Materials and Methods
bleeding, hypothermia, blood loss, Postoperative pain, pain, shivering, NRS
BLEEDING, BLOOD LOSS, ADVERSE EVENTS, CAVITY, COLD
This prospective randomized controlled study was approved by the Institutional Review Board (KYUH 2021-08-007) of our hospital and registered at the Korean Clinical Research Information Service (We included patients aged 19-79 years with an American Society of Anesthesiologists Physical Status I-II who underwent elective urological surgery with an expected surgical duration of ≥ 60 min. The exclusion criteria were surgery involving large amounts of bleeding or transfusions were expected; surgery requiring carbon dioxide insufflation in the abdominal cavity; a patient preoperative body temperature of < 36.0°C or > 37.5°C; a patient body mass index of > 35 kg/mThe patients were randomly assigned to one of two groups at a 1:1 ratio by an assistant unrelated to this study using online randomization software (Researcher Randomizer; www.randomizer.org) and the patient's group allocation was concealed in sealed opaque envelopes. The patients in the experimental (prewarming and phenylephrine infusion) group (PP group) received active prewarming for 20 min using a forced-air warming device and intravenous phenylephrine infusion during anesthesia, while those in the control group (C group) received usual care (i.e., no active prewarming and intermittent administration of vasoactive agents depending on blood pressure and HR). Upon patient arrival at the preoperative holding area, an anesthesia resident not involved in data collection opened an opaque, sealed envelope containing the patient's group allocation.At our hospital, the ambient temperatures of the preoperative holding area and post-anesthesia care unit (PACU) were adjusted to a target range of 22-25°C. The ambient operating room temperature was measured using a digital thermometer (Model No. TH01D, Kyungin, South Korea) mounted on a wall away from a cooling or heating unit and recorded at the start and end of the surgery.The patients fasted for at least 8 hrs and did not receive premedication. In the preoperative holding area, their sublingual temperature was measured by a trained anesthesiology resident by placing the probe (Welch-Allyn SureTemp Plus Electronic Thermometer Model 692, Welch Allyn Inc., Skaneateles Falls, NY, USA; accurate to ± 0.1°C for patient temperatures in the range of 26.7-43.4°C) under the tongue in the posterior sublingual pocket lateral to the center of the lower jaw. Thereafter, patients in the C group received standard preoperative passive insulation using a cotton blanket, whereas those in the PP group received active warming using a forced-air blanket (Bair HuggerUpon arrival in the operating room, standard monitoring, including pulse oximetry, electrocardiography, non-invasive automated blood pressure measurement, patient state index (PSI; SedLine®; Masimo Corp., Irvine, CA, USA) assessment, and acceleromyography (TOF-Watch SXAnesthesia was maintained with desflurane and 50% nitrous oxide (0.8-1.2 of age-adjusted minimum alveolar concentration) to maintain the PSI at 25-50. In the PP group, phenylephrine infusion was initiated at an initial dose of 0.3 μg/kg/min immediately after anesthesia induction and allowed up to 0.7 μg/kg/min as long as the SBP did not exceed 120% of the preanesthetic SBP (baseline). The phenylephrine infusion was maintained until the end of surgery at a dose range of 0.3-0.7 μg/kg/min. In contrast, in the C group, phenylephrine was administered intermittently at 50-100 μg when the SBP decreased to < 80% of the baseline. In both groups, nicardipine (0.5 mg) was administered intravenously if the SBP exceeded 120% of the baseline or 180 mmHg. When the SBP decreased to < 80% of the baseline and the HR was < 50 beats/min, ephedrine (5-10 mg) was administered intravenously. When the HR was < 45 beats/min or > 120 beats/min, atropine (0.5 mg) or esmolol (10 mg) was administered.At the end of surgical preparation, including positioning, surgical scrubbing, and draping, all patients received forced-air warming on their upper body at a set temperature of 38°C throughout the surgery. During anesthesia, inhaled gas was supplied through a respiratory circuit heated to 39.5°C and humidified, and intravenous and irrigation fluids were administered at room temperature. After anesthesia, the volumes of intravenous and irrigation fluids and blood loss estimated by the surgeon were recorded.In the PACU, forced-air warming (set temperature 43°C) was applied when the patient's body temperature was < 36°C or the patient complained of feeling cold or when shivering was observed. If shivering was present, 25 mg meperidine was administered intravenously. Postoperative pain was evaluated using a numeric rating scale (NRS; 0 = no pain, 10 = worst pain imaginable); if an NRS score of > 4 and analgesics were requested, 0.5-1 μg/kg of fentanyl was administered intravenously. All adverse events occurring in the PACU were recorded.In this study, hypothermia was defined as a sublingual or nasopharyngeal temperature of < 36°C, and the hypothermia severity was graded as mild (35.5-35.9°C), moderate (35.0-35.4°C), or severe (34.5-34.9°C) 