Is Timing a Factor In Flow Measurements Performed During Hemodialysis?
NKF-KDOQI guidelines recommend that the vascular access flow assessment be performed during the first 90 minutes of hemodialysis to eliminate error caused by decrease in cardiac output or blood pressure related to ultrafiltration and/or hypotension. This measurement time restriction to within the first 90 minutes limits the number of measurements that can be performed by one operator, which is a significant issue in clinical practice.
To test the need to take measurements during the first 90 minutes of hemodialysis, clinicians from Seoul’s Catholic University and Daegu’s Yeungnam University studied the effect of intradialytic change in blood pressure and ultrafiltration volume on the variation in access flow measured by ultrasound dilution. The effect of patients’ demographic parameters on access flow also was evaluated.
For their study, vascular access flow was measured by a Transonic HD03 Monitor in 30 patients during 89 HD sessions. Flow measurements were performed at 30 minutes, 120 minutes and 240 minutes after the start of HD. The results were evaluated for variation. Sixteen patients had fistulas; 14 had grafts.
Their results demonstrated that mean access flow over all sessions decreased by 6.1% over time (1265±568 mL/min after 30 minutes, 1260±599 mL/min after 120 minutes, and 1197±576 mL/min after 240 minutes). Noteworthy was the fact that a ≥5% decrease in mean arterial pressure during HD significantly reduced access flow, and mean arterial pressure did not correlate with ultrafiltration volume. No other variable (ultrafiltration volume, sex, age, presence of diabetes, type or location of access, body surface area, hemoglobin, serum albumin level) interacted significantly with the effect of time on access flow.
From this data the clinicians concluded that the variation in access flow during HD is relatively small. They found, however, that decreased blood pressure is a risk factor for variation in access flow measured by ultrasound dilution. In most patients whose blood pressures are stable during HD, the access flow can be measured at any time during the HD treatment.