I. Related Terms and Definitions Surgical site infection ,SSI, refers to infections occurring in superficial incisions, deep incisions and organs, and refers to surgery-related infections occurring in patients within 30d after surgery and surgery without implants, and within 90d after surgery and surgery with implants. Intraoperative hypothermia (intraoperative hypothermia) is an intraoperative body core temperature of less than 36°C, also known as accidental intraoperative hypothermia, is a very common complication in anaesthesia and surgery.
Second, the risk factors of surgical site infection SSI is the most common and highest incidence of health care related infections in low- and middle-income countries, with an incidence rate of 11.8% (1.2%-23.6%), and the incidence rate of SSI in China is the third highest in HAI, accounting for 14-16% of inpatient infections.The risk factors of SSI include patient factors, surgical factors, and environmental factors, among others. Patient factors include age, nutritional status, immune function, and underlying diseases. Surgical factors include duration of surgery, type of incision, surgical technique, and intraoperative bleeding. Environmental factors include operating room temperature, humidity, air quality, etc.
There are many risk factors for intraoperative hypothermia, including patient factors, surgical factors, anaesthesia factors, environmental factors, and whether or not to intervene. Patient factors include: age >60 years old, BMI <25kg/m2, patients with ASA grade II or above, and patients with low preoperative basal body temperature, etc. Surgical factors include: the higher the surgical grade, surgical method (open or minimally invasive surgery), surgical time >2h, and failure to warm up the intraoperative irrigation solution, etc. Anesthesia factors include: anesthesia method, anesthesia time, and anesthesia medication, etc., which lead to the occurrence of intraoperative hypothermia. The anaesthesia factors include: anaesthesia method, anaesthesia time and anaesthesia drugs, etc.; the environmental factors are mainly the temperature of the operating room, usually the temperature of the operating room is lower than 21 ℃, the risk of hypothermia in the patient is higher.
The influence of intraoperative hypothermia on surgical site infection Intraoperative heat preservation refers to maintaining the patient's body temperature within the normal range during surgery to avoid the occurrence of hypothermia. Hypothermia refers to a body temperature below 36°C, which is one of the common complications in surgery and can lead to a series of adverse consequences, such as increasing cardiovascular complications, affecting coagulation, prolonging anaesthesia awakening time, and increasing postoperative pain. Intraoperative heat preservation can not only improve the comfort of patients, but also reduce the risk of surgical site infection and reduce the incidence of surgical site infection.
V. Evidence-based level of maintaining normal body temperature during surgery The 2019 Chinese Guidelines for the Prevention of Surgical Site Infections suggests the use of thermal insulation facilities for whole-body warming during surgery in the operating theatre to reduce surgical site infections. Maintaining perioperative normothermia is recommended (Level of recommendation: conditional recommendation. Quality of evidence: moderate quality evidence). Deep body temperature ≥36°C should be maintained during the perioperative period. Intraoperative and postoperative hypothermia is caused by a combination of impaired thermoregulation due to anaesthesia and exposure to hypothermia in the operating theatre. Unintended hypothermia is associated with increased cardiovascular complications, impaired coagulation, slowed wound healing, decreased immune function, and increased risk of SSI infection.
VI.PERIOPERATIVE WARMING STRATEGIES Methods of perioperative warming include preoperative pre-warming, intraoperative warming, and postoperative warming. (I) Preoperative pre-insulation Preoperative pre-insulation refers to preoperative measures in which the patient receives active insulation to increase energy storage and hypothermia thresholds, and to reduce core body temperature reduction and heat redistribution. Pre-warming significantly reduces the incidence of perioperative hypothermia. The increase in peripheral heat after 30 min of pre-warming can offset the loss of heat from redistribution in the first hour after induction of anaesthesia. Preoperative pre-warming is recommended to be done by inflatable warming for at least 10min.
（Intraoperative warming refers to the measures taken to maintain the patient's body temperature throughout the process from the beginning of anaesthesia to the end of surgery when the patient leaves the operating room. Maintaining the patient's intraoperative body temperature can effectively reduce the occurrence of perioperative adverse events. The main measures of intraoperative heat preservation are physical heat preservation measures, mainly passive heat preservation, active heat preservation and environmental heat preservation. Passive insulation: Passive insulation promotes heat retention and should be used throughout the operation, including insulation measures such as artificial noses, cotton blankets, surgical sheets, reflective blankets and thermal blankets. Passive insulation reduces heat loss by approximately 30 per cent, and its effectiveness is related to the material, area and number of layers of coverings. Active insulation: active insulation mainly refers to the use of heating devices to generate heat to be applied to the skin and other peripheral tissues. Measures such as inflatable heating devices, intravenous infusion heating devices, conductive heating systems, warm cavitary irrigation fluid or CO2 pneumoperitoneal gas heating can be used. Ambient temperature control: the ambient temperature can be set as the comfortable temperature of the operating room team, and it is generally recommended at home and abroad that the temperature of the operating room should not be lower than 21℃ for adults during surgery, and the temperature of the operating room for paediatric surgery should not be lower than 23℃. (C) postoperative thermal insulation postoperative thermal insulation refers to the postoperative refers to the recovery phase within 24h after the patient leaves from the operating theatre, continue to maintain the patient's body temperature after surgery. Dynamic assessment of the patient's thermal comfort, when the patient has symptoms of hypothermia, such as chills, preferred inflatable heating device to keep warm, if the symptoms do not improve, drugs can be given to reduce or inhibit the chills.
Summary
Intraoperative warming is one of the most important measures to prevent surgical site infection. By maintaining the patient's body temperature within the normal range, it can improve the immunity of the body, reduce intraoperative bleeding, shorten the operation time, reduce postoperative pain, and improve the comfort of the patient. Therefore, healthcare professionals should pay attention to intraoperative warmth and take effective measures for intraoperative and postoperative thermal insulation to reduce the incidence of surgical site infections.