homeostasis - Science-Education-Research

Is 6% kidney function just as good as 8% kidney function?

A case of justifying dubious medical ethics by treating epistemology as ontology

Keith S. Taber

I was puzzled by something I heard a hospital doctor say regarding kidney functioning. The gist of his comments were that

once kidney function was below about 10% of normal functioning…
then protecting remaining kidney function was not important…
because estimates of function at that level are unreliable.

I thought this was an illogical argument as it confused ontology (the state of the kidneys and their functioning) and epistemology (how well we can measure kidney function).

The kidneys are essential organs that regulate hydration levels and eliminate toxic materials from the body. They are 'essential' in the sense that without kidney function someone soon dies. Typically healthy people have plenty of scope for contingency in the capacity of their kidneys. (Living kidneys donors give up one of their two kidneys for transplantation, so, after donation, they will only have, at best, 50%,of normal functioning.) So when people's kidneys start to deteriorate due to disease the patient can continue with normal life for some time. I am not an expert, but from what I understand, a person can manage a normal life with 20% of normal functioning.

Of course there reaches a point in progressive kidney disease when the remaining capacity is not enough to keep someone alive for an extended period. So if kidney function drops to something like an eighth of normal healthy functioning, the situation gets critical.

Kidney dialysis

These days people can have dialysis if their kidneys fail. Someone with 0% kidney function – someone who never excretes any urine at all – can be kept alive indefinitely by dialysis. However this is not ideal. The patient has to attend a clinic and have treatment for 3-4 hours at a time, usually three times a week. No time off – no holidays from dialysis if the patient wants to continue living (and some decide they would rather not continue living, although most 'tolerate' the treatment). Often patients feel unwell on, or after, dialysis – they may say they feel 'washed out', for example. Dialysis also costs the health service (or in some countries, the patient) a good deal of money.

Dialysis patients also have to be very careful about diet and avoid some foods (e.g., eating bananas can lead to dangerously high levels of potassium that can interfere with heart function and could lead to a heart attack), as sessions of dialysis (with no, or very little, blood filtration occurring in-between) is never as good as having constantly functioning kidneys.

Then there's the problem of fluid intake

Dialysis patients are asked to limit their intake of fluids. A healthy person who drinks a lot (whether tap water, tea, beer, etc.) simply produces more urine. Most dialysis patients, however, produce little, if any, urine, and the difference between what they 'should' excrete (to maintain homeostasis), and what they can actually excrete, needs to be removed during the dialysis process. So, whatever water a patient takes in drinks during the 45 or so hours between sessions (and is not lost through some other mechanism such as sweating or breathing), is all taken off during three or so hours on the machine. This brings about changes in the blood volume much more quickly than is comfortable. As the body cannot remove excess fluid via the kidneys, fluid intake means the fluid levels build up between dialysis sessions which can lead to various complications such as increases in blood pressure.

Dr McCoy is unimpressed by 20th Century medicine (Star Trek IV: The Voyage Home, Paramount Pictures)

So, having kidney function of, say, 10% or less of normal is a real pain and requires reorganising your entire life around your dialysis sessions (or perhaps getting a transplant if you are strong enough for surgery and are lucky enough that a good match can be found).

That provides some background in considering whether, once kidneys have deteriorated below, say 10%, it really makes any difference in worrying about the actual level. If you have 8% of normal functioning and are on dialysis for life, why would it matter if that fell to 6%?

An actual case

The context of this question was a patient with kidney failure or end-stage renal disease (a haemodialysis* patient, who would only live a matter of days without regular treatment) who was given a CAT scan** using a contrast medium*** to show up features that would not be observable otherwise. Such media are widely considered to have some toxicity in relation to the kidneys (Ahmed, Williams & Stott, 2009), but in a healthy person they are eliminated through the kidneys quite quickly and any risk is considered small. A person with kidney failure does not eliminate toxins in this way, and so when a scan is indicated, it can be scheduled for just before their next dialysis session.

"In every study comparing patients with and without some degree of renal insufficiency [kindeys not functioning adequately], renal insufficiency increased the likelihood of RCIN [radiocontrast-medium-induced nephropathy, i.e., kidney damage due to the use of contrast media]"

"Both peritoneal and hemodialysis remove substantial amounts of the contrast medium (50% to 90% of the dose); hemodialysis is more effective."

Solomon, 1998: 230, 236.

This patient, however, was admitted to a hospital very ill. The emergency department doctor ordered an immediate scan – late at night, at a weekend – but told the patient that the on-call dialysis staff could be called in to give dialysis after the scan. At the X-ray department, the radiographer then said that this was not needed, as long as the patient had dialysis within 24 hours of the scan.

The renal doctor's viewpoint

The next afternoon, the patient had still not gone for dialysis when the hospital renal doctor visited the patient. This doctor took the view that as the patient was due their regular dialysis the following day (i.e., about 38 hours after the scan), there was no point sending the patient for an additional dialysis session, as – after all – the kidneys had already failed sufficiently for the patient to be relying on dialysis for survival.

The patient's viewpoint

The counter-argument presented to the renal specialist (by the patient's spouse) was that even at this point further deterioration should be avoided if possible – that even if 8% of normal kidney function was not good, it was inherently better than 6% of normal kidney function.

After all, if for some reason a patient was further compromised (by an unrelated illness, or by delay in accessing normal dialysis due to some unexpected contingency) a few percentage points – making a small difference in how much the body could remove toxins and excess fluid from the blood by itself between dialysis sessions – could still be the critical factor in determining whether the person survived. (Those attending hospital dialysis notice the high frequency of fellow regular patients who, suddenly, are no longer attending for treatment.)

The renal doctor's justification

The doctor responded to this with the counter-argument that once kidney function was this low, there was no reason to be concerned about a change in measured kidney function from (say) 8% to 6% as the difference between such measurements was within the usual variations in measurements found in patients from time to time.

There are two issues here of interest.

Consent that is conditional is not consent if the conditions are broken

One issue relates to ethics (here, medical ethics). A patient consented to a diagnostic procedure with a possible risk of side effects on the understanding that a suitable counter measure would be taken immediately after the procedure to minimise any detrimental effect. The hospital undertook the procedure, but then decided (when it was too late for the patient to withdraw consent) not to follow through on the promised counter-measure. In effect, a procedure was carried out without consent as the consent was (as was made absolutely clear by the patient) conditional on the scan being followed by dialysis.

Reasons for refusing to provide treatment

The second issue relates to the justification given by the doctor as reported above.

The day after the explanation about measurement not clearly distinguishing between 8% and 6% functioning had been made, when dialysis was finally provided, another renal specialist offered a different justification entirely – that the potential risk to kidneys of the contract medium was just a myth. However, the earlier conversations

in the emergency department;
in the X-ray department; and
with the first renal doctor within 24 hours of the scan,

were all clearly undertaken on the basis that both patient and medical staff thought the contrast medium was potentially damaging to kidneys.

"These contrast media can occasionally cause kidney damage, especially in patients who already have kidney disease"

Ahmed, Williams & Stott, 2009

In the context of that discourse, the first renal specialist had argued that because (a) the precision of estimates of kidney function was not great enough to reliably measure a difference between 6% and 8% functionality, then (b) there was no need to be concerned about treatment which could potentially cause damage bringing about deterioration of this order.

Presumably,

at any one time, a person's kidney function will be at a certain level.
If the kidney is then further damaged by toxins then that functionality will drop.
A more damaged kidney is inherently less desirable than a less damaged (better functioning) kidney.
So further damage to an already damaged kidney is inherently undesirable,
and should be avoided if possible, if the costs of doing so are not too high.

The state of a diseased person's kidneys could vary slightly 'naturally' in response to various factors related to their general health, diet, environment, etcetera. This is an ontological consideration – the actual state of the kidneys changes. This may well mean that changes of a few percent between measurements could just be natural fluctuation.

It may therefore be difficult to tell if a person's kidneys have become more damaged due to a particular event, such as a diagnostic scan. That is an epistemological issue – the limitation on how well we can identify a specific change that is masked by noise.

Presumably, there are also various factors that limit the precision of such estimates – all measurements are subject to errors, and small (real) differences may be difficult to identify if they are at the level of the likely measurement error. That is also an epistemological issue.

But, just because an effect cannot be clinically measured (epistemology), that does not mean it is not real and will not have consequences (ontology). A drop from 8% kidney function to 6% kidney function is only a change of 2% compared with normal functioning, BUT it is a loss of 25% of the patient's actual kidney function.

A small deterioration in already severely compromised kidneys may seem insignificant to the renal doctor because he does not think he could reliably measure the change. One day it could be the difference between life and death to the kidneys' owner.

Sources cited:

Ahmed, A., Williams, G., & Stott, I. (2009). Patient information-What I tell my patients about contrast medium nephrotoxicity. British Journal of Renal Medicine, 14(3), 15-18.
Solomon, R. (1998). Contrast-medium-induced acute renal failure. Kidney international, 53(1), 230-242.

* haemodialysis involves the patient having permanent 'plumbing' installed that allows their vascular system to be connected to a dialysis machine, so the blood can be diverted to the machine to be cleaned. This usually done using blood vessels in the arm. In the case discussed the surgeon cut into the neck and chest (with the patient fully conscious), and connected tubing to a vein in the neck. The tubing was run beneath the skin to exit in the chest below the neckline, where a fitting acted as a tap and connector for the external tubing to the machine. Very special care has to be taken to keep the area clean, and the dressing dry, as the plumbing provides a direct route into the bloodstream. (Baths, swimming, hot-tubs, etc. are not advisable.)

[Peritoneal dialysis is an alternative treatment that involves a catheter being implanted in the abdomen, and being used to allow a solution into the abdominal cavity, which is later removed after it has absorbed waste materials. The patient can manage the process at home, but needs to change the solution in the abdomen a number of times each day.]

** computerised tomography: a process that uses a series of X-ray bursts to collect data that can be compiled into a 3-D image.

*** a substance that shows up on X-ray scans, and which when injected into the blood helps detect vascular structures. (The term is generic – it also applies to substances swallowed before scans of the alimentary canal.)

Note: this post was originally prepared in October 2015, but was not published at the time when the patient was alive and attending for treatment.

The brain thinks: grow more fur

The body senses that it's cold, and the brain thinks how is it going to make the body warmer?

Keith S. Taber

Bert was a participant in the Understanding Science Project. In Y11 he reported that he had been studying about the environment in biology, and done some work on adaptation. he gave a number of examples of how animals were adapted to their environment. One of these examples was the polar bear.

…our homework we did about adapting, like how polar bears adapt to their environments, and camels….
And so a polar bear has adapted to the environment?
Yeah.
So how has a polar bear adapted to the environment?
Erm, things like it has white fur for camouflage so the prey don't see it coming up. Large feet to spread out its weight when it's going over like ice. Yeah, thick fur to keep the body heat insulated.

Bert gave a number of other examples, including dogs that were bred with particular characteristics, although he explained this in terms of inheritance of acquired characteristics: suggesting that dogs that have been taught over and over to retrieve have puppies that automatically have already got that sense. Bert realised that this example was due to the work of human breeders, and took the polar bear as an example of a creature that had adapted to its environment.

Yeah, so how does adaption take place then? You've got a number of examples there, bears and dogs and camels and people. So how does adaption take place?
I don't know. It may have something to do with negative feedback.
That's impressive.
Like you have like, you always get like, you always get feedback, like in the body to release less insulin and stuff like that. So in time people like or whatever, organisms, learn to adapt to that. Because if it happens a lot that makes a feedback then it comes, yeah then they just learn to do that.
Okay. Give me an example of that. I'm trying to link it up in my head.
Okay, like the polar bear, like I don't know. It may have started off just like every other bear, but because it was put in that environment, like all the time the body was telling it to grow more fur and things like that, because it was so cold. So after a while it just adapted to, you know, always having fur instead of, you know, like dogs shed hair in the summer and stuff. But like if it was always then they'd just learn to keep shedding that hair.
So if it was an ordinary bear, not a polar bear, and you stuck it in the Arctic, it would get cold?
Yeah.
But you say the body tells it to grow more fur?
Erm, yeah.
How does that work?
I'm not sure, it just … I don't know. Like, erm, like the body senses that it's cold, it goes to the brain, and the brain thinks, well how is it going to go against that, you know, make the body warmer. And so it kind of, you know, it gives these things.
Is that an example of feedback?
Yes.

So Bert seemed to have notion of (it not the term) homoeostasis, that allowed control of such things as levels of insulin. He recognised thus was based on negative feedback – when some problematic condition was recognised (e.g. being too cold) this would trigger a response (e.g., more insulation)to bring about a countering change.

However, in Bert's model, the mechanism was not automatic. Rather it depended upon conscious deliberation: "the brain thinks, well how is it going to …make the body warmer". Bert thought that this process which initially was based on deliberation then became automatic over many generations.

This seems to assume that bears think in similar terms to humans, that they identify a problem and reason a way through. This might be considered an example of anthropomorphism, something that is very common in student (indeed human) thinking. To what extent it may be reasonable to assign this kind of conscious reasoning to bears is an open question.

However there was a flaws in the process described by Bert that he might have spotted himself. This model suggested that once the bear had become aware of the issue, and the needs to address, it would be able to grow its fur accordingly. That is, as a matter of will. Bert would have been aware that he is able to control some aspects of his body voluntarily (e.g., to raise his arm), but he cannot will his hair to grow at a different rate.

Of course, it may be countered that I am guilty of a kind of anthropomorphism-in-reverse: Bert is not a bear, but rather a human who does not need to control hair growth according to environment. So, just because Bert cannot consciously control his own hair growth, this need not imply the same is true for a bear. However, Bert also used the example of insulin levels, very relevant to humans, and he would presumably be aware that insulin release is controlled in his own body without his conscious intervention.

As often happens in interviewing students (or human conversations more generally) time to reflect on the exchange raises ideas one did not consider at the time, that one would like to be able to to text out by asking further questions. If things that were once deliberate become instinctive over time, then it is not unreasonable in principle to suggest things that are automatic now (adjusting insulin levels to control blood glucose levels) may have once been deliberate.

After all, people can control insulin levels to some extent by choosing to eat a different diet. And indeed people can learn biofeedback relaxation techniques that can have an effect on such variables as blood pressure, and some diabetics have used such techniques to reduce their need for medical insulin. So, did Bert think that people had once consciously controlled insulin levels, but over generations this has become automatic?

In some ways this does not seem a very likely or promising idea – but that is a judgement made from a reasonably high level of science knowledge. It is important to encourage students to use their imaginations and suggest ideas as that is an important aspect of how science woks. Most scientific conjectures are ultimately wrong, but they may still be useful tools for moving science on. In the same way, learners' flawed ideas, if explored carefully, may often be useful tools for learning. At the time of the interview, I felt Bert had not really thought his scheme through. That may well have been so, but there may have been more coherence and reflection behind his comments than I realised at the time.