Continuous haematocrit monitoring during intradialytic hypotension: precipitous decline in plasma refill rates.

BACKGROUND Intradialytic hypotension (IDH) during ultrafiltration remains a major source of haemodialysis related morbidity, despite technological advances including continuous haematocrit monitoring and automated blood volume controlled dialysis machines. We hypothesized that studying the relationship between ultrafiltration rate and plasma refill rate (UFR, PRR) before and during IDH would provide insight into its mechanism and possible prevention. METHODS We retrospectively identified 17 patients (mean age 50 years) with IDH treated solely by turning off the ultrafiltration, none having received hypertonic saline, mannitol or albumin. All patients had archived data for continuous haematocrits, UFR, ultrafiltration goal, vital signs and symptoms. We used the Crit-Line III optical haematocrit monitor to calculate the PRR for intervals preceding and during IDH. RESULTS Prior to IDH the PRR was 1360+/-550 ml/h; which was less than the UFR of 1471+/-602 ml/h and was associated with a 4.4% rise in haematocrit. However, during IDH the PRR was dramatically lower (P<0.001): only 242+/-151 ml/h. The PRR was not correlated (P>0.05) with the absolute, per cent change or rate of rise in haematocrit, UFR, ultrafiltration goal or heart rate. CONCLUSIONS On-line haematocrit monitoring allows for the calculation of plasma volume changes, UFR and PRR, and the mismatch in those rates helps explain the physiology of hypotension episodes. The precipitous fall in PRR during sudden IDH supports activation of the cardiodepressor Bezold-Jarisch reflex. As both the UFR and PRR variables can change during a single dialysis session, this supports the use of devices with automated continuous adjustments of the UFR and suggests additional profiling methodologies.