Hypothermia is a common complication in pediatric anesthesia. Hypothermia will prolong the recovery time of anesthesia, and may also lead to increased oxygen consumption, prolonged blood coagulation time, and affect the metabolism of anesthetic drugs and postoperative immune function. Sevoflurane is the most commonly used inhaled anesthetic in children. This study explored the effect of sevoflurane on the sweat threshold of pediatric patients and analyzed the characteristics of body temperature regulation in children of different ages under anesthesia, which will help to understand the mechanism of body temperature regulation in children under anesthesia, and also provide a scientific basis for clinical anesthesia temperature management.

Standardized anesthesia induction was used for all participants. The first step was mask oxygen inhalation under 5 L/min pure oxygen, and 8% sevoflurane was inhaled for induction. Once the child lost consciousness, the concentration of sevoflurane was reduced to 3%-5% and maintained at 1.2 MAC as much as possible. Tracheal intubation was then assisted with cisatracurium 0.2 mg/kg. Mechanical ventilation was maintained during the operation, and the end-tidal carbon dioxide level was monitored and maintained at about 35 mmHg. Caudal anesthesia with 0.25% ropivacaine was used to provide surgical site analgesia. TOF was performed throughout the procedure to monitor the depth of neuromuscular block. Core temperature was measured in the distal esophagus. The esophageal probe was inserted after intubation to a depth of one quarter of the patient's height plus 4.5 cm. Changes in surface humidity were monitored using an OM-62 humidity sensor, which was placed above the nipple line in the upper chest and suspended in the ostomy bag. The ostomy bag will be custom-cut as needed to ensure optimal fit and precise airflow control. Infants and young children (<6 years) will use a 4-cm diameter opening, while older children (6 to 12 years) will use a 6-cm diameter opening. To ensure smooth airflow in the stoma bag, a low flow meter will be used to accurately adjust the airflow rate to 0.5L/min. Skin water loss (in g/m²/h) will be calculated from airflow rate, temperature, and relative humidity, and sweating on the child's forehead will be observed and recorded every 3 minutes. The skin surface was wrapped with a plastic film to limit evaporation. An air mattress was used to cover the body up to the nipple line. Two disposable covers were placed on each chest and leg and connected to an inflatable heating device, respectively. The inflatable heating device was set to 43 ° C until the esophageal temperature reached 38 ° C. Core temperature as well as temperature and humidity in the ostomy bag were collected every minute. The Hotline system was used to warm the intravenous infusion. Once the patient's core temperature reached 38 ° C or the procedure was over, active warming was stopped. Heart rate and pulse oxygen saturation were continuously monitored, and blood pressure was measured every 3 minutes. Simulated data from the heart rate monitor, sweat sensor, respiratory gas monitor, and pulse oximeter were recorded at 3-min intervals using the data acquisition system described above. The end-expiratory anesthetic concentration during the whole procedure was also recorded.

Inclusion Criteria:

1. Age: 0-12 years old;
2. American Society of Anesthesiologists physical status I or II;
3. Weight within the normal range and body-mass index (BMI) for age between the 25th and 85th percentiles;
4. scheduled elective lower-body surgery under general anesthesia, expected to last at least 1 hour.

Exclusion Criteria:

1. The guardian of the child refused to participate in the study;
2. Operations involving extensive incisions, such as massive debridement or other operations requiring removal of large amounts of tissue;
3. Contraindications to esophageal temperature probe insertion (e.g., esophageal varices, congenital anomalies);
4. Thyroid dysfunction or autonomic dysfunction;
5. Premature infants (≤1 year old).