Abstract
This study was designed to measure viscosity, osmolality and in vitro flow rates via nasogastric tubes for 6 types of commercially available and 9 hospital-blenderized enteral solutions and to examine the effect of viscosity and osmolaility of enteral formula on the flow rates in gravity drip administration. Each solution was infused through 18, 16, 14, 12 French sizes of silicone rubber tube. Flow rates were measured six times at $25^{\circ}C$ using formula bags and drip sets hung at a uniform height on a intravenous drip stand with tube uniformly positioned in collecting container. Viscosity ranged widely from 16.0 to 195.5 cps with mean, 64.61$\pm$64.42 for hospital-blenderized formula while mean viscosity of commercial formula was 7.60$\pm$4.84 cps. Mean osmolality of commercial formula and hospital-blenderized formula were 370$\pm$100.80, 540.33$\pm$89.37 mOsm/kg respectively. There was negative relationship between viscosity of formula and flow rates through tubes but no significant relationship between flow rates and osmolalty. Some of hospital-blenderized formula was too viscous to be infused througth tube with gravity drip administration and the recipe of formula requires to be modiifed. On the other hand, commercial formula with the low viscosity flows too rapidly with large bore size tubes. Smaller size of tube must be selected for hyperosmolar solution to decrease possible side effects associated with tube feeding. Two kinds of regression equations for flow rates obtained according to viscosity and tube sizes were also presented for the purpose of practical uses. In conclusion, this study emphasizes that viscosity of fomula, osmolality, patient's tolerance and comfort, caloric density should be considered in the selection of tubes for gravify drip administration.
