[B]Dear Jane
You are looking for numbers again! I have emphasized before that humans are individuals – not machines – and unlike machines where numbers and needs tend to be constant, this is not now or ever so in humans. What is ideal for one will not always be ideal for another. There is no one number, no one BP measurement (upper or lower limit), no one volume, no set intake that suits or is appropriate to all. In any one individual, too, values set as targets may alter, time to time and circumstance to circumstance. If we were all set to some magic ‘normal’, life would be very easy. Unfortunately, we are not.
‘Art’ plays a huge role in medicine. Science matters - enormously - but so, too, does the application of that science - to the individual - and this is the ‘art’ half (and it should be half) of the equation. The ‘art’ is knowing when the science is not always right or applicable - in and for that specific circumstance.
That said … and re-emphasised … I will try to give some answers … but in so doing, will know that in some circumstances, the numbers I now try to give you in answer to your questions will be wrong – for that individual and at that time![/B]
1) What is considered normal bp? I know at one time it was 120/80, but subsequently wasn’t a new standard set? What is considered low bp and what is considered extremely low bp?
[B]Current recommendations for a target BP as recommended by most International Heart Associations and International Kidney Disease Guideline documents are listed below (copied to here from a standard BP reference document).
A) For people with typical diastolic hypertension who are not at high risk, the traditional goal of reducing the blood pressure to less than 140/90 appears adequate.
B) For elderly people with isolated systolic hypertension, caution should be taken to avoid reducing the diastolic pressure to less than 65 - 70. Less than optimal lowering of the systolic pressure should be accepted in order to avoid reducing the diastolic pressure too far.
C) For certain “high-risk” patients with diastolic hypertension, more aggressive therapy to reduce the diastolic pressure to 80 or less should be considered. These include:
• Those with diabetes. Reducing the blood pressure to 130/80 or less reduces the risk of cardiac disease.
• Those with renal insufficiency (kidney disease.) Reducing the blood pressure to 125/75 or less appears to slow the progression of kidney disease.
• Black patients. For reasons not well understood, African American patients continue to have high risk for hypertensive complications unless their diastolic blood pressure is reduced to below 85.
Targets for dialysis patients are no different. It should be noted that these are targets and that, in individuals, these may need to be varied depending upon their individual circumstance and their clinical situation.[/B]
2) If a patient has low bp and goes up on his dry weight, how long should it take for the bp to stabilize- immediately, or should it take days or longer?
BP should usually respond quite promptly, within a single inter-treatment time span.
3) I know nocturnal patients have different capacities for fluid intake, but what is the minimum amount of fluid one with zero output should be able to drink in a day so as to not become dehydrated? If one on nocturnal has a toned down thirst mechanism and has trouble taking in enough fluid at a time (feels too full), or in a day, what are the possible causes and remedies?
[B]Non-renal, non-dialytic fluid losses will vary according to circumstance. For example: hotter climates, sweating, fever, illness associated with vomiting or diarrhoea and respiratory illness etc will increase unmeasured (or ‘insensible’) losses. In addition, fluid requirements will differ in from male to female, body size to body size, weight to weight, exercise to non-exercise, winter to summer … and may be impacted by clinical factors like (but not restricted to) diabetes and sugar control, medication and other contributors. It would be misleading to be drawn into a set ‘statement’ on exact volumes to drink or not to drink … and I cannot (will not) not make one as I will mislead as much as inform.
That said, in normal 16-23 degree mean daytime temperature zones (a temperate climate) without major wind-added convective losses and in a normal afebrile adult, insensible losses are likely around 500ml/day. In addition, the body requires fluid … 250-500 ml/day … so that most will need 750-1000 ml/day to remain in balance. But this is such a variable number that, again, the appropriate amount of fluid to take in, daily, must be discussed with the individual patient, as it suits and is appropriate for that individual.[/B]
4) If bp is too low and a nocturnal patient goes up on his dry weight, but starts to become edemic and less well feeling, what does this signify?
Remember that a low BP is not always just volume and fluid-related. The heart drives our BP. The kidneys may control it but the heart makes it. Is there heart disease, a poor cardiac output, problems with leaky or narrowed heart valves – especially with the aortic valve … or a myriad other contributors beyond volume. Yes, volume is important in dialysis patients and the commonest and most obvious place to look for problems – but volume and dry weight is not the only cue in the rack! Moreover, is there coexisting diabetic autonomic neuropathy which is causing the BP to fall when the patient stands up. Here is an example of where a lying BP may need to be a little higher than ideal to prevent too low an erect BP. Again, as I have said before, we are individuals – and rules made to fit the herd may not apply.
5) What does it mean if a nocturnal patient has low bp, but is asymptomatic?
It may mean a poor heart (in one of many ways – output, valvular disease etc. (as above). It may mean the dry weight needs to be adjusted. It may be medication related – yet that medication may still be indicated and important … despite the number. Or … It may mean nothing of great significance.
6) Are there tests that can be taken to ascertain why a nocturnal patient has low bp if there doesn’t seem to be a way to resolve the problem?
Yes … from what I have said, an echocardiogram and other cardiac tests might be indicated. An assessment of the function of adrenal gland function may be useful as Addisons’ disease (an under-active adrenal gland with low mineralocorticoid hormone production) is almost certainly under-diagnosed and under-recognized in renal failure where ALL tends to be ascribed to volume – and little else.
7) When one loses output does anything change internally?
[B]Here, I am assuming you mean urinary output. Jane, I have done this for you before, I think – or someone else just recently. I have discussed the loss of residual renal function and the effects this loss can have on fluid intake freedom, the tendency to circulatory overload and the risks that entails for the heart and circulation.
As time passes, residual renal substance scars and shrinks such that all that is left are two small nubbins of non-functioning, largely fibrous renal tissue. Sludging and stasis (sluggish and lessening urine flow) leads to accretions – secretions and deposits of … ‘goo’ … will do – in what remains of the renal tubular structures. This causes tubular blockages and, then, cyst formation behind these as the urine flow and pressure is now inadequate to ‘flush out’ the ‘goo’ causing these blockages. Cysts form and largely further replace any remaining renal tissue. And, so, the kidneys reach the end of their road as rather ‘grotty’-looking blobs of unrecognizable tissue with now no remaining useful function.
I surmise that is what you meant by the question.[/B]