Reply
E-mail: Andrew.Davenport{at}royalfree.nhs.ukSir,
We thank the editor for the right to reply, as Shaldon and Lysaght have made a series of allegations that we wish to refute. They suggest that we have claimed that our studies using wearable artificial kidney and ultrafiltration devices were original. This is not correct; we wrote, ‘One potential advance would be to develop a dialysis system that was wearable, so that patients could do dialysis at home. This idea is not new, with a wearable artificial kidney being reported in the 1970s’ [1]. Similarly, for the wearable ultrafiltration device study we wrote, ‘This is not a new concept, as the first attempts to provide such continuous treatments, date back more than 30 years ago, to the pioneering reports by Kolff’ [2]. Shaldon and Lysaght have taken one sentence out of context, ‘This study describes the first human use of a wearable haemofiltration device to manage fluid overload’. This sentence was preceded by, ‘We have previously described the feasibility, safety, and efficacy of the wearable artificial kidney (WAK), as well as its use as an ultrafiltration device, in animal studies’, and followed by ‘As such, this was a preliminary study, designed as proof of concept, and also to assess both patient tolerability and safety’. The sentence quoted by Shaldon and Lysaght refers to the first human trial using our wearable ultrafiltration device, as all the previous studies with this device had been laboratory and/or animal based.
Shaldon and Lysaght have suggested that we may have staged a media event. This is not correct. The wearable ultrafiltration device trial was completed and submitted to Kidney International. Their reviewers, much maligned by Shaldon and Lysaght, requested a major revision, followed by further revision, before the paper was finally accepted. It was only then that the wearable dialysis study was submitted to the Lancet, where it was fast tracked and rapidly published. Thus, due to the different publication policies of the two journals, the studies were published within a short period of time, rather than some staged media event as suggested by Shaldon and Lysaght.
Shaldon and Lysaght comment that both of these devices were worn for short periods of time. However, as both studies were pilot phase I trials, designed as proof of concept and safety trials, then the regulatory authorities, particularly the UK Medicines Health Regulatory Authority (MHRA) specified the duration and conduct of the study.
Earlier prototypes relied on arterial or arterialised blood supply, without the safety features of current haemodialysis machines, and as such exsanguination was a real threat [3]. The wearable devices we have trialled are worn on an ergonomically designed belt around the waist, with the latest version weighing around 2 lbs, designed for central venous catheter access. In these pilot trials, heparin was used for anticoagulation, but this is not our long-term plan [4]. The MHRA were concerned about the possibility of disconnections, and whereas current haemodialysis machines may continue to exsanguinate patients in cases of venous disconnection, these wearable devices have safety systems designed to stop the blood pump in cases of venous disconnection. One patient in the WAK trial suffered a venous needle disconnection, and the safety devices switched into action and prevented blood loss [1].
Three times weekly outpatient haemodialysis, based on urea Kt/V prescription, can lead to inadequate dialysis, particularly for small men and women [5], often complicated by hypertension [6] with frequent episodes of intradialytic hypotension [7]. Thus, we believe that there needs to be a change in the paradigm for treating patients with end-stage kidney disease. Continuous treatments have the benefit of cardiovascular stability [8], and also allow time for the removal of so-called uraemic ‘middle molecules’. In addition, a wearable ultrafiltration device may provide support for other patients with diuretic resistant cardiac failure and ascites due to chronic liver disease [9]. We remain committed to the continued development of these wearable devices, and are continuing our efforts in the quest for advancing dialysis technology to improve patients’ quality of life and outcomes.
Conflict of interest statement. Victor Gura MD is a Director, the Chief Scientist and Chief Medical Officer of Xcorporeal Inc.
1 UCL Center for Nephrology, Royal Free & University College Medical School, London, UK 2 Department of Nephrology, Dialysis and Transplantation, St. Bortolo Hospital & International Renal Research Institute Vicenza 3 Cedars Sinai Medical Center, David Geffen School of Medicine, UCLA, LA, USA
References
- Davenport A, Gura V, Ronco C, et al. A wearable haemodialysis device for patients with end-stage renal failure: a pilot study. Lancet (2007) 370:2005–2010.[Medline]
- Gura V, Ronco C, Nalesso F, et al. A wearable haemofilter for continuous ambulatory ultrafiltration. Kidney Int (2008) 73:497–502.[CrossRef][Web of Science][Medline]
- Murisasco A, Reynier JP, Ragon Y, et al. Continuous arterio-venous haemofiltration in a wearable device to treat end stage renal disease. Trans Am Soc Artif Organs (1986) 32:567–571.
- Davenport A. Anticoagulation for continuous renal replacement therapy. Contrib Nephrol (2004) 144:228–238.[CrossRef][Web of Science][Medline]
- Spalding EM, Chandna SM, Davenport A, et al. Kt/V underestimates the haemodialysis dose in women and small men. Kidney Int (2008) in press PMID 18509325.
- Davenport A, Cox C, Thuraisingham R. Achieving blood pressure targets during dialysis improves control but increases intradialytic hypotension. Kidney Int (2008) 73:759–764.[CrossRef][Web of Science][Medline]
- Davenport A. Intradialytic complications during haemodialysis. Hemodial Int (2006) 10:162–167.[CrossRef][Medline]
- Gibney N, Cerda J, Davenport A, et al. Volume management by renal replacement therapy in acute kidney injury. Int J Artif Organs (2008) 31:145–155.[Web of Science][Medline]
- Davenport A. Ultrafiltration in diuretic-resistant volume overload in nephritic syndrome and patients with ascites due to chronic liver disease. Cardiology (2001) 96:190–195.[CrossRef][Web of Science][Medline]
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