Gastric fluid volume and pH in elective patients following unrestricted oral fluid until three hours before surgery

Abstract

This clinical study was designed to assess the results of new preoperative fasting guidelines in which patients are instructed that they must not eat any solid food after midnight, but that they may drink unrestricted amounts of clear fluid until three hours before their scheduled time of surgery. We studied 199 healthy, elective surgical inpatients aged 18- 70 yr to determine whether there was any corrélation between the ingestion interval or the volume of fluid ingested, with the volume and pH of residual gastric fluid at induction of anaesthesia. Pregnant patients, and those with gastric disorders or who were taking medications that affect gastric motility or secretion, were excluded. Either no premedication was given, or oral diazepam 5- 15 mg was given 90 min preoperatively. Of the 199 patients, 105 ingested 50- 1200 ml on the morning of surgery. The ingestion-induction interval was less than three hours in 12 patients whose actual surgery time was ahead of schedule. The remaining 94 patients did not drink because they were scheduled for surgery before 11:00 (n = 51), they did not want to drink (n = 24), or they were advised not to drink by their nurse or surgeon (n = 16). Following induction of anaesthesia, gastric fluid was aspirated through a #18 Salem sump orogastric tube, the volume was recorded and pH was measured with à calibrated pH meter. Patients were divided retrospectively into four groups (in three of which patients ingested fluid) according to the ingestion-induction interval (1.3- 3.0 hr, 3.1- 5.0 hr, 5.1- 8.0 hr, and nothing by mouth after midnight). Values (mean ± SD) for residual gastric fluid volume (22 ± 19, 32 ± 26, 28 ± 19, 25 ± 19 ml) and pH (1.5 ± 0.3, 1.7 ± 1.3, 1.6 ± 1.1, 1.6 ± 0.9) showed no statistically significant differences among the four groups. Within each of the three fluid groups there was no correlation between volume of fluid ingested and residual gastric fluid volume. We conclude that healthy inpatients should be allowed to ingest unrestricted clear fluid until three hours before the scheduled time of surgery. © 1991 Canadian Anesthesiologists.