Initial management should comprise:
- Optimisation of circulation where there is any question of its adequacy
- Diagnosis of cause
- Removal of potential nephrotoxins (especially drugs)
Note that there is no evidence that dopamine is of benefit other than through its action as an inotrope - but inotropes may be valuable in heart disease or shock. There are some reasons to suspect that dopamine may be potentially harmful as it impairs splanchnic perfusion. Loop diuretics may increase urine output in those with less severe degrees of renal failure, but there is no evidence that they improve outcome (requirement for dialysis, or mortality) and some evidence that they can be harmful. Most interventions tested in prevention of ARF after radiographic contrast administration are ineffective or harmful (eg loop diuretics), apart from fluid administration alone: and N-acetylcysteine may at least do no harm (See Radiology).
Renal replacement therapy
Indications for dialysis are
- Pulmonary oedema, or severe volume overload with oliguria
- Worsening figures with no prospect of early reversal
Neither age nor comorbid conditions (that might lead you to question longterm RRT) should be considered as automatically disqualifying dialysis for ARF if there is a substantial chance of recovery. BUT:
- avoid dialysis if aggressive treatment is otherwise inappropriate
- remember that exposure to dialysis membranes may prolong ARF
- there is no evidence that early dialysis improves outcome
Peritoneal dialysis is now rarely used for ARF in the UK, though it can be effective if the patient is not too catabolic and ultrafiltration requirements not too extreme.
Continuous or very slow treatments (haemofiltration or haemodialysis)
- are better tolerated in haemodynamically unstable
- permit large and variable volumes of fluid removal
- are preferred in patients with encephalopathies
- involve continuous anticoagulation
- prolong exposure of patient to artificial membranes
- do not achieve better outcomes
- can also under-provide small molecule clearance (continuous treatments rarely are continuous)
Patients with ARF need at least as much dialysis, and frequently more (because of catabolism) than patients with ESRF. Therefore Kt/V or URR should be at least as good. Dialysis usually need to be more frequent and daily treatments should be regarded as the norm in the early phase, or if fluid fluxes are substantial (e.g., from feeding).
Preventing disequilibration Disequilibration is a state of clouding of consciousness, confusion and sometimes fits following dialysis. Disequilibration is most likely:
- in patients at ESRF after prolonged CRF
- when urea, creatinine etc are very high
- in patients with cerebral disease and in the elderly
If the risk is significant it is sensible to give a low-clearance (e.g., Kt/V 0.5, or 30% URR) and low intensity (low blood flow and/or small dialyser) treatment initally, intermediate the next day, a full treatment (e.g., Kt/V 1.2, URR 70%) the third day, if figures permit.
A ‘gentle start’ is inappropriate if fast removal of small molecules is required - e.g., in severe hyperkalaemia or for removal of low molecular weight poisons such as salicylate. CVVH is also inappropriate in these cricumstances (unless the toxin is of molecular size better removed by haemofiltration).
First dialysis treatments can and should be less cautious in catabolic patients in whom figures are rising fast.
Haemofiltration, whether contiuous or intermittent, is less efficient at removal of small molecules including toxins. Prolonged haemolfiltration commonly leads to phospate depletion, replacement may be required, and it clears some drugs (e.g., vancomycin) faster than haemodialysis.
Amount of dialysis
Detailed calculations of dialysis dose is beyond the scope of this summary, but see the brief description under 'Haemodialysis'. Note that for haemofiltration, Kt is equal to (or for urea, >90% of) the total volume of fluid exchanged.
ComparisonsFor very crude comparison of small molecule clearance by continuous versus intermittent treatments, the following figures are provided. HD figures are for urea clearance by F8 dialyser, ignoring UF.
|Normal GFR||150 l/day|
|Daily intermittent HF||15-25 l/day|
|Continuous HF at 1 l/hr||24 l/day|
|Continuous HF at 2l/hr||48 l/day|
|Daily HD x 4hr at QB = 200ml/min||46 l/day|
Is important, and is described further in the DIET section.
Patients with acute renal failure should receive H2-blockers or PPls. Prophylaxis against DVT should usually be ued in bed-bound patients.
Acknowledgements: Neil Turner and John Neary were the main authors for this page. The last modified date is shown in the footer.
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