Validation of transcutaneous NIRS monitoring of bladder hemodynamics and oxygenation using a rabbit model

Abstract

Transcutaneous near infrared spectroscopy (NIRS) is a recognized means of non-invasively monitoring changes in the concentration of oxygenated and deoxygenated hemoglobin in tissue. However in applications of this technique to the bladder, because the combined thickness of the detrusor muscle and the wall of the organ is only a few millimeters, the question arises whether the trends and variations in hemoglobin concentration detected transcutaneously reflect physiologic changes occurring in the detrusor or are influenced by the effect of overlying tissue on the NIRS signal. In this study a rabbit model was used so that NIRS data could be collected transcutaneously and then with the optical probe applied directly the anterior bladder wall after surgical exposure of the organ, and the data compared. Studies were done with an Oxymon dual channel spectrometer on 6 anaesthetized New Zealand white rabbits using interop- tode distances adjusted for the two measurement sites, a consistent bladder filling and emptying protocol, and exposure to a brief period of controlled hypoxia (oxygen saturation decrease to 80%). Consistent data were obtained from transcutaneous and direct bladder wall measurements which confirms that transcutaneous NIRS monitoring does reflect changes occurring within the detrusor muscle in the anterior bladder wall. Hence, transcutaneous monitoring in humans using appropriate methodology and inter-optode spacing can be expected to avoid any potentially con- founding signals from tissues in the abdominal wall overlying the bladder.