The present study was undertaken to assess the impact of acute discontinuation (AD) of total parenteral nutrition (TPN) on serum glucose, insulin, and glucagon levels and on the generation of symptomatic hypoglycemia. Fifty studies were performed in 48 patients. In none of the 30 studies of 1 hour duration nor in the 20 studies of 8 hours duration was there a single episode of symptomatic hypoglycemia. One patient had a glucose below normal (60 mg/dl) during the first hour after AD. Glucose and insulin concentrations were elevated at the start of TPN discontinuation but returned to normal values within 60 minutes and remained there during the successive 7 hours of study. Although glucagon levels were slightly elevated at zero time, no significant decrease occurred. There was no evidence for counter-regulation based on the patterns of glucose and hormone levels. With some restrictions, acute discontinuation is a safe, rapid method of ending a prolonged TPN infusion.TNHE SEQUENTIAL REDUCTION of glucose concentration before discontinuation oftotal parenteral nutrition (TPN) is termed tapering. The theoretical basis for tapering is that the endocrine pancreas is "turned on" by the continuous infusion ofa glucose load at approximately 0.6 g glucose/min. The sudden withdrawal of the glucose by discontinuing TPN, in the presence of elevated insulin levels, was thought to result in a rapid reduction of serum glucose levels. The total glucose and amino acid load delivered daily with TPN is calorically equivalent to that taken during the three meals normally ingested. However, man, as a "meal eater," usually has a cyclic elevation in serum glucose and serum immunoreactive insulin (IRI) levels. The cyclic phenomenon is very different from the persistently elevated levels of The purpose of this study was to examine the effects of acute cessation of a glucose infusion in patients receiving prolonged infusions of TPN. The effects of diabetes, exogenous insulin administration, and primary diagnosis were also evaluated. Specifically, the presence or absence of the phenomenon of rebound hypoglycemia was evaluated following acute cessation of the standard glucose infusion rates used in TPN (0.55 g glucose/min). Materials and MethodsPatients who were placed on total parenteral nutrition for at least 7 days were eligible for inclusion into the study. The study protocol was judged to contain the appropriate ethical standards by the Committee on the Conduct of Human Research at the Medical College of Virginia. The presence of diabetes or the need for exogenous insulin while on TPN did not constitute an exclusion. Those excluded were patients with hepatic failure, renal failure requiring dialysis, or clinical features of an underlying or primary disease that would obfuscate the clinical diagnosis of hypoglycemia (e.g., coma, expressive aphasia, and inability to communicate).A total of48 patients were included in one oftwo study protocols involving observation periods of 1 or 8 hours.524