AGING EXAGGERATES THE BLOOD-GLUCOSE RESPONSE TO TOTAL PARENTERAL-NUTRITION

OBJECTIVE: To determine the effect of age on the blood glucose and ins ulin responses to a clinical model of glucose loading (i.e., total par enteral nutrition [TPN] with hypertonic glucose), in patients with a v ariety of conditions. DESIGN: A Prospective cohort study. SETTING: An adult university hospital. PATIENTS: Seventy-one consecutive, clinical ly stable patients receiving central TPN, excluding those with metabol ic disease or receiving relevant medications. INTERVENTION: None. MAIN OUTCOME MEASURES: Serum levels of glucose, insulin, C-peptide and cor tisol determined in peripheral venous blood obtained immediately befor e initiating TPN and again 48 to 96 hours later; acute physiology scor e (APS) and habitual level of physical activity (HAL). RESULTS: Serum levels of glucose, insulin and C-peptide increased following initiatio n of TPN (all p < 0.001). The serum glucose level during TPN administr ation increased as a function of both patient age and severity of illn ess (APS) (r(2) = 0.37, all p < 0.01), whereas the serum insulin level was inversely related to age and increased as a function of serum glu cose, glucose rate of infusion and HAL (r(2) = 0.57, all p < 0.05). Th e serum C-peptide:insulin molar ratio did not vary with age. CONCLUSIO NS: Aging and severity of illness interact to exaggerate the increases in blood glucose that accompany TPN with hypertonic glucose. Serum in sulin responses to TPN decline with aging, likely reflecting reduced i nsulin secretion. Diminished insulin responses may contribute to hyper glycemia and represent a diminished anabolic signal in such patients. The acutely ill elderly patient is predisposed to hyperglycemia and sh ould be monitored carefully even when pre-TPN blood glucose values are normal.