Continuous monitoring and control of plasma glucose during operation for removal of insulinomas

A glucose-controlled insulin and glucose infusion system (Biostator system, Miles Laboratories Inc., Elkhart, Ind.) was used during operation for removal of four suspected insulinomas. In two patients the Biostator system continuously monitored plasma glucose levels and, through a computer-controlled feedback mechanism, automatically infused insulin or glucose as needed. In this way plasma glucose could be kept at approximately 110 mg/dl throughout the procedure. In one patient a rise in insulin infusion rate and a fall in glucose infusion rate followed removal of the tumor. In the other, absence of these findings was consistent with the clinical suspicion that the source of hypoglycemia had not been removed. In two other patients the Biostator system continuously monitored the patient's plasma glucose, without feedback-controlled administration of insulin or glucose. This demonstrated that, in these patients, tumor manipulation and removal did not lead to severe hypoglycemia, and thus eliminated any need to prophylactically infuse large amounts of glucose. Successful tumor removal was followed by a rise in blood glucose levels in both of these individuals. The glucose-controlled insulin and glucose infusion system appears to be a useful instrument for intraoperative management of patients with suspected insulinomas.