Intraoperative core temperature patterns, transfusion requirement, and hospital duration in patients warmed with forced air. Anesthesiology. 2015;122:276-285. [PMID: 25603202 DOI: 10.1097/aln.0000000000000551]

Effects of perioperative warm socks-wearing in maintaining core body temperature of patients undergoing spinal surgery

AIMS AND OBJECTIVES

To investigate whether warming the feet with socks would prevent hypothermia among patients undergoing spinal surgery.

BACKGROUND

Perioperative hypothermia is a common health problem among spinal surgery patients.

RESEARCH DESIGN

This study used a quasi-experimental design.

METHODS

Seventy-two patients were assigned to two groups. The control group (n = 36) received usual care without the warmed socks. The intervention group (n = 36) received usual care plus warmed socks during operation and recovery period. Data were collected during (180 min) and after the surgery (30 min) during the period of 7 February-10 April 2015. Core body temperature, shivering response and subjective thermal comfort of the two groups were compared over time using the repeated-measures ANOVA.

RESULTS

The oesophageal temperature of the socks-wearing group was maintained between 36.36-36.45°C during surgery (mean = 36.41 ± 0.03, 95% CI = 36.34-36.47), whereas that of the control was between 35.75-35.97°C (mean = 35.98 ± 0.03, 95% CI = 35.92-36.04). The tympanic temperature in the recovery room of the socks-wearing group was between 36.28-36.38°C (mean = 36.37 ± 0.04, 95% CI = 36.29-36.45) and that of the control group was 35.90-36.04°C (mean = 35.95 ± 0.04, 95% CI = 35.88-36.05). Shivering response of the intervention group (mean = 0.04 ± 0.08, 95% CI = -0.13 to 0.21) was significantly lower than that of the control group (mean = 0.47 ± 0.08, 95% CI = 0.30-0.64) in the recovery room (F = 4.28, p < .001). As for subjective thermal comfort, the intervention group (mean = 4.86 ± 0.13, 95% CI = 4.62-5.13) was significantly lower than that of the control group (mean = 3.08 ± 0.13, 95% CI = 2.82-3.33) in the recovery room (F = 98.13, p < .001). As for the frequency of pethidine medication, the intervention group was significantly lower than that of the control (χ²  = 5.14, p = .023).

CONCLUSION

The use of perioperative warmed socks for spinal surgery patients was effective in maintaining perioperative core temperature, preventing shivering and maintaining subjective thermal comfort.

RELEVANCE TO CLINICAL PRACTICE

Considering cost-effectiveness of warmed socks, it might be worth trying option for the maintenance of core temperature in spinal surgery patients.

Warming of Irrigation Fluids for Prevention of Perioperative Hypothermia During Arthroscopy: A Systematic Review and Meta-analysis

PURPOSE

To determine whether warming of irrigation fluids (32°C-40°C) compared with using room-temperature irrigation fluids (20°C-22°C) decreases the risk of perioperative hypothermia (<36°C) for patients undergoing shoulder, hip, or knee arthroscopy.

METHODS

One reviewer, with the assistance of a medical librarian, searched the following databases: PubMed, Embase, Cochrane Central, SPORTDiscus, Web of Science, and CINAHL (Cumulative Index to Nursing and Allied Health Literature). Level I and II studies involving shoulder, hip, or knee arthroscopy were included. Two reviewers screened the abstracts and titles. Two reviewers assessed the risk of bias of selected studies using The Cochrane Collaboration tool. Meta-analyses were conducted on the following outcomes: hypothermia, lowest temperature, maximum temperature drop, and shivering.

RESULTS

Seven studies of patients undergoing arthroscopy were included in the qualitative synthesis (5 shoulder studies, 1 hip study, and 1 knee study; 501 patients). The study involving knee arthroscopy was excluded from the meta-analyses because of insufficient data and high clinical heterogeneity (surgical site distal to the core, not involving extravasation of large amounts of fluid). The remaining 6 studies were included in 1 or more meta-analyses: hypothermia (5 shoulder and 1 hip study), lowest temperature (3 shoulder and 1 hip study), maximum temperature drop (2 shoulder and 1 hip study), and shivering (5 shoulder and 1 hip study). Warming of irrigation fluids for shoulder or hip arthroscopy significantly decreased the risk of hypothermia (odds ratio, 0.15; 95% confidence interval [CI], 0.06-0.40; P = .0001), increased the lowest mean temperature (mean difference, 0.46°C; 95% CI, 0.11°C-0.81°C; P = .01), decreased the maximum temperature drop (mean difference, -0.64°C; 95% CI, -0.94°C to -0.35°C; P < .0001), and decreased the risk of shivering (odds ratio, 0.25; 95% CI, 0.07-0.86; P = .03).

CONCLUSIONS

When irrigation fluids are warmed for shoulder and hip arthroscopy, the risk of hypothermia is less, the drop in intraoperative temperature is less, the lowest body temperature is higher, and the risk of postoperative shivering is reduced.

LEVEL OF EVIDENCE

Level II, systematic review of Level I and II studies.

Blood-loss Management in Spine Surgery

Substantial blood loss during spine surgery can result in increased patient morbidity and mortality. Proper preoperative planning and communication with the patient, anesthesia team, and operating room staff can lessen perioperative blood loss. Advances in intraoperative antifibrinolytic agents and modified anesthesia techniques have shown promising results in safely reducing blood loss. The surgeon's attention to intraoperative hemostasis and the concurrent use of local hemostatic agents also can lessen intraoperative bleeding. Conversely, the use of intraoperative blood salvage has come into question, both for its potential inability to reduce the need for allogeneic transfusions as well as its cost-effectiveness. Allogeneic blood transfusion is associated with elevated risks, including surgical site infection. Thus, desirable transfusion thresholds should remain restrictive.

Intraoperative factors associated with postoperative complications in body contouring surgery

BACKGROUND

Several preoperative factors have been shown to influence outcome of body contouring surgeries. The effect of intraoperative features, including fluid volume administered, hemodynamic and respiratory parameters, and body temperature on postoperative complication, has not been reported to date.

MATERIALS AND METHODS

All subsequent patients undergoing body contouring surgery in the Tel Aviv Medical Center between 2007 and 2012 were enrolled. Demographic and intraoperative data were collected and analyzed for possible associations with postoperative complications, including formation of seroma, hematoma/bleeding, other surgical site complications (infection, adhesiolysis, or need for debridement), formation of a hypertrophic scar, any documented, infection or a composite outcome of any of the previously mentioned.

RESULTS

Data of 218 patients were assessed. Mean (standard deviation) age of patients was 41(14) y. Intraoperative administration of higher volumes of fluids was significantly associated with formation of seroma (P = 0.01), hematoma/bleeding (P = 0.03), hypertrophic scar (P = 0.01), surgical site complications (P = 0.01), and a composite outcome (P < 0.001). Development of hematoma/bleeding was associated with longer periods of low (<35.6°C) intraoperative core temperature (72% versus 50% of surgery duration in patients who did not develop this complication, P < 0.05). Surgical site complications were associated with longer periods of intraoperative oxygen desaturation (saturation ≤92%, 4.2% versus 0.9% of surgery duration in patients who did not develop surgical site complications, P < 0.01).

CONCLUSIONS

Intraoperative moderate hypothermia, hypoxemia, and liberal fluid administration are associated with worse surgical outcome in patients undergoing body contouring surgery. Increased awareness of the potential adverse effects of these factors in body contouring surgery will enhance interventions aimed at avoiding and promptly treating such events.

The impact of operative time and hypothermia in acute burn surgery

BACKGROUND

Prolonged operative time and intraoperative hypothermia are known to have deleterious effects on surgical outcomes. Although millions of burn injuries undergo operative treatment globally every year, there remains a paucity of evidence to guide perioperative practice in burn surgery. This study evaluated associations between hypothermia and operative time on post-operative complications in acute burn surgery.

METHOD

A historical cohort study from January 1, 2006 to October 31, 2015 was completed at an American Burn Association verified burn centre. 1111 consecutive patients undergoing acute burn surgery were included, and 2171 surgeries were analyzed. Primary outcomes included post-operative complications, defined a priori as either infectious or noninfectious. Statistical analysis was undertaken using a modified Poisson model for relative risk, adjusted for total body surface area, inhalation injury, co-morbidities, substance abuse, and age.

RESULTS

The mean operative time was 4.4h (SD 3.7-4.7h; range 0.58-11h), and 18.6% of patients became hypothermic intra-operatively. Operative time was independently associated with the incidence of hypothermia (p<0.05), and both infectious (RR1.5; 1.2-1.9, p<0.0004) and non-infectious complications (RR2.3; 1.3-4.1, p<0.0066). In patients with major burns (TBSA≥20%), hypothermia predisposed to infectious (RR1.3; 1.1-1.5, p<0.0017) and non-infectious complications (RR1.7; 1.2-2.5; p<0.0049). Risk stratification revealed that hypothermic patients with major burns undergoing prolonged surgery had an increased risk of both infectious (RR1.4; 1.1-1.7, p<0.0068) and non-infectious complications (RR1.8; 1.1-3.0, p<0.0132) when compared with those without these risk factors.

CONCLUSIONS

Patients who undergo prolonged surgeries and become hypothermic are more likely to develop complications. We therefore advocate for diligent adherence to strategies to prevent hypothermia and recommend limiting operative time in clinical circumstances where intraoperative measures are unlikely to adequately prevent hypothermia.

[Prewarming according to the AWMF S3 guidelines on preventing inadvertant perioperative hypothermia 2014 : Retrospective analysis of 7786 patients]

BACKGROUND

Inadvertent perioperative hypothermia, which is defined as a core body temperature of less than 36.0 °C, can have serious consequences in surgery patients. These include cardiac complications, increased blood loss, wound infections and postoperative shivering; therefore, the scientific evidence that inadvertent perioperative hypothermia should be avoided is undisputed and several national guidelines have been published summarizing the scientific evidence and recommending specific procedures. The German AWMF guidelines were the first to emphasize the importance of prewarming for surgery patients to avoid inadvertant perioperative hypothermia; however, in contrast to intraoperative warming, prewarming is so far not sufficiently implemented in clinical practice in many hospitals. Furthermore, a recent study has questioned the effectiveness of prewarming.

OBJECTIVE

The aim of this retrospective investigation was to evaluate the hypothermia rates that can be achieved when prewarming in the anesthesia induction room is introduced into the clinical practice and performed in addition to intraoperative warming.

MATERIAL AND METHODS

The ethics committee of the Medical Faculty of the Martin Luther University Halle Wittenberg gave approval for data storage and retrospective data analysis from the anesthesia database. According to the existing local standard operating procedure, prewarming with forced air was performed in addition to intraoperative warming in the anesthesia induction room in 3899 patients receiving general anesthesia with a duration of 30 min or longer from January 2015 to December 2016. The results were compared with a control group of 3887 patients from July 2012 to August 2014 who received intraoperative warming but were not subjected to prewarming. Tracheal intubation was carried out in all patients and temperature measurements after the induction of anesthesia were performed using esophageal, urinary catheter or intra-arterial temperature probes.

RESULTS

The mean duration of prewarming was 25 min in the treatment group. Patients subjected to prewarming showed an intraoperative hypothermia rate of 15.8% and a postoperative hypothermia rate of 5.1%. Patients without prewarming showed an intraoperative hypothermia rate of 30.4% and a postoperative hypothermia rate of 12.4%. This means a 52% reduction of the intraoperative hypothermia rate and a 41% reduction of the postoperative hypothermia rate for patients who received prewarmimg (p < 0.0001). Multivariate logistic regression revealed that the lack of prewarming was independently associated with intraoperative hypothermia with an odds ratio of 2.5 (95% confidence interval CI 2.250-2.841; p < 0.0001) and postoperative hypothermia with an odds ratio of 2.8 (95% CI 2.316-3.277; p < 0.0001).

CONCLUSION

Prewarming, as recommended in the AWMF guidelines, resulted in a significant and clinically relevant reduction in the incidence of inadvertent perioperative hypothermia; therefore, prewarming can still be regarded as an effective method to avoid perioperative hypothermia. Hypothermia rates of 15.8% intraoperatively and 5.1% postoperatively can be achieved in clinical practice, when prewarming is performed in addition to intraoperative warming in the anesthesia induction room directly before the start of surgical procedures.

Esophageal Heat Transfer for Patient Temperature Control and Targeted Temperature Management

Controlling patient temperature is important for a wide variety of clinical conditions. Cooling to normal or below normal body temperature is often performed for neuroprotection after ischemic insult (e.g. hemorrhagic stroke, subarachnoid hemorrhage, cardiac arrest, or other hypoxic injury). Cooling from febrile states treats fever and reduces the negative effects of hyperthermia on injured neurons. Patients are warmed in the operating room to prevent inadvertent perioperative hypothermia, which is known to cause increased blood loss, wound infections, and myocardial injury, while also prolonging recovery time. There are many reported approaches for temperature management, including improvised methods that repurpose standard supplies (e.g., ice, chilled saline, fans, blankets) but more sophisticated technologies designed for temperature management are typically more successful in delivering an optimized protocol. Over the last decade, advanced technologies have developed around two heat transfer methods: surface devices (water blankets, forced-air warmers) or intravascular devices (sterile catheters requiring vascular placement). Recently, a novel device became available that is placed in the esophagus, analogous to a standard orogastric tube, that provides efficient heat transfer through the patient's core. The device connects to existing heat exchange units to allow automatic patient temperature management via a servo mechanism, using patient temperature from standard temperature sensors (rectal, Foley, or other core temperature sensors) as the input variable. This approach eliminates vascular placement complications (deep venous thrombosis, central line associated bloodstream infection), reduces obstruction to patient access, and causes less shivering when compared to surface approaches. Published data have also shown a high degree of accuracy and maintenance of target temperature using the esophageal approach to temperature management. Therefore, the purpose of this method is to provide a low-risk alternative method for controlling patient temperature in critical care settings.

Forced air warming during sedation in the cardiac catheterisation laboratory: a randomised controlled trial

OBJECTIVE

Forced air warming (FAW) during general anaesthesia is a safe and effective intervention used to reduce hypothermia. The objective of this study was to determine if FAW reduces hypothermia when used for procedures performed with sedation in the cardiac catheterisation laboratory.

METHODS

A parallel-group randomised controlled trial was conducted. Adults receiving sedation in a cardiac catheterisation laboratory at two sites were randomised to receive FAW or usual care, which involved passive warming with heated cotton blankets. Hypothermia, defined as a temperature less than 36°C measured with a sublingual digital thermometer after procedures, was the primary outcome. Other outcomes were postprocedure temperature, shivering, thermal comfort and major complications.

RESULTS

A total of 140 participants were randomised. Fewer participants who received FAW were hypothermic (39/70, 56% vs 48/69, 70%, difference 14%; adjusted RR 0.75, 95% CI=0.60 to 0.94), and body temperature was 0.3°C higher (95% CI=0.1 to 0.5, p=0.004). FAW increased thermal comfort (63/70, 90% vs51/69, 74% difference 16%, RR 1.21, 95% CI=1.04 to 1.42). The incidence of shivering was similar (3/69, 4% vs 0/71 0%, difference 4%, 95% CI=-1.1 to 9.8). One patient in the control group required reintervention for bleeding. No other major complications occurred.

CONCLUSION

FAW reduced hypothermia and improved thermal comfort. The difference in temperature between groups was modest and less than that observed in previous studies where use of FAW decreased risk of surgical complications. Therefore, it should not be considered clinically significant.

TRIAL REGISTRATION NUMBER

ACTRN12616000013460.

Perioperative hypothermia during hip fracture surgery: An observational study

RATIONALE

Elderly patients are at high risk of accidental perioperative hypothermia. The primary objective of this study was to measure the changes in body temperature and the incidence of hypothermia in elderly patients undergoing hip fracture surgery.

METHODS

We conducted a prospective observational study on all adult patients undergoing surgery for fractured neck of femur between December 2013 and July 2014. We monitored their temperatures in different perioperative areas at multiple time points and also noted the warming methods used.

RESULTS

Eighty-seven patients were included in this study. A significant drop in body temperature (0.7°C, 95% CI: 0.6-0.9, P < 0.001) occurred from their arrival at the operating theatre until their arrival at the recovery room. A significant drop of 0.2°C (95% CI: 0.1-0.4, P < 0.001) was observed at the holding bay area. One third of the patients were noted to be hypothermic when they arrived at the recovery room.

CONCLUSION

These results indicate that despite the use of active warming methods for most patients, significant hypothermia is still an issue amongst elderly patients undergoing hip fracture surgery. Further improvement is necessary to prevent hypothermia in this high-risk group of patients.

Comparison of forced-air and water-circulating warming for prevention of hypothermia during transcatheter aortic valve replacement

Introduction

Transcatheter Aortic Valve Replacement (TAVR) procedures at our institution were complicated by perioperative hypothermia despite use of the standard of care forced-air convective warming device (the BairHugger, Augustine Medical Inc, Eden Prairie, MN, USA). To remedy this problem, we initiated a quality improvement process that investigated the use of a conductive warm water-circulating device (the Allon ThermoWrap, Menen Medical Corporation, Trevose, PA, USA), and hypothesized that it would decrease the incidence of perioperative hypothermia.

Methods

We compared two different intraoperative warming devices using a historic control. We retrospectively reviewed intraoperative records of 80 TAVRs between 6/2013 and 6/2015, 46 and 34 of which were done with the forced-air and water-circulating devices, respectively. Continuous temperature data obtained from pulmonary artery catheter, temperature upon arrival to cardiothoracic ICU (CTU), age, BSA, height, and BMI were compared.

Results

Patients warmed with both devices were similar in terms of demographic characteristics. First recorded intraoperative temperature (mean 36.26 ± SD 0.61 vs. 35.95 ± 0.46°C, p = 0.02), lowest intraoperative temperature (36.01 ± 0.58 vs. 34.89 ± 0.76°C, p<0.001), temperature at the end of the procedure (36.47 ± 0.51 vs. 35.17 ± 0.75°C, p<0.001), and temperature upon arrival to the CTU (36.35 ± 0.44 vs. 35.07 ± 0.78°C, p<0.001) were significantly higher in the water-circulating group as compared to the forced-air group.

Conclusion

A quality improvement process led to selection of a new warming device that virtually eliminated perioperative hypothermia at our institution. Patients warmed with the new device were significantly less likely to experience intraoperative hypothermia and were significantly more likely to be normothermic upon arrival to the CTU.

Warmed, humidified CO2 insufflation benefits intraoperative core temperature during laparoscopic surgery: A meta-analysis

BACKGROUND

Intraoperative hypothermia is linked to postoperative adverse events. The use of warmed, humidified CO₂ to establish pneumoperitoneum during laparoscopy has been associated with reduced incidence of intraoperative hypothermia. However, the small number and variable quality of published studies have caused uncertainty about the potential benefit of this therapy. This meta-analysis was conducted to specifically evaluate the effects of warmed, humidified CO₂ during laparoscopy.

METHODS

An electronic database search identified randomized controlled trials performed on adults who underwent laparoscopic abdominal surgery under general anesthesia with either warmed, humidified CO₂ or cold, dry CO₂ . The main outcome measure of interest was change in intraoperative core body temperature.

RESULTS

The database search identified 320 studies as potentially relevant, and of these, 13 met the inclusion criteria and were included in the analysis. During laparoscopic surgery, use of warmed, humidified CO₂ is associated with a significant increase in intraoperative core temperature (mean temperature change, 0.3°C), when compared with cold, dry CO₂ insufflation_. CONCLUSION: Warmed, humidified CO₂ insufflation during laparoscopic abdominal surgery has been demonstrated to improve intraoperative maintenance of normothermia when compared with cold, dry CO_2.

Factors that influence effective perioperative temperature management by anesthesiologists: a qualitative study using the Theoretical Domains Framework

PURPOSE

Inadvertent perioperative hypothermia (IPH) is associated with a range of adverse outcomes. Safe and effective warming techniques exist to prevent IPH; however, IPH remains common. This study aimed to identify factors that anesthesiologists perceive may influence temperature management during the perioperative period.

METHODS

After Research Ethics Board approval, semi-structured interviews were conducted with staff anesthesiologists at a Canadian academic hospital. An interview guide based on the Theoretical Domains Framework (TDF) was used to capture 14 theoretical domains that may influence temperature management. The interview transcripts were coded using direct content analysis to generate specific beliefs and to identify relevant TDF domains perceived to influence temperature management behaviour.

RESULTS

Data saturation was achieved after 15 interviews. The following nine theoretical domains were identified as relevant to designing an intervention for practices in perioperative temperature management: knowledge, beliefs about capabilities, beliefs about consequences, reinforcement, memory/attention/decision-making, environmental context and resources, social/professional role/identity, social influences, and behavioural regulation. Potential target areas to improve temperature management practices include interventions that address information needs about individual temperature management behaviour as well as patient outcome (feedback), increasing awareness of possible temperature management strategies and guidelines, and a range of equipment and surgical team dynamics that influence temperature management.

CONCLUSION

This study identified several potential target areas for future interventions from nine of the TDF behavioural domains that anesthesiologists perceive to drive their temperature management practices. Future interventions that aim to close the evidence-practice gap in perioperative temperature management may include these targets.

Effectiveness of active and passive warming for the prevention of inadvertent hypothermia in patients receiving neuraxial anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

Perioperative hypothermia is a common complication of anesthesia that can result in negative outcomes. The purpose of this review is to answer the question: Does the type of warming intervention influence the frequency or severity of inadvertent perioperative hypothermia (IPH) in surgical patients receiving neuraxial anesthesia?

DESIGN

Systematic review and meta-analysis.

SETTING

Perioperative care areas.

PATIENTS

Adults undergoing surgery with neuraxial anesthesia.

INTERVENTION

Perioperative active warming (AW) or passive warming (PW).

MEASUREMENTS

PubMed, CINAHL, Embase, and Cochrane Central Register of Controlled Trials were searched. Inclusion criteria were: randomized controlled trials; adults undergoing surgery with neuraxial anesthesia; comparison(s) of AW and PW; and temperature measured at end of surgery/upon arrival in the Postanesthesia Care Unit. Exclusion criteria were: no full-text available; not published in English; studies of: combined neuraxial and general anesthesia, warm intravenous or irrigation fluids without using AW, and rewarming after hypothermia. Two independent reviewers screened abstracts and titles, and selected records following full-text review. The Cochrane Collaboration's tool for assessing risk of bias was used to evaluate study quality. A random-effects model was used to calculate risk ratios for dichotomous data and mean differences for continuous data.

MAIN RESULTS

Of 1587 records, 25 studies (2048 patients) were included in the qualitative synthesis. Eleven studies (1189 patients) comparing AW versus PW were included in the quantitative analysis. Meta-analysis found that intraoperative AW is more effective than PW in reducing the incidence of IPH during neuraxial anesthesia (RR=0.71; 95% CI 0.61-0.83; p<0.0001; I²=32%). The qualitative synthesis revealed that IPH continues despite current AW technologies.

CONCLUSIONS

During neuraxial anesthesia, AW reduces IPH more effectively than PW. Even with AW, IPH persists in some patients. Continued innovation in AW technology and additional comparative effectiveness research studying different AW methods are needed.

Blood clotting behavior is innately modulated in Ursus americanus during early and late denning relative to summer months

Remarkably, American black bears (Ursus americanus) are capable of varying their heart rates to coincide with their breathing, creating pauses of 30 s or more, yet they do not appear to suffer from embolic events. We evaluated some features of the clotting cascade of black bears, providing novel insights into the underlying mechanisms they evoke for embolic protection during hibernation. We measured activated clotting time, prothrombin time and activated partial thromboplastin time during early denning (December), late denning (March) and summer (August). Activated clotting time during early hibernation was ∼3 times longer than that observed among non-hibernating animals. Clotting time was reduced later in hibernation, when bears were within ∼1 month of emerging from dens. Prothrombin time was similar for each seasonal time point, whereas activated partial thromboplastin time was highest during early denning and decreased during late denning and summer. We also examined D-dimer concentration to assess whether the bears were likely to have experienced embolic events. None of the non-parturient bears exceeded a D-dimer concentration of 250 ng ml^-1 (considered the clinical threshold for embolism in mammals). Our findings suggest there is unique expression of the clotting cascade in American black bears during hibernation, in which extrinsic pathways are maintained but intrinsic pathways are suppressed. This was evaluated by a significant difference between the activated clotting time and activated partial thromboplastin time during the denning and non-denning periods. These changes are likely adaptive, to avoid clotting events during states of immobilization and/or periods of asystole. However, an intact extrinsic pathway allows for healing of external injuries and/or foreign body responses.

Postoperative hypothermia and surgical site infection following peritoneal insufflation with warm, humidified carbon dioxide during laparoscopic colorectal surgery: a cohort study with cost-effectiveness analysis

Background

Surgical Site Infection (SSI) occurs in 9 % of laparoscopic colorectal surgery. Warming and humidifying carbon dioxide (CO₂) used for peritoneal insufflation may protect against SSI by avoiding postoperative hypothermia (itself a risk factor for SSI). This study aimed to assess the impact of CO₂ conditioning on postoperative hypothermia and SSI and to perform a cost-effectiveness analysis.

Methods

A retrospective cohort study of patients undergoing elective laparoscopic colorectal resection was performed at a single UK specialist centre. The control group (n = 123) received peritoneal insufflation with room temperature, dry CO₂, whereas the intervention group (n = 123) received warm, humidified CO₂ (using HumiGard™, Fisher & Paykel Healthcare). The outcomes were postoperative hypothermia, SSI and costs. Multivariate analysis was performed.

Results

A total of 246 patients were included in the study. The mean age was 68 (20–87) and mean BMI 28 (15–51). The primary diagnosis was cancer (n = 173), and there were no baseline differences between the groups. CO₂ conditioning significantly decreased the incidence of postoperative hypothermia (odds ratio 0.10, 95 % CI 0.04–0.23), with hypothermic patients found to be at increased risk of SSI (odds ratio 4.0, 95 % CI 1.25–12.9). Use of conditioned CO₂ significantly decreased the incidence of SSI by 66 % (p = 0.04). The intervention group incurred costs of £155 less per patient. The incremental cost-effectiveness ratio was negative.

Conclusion

CO₂ conditioning during laparoscopic colorectal surgery is a safe, feasible and a cost-effective intervention. It improves the quality of surgical care relating to SSI and postoperative hypothermia.

Perioperative Heat Loss Prevention-A Feasibility Trial

Preventing unplanned perioperative hypothermia is crucial. Thermal reflective blankets may reduce heat loss, promote normothermia, increase patient comfort, and decrease cotton blanket expenses. Our purpose was to determine whether a thermal reflective blanket plus one warmed cotton blanket provides better temperature control and thermal comfort than warmed cotton blankets only. We compared two groups of perioperative patients who received a thermal reflective blanket plus one warmed cotton blanket (n = 110) or warmed cotton blankets only (n = 114) for temperature control and comfort, and we evaluated outcomes in the preoperative holding area, the OR, and the postanesthesia care unit. There were no significant differences in patient temperature or comfort between groups. Use of thermal reflective blankets led to significantly reduced use of warmed cotton blankets (t₂₀₉ = -10.51, P < .001), and a cost threshold for clinical adoption was identified. The hospital opted not to purchase thermal reflective blankets because of equivalent performance and minimal cost savings.

Time Trends and Predictors of Abnormal Postoperative Body Temperature in Infants Transported to the Intensive Care Unit

Background. Despite increasing adoption of active warming methods over the recent years, little is known about the effectiveness of these interventions on the occurrence of abnormal postoperative temperatures in sick infants. Methods. Preoperative and postoperative temperature readings, patient characteristics, and procedural factors of critically ill infants at a single institution were retrieved retrospectively from June 2006 until May 2014. The primary endpoints were the incidence and trend of postoperative hypothermia and hyperthermia on arrival at the intensive care units. Univariate and adjusted analyses were performed to identify factors independently associated with abnormal postoperative temperatures. Results. 2,350 cases were included. 82% were normothermic postoperatively, while hypothermia and hyperthermia each occurred in 9% of cases. During the study period, hypothermia decreased from 24% to 2% (p < 0.0001) while hyperthermia remained unchanged (13% in 2006, 8% in 2014, p = 0.357). Factors independently associated with hypothermia were higher ASA status (p = 0.02), lack of intraoperative convective warming (p < 0.001) and procedure date before 2010 (p < 0.001). Independent associations for postoperative hyperthermia included lower body weight (p = 0.01) and procedure date before 2010 (p < 0.001). Conclusions. We report an increase in postoperative normothermia rates in critically ill infants from 2006 until 2014. Careful monitoring to avoid overcorrection and hyperthermia is recommended.

Effect of Prewarming during Induction of Anesthesia on Microvascular Reactivity in Patients Undergoing Off-Pump Coronary Artery Bypass Surgery: A Randomized Clinical Trial

Background

General anesthesia may induce inadvertent hypothermia and this may be related to perioperative cardiovascular complications. Microvascular reactivity, measured by the recovery slope during a vascular occlusion test, is decreased during surgery and is also related to postoperative clinical outcomes. We hypothesized that microvascular changes during surgery may be related to intraoperative hypothermia. To evaluate this, we conducted a randomized study in patients undergoing off-pump coronary artery bypass surgery, in which the effect of prewarming on microvascular reactivity was evaluated.

Methods

Patients scheduled for off-pump coronary artery bypass surgery were screened. Enrolled patients were randomized to the prewarming group to receive forced-air warming during induction of anesthesia or to the control group. Measurement of core and skin temperatures and vascular occlusion test were conducted before anesthesia induction, 1, 2, and 3 h after induction, and at the end of surgery.

Results

In total, 40 patients were enrolled and finished the study (n = 20 in the prewarming group and n = 20 in the control group). During the first 3 h of anesthesia, core temperature was higher in the prewarming group than the control group (p < 0.001). The number of patients developing hypothermia was lower in the prewarming group than the control group (4/20 vs. 13/20, p = 0.004). However, tissue oxygen saturation and changes in recovery slope following a vascular occlusion test at 3 h after anesthesia induction did not differ between the groups. There was no difference in clinical outcome, including perioperative transfusion, wound infection, or hospital stay, between the groups.

Conclusions

Prewarming during induction of anesthesia decreased intraoperative hypothermia, but did not reduce the deterioration in microvascular reactivity in patients undergoing off-pump coronary artery bypass surgery.

Trial Registration

ClinicalTrials.gov NCT02186210

Active perioperative patient warming using a self-warming blanket (BARRIER EasyWarm) is superior to passive thermal insulation: a multinational, multicenter, randomized trial

STUDY OBJECTIVE

Incidence of inadvertent perioperative hypothermia is still high; therefore, present guidelines advocate "prewarming" for its prevention. Prewarming means preoperative patient skin warming, which minimizes redistribution hypothermia caused by induction of anesthesia. In this study, we compared the new self-warming BARRIER EasyWarm blanket with passive thermal insulation regarding mean perioperative patient core body temperature.

DESIGN

Multinational, multicenter randomized prospective open-label controlled trial.

SETTING

Surgical ward, operation room, postanesthesia care unit at 4 European hospitals.

PATIENTS

A total of 246 adult patients, American Society of Anesthesiologists class I to III undergoing elective orthopedic; gynecologic; or ear, nose, and throat surgery scheduled for 30 to 120 minutes under general anesthesia.

INTERVENTIONS

Patients received warmed hospital cotton blankets (passive thermal insulation, control group) or BARRIER EasyWarm blanket at least 30 minutes before induction of general anesthesia and throughout the perioperative period (intervention group).

MEASUREMENTS

The primary efficacy outcome was the perioperative mean core body temperature measured by a tympanic infrared thermometer. Secondary outcomes were hypothermia incidence, change in core body temperature, length of stay in postanesthesia care unit, thermal comfort, patient satisfaction, ease of use, and adverse events related to the BARRIER EasyWarm blanket.

MAIN RESULTS

The BARRIER EasyWarm blanket significantly improved perioperative core body temperature compared with standard hospital blankets (36.5°C, SD 0.4°C, vs 36.3, SD 0.3°C; P<.001). Intraoperatively, in the intervention group, hypothermia incidence was 38% compared with 60% in the control group (P=.001). Postoperatively, the figures were 24% vs 49%, respectively (P=.001). Patients in the intervention group had significantly higher thermal comfort scores, preoperatively and postoperatively. No serious adverse effects were observed in either group.

CONCLUSIONS

Perioperative use of the new self-warming blanket improves mean perioperative core body temperature, reduces the incidence of inadvertent perioperative hypothermia, and improves patients' thermal comfort during elective adult surgery.

Perioperative thermoregulation and heat balance

Core body temperature is normally tightly regulated to within a few tenths of a degree. The major thermoregulatory defences in humans are sweating, arteriovenous shunt vasoconstriction, and shivering. The core temperature triggering each response defines its activation threshold. General anaesthetics greatly impair thermoregulation, synchronously reducing the thresholds for vasoconstriction and shivering. Neuraxial anaesthesia also impairs central thermoregulatory control, and prevents vasoconstriction and shivering in blocked areas. Consequently, unwarmed anaesthetised patients become hypothermic, typically by 1-2°C. Hypothermia results initially from an internal redistribution of body heat from the core to the periphery, followed by heat loss exceeding metabolic heat production. Complications of perioperative hypothermia include coagulopathy and increased transfusion requirement, surgical site infection, delayed drug metabolism, prolonged recovery, shivering, and thermal discomfort. Body temperature can be reliably measured in the oesophagus, nasopharynx, mouth, and bladder. The standard-of-care is to monitor core temperature and to maintain normothermia during general and neuraxial anaesthesia.

Forced air warming to maintain normoTHERMIa during SEDation in the cardiac catheterization laboratory: protocol for the THERMISED pilot randomized controlled trial

AIM

To determine whether applying forced air warming attenuates the impact of sedation-induced impairment of thermoregulation on body temperature of patients who are sedated during interventional procedures in the cardiac catheterization laboratory.

BACKGROUND

A moderate proportion of sedated patients who undergo procedures in the cardiac catheterization laboratory with only passive warming become hypothermic. Hypothermia in the surgical population is associated with increased risk of adverse cardiac events, infections, thrombotic and haemorrhagic complications and prolonged hospital stay. For this reason, investigation of the clinical benefits of preventing hypothermia in sedated patients using active warming is required.

DESIGN

Randomized controlled trial.

METHODS

A total of 140 participants undergoing elective interventional procedures with sedation in a cardiac catheterization laboratory will be recruited from two hospitals in Australia. Participants will be randomized to receive forced air warming (active warming) or usual care (passive warming with heated cotton blankets) throughout procedures. The primary outcome is hypothermia (defined as temperature less than 36°C) at the conclusion of the procedure. Secondary outcomes are postprocedure temperature, postprocedural shivering, thermal discomfort, major complications, disability-free survival to 30 days postprocedure, cost-effectiveness and feasibility of conducting a larger clinical trial.

DISCUSSION

The results from this study will provide high-level evidence for practice in an area where there is currently no guidance. Findings will be easily translatable into clinical practice because most hospitals already have forced air warming equipment available for use during general anaesthesia.

REGISTRATION NUMBER

ACTRN12616000013460.

Perioperative hypothermia: Causes, consequences and treatment

Perioperative hypothermia, core temperature below 36.0 °C, transpires due to disruption of thermoregulation by anesthesia coupled with cold exposure to procedural surroundings and cleansing agents. Although most publications have focused on thermoregulation disruption with general anesthesia, neuraxial anesthesia may also cause significant hypothermia. The clinical consequences of perioperative hypothermia are multiple and include patient discomfort, shivering, platelet dysfunction, coagulopathy, and increased vasoconstriction associated with a higher risk of wound infection. Furthermore, postoperative cardiac events occur at a higher rate; although it is unclear whether this is due to increased oxygen consumption or norepinephrine levels. Hypothermia may also affect pharmacokinetics and prolong postoperative recovery times and hospital length of stay. In order to combat perioperative hypothermia, many prevention strategies have been examined. Active and passive cutaneous warming are likely the most common and aim to both warm and prevent heat loss; many consider active warming a standard of care for surgeries over one hour. Intravenous nutrients have also been examined to boost metabolic heat production. Additionally, pharmacologic agents that induce vasoconstriction have been studied with the goal of minimizing heat loss. Despite these multiple strategies for prevention and treatment, hypothermia continues to be a problem and a common consequence of the perioperative period. This literature review presents the most recent evidence on the disruption of temperature regulation by anesthesia and perioperative environment, the consequences of hypothermia, and the methods for hypothermia prevention and treatment.

Heat Transfer in Health and Healing

Our bodies depend on an exquisitely sensitive and refined temperature control system to maintain a state of health and homeostasis. The exceptionally broad range of physical activities that humans engage in and the diverse array of environmental conditions we face require remarkable strategies and mechanisms for regulating internal and external heat transfer processes. On the occasions for which the body suffers trauma, therapeutic temperature modulation is often the approach of choice for reversing injury and inflammation and launching a cascade of healing. The focus of human thermoregulation is maintenance of the body core temperature within a tight range of values, even as internal rates of energy generation may vary over an order of magnitude, environmental convection, and radiation heat loads may undergo large changes in the absence of any significant personal control, surface insulation may be added or removed, all occurring while the body's internal thermostat follows a diurnal circadian cycle that may be altered by illness and anesthetic agents. An advanced level of understanding of the complex physiological function and control of the human body may be combined with skill in heat transfer analysis and design to develop life-saving and injury-healing medical devices. This paper will describe some of the challenges and conquests the author has experienced related to the practice of heat transfer for maintenance of health and enhancement of healing processes.