Plasma level changes of fentanyl and midazolam after release of a prolonged thigh tourniquet

Abstract

In 14 elderly orthopedic patients undergoing total knee joint replacement, the influence of complete arterial occlusion of the limb on the course of plasma levels of fentanyl and midazolam was examined. The patients were premedicated with midazolam intramuscularly (0.05 mg/kg) and were then given neurolept anesthesia in dosages of 0.1 mg/kg midazolam and 0.01 mg/kg fentanyl intravenously prior to the placement of the tourniquet. Up to 4 h after the tourniquet was released, plasma levels of fentanyl and midazolam as well as pH value, PaCO2 and plasma lactate levels were measured. In 12 patients there was an increase in fentanyl and in 10 patients an increase in midazolam plasma levels after tourniquet release. The maximum increase varied between 1 min and 2 h after release. The plasma levels of midazolam after removal of the tourniquet varied greatly between individuals. Especially patients older than 70 years showed excessively high concentrations of midazolam. These results would indicate that there can be a clinically significant increase of fentanyl and midazolam levels due to initial reperfusion of the lower extremity following prolonged ischemia. Therefore a correspondingly extended period of postoperative surveillance is advisable.

The arterial tourniquet: pathophysiological consequences and anaesthetic implications

“…Schmitt et al . [98] examined the effect of a thigh tourniquet on the plasma levels of fentanyl and midazolam administered intravenously before tourniquet inflation. There was a significant and sustained increase in the plasma concentration of both drugs after reperfusion of the limb.…”

Simultaneous Determination of Fentanyl and Midazolam in Plasma Using Direct Solid-Phase Microextraction Before Gas Chromatography–mass Spectrometry Analysis

“…3C. These concentrations correspond to plasma concentrations found in the literature for the monitoring of midazolam and fentanyl in patients undergoing orthopaedic operations [44] or trauma surgery [45] or coronary bypass surgery. [39] The developed method can be useful for the determination of these drugs in forensic science.…”

The pathophysiology of the arterial tourniquet: a review

“…In order to prevent postoperative infection, prophylactic antibiotics need to reach the tissues in adequate concentrations before tourniquet inflation -at least 5 minutes is required (41,45) . These increased levels may be clinically significant, especially in the elderly, and prolonged postoperative observation (up to 4 hours) is necessary (42) . These increased levels may be clinically significant, especially in the elderly, and prolonged postoperative observation (up to 4 hours) is necessary (42) .…”