Ultrasound assessment of the effect of patient position and body shape on peri-operative renal transplant cortical resistive indices and perfusion.

Abstract

Background: Multiple factors impact kidney perfusion peri-operatively. The aim of this study was to evaluate the effect of patient position and size on renal transplant perfusion.

Methods: Consecutive adult recipients of 123 single renal grafts were studied. Renal artery velocity, renal vein velocity and cortical resistive indices were measured in supine, oblique and decubitus positions on post-operative days 1, 3, 7 and 30, and standing on days 7 and 30.

Results: Positional resistive indices were significantly lower than the supine resistive indices except in the day 1 oblique scan. Greater reductions in resistive indices occurred in grafts with higher supine cortical resistive indices, higher renal vein velocities and greater change in renal vein velocities. Renal artery velocities, renal vein velocities and resistive indices progressively decreased with greater positional change. Although renal vein velocities correlated poorly with resistive indices in individual patients, mean resistive indices correlated well (r ² = 0.73) with mean renal vein velocities for scans in different positions and on different days, and less so with mean renal artery velocities (r ² = 0.37). Supine abdominal girth and change in girth with position were more strongly associated with larger changes in supine resistive indices than recipient weight, body mass index or peri-operative weight gain.

Conclusions: Peri-operative renal transplant resistive indices, renal artery velocities and renal vein velocities improve with patient positional change due to reduced compression of the graft and renal vein, with implications for post-operative ultrasound scanning protocols, documentation and reporting. Peri-operative patient position, especially for at-risk grafts, is a modifiable risk factor for poorer graft outcomes. Patients should be nursed in the decubitus position rather than supine. Abdominal girth is more relevant to pre-operative patient assessment than weight or body mass index.