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In vitro simulation of nasogastric tube delivery of enteral formulas was used to study the mechanism and prevention of non-medication-induced nasogastric tube occlusion. Enteral nutrition products--Osmolite, Ensure, Vital High Nitrogen, and Vivonex T.E.N.--were placed in glass beakers and titrated with hydrochloric acid to determine the pH at which clotting would occur. Factors such as pH, protein content, viscosity, electrolyte composition, flow rate, and tube design were evaluated to determine their effects on coagulation of formula. Addition of simethicone emulsion and docusate sodium to the formulas and siliconization of the nasogastric tubes were studies for their effect on prevention of clog formation. Clumping began to occur at pH 4.6 (the isoelectric point for casein) for Ensure and Osmolite; addition of protein supplement did not change the pH at which coagulation occurred. Vital High Nitrogen and Vivonex T.E.N. formulations did not clump in the beakers. Ensure and Osmolite coagulated within 35 seconds at pH 4.6 or less and remained unchanged at pH greater than 6.0. Addition of sodium or calcium caseinate greatly increased the tendency of the formulas to coagulate. Viscosity of the formula increased markedly as pH decreased. Addition of electrolytes had no effect on precipitation or clumping. Slow or no flow rates within nasogastric tubes placed in simulated gastric juice decreased the pH and caused clumping of formulas within the tubes in a retrograde manner. Flow time or clog formation was not affected by the addition of simethicone or docusate sodium or siliconization of the nasogastric tube.(ABSTRACT TRUNCATED AT 250 WORDS)

Publisher Summary This chapter describes the most important anatomical and physiological features of the laboratory rat. The body of a normal, healthy Norway rat is long and slender. The tail is hairless and may be as long as 85% of the total body. The tail is proportionately longer in females than in males. Growth rates and maturation times for rats varies by strain. Body weight varies greatly, not only with age but with stock, strain, and source of the rat. Both fore- and hindlimbs have five digits. The first digit is greatly reduced on the forelimb and has a flattened nail unlike the more rounded nails of the other digits. Typical pads are present and likely provide cushion against forces placed on the feet during walking and rest. The forelimb has five apical pads, three interdigital pads, and two basal pads. The skeleton of the rat is typical for mammals. The rat has been used extensively as a model for studying the effect of space flight and microgravity on the skeletal system.