Gastric Fluid Volume Change After Oral Rehydration Solution Intake in Morbidly Obese and Normal Controls: A Magnetic Resonance Imaging-Based Analysis

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Although preoperative fluid intake 2 hours before anesthesia is generally considered safe, there are concerns about delayed gastric emptying in obese subjects. In this study, the gastric fluid volume (GFV) change in morbidly obese subjects was investigated after ingesting an oral rehydration solution (ORS) and then compared with that in nonobese subjects.


GFV change over time after the ingestion of 500 mL of ORS containing 2.5% carbohydrate (OS-1) was measured in 10 morbidly obese subjects (body mass index [BMI], >35) scheduled for bariatric surgery and 10 nonobese (BMI, 19–24) using magnetic resonance imaging. After 9 hours of fasting, magnetic resonance imaging scans were performed at preingestion, 0 min (just after ingestion), and every 30 minutes up to 120 minutes. GFV values were compared between morbidly obese and control groups and also between preingestion and postingestion time points.


The morbidly obese group had a significantly higher body weight and BMI than the control group (mean body weight and BMI in morbidly obese, 129.6 kg and 46.3 kg/m2, respectively; control, 59.5 kg and 21.6 kg/m2, respectively). GFV was significantly higher in the morbidly obese subjects compared with the control group at preingestion (73 ± 30.8 mL vs 31 ± 19.9 mL, P = .001) and at 0 minutes after ingestion (561 ± 30.8 mL vs 486 ± 42.8 mL; P < .001). GFV declined rapidly in both groups and reached fasting baseline levels by 120 minutes (morbidly obese, 50 ± 29.5 mL; control, 30 ± 11.6 mL). A significant correlation was observed between preingestion residual GFV and body weight (r = .66; P = .001).


Morbidly obese subjects have a higher residual gastric volume after 9 hours of fasting compared with subjects with a normal BMI. However, no differences were observed in gastric emptying after ORS ingestion in the 2 populations, and GFVs reached baseline within 2 hours after ORS ingestion. Further studies are required to confirm whether the preoperative fasting and fluid management that are recommended for nonobese patients could also be applied to morbidly obese patients.

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