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Dialysis
Indications for dialysis
The indications for dialysis in uraemic patients are well known – fluid overload, severe acidosis, hyperkalaemia, uraemic encephalopathy and severe hyper or hyponatraemia. Many patients with only modest elevations of potassium can have this corrected with ion exchange resins orally or rectally if vomiting. In an emergency, it is probably acceptable to treat intractable fluid overload with ventilation and PEEP while organising dialysis, and if the patient settles on this therapy and there are no other pressing indications it is probably preferable to postpone dialysis until the morning, when more experienced staff may be available.
Acidosis on its own may respond to sodium bicarbonate 50-100 ml of the 8.5% solution, i.e. 1 mmol/ml, infused over 6 hours in 1000 ml of 5% DW. An oral version (Shohl’s solution) is also available – give 20 ml 3x/d. Beware of sodium overloading with both options. (Shohl’s solution contains 140g citric acid and 98g sodium citrate in 1 litre of water, with 1 ml containing 1 mmol of base.)
Haemodialysis
In a setting where the equipment and machine is available, this offers slightly better clearance, and there are even some indications that mortality using this technique may be lower than with peritoneal dialysis
Contraindications to haemodialysis
Hypotension or poor haemodynamic control (e.g. severe LVF due to a myopathic ventricle) an uncorrected severe bleeding tendency, and a restless and uncontrollable patient are all relative contraindications.
Technique
The technique for line insertion is essentially that of Seldinger central line insertion, except using a double lumen catheter. Ideally, lines should be inserted in the right internal jugular, or perhaps the right subclavian. The femoral veins are alternatives. Left sided insertion carries a higher rate of catheter erosion of a central vein, but can be used if no other site is available.
Once the line is in, check its position on CXR, and then plan the first dialysis session: it should be short (2 hours is reasonable) and unless fluid overload is the key reason for dialysis, ultrafiltration to remove fluid should be kept to a relative minimum – e.g. about 250 ml for the session.
Complications
- Hypotension – slow or stop dialysis temporarily. Raise the patient’s legs and drop the head of the bed. If this does not restore adequate BP, then infuse 200 ml of saline.
- Cramps. Particularly a problem with individuals who pick up a lot of fluid between intermittent dialysis sessions. Treatment is largely anecdotal, and mechanisms are poorly understood. Some authorities are enthusiastic about a bolus of 50% dextrose.
- Difficulties with the venous access lines.
- Nausea and vomiting.
- Bleeding from line site.
- Catheter sepsis.
Stopping dialysis.
There are three main indications for stopping acute dialysis:
- The patient is getting better and no longer needs it. In the setting of responding acute renal failure, passage of adequately concentrated urine in adequate volumes usually precedes normalisation of creatinine. In patients on dialysis, the machine is dropping the creatinine, and patients often end up running a bit dry so they may not appear to be producing much urine. The trick is to lengthen the interval between dialysis sessions, and observe the serum creatinine during this time. It the creatinine is still shooting up between sessions it is still too early to stop. If it hardly budges over two days, it’s worth trying without dialysis for a few more days, and if there is then clear evidence that adequate urine is being passed as well as no creatinine rise, it is then appropriate to remove the catheter.
- Failed postulate of reversible acute on chronic renal failure, and not a candidate for long term renal replacement therapy (most such patients warrant biopsy to confirm non-reversibility).
- Clear evidence of other organ system disease which has now rendered ongoing dialysis futile.
Emergency management of fluid overload without dialysis
This is not usually successful, but there are a few options (in no particular order):
- Start with meticulous fluid restriction – its extraordinary how often patients with apparently intractable fluid overload have empty bottles of water or juice at the bedside, or even a drip still running merrily. In the setting of relative anuria, even a tiny saline load can be very difficult to handle
- If the patient is still passing urine, even if in reduced quantities, it may be possible to induce a diuresis with a high dose of intravenous furosemide – e.g. 500mg infused over 20 minutes. If the patient has actually been taking furosemide already in CRF type doses, this is not often successful.
- The production of diarrhoea with oral mannitol or equivalent has been used in some resource-constrained environments. Its success is poorly validated.
- If you have a ventilator but no facilities for dialysis (unlikely – PD is usually possible), or if the patient needs ventilation for another reason, it is sometimes possible to tide a patient over for a few hours by ventilating with relatively high PEEP. Obviously this doesn’t result in any fluid loss, and so should only be seen as a very short-term strategy.