A new photoplethysmographic device for continuous assessment of urethral mucosa perfusion: evaluation in a porcine model.

ABSTRACT

This study proposes to evaluate an innovative device consisting of an indwelling urinary catheter equipped with a photoplethysmography (PPG) sensor in contact with the urethral mucosa that provides a continuous index called urethral perfusion index (uPI). The goal of this study was to determine if the uPI could bring out tissue perfusion modifications induced by hypotension and vasopressors in a porcine model. Twelve piglets were equipped for heart rate, MAP, cardiac index, stroke volume index, systemic vascular resistance index and uPI monitoring. The animals were exposed to different levels of mean arterial pressure (MAP), ranging from low to high values. Friedman tests with a posteriori multiple comparison were performed and a generalized linear mixed model (GLMM) was used to assess the relationship between uPI and MAP. Urethral Perfusion Index and other haemodynamic parameters varied significantly at the different time-points of interest. There was a positive correlation between MAP and uPI below a specific MAP value, called dissociation threshold (DT). Above this threshold, uPI and MAP were negatively correlated. This relationship, assessed with the GLMM, yielded a significant positive fixed effect coefficient (+ 0.2, P < 0.00001) below the DT and a significant negative fixed effect (- 0.14, P < 0.00001) above DT. In an experimental setting, the PPG device and its index uPI permitted the detection of urethral mucosa perfusion alterations associated with hypotension or excessive doses of vasopressors. Further studies are needed to evaluate this device in a clinical context.