Intraoperative studies are performed with a 5 MHz linear array probe with Doppler color flow. The probe head is placed in a sterile plastic sheath containing acoustic gel. The operative field is flooded with warm saline, and scanned images are first obtained in the longitudinal projection. Care is taken to image the aorta, the renal artery origin, and the entire renal artery from origin to hilum. All defects seen in longitudinal projection are imaged in transverse fashion to confirm their anatomic presence and estimate the contribution to luminal narrowing. Doppler samples are then obtained proximal and distal to the imaged defects in longitudinal projection to determine their potential contribution to flow disturbance. Finally, intrarenal Doppler signals from the interlobar, and arcuate branches are obtained in the upper, midportion, and lower pole of the kidney.

The criteria for intraoperative defects creating ≥60% diameter reduction are similar to surface renal duplex sonography studies (Table 50.1). These criteria have been validated in an animal model of graded renal artery stenosis and compared with pre- and post-op angiography in more than 100 patients. Unlike surface duplex sonography in which the Doppler sample is large relative to the renal artery diameter, the Doppler sample can be accurately positioned within the mid-center of arterial flow. However, at this mid-center location, at least moderate spectral broadening is inherent to the Doppler spectrum after open repair in the absence of anatomic defect.

During intraoperative renal duplex sonography, the interaction between surgeon and vascular technologist is important. Both B scan images and velocity estimates from spectral data are enhanced by the participation of a vascular technologist. Although the surgeon is responsible for the manipulation of the probe head to ensure optimal B mode images at likely sites of technical error, the power and time adjustments to minimize artifact are best made by an experienced technologist. Close cooperation is required to obtain complete pulse Doppler sampling and estimate velocities associated with B scan defects. Though often overlooked, the participation in intraoperative studies enhances the technologist’s subsequent ability to obtain satisfactory surface renal duplex images during follow-up surveillance.

In over 500 intraoperative renal duplex sonographies after renal artery reconstruction, the average time for intraoperative scan was less than 5 min [10]. Complete B scan and Doppler-derived velocity data were obtained in over 98% of cases. Renal duplex sonography was considered normal, free of any B scan defect in 77% of cases, while B scan defects were present in 23%. Eleven percent of defects had Doppler velocity estimates exceeding 1.8 meters per second with post-stenotic turbulence, and these were defined as major. These major defects underwent immediate operative revision, and in each case, a significant defect was discovered and corrected. Successful revision was verified by a second intraoperative duplex study. In follow-up, 97% of these open operative repairs have maintained primary patency without recurrent stenosis at 5 years’ follow-up. Neither minor B scan defects uncorrected nor corrected major B scan defects have correlated with subsequent failure of open repair.

B scan defects designated as major or minor by Doppler velocity criteria provide accurate information to guide intraoperative revision. There are, however, special circumstances that deserve comment. Intraoperative duplex study after renal repair may occasionally demonstrate peak systolic velocity that exceeds criteria for critical stenosis in the absence of anatomic defect. In these circumstances, peak systolic velocity is elevated uniformly throughout the repair with no focal velocity change and no distal turbulent wave form. Intraoperative studies of this type are most commonly encountered after renal artery repair in children and young adults for non-atherosclerotic disease. Increased peak systolic velocity can also be observed in transition from main renal artery to segmental renal vessels after branch renal artery repair. In the absence of the defect, no distal turbulent waveform will be observed. Finally a renovascular repair to a solitary kidney frequently has elevated velocities throughout without evidence of turbulence.

Other special considerations concern diastolic features of the Doppler spectrum in the absence of technical error. An abnormal diastolic spectrum may be observed after revascularization of chronic renal ischemia reflecting an increase vascular resistance in response to reperfusion. The spectrum may demonstrate brief acceleration times and virtually no diastolic flow. These changes reflect a reactive vasospasm which can be defined by interarterial administration of 30 mg papavarine. The Doppler spectral signature characteristic for renal artery flow will normalize within 2–3 min (Fig. 50.2).

The rates of primary patency of open renal artery repair without recurrent stenosis are estimated at 96% at 5 year follow-up. This patency rate was achieved after revision of major B scan defects in 12% of repair [11]. Although a disproportionate number of major defects were observed after transaortic endarterectomy, when revision was directed by intraoperative completion duplex, equivalent patency was observed among different reconstructive techniques. The significance of primary patency after open operative repair is profound. Whether by restenosis or occlusion treated by either reconstruction or nephrectomy, failed open operative renovascular repair is associated with an increased risk of eventual dialysis dependence which is significant and independent of other risk factors [11].