Tuesday, May 17, 2016

Seminal Articles in Health Policy

So this is a little out of my wheelhouse, but yesterday this tweet came across my tweet stream:

Ari Friedman replied

Which was simultaneously a great answer and kind of useless. He then sent me a bibliography, here is his list with links:

  1. Arrow K. Uncertainty and the Welfare Economics of Medical Care. 1963;53(5). (PDF)
  2. Pauly M. The economics of moral hazard: comment. American Economic Review 1968;58(3):531–7.  (PDF)
  3. Cutler DM, Reber S. Paying For Health Insurance: The Trade-Off Between Competition And Adverse Selection. The Quarterly Journal of Economics 1998. (PDF)
  4. Taubman SL, Allen HL, Wright BJ, Baicker K, Finkelstein AN. Medicaid Increases Emergency-Department Use: Evidence from Oregon’s Health Insurance Experiment. Science 2014;343(6168):263–8.  (PDF)
  5. Cohen JT, Neumann PJ, Weinstein MC. Does Preventive Care Save Money? Health Economics and the Presidential Candidates. N Engl J Med 2008;358(7):661–3.  (PDF | NEJM)
  6. Burns LR, Pauly MV. Accountable Care Organizations May Have Difficulty Avoiding The Failures Of Integrated Delivery Networks Of The 1990s. Health Aff 2012;31(11):2407–16. (PDF)
Cedric Dark tweeted:

I will add to this when he gets back to me.

Wednesday, May 11, 2016

Do you give a Flux about Flux?

There is a spirited debate in our hospital system about the use and availability of high flux membranes. Part of the debate centered around middle molecule clearance and its relationship to uremia. I fell back to my old standard the HEMO trial.
A study as long and as expensive as HEMO will not be let to rot after its first paper, and the research parasites extracted a number of tantalizing findings. In 2003 JASN published an analysis that looked at flux when patients were divided by vintage. Dialysis patients who have been on dialysis for more than 3.7 years had improved outcomes with high flux dialyzers:
In the subgroup that had been on dialysis for >3.7 yr, randomization to high-flux dialysis was associated with lower risks of all cause mortolity (RR, 0.68; 95% CI, 0.53 to 0.86; P = 0.001), and cardiac deaths (RR, 0.63; 95% CI, 0.43 to 0.92; P = 0.016), compared with low-flux dialysis.

Though the data is not so compelling when the vintage is divided by quintiles:

Even more damning ,was the fact that the longer the patients were randomized, the smaller the effect of high flux membranes:

Longer years of follow-up should show more protection from high-flux membranes (lower RR in the table) but the opposite is actually seen.

Additional post-hoc analysis was done here, showing decreased cerebrovascular disease for longer vintage patients:

I then came across the membrane permeability outcome study, MPO, published in 2009 in JASN. This European study was designed to answer the following question:
This prospective, randomized Membrane Permeability Outcome (MPO) study was designed to compare the impact of membrane permeability on survival in incident HD patients who had either low ( 4 g/dl) or normal albumin ( 4 g/dl) and were treated with a minimum dialysis dose (single-pool Kt/V [spKt/V]) of 1.2. 

Use of incident patients will eliminate the vintage advantage seen in the two post-hoc HEMO studies discussed above. Separating patients based on albumin at baseline seems a bit wonky. Lots of patients have low albumin at the start of dialysis. And I doubt there is an inherent biological reason for this. Turns out, the two tiers were due to pokey enrollment after 11 months and they changed enrollment rules.  They also changed the rules by extending the time patients could take to get to a spKt/V from 1 month to 3 months. The things we do for enrollment!

The top-line results showed no difference in survival by flux:

But when the authors looked at the pre-specified sub-group analysis for patients with a baseline albumin less than 4, the data showed protection with high-flux membranes:
This isn't just any pre-specified sub-group, this was supposed to be the entire cohort, and only became a sub-group after they amended the protocol.
They also found an interaction between flux and diabetes. This was post-hoc analysis:

So, in the end this seems like a tale told by an idiot (your truly), full of sound and fury signifying nothing because we have all moved on to high flux dialyzers, except in the hospital where F16 low flux dialyzers are available and cheaper than their high flux brethren.

My concerns with the wearable artificial kidney

Last week the Wearable Artificial Kidney reached some sort of new benchmark and a bunch of press ensued. I stumbled across this one.

And I tweeted:

This was a popular tweet 

but not a popular opinion. Most people say that it is great to see out of the box thinking in nephrology. They advised me not to look at the technology as it is today but envision where this technology could go.

I appreciate the technology and can totally see how something like this:

Could undergo a transition analogous to this:

My concern is not the size of the equipment, though by the looks of it, they still have a formidable chasm to cross. My concern has to do with access. This is hemodialysis. It still needs a way to get blood out of the body, into the machine, and back into the body, reliably, continuously and safely. This is not a trivial task and tunneled catheters have a high rate of infection and mortality. 

Persons using catheters had increased risk of all-cause mortality (RR=1.38, 95% CI=1.25–1.52), fatal (RR=1.49, 95% CI=1.15–1.93) and nonfatal (RR=2.78, 95% CI=1.80–4.29) infection, cardiovascular event (RR=1.26, 95% CI=1.11– 1.43), and hospitalization (RR=1.51, 95% CI=1.30–1.75) compared with those individuals using grafts. From Ravani, JASN 24:465-73, 2013.

They are public enemy number one in dialysis units and this technology depends on them. Vascular access is the weak link of hemodialysis, whether it is in-center, home or a WAK. And adding mobility, continuous use, and patient error to the equation probably will not help.

I look forward to sheepishly reading this post one day in our WAK future, but I suspect that future is populated by hover boards and self tieing shoes.

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