| Summary: | While the use of pneumatic surgical tourniquet systems to maintain a bloodless surgical field
in limb surgeries has become commonplace, their use may occasionally result in serious
complications such as nerve injury and there is evidence that some injury occurs as a result of
each usage. It is commonly accepted that these complications are a result of the pressure
applied by the tourniquet cuff to the underlying tissue. The use of an adaptive surgical
tourniquet system which adapts to maintain the minimum tourniquet pressure required for
surgery may allow the use of tourniquet pressures that are on average much lower than could
be achieved using a conventional tourniquet system set at a constant pressure and this lower
pressure may result in reduced injury and thus improved safety.
Although many variables affect the minimum tourniquet pressure required to prevent the flow
of blood underneath the tourniquet cuff, intraoperative changes in that minimum tourniquet
pressure are primarily a function of intraoperative changes in blood pressure. Prior to work
described in this thesis, no clinically acceptable means had been developed for estimating
changes in required tourniquet pressure due to changes in patient blood pressure at
sufficiently frequent intervals to facilitate the operation of an adaptive surgical tourniquet
system.
In the research described in this thesis, the measurement of "pulse wave transit time"
(PWTT), defined as the time required for the arterial pulse wave to propagate along a fixed
arterial path, was investigated as a novel technique to allow the continuous estimation of
"limb occlusion pressure" (LOP) for the control of adaptive surgical tourniquet systems. An experimental system was designed and built which measures PWTT using the output from an
ECG monitor and an arterial pulse sensor. Initially, data was collected using the
measurement system from 16 patients undergoing orthopedic surgical procedures. Based on
analysis of this data it was concluded that in relatively short procedures performed on nonelderly
subjects there existed a strong correlation between PWTT and LOP, and therefore it
was concluded that measured PWTT provided an accurate method of continuously estimating
LOP in these cases. However, in lengthy cases involving elderly patients, a poor correlation
was found between PWTT and LOP. It was concluded that this was the result of the relative
non-compliance of the arteries of elderly subjects and the administration of a wide variety of
drugs affecting arterial compliance. Based on these findings, it was determined that in order to
achieve a clinically acceptable level of reliability, a system which continuously estimates LOP
based on the measurement of PWTT must integrate periodic estimates from a conventional
blood pressure measurement device. These periodic estimates are required in order to
develop a patient-specific model relating LOP to PWTT, and to identify subjects for whom
PWTT is poorly correlated with LOP.
An improved system was then proposed based on the integration of the PWTT measurement
system with a patient monitor commonly used in operating rooms to provide blood pressure
estimates periodically. Applying the algorithm proposed for the improved system
retrospectively to the clinical data obtained from the initial study of 16 surgical patients yielded
a 9 percent reduction in the time-averaged tourniquet pressure and a 27 percent average
decrease in pressure during the periods of adaptive operation. A follow-up study on 8
additional surgical patients yielded a 12 percent estimated decrease in time-averaged
tourniquet pressure and a 25 percent reduction in tourniquet pressure during periods of
adaptive operation. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
|
|---|
