Skin-surface Warming Research Articles

Effect of pre-warming on perioperative hypothermia during holmium laser enucleation of the prostate under spinal anesthesia: a prospective randomized controlled trial

BackgroundThe purpose of this study is to assess whether the application of preoperative forced air warming set to high temperature (> 43 °C) for brief period can increase temperature on admission to the postanesthesia care unit (PACU) and prevent hypothermia or shivering during holmium laser enucleation of the prostate performed under spinal anesthesia.MethodsFifty patients were enrolled were assigned randomly to receive passive insulation (control group, n = 25) or forced-air skin surface warming for 20 min before spinal anesthesia (pre-warming group, n = 25). The primary outcome was temperature at PACU admission.ResultsThe pre-warming group had a significantly higher temperature on admission to the PACU than the control group (35.9 °C [0.1] vs 35.6 °C [0.1], P = 0.023; 95% confidence interval of mean difference, 0.1 °C–0.5 °C). The trend of decreasing core temperature intraoperatively was not different between groups (P = 0.237), but intraoperative core temperature remained approximately 0.2 °C higher in the pre-warming group (P = 0.005). The incidence of hypothermia on admission to the PACU was significantly lower in the pre-warming group (56% vs 88%, P = 0.025). Shivering occurred in 14 patients in the control group, and 4 patients in the pre-warming group (P = 0.007).ConclusionBrief pre-warming at 45 °C increased perioperative temperature and decreased the incidence of hypothermia and shivering. However, it was not sufficient to modify the decline of intraoperative core temperature or completely prevent hypothermia and shivering. Continuing pre-warming to immediately before induction of spinal anesthesia or combining pre-warming with intraoperative active warming may be necessary to produce clearer thermal benefits in this surgical population.Trial registrationThis trial was registered with Clinicaltrials.gov, NCT03184506, 5th June 2017.

Warming before and after epidural block before general anaesthesia for major abdominal surgery prevents perioperative hypothermia: A randomised controlled trial.

Epidural analgesia (EDA) is known to be an independent risk factor for perioperative hypothermia and its many known adverse effects. Combined general and epidural anaesthesia decreases intraoperative core temperature more rapidly than general anaesthesia alone. Hence, adequate warming procedures are needed for these patients. We evaluated the effects of active skin-surface warming before and/or after initiation of EDA during general anaesthesia as a procedure to prevent perioperative hypothermia. A randomised controlled trial. Department of Anaesthesiology in a general hospital in Germany from January 2013 until August 2014. After obtaining written informed consent, we included 99 adult patients undergoing elective major abdominal surgery under combined general anaesthesia and EDA with an expected duration of surgery of at least 120 min. Patients were excluded if they were under 18 years of age, classified as American Society of Anesthesiologists' physical status 4 or higher or if patients refused EDA. Patients were randomly assigned to one of three groups and received either only passive insulation, 15 min of active air-forced warming after EDA and before induction of general anaesthesia, or two periods, each of 15 min, of active air-forced warming before and after EDA. Core and skin temperatures were measured at several time points throughout the study. The primary outcome measure was the incidence of hypothermia on arrival in the ICU. The secondary outcome measure was the incidence of postoperative shivering. In addition, the perioperative change in body core temperature was recorded. Without prewarming (n = 32), 72% of patients became hypothermic (<36°C) at the end of anaesthesia. Fifteen minutes of warming after insertion of the epidural catheter and before initiation of general anaesthesia reduced the incidence of postoperative hypothermia to 6% (n = 33). After two periods of 15 min of warming before and after insertion of the epidural catheter, no patient became hypothermic (n = 34). Prewarming in either 'warming' group prevents the initial temperature drop which was observed in the control group. Warming for 15 min before and after initiation of EDA in patients receiving combined anaesthesia is effective in preventing postoperative hypothermia. This trial was registered with ClinicalTrials.gov (identifier: NCT01795482).

The efficacy of pre-warming on reducing intraprocedural hypothermia in endovascular coiling of cerebral aneurysms.

BackgroundThe anesthetic management of patients undergoing endovascular treatment of cerebral aneurysms in the interventional neuroradiology suite can be challenged by hypothermia because of low ambient temperature for operating and maintaining its equipments. We evaluated the efficacy of skin surface warming prior to induction of anesthesia to prevent the decrease in core temperature and reduce the incidence of hypothermia.MethodsSeventy-two patients were randomized to pre-warmed and control group. The patients in pre-warmed group were warmed 30 minutes before induction with a forced-air warming blanket set at 38°C. Pre-induction tympanic temperature (Tpre) was measured using an infrared tympanic thermometer and core temperature was measured at the esophagus immediately after intubation (T0) and recorded at 20 minutes intervals (T20, T40, T60, T80, T100, and T120). The number of patients who became hypothermic at each time was recorded.ResultsTpre in the control and pre-warmed group were 36.4 ± 0.4°C and 36.6 ± 0.3°C, whereas T0 were 36.5 ± 0.4°C and 36.6 ± 0.2°C. Core temperatures in the pre-warmed group were significantly higher than the control group at T20, T40, T60, T80, T100, and T120 (P < 0.001). Compared to T0, core temperatures at each time were significantly lower in both two groups (P = 0.007 at T20 in pre-warmed group, P < 0.001 at the other times in both groups). The incidence of hypothermia was significantly lower in the pre-warmed group than the control group from T20 to T120 (P = 0.002 at T20, P < 0.001 at the other times).ConclusionPre-warming for 30 minutes at 38°C did not modify the trends of the temperature decrease seen in the INR suite. It just slightly elevated the beginning post intubation base temperature. The rate of decrease was similar from T20 to T120. However, pre-warming considerably reduced the risk of intraprocedural hypothermia.Trial registrationClinical Research Information Service (CRiS) Identifier: KCT0001320. Registered December 19th, 2014.

Forced-air warming: An effective method?

British Journal of Healthcare ManagementVol. 21, No. 1 Patient WarmingForced-air warming: An effective method?Arwinder SinghArwinder SinghSearch for more papers by this authorArwinder SinghPublished Online:15 Jan 2015https://doi.org/10.12968/bjhc.2015.21.1.26AboutSectionsView articleView Full TextPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareShare onFacebookTwitterLinked InEmail View article References Bräuer A, Pacholik L, Perl T, English MJ et al. (2004) Conductive heat exchange with a gelcoated circulating water mattress. Anesth Analg 99(6): 1742–6 Crossref, Google ScholarCamus Y, Delva E, Just B, Lienhart A (1993) Leg warming minimizes core hypothermia during abdominal surgery. Anesth Analg 77(5): 995–9 Crossref, Google ScholarEngelen S, Himpe D, Borms S et al. (2010) A comparison of under-body forced-air and resistive heating during hypothermic bypass. ASA abstracts, A075. http://tinyurl.com/nrq72ra (accessed 16 September 2014) Google ScholarKim JY, Shinn H, Oh YJ, Hong YW et al. 2006) The effect of skin surface warming during anesthesia preparation on preventing redistribution hypothermia in the early operative period of off-pump coronary artery bypass surgery. Eur J Cardiothorac Surg 29(3): 343–7 Crossref, Google ScholarMahoney CB, Odom J (1999) Maintaining intraoperative normothermia: A meta-analysis of outcomes with costs. AANA J 67(2): 155–63 Google ScholarMatsuzaki Y, Matsukawa T, Ohki K, Yamamoto Y et al. (2003) Warming by resistive heating maintains perioperative normothermia as well as forced air heating. Br J Anaesth 90(5): 689–91 Crossref, Google ScholarMcGovern PD, Albrecht M, Belani KG, Nachtsheim C et al. (2011) Forced air warming and ultra-clean ventilation do not mix: an investigation of theatre ventilation, patient warming and joint replacement infection in orthopaedics. J Bone Joint Surg Br 93(11): 1537–44. doi: https://doi.org/10.1302/0301-620X.93B11.27124 Crossref, Google ScholarPlattner O, Rodner G, Schopper C et al. (2010) Comparison of forced-air and a new resistive warming device for intraoperative rewarming. ASA abstracts, A076. http://tinyurl.com/q2hnngf (accessed 16 September 2014) Google ScholarTaguchi A, Ratnaraj J, Kabon B, Sharma N et al. (2004) Effects of a circulating-water garment and forced-air warming on body heat content and core temperature. Anesthesiology 100(5): 1058–64 Crossref, Google ScholarWinkler M, Akça O, Birkenberg B, Hetz H et al. (2009) Aggressive warming reduces blood loss during hip arthroplasty. Anesth Analg 91(4): 978–84 Crossref, Google Scholar FiguresReferencesRelatedDetails 2 January 2015Volume 21Issue 1ISSN (print): 1358-0574ISSN (online): 1759-7382 Metrics History Published online 15 January 2015 Published in print 2 January 2015 Information© MA Healthcare LimitedPDF download

The Incidence and Prevention of Hypothermia in Newborn Bonding after Cesarean Delivery

Little is known about thermoregulation of the newborn while bonding on the mother's chest immediately after cesarean delivery. Newborn hypothermia is associated with serious complications and should be avoided. Therefore, we evaluated whether newborns develop hypothermia during intraoperative bonding while positioned on their mothers' chests and investigated the effects of active cutaneous warming of the mothers and babies during a 20-minute intraoperative bonding period. We enrolled 40 parturients scheduled for elective cesarean delivery under spinal anesthesia. Mothers and their newborns were randomized to receive either passive insulation or forced-air skin-surface warming during the surgical procedure and bonding period. The primary outcome was neonatal core temperature at the end of the bonding period. Core temperatures of the newborns were measured with a rectal probe. Body temperatures of the mothers were assessed by sublingual measurements. Skin temperatures, thermal comfort of the mothers, and perioperative shivering were evaluated. Without active warming from the beginning of the surgical procedure until the end of the bonding period, the mean (SD) neonatal core temperature decreased to 35.9 (0.6)°C. Seventeen of 21 (81%) newborns became hypothermic (defined as a core temperature below 36.5°C). Active skin-surface warming from the beginning of the surgical procedure until the end of the bonding period resulted in a neonatal core temperature of 37.0 (0.2)°C and a decreased incidence of hypothermia (1 of 19 (5%) newborns (P < 0.0001)). In addition, active warming increased the mean skin temperatures of the infants, maternal core and skin temperatures, maternal thermal comfort, and reduced perioperative shivering. Active forced-air warming of mothers and newborns immediately after cesarean delivery reduces the incidence of infant and maternal hypothermia and maternal shivering, and increases maternal comfort.

The effect of short time periods of pre‐operative warming in the prevention of peri‐operative hypothermia

The aim of our study was to evaluate the performance of different durations of active pre-operative skin-surface warming (pre-warming) to prevent peri-operative hypothermia and postoperative shivering. We randomly assigned 200 patients, scheduled for surgery of 30-90 min under general anaesthesia, to receive passive insulation or forced-air skin surface warming for 10, 20 or 30 min. Body temperature was measured at the tympanic membrane. Shivering was graded by visual inspection. There were significant differences in changes of core temperature between the non-pre-warmed group and all the pre-warmed groups (p < 0.00001), but none between the three pre-warmed groups (p = 0.54). Without pre-warming, 38/55 (69%) patients became hypothermic (< 36 °C) at the end of anaesthesia, whereas only 7/52 (13%), 3/43 (7%) and 3/50 (6%) patients following 10, 20 or 30 min pre-warming, respectively, became hypothermic (p < 0.001 vs no pre-warming). Shivering was observed in 10 patients without, and in three, three and one patients with pre-warming in the respective groups (p = 0.02). Pre-warming of patients for only 10 or 20 min before general anaesthesia mostly prevents hypothermia and reduces shivering.

The effect of different warming methods on sensory nerve conduction velocity in shipyard workers occupationally exposed to hand–arm vibration

Segmental sensory nerve conduction velocity (SNCV) was measured from the wrists to the hands and digits in a population of 134 (126 men and 8 women) vibration-exposed shipyard workers following systemic warming using a bicycle ergometer. Results were compared to earlier nerve conduction tests, identical in execution, except that the warming process was segmental and cutaneous. The study was designed to investigate whether SNCVs, which were selectively slow in the fingers after segmental cutaneous (skin surface) warming, would be affected differently by systemic warming. Wrist-palm, palm-proximal digit, and digital sensory nerve segments were assessed antidromically by stimulating at the wrist with recording electrodes placed distally. The same subjects were cutaneously warmed in 2001 to >or=31 degrees C and were systemically warmed 28 months later in 2004 by ramped sustained exercise to 100 W for 12 min. Skin temperatures were measured by traditional thermistry and by infrared thermal images taken over the hand and wrist surfaces. When systemic warming was compared to segmental cutaneous warming, SNCVs were increased by 15.1% in the third digit and 20.4% in the fifth digit of the dominant hand. Respective increases in the non-dominant hand were 11.0% and 19.4%. A strong association between increased surface skin temperature and faster SNCV, which had been observed after segmental cutaneous warming, was largely eliminated for both digit and palmar anatomic segments after systemic warming. Significant differences in SNCV between vibration-exposed and non-exposed workers, which had been observed after segmental cutaneous warming, were eliminated after systemic warming. Systemic warming had only a small effect on the wrist-palm (transcarpal) segmental SNCVs. Reduced SNCV in the digits was observed in vibration-exposed and non-exposed workers. Substituting exercise-induced systemic warming for segmental cutaneous warming significantly increased SNCV in the digits and appeared to reduce differences in SNCV between vibration-exposed and non-exposed workers. These findings persisted despite a substantial time interval between tests, during which the subjects continued to work. There may be more general implications for diagnosing clinical conditions in industrial workers, such as the carpal tunnel syndrome and the hand-arm vibration syndrome.

Preoperative warming combined with intraoperative skin-surface warming does not avoid hypothermia caused by spinal anesthesia in patients with midazolam premedication.

Inadvertent perioperative hypothermia is common during spinal anesthesia and after midazolam administration. The aim of this study was to evaluate the effects of intraoperative skin-surface warming with and without 45 minutes of preoperative warming in preventing intraoperative and postoperative hypothermia caused by spinal anesthesia in patients with midazolam premedication. Prospective and randomized study at Hospital das Clínicas, Universidade Estadual Paulista, Botucatu. Thirty patients presenting American Society of Anesthesiologists (ASA) physical status I and II who were scheduled for elective lower abdominal surgery were utilized. The patients received midazolam premedication (7.5 mg by intramuscular injection) and standard spinal anesthesia. Ten patients (Gcontrol) received preoperative and intraoperative passive thermal insulation. Ten patients (Gpre+intra) underwent preoperative and intraoperative active warming. Ten patients (Gintra) were only warmed intraoperatively. After 45 min of preoperative warming, the patients in Gpre+intra had significantly higher core temperatures than did the patients in the unwarmed groups (Gcontrol and Gintra) before the anesthesia (p < 0.05) but not at the beginning of surgery (p > 0.05). The patients who were warmed intraoperatively had significantly higher core temperatures than did the patients in Gcontrol at the end of surgery (p < 0.05). All the patients were hypothermic at admission to the recovery room (T CORE < 36 degrees C). Forty-five minutes of preoperative warming combined with intraoperative skin-surface warming does not avoid but minimizes hypothermia caused by spinal anesthesia in patients with midazolam premedication.

The effect of skin surface warming on pre‐operative anxiety in neurosurgery patients*

Skin surface warming of patients not only improves thermal comfort, but has been shown to reduce anxiety in a pre-hospital setting. We tested the hypothesis that pre-operative warming can reduce pre-operative anxiety as effectively as a conventional dose of intravenous midazolam in patients undergoing neurosurgery. We randomly allocated 80 patients to four groups in the pre-operative holding area. Treatment was applied for 30-45 min with (1) passive insulation and placebo; (2) passive insulation and intravenous midazolam (30 microg.kg-1); (3) warming with forced-air and placebo; and (4) warming with forced-air and intravenous midazolam (30 microg.kg-1). Thermal comfort levels (VAS 0-100 mm) and anxiety levels (VAS 0-100 mm, Spielberger State-Trait Anxiety Inventory) were assessed twice: before the designated treatment was started and before induction of anaesthesia. In the midazolam and the midazolam/warming groups, anxiety VAS and Spielberger state anxiety scores decreased by -19 (95% CI: -29 to -9, p<0.01) and -10 (95% CI: -14 to -6, p<0.01), respectively. In the warming and the combined groups, thermal VAS increased by +26 (95% CI: 17-34, p<0.01). Pre-operative warming did not reduce anxiety VAS (p=0.11) or Spielberger state anxiety (p=0.19). The results of our study indicate that pre-operative warming can be recommended solely to improve thermal comfort, not to replace anxiolytic premedication regimens.

A comparison of the Effects of Intravenous Fluid Warming and Skin Surface Warming on Peri-operative Body Temperature and Acid Base Balance of Elderly Patients with Abdominal Surgery

The purpose of this study was to compare the effects of intravenous fluid warming and skin surface warming on peri-operative body temperature and acid base balance of abdominal surgical patients under general anesthesia. Data collection was performed from January 4th, to May 31, 2004. The intravenous fluid warming(IFW) group (30 elderly patients) was warmed through an IV line by an Animec set to 37 degrees C. The skin surface warming (SSW) group (30 elderly patients) was warmed by a circulating-water blanket set to 38 degrees C under the back and a 60W heating lamp 40 cm above the chest. The warming continued from induction of general anesthesia to two hours after completion of surgery. Collected data was analyzed using Repeated Measures ANOVA, and Bonferroni methods. SSW was more effective than IFW in preventing hypothermia(p= .043), preventing a decrease of HCO(3)(-)(p= .000) and preventing base excess (p= .000) respectively. However, there was no difference in pH between the SSW and IFW (p= .401) groups. We conclude that skin surface warming is more effective in preventing hypothermia, and HCO(3)(-) and base excess during general anesthesia, and returning to normal body temperature after surgery than intravenous fluid warming; however, skin surface warming wasn't able to sustain a normal body temperature in elderly patients undergoing abdominal surgery under general anesthesia.

Meperidine and skin surface warming additively reduce the shivering threshold: a volunteer study

IntroductionMild therapeutic hypothermia has been shown to improve outcome for patients after cardiac arrest and may be beneficial for ischaemic stroke and myocardial ischaemia patients. However, in the awake patient, even a small decrease of core temperature provokes vigorous autonomic reactions–vasoconstriction and shivering–which both inhibit efficient core cooling. Meperidine and skin warming each linearly lower vasoconstriction and shivering thresholds. We tested whether a combination of skin warming and a medium dose of meperidine additively would reduce the shivering threshold to below 34°C without producing significant sedation or respiratory depression.MethodsEight healthy volunteers participated on four study days: (1) control, (2) skin warming (with forced air and warming mattress), (3) meperidine (target plasma level: 0.9 μg/ml), and (4) skin warming plus meperidine (target plasma level: 0.9 μg/ml). Volunteers were cooled with 4°C cold Ringer lactate infused over a central venous catheter (rate ≈ 2.4°C/hour core temperature drop). Shivering threshold was identified by an increase of oxygen consumption (+20% of baseline). Sedation was assessed with the Observer's Assessment of Alertness/Sedation scale.ResultsControl shivering threshold was 35.5°C ± 0.2°C. Skin warming reduced the shivering threshold to 34.9°C ± 0.5°C (p = 0.01). Meperidine reduced the shivering threshold to 34.2°C ± 0.3°C (p < 0.01). The combination of meperidine and skin warming reduced the shivering threshold to 33.8°C ± 0.2°C (p < 0.01). There were no synergistic or antagonistic effects of meperidine and skin warming (p = 0.59). Only very mild sedation occurred on meperidine days.ConclusionA combination of meperidine and skin surface warming reduced the shivering threshold to 33.8°C ± 0.2°C via an additive interaction and produced only very mild sedation and no respiratory toxicity.

Perioperatives Wärmemanagement

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

The effect of skin surface warming during anesthesia preparation on preventing redistribution hypothermia in the early operative period of off-pump coronary artery bypass surgery

Redistribution hypothermia adversely affects hemodynamics and postoperative recovery in patients undergoing cardiac surgery. In off-pump coronary bypass surgery (OPCAB), maintaining the temperature is important because warming by cardiopulmonary bypass is omitted. Pre-warming studies reported earlier showing pre-warming as an effective means of preventing redistribution hypothermia was time consuming since it required at least 1-2h to pre-warm the patients before the surgery. Because pre-warming for such a long time is impractical in clinical practice, this study evaluated the efficacy of active warming during the preanesthetic period for the prevention of redistribution hypothermia in the early operative period of OPCAB. After gaining the approval of Institutional Review Board and informed consent from the patients, 40 patients undergoing OPCAB were divided into control and pre-warming groups. The patients in control group (n=20) were managed with warm mattresses and cotton blankets, whereas patients in pre-warming group (n=20) were actively warmed with a forced-air warming device before the induction of anesthesia. Hemodynamic variables and temperature were recorded before anesthesia (Tpre) and at 30 min intervals after anesthesia for 90 min (T30, T60, and T90). Active warming duration was 49.7+/-9.9 min. There were no statistically significant differences in skin temperature, core temperature and hemodynamic variables between the two groups at preinduction period except for mean arterial pressure and central venous pressure. The core temperature at T30, T60, and T90 was statistically higher in pre-warming group than that in control group. Core temperature of six (30%) and seven patients (35%) in control group was reduced below 35 degrees C at T60 and T90, respectively, whereas core temperature of only one patient (5%) in pre-warming group was reduced below 35 degrees C at T90 (P=0.02). Active warming using forced air blanket before the induction of anesthesia reduced the incidence and degree of redistribution hypothermia in patients undergoing OPCAB. It is a simple method with reasonable cost, which does not delay the induction of anesthesia nor the surgery.

Preoperative Combined with Intraoperative Skin Surface Warming Avoids Hypothermia Caused by General Anesthesia and Surgery

Survey of Anesthesiology: June 2004 - Volume 48 - Issue 3 - p 162 doi: 10.1097/01.sa.0000125841.48382.24

Preoperative combined with intraoperative skin-surface warming avoids hypothermia caused by general anesthesia and surgery

Study objectives To evaluate the effects of intraoperative skin-surface warming with and without 1 hour of preoperative warming, in preventing intraoperative hypothermia, and postoperative hypothermia, and shivering, and in offering good conditions to early tracheal extubation. Design Prospective, randomized, blind study. Setting Teaching hospital. Patients 30 ASA physical status I and II female patients scheduled for elective abdominal surgery. Interventions Patients received standard general anesthesia. In 10 patients, no special precautions were taken to avoid hypothermia. Ten patients were submitted to preoperative and intraoperative active warming. Ten patients were only warmed intraoperatively. Measurements and main results Temperatures were recorded at 15-minute intervals. The patients who were warmed preoperatively and intraoperatively had core temperatures significantly more elevated than the other patients during the first two hours of anesthesia. All patients warmed intraoperatively were normothermic only at the end of the surgery. The majority of the patients warmed preoperatively and intraoperatively or intraoperatively only were extubated early, and none had shivering. In contrast, five unwarmed patients shivered. Conclusions One hour of preoperative warning combined with intraoperative skin-surface warming, not simply intraoperative warming alone, avoided hypothermia caused by general anesthesia during the first two hours of surgery. Both methods prevented postoperative hypothermia and shivering and offered good conditions for early tracheal extubation.

A Comparative Study of Three Warming Interventions to Determine the Most Effective in Maintaining Perioperative Normothermia

A Comparative Study of Three Warming Interventions to Determine the Most Effective in Maintaining Perioperative Normothermia

Benefits of intraoperative skin surface warming in cardiac surgical patients

We have investigated patients undergoing cardiac surgery with hypothermic bypass to see if the addition of skin surface warming during systemic rewarming on bypass (heated group, n = 43) would improve perioperative thermal balance compared with conventional management without skin warming (control group, n = 43) in an open, randomized, controlled study. Intraoperative skin warming with a water mattress and forced warm air over the face, neck and shoulders attenuated the afterdrop in nasopharyngeal temperature after weaning from bypass (2.3 (1.2) degrees C and 1.3 (0.5) degrees C in the control and heated groups, respectively) (P < 0.05) and resulted in higher rectal temperature 4 h after surgery. Despite similar standard coagulation tests, heated patients had lower blood loss via the chest tubes (600 (264) ml vs 956 (448) ml in control patients) (P < 0.05) and less requirements for i.v. colloid infusion (1662 (404) ml vs 1994 (389) ml) (P < 0.05). There was a significant inverse correlation between rectal temperature on arrival in the ICU and postoperative blood loss (r = 0.57, P < 0.001). These data suggest that additional skin surface warming with a water mattress and forced warm air helped to preserve perioperative thermal balance and may contribute to reduced bleeding after cardiac surgery.

The effects of forced-air warming on postbypass central and skin temperatures and shivering activity

Study Objective: To test the hypothesis that forced-air skin-surface warming used prophylactically after hypothermic cardiopulmonary bypass (CPB) would: (1) decrease the incidence and severity of postbypass shivering, (2) rapidly increase skin-surface temperatures when compared with standard warmed cotton blankets, and (3) not contribute to excessive central temperature elevation. Design: Prospective, randomized, nonblinded comparison of two rewarming techniques. Setting: Multidisciplinary intensive care unit at a tertiary care, private teaching hospital. Patients: Following hypothermic CPB, 47 patients underwent postoperative rewarming by using either conduction (warmed cotton blankets) or convection (forced-air cover) techniques. Measurements and Main Results: Central and skin temperatures were measured at 30-minute intervals for 5.5 hours postoperatively. Four lead electromyographic recordings were used to objectively document shivering activity. Antihypertensives, opioids, sedatives, and muscle relaxants were administered per patient need and recorded. The forced-air cover markedly decreased the overall incidence, duration, and magnitude of significant shivering compared with the warmed cotton blankets. Forced-air therapy produced clinically significant increases in skin surface temperatures, but avoided excessive central temperature elevation when compared with passive rewarming with cotton blankets. Conclusion: Convection warming, when compared with conductive warming with cotton blankets, limited the incidence, magnitude, and duration of shivering following hypothermic cardiac surgery. This suggests an important role of cutaneous thermal input in the mediation of the shivering response. The central tissue compartment is buffered from the effects of skin-surface warming and, thus, forced-air therapy will not lead to excessive central temperature elevation in this patient population when compared with cotton blanket rewarming.

Delayed forced air warming prevents hypothermia during abdominal aortic surgery

We have evaluated the efficacy of the delayed forced air warming during abdominal aortic surgery in 18 patients. Patients were allocated randomly to one of two groups: the control group (n = 9) received no intraoperative warming device; the Bair-Hugger group (n = 9) had active skin surface warming with an upper body cover. The device was activated when core temperature decreased to less than 36 degrees C. The reduction in core temperature was 0.6 degrees C during the first hour after induction and 0.4 degrees C during the second hour in both groups. In the control group, core temperature continued to decrease until the end of surgery, whereas in the Bair-Hugger group, the reduction in core temperature stopped after 1 h of warming, and then rewarming began. At the end of surgery, core temperature in the Bair-Hugger group was similar to core temperature before induction, and was higher than core temperature in the control group (P < 0.003).

Thermoregulation and Heart Rate Variability

1. Heart rate variability is modulated by multiple control systems, including autonomic and hormonal systems. Long-term variability, i.e. the very low-frequency band of the power spectra, has been postulated to reflect thermoregulatory vasomotor control, based upon thermal entrainment experiments. However, the relationship between thermoregulatory responses (vasoconstriction and shivering) and heart rate variability has not been studied. 2. We performed two distinct protocols in a series of human subjects. In the first protocol, core temperature was reduced by intravenous infusion of cold saline, while skin temperature was unchanged. The second protocol involved skin-surface warming and cooling until shivering developed. Power spectral analysis was performed using a fast Fourier transformation, and the area in three distinct band-widths was determined. 3. Very low-frequency power (0.0039-0.04 Hz) increased significantly in response to core cooling, peripheral vasoconstriction and shivering, while both very low- and low- (0.04-0.15 Hz) frequency power increased in response to skin-surface cooling. Heart rate decreased during core cooling-induced vasoconstriction, suggesting a direct thermal response, and increased in relation to the metabolic demands associated with shivering. 4. Our results suggest that very low-frequency power is modulated by thermal stimuli which result in core hypothermia and thermoregulatory activity, while skin-surface cooling without core hypothermia does not selectively modulate this frequency band.