive benefits of pre-operative warming. Older participants responded better to passive warming measures: as age increased, temperature also increased. Passive warming measures were found to be less expensive than forced-air systems (savings of > $7 per patient). Conclusions Passive warming methods maintained patient temperatures throughout the perioperative process. Additionally, passive warming demonstrated a statistically significant increase in temperature from admission to transfer to OR in older participants and a clinically significant decrease in PACU LOS. Implications for Perianesthesia Nurses and Future Research Passive warming is a suitable, cost-effective alternative when forced-air warming is not feasible. Additional inquiry into the use of passive warming is warranted. Perioperative normothermia is vital to reduction of surgical morbidity and mortality and improved surgical patient outcomes. Preoperative patient warming with active or passive warming measures is a key factor to maintaining normothermia throughout the perioperative process. Potential for development of perioperative hypothermia is associated with use of regional anesthetic procedures (RAPs). Use of active warming during RAP placement is not feasible because of sterility requirements and patient positioning during RAP placement. To determine if application of preoperative passive warming methods would maintain body temperature in patients receiving RAPs and contribute to reduced length of stay in PACU at a Level 1 trauma center in Middle Tennessee. After being deemed IRB Exempt, this QI project utilized a convenience sample of 120 patients receiving RAP in conjunction with an elective orthopedic, abdominal, or thoracic surgical procedure. Passive warming trial: 53 patients received warming via thermal insulated surgical cap ($1.54/ea) & activated chemical warmer ($0.54/ea) placed on the inner, upper aspect of one arm. Retrospective review: 67 patients received warming using forced warm air gown ($9.75/ea). All preoperative warming measures remained in place approximately 90 minutes. Tympanic temperature was assessed upon admission, at transfer to OR, after induction of general anesthesia, and upon arrival to PACU. No difference in mean temperatures was found between groups post-induction or upon admission to PACU. Additionally, 51.9% of passive group (n = 28) experienced an increase in temperature compared to 48.2% (n = 26) of retrospective group. A statistically significant, positive correlation was found between admission temperature and transfer to OR temperature with age (p = 0.18). Passive group averaged 13.5-minute shorter PACU LOS. Passive warming affords the RAP population opportunity to receive benefits of pre-operative warming. Older participants responded better to passive warming measures: as age increased, temperature also increased. Passive warming measures were found to be less expensive than forced-air systems (savings of > $7 per patient). Passive warming methods maintained patient temperatures throughout the perioperative process. Additionally, passive warming demonstrated a statistically significant increase in temperature from admission to transfer to OR in older participants and a clinically significant decrease in PACU LOS.

Improving intraoperative temperature management in elective repeat cesarean deliveries: a retrospective observational cohort study

BackgroundInadvertent perioperative hypothermia (< 36 °C) occurs frequently during elective cesarean delivery and most institutions do employ perioperative active warming. The purpose of this retrospective observational cohort study was to determine if the addition of preoperative forced air warming in conjunction with intraoperative underbody forced air warming improved core temperature and reducing inadvertent perioperative hypothermia during elective repeat elective cesarean delivery with neuraxial anesthesia.MethodsWe evaluated the addition of perioperative active warming to standard passive warming methods (preheated intravenous/irrigation fluids and cotton blankets) in 120 parturients scheduled for repeat elective cesarean delivery (passive warming, n = 60 vs. active + passive warming, n = 60) in a retrospective observational cohort study. The primary outcomes of interest were core temperature at the end of the procedure and a decrease in inadvertent perioperative hypothermia (< 36 °C). Secondary outcomes were surgical site infections and adverse markers of neonatal outcome.ResultsThe mean temperature at the end of surgery after instituting the active warming protocol was 36.0 ± 0.5 °C (mean ± SD, 95% CI 35.9–36.1) vs. 35.4 ± 0.5 °C (mean ± SD, 95% CI 35.3–35.5) compared to passive warming techniques (p < 0.001) and the incidence of inadvertent perioperative hypothermia at the end of the procedure was less in the active warming group - 68% versus 92% in the control group (p < 0.001). There was no difference in surgical site infections or neonatal outcomes.ConclusionsPerioperative active warming in combination with passive warming techniques was associated with a higher maternal temperature and lower incidence of inadvertent perioperative hypothermia with no detectable differences in surgical site infections or indicators of adverse neonatal outcomes.

Benefits of Passive Warming on Surgical Patients Undergoing Regional Anesthetic Procedures

The purpose of this quality improvement project was to determine if application of preoperative passive warming methods would maintain body temperature in patients receiving regional anesthetic procedures (RAPs). A nonrandomized quasi-experimental design was used. A passive warming trial using a convenience sample of 53 RAP patients warmed with passive measures was compared with data collected from 67 retrospective chart reviews of RAP patients warmed per standard unit policy-typically active forced warm air. Passive measures included a thermal reflective surgical cap and an activated chemical warmer. Passive warming methods maintained temperatures throughout the perioperative process. No significant variations in mean temperatures were noted. As age increased, the difference in temperature from admit to transfer to operating room also increased (P=.0182). Passive warming is a suitable cost-effective alternative when forced-air warming is not feasible. Additional inquiry into the use of passive warming is warranted.

The effect of intraoperative hypothermia upon blood transfusion needs and length of stay among gastrointestinal system cancer surgery.

This cross-sectional study was performed to evaluate the relationship between intraoperative body temperature and the need for blood transfusion and length of stay in the post-anaesthetic care unit (PACU) or in the intensive care unit (ICU) among 79 patients undergoing elective oncology surgery of the digestive system. There was a statistically significant correlation between a lower temperature during surgery and medical diagnosis (p=.009), the use of bupivacaine anaesthesia (p=.016), anaesthesia time (p=.003) and anaesthesia type (p=.033), surgery time (p=.021) and surgery type (p=.002), volumes infused during the intraoperative period (p=.006), admission to the ICU (p=.032) and length of stay in PACU (p=.029). The lower the temperature when the patient is admitted to the operating room, the lower the temperature during the procedure (p˂.001). There was no association between the body temperature of patients and blood transfusion (p=.619). Hypothermia was associated with increased length of stay in the PACU, but was not associated with the need for blood transfusion during the intra- and postoperative periods. The use of preoperative passive warming methods allows patients to reach the operating room hypothermic.

Comparing New-Technology Passive Warming Versus Traditional Passive Warming Methods for Optimizing Perioperative Body Core Temperature

Hypothermia puts surgical patients at risk for adverse outcomes. Traditional passive warming methods are mostly ineffective in reducing hypothermia. New-technology passive warming holds promise as an effective method for promoting and sustaining normothermia throughout surgery. The purpose of this retrospective cohort study was to compare the effectiveness of new-technology passive warming with traditional methods. We measured core body temperature at anesthesia induction and at the end of surgery for patients undergoing robotic-assisted prostatectomy/hysterectomy in the lithotomy position who received either new-technology passive warming (n = 30) or traditional linens and gel pads (n = 35). The traditionally warmed cohort had no change in temperature (35.9° C ± 0.6° C presurgery vs 35.9° C ± 0.7° C postsurgery; t = 0.47; P = .66). The intervention cohort showed a significant increase in temperature (35.75° C ± 0.52° C presurgery vs 36.30° C ± 0.53° C postsurgery; t = 4.64; P < .001). A repeated-measure analysis of variance adjusting for surgery duration and fluid administration confirmed the significance (F = 17.254; P < .001), suggesting that new-technology passive warming may effectively complement active warming to reduce perioperative hypothermia.

Comparison of two passive warming devices for prevention of perioperative hypothermia in dogs.

To compare effects of two passive warming methods combined with a resistive heating mat on perioperative hypothermia in dogs. Fifty-two dogs were enrolled and randomly allocated to receive a reflective blanket (Blizzard Blanket) or a fabric blanket (VetBed). In addition, in the operating room all dogs were placed onto a table with a resistive heating mat covered with a fabric blanket. Rectal temperature measurements were taken at defined points. Statistical analysis was performed comparing all Blizzard Blanket-treated to all VetBed-treated dogs, and VetBed versus Blizzard Blanket dogs within spay and castrate groups, spay versus castrate groups and within groups less than 10 kg or more than 10 kg bodyweight. Data from 39 dogs were used for analysis. All dogs showed a reduction in perioperative rectal temperature. There were no detected statistical differences between treatments or between the different groups. This study supports previous data on prevalence of hypothermia during surgery. The combination of active and passive warming methods used in this study prevented the development of severe hypothermia, but there were no differences between treatment groups.

The clinical effectiveness of interventions to assist perioperative temperature management for women undergoing cesarean section: a systematic review

Background Women undergoing cesarean sections are vulnerable to the adverse effects associated with inadvertent perioperative hypothermia. Effective methods for preventing or managing hypothermia in this group would be valuable. Objectives To synthesize the best available evidence in relation to preventing and/or treating hypothermia in mothers after cesarean sections. Inclusion criteria Types of participants Adult patients of any ethnic background, with or without co-morbidities, undergoing any mode of anesthesia for any type of cesarean section were included. Types of interventions Active or passive warming methods, versus usual care or placebo, that aim to limit or manage core heat loss as applied to women undergoing cesarean sections are included. Types of studies Randomized controlled trials that met the inclusion criteria were considered. Types of outcomes Primary outcome: maternal core temperature during preoperative, intraoperative and postoperative phases of care. Secondary outcomes: newborn core temperature at birth, umbilical pH measured via blood gas analysis, Apgar scores, length of Post Anesthetic Care Unit stay, maternal thermal comfort. Search strategy A comprehensive search was undertaken of the following databases from their inception until May 2012: ProQuest, Web of Science, Scopus, Dissertation and Theses PQDT (via ProQuest), Current Contents, CENTRAL, MedNar, OpenGrey and Clinical Trials. There were no language restrictions. Methodological quality Retrieved papers were assessed for methodological quality by two independent reviewers using the standardized critical appraisal instruments for randomized controlled trials from the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instruments (JBI-MAStARI). Data collection Two independent reviewers extracted data from the included papers using a customized data extraction tool. Data synthesis Where meta-analysis was possible, results were combined in a fixed effects meta-analysis using the Cochrane Collaboration Review Manager software. Due to heterogeneity for one comparison/outcome, random effects meta-analysis was also used. Results Twelve studies with a combined total of 719 participants were included. Intravenous fluid warming was found to be effective at maintaining maternal temperature and also aided in shivering prevention. Intravenous fluids did not improve thermal comfort or neonatal temperature, and the effectiveness on Apgar scores and umbilical pH remains unclear. Warming devices, including forced air warming devices and under-body carbon polymer mattresses, were effective at preventing hypothermia; however effectiveness increased if applied preoperatively. Preoperative body warming devices also reduced shivering. Preoperative forced air warming improves neonatal temperatures. Forced air warming did not improve Apgar scores. The effectiveness of body warming devices on umbilical pH and thermal comfort remains unclear. Leg wrapping was not effective for maintaining maternal temperature. Conclusions Intravenous fluid warming, by any method, improves maternal temperature for women undergoing cesarean section and reduces shivering. Preoperative body warming devices also improve maternal temperature, in addition to reducing shivering. Implications for practice Preoperative warming strategies should be utilized where possible for women undergoing cesarean section (Level 2) and preoperative and/or intraoperative warmed IV fluids should be standard practice (Level 1). Under-body warming mattresses should be used (Level 1) and upper body forced air warming should be utilized preoperatively (Level 2). Additional strategies, such as ambient temperature maintenance, should be used to maintain thermal comfort (Level 2). Warming strategies have less effect when intrathecal opioids are administered (Level 2). Implications for research Research is needed to investigate the effectiveness of interventions in emergency caesarean section surgery. Larger scale studies of warming interventions using standardized and clinically meaningful temperature measurement time points are also required.

地球温暖化が山岳域と極域の生態系に与える影響

Artificial warming experiments on alpine, subalpine, boreal, and subboreal ecosystems are reviewed to understand the impacts of global warming on the ecosystems of these regions. Among various warming methods, passive warming methods, especially open top chambers (OTC), have mainly been used in these outland regions due to limited electricity supplies and need for regular maintenance. Many researchers have studied the effects of experimental warming on variable ecological variables. The authors classify those variables into: (1) phenology, (2) plant growth, (3) plant reproduction, (4) plant community and diversity, (5) net primary production, and (6) biogeochemical cycle. After reviewing the effects on these variables observed with warming experiments, the following are discussed: i) differences in response speed between ecological variables, ii) local environment-dependence of warming effects, and iii) possible solutions to undesirable side-effects of OTC, such as snow deposition change, followed by future challenges for warming experiments in the ecosystems of these regions.

Effectiveness of strategies for the management and/or prevention of hypothermia within the adult perioperative environment

Inadvertent hypothermia is common in patients undergoing surgical procedures with a reported prevalence of perioperative hypothermia ranging from 50% to 90%. Hypothermia within the perioperative environment may have many undesired physiological effects that are associated with postoperative morbidity. There are different options for treating and/or preventing hypothermia within the adult perioperative environment, which include active and passive warming methods. This systematic review was undertaken to provide comprehensive evidence on the most effective strategies for prevention and management of inadvertent hypothermia in the perioperative environment. The objective of this review was to identify the most effective methods for the treatment and/or preventions of hypothermia in intraoperative or postoperative patients. Adult patients ≥ 18 years of age, who underwent any type of surgery were included in this review. Types of interventions included were any type of linen or cover, aluminium foil wraps, forced-air warming devices, radiant warming devices and fluid warming devices. This review considered all identified prospective studies that used a clearly described process for randomisation, and/or included a control group. The primary outcome of interest was change in core body temperature. Two independent reviewers assessed methodological validity of papers selected for retrieval and any disagreements were resolved through discussion. Nineteen studies with a combined 1451 patients who underwent different surgical procedures were included in this review. Meta-analysis was not possible. Forced-air warming in pregnant women scheduled for caesarean delivery under regional anaesthesia prevented maternal and foetal hypothermia. Intravenous and irrigating fluids warmed (38-40°C) to a temperature higher than that of room temperature by different fluid warming devices (both dry and water heated) proved significantly beneficial to patients in terms of stable haemodynamic variables, and higher core temperature at the end of the surgery. Water garment warmer was significantly (P < 0.05) effective than forced-air warming in maintaining intraoperative normothermia in orthotopic liver transplantation patients. Extra warming with forced air compared to routine thermal care was effective in reducing the incidence of surgical wound infections and postoperative cardiac complications. Passive warming with reflective heating blankets or elastic bandages wrapped around the legs tightly were found to be ineffective in reducing the incidence or magnitude of hypothermia. There are significant benefits associated with forced-air warming. Evidence supports commencement of active warming preoperatively and monitoring it throughout the intraoperative period. Single strategies such as forced-air warming were more effective than passive warming; however, combined strategies, including preoperative commencement, use of warmed fluids plus forced-air warming as other active strategies were more effective in vulnerable groups (age or durations of surgeries).

Microclimate impacts of passive warming methods in Antarctica: implications for climate change studies

Passive chambers are used to examine the impacts of summer warming in Antarctica but, so far, impacts occurring outside the growing season, or related to extreme temperatures, have not been reported, despite their potentially large biological significance. In this review, we synthesise and discuss the microclimate impacts of passive warming chambers (closed, ventilated and Open Top Chamber—OTC) commonly used in Antarctic terrestrial habitats, paying special attention to seasonal warming, during the growing season and outside, extreme temperatures and freeze–thaw events. Both temperature increases and decreases were recorded throughout the year. Closed chambers caused earlier spring soil thaw (8–28 days) while OTCs delayed soil thaw (3–13 days). Smaller closed chamber types recorded the largest temperature extremes (up to 20°C higher than ambient) and longest periods (up to 11 h) of above ambient extreme temperatures, and even OTCs had above ambient temperature extremes over up to 5 consecutive hours. The frequency of freeze–thaw events was reduced by ~25%. All chamber types experienced extreme temperature ranges that could negatively affect biological responses, while warming during winter could result in depletion of limited metabolic resources. The effects outside the growing season could be as important in driving biological responses as the mean summer warming. We make suggestions for improving season-specific warming simulations and propose that seasonal and changed temperature patterns achieved under climate manipulations should be recognised explicitly in descriptions of treatment effects.

Preventing Hypothermia: Comparison of Current Devices Used by the US Army in an In Vitro Warmed Fluid Model

The purpose of this study was to develop an in vitro torso model constructed with fluid bags and to determine whether this model could be used to differentiate between the heat prevention performance of devices with active chemical or radiant forced-air heating systems compared with passive heat loss prevention devices. We tested three active (Hypothermia Prevention Management Kit [HPMK], Ready-Heat, and Bair Hugger) and five passive (wool, space blankets, Blizzard blankets, human remains pouch, and Hot Pocket) hypothermia prevention products. Active warming devices included products with chemically or electrically heated systems. Both groups were tested on a fluid model warmed to 37 degrees C versus a control with no warming device. Core temperatures were recorded every 5 minutes for 120 minutes in total. Products that prevent heat loss with an actively heated element performed better than most passive prevention methods. The original HPMK achieved and maintained significantly higher temperatures than all other methods and the controls at 120 minutes (p < 0.05). None of the devices with an actively heated element achieved the sustained 44 degrees C that could damage human tissue if left in place for 6 hours. The best passive methods of heat loss prevention were the Hot Pocket and Blizzard blanket, which performed the same as two of the three active heating methods tested at 120 minutes. Our in vitro fluid bag "torso" model seemed sensitive to detect heat loss in the evaluation of several active or passive warming devices. All active and most passive devices were better than wool blankets. Under conditions near room temperature, passive warming methods (Blizzard blanket or the Hot Pocket) were as effective as active warming devices other than the original HPMK. Further studies are necessary to determine how these data can translate to field conditions in preventing heat loss in combat casualties.

Appropriate experimental ecosystem warming methods by ecosystem, objective, and practicality

The temperature of the Earth is rising, and is highly likely to continue to do so for the foreseeable future. The study of the effects of sustained heating on the ecosystems of the world is necessary so that we might predict and respond to coming changes on both large and small spatial scales. To this end, ecosystem warming studies have been performed for more than 20 years using a variety of methods. These warming methods fall into two general categories: active and passive. Active warming methods include heat-resistance cables, infrared (IR) lamps and active field chambers. Passive warming methods include nighttime warming and passive field chambers. An extensive literature review was performed and all ecosystem warming study sites were compiled into a master list. These studies were divided by latitude and precipitation, as well as the method type used and response variables investigated. The goals of this study were to identify: (1) the most generally applicable, inexpensive and effective heating methods; and (2) areas of the world that are understudied or have been studied using only limited warming methods. It was found that the most generally applicable method, and the one that is most true to climate change predictions, is IR heating lamp installation. The least expensive method is passive chambers. The extreme lower and upper latitudes have been investigated least with ecosystem warming methods, and for the upper-mid-latitudes (60–80°) there have been limited studies published using methods other than passive chambers. Ecosystem warming method limitations and recommendations are discussed.

Heat retention using passive systems during anaesthesia: comparison of two plastic wraps, one with reflective properties

Hypothermia during prolonged surgery may be prevented by active and passive warming methods. We have compared randomly two types of occlusive body wraps in groups of 20 patients. One wrap had additional reflective properties which, by reducing radiative in addition to convective and evaporative heat loss, was expected to improve heat conservation. Patients were studied during hepatopancreatobiliary surgery and both groups were similar in characteristics. Skin and core body temperatures increased and core temperature exceeded 37 degrees C in 40% of patients in both groups. This continuous increase in temperature was unexpected and the observed heat gain may have been stimulated endogenously by the type of surgery rather than that supplied externally. Overall, mean hourly heat gain was similar in both groups: 71 (SD 28) kJ h-1 in the reflective group and 67 (33) kJ h-1 in the other group.