Intraoperative Evaluation of Renal Blood Flow During Laparoscopic Partial Nephrectomy with a Novel Doppler System

Introduction

P rior to renal surgery, the renal vascular anatomy is typically assessed by preoperative imaging consisting of either computed tomography (CT) or magnetic resonance imaging (MRI). However, cross-sectional imaging is not always accurate in assessing the details of the renal vasculature. ^1,2 Accessory and aberrant vessels may exist, which are not evident on CT or MRI, and can potentially complicate the hilar dissection. ³ In addition, previous surgical procedures, infections, and adenopathy may make hilar dissection difficult, enhancing the challenges of identification and control of the renal vessels. One method of real-time determination of blood flow to the kidney is by intraoperative ultrasound through Doppler continuous flow monitoring (CFM). ⁴ Our team routinely applies CFM to determine whether the arterial supply to the kidney is fully controlled prior to stapling the renal vein during a radical nephrectomy or nephroureterectomy. Similarly, we often apply CFM to confirm adequate interruption of the arterial supply to the kidney, or specific portions of the kidney, after renal artery clamping during laparoscopic partial nephrectomy (LPN). Confirmation of interrupted blood supply to the kidney, or a portion of the kidney with segmental clamping, assures that there is minimal risk of significant blood loss. Additionally, as the field is more likely to be dry, CFM confirmation of blood flow interruption helps to optimize proper excision of tumors with a negative margin and precise reconstruction of the renal defect. Our team routinely uses intraoperative ultrasound during LPN for its ability to both delineate the renal mass in question and evaluate the blood flow to the kidney before, during, and after clamping of the renal artery. Recently, a disposable laparoscopic Doppler probe (DP) was introduced, which can establish blood flow to organs. We report our preliminary experience comparing this novel probe system to a standard ultrasound CFM system during LPN.

Materials and Methods

The study was performed with internal review board approval. Between November 2009 and January 2010, 20 LPNs were performed by a single surgeon (J.L.). In each case, we used both a standard laparoscopic ultrasound (SUS) with Doppler CFM (BK Medical Systems, Peabody, MA) and the novel laparoscopic Doppler system (Vascular Technology, Nashua, NH) to assess renal parenchymal blood flow before, during, and after renal vascular control.

The DP consists of an 18-inch disposable laparoscopic sterile probe with a 5-mm tip and an 8-MHz sensor that transmits the Doppler signal from a transceiver. Ultrasound waves are emitted from the tip of the probe. Once the blood flow is detected, the signal is reflected back to the probe tip and an audible signal is produced, indicating the presence and velocity of blood flow. The DP is not capable of producing an image and can only establish blood flow.

Our standard LPN technique incorporates the standard ultrasound technology to evaluate the target lesion (shape, depth, echotexture, vascularity), to evaluate the normal surrounding parenchyma to assure that there are no additional suspicious lesions (complex cyst or mass), and to confirm interruption of blood flow after clamping of the renal vasculature prior to resection. In each case, we also applied the DP (Vascular Technology) before and after vascular control to assess parenchymal blood flow around the area of the tumor.

In each case, after colon mobilization and hilar dissection, we performed a standard ultrasound evaluation of the kidney to characterize the target lesion(s), to confirm the normal nature of surrounding tissue, and to assess the ability to control the vascular supply to the tumor and surrounding renal parenchyma. We additionally evaluated the blood supply to the tumor and its surrounding tissue with the DP. Blood supply interruption was evaluated by gently compressing the renal artery with an atraumatic laparoscopic bipolar grasper (Aesculap, Center Valley, PA) while monitoring the blood supply. For both the SUS and DP evaluations, we documented whether the systems were able to confirm normal blood supply before clamping and interruption of the flow after transient clamping. After confirming that the dissected vessel(s) would adequately control the area of renal resection in this manner, we performed definitive vascular clamping with two bulldog clamps (Aesculap) deployed on the renal artery. We again evaluated blood supply interruption to the kidney with both systems and documented the time required for the evaluations. Tumor resection was performed using a laparoscopic scissor. The renal parenchymal defect is reconstructed and the bulldog clamps are removed. The adequacy of vascular control as assessed by the degree of bleeding during the parenchymal transection was recorded.

Results

Twenty LPN were evaluated with the SUS and DP. There were 10 left-sided procedures and 10 right-sided procedures performed. The mean tumor size was 3.0 cm (range: 1.2–6.3 cm). There were nine upper-pole tumors, six lower-pole tumors, and five tumors located in the interpolar region. Eleven tumors had an anterior location and nine were located posteriorly. Fourteen procedures were performed transperitoneally and six were done using a retroperitoneal approach. In 12 LPN, hilar control consisted of clamping only the renal artery, whereas occlusion of both the artery and vein was elected in eight cases. Vascular control was obtained by using the bulldog clamps in all but one LPN, which was controlled using a Satinsky clamp for en-bloc clamping of the artery and vein. In this case, limited hilar dissection was performed because of significant reactivity from prior renal surgery, and therefore, the Satinsky was used to clamp the artery and vein simultaneously. After additional measures to control hemostasis, the Satinsky was removed successfully without evidence of further bleeding.

Using the SUS, blood flow prior to clamping and ischemia (no flow) were detected in all 20 (100%) patients. The average time to evaluate blood flow to the kidney with an SUS was 68.6 seconds (range: 20–155). The DP detected preclamp flow and ischemia in 17 of 20 (85%) patients. The mean time for assessment using the DP system was 44.5 seconds (range: 15–180). Two patients (10%) required reclamping after both SUS and DP systems detected persistent flow after initial clamping. In both cases, additional dissection revealed a second renal vessel, which required a modification in the hilar clamping. After reclamping, both systems documented the absence of flow.

Subjective quality of each hilar dissection (excellent, moderate, poor) was determined by the primary surgeon. There was excellent dissection in 17 patients, moderate in 2, and poor in 1. Two tumors were located in the renal hilum. The blood flow in one of these tumors was difficult to assess using the Vascular Technologies, Inc (VTI) probe because of challenging surgical angles, but it was documented with the standard CFM Doppler. In the other hilar tumor, both Doppler systems detected the presence of flow and ischemia with clamping. Further surgical dissection revealed a second renal artery that was not detected by either Doppler system.

Discussion

Laparoscopy continues to evolve and is becoming a mainstream approach for many types of renal surgery. The rapid evolution in the surgical technologies that are available to the surgeon demands a constant reevaluation of how renal surgery can be optimally performed. One of the major contemporary challenges of laparoscopic renal surgery includes hemostasis. Increased information regarding the status of the blood supply to the kidney is valuable to the surgeon to decide whether the hilar vessels are to be ligated and stapled or temporarily clamped and preserved. Currently, preoperative cross-sectional imaging (CT or MRI) is used to plan for the surgical approach to the kidney. However, accessory and/or aberrant renal vessels as well as alterations in anatomy may be present in certain patients and not always identifiable using cross-sectional imaging. Therefore, intraoperative ultrasound is used by some surgeons to both delineate renal and tumor anatomy as well as to assess the blood flow to the kidney using CFM Doppler. ⁵ Intraoperative Doppler ultrasound can identify the size, depth, and location of renal tumors during open and laparoscopic partial nephrectomy and determine the blood flow to the tumor. Doppler has been used previously in a variety of other surgical procedures (hemi-colectomy, cholecystectomy, pelvic lymph node dissection, and cryoprobe needle placement during renal cryoablation). ⁶

A novel DP has been recently introduced and has been previously described for renal applications. Sethi and colleagues described their experience using the DP in 20 patients who had undergone various renal surgeries. Outcomes included the time to complete the Doppler evaluation, time to isolate the renal hilum, identification of accessory or aberrant vessels, and an alteration in operative management as a result of the Doppler survey. In addition, the surgeon subjectively assessed the ease of use. Preoperative imaging with CT and vascular anatomy determined with the VTI probe were similar in all but one case in which an accessory vessel was not seen on CT, but found using the VTI Doppler. The mean time to identify the renal vessels was 34.9 seconds and it was judged to be “very easy” to use in each case. The Doppler evaluation facilitated dissection of the renal hilum in 40% of cases and did not hinder dissection or lead to negative outcomes in any case. ⁷ Hyams and coworkers reported on 20 patients who were undergoing a variety of laparoscopic renal surgeries and were evaluated intraoperatively with the VTI probe. ⁸ The Doppler was used to guide hilar dissection, confirm ischemia with clamping prior to partial nephrectomy, and identify the presence of a crossing vessel prior to laparoscopic pyeloplasty. Nine accessory vessels were detected in patients undergoing radical nephrectomy or nephroureterectomy. One crossing vessel was identified and one patient undergoing partial nephrectomy demonstrated persistent parenchymal blood flow after temporary arterial clamping. This allowed for adjustment of the hilar clamp prior to resection. Overall, the use of the probe altered surgical management in 35% of cases.

In this study, the SUS identified measurable ischemia in 100% of LPN cases, which was slightly improved over the DP, which detected ischemia in 85% of cases. The inability of the DP to detect flow in three cases is not clearly defined. It is possible that the presence of scar tissue may have interfered with the detection of blood flow. Alternatively, the angles of access did not allow for an adequate interface between the end of the probe and the renal parenchyma. The key finding was that both probes identified the persistence of blood flow in two cases, leading to additional hilar dissection and detection of a second vessel supplying the kidney. Reclamping was initiated in each case and both systems subsequently detected ischemia, which likely prevented unnecessary intraoperative hemorrhage.

Specific advantages of the DP include its size (5-mm tip), making it deployable through a standard 5-mm trocar. Although the DP cannot create an image, it is superior to the SUS in that the diminutive size of the end-effector allows for very precise determination of blood supply to different areas of the kidney. We have previously used the DP to allow for precise clamping of segmental arteries in selected cases. The DP can demonstrate nicely the precise area that a segmental vessel supplies and has allowed us to preserve blood supply to the majority of the kidney in selected partial nephrectomy cases. Highly selective segmental clamping partial nephrectomy may help to preserve renal function, minimize morbidity, and improve the efficiency of the LPN.

The DP is disposable and has a simple design with the Doppler mechanism located at the end of the probe, making tissue interaction convenient. Minimal manual dexterity is required for proper intraoperative use. The probe only requires a small amount of water or fluid to function in contrast to gel lubrication, which is necessary when using the SUS.

Finally, the cost of the 8-MHz DP transceiver is $998.00 (one-time expense) and $137.00 for the disposable end-effector probes. In contrast, the SUS system applied in this study costs $85,000 as a one-time cost and then requires sterilization between cases or application of a protective condom. For institutions where an SUS system is not financially viable, the DP is a reasonable alternative. In addition, we have found the DP to be an excellent complimentary technology to an SUS system in that the smaller DP end-effector can more precisely characterize blood flow to different kidney segments.

Conclusions

Intraoperative Doppler ultrasound is a key tool for evaluating patients who are undergoing LPN. In addition to tumor characteristics such as location, size, and depth, assessment of blood flow before and after clamping of the renal hilum is an important information prior to surgery. Parenchymal blood flow can be determined by either the standard Doppler ultrasound/CFM or the disposable VTI probe. The VTI probe has proven to be a simple, safe, and cost-effective alternative compared with the standard Doppler ultrasound. However, its accuracy in assessing parenchymal and renal tumor blood flow is slightly inferior compared with the CFM on the SUS.