An evaluation of underbody forced-air and resistive heating during hypothermic, on-pump cardiac surgery*

A Warm Air Blanket is Superior to a Heated Mattress in Preventing Perioperative Hypothermia in Orthopedic Arthroplasties, a Time-Series Analyses

BACKGROUND

Hypothermia is a common perioperative problem that can lead to severe complications. We evaluated whether a heated mattress (HM) is superior to a warm air blanket (WA) in preventing perioperative hypothermia in patients undergoing total hip arthroplasty (THA) or total knee arthroplasty (TKA).

METHODS

A retrospective cohort study was performed in a teaching hospital and data were collected for all patients undergoing THA or TKA between January 1, 2015 and May 1, 2022. We used logistic and linear regressions to analyze hypothermia occurrence and important complications. Results were adjusted for confounders and time, and was present in all subgroups and after imputation of missing data.

RESULTS

In total, 4,683 of 5,497 patients had information on type of heating. We found more perioperative hypothermia in patients treated with an HM compared to a WA for both THA (odds ratio-adjusted 1.42 [1.0 to 1.6] P = .06) and TKA (odds ratio-adjusted 2.10 [1.5 to 3.0] P < .01). There was no difference in postoperative infections between groups (all between 0.5% and 1.3%). Patients who had an HM significantly stayed longer in the postoperative ward (a mean difference of 4 [TKA] to 6 [THA] minutes, P < .01), but there was no difference in hospital stay.

CONCLUSION

A WA is superior compared to an HM in preventing perioperative hypothermia, with no increased risk of complications. Patients who have an HM stayed longer at the postoperative ward, potentially because of higher hypothermia rates. Therefore, it is suggested to use a WA instead of an HM.

Health Technology Assessment for the Prevention of Peri-Operative Hypothermia: Evaluation of the Correct Use of Forced-Air Warming Systems in an Italian Hospital

This study investigates the implications of using a system for the maintenance of normothermia in the treatment of patients undergoing surgery, determining whether the FAW (Forced-Air Warming) systems are more effective and efficient than the non-application of appropriate protocols (No Technology). We conducted Health Technology Assessment (HTA) analysis, using both real-world data and the data derived from literature, assuming the point of view of a medium-large hospital. The literature demonstrated that Inadvertent Perioperative Hypothermia (IPH) determines adverse events, such as surgical site infection (FAW: 3% vs. No Technology: 12%), cardiac events (FAW: 3.5% vs. No Technology: 7.6%) or the need for blood transfusions (FAW: 6.2% vs. No Technology: 7.4%). The correct use of FAW allows a medium saving of 16% per patient to be achieved, compared to the non-use of devices. The Cost Effectiveness Value (CEV) is lower in the hypothesis of FAW: it enables a higher efficacy level with a contextual optimization of patients' path costs. The social cost is reduced by around 30% and the overall hospital days are reduced by between 15% and 26%. The qualitative analyses confirmed the results. In conclusion, the evidence-based information underlines the advantages of the proper use of FAW systems in the prevention of accidental peri-operative hypothermia for patients undergoing surgery.

Reoperation for bleeding after cardiac surgery

BACKGROUND

Postoperative cardio-surgical haemostatic management is centre-specific and experience-based, which leads to a variability in patient care. This study aimed to identify which postoperative haemostatic interventions may reduce the need for reoperation after cardiac surgery in adults.

METHODS

A retrospective case-control study in a tertiary centre. Adult, elective, primary cardiac surgical patients were selected (n = 2098); cases (n = 42) were patients who underwent reoperation within 72 h after the initial surgery. Interventions administered to control surgical bleeding were compared for the need to re-operate using multiple logistic regression.

RESULTS

Rate of cardiac surgical reoperation was 2% in the study population. Three variables were found to be associated with cardiac reoperation: preoperative administration of fresh frozen plasma (OR 5.45, CI 2.34-12.35), cumulative volume of chest tube drainage and cumulative count of packed red blood cells transfusion on ICU (OR 1.98, CI 1.56-2.51).

CONCLUSION

No significant difference among specific types of postoperative haemostatic interventions was found between patients who needed reoperation and those who did not. Perioperative transfusion of fresh frozen plasma, postoperative transfusion of packed cells and cumulative volume of chest tube drainage were associated with reoperation after cardiac surgery. These variables could help predict the need for reoperation.

Resistant fabric warming is a viable alternative to forced-air warming to prevent inadvertent perioperative hypothermia during hemiarthroplasty in the elderly

BACKGROUND

Surgical site infection (SSI) is associated with inadvertent perioperative hypothermia (IPH). This can be prevented by active patient warming. However, results from comparisons of warming techniques are conflicting. They are based mostly on elective surgery, are from small numbers of patients, and are dominated by the market leader, forced-air warming (FAW). Furthermore, the definition of hypothermia is debatable and systematic reviews of warming systems conclude that a stricter control of temperature is required to study the benefits of warming.

AIM

To analyse core temperatures in detail in a large subset of elderly patients who took part in a randomized trial of patient warming following hemiarthroplasty who had received constant zero-flux thermometry to record their temperature.

METHODS

Regression models with a fixed effect for warming group and covariates related to temperature were compared for 257 participants randomized to FAW or resistant fabric warming (RFW) from a prior clinical trial.

FINDINGS

Those in the RFW group were -0.08°C cooler and had a cumulative hypothermia score -1.87 lower than those in the FAW group. There was no difference in the proportion of hypothermic patients at either <36.5°C or <36.0°C.

CONCLUSIONS

This is the first study to provide accurate temperature measurements in patients undergoing a procedure predominantly under regional rather than general anaesthetic. It shows that RFW is a viable alternative to FAW for preventing IPH during hemiarthroplasty. Further studies are needed to measure the benefits of patient warming in terms of clinically important outcomes.

Underbody blankets have a higher heating effect than overbody blankets in lithotomy position endoscopic surgery under general anesthesia: a randomized trial

BACKGROUND

Surgery under general anesthesia results in temperature decrease due to the effect of anesthetics and peripheral vasodilation on thermoregulatory centers. Perioperative temperature control is therefore an issue of high importance. In this study, we aimed to compare the warming effect of underbody and overbody blankets in patients undergoing surgery in the lithotomy position under general anesthesia.

METHODS

From September 2018 to October 2019, 99 patients undergoing surgery for colorectal cancer in the lithotomy position were included in this randomized controlled trial and assigned to the intervention group (underbody blanket) or control group (overbody blanket).

RESULTS

The central temperature was significantly higher in the underbody blanket group than in the overbody blanket group at 90 min after the beginning of the surgery (p = 0.02); also in this group, the peripheral temperature was significantly higher 60 min after the beginning of the surgery (p = 0.02). Regarding postoperative factors, the underbody blanket group had a significantly lower frequency of postoperative shivering (p < 0.01) and a significantly shorter postoperative hospital stay (p = 0.04) than the overbody blanket group.

CONCLUSIONS

We recommend the use of underbody blankets for intraoperative temperature control in patients undergoing surgery in the lithotomy position under general anesthesia. Underbody blankets showed improved rise and maintenance of central and peripheral temperature, decreased the incidence of postoperative shivering, and shortened the postoperative length of hospital stay.

Surgical Site Infections in Cardiac Surgery

Surgical site infection (SSI) can be a significant complication of cardiac surgery, delaying recovery and acting as a barrier to enhanced recovery after cardiac surgery. Several risk factors predisposing patients to SSI including smoking, excessive alcohol intake, hyperglycemia, hypoalbuminemia, hypo- or hyperthermia, and Staphylococcus aureus colonization are discussed. Various measures can be taken to abolish these factors and minimize the risk of SSI. Glycemic control should be optimized preoperatively, and hyperglycemia should be avoided perioperatively with the use of intravenous insulin infusions. All patients should receive topical intranasal Staphylococcus aureus decolonization and intravenous cephalosporin if not penicillin allergic.

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.

Comparing Forced-Air to Resistive-Polymer Warming for Perioperative Temperature Management: A Retrospective Study

PURPOSE

Compare perioperative temperature management between forced-air warming (FAW) and resistive-polymer heating blankets (RHBs).

DESIGN

A retrospective, quasi-experimental study.

METHODS

Retrospective data analysis of nonspine orthopedic cases (N = 426) over a one-year period including FAW (n = 119) and RHBs (n = 307).

FINDINGS

FAW was associated with a significantly higher final intraoperative temperature (P = .001, d = 0.46) than the RHB. The incidence of hypothermia was not found to be significantly different at the end (P = .102) or anytime throughout surgery (P = .270). Of all patients who started hypothermic, the FAW group had a lower incidence of hypothermia at the end of surgery (P = .023).

CONCLUSIONS

FAW was associated with higher final temperatures and a greater number of normothermic patients than RHBs. However, no causal relationship between a warming device and hypothermia incidence should be assumed.

Heating and Cooling Rates With an Esophageal Heat Exchange System

BACKGROUND

The Esophageal Cooling Device circulates warm or cool water through an esophageal heat exchanger, but warming and cooling efficacy in patients remains unknown. We therefore determined heat exchange rates during warming and cooling.

METHODS

Nineteen patients completed the trial. All had general endotracheal anesthesia for nonthoracic surgery. Intraoperative heat transfer was measured during cooling (exchanger fluid at 7°C) and warming (fluid at 42°C). Each was evaluated for 30 minutes, with the initial condition determined randomly, starting at least 40 minutes after induction of anesthesia. Heat transfer rate was estimated from fluid flow through the esophageal heat exchanger and inflow and outflow temperatures. Core temperature was estimated from a zero-heat-flux thermometer positioned on the forehead.

RESULTS

Mean heat transfer rate during warming was 18 (95% confidence interval, 16-20) W, which increased core temperature at a rate of 0.5°C/h ± 0.6°C/h (mean ± standard deviation). During cooling, mean heat transfer rate was -53 (-59 to -48) W, which decreased core temperature at a rate of 0.9°C/h ± 0.9°C/h.

CONCLUSIONS

Esophageal warming transferred 18 W which is considerably less than the 80 W reported with lower or upper body forced-air covers. However, esophageal warming can be used to supplement surface warming or provide warming in cases not amenable to surface warming. Esophageal cooling transferred more than twice as much heat as warming, consequent to the much larger difference between core and circulating fluid temperature with cooling (29°C) than warming (6°C). Esophageal cooling extracts less heat than endovascular catheters but can be used to supplement catheter-based cooling or possibly replace them in appropriate patients.

The opinions of ambulance personnel regarding using a heated mattress for patients being cared for in a cold climate - An intervention study in ambulance care

The purpose of the study was to describe the opinions of ambulance personnel regarding differences between using a heated mattress and a standard ambulance mattress. This study was an intervention study with pre- and post-evaluation. Evaluations of the opinions of personnel regarding the standard unheated mattress were conducted initially. After the intervention with new heated mattresses, follow-up evaluations were conducted. Ambulance personnel (n=64) from an ambulance station in northern Sweden took part in the study, which ran from October 2014 until February 2016. There were differences in opinions regarding the standard unheated mattress and the new heated mattress. The evaluation of the proxy ratings by the personnel showed that the heated mattress was warmer than the standard mattress, more pleasant to lie on and that patients were happier and more relaxed than when the standard mattress was used. The ambulance personnel in this study rated the experience of working with the heated mattress as very positive and proxy rated that it had a good effect on patient comfort. A heated mattress can be recommended for patients in ambulance care, even if more research is needed to receive sufficient evidence.

Forced-Air Warming in Patients Undergoing Endovascular Procedures: Comparison between 2 Thermal Blanket Models

BACKGROUND

The purpose of this study was to compare the efficiency between 2 thermal blanket models: the upper blanket and the underbody blanket in patient heating and hypothermia prevention during endovascular surgery.

METHODS

Fifty patients, American Society of Anesthesiologists physical status 2-4, receiving endovascular surgery repair of infrarenal abdominal aortic aneurysm or lower limb angioplasty by endovascular technique were studied. Primary outcome was to determine which forced-air blanket is more warming effective during the surgeries. Age, type of surgery, gender, body mass index, surgery duration, and initial patient temperature were analyzed to determine possible hypothermia association as secondary outcomes. Patients were randomized and split into 2 groups based on blanket model. All patients received general anesthesia, and temperature was obtained by an esophageal thermometer inserted after tracheal intubation and registered at intervals of 15 min until extubation.

RESULTS

Groups significantly differed in body temperature (P = 0.006) and hypothermia occurrence (P = 0.020). The underbody blanket group hada higher ratio of hypothermic patients and a lower average temperature at the end of surgery. The average temperature after 60 min in the underbody blanket group was lower than the upper blanket group,although this difference was only significant after 150 min (P = 0.020).

CONCLUSIONS

We conclude that upper thermal blanket is more effective thanunderbody thermal blanket in patient warming and hypothermia prevention during endovascular abdominal aortic aneurysm repair and lower limb angioplasty after 150 min of anesthetic-surgical time duration.

Consensus Review of Optimal Perioperative Care in Breast Reconstruction: Enhanced Recovery after Surgery (ERAS) Society Recommendations

BACKGROUND

Enhanced recovery following surgery can be achieved through the introduction of evidence-based perioperative maneuvers. This review aims to present a consensus for optimal perioperative management of patients undergoing breast reconstructive surgery and to provide evidence-based recommendations for an enhanced perioperative protocol.

METHODS

A systematic review of meta-analyses, randomized controlled trials, and large prospective cohorts was conducted for each protocol element. Smaller prospective cohorts and retrospective cohorts were considered only when higher level evidence was unavailable. The available literature was graded by an international panel of experts in breast reconstructive surgery and used to form consensus recommendations for each topic. Each recommendation was graded following a consensus discussion among the expert panel. Development of these recommendations was endorsed by the Enhanced Recovery after Surgery Society.

RESULTS

High-quality randomized controlled trial data in patients undergoing breast reconstruction informed some of the recommendations; however, for most items, data from lower level studies in the population of interest were considered along with extrapolated data from high-quality studies in non-breast reconstruction populations. Recommendations were developed for a total of 18 unique enhanced recovery after surgery items and are discussed in the article. Key recommendations support use of opioid-sparing perioperative medications, minimal preoperative fasting and early feeding, use of anesthetic techniques that decrease postoperative nausea and vomiting and pain, use of measures to prevent intraoperative hypothermia, and support of early mobilization after surgery.

CONCLUSION

Based on the best available evidence for each topic, a consensus review of optimal perioperative care for patients undergoing breast reconstruction is presented.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Temperature management under general anesthesia: Compulsion or option

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

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.

Thermogenesis induced by amino acid administration prevents intraoperative hypothermia and reduces postoperative infectious complications after thoracoscopic esophagectomy

Minimally invasive thoracoscopic esophagectomy has potential advantages in minimizing the impairment of respiratory function and reducing surgical stress. However, thoracoscopic esophagectomy occasionally results in anesthesia-induced hypothermia, particularly in cases involving artificial pneumothorax with CO2. Thermogenesis induced by amino acid administration has been reported during anesthesia. Here, we tested the efficacy of amino acid treatment for the prevention of hypothermia, and we investigated the potential of this treatment to reduce postoperative infectious complications after thoracoscopic esophagectomy. We conducted a randomized trial in patients with esophageal cancer who underwent thoracoscopic esophagectomy in the prone position in two groups and analyzed the incidences of hypothermia and surgical complications. One-hundred and thirty patients were randomized. Administration of amino acids resulted in a significant increase in core body temperature. In the saline (n = 60) and amino acid (n = 70) administration groups, 30% and 14.2% of patients, respectively, experienced infectious surgical complications (P = 0.029), and 21.6% and 22.8% of patients, respectively, experienced noninfectious surgical complications (P = 0.86). Univariate analysis revealed that blood loss and amino acid administration were significant factors for infectious surgical complications. Multivariate analysis revealed that amino acid administration was an independent factor reducing infectious surgical complications (P = 0.025, 95% confidence interval: 0.105-0.864). Administration of amino acids prevents hypothermia and reduces postoperative infectious complications after thoracoscopic esophagectomy.

Comparison of resistive heating and forced-air warming to prevent inadvertent perioperative hypothermia

BACKGROUND

Forced-air warming is a commonly used warming modality, which has been shown to reduce the incidence of inadvertent perioperative hypothermia (<36°C). The reusable resistive heating mattresses offer a potentially cheaper alternative, however, and one of the research recommendations from the National Institute for Health and Care Excellence was to evaluate such devices formally. We conducted a randomized single-blinded study comparing perioperative hypothermia in patients receiving resistive heating or forced-air warming.

METHODS

A total of 160 patients undergoing non-emergency surgery were recruited and randomly allocated to receive either forced-air warming (n=78) or resistive heating (n=82) in the perioperative period. Patient core temperatures were monitored after induction of anaesthesia until the end of surgery and in the recovery room. Our primary outcome measures included the final intraoperative temperature and incidence of hypothermia at the end of surgery.

RESULTS

There was a significantly higher rate of hypothermia at the end of surgery in the resistive heating group compared with the forced-air warming group (P=0.017). Final intraoperative temperatures were also significantly lower in the resistive heating group (35.9 compared with 36.1°C, P=0.029). Hypothermia at the end of surgery in both warming groups was common (36% forced air warming, 54% resistive heating).

CONCLUSION

Our results suggest that forced-air warming is more effective than resistive heating in preventing postoperative hypothermia.

CLINICAL TRIAL REGISTRATION

NCT01056991.

Effect evaluation of a heated ambulance mattress-prototype on thermal comfort and patients' temperatures in prehospital emergency care--an intervention study

Background

The ambulance milieu does not offer good thermal comfort to patients during the cold Swedish winters. Patients’ exposure to cold temperatures combined with a cold ambulance mattress seems to be the major factor leading to an overall sensation of discomfort. There is little research on the effect of active heat delivered from underneath in ambulance care. Therefore, the aim of this study was to evaluate the effect of an electrically heated ambulance mattress-prototype on thermal comfort and patients’ temperatures in the prehospital emergency care.

Methods

A quantitative intervention study on ambulance care was conducted in the north of Sweden. The ambulance used for the intervention group (n=30) was equipped with an electrically heated mattress on the regular ambulance stretcher whereas for the control group (n=30) no active heat was provided on the stretcher. Outcome variables were measured as thermal comfort on the Cold Discomfort Scale (CDS), subjective comments on cold experiences, and finger, ear and air temperatures.

Results

Thermal comfort, measured by CDS, improved during the ambulance transport to the emergency department in the intervention group (p=0.001) but decreased in the control group (p=0.014). A significant higher proportion (57%) of the control group rated the stretcher as cold to lie down compared to the intervention group (3%, p<0.001). At arrival, finger, ear and compartment air temperature showed no statistical significant difference between groups. Mean transport time was approximately 15 minutes.

Conclusions

The use of active heat from underneath increases the patients’ thermal comfort and may prevent the negative consequences of cold stress.

Effect evaluation of a heated ambulance mattress-prototype on body temperatures and thermal comfort--an experimental study

Background

Exposure to cold temperatures is, often, a neglected problem in prehospital care. One of the leading influences of the overall sensation of cold discomfort is the cooling of the back. The aim of this study was to evaluate the effect of a heated ambulance mattress-prototype on body temperatures and thermal comfort in an experimental study.

Method

Data were collected during four days in November, 2011 inside and outside of a cold chamber. All participants (n = 23) participated in two trials each. In one trial, they were lying on a stretcher with a supplied heated mattress and in the other trial without a heated mattress. Outcomes were back temperature, finger temperature, core body temperature, Cold Discomfort Scale (CDS), four statements from the state-trait anxiety – inventory (STAI), and short notes of their experiences of the two mattresses. Data were analysed both quantitatively and qualitatively. A repeated measure design was used to evaluate the effect of the two mattresses.

Results

A statistical difference between the regular mattress and the heated mattress was found in the back temperature. In the heated mattress trial, the statement “I am tense” was fewer whereas the statements “I feel comfortable”, “I am relaxed” and “I feel content” were higher in the heated mattress trial. The qualitative analyses of the short notes showed that the heated mattress, when compared to the unheated mattress, was experienced as warm, comfortable, providing security and was easier to relax on.

Conclusions

Heat supply from underneath the body results in increased comfort and may prevent hypothermia which is important for injured and sick patients in ambulance care.

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.