The loss-of-resistance technique in epidural anesthesia is the accepted standard for
indicating the entry of the needle into the epidural space. In conventional epidurals, it is
also the only feedback mechanism to confirm needle entry. Unsuccessful epidurals due to
the technical difficulties can result in mild to severe complications. These difficulties
include correctly choosing the puncture site and needle trajectory, which are determined
solely by palpation and the experience of the anesthesiologist. Instrumentation of the
thumb's force on the plunger of the syringe, displacement of the plunger and fluid
pressure is developed for laboratory and clinical trials to study the dynamics of the loss-of-
resistance technique. Instrumentation of the loss-of-resistance technique was
performed on culled domestic pigs using standard epidural procedures. A static and decay
model, based on physical properties and empirical data, are used for estimating the
pressure from the force and displacement values. The decay model is shown to be
reasonably accurate and allows the omission of the pressure sensor in clinical trials.
Furthermore, the accuracy of decay model is further improved for the "smooth" protocol
performed by the anesthesiologist, over the "bouncing" protocol. The loss-of-resistance,
indicated orally by the anesthesiologist, is consistent with the rapid fall in all three
measurements. The oral indication of the loss-of-resistance slightly lags that of the
measured values and is consistent with the lag in oral communication. The
instrumentation of the loss-of-resistance is further confirmed by direct and indirect
measurements from ultrasound images of the epidural space and needle. However,
obtaining good image quality is difficult due to the steep needle angle and the
surrounding bone structures. An adaptive spatial compounding algorithm is developed to
improve important features such as the bone and epidural space. A specially constructed
phantom with speed-of-sound distortion is used to compare several variations of the
algorithm. The adaptive spatial compounding using median-based averaging produced
image quality with the best balance for point resolution, edge resolution and noise
reduction in homogeneous regions. In porcine studies, the technique shows visible
improvements of the epidural space and surrounding features.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat