Determination of the Duration of Action of a Lidocaine and a Bupivacaine Digital Nerve Block in Human Volunteers

The Masimo SpHb™ (SpHb) is a device used to monitor the blood hemoglobin level via a sticky sensor connected to a finger. Our results from 2 recent studies undertaken with this device concluded: 1) that it is not always accurate when the finger is cold such as during surgical blood loss, and 2) a local nerve block to the finger improved the finger temperature and the accuracy of the device.

Our purpose is to investigate the duration of effect of two local nerve blocking drugs (lidocaine and bupivacaine - both FDA approved drugs in routine use) in a finger on each hand. Having a better understanding of how long the nerve block lasts could help determine when an additional block might be necessary to maintain the accuracy of the device during surgical blood loss.

We previously listed the primary outcome for this study as the time until return to baseline finger temperature. However, in blinded looks at the data it became clear that defining time until return to baseline from the serial temperature measurements in an objective fashion would be extremely difficult and potentially controversial. We have modified the primary outcome to be the change in the average temperature from baseline to post-intervention.