By Peter Laird, MD
Since starting on the NxStage System One in June of 2009, I have continued to look for its maximum efficiency in my own personal treatments just as I did while doing self care incenter. One of the frustrating aspects of using the NxStage machine is the lack of available medical studies on specific issues. The Nxstage literature base is quite incomplete at this time and many more studies need to be completed. Fortunately, we have a recent publication from Hemodialysis International that begins to answer some of these questions of how effective is the NxStage System One when compared to the standard incenter thrice weekly dialysis at the level of solute kinetics (thanks to RenalWEB for highlighting these articles). Solute kinetics with short-daily home hemodialysis using slow dialysate flow rate:
The weekly treatment time for the patients averaged 17.4 h/wk, a figure higher than the average weekly treatment time embraced by many US in-center dialysis units where a thrice-weekly regimen is practiced. The removal rates and clearance values in the present study should therefore be interpreted in the context of increased weekly dialysis time. While the low dialysate flow rate reduces urea removal, the increase in the frequency of the treatments improves it. In the case of phosphorus and β2M, increased dialysis time is more critical for their removal and compensates for the low dialysate volume.
In my own review prior to starting the NxStage System One last June, I noted that the relationship between NxStage dialysis flow rates and clearance is nearly linear until you go over a dialysate flow rate of 200 ml/min. Most recommendations for the dosage of NxStage are based on the Filtration Fraction (FF) or percent dialysate flow rate compared to blood flow rate. However, when looking at the actual flow rates instead of the FF, it is my belief that the recommended NxStage dosages are simply too low. In my case, at 90 kg, the NxStage dosage recommendation is 20L with a FF of 35%. In my training, I started on this dosage which I did not find adequate for improving my symptoms and my energy levels even though I did hit the targeted Kt/V of 0.5 with 20L.
When I went home, we started at 30L, FF 35% with my Kt/V improving to 0.77. With a blood flow rate of 360 to minimize my venous and arterial pressures, the actual dialysate flow rate is 126 ml/minute completing treatment in 238 minutes (3 hours and 58 minutes). My phosphorus (PO4) level increased by 30% from my usual incenter values on the 20L regimen despite continuing the same restrictive diet. Dr. Scott Rasgon likewise found this in his published data of NxStage users in their program at Kaiser Permanente Sunset medical center. Due to the concern of long term PO4 elevations and looking at the clearance charts for NxStage, I approached my nephrologist about going outside of standard NxStage parameters to maximize the effective volume of dialysate to see if I could improve my PO4 levels, which act like a middle molecule. He agreed to increase my dosage to 40L of dialysate at a FF of 45% (162 ml/min dialysate flow rate) to keep the treatment time near the four hour level of my 30L treatments. I was pleased to find my energy levels improved as well as increasing my spKt/V to 0.93, 86% higher than at my 20L dosage, and my PO4 levels returned to my pre-NxStage levels at 3.5 from the 4.6 level on the lower 20L dosage without any binders which I have not ever been on to date.
20L Time 158 minutes FF 35% (BFR 360/min - DFR 126/min) spKt/V- 0.5
30L Time 238 minutes FF 35% (BFR 360/min - DFR 126/min) spKt/V- 0.77
40L Time 246 minutes FF 45% (BFR 360/min - DFR 162/min) spKt/V- 0.93
NxStage dosing is supported by the Standardized Kt/V value of 2.0/week with in center thrice weekly dialysis per KDOQI standards. The single pooled Kt/V (spKt/V) values are not linear which means you can’t simply add the daily values to obtain a weekly value. The level of spKt/V of 0.5 comes from the fact that this will produce a Standard weekly Kt/V (stKt/V) of 2.1 which falls within the recommended KDOQI standards. Northwest Kidney Centers has set their weekly stKt/V at 2.5 (PDF link) which is also the standard weekly Kt/V goal of the Frequent Hemodialysis Network as well.
The target weekly or standard Kt/V for urea in the current frequent hemodialysis trials will be approximately 2.5 in the conventional thrice-weekly arm, 3.8 in the daily in-center hemodialysis arm, and 5.6 in the nocturnal arm.
I greatly appreciate the recent study from Hemodialysis International on the solute kinetics of the NxStage at standard recommended dosages. However, I must question from my own personal experiences with the NxStage System One whether maximizing the efficiency of dialysate flow rates paradoxically reduces the maximum clearances at the patients level. It is certainly a wonderful thing to watch numbers and efficiencies improve, but if it does not translate to maximum patient benefits then we should abandon this approach and look at maximizing total dialysate dosage for patients on the NxStage instead. For an increase of dialysis time by over 30%, I gained an 86% increased spKt/V and ~25% reduction of my phosphorus levels by exceeding standard NxStage dosage recommendations as well as using a higher Filtration Fraction. The theoretical loss of dialysate efficiency at higher dialysate flow rates and Filtration Fractions may be offset by a simple increase dialysis dosage that translates into higher urea, phosphorus and B2M kinetics as I found in my personal NxStage experiences. This simply question has not yet been answered in the NxStage literature, but it needs to be considered.
How good can the NxStage machine be if taken to the max? Indeed, optimal dialysis paradigms operate on the simple concept of maximizing frequency, time and clearances in standard machines. It is time for investigators to explore this aspect of the NxStage System One noting urea, phosphorus and B2M clearances over a broader range of dialysate flow rates and Filtration Fractions which will allow higher total clearances comparable to standard incenter machines. My own anecdotal experience suggests that there is significant room for improvement over standard NxStage dosage paradigms (PDF link) published to date that should be explored to eliminate the low clearance shortfall that has kept many nephrologists from recommending the NxStage to their patients despite the advantages of having a portable machine. It is time to take the NxStage System One to the max.