J Vasc Access 2014; 15 ( Suppl 7 ): S6-S9 DOI: 10.5301/jva.5000253

Intraoperative assessment of vascular access Francois Saucy, Sébastien Déglise, Thomas Holzer, Lucie Salomon, Stephan Engelberger, Jean-Marc Corpataux Thoracic and Vascular Department, University Hospital, Lausanne - Switzerland

ABSTRACT Purpose: The intraoperative quality assessment of the arteriovenous fistula for hemodialysis is an essential process to limit early failure due to technical problems or inadequate vascular quality. This step is not clearly defined in the literature with no recommendations. Methods: We selected published articles related to the topic of intraoperative quality control of the vascular access for hemodialysis. Results: The intraoperative blood flow measurement greater than 120 ml/min in autologous fistula and less than 320 ml/min in arteriovenous graft was described as predictive factors for early failure. Conclusions: The blood flow measurement should be performed after the confection of the anastomosis. When blood flow is limited, fistulography is an essential step to assess patency. Key words: Arteriovenous fistula, Blood flow, Hemodialysis, Intraoperative maturation failure Accepted: March 7, 2014

INTRODUCTION The confection of a vascular access (VA) for hemodialysis is an essential step in the life of a patient suffering from end-stage renal disease. Indeed, this is usually the beginning of a long process with a significant number of surgical and interventional procedures. Reinterventions and problems related to the VA are major causes of hospitalization of a dialysed patient. Therefore, we should focus our attention to the VA in order to limit the reintervention rate. This process begins with the selection of the appropriate hemodialysis access. Peritoneal dialysis should always be proposed and selected when possible. When hemodialysis is the good option, preoperative assessment is mandatory. General criteria such as gender, comorbidities, age, and race should be considered when VA is evoked (1). Moreover, ultrasound preoperative arterial and venous mapping is the next step to select the appropriate type of VA (2). Nevertheless, a recent randomized controlled trial has failed to demonstrate a benefit of the preoperative ultrasound (US) mapping over the physical examination (3). Preoperative vessel diameter evaluation is a critical point, as small venous diameter is associated with a primary failure in autologous fistulae (4). In many countries, the diameter is also evaluated clinically by using a garot and looking at the superficial veins of the upper limb. This method is difficult to S6

reproduce and has an important variability between observers. Therefore, ultrasound is now recommended by international guidelines (5). Nevertheless, the accuracy of ultrasound to measure the diameter is dependent on the observer and factors related to the hemodynamic of the patient, which can modify the diameter of the superficial vein. Preoperative and intraoperative assessment: both are complementary Even if the preoperative diameter was considered optimal for the VA confection, intraoperative diameter remains the final evaluation and should be therefore taken into consideration for the correct VA confection. Superficial veins are not the unique parameter, but arterial diameter and vessel quality are also important to evaluate preoperatively and intraoperatively. The quality of the arterial vessel wall is mainly related to the presence of calcification and stenosis. These lesions are usually observed preoperatively by ultrasound (6). Nevertheless, palpation of the artery selected for the VA confection is an essential step of the VA intervention. The presence of calcification could prevent the clamping of the artery by surgical clamp, necessitating the endoluminal clamping with balloons or thermosensitive gel (7). When pulsation

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Saucy et al

is not detected, the vascular surgeon should consider the presence of an arterial stenosis. In this situation, an intraoperative Doppler ultrasound is a good option to measure the peak systolic velocity (PSV) and to evaluate the Doppler waveform. When an arterial stenosis is detected intraoperative, its correction by endovascular or surgical approach is mandatory before the arteriovenous anastomosis. Endovascular approach is preferred when the stenosis is distant of the anastomosis avoiding a secondary incision. Moreover, fistulography enables to visualize the stenosis and to assess its severity. This situation should be seldom, as preoperative arterial evaluation gives important details concerning the arterial flow at the selected site for the VA confection. Intraoperative assessment is dedicated to limit primary failure due to technical problems such as anastomotic stenosis, venous kinking, and preanastomotic stenosis. All these lesions will affect intraoperative blood flow, which is crucial for the maturation of the VA. Indeed, a low blood flow on the first postoperative day is related to dysmaturation (8). Moreover, when blood flow is too high and related to steal syndrome, intraoperative assessment could also play a role in the evaluation of the treatment of steal syndrome (9). The intraoperative assessment is crucial to validate the primary treatment of steal syndrome by decreasing blood flow when necessary by increasing distal perfusion to the hand (9). The preoperative period is important to plan the intervention. Nevertheless, decisions should be taken during the intervention if the preoperative assessment differs from the intraoperative observation.

Fig. 1 - Measuring blood flow in an end-to-side anastomosis with a flow probe placed around the outflow vein.

Fig. 2 - Blood flow (in ml/min) in functioning (black box) and nonfunctioning radiocephalic AVF (white box). Reprinted from Saucy et al (13).

Evaluation of intraoperative blood flow Transit time principle (Medistim ASA, Oslo, Norway) is used to measure the blood flow with accuracy inside the feeding artery (10). Flow probes are available from 1.5 mm to 7 mm to fit the external diameter of the vessel (Fig. 1). Once placed around it, the measurement of the blood flow is immediate, but stabilization is mandatory. Usually, we wait 1-3 minutes until the blood flow value is stabilized. If blood flow is not stable, we take into consideration three consecutive values and assumed the mean of these three values. At the same time, we record the arterial systolic and diastolic blood pressure to correlate with the blood flow in order to calculate the 100 blood flow value (Q100). This value is the normalization of the blood flow for an arterial blood pressure of 100 mmHg. This permits to correlate the intraoperative and postoperative values. Indeed, blood pressure influences the blood flow with subsequent difficulty in correlation between two measurements. The transit time principle was used mainly in the coronary bypasses (11), and now, few publications re-

ported the use of transit time principles in arteriovenous fistulae (AVF) (12, 13). This step measuring blood flow should be used at the end of the anastomosis confection. Nevertheless, the correlation of the intraoperative blood flow with midterm outcomes such as patency rates have a low level of evidence. The question is related to the need of simultaneous intervention when blood flow is considered too low for an autologous AVF and arteriovenous graft (AVG). Presence of a very limited blood flow typically less than 120 ml/min in AVF should be considered a potential risk for subsequent early failure of the AVF (Fig. 2) (13). Johnson et al also showed an increased risk of failure in AVG with intraoperative blood flow less than 320 ml/min (14). When blood flow is dramatically low, fistulography is a correct option at that time in order to observe any potential lesion at the anastomosis or in the venous outflow. This limited blood flow is sometimes present with an increased pulsatility index (PI). PI is derived from volumetric flow data by the following formula: (maximum flow–minimum flow)/mean flow. As the difference in maximum and

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Intraoperative assessment of vascular access

minimum flow increases, PI also increases along with the risk of early graft failure. This index represents the peripheral resistance and is typically below 1.0 in AVF and below 5 in peripheral bypasses with optimal outflow (11, 15). When PI is above 1.0 and blood flow value below 120 ml/min, stenosis or kinking in the venous outflow should be investigated by intraoperative duplex scan or fistulography. The choice of the diagnostic method is dependent on the local expertise and availability of fluoroscopy or ultrasound in the operating room. Duplex ultrasound has the advantage not only to observe the stenosis in a 2D vision but also to give some important information such as PSV. On the other side, fluoroscopy permits to investigate and treat central venous stenosis not detected in the preoperative screening. Moreover, fistulography can be followed by endovascular treatment. The presence of a thrill at the venous side of the fistula is a good predictive factor that the blood flow is sufficient with subsequent good early-term results (16). Nevertheless, the absence of thrill is not always related to very early failure. Moreover, the interobserver variance of the perception of the thrill is probably rather high, with a high false negative value. The pulsation of the venous outflow is usually not a good sign correlated with increased resistance that can be measured by the PI. The evolution of the blood flow can be described from the period just after the confection of the anastomosis and during the follow-up. Usually, the blood flow increases during the first month and then tends to stabilize. The optimal fistula is achieved when blood flow is in a good range, typically above 600 ml/min and less than 2500 ml/min for the AVF and easy to puncture. These two important characteristics are difficult to predict with intraoperative observation, but blood flow seems to be a critical issue. Surgical technique: details matter The surgical dissection should be limited to the focused area where the anastomosis is performed. The minimal touch technique is always recommended in order to limit the trauma to the vessel wall. Furthermore, the anastomosis should be done with a magnification lens or with a microscope. Another important point is the tunneling of the vein or the graft. This should be done with a dedicated tunneler with a 1:1 diameter in order to limit the space between the vein and the soft tissue. Indeed, this dead space is immediately filled by serum and play a role in the postoperative upper limb edema observed in the postoperative period. The direction of the tunneler should avoid any soft tissue lesion such as previous scar, skin erosion, and any lesion that will limit the cannulation of the graft or vein. S8

Monitoring the high flow correction When high flow is present in the AVF, symptoms are inconstant. Hand peripheral ischemia is one of the critical situations due to high peripheral resistance limiting the flow to the hand (9). The treatment is mandatory to decrease pain and risk of critical ischemia. Therefore, many treatments are designed to limit the blood flow in the AVF. In this situation, the measurement of the intraoperative blood flow is important to avoid any overlimitation of the flow, which represents a risk of occlusion. This measurement permits to calibrate the restriction of the flow to achieve an acceptable value, and be followed by fistulography in order to visualize a rapid flow to the fingers, which is probably a positive sign for the distal revascularization (12). When a high-flow AVF is present, the blood flow increases dramatically with a parallel enlargement of the venous diameter. This high-flow AVF is a specific situation and no data in the literature showed a correlation between high flow intraoperatively and high flow during the follow-up. Nevertheless, systematic fistulography is not recommended in the international guidelines. Some surgical teams are using this technique to control the patency of the fistula and to look at any lesion in the outflow vein that can limit its patency at short or midterm. The vasospasm: something to avoid The vasospasm is observed in a young patient and should be controlled during the operation with drugs. This spasm is related to sympathetic stimulation. The locoregional anesthesia has a potential role in vasodilatation and limits the vasospasm (17). When the vasospasm is present, papaverin can be locally used or nitroglycerine by direct puncture of the vein (18). This increase of blood flow in the outflow vein is immediately observed when the spasm is relieved. Another possibility to decrease the spasm is to put a warm blanket upon the upper arm in order to keep it warm. The prevention is to avoid the manipulation of the vein, its dilatation with saline serum, or squeletting a long portion of the vein with subsequent trauma to the venous wall. In conclusion, unlike preoperative assessment, intraoperative quality control of VA is not clearly defined in the literature. The clinical evaluation including the presence of thrill after the anastomosis confection is not sufficient to predict the early and midterm results. The use of transit time principle to measure intraoperative blood flow has an increased popularity. Nevertheless, the surgical optimal skills are mandatory to obtain reproducible results, but blood flow measurement could be an interesting adjunct when high blood flow is problematic.

© 2014 Wichtig Publishing - ISSN 1129-7298

Saucy et al

Financial support: The authors have no financial disclosures to make.

Conflict of interest: The authors have no conflict of interest.


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Address for correspondence: Francois Saucy, MD, FEBVS Thoracic and Vascular Surgery University Hospital Rue du Bugnon 46 1011 Lausanne, Switzerland [email protected]

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Intraoperative assessment of vascular access.

The intraoperative quality assessment of the arteriovenous fistula for hemodialysis is an essential process to limit early failure due to technical pr...
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