CQI: hemodialysis vascular access flow monitoring.

One of the main ongoing challenges in nephrology is maintaining a good, well-functioning vascular access. Vascular access problems lead to complications such as access recirculation causing decreased adequacy of dialysis as shown by kinetic modelling and access clotting. Access flow measurement using ultrasound dilution technique is an accurate and better indicator of impending access stenosis than recirculation (urea method). The measurement is non-invasive, the procedure simple, and the monitor accessible at the bedside. The Adam Linton Dialysis Unit of the London Health Sciences Centre, Victoria Campus is currently monitoring access flows (Qa) as a continuous quality initiative using ultrasound dilution technique. Access recirculation (AR) is determined and Qa measurements are done bimonthly on all chronic in-centre and self-care dialysis patients with either arteriovenous fistula or Gore-tex grafts. Qa's of <550 ml/min or 20% decrease in flows are investigated by angiography and early intervention is instituted either by angioplasty or fistula repair. Our unit's goal is to be proactive in our investigation and in our nursing and medical interventions. From our experience, the problem with responding to poor clearances by checking for recirculation after the fact is that valuable time is lost for proactive intervention to preserve the access site and may in fact be too late. In four different patient situations we are able to show how our different interventions have improved Qa's and eliminated AR resulting in increased Kt/V. The intent of this article is to show that Qa measurement can be an ideal way to monitor hemodialysis vascular accesses over time. It provides a means to detect impending access dysfunction before the Qa has decreased enough to have induced AR and/or under-dialysis. By early intervention, optimum dialysis efficiency is achieved and the prescribed Kt/V [urea] is delivered.

On-line optical sensing of blood volume changes to prevent intradialytic hypovolemia.

Intradialytic hypovolemia is a common complication of hemodialysis treatments. Blood volume changes that occur during dialysis can be followed by on-line optical sensing of the patient's hematocrit. Characteristic curves of blood volume changes can be seen in fluid overloaded patients with symptoms of hypovolemia, i.e. cramps, hypotension. The relative blood volume changes in those who have fluid removed to their ideal "dry" weight without symptoms will be shown in comparison. As Phase I of a CQI project, the nephrologist and dialysis nurses at the London Health Sciences Centre performed a cross-sectional study to define the frequency of these curves and their relationship to intradialytic symptoms. The analysis of these curves can be used to re-assess "dry" weights, prevent intradialytic hypovolemia and decrease the use of antihypertensive agents. The correlation of our findings with the results of an independent hypotensive CQI study will be presented.

A comparison of methods for the measurement of hemodialysis access recirculation: an update.

The Crit-Line Model III (CRIT) was compared with the Transonics Hemodialysis Monitor (TRANS) with regard to its ability to measure access recirculation (AR). Patients were studied during routine dialysis before and after dialysis line reversal done to induce AR. A strong correlation between CRIT and TRANS AR measurements was obtained (r=0.95; p=0.000; n=58) and CRIT values were repeatable (normalized SD from mean 7.82%). The CRIT values were not identical to TRANS; at low AR values (< 20%) they overestimated, and at higher values they underestimated. Provided this is appreciated, CRIT AR values are clinically useful.

A comparison of methods for the measurement of hemodialysis access recirculation and access blood flow rate.

The ability to accurately measure access recirculation (AR) is of importance because its presence indicates access dysfunction and may explain why a prescribed Kt/V (urea) has not been delivered. The ability to measure access flow (Qa) allows access monitoring and the detection of impending access dysfunction. AR can be measured by indicator dilution or conductivity tracer techniques. Qa calculation is simple if AR can be detected. The previous techniques are used while the patient's blood lines are reversed to induce AR, and the Krivitski equation gives: Qa = Qb [1-r/r] where Qb = dialyzer blood flow and r = proportion of AR induced. Three methods for AR and Qa measurements were directly compared: 1) ultrasound dilution (Transonics Hemodialysis Monitor, Transonics Systems Incorporated) (TRANS); 2) hematocrit dilution (Crit-Line Monitor, In-Line Diagnostics) (CRIT); and 3) differential conductivity (Hemodynamic Monitor, GAMBRO Healthcare Incorporated) (HDM). Patients were cannulated in a standard fashion and dialysis commenced with lines in normal configuration. A HDM test was performed and, if AR = zero, the lines were reversed to induce AR. HDM, TRANS, and CRIT tests for AR were next done in rapid succession for direct comparison. Each test was repeated three times in succession, the device in random order, to assess test repeatability. Qb was taken from the 1) dialysis machine pump, and 2) directly from TRANS and Qa calculated, using 1) and 2) AR results. In comparison to TRANS, AR results were virtually identical for HDM (TRANS AR = 1.04 HDM-AR + 0.02, r = 0.98, p = 0.0000), and good for CRIT (CRIT-AR = 0.84 TRANS-AR - 0.2, r = 0.81, p = 0.001), but CRIT underestimated the values. Repeatability was assessed by normalizing (%) the SD of repeated measurements; values were 7.5% (HDM), 9.1 % (TRANS), and 17.4% (CRIT). Qa value comparisons were similar (minimal r = 0.83) regardless of Qb source, but CRIT overestimated the value; repeatability data showed 10.6% (HDM), 13.0% (TRANS), and 25.2% (CRIT) (n ranged from 15-64). In summary, TRANS and HDM appear equal as far as accuracy and repeatability of measurements; CRIT results correlated well, but tended to underestimate AR and overestimate Qa, and was less reproducible.