Influence of Fasting Duration on Body Fluid and Hemodynamics

Fasting before general anesthesia aims to reduce the volume and acidity of stomach contents, which reduces the risk of regurgitation and aspiration. Prolonged fasting for many hours prior to surgery could lead to unstable hemodynamics, however. Therefore, preoperative oral intake of clear fluids 2 hours prior to surgery is recommended to decrease dehydration without an increase in aspiration risk. In this study, we investigated the body fluid composition and hemodynamics of patients undergoing general anesthesia as the first case of the day versus the second subsequent case. We retrospectively reviewed the general anesthesia records of patients over 20 years old who underwent oral maxillofacial surgery. We investigated patient demographics, preoperative fasting time, anesthetic time, urine output, infusion volume, and opioid and vasopressor use. With respect to body fluid and hemodynamics, we extracted the data from the induction of anesthesia through 2 hours of anesthesia time. Thirty patients were suitable for this study. Patients were divided into 2 groups: patients who underwent surgery as the first case of the day (am group: n = 15) and patients who underwent surgery as the second case (pm group: n = 15). There were no significant differences between the 2 groups in patient demographics. In the pm group, fasting time for a light meal (832 minutes) was significantly longer than for the am group (685 minutes), p = .005. In the pm group, fasting time for clear fluids (216 minutes) was also significantly longer than for the am group (194 minutes), p = .005. Body fluid composition was not significantly different between the 2 groups. In addition, cardiac parameters intraoperatively were stable. In the pm group, vasopressors were used in 4 patients at the induction of anesthesia (p = .01). There were not statistically significant changes in cardiac function or body fluid composition between patients treated as the first case of the day vs patients who underwent surgery with general anesthesia as the second case of the day.