A 50-year-old man with small-bowel fistula has been receiving TPN for the previous 3 weeks through a single-lumen central venous catheter. He is scheduled for exploratory laparotomy and closure of fistula. On the morning of the day of surgery, TPN is discontinued and intra-venous infusion with balanced salt solution (Ringer's lactate) is staed. An hour later, the patient is found to be anxious, sweating, and tachycardic. What is the most likely cause?

Patients on TPN with hypeonic glucosesolutions have elevated islet-cell production of insulin. - Sudden cessation of TPN can lead to rebound hypoglycemia, because pancreatic islet-cell insulin secretion is not immediately downregulated. Symptoms are attributable to high catecholamine release secondary to hypo-glycemia. - In general, the TPN rate should be reduced to 50 mL/h during surgery. This prevents both hypoglycemia and the hyperglycemia seen with higher infusion rates. Weaning from TPN should be done gradually over 24-48 hours.