Author: Professor Dai Ziyi / Huang Yuguang
This article is transferred from: J Clin Anesthesia, May 2021, Vol. 37, No. 5, Volume 37, Issue 5 of the Journal of Clinical Anesthesiology, May 2021
The normal body temperature regulation systemis composed of three parts: temperature sensor, body temperature regulation center and effector. The core body temperature is tightly regulated and maintained at about 37 ℃, and the peripheral body temperature is 2 ℃ to 4 ℃ lower than the core body temperature. Different from purposeful therapeutic hypothermia, perioperative core body temperature lower than 36.0 ℃ caused by non-medical plan is called perioperative accidental hypothermia (IPH), also known as perioperative hypothermia.
The incidence of IPH in various operations is 7% to 90%, which can lead to cardiovascular events, postoperative infections, and increased risk of blood transfusion. The occurrence of IPH is affected by many factors such as anesthesia, surgery, and the patient's own condition. Therefore, prevention and treatment of IPH has become an important part of accelerated rehabilitation surgery (ERAS).
There are guidelines that recommend the prevention of IPH, but do not clarify the specific best practices for perioperative temperature management. Although a large number of active thermal insulation measures have been put into clinical use, the incidence of IPH is still high, and there is an urgent need for more efficient methods to prevent IPH. In this paper, the effectiveness of existing IPH prevention strategies will be compared and discussed based on the latest research progress.
IPH overview
Adverse outcome: IPH is a common intraoperative complication. The intraoperative body temperature of patients decreased by 2 ℃, the risk of infection at the surgical site increased to three times that of patients with normal body temperature, and the wound suture removal time was delayed by 1 day compared with patients with normal body temperature. The incidence of postoperative cardiovascular events (including unstable angina or myocardial ischemia, cardiac arrest, and myocardial infarction) in IPH patients was significantly higher than that in patients with normal body temperature (6.3% vs 1.4%, P=0.02).The risk of intraoperative blood transfusion increased with the degree of hypothermia and duration of hypothermia.
Research by Allen et al. have shown that IPH of maternal cesarean section under subarachnoid block may affect the body temperature of the fetus, leading to an increase in the incidence and mortality of neonatal respiratory distress syndrome, hypoglycemia. In addition, IPH can also lead to complications such as increased demand for mechanical ventilation, increased incidence of pressure ulcers, impaired metabolism of anesthetic drugs, increased incidence of chills, and decreased thermal comfort, thereby prolonging the observation time in the post-anaesthesia monitoring and treatment room (PACU). Intensive care unit (ICU) observation time and hospital stay.
Mechanism and risk factors: Perioperative core body temperature drops through 3 periods: rapid decline period, anesthetics damage the body temperature regulation center, reduce vasoconstriction and chills threshold, cause vasodilation, so that body heat within 1 hour after induction of anesthesia The core is redistributed to the periphery.During the slow linear decline period, the intraoperative heat loss mainly caused by radiation and convection exceeds the metabolic heat production, resulting in a slow decline in body temperature for 2 hours.In a plateau, hypothermia eventually triggers vasoconstriction, limiting further loss of core heat and balancing the body's heat production and dissipation.
The risk of IPH is related to multiple factors such as the patient's own condition, anesthesia, surgery, environmental temperature, perioperative medication, and insulation state. The risk of IPH was directly increased by anaesthesia related factors, such as anesthesia time >2 h, anesthetic drugs, intraoperative infusion of unwarmed fluid >1 000 ml, and combined anesthesia. Patients with age ≥60 years, BMI<25 kg/m2, ASA class ⅱ or above, low basal body temperature before surgery, and history of impaired thermoregulation. Operation-related factors such as operation time >2 h, open surgery, high surgical grade, intraoperative use of unheated rinsing fluid >500 mL, and low operating room temperature indirectly increased the risk of IPH.
Research by Miyazaki et al. showed that in the process of establishingpneumoperitoneum during laparoscopic surgery, cold and dry CO2 gas can directly contact the entire inner surface of the abdominal cavity and take away a lot of heat, but the heat insulation of visceral fat prevents the temperature of internal organs under the pneumoperitoneum from falling. Thus reducing the risk of intraoperative hypothermia. Therefore, the researchers suggest that the waist-to-hip ratio reflecting visceral obesity should be included as a predictor of core body temperature during laparoscopic surgery to effectively assess the risk of intraoperative hypothermia.
Perioperative temperature management
Assess IPH risk: Clinical guidelines recommend continuous assessment of IPH risk throughout the perioperative period based on the patient's IPH risk factors, body temperature monitoring, thermal comfort, and signs and symptoms of hypothermia. A domestic multi-center study included major risk factors for IPH such as patient BMI, preoperative basal body temperature, surgery scale, and anesthesia time to construct a predictive model of IPH probability for general anesthesia patients to assist the surgical team in predicting the risk of hypothermia during surgery. Analyzing the necessity and effectiveness of body temperature protection measures, and effectively preventing IPH based on risk stratification management. The actual clinical application effect of this model is being further tested by multi-center and large samples.
Temperature monitoring: Perioperative patient temperature monitoring should be as much as possible to maintain the same position and method as before entering the operating room. Temperature monitoring starts 1 hour before anesthesia, and continuous monitoring during the operation or at least once every 15 to 30 minutes, from the end of the operation to leaving Body temperature monitoring is still required during PACU. The core body temperature can best reflect the body's heat status. The monitoring sites include the pulmonary artery, distal esophagus, nasopharynx and tympanic membrane, but most of these sites are inconvenient to measure. Among the other monitoring parts, the oral cavity is closest to the core body temperature and is suitable for awake patients, followed by the armpits, bladder, and rectum. The measurement results of infrared ear temperature and temporal artery temperature are inaccurate. The core body temperature of children is higher than that of adults (36.5～38.0 ℃) and the temperature drops faster. The guidelines recommend rectal temperature measurement for children under 2 years of age. The new sensor derived from the new zero heat flow technology can provide non-invasive, hygienic, and continuous monitoring of core body temperature, which is more suitable for patients with intraspinal anesthesia. Given that various temperature measurement technologies are sufficiently accurate, the current accuracy of body temperature monitoring depends more on the measurement site.
Non-pharmaceutical insulation measures: including passive insulation, active insulation and increasing the ambient temperature.
1. Passive insulation: Passive insulation should run through the entire perioperative period, including conventional care such as cotton blankets and surgical drapes, and thermal insulation measures such as reflective blankets. Passive insulation can reduce heat loss by 30%, and its insulation effect is related to the coverage area and the number of layers. A prospectie study into line (elective surgical procedures operation time < 1 h) in adult patients with 328 cases, preoperative application of reflective blanket or routine care for thermal insulation cotton blanket, the patients were randomly divided into two groups. The results showed that reflective blankets can be significant The preoperative temperature difference between the temporal artery and the foot was reduced, and the temperature of the foot was increased. There was no significant difference in the minimum core body temperature between the two groups during the operation, indicating that the reflective blanket can increase the body's peripheral heat reserve more than the conventional nursing blanket. Research by Smith et al. have shown that the new Orve+wrap insulation blanket can absorb heat and transfer heat to the patient after preheating, and can achieve the same effect as the inflatable heating device in the short-term postoperative heat preservation (<60 min).
2. Active heat preservation: Active heat preservation includes body surface warming, warming infusion, warming washing fluid, etc.
(1) Single active heat preservation: Forced-air warming (FAW) is currently the most commonly used active heat preservation method, and its heat preservation effect is related to the heat preservation part and the heat preservation temperature. Min et al. selected 123 patients undergoing thoracoscopic surgery for a randomized controlled trial (RCT). The patients were in a lateral position during the operation. The results showed that the incidence of intraoperative hypothermia in the upper body air-inflation heating group was significantly lower than that of the lower body air-inflation heating group ( 34% vs 57%, P=0.011). Zhou Yanrong et al. selected 60 children undergoing fracture surgery. The children were randomly divided into three groups according to the different temperatures (32, 38, and 43℃) given during the operation. The results showed that the temperature of children in the 38℃ inflating and heating group was the most stable and the level of inflammatory factors was the lowest.
Patients of different ages have different optimal inflation and heating temperatures. Xu et al. study selected 243 elderly patients undergoing arthroplasty. According to postoperative rewarming measures for patients with hypothermia, the patients were randomly divided into group C (conventional blanket) and group F1 (38℃ inflatable heating), F2 group (42℃ inflatable heating), the results showed that the shortest F2 group after temperature, highest efficiency, The incidence of arrhythmia and chills was the lowest, so 42 ℃ may be the optimal inflating temperature for the elderly. Studies by Gosling et al. showed that the incidence of postoperative hypothermia was 29.9% in patients who used air-filled heating during coronary artery bypass grafting, and 7.6% in patients who used circulating water heating. The postoperative body temperature of the patient was 0.5℃ higher than that of the patient who used air-filled heating, indicating that during thoracotomy, the circulating water device may be more effective in preventing and treating IPH than air-filled heating.
Laparoscopic surgery also has the risk of IPH. Research by Dean et al. showed that compared with cold and dry CO2, the intraoperative establishment of warming and humidification CO2 pneumoperitoneum could effectively increase the intraoperative core body temperature by 0.3 ℃ (95%CI 0.1-0.6, P<0.001). A Meta analysis showed that, compared with passive thermal insulation, intraoperative active thermal insulation can effectively reduce the incidence of IPH in patients with spinal anesthesia (RR=0.71, 95%CI 0.61～0.83, P<0.001), but even if active thermal insulation is used, IPH may still occur in some patients, so the combined effects of different insulation strategies need to be further studied.
(2) Pre-heat preservation: Pre-heat preservation can effectively reduce heat redistribution, make patients rewarming faster during surgery, and reduce the incidence of IPH and adverse outcomes. A systematic review of 14 RCTS showed that inflating and pre-heat preservation can effectively reduce the incidence of IPH in patients undergoing general anesthesia and intraspinal anesthesia, while the application of other heating systems in preinsulation needs further study. Studies have shown that the pre-heat preservation time is generally 15 min to 2h, and the recommended average pre-heat preservation time is 30 min. At least 10 min preheat preservation time is needed to effectively maintain the normal body temperature during surgery. Research by Alfonsi et al. showed that pre-thermal insulation combined with intraoperative thermal insulation can effectively prevent IPH (OR=0.48, 95%CI 0.24～0.96, P=0.025). Therefore, clinical measures of prethermal insulation combined with intraoperative thermal insulation should be further studied to increase the effectiveness of thermal insulation strategy.
Munday and other studies have shown that for women undergoing cesarean section under intraspinal anesthesia, intraoperative conventional heating and infusion combined with short-term preheat preservation (20 min) cannot prevent intraoperative hypothermia. Grote et al. showed that the interruption of thermal insulation between the end of pre-thermal insulation and the start of intraoperative thermal insulation could reduce the effect of pre-thermal insulation, and the interruption time was significantly positively correlated with the incidence of intraoperative hypothermia (P<0.001).
(3) Composite insulation: The guidelines suggest that the use of composite insulation to enhance active insulation. Zhang et al. compared the effects of different heat preservation methods on IPH in patients undergoing transurethral resection of the prostate under subarachnoid block. The study selected 443 elderly patients and randomly divided them into group F (intraoperative inflation heating) , E group (using electric blanket during the operation) and FE group (using inflatable heating and electric blanket during the operation), the device temperature is set to 38℃, the results showed that, compared with the FE group, the heart rate and average artery of the F group and the E group The blood pressure increased significantly, the temperature of the esophagus decreased significantly, the incidence of chills and arrhythmia increased significantly, and patient satisfaction decreased significantly.
Chebbout et al. selected 132 women who had undergone cesarean section with subarachnoid block. All women received warming and infusion. According to the absence of other active heat preservation, intraoperative air heating, and intraoperative mattress heating In the three groups, the results showed that there was no statistically significant difference in the average core body temperature between the mothers and the newborns in the three groups. Therefore, the researchers believe that only the use of warming infusions during the operation can prevent maternal IPH, and the addition of other active warmth does not increase the benefit.
Rao Yuquan et al. selected 80 patients undergoing spinal surgery under general anesthesia, and they were randomly divided into four groups: intraoperative heating and infusion group (FW group), intraoperative inflatable heating blanket group (AW group), intraoperative heating and infusion + inflatable heating Blanket group (FA group) and pre-operation inflatable heating blanket pre-warm for 30 min + intraoperative heating infusion + inflatable heating blanket group (PFA group), the results showed that compared with FW group, AW group, FA group and PFA group cut Body temperature increased significantly after 60 minutes after skin and 10 minutes after entering PACU, the incidence of postoperative chills was significantly reduced, and patient satisfaction increased significantly, suggesting that the effect of inflatable heating is better than heating infusion, but at different points in the AW group and FA group The difference in core body temperature between the PFA group and the PFA group was not statistically significant.
3. Increase the ambient temperature: It is generally recommended at home and abroad that the temperature in the operating room for adults should not be lower than 21℃. A 3 x 2 factorial experiment according to different environmental temperature in (19, 21, 23 ℃) and passive insulation or gas heating to randomly assigned 292 patients, the results showed that the environmental temperature on the gas heating temperature had no obvious effect on the patient, the use of passive insulation core body temperature can have an impact on patients, 1 ℃ ambient temperature increase, The core body temperature at the end of surgery was increased by 0.13 ℃ (95%CI 0.07-0.20, P<0.01).
For children with surgery, the operating room temperature should not be lower than 24℃. A single-center RCT divided the cesarean women who received intraoperative warming and infusion into two groups according to the temperature of the operating room (20 ℃ and 23℃). The study showed that moderately increasing the ambient temperature to 23℃ can significantly reduce the newborn ( 35% vs 50%, P<0.001) and maternal (69% vs 77%, P=0.008) incidence of postoperative hypothermia, no effect on the incidence of neonatal complications such as hypoglycemia and metabolic acidosis.
Drug intervention: Studies have shown that effective drug mechanisms for preventing IPH are mainly divided into reducing calorie redistribution (such as: phenylephrine) and increasing metabolic heat production (such as: fructose, amino acids). A single blind RCT study to investigate the effect of different general anesthesia induction methods on reducing heat redistribution showed that both sevoflurane inhalation induction and prophylactic administration of phenylephrine before intravenous induction of propofol were effective in reducing redistributive hypothermia between 0.4 and 0.5℃. Aoki et al. compiled 14 RCT analyses and showed that amino acid infusion can increase body temperature by 0.46℃ (95% CI 0.31～0.62, P<0.001), reduce the occurrence of chills, and shorten the time of extubation and hospitalization.
Summary
IPH is a common perioperative complication. At present, evidence-based guidelines for the prevention of IPH have been formulated internationally. Future research should comprehensively consider factors such as clinical benefits and potential risks, starting from the incidence of IPH and its complications, and comparing different insulation strategies from multiple angles. In clinical practice, the perioperative temperature management strategies of different types of surgery should be combined with their characteristics and have their own focus, and at the same time, individualized management of patients with different underlying diseases should be implemented. In addition, factors such as the degree of attention of medical staff, multidisciplinary collaboration, and policy support may be important factors in promoting the temperature protection of clinical patients.
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