Hypertension and decreased renal blood flow following methylene blue injection.

Renal blood flow (RBF) and arterial blood pressure (BP) were monitored in 12 patients undergoing nephrolithotomy in the lateral flexed position. All patients were preoxygenated and were anesthetized with sodium thiopental, N2O, O2, and fentanyl. Maintenance relaxation was obtained with pancuronium bromide. Arterial pressure was monitored by percutaneous arterial catheter. Following exposure of the kidney and renal pedicle, an electromagnetic flow probe was attached to the renal artery and baseline flows recorded. Following baseline measurements, 20 ml of 1 percent methylene blue was given intravenously. All patients studied showed an immediate rise in BP, and 11/12 showed a simultaneous decrease in RBF. The average fall in RBF was 35 percent at one minute. Both parameters returned to normal values on the average in 177 seconds. The decreased RBF appeared to be part of a generalized vasoconstrition caused either by sympathetic reflexes or by the direct action of methylene blue.