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?: (A) Anxiety, (B) Hypoglycemia, (C) Hypovolemia, (D) Unexplained hemorrhage
Answer is B. 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.