Ninety minutes after drinking a glucose-containing solution, MRI analysis revealed that gastric fluid volume was less than 1 mL/kg. (Image source: Thinkstock)

Ninety minutes after drinking a glucose-containing solution, MRI analysis revealed that gastric fluid volume was less than 1 mL/kg. (Image source: Thinkstock)

We all know that preoperative clear liquid administration is allowed two hours before the initiation of anesthesia. Recent research has also shown that when given before surgery, a nutritional supplement composed of a carbohydrate-loaded beverage can enhance recovery after certain operations (e.g., colonic resection) and can facilitate healing. Such oral nutritional supplements are clear fluids, but how does gastric emptying following oral nutrition supplements compare to a standard oral rehydration solution of just glucose and electrolytes? Dr. Kanji Uchida, Department of Anesthesiology and Pain Relief Center, The University of Tokyo Hospital, Tokyo, Japan, and colleagues used magnetic resonance imaging to measure changes in gastric volume when patients were given a standard rehydration or an oral nutrition supplements. Their results are summarized in “The Effects on Gastric Emptying and Carbohydrate Loading of an Oral Nutritional Supplement and an Oral Rehydration Solution: A Crossover Study with Magnetic Resonance Imaging,” a manuscript published in the June 2014 issue of Anesthesia & Analgesia.

The study included ten otherwise healthy volunteers. They were asked to drink either 500 mL of a conventional glucose containing oral rehydration solution (270 mOsm/L) or the same volume of a carbohydrate loaded arginine-containing oral nutritional supplement (545 mOsm/L). The volunteers consumed the liquid within 3 minutes. MRI scans were performed 30, 60, 90, and 120 minutes after fluid consumption. Gastric fluid volume decreased in both groups after ingestion. The gastric fluid volume of all participants after administration of the rehydration solution was less than 1 mL/kg at 90 minutes. At 120 minutes, none of the volunteers given the arginine-containing supplement had a gastric fluid volume that was less than 1 mL/kg. Blood glucose values were higher after drinking the nutritional supplement. Only men were included in this study and the volunteers were healthy.

Anxiety is probably greater for patients undergoing surgery, and it is not clear how anxiety might have affected outcome. The authors also did not include a control group of patients who only drank water in the study. Nonetheless, oral rehydration solutions with glucose given two hours before surgery may be safe in terms of risk of gastric aspiration, but carbohydrate loaded oral nutritional supplements are associated with significant gastric volumes and elevated glucose.