Factors Influencing the Occurrence of Intraoperative Hypothermia in Patients Undergoing General Anesthesia Intervention: A Study in a Tertiary Care Hospital

Introduction

Inadvertent perioperative hypothermia (IPH) is an inadvertent perioperative core body temperature lower than 36 °C due to various reasons [1]. It is a recognized and common complication in the perioperative period. Prevention is the best management method [2]. The incidence of perioperative hypothermia is high (7–90%), with 39.9% reported in Beijing in 2015 and 44.5% reported in a cross-sectional investigation in 2017 [3–5]. Hypothermia can enhance the discomfort of patients during anesthesia and recovery, such as reducing metabolism of anesthetic drugs and delaying recovery. Increased incidence of adverse events, such as infection and wound complications, cardiovascular complications, decreased coagulation, and increased need for blood transfusions, can occur [6,7]. With the development of medical technology, interventional surgery has been widely used in clinical practice because of its lower trauma and faster recovery [8]. However, due to the use of anesthetic drugs and the complicated and time-consuming procedures of interventional surgery, intraoperative and postoperative hypothermia of patients can be caused, and the problem of intraoperative hypothermia of patients undergoing interventional surgery under general anesthesia requires urgent attention [9,10]. The current research on intraoperative hypothermia mostly focuses on open surgery, such as gastrointestinal surgery, orthopedics, thoracic obstetrics, and gynecology, and focuses on the application of thermal insulation equipment and nursing intervention, and there are no relevant studies on the current occurrence of hypothermia during interventional surgery and its influencing factors [11–13]. Therefore, this retrospective study included 184 patients to investigate the incidence and related factors of hypothermia during anesthesia in a single center in China from January to October 2023.

Material and Methods

STUDY DESIGN:

The investigators wrote the study protocol and submitted the informed consent form and other materials to the Biomedical Ethics Review Committee of West China Hospital of Sichuan University, which approved the study after strict review and modification (approval number: 2021541). The investigators informed all patients of the purpose and methods of the study before surgery, clarified the patients’ informed consent, and instructed them to sign the informed consent form.

Patients undergoing general anesthesia interventional surgery in a grade III hospital in Sichuan Province from January 2023 to October 2023 were selected by a convenience sampling method as the study participants. The inclusion criteria were as follows: (1) patients who planned to undergo interventional surgery under general anesthesia; (2) age ≥18 years old; and (3) clear consciousness and ability to communicate normally. The exclusion criteria were as follows: (1) preoperative core body temperature >37.5°C due to infectious diseases and other reasons; (2) serious complications occurred during perioperative period, such as intraperitoneal hemorrhage and ruptured intracranial aneurysm; (3) patients undergoing re-operation within 24 h; and (4) cognitive impairment or communication disorder.

The sample size was calculated as follows. The number of positive samples was taken from 5 to 10 times the number of variables. Through systematic literature review and expert consultation, we identified 20 factors that can affect IPH. Therefore, the number of positive samples was 100 to 200, and the incidence of hypothermia was 44.3% to 72.7%, while 58.5% was taken in this study. The final sample size should be 170 to 341 cases. In this study, a total of 190 patients met the inclusion criteria, including 2 patients who refused to participate and 4 patients who were missing important data items; a total of 184 patients were included in this study.

DETA COLLECTION:

The collected data included 5 demographic factors (age, sex, height, weight, body mass index), 4 preoperative related factors (preoperative fasting time, preoperative basal body temperature, preoperative heart rate, preoperative blood pressure), and 10 operation-related factors (American Society of Anesthesiologists classification, operation name, operation time, anesthesia time, intraoperative fluid replacement, intraoperative fluid loss, set operating room temperature, warming duration, post-anesthesia body temperature, temperature at beginning of surgery).

To ensure the consistency of the study, the investigators involved in this study were trained in the use of the electronic medical record system and the general questionnaire filling method. The investigators obtained the general information of the patients through the hospital electronic medical record system before the operation, and obtained the temperature information of the operating room through the temperature and humidity control system of the operating room. Surgery-related information was reviewed by the investigator after surgery and filled in according to the anesthesia record sheet. Each questionnaire was completed on the day of the end of the operation and was handed over to a designated person for custody, with 10% of the patient data taken for review.

HYPOTHERMIA COMPLICATIONS AND MANAGEMENT:

A perioperative core body temperature below 36°C due to various reasons is known as perioperative hypothermia, also known as perioperative accidental hypothermia [14]. Hypothermia is caused when the body gives off more heat than it absorbs or produces, resulting in the body’s inability to produce enough heat to maintain a sufficient temperature for normal functioning. Although the underlying causes of accidental hypothermia are excessive cold stress and insufficient heat production by the body (thermogenesis), there are other factors that increase the risk of hypothermia [15]. Perioperative hypothermia can have a variety of deleterious effects, such as cardiac arrhythmias and ischemia, increased peripheral vascular resistance, leftward shift of the hemoglobin-oximetry curve, reversible coagulation dysfunction (platelet dysfunction), postoperative proteolytic metabolism, altered stress response, altered mental status, impaired renal function, decreased medication metabolism, decreased incidence of wound healing, and increased incidence of infection [16]. Once hypothermia has occurred, it is important that the patient be rewarmed promptly to minimize potential complications. There are several interventions that can be used to rewarm the patient. Active heating, particularly forced air heating, appears to reduce the clinically important time it takes for patients with postoperative hypothermic to reach normothermia (between 36°C and 37.5°C) [17].

STATISTICAL METHODS:

All information obtained was organized on an Excel spreadsheet (Microsoft, Redmond, WA, USA) and analyzed using SPSS version 26.0 (IBM Corp, Armonk, NY, USA). Measurements were expressed as mean±standard deviation, and t tests were used to detect differences between groups. Descriptive information was expressed as frequencies and percentages and compared using the chi-square test. Logistic regression analysis was performed to assess potential risk factors. Results were expressed as ratios and 95% confidence intervals. Statistical significance was set at P<0.05.

Results

GENERAL INFORMATION OF PATIENTS:

A total of 184 patients undergoing interventional surgery under general anesthesia were included in this study, including 77 men (41.85%) and 107 women (58.15%), aged 24 to 85 (56.72±12.09) years old. A total of 139 patients (75.54%) underwent cerebrovascular surgery and 45 patients (24.46%) underwent digestive system surgery.

OCCURRENCE OF HYPOTHERMIA DURING SURGERY:

IPH occurred in 64 of the 184 patients (34.78%), with 5 (7.81%) cases occurring before the operation, 7 (10.94%) before the operation after anesthesia, and 52 (81.25%) during the operation.

UNIVARIATE ANALYSIS OF INTRAOPERATIVE HYPOTHERMIA IN PATIENTS:

The occurrence of intraoperative hypothermia in patients undergoing interventional surgery under general anesthesia was taken as the dependent variable, and socio-demographic characteristics, preoperative relevant characteristics, operative relevant characteristics, and anesthesia characteristics were taken as independent variables. The results showed that set operating room temperature, preoperative fasting time, age, operation time, anesthesia time, preoperative core body temperature, post-anesthesia body temperature, and body temperature at the beginning of surgery were the influencing factors for the occurrence of intraoperative hypothermia in patients with general anesthesia intervention (P<0.05), as shown in Table 1.

The variables with P<0.05 in the univariate analysis were taken as independent variables and the occurrence of IPH was taken as the dependent variable for logistic regression analysis. The results showed that age, duration of anesthesia, set operating room temperature, and body temperature at the beginning of the operation were independent influencing factors of IPH, as shown in Table 2.

Discussion

We conducted a retrospective single-center study to determine the risk factors of hypothermia in patients undergoing interventional surgery under general anesthesia. Our results showed that age, duration of anesthesia, set operating room temperature, and body temperature at the beginning of the operation were closely related to the occurrence of hypothermia during the operation. Our research showed that IPH occurred in 64 of 184 patients (34.78%), with 5 (7.81%) cases before the operation, 7 (10.94%) before the operation after anesthesia, and 52 (81.25%) during the operation. Our findings were similar to those of Frisch et al, who found the incidence of intraoperative hypothermia in patients was 32.6% to 43.9% [18].

Our study included patients aged 24 to 85 years, with a mean age of 56±12.09 years. The mean age of the intraoperative hypothermia group was 59.09±12.08 years, and the mean age of the group without hypothermia was 52.74±11.11 years, with a significant difference between the 2 groups (P=0.001). Güven et al [19] reported that the elderly are more prone to intraoperative hypothermia due to their lower basal metabolic rate and delayed sympathetic response to hypothermia, which is consistent with the results of the present study. We should pay more attention to elderly patients, identify the signs of intraoperative hypothermia in patients undergoing general anesthesia intervention at an early stage, appropriately increase the operating room temperature before and after surgery, use heating blankets to control core body temperature when necessary, or warm the infusion fluid to reduce heat loss and avoid intraoperative hypothermia [20].

In this study, the hypothermia group had a longer anesthesia time than did the group without hypothermia, and results showed that prolonged anesthesia time was an important factor in the development of intraoperative hypothermia in patients, which is consistent with the results of Emmert et al [21]. The longer the duration of anesthesia, the more likely the occurrence of intraoperative hypothermia. When the duration of anesthesia ≥3 h, the risk of hypothermia increased by 4.02 times [22]. This may be related to peripheral vascular dilation after anesthesia, which can easily lead to hypotension. At the same time, with prolonged anesthesia, the body temperature regulation center is inhibited, and the reflex is dull, which can easily lead to hypothermia. It is recommended to enhance intraoperative monitor and record the patient’s body temperature before and during anesthesia induction. If the operation is difficult and the duration of anesthesia is expected to be long, family members and relevant medical staff should be informed in advance and insulation measures should be taken.

The set operating room temperature was an influential factor for hypothermia during general anesthesia intervention, which is consistent with the results of Li et al [23]. In clinical work, the temperature of an interventional operating room is usually set at 20°C to 23°C. However, relevant studies have shown that when the ambient temperature is less than 23°C, the risk of patients with hypothermia increases [24,25]. During surgery, we should dynamically adjust the operating room temperature according to the actual situation, such as the season and the thermal comfort of patients, to reduce the heat dissipation of the patient’s body. Meanwhile, body temperature at the beginning of surgery was also an influential factor in the present study, which is consistent with the results of Moola et al [26]. Previous studies have shown that when the preoperative body temperature is higher, the temperature difference between the peripheral skin and core is smaller. The decrease of redistribution of core heat can reduce the occurrence of hypothermia [27]. Moola et al reported that taking warming measures before surgery to prevent hypothermia before surgery could prevent intraoperative hypothermia, which was consistent with the conclusion in the present study, that body temperature at the beginning of surgery affected the occurrence of intraoperative hypothermia. Therefore, we should take effective thermal insulation measures during the whole process of preoperative preparation, transportation, waiting, and entering the operating room [28].

As an observational study, this study had a few limitations. This was a single-center study, there may have been information bias and patient selection bias in the process of data collection, and the sample size was limited. Patient temperature values were derived from electronically captured intraoperative clinical data. Although the use of electronic data capture can reduce human error, it can occasionally introduce spurious values due to increased oral secretions or sensor translocation. The extrapolation of the results still needs to be further verified by multi-center data. In addition, risk prediction tools for intraoperative hypothermia suitable for different surgeries should be further constructed in the future to lay a foundation for accurate intervention of intraoperative hypothermia.

Conclusions

The incidence of intraoperative hypothermia in patients undergoing general anesthesia is high. Age, duration of anesthesia, set operating room temperature, and body temperature at the beginning of the operation are independent risk factors for intraoperative hypothermia in patients undergoing general anesthesia. Clinical medical staff should identify the high-risk groups of intraoperative hypothermia in patients undergoing general anesthesia intervention, and implement efficient intraoperative hypothermia management for patients undergoing general anesthesia intervention in a timely manner to reduce the incidence of intraoperative hypothermia.