Can antihypertensive medications control BP in haemodialysis patients

Sir, Allow me to comment on the ‘Personal Opinion’ of Dr Scribner on whether antihypertensive medications can control hypertension in haemodialysis (HD) patients [1]. The Oxford Dictionary defines ‘opinion’ as ‘a judgement or belief based upon grounds short of proof’. Now, whilst I entirely agree with Dr Scribner that the most effective way to control hypertension in dialysis patients is with the use of a salt restricted diet, I am not sure that I can accept his hypothesis that this is related to a ‘normalization’ of the extracellular volume (ECV). Our initial attempts to measure ECV in HD patients by exchangeable sodium suggested that after an initial reduction in ECV which corresponded to the volume and weight loss correction, there was a lag period of several weeks to months in which there was no change in ECV or indeed a slight increase, whilst blood pressure continued to fall to below 100 mmHg mean arterial pressure [2]. The observation more recently that this blood pressure reduction is associated with a reduction in peripheral vascular resistance, without a decrease in cardiac output suggests that alternative mechanisms may be considered [3]. Amongst such are the reduction in plasma 1‐ADMA (asymmetric dimethyl arginine), a known inhibitor of nitric oxide synthetase [4]. Alternatively, a sodium overload could lead to an inhibition of the Na+/K+‐ATPase via an endogenous digitalis‐like substance, the result of which would be an increase of the intracellular sodium and calcium concentration with an increased tone of vascular smooth muscle cells. Reducing the sodium load could reverse this mechanism [5]. Finally, a link between sympathetic overactivity as it is found in HD patients and the sodium overload could be an alternative hypothesis [6]. Whatever the rational explanation for the empirical benefit of salt restriction in the hypertensive dialysis patient, the clinical benefit is undeniable and associated with the best survival data in the world. As this phenomenon may be reproducible without lengthening dialysis time [7,8], it is possible to achieve with virtually no added cost and does not impose a boring and unpalatable diet upon the patient. Indeed, it is worth remembering that in Tuscany, where regional Italian Cuisine arguably reaches its pinnacle, salt free bread is the regular bread sold in the bakeries. Perhaps the time has come to cast aside Neptune's poisoned chalice and give the well dialysed patient a longer‐and healthier life with fewer complications and no added expense. Sir, My friend, Stanley Shaldon, makes a good point when he re‐emphasizes the importance of a sodium restricted diet. And he is correct in pointing out the lag time between ECV changes and BP changes [1]. I also agree with his point that the mechanisms by which changes in ECV effect changes in BP are not well delineated. Nevertheless, time averaged changes in ECV do indeed affect BP and can be used to control BP in the dialysis patient as the group in Tassin has so clearly demonstrated over the decades.