Novel use of the Nexfin™ HD monitor for real-time physiological assessment of blood flow during creation of an upper extremity arteriovenous fistula.

Abstract

To the Editor, Arteriovenous fistulas (AVFs) must meet certain criteria regarding diameter and flow rate (Qa) upon maturation to be considered adequate for use in hemodialysis as well as to reduce the risk of negative sequelae such as high-output cardiac failure. In spite of extensive preoperative vessel assessment, 20-50% of AVFs fail to meet these criteria and must undergo surgical revision. Intraoperative assessment of AVF patency often relies on clinical evaluation for the presence of a venous thrill post-anastomosis, but this method is highly operator-dependent and a poor predictor of long-term AVF outcomes. While more objective devices exist to assess intraoperative flow (i.e., devices to measure transit time), they are invasive and require expert surgical skill to produce accurate and reliable readings. In addition, there is poor evidence to correlate a specific range of measured transit times with improved rates of maturation. Creation of an AVF results in a welldocumented increase in cardiac output (CO) due to a rapid decrease in systemic vascular resistance (SVR) postarteriovenous anastomosis. Continuous measurement of CO by noninvasive means may provide a more objective and reproducible intraoperative method of measuring AVF patency and predicting long-term outcomes. We present the novel use of photoplethysmographic technology with the Nexfin HD monitor (BMEYE, Amsterdam, The Netherlands). This device was used for intraoperative assessment of CO during creation of a brachiocephalic AVF in a 60-yr-old male with end-stage renal disease (glomerular filtration rate 19 mL min) and type 2 diabetes mellitus. The patient gave his consent for publication of this report. Anesthesia options were discussed and we elected to proceed with the procedure under general anesthesia. The patient was placed in the supine position and, in addition to using standard hemodynamic monitors, a Nexfin cuff was placed on the index finger of the patient’s non-operative arm. The Nexfin uses finger cuff-based photoplethysmography to provide noninvasive continuous blood pressure, CO, SVR, and heart rate monitoring. Induction of anesthesia was uneventful and surgical management of the case was routine. Clinically, the surgical team was satisfied with the newly created AVF. Hemodynamic monitoring by Nexfin showed a baseline CO pre-AVF that ranged from 5.4-5.8 L min and increased to 7.0 L min immediately after the fistula was established (Figure). Systemic vascular resistance dropped from 955 dyn sec cm pre-AVF to 916 dyn sec cm post-anastomosis. The patient tolerated the procedure well and remained hemodynamically stable during the surgery and postoperatively until discharge. Current intraoperative methods to determine AVF adequacy are limited to subjective clinical assessments or invasive and operator-dependent Qa measurement devices. These methods are poor predictors of long-term AVF adequacy and continue to result in high AVF failure rates, particularly in females, the elderly, and diabetics. Intraoperative continuous monitoring of CO may provide an additional means of assessing AVF patency. This method would have traditionally required invasive arterial pressure (IAP) monitoring. Nevertheless, newer noninvasive CO monitors such as Nexfin are comparable with IAP for hemodynamic monitoring in the majority of patients undergoing surgery, but they do not come with any C. Fitch, BScN (&) R. Earle, BSc A. Sawka, MD H. Vaghadia, MBBS Departments of Anesthesia and Vascular Surgery, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada e-mail: christiemfitch@gmail.com