This prospective, single-blind, randomized, controlled study was approved by the Ethics Committee of the First Affiliated Hospital of Zhengzhou University（2020-KY-176），and was registered at http://www.chictr.org.cn/index.aspx(ChiCTR2000039162) on 20 October 2020. All patients signed the informed consent. Our methodology was executed in accordance with the international guidelines for randomized clinical studies according CONSORT Guidelines.
75 patients scheduled for elective laparoscopic hysterectomy. Inclusion criterion:1) Aged 40-65 years；2) American Society of Anesthesiologists’ physical status class of Ⅰ to Ⅱ; 3) No serious heart, liver, kidney disease;4) No history of severe respiratory or cerebrovascular disease. Exclusion criterion: 1) preoperative anemia; 2) intraoperative blood transfusion; 3) switch to open surgery.75 patients were randomly divided into 3 groups using a random number table: control group(A), infusion heating group(B) or incubator group(C).
No patients were premedicated and the operating room was kept at 22-24°C. All three groups use warming blankets and turn them on an hour in advance so that the warming blanket reaches the preset temperature(38°C). After entering the operating room, patients in the three groups were first injected with 500ml Ringer's lactate solution and then with 500ml succinylated gelatin, the infusion speed was controlled at 10ml/min. In group A, the infusion fluid was not treated and the temperature was room temperature; In group B, the infusion fluid was heated by the infusion thermometer, and the target temperature of the infusion thermometer was set at 37°C; In group C, the infusion fluid was stored in an incubator with the target temperature set at 37°C.
Nasopharyngeal temperature was monitored after anesthesia induction in all three groups, and vital signs were kept stable during the operation. If the intraoperative nasopharyngeal temperature of the patient is lower than 35°C, the temperature of the warming blanket will be increased to maintain the nasopharyngeal temperature of the patient above 35°C.
The primary outcome was nasopharyngeal temperature at 5min after anesthesia induction(T1),30min(T2),60min (T3), and 90min (T4) at the beginning of surgery in the three groups. Secondary outcome was wake-up time in three groups.
SPSS was used for all statistical analysis (version 22.0, SPSS Inc, Chicago, IL, USA), measurement data were expressed as mean ± standard deviation, and analysis of variance was used for comparison between groups, the nasopharyngeal temperature was compared at different time points by repeated measurement ANOVA, Chi-square test was used to compare counting data, and P < 0.05 was considered statistically significant.
The sample size was calculated using GPower (version 220.127.116.11, Franz Faul, Universitat Kiel, Germany), studies have shown that a core temperature difference of 0.5°C is clinically significant because 0.5°C is the smallest difference associated with hypothermic complications . With the significance level(α) set at 0.05, power(1-β) at 0.9, then each group needs to include 22 patients, assuming that the rate of withdrawal is 10%, then each group will eventually have 25 patients enrolled.