Diagnostic monitoring of plasma levels of glucose and insulin during surgery for insulinoma.

With serial measurement of blood sugar levels during surgery in three patients with solitary insulinoma, we confirmed the location, then later, the complete elimination of the insulin-secreting tumor. Following vigorous massage of the tumor, blood sugar levels decreased while the levels progressively increased within 20 min following removal of the tumor. Subsequent measurement of simultaneous plasma insulin levels provided further confirmation. Plasma levels of insulin increased in accordance with massage of the tumor. Prior to removal of the tumor, the levels progressively decreased to less than the preoperative levels. For success in detecting slight changes in blood sugar levels secondary to increase or decrease of insulin secretion during surgery for insulinoma, (1) controlled infusion of glucose to keep blood sugar levels around 80 mg/dl and (2) frequent rapid determination of blood sugar levels are considered to be important.