We have shown previously that administration of endotoxin induces a smaller decrease of body temperature in spontaneously hypertensive rats (SHR) than in normotensive Brown Norway (BN) rats. Several studies have suggested that tumor necrosis factor alpha (TNFalpha) is one of the mediators of the body-temperature response to endotoxin. To test whether the TNFalpha gene could be involved in determination of the observed difference in the body-temperature response to endotoxin, we studied SHR (n = 6) and a congenic strain, SHR.1N (n = 5), which differs from SHR by a segment of chromosome 20 originating from BN and containing the TNFalpha gene. Body temperature was recorded continuously by means of radiotelemetry. We showed that, in both strains, an intraperitoneal injection of endotoxin (500 microg/kg of body weight) induces a rapid hyperthermic phase (20-40 minutes post-injection), which is followed, first, by a hypothermic phase (100-120 minutes post-injection) and, then, by a late hyperthermic phase (seven hours). Although both strains demonstrated a similar trend in the response, a significant difference was observed between the two response curves (P = 0.0001). Further analysis at each time point revealed that the two strains differed significantly at a peak of the hypothermic phase (P = 0.035) and the late hyperthermic phase (P = 0.035). In conclusion, these data indicate that the differential chromosomal segment of SHR.1N contains a gene(s) causally related to the body-temperature response to endotoxin. In the light of previously published data, the TNFalpha gene appears to be the most likely candidate gene within the segment.
Perioperative hypothermia can lead to surgical complications, including bleeding, infection, increased patient discomfort, and longer recovery time. Plastic surgeons have become increasingly aware of this important patient safety issue.
The authors evaluate the impact of perioperative warming in an outpatient plastic surgery setting.
A retrospective review was performed of 108 patients who received several simple measures to prevent perioperative hypothermia. Patients dressed in warm clothing and were covered with an electric blanket in both the holding area and the recovery room. Intraoperative interventions included higher ambient room temperature, skin exposure only at the surgical site, forced-air warming, and the use of warmed fluids. This warmed group was compared with a historical control group of 106 patients who underwent plastic surgery in the period immediately before implementation of these measures. Patient demographics and procedural characteristics were similar for the 2 groups.
The requirement for intraoperative analgesia was significantly lower for the warmed group (111 vs 125 µg fentanyl in the control group; P = .042). Patients in the warmed group required less time in the recovery room and met discharge criteria sooner (127 vs 141 minutes; P = .001). No significant difference was observed in the incidence of complications.
Simple measures to maintain perioperative normothermia improve patient comfort and recovery following aesthetic surgery. Through a continuous-improvement culture, the authors have successfully implemented warming strategies that prevent perioperative hypothermia and improve surgical outcomes.
Comment In: Aesthet Surg J. 2012 Jul;32(5):62122745451
A 68-year-old woman presented in wintertime in a cold climate with ataxia and numbness in her legs and was found to be profoundly hypothermic in hospital. No endocrine or neurological cause for hypothermia could be distinguished. Physiological investigation, including a sympathetic release test, exposure to gradually increasing environmental temperatures and prolonged exposure to a high temperature suggested she was at that time regulating her core temperature around a set value which was several degrees lower than normal. Metabolic rate was 42 per cent below the value predicted from standard tables. Further measurements over a one-month period in a warm climate suggested a poikilothermic temperature control mechanism, with a possible risk of environmental hyperthermia. No pathological basis for this disorder has yet been identified, but it is suggested that a small localized hypothalamic vascular event has occurred.
Mild to moderate systemic hypothermia is commonly used as a cerebral protective strategy during adult cardiac surgery. The benefits of this strategy for routine cardiac surgery have been questioned and the adverse effects of hyperthermia demonstrated. The purpose of the present study was to examine current temperature management and monitoring practices during adult cardiac surgery using CPB in Canada.
Web-based survey referring to adult cases undergoing cardiac surgery using CPB without the use of deep hypothermic circulatory arrest. Thirty-two questionnaires were completed, representing a 100% response rate.
The usual management is to cool patients during CPB at 30 (94%) centers for low-risk (isolated primary CABG) cases and at 31 (97%) centers for high-risk (all other) cases. The average nadir temperature at the target site achieved on CPB is 34°C (range 28°C - 36°C). At 26 (81%) centers, patients are typically rewarmed to a target temperature between 36°C and 37°C before separation from CPB. Only 6 (19%) centers reported that thermistors and coupled devices used to monitor blood temperature are checked for accuracy or calibrated according to the product operating directive's schedule or more often.
Contemporary management of adult cardiac surgery under CPB still involves induction of mild to moderate systemic hypothermia. Significant practice variation exists across the country with respect to target temperatures for cooling and rewarming, as well as the site for temperature monitoring. This probably reflects the lack of definitive evidence. There is a need for well-conducted clinical trials to provide more robust evidence regarding temperature management.
BACKGROUND: Total handwear insulation (I(T)) is dependent on the rate of heat transfer in air through the skin-handwear interface, handwear layers, and the surface boundary air layer. As altitude increases, the corresponding decrease in air pressure reduces convective heat loss. As convective heat losses decline, I(T), which is inversely related to the rate of heat loss, should increase. Increasing air velocity also reduces the insulation (Ia) provided by the boundary layer. METHODS: The military issue test handwear, Light-duty glove (LD), Trigger-finger mitten (TF), and Arctic mitten (AM), were fitted over a biophysical hand model. Model surface temperatures were 25 degrees C, and air temperature was 10 degrees C. The handwear was tested at simulated altitudes of sea level (101 kPa), 2500 m (75 kPa) and 5000 m (54 kPa) in still air and at 5 m x s(-1). RESULTS: Overall, the effects of wind and altitude on I(T) were significant. Differences for I(T) between 0 and 5000 m were significant for LD and TF. Increases in I(T) greater than 10% are considered of sufficient magnitude to alter comfort sensation. CONCLUSIONS: Differences of that magnitude occurred most frequently between 0 and 5000 m. The present results are consistent with an increase in I(T) with increasing altitude. Changes in I(T) were greater in still air and for less insulated handwear where the contribution of Ia to I(T) was more important.
The obvious hazard of a cold exposure under natural as well as artificial conditions is tissue cooling and the associated sequel of more or less harmful effects from cold injury to discomfort. The nature, risk and magnitude of effects depend largely on the cooling effect, which results from the interaction of climatic factors (air temperature, mean radiant temperature, humidity and wind), protection (clothing) and metabolic heat production (activity). Assessment of cold stress should be based on methods which measure or predict this cooling effect in a relevant and reliable way. The nature of cooling encompasses (1) whole-body cooling, (2) extremity cooling, (3) convective cooling (wind chill), (4) conductive cooling (contact) and (5) airway cooling. The review contains a description of methods for evaluation of the various types of cold stress, as well as a discussion of their capacity and limitations. On the basis of selected methods, recommendations related to lowest permissible temperatures and other measures are discussed and compared with published data. Apparently, local cooling in most cases produces discomfort and harmful effects, before more significant whole-body cooling develops. With strong wind or movement at very low temperature, frostnip of unprotected skin may quickly develop. For most other conditions extremity (digit) cooling determines duration of exposure. However, as digit cooling largely depends on whole-body heat balance, it is important to control body cooling by selection and use of appropriate protective clothing.