Effects of Bolus and Continuous Nasogastric Feeding on Small Bowel Water Content and Blood Flow

• Background. Nutritional support is often required for undernourished patients who are unable to meet daily nutritional requirements. This is often due to lack of consciousness or problems with swallowing, Nasogastric (NG) feeding is often employed to provide active enteric nutritional support. The current approach for delivering this support usually involves pump-assisted continuous feeding spread throughout the course of a day. However, this practice is far from physiological and may promote excessive secretion of fluid into the small bowel, contributing to gastrointestinal symptoms frequently experienced by NG fed patients. Rarely, continuous enteral tube feeding has been associated with small bowel ischaemia or necrosis, although this observation has almost always been made in the critically ill. Bolus feeds given in larger volumes over shorter time periods replicate the pattern of normal feeding. Consequently gastric emptying using this method is slowed and may, therefore, reduce the metabolic demand on the small intestine and prevent excessive accumulation of small bowel fluid.
• Aims. This study aims to investigate the influence of bolus or continuous NG feeding on small bowel fluid content and superior mesenteric blood flow. Our hypothesis is that bolus NG feeding results in lower small bowel fluid secretion and a reduction in superior mesenteric artery blood flow in comparison to individuals who are bolus NG fed.
• Experimental protocol and methods.

This is a single-centre, cross-over study involving 12 healthy volunteers. Two studies will be undertaken for each volunteer approximately 7 days apart:

• Tube bolus (TB): feed administered via the NG tube over 5 min.
• Continuous tube drip feeding (TD): feed pump delivered via the NG tube over 4 h.

The sequence of treatment allocations will be concealed to assessors until all interventions, data collection, and statistical analysis has been completed.

Subjects will be asked to arrive at 8:30 a.m. at the Sir Peter Mansfield Magnetic Resonance 1.5T, University of Nottingham, having abstained from alcohol, caffeine-containing drinks, and any medication for at least 24 h prior to the study, as well as having fasted overnight. An 80 cm 8FR Freka (Fresenius Kabi, Runcorn, UK) fine bore nasogastric (NG) tube will be inserted into the stomach via the nose as well as a cannula in the ante cubital fossa for blood sampling. The position of the NG tube will be verified by magnetic resonance imaging (MRI). Once the tube is sited, the volunteer will be asked to sit for 5 min in order to allow the tubes to settle and the body adapt to their presence. Following NG intubation subjects will undergo baseline MRI scanning and blood sampling for glucose, insulin and PYY. Feeding will commence at time 0. Scanning and blood tests will proceed at 30 min intervals for a total of 4 h. The feed used in all studies will be 400 ml of Resource® Energy Vanilla nutrient drink (Nestle Nutrition, Société des Produits Nestlé S.A), which is typical of a standard oral supplement.

In the TB study arm the supplement will be administered through the NG tube via syringes over 5 min; and in the TD study the feed will be administered using a pump at a rate of 100 ml/h for 4 h.

• Measurable end points/statistical power of the study. Primary endpoint: Small bowel water content (SBWC). Secondary endpoints: Superior mesenteric artery blood flow, gastric content emptying time, plasma concentrations of glucose, insulin and peptide YY (PYY). Previous work using mannitol and glucose indicates that mean (SD) SBWC at 40 minutes postprandially after ingesting 300ml glucose was 47 (SD 15) and using n=10 we calculate we can detect a difference of 17 ml (36%) between interventions with 90% power. We plan to recruit 12 to allow for dropouts.

Inclusion criteria

• Healthy
• Male
• Able to undergo safe magnetic resonance scanning

Exclusion criteria

• Female
• Chronic medical conditions
• Regular medication
• Unable to undergo safe magentic resonance scanning
• Previous abdominal surgery
• Smoking