Maintain Core Temperature Research Articles

Estimation of the difference between peritoneal microenvironment and core body temperature during laparoscopic surgery – a prospective observational study

Maintaining patients’ temperature during surgery is beneficial since hypothermia has been linked with perioperative complications. Laparoscopic surgery involves the insufflation of carbon dioxide (CO2) into the peritoneal cavity and has become the standard in many surgical indications since it is associated with better and faster recovery. However, the use of cold and dry CO2 insufflation can lead to perioperative hypothermia. We aimed to assess the difference between intraperitoneal and core temperatures during laparoscopic surgery and evaluate the influence of duration and CO2 insufflation volume by fitting a mixed generalized additive model. In this prospective observational single-center cohort trial, we included patients aged over 17 with American Society of Anesthesiology risk scores I to III undergoing laparoscopic surgery. Anesthesia, ventilation, and analgesia followed standard protocols, while patients received active warming using blankets and warmed fluids. Temperature data, CO2 ventilation parameters, and intraabdominal pressure were collected. We recruited 51 patients. The core temperature was maintained above 36 °C and progressively raised toward 37 °C as pneumoperitoneum time passed. In contrast, the intraperitoneal temperature decreased, thus creating a widening difference from 0.4 [25th–75th percentile: 0.2–0.8] °C at the beginning to 2.3 [2.1–2.3] °C after 240 min. Pneumoperitoneum duration and CO2 insufflation volume significantly increased this temperature difference (P < 0.001 for both parameters). Core vs. intraperitoneal temperature difference increased linearly by 0.01 T °C per minute of pneumoperitoneum time up to 120 min and then 0.05 T °C per minute. Each insufflated liter per unit of time, i.e. every 10 min, increased the temperature difference by approximately 0.009 T °C. Our findings highlight the impact of pneumoperitoneum duration and CO2 insufflation volume on the difference between core and intraperitoneal temperatures. Implementing adequate external warming during laparoscopic surgery effectively maintains core temperature despite the use of dry and unwarmed CO2 gases, but peritoneal hypothermia remains a concern, suggesting the importance of further research into regional effects.Trial registration: Clinicaltrials.gov: NCT04294758.

Biomarker patterns and mechanistic insights into hypothermia from a postmortem metabolomics investigation

Postmortem metabolomics holds promise for identifying crucial biological markers relevant to death investigations and clinical scenarios. We aimed to assess its applicability in diagnosing hypothermia, a condition lacking definitive biomarkers. Our retrospective analysis involved 1095 postmortem femoral blood samples, including 150 hypothermia cases, 278 matched controls, and 667 randomly selected test cases, analyzed using UHPLC-QTOF mass spectrometry. The model demonstrated robustness with an R2 and Q2 value of 0.73 and 0.68, achieving 94% classification accuracy, 92% sensitivity, and 96% specificity. Discriminative metabolite patterns, including acylcarnitines, stress hormones, and NAD metabolites, along with identified pathways, suggest that metabolomics analysis can be helpful to diagnose fatal hypothermia. Exposure to cold seems to trigger a stress response in the body, increasing cortisol production to maintain core temperature, possibly explaining the observed upregulation of cortisol levels and alterations in metabolic markers related to renal function. In addition, thermogenesis seems to increase metabolism in brown adipose tissue, contributing to changes in nicotinamide metabolism and elevated levels of ketone bodies and acylcarnitines, these findings highlight the effectiveness of UHPLC-QTOF mass spectrometry, multivariate analysis, and pathway identification of postmortem samples in identifying metabolite markers with forensic and clinical significance. The discovered patterns may offer valuable clinical insights and diagnostic markers, emphasizing the broader potential of postmortem metabolomics in understanding critical states or diseases.

Prewarming Parturients for Cesarean Section Does Not Raise Wound Temperature But Body Heat and Level of Comfort: A Randomized Trial

PurposePrewarming before cesarean section lowers the rates of surgical site infections (SSIs). We hypothesized that this effect is explained due to a higher core temperature resulting in a higher wound temperature. DesignWe conducted an open-labeled randomized study with on-term parturients scheduled for elective cesarean section under spinal anesthesia. Participants were randomized into an intervention group (prewarming) and a control group. MethodsCore and wound temperature, comfort level, and examination results were taken at defined times until discharge from the postanesthesia care unit (PACU). There was a follow-up visit and interview 1 day after the procedure. The primary outcome was a difference in wound temperature. The secondary outcomes were differences in core temperature, patient comfort, blood loss, SSI, and neonatal outcome. FindingsWe randomized a total of 60 patients, 30 per group. Prewarming lead to a significantly higher core temperature. Additionally, patient comfort was significantly higher in the prewarming group even after discharge from PACU. We did not find a difference in wound temperature, SSI, neonatal outcome, or blood loss. ConclusionsPrewarming before cesarean section under spinal anesthesia maintains core temperature and improves patient comfort but does not affect wound temperature.

Housing-temperature reveals energy intake counter-balances energy expenditure in normal-weight, but not diet-induced obese, male mice

Most metabolic studies on mice are performed at room temperature, although under these conditions mice, unlike humans, spend considerable energy to maintain core temperature. Here, we characterize the impact of housing temperature on energy expenditure (EE), energy homeostasis and plasma concentrations of appetite- and glucoregulatory hormones in normal-weight and diet-induced obese (DIO) C57BL/6J mice fed chow or 45% high-fat-diet, respectively. Mice were housed for 33 days at 22, 25, 27.5, and 30 °C in an indirect-calorimetry-system. We show that energy expenditure increases linearly from 30 °C towards 22 °C and is ~30% higher at 22 °C in both mouse models. In normal-weight mice, food intake counter-balances EE. In contrast, DIO mice do not reduce food intake when EE is lowered. By end of study, mice at 30 °C, therefore, had higher body weight, fat mass and plasma glycerol and triglycerides than mice at 22 °C. Dysregulated counterbalancing in DIO mice may result from increased pleasure-based eating.

Integrated Analysis of Transcriptome, microRNAs, and Chromatin Accessibility Revealed Potential Early B-Cell Factor1-Regulated Transcriptional Networks during the Early Development of Fetal Brown Adipose Tissues in Rabbits.

In domestic mammals, cold stress decreases the survival rate of newborns and increases the cost of management. Brown adipose tissue (BAT) is the main thermogenic organ for cubs, and well-developed fetal BAT (FBAT) is beneficial for newborns to maintain core temperatures during the first several days of life. However, our knowledge of the epigenetic mechanisms during the early development of FBAT remains largely unknown. Rabbits (Oryctolagus cuniculus) are economically important domestic animals. In this study, a histological analysis shows that the tissue content, thermogenic capacity, and lipid content of FBAT dramatically increases from gestational day 21 (G21) to gestational day 24 (G24) in rabbits. RNA-seq, microRNA-seq (miRNA-seq), and the assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) show that many genes, miRNAs, and chromatin-accessible regions (referred to as peaks) were identified as significantly changed from G21 to G24, respectively. The upregulated genes from G21 to G24 were significantly enriched in the mitochondrial metabolism and thermogenesis-related signal pathways. The integrated analysis of transcriptome and chromatin accessibility reveals that the peaks in the promoters have a more regulatory effect than peaks in other genomic elements on the expression of their nearby genes in FBATs. The upregulated genes that are associated with increased chromatin accessibility in the promoter regions are involved in the energy metabolism-related signaling pathways. The genes that have a greater tendency to be regulated by miRNAs than the chromatin accessibility in gene promoters are involved in the apelin, insulin, and endocytosis signaling pathways. Furthermore, genome-wide transcription factor (TF) footprinting analysis identifies early B-cell factor1 (EBF1) as playing a key role during early FBAT development. The carbon metabolism, citrate cycle, and PPAR signaling pathways are significantly enriched by the predicted EBF1-regulated cascade TF-network. In conclusion, our work provides a framework for understanding epigenetics regulatory mechanisms underlying the early development of FBAT and identifies potential TF involved in the early development of FBAT in rabbits.

Ad libitum drinking prevents dehydration during physical work in the heat when adhering to occupational heat stress recommendations

ABSTRACT Government entities issue recommendations that aim to maintain core temperature below 38.0°C and prevent dehydration [>2% body mass loss] in unacclimated workers exposed to heat. Hydration recommendations suggest drinking 237 mL of a cool sport drink every 15–20 min. This is based on the premise that ad libitum drinking results in dehydration due to inadequate fluid replacement, but this has never been examined in the background of recommendation compliant work in the heat. Therefore, we tested the hypothesis that ad libitum drinking results in >2% body mass loss during heat stress recommendation compliant work. Ten subjects completed four trials consisting of 4 hours of exposure to wet bulb globe temperatures (WBGT) of 24.1 ± 0.3°C (A), 26.6 ± 0.2°C (B), 28.5 ± 0.2°C (C), 29.3 ± 0.6°C (D). Subjects walked on a treadmill and work-rest ratios were prescribed as a function of WBGT [work:rest per hour – A: 60:0, B: 45:15, C: 30:30, D: 15:45] and were provided 237 mL of a cool sport drink every 15 min to drink ad libitum. Mean core temperature was higher in Trial A (37.8 ± 0.4°C; p = 0.03) and Trial B (37.6 ± 0.3°C; p = 0.01) versus Trial D (37.3 ± 0.3°C) but did not differ between the other trials (p ≥ 0.20). Body mass loss (A: −0.9 ± 0.7%, B: −0.7 ± 0.5%, C: −0.3 ± 0.5%, D: −0.4 ± 0.6%) was greater in Trial A compared to Trial D (p = 0.04) and was different from 2% body mass loss in all trials (p ≤ 0.01). Ad libitum drinking during recommendation compliant work in the heat rarely resulted in dehydration. Registered Clinical Trial (NCT04767347)

Relationship between aerobic fitness and lower limb skin temperature during cycling exercise testing among well-trained athletes and nonathletes: a cross-sectional study

BackgroundDuring prolonged physical exercise, the skin plays an important role in thermoregulation by dissipating heat to maintain core temperature. Moreover, thermal variation may be influenced by the physical fitness level of an individual. The aim of the present study was to determine the relationship between aerobic fitness and lower limb skin temperature during graded cycling exercise testing in well-trained athletes and nonathletes. MethodsTwelve trained athletes (mean ± SD maximal oxygen consumption [VO2max], 52.44 ± 4.5 ml/kg/min) and 12 nonathletes (VO2max, 36.95 ± 4.9 ml/kg/min) participated in this study. The regional skin temperature over the lower limbs was monitored continuously during incremental exercise testing using a thermal camera, and cardio-respiratory parameters were assessed and recorded using a metabolic analyzer (K5, COSMED, Rome, Italy). ResultsThe mean skin temperature of athletes at a high intensity of exercise was 27.23 ± 0.3 °C while that of nonathletes was 29.03 ± 0.44 °C, a difference that was statistically significant (p < 0.05). A negative correlation was observed between skin temperature and cardiovascular parameters (VO2max and heart rate) in athletes, while no such correlation was found among nonathletes. ConclusionThe present study demonstrated a negative correlation between oxygen consumption and lower limb skin temperature in athletes, while the correlation was poor in nonathletes. This suggests that physical fitness level may influence the pattern of alterations in lower limb skin temperature, which supports the hypothesis that athletes exhibit better heat dissipation mechanisms than nonathletes.

Voluntary drinking prevents dehydration when following occupational heat stress recommendations

INTRODUCTIONFederal and local entities issue guidance that aims to maintain core temperature (TC) below 38.0°C in unacclimated workers exposed to heat. These heat stress recommendations prescribe work‐rest ratios as a function of wet bulb globe temperature (WBGT) and metabolic heat production (Hprod). Hydration recommendations are less nuanced and suggest drinking 237 mL of a cool sport drink every 15‐20 min for work in the heat exceeding 2 h. This drinking regimen is based on the premise that ad libitum drinking during heat exposure results in dehydration [defined as &gt;2% body mass loss (BML)] due to inadequate drinking. To our knowledge, this hydration guidance has not been examined under heat stress recommendation compliant scenarios. Thus, it is unknown if ad libitumdrinking results in dehydration during recommendation compliant work in the heat.PURPOSETest the hypothesis that ad libitum drinking during heat stress recommendation compliant work in the heat will result in &gt;2% BML.METHODSSix, healthy, unacclimated, euhydrated subjects (2 women; 27±5 y) completed four trials consisting of 4 h (half a workday) of exposure to WBGTs of 23.9±0.2°C (A), 26.3±0.9°C (B), 28.4±0.1°C (C), 29.2±0.7°C (D). Subjects walked on a treadmill evoking a Hprod of 481±95 W, which is the average Hprod for outdoor workers in the U.S. NIOSH‐compliant work‐rest ratios were prescribed as a function of WBGT and Hprod [work:rest per hour (in min) ‐ A: 60:0, B: 45:15, C: 30:30, D: 15:45] and subjects were provided 237 mL of a cool (10±4°C) flavor preferred sport drink (Gatorade) every 15 min and drank ad libitum. BML was determined from changes in nude body mass and correction for fluid intake and urine loss provided an estimate of sweat rate. TC (telemetry pill) is reported as an average over the trial and as the percent of time TC exceeded 38.0°C (Time &gt;38). Thirst perception (1 = not thirsty, 9 = very, very thirsty) is reported as an average over the trial. Data are presented as mean±SD (parametric) or median (interquartile range) (nonparametric).RESULTSAverage TC was higher in Trial A (37.8±0.4°C; p=0.05) and Trial B (37.6±0.3°C; p=0.03) versus Trial D (37.3±0.4°C) but did not differ between the other trials (p≥0.20). Time &gt;38 did not differ between trials (A: 24 (5,43)%, B: 6 (0,5)%, C: 0 (0,5)%, D: 0 (0,0)%; p=0.17). Sweat rate was higher in Trial A (0.5±0.1 L/h) versus Trial D (0.4±0.1 L/h; p=0.05) but did not differ between any other trials (p≥0.12). Thirst perception (A: 2±1 a.u., B: 2±0 a.u, C: 2±1 a.u, D: 2±0 a.u; p=0.20) and fluid intake (A: 1.6±0.6 L, B: 1.5±0.5 L, C: 1.7±0.5 L, D: 1.6±0.7 L; p=0.88) did not differ between trials. BML did not differ between trials (A: ‐0.9±0.9%, B: ‐0.8±0.6%, C: ‐0.5±0.4%, D: ‐0.3±0.6%; p=0.24). One subject in one trial lost &gt;2% body mass (Trial A: ‐2.7%).CONCLUSIONAd libitumdrinking during recommendation compliant work in the heat rarely resulted in dehydration. Modification of work‐rest ratios across a range of WBGTs while working at a fixed Hprod mostly maintained TC &lt;38.0°C when ad libitumdrinking was permitted. Thus, absolute fluid prescription may not be necessary to prevent dehydration if adhering to occupational heat stress recommendations and cool fluids are readily available.

Temperature Regulation during Cold Water Immersion is Modified by Normobaric Hypoxia

Purpose Indigenous diving populations and recreational breath-hold divers often develop hypoxia while diving in cold water. Hypoxia may delay the onset and reduce magnitude of shivering during cold exposure. It is unclear if these hypoxia-induced alterations in the control of shivering reduce total energy expenditure, a function of both shivering and non-shivering thermogenesis, and/or modify the ability to maintain core temperature during cold water immersion. Therefore, this study tested the hypothesis that normobaric hypoxia decreases total energy expenditure and results in a greater decrease in core temperature during one hour of head out cold water immersion. Methods In a randomized crossover design, 6 healthy adults (27 ± 2 y, 1 woman) completed one hour of head out cold (22°C) water immersion breathing either normobaric normoxia (FiO2 = 0.21) or normobaric hypoxia (FiO2 = 0.13). Data were collected for 10 minutes prior to water immersion (baseline) and during water immersion. Energy expenditure was estimated from oxygen consumption (V̇O2) and respiratory exchange ratio (RER) measured via indirect calorimetry. Arterial oxyhemoglobin saturation (SpO2) was estimated using pulse oximetry on the forehead. Rectal temperature was used to estimate core temperature. Brown adipose tissue activation was estimated by measuring bilateral supraclavicular skin temperature. In a subset of subjects (n = 2) skin temperature was measured bilaterally on the back over the trapezius muscle, to confirm the unique profile of changes in supraclavicular skin temperature. Data during cold water immersion were compared relative to the last two-minutes of baseline and integrated throughout water immersion (60 minutes). Data are presented as mean ± SD. Results During water immersion, SpO2 was lower in hypoxia (90 ± 3%) compared to normoxia (98 ± 2%, P < 0.01). Baseline rectal temperature was not different between hypoxia (37.3 ± 0.2°C) and normoxia (37.4 ± 0.2°C, P = 0.52). At the end of water immersion, rectal temperature in hypoxia (36.6 ± 0.4°C) was lower than in normoxia (36.9 ± 0.3°C, P < 0.01). No differences in the total increase above baseline during water immersion were observed in V̇O2 (Hypoxia: 28.3 ± 7.2L; Normoxia: 29.5 ± 6.8 L, P = 0.74) or energy expenditure (Hypoxia: 191 ± 69 KJ·min; Normoxia: 143 ± 81 KJ·min, P = 0.32) between trials. Supraclavicular skin temperature increased with water immersion (P < 0.01), while back skin temperature decreased (P = 0.02). No differences were observed in the total increase from baseline in supraclavicular skin temperature (Hypoxia: 66.6 ± 30.3°C·min; Normoxia: 66.1 ± 35.3°C·min, P = 0.54) or total decrease from baseline in back skin temperature (Hypoxia: -42.3 ± 30.8°C·min; Normoxia: -56.6 ± 7.9 °C·min, P = 0.14). Conclusions These preliminary findings support that, compared to normoxia, normobaric hypoxia promotes a greater reduction in core temperature during one hour of head out cold water immersion. The mechanism(s) underlying this observation remains unclear as no differences in energy expenditure and brown adipose tissue activation were observed, but alterations in cutaneous blood flow cannot be excluded.

Induced normothermia ameliorates the procoagulant host response in human endotoxaemia

BackgroundDysregulation of coagulation occurs commonly in sepsis, ranging from mild coagulopathy with decreased platelets to disseminated intravascular coagulation (DIC). We investigated the effect of induced normothermia on coagulation during lipopolysaccharide (LPS)-induced endotoxaemia in healthy volunteers. MethodsTwelve volunteers received an infusion of bacterial lipopolysaccharide (Escherichia coli; 2 ng kg−1) and were assigned to either induced normothermia or control. Induced normothermia to maintain core temperature at 37°C consisted of external surface cooling, cold i.v. fluids, and medication to reduce shivering (buspirone, clonidine, and magnesium sulphate). The primary outcome was the DIC score (International Society on Thrombosis and Haemostasis guideline). Prothrombin time (PT), activated partial thromboplastin time (aPTT), D-dimer, plasma von Willebrand factor (vWf), and rotational thromboelastometry (ROTEM) were measured before and 1, 3, 6, and 8 h after LPS infusion. Differences between groups were tested with a mixed effects model. ResultsIn control subjects, lipopolysaccharide caused a fever, transiently decreased platelet levels and lowered activated partial thromboplastin time, while prolonging prothrombin time and increasing D-Dimer and vWf levels. Normothermia prevented the DIC-score exceeding 4, which occurred in 50% of control subjects. Normothermia also reduced the fall in platelet count by 67x109 L−1([95%CI:27-107]; p=0.002), aPTT (mean difference:3s [95%CI:1-5]; p=0.005) and lowered vWf levels by 89% ([95%CI:6-172]; p=0.03), compared to the fever group. ROTEM measurements were unaffected by lipopolysaccharide. ConclusionIn human endotoxaemia, induced normothermia decreases markers of endothelial activation and DIC. Maintaining normothermia may reduce coagulopathy in hyperinflammatory states.

Adipose tissue: from amorphous filler to metabolic mastermind

Adipose tissue plays a central role in the control of systemic glucose homeostasis through two major mechanisms: fat storage and secretion of specific cytokines known as adipokines. Fat storage in adipose tissue is critically important, as it prevents lipid deposition in liver and muscle, which in turn results in insulin resistance and increased risk of type 2 diabetes. Secretion of adipokines, such as leptin, protects from fuel depletion through appetite control, and other adipokines control fuel distribution and utilization. Fat storage capacity of adipose tissue increases through two mechanisms, adipocyte hypertrophy and adipocyte hyperplasia. Adipose tissue depots expand differently in diverse individuals and confer varying degrees of metabolic disease risk. There are multiple adipocyte subtypes that together mediate the functions of adipose tissue. They do so through specialized functions such as thermogenesis, which burns fuel to maintain core temperature, and through selective secretion of different adipokines. Much progress has been made in understanding the mechanisms by which adipose tissue controls systemic metabolism, increasing our hope of developing new, effective therapies for metabolic diseases.

Physiologic-Based Cord Clamping Maintains Core Temperature vs. Immediate Cord Clamping in Near-Term Lambs.

Background: Physiologic-based cord clamping (PBCC) involves deferring umbilical cord clamping until after lung aeration. It is unclear if infant is at risk of becoming hypothermic during PBCC.Objectives: To test if PBCC would maintain core temperature more effectively than immediate cord clamping (ICC).Design: At 0.93 gestation, fetal lambs were surgically exteriorized and instrumented from pregnant ewes under general anesthesia. Prior to the start of the experiment, lambs were thoroughly dried, placed on hot water bottles, and core temperature was continuously monitored using a rectal thermometer. PBCC lambs (n = 21), received intermittent positive pressure ventilation (iPPV) for ≥5 min prior to umbilical cord clamping. In ICC lambs (n = 23), iPPV commenced within 60 s after umbilical cord clamping. iPPV was provided with heated/humidified gas. Lambs were moved under a radiant warmer after umbilical cord clamping. Additional warmth was provided using a plastic overlay, hairdryer, and extra water bottles, as needed. Two-way mixed and repeated measures one-way ANOVAs were used to compare temperature changes between and within a single group, respectively, over time.Results: Basal fetal parameters including core temperature were similar between groups. ICC lambs had a significant reduction in temperature compared to PBCC lambs (p < 0.001), evident by 1 min (p = 0.002). ICC lambs decreased temperature by 0.51°C (± 0.42) and 0.79°C (± 0.55) at 5 and 10 min respectively (p < 0.001). In PBCC lambs, temperature did not significantly change before or after umbilical cord clamping (p = 0.4 and p = 0.3, respectively).Conclusions: PBCC stabilized core temperature at delivery better than ICC in term lambs. Hypothermia may not be a significant risk during PBCC.

Effects of postoperative active warming and early exercise on postoperative body temperature distribution: Non-blinded and randomized controlled trial.

We tested a hypothesis that postoperative active warming and/or arm leg stretches reduce the difference between core and skin temperatures (primary variable) improving the peripheral circulation immediately after major abdominal surgery. Fifty-one patients undergoing major abdominal surgeries were randomly assigned to receive one of three interventions immediately after surgery; routine care (control group), mild intermittent exercise on the bed (exercise group), and forced-air warming (warming group). Core and skin temperatures and perfusion index were continuously measured from anesthesia induction to 12 h after arrival at the ward. Core body temperature was maintained over 37°C with a relatively greater gap between core and skin temperatures over 1°C and reduced perfusion index in the early postoperative period in the control group. In the warming group, the reduced skin temperature at arrival at the ward approximated to the core temperature leading to significant reduction of the temperature gap and increasing the perfusion index to the preoperative level. Although less evident, both the temperature gap and peripheral perfusion significantly improved in the exercise group after 6 and 8 h after arrival at the ward, respectively. Vasoconstriction in response to cessation after anesthesia and surgery serves to maintain core temperature, but impairs peripheral circulation. Active warming and intermittent mild exercise immediately after arrival at the ward reduces the temperature gap and improves peripheral circulation during the early postoperative period. While cost-effectiveness needs to be considered before clinical application of the intervention, the cost-free mild exercise may be a feasible option for improving postoperative patient care.

Effect of heated humidified ventilation on intraoperative core temperature and prognosis in normothermic thoraco-abdominal aortic aneurysm repair.

BackgroundTo evaluate whether the heated humidified ventilation can effectively maintain core temperature and improve prognosis in normothermic thoraco-abdominal aortic aneurysm repair surgery.MethodsPatients who were scheduled for normothermic thoraco-abdominal aortic aneurysm repair surgery were randomized into the group using heated humidified ventilation combined with water blanket and the group using water blanket only. During the operation, the core temperature will be measured every 30 minutes. We analyzed intraoperative core-temperature, coagulation function and in-hospital mortality.ResultsHHV&WB group showed lesser decrease in core temperature than WB groups in the first two hours, while WB group had a higher body temperature at the third to fifth hour (2-hour: 35.45±0.47 vs. 35.24±0.59 °C, P=0.284; 5-hour: 35.38±0.70 vs. 35.51±0.88 °C, P=0.664). There was less blood loss, dosage of coagulation drugs and in-hospital mortality (13.33% vs. 20.00%, P=1) in the HHV&WB group.ConclusionsHeated humidified ventilation can improve the prognosis of normothermic thoraco-abdominal aortic aneurysm repair surgery to some extent, but it can only maintain the core temperature during the first 2 hours.

Cannabinoid Receptor Agonist WIN55, 212-2 Adjusts Lipid Metabolism in a Rat Model of Cardiac Arrest.

The objective of this study was to investigate the effects of pharmacologically induced hypothermia with WIN55, 212-2 (WIN)on postresuscitation myocardial function, microcirculation, and metabolism-specific lipids in a rat cardiac arrest (CA) model. Ventricular fibrillation was electrically induced and untreated for 6 minutes in 24 Sprague-Dawley rats weighing 450-550 g. Cardiopulmonary resuscitation including chest compression and mechanical ventilation was then initiated and continued for 8 minutes, followed by defibrillation. At 5 minutes after restoration of spontaneous circulation (ROSC), animals were randomized into four groups: (1) normothermia with vehicle (NT); (2) physical hypothermia with vehicle (PH); (3) WIN55, 212-2 with normothermia (WN); and (4) WIN55, 212-2 with hypothermia (WH). For groups of WN and WH, WIN was administered by continuous intravenous infusion with a syringe pump for 4 hours. PH started at 5 minutes after resuscitation. NT maintained core temperature at 37°C ± 0.2°C with the aid of a heating blanket. Hypothermia groups maintained temperature at 33°C ± 0.5°C for 4 hours after ROSC. There was a significant improvement in myocardial function as measured by ejection fraction, cardiac output, and myocardial performance index in animals treated with WH and PH beginning at 1 hour after start of infusion. In the WH and PH groups, buccal microcirculation was significantly improved compared with NT and WN. Plasma at pre-CA and ROSC 4 hours was harvested for lipid metabolism. The WH group appeared to be closer to baseline than the other groups in lipid metabolism. lysophosphatidylcholine (LPC) 18:2, free fatty acid (FFA) 22:6, and ceramide (CER) (24:0) changed significantly among the lipidomic data compared with NT (p < 0.05). Postresuscitation hypothermia improved myocardial function and microcirculation. WH-mediated lipid metabolism had the best metabolic outcome to bring back the animals to normal metabolism, which may be protective to improve outcomes of CA. LPC 18:2, FFA 22:6, and CER (24:0) may be important predictors of outcomes of CA.

Comparison of Prophylactic Intravenous Pethidine versus Intravenous Ondansetron in Prevention Post Spinal Shivering in Hysterectomy

AbstractBackground: Spinal anesthesia is known to significantly impair thermoregulation; shivering associated with spinal anesthesia is reported up to 55%. Pethidine probably acts directly on the thermoregulatory center or via opioid receptors. Mechanism of action of 5HT antagonist as anti-shivering is thought to be related to inhibition of serotonin reuptake on the preoptic anterior hypothalamic region.Aim of Study: This study was designed to compare the effectiveness of intravenous Pethidine versus intravenous Ondansetron for prevention of post-spinal shivering (primary outcome), hemodynamic changes, side effects of both groups were also evaluated (secondary outcome).Material and Methods: Patients were randomly assigned allocated into two groups (Group P n=30 patients) received pethidine 0.4mg/kg and (Group O n=30 patients) received Ondansetron 4mg as premedication (each drug was mixed into 10ml isotonic saline and given to the patient, slowly IV).Results: Non-significant differences between two groups as regards episodes of shivering, grading of shivering and tympanic temperature, but there is delayed onset of shivering episodes in pethdine group. There was statistically significant decrease in patients had nausea and vomiting in O group. While there was no statistically significant difference as regard sedation in both groups.Conclusion: The use of Prophylactic 4mg Ondansetron (5HT3 antagonist) is equally effective as 0.4mg/kg pethidine in the prevention of perioperative shivering following spinal anesthesia, maintains core temperature and Prophylactic Ondansetron also reduces the need of antiemetics.

Savanna elephants maintain homeothermy under African heat

To conserve body water, mammals may reduce evaporative water loss by storing heat, allowing core body temperature to rise more than usual during the day, and to fall more than usual during the cooler night, so demonstrating heterothermy. It has been proposed that elephants are heterothermic, but body temperature never has been measured in elephants over 24h at environmental temperatures higher than body temperature, where elephants would have to rely on evaporative cooling to maintain homeothermy. We used ingested temperature data loggers to record core temperature of four partly free-ranging savanna elephants exposed to high solar radiation and environmental temperatures that exceeded core temperature (> 36°C) in their natural habitat. The elephants maintained core temperature at an average 36.6°C within narrow daily limits of about 1.3°C. While mean 24-h core temperature increased with maximum air temperature, it did not increase with mean air temperature. Maximum and minimum daily core temperatures also did not change with maximum air temperatures. As a result, core temperature range remained constant despite large variations in daily air temperatures. Contrary to the view that elephants exhibit heterothermy to cope with heat, savanna elephants in their natural habitat with access to adequate resources of food and water, and able to use thermoregulatory behaviour, maintained homeothermy.

Leptin regulation of core body temperature involves mechanisms independent of the thyroid axis

The ability to maintain core temperature within a narrow range despite rapid and dramatic changes in environmental temperature is essential for the survival of free-living mammals, and growing evidence implicates an important role for the hormone leptin. Given that thyroid hormone plays a major role in thermogenesis and that circulating thyroid hormone levels are reduced in leptin-deficient states (an effect partially restored by leptin replacement), we sought to determine the extent to which leptin's role in thermogenesis is mediated by raising thyroid hormone levels. To this end, we 1) quantified the effect of physiological leptin replacement on circulating levels of thyroid hormone in leptin-deficient ob/ob mice, and 2) determined if the effect of leptin to prevent the fall in core temperature in these animals during cold exposure is mimicked by administration of a physiological replacement dose of triiodothyronine (T3). We report that, as with leptin, normalization of circulating T3 levels is sufficient both to increase energy expenditure, respiratory quotient, and ambulatory activity and to reduce torpor in ob/ob mice. Yet, unlike leptin, infusing T3 at a dose that normalizes plasma T3 levels fails to prevent the fall of core temperature during mild cold exposure. Because thermal conductance (e.g., heat loss to the environment) was reduced by administration of leptin but not T3, leptin regulation of heat dissipation is implicated as playing a uniquely important role in thermoregulation. Together, these findings identify a key role in thermoregulation for leptin-mediated suppression of thermal conduction via a mechanism that is independent of the thyroid axis.

PPARγ agonist rosiglitazone switches fuel preference to lipids in promoting thermogenesis under cold exposure in C57BL/6 mice

Brown and beige adipose tissues play key roles in adaptive thermogenesis, which is essential for homoiotherms to maintain core temperature under cold exposure. PPARγ is a transcriptional regulator critical for brown adipose tissue (BAT) recruitment and white adipose tissue (WAT) browning. Here we evaluated the impact of PPARγ activation on thermogenic activity in C57BL/6 mice under thermo-neutral and 4 °C cold environment, and revealed the regulating mechanism and metabolic basis. Rosiglitazone slowed body temperature loss in cold environment in C57BL/6 mice, suppressed cold-induced decreases in blood glucose, reversed cold-promoted 18F-FDG uptake, and increased lipid consumption in BAT. Serum/adipose tissue metabolomic and transcriptomic analyses revealed that cold exposure and rosiglitazone affect metabolism in different way, especially in terms of free fatty acid/lipid metabolism. While all tested treatments stimulated stored-substance mobilization in epididymal WAT, in heat-generating adipose tissues (BAT and subcutaneous WAT), rosiglitazone-only treatment promoted the storage of substances such as lipids for subsequent thermogenic activation; conversely, cold exposure favoured glucose consumption and mobilization/transport of extracellular lipids. When combined with cold exposure, rosiglitazone treatment preferentially triggered BAT lipid consumption, mobilized and transported lipids from epididymal to subcutaneous WAT, and reduced glucose usage. Thus, rosiglitazone might promote thermogenesis under cold exposure by switching fuel preference. SignificanceIn current study, for the first time, PPARγ agonism by rosiglitazone was proved to promote thermogenesis under near-freezing conditions and enhance the heat generating response against cold-induced hypothermia in mice by switching the fuel preference from carbohydrates to lipids. The lipid substrates stored in BAT in response to PPARγ activation are spared for eventual thermogenic activation. These findings thus underline the remarkable actions of PPARγ in the control of energy metabolism in adipose tissues, especially the BAT.

Chapter 15 - Thermal comfort

The processes of thermoregulation are roughly divided into two categories: autonomic and behavioral. Behavioral thermoregulation alone does not have the capacity to regulate core temperature, as autonomic thermoregulation. However, behavioral thermoregulation is often utilized to maintain core temperature in a normal environment and is critical for surviving extreme environments. Thermal comfort, i.e., the hedonic component of thermal perception, is believed to be important for initiating and/or activating behavioral thermoregulation. However, the mechanisms involved are not fully understood. Thermal comfort is usually obtained when thermal stimuli to the skin restore core temperature to a regulated level. Conversely, thermal discomfort is produced when thermal stimuli result in deviations of core temperature away from a regulated level. Regional differences in the thermal sensitivity of the skin, hypohydration, and adaptation of the skin may affect thermal perception. Thermal comfort and discomfort seem to be determined by brain mechanisms, not by peripheral mechanisms such as thermal sensing by the skin. The insular and cingulate cortices may play a role in assessing thermal comfort and discomfort. In addition, brain sites involved in decision making may trigger behavioral responses to environmental changes.