We read with interest the paper of Barth et al., who established a critical decline in relative blood volume (RBVcrit) for intra-dialytic morbid events in patients prone to intra-dialytic hypotension [1]. As the authors indicate, the establishment of a critical decline in blood volume is of prime importance for the success of blood volume controlled feedback technologies in the prevention of hypotensive episodes during haemodialysis.
The role of hypovolaemia in the pathogenesis of intra-dialytic episodes is well recognized. However, its role in the pathogenesis of minor intra-dialytic complaints, such as nausea, cramps and headache, which occur quite frequently during haemodialysis and also in haemodynamically stable patients, is less well established.
We studied the presence of RBVcrit in 24 patients with >1 (major or minor) intra-dialytic symptom per month. Moreover, we assessed whether a correction factor for intra-dialytic weight loss (WL) could enhance its discriminatory value. 359 treatments were analysed. Symptomatic hypotension occurred in 47 treatments, whereas minor intra-dialytic complaints occurred in 71 treatments. The decline in RBV differed significantly between treatments with (9.3±3.5%) and without symptomatic hypotensive episodes (8.2±3.4; P<0.01), as held true for RBVcrit:WL (3.3±1.0 vs 4.5±4.0%/kg; P<0.01). The decline in RBV, uncorrected for WL was not significantly different between treatments with and without minor complaints (9.0±3.0 vs 8.2±3.4%; P = 0.09), but became significantly different when corrected for WL (3.7±1.1 vs 3.0±1.1%/kg; P<0.01). In patients with minor intra-dialytic complaints the intra-individual SD for the RBVcrit and RBVcrit:WL was 1.7% and 0.7%/kg.
Thus, a relation also exists between minor intra-dialytic complaints and a decline in RBV during haemodialysis. Nevertheless, in view of the relatively small absolute differences between uncomplicated and symptomatic treatments, the intra-individual variability for RBVcrit is not to be neglected. However, the establishment of RBVcrit (which might benefit from correction for WL) may also be useful in patients with minor intra-dialytic complaints, as we showed earlier that these patients may also benefit from blood volume controlled feedback treatment [2].
Conflict of interest statement. None declared.
1Maxima Medical Centre 2University Hospital Maastricht Email: jkoo{at}groupwise.azm.nl
References