Changes in the Respiratory Quotient during Surgery with or without Carbohydrate Loading

Usually glucose is used as an energy source intraoperatively, and recently maltose containing fluids was introduced as intraoperative fluid supply. However, the optimal dosage and form of intraoperative carbohydrate have not yet been known. The authors compared changes in the RQ during surgery without any energy source supply, and with administration of glucose or maltose in twenty eight males and females to know the effects of carbohydrates administration on RQ during surgery and to estimate the optimal dosage and form of intraoperative carbohydrates. Patients in group 1 received no carbohydrates during the operation; in groups 2 and 3, patients were given 0.25g glucose/kg and 0.5g glucose/kg/hr respectively, and patients in groups 4 and 5 received maltose at the speed of 0.25g/kg/hr, respectively. No differences in RQ were observed before the beginning of surgery among groups. In group 1, the RQ decreased from 0.85 ± 0.08 (X ± S.D.) to 0.72 ± 0.04 at 150 min after the beginning of the operation. In groups 2 and 3 (the glucose groups) and group 4 (the maltose group), the RQ also had fallen at 150 min, from 0.86 ± 0.06 to 0.74 ± 0.06 (group 2), 0.86 ± 0.05 to 0.80 ± 0.05 (group 3), 0.86 ± 0.03 to 0.81 ± 0.03 (group 4). Group 5 was the only group in which we could not observe any significant change of RQ during surgery (0.85 ± 0.06 to 0.84 ± 0.03).

Without carbohydrates administration, the RQ decreased to nearly 0.7, indicating that the main energy source of the patients changed from carbohydrates to lipids. This reduction of RQ during operation can be inhibited with administration of carbohydrates, which suggests that the administered carbohydrates were utilized as the energy source during the time of surgery, and maltose 0.5g/kg/hr is thought to be suitable for intraoperative use as an energy source.