Current concepts of ARF on the ICU
Dr John Griffiths DICM MRCP FRCA MA
Focus on Acute Kidney Injury
The lack of general consensus as to the 'true' definition of Acute Kidney Injury (AKI) has been a major factor in hampering both clinical research into ARF on the ICU but also meaningful comparison between relevant trials.
A significant breakthrough was the development of the 'RIFLE' classification for AKI by the Acute Dialysis Quality Initiative Group (Table 1):
Table 1. Risk, Injury, Failure, Loss, and End-stage Kidney (RIFLE) classification
Urine output criteria
Serum creatinine × 1.5
< 0.5 ml/kg/hour × 6 hours
Serum creatinine × 2
< 0.5 ml/kg/hour × 12 hours
Serum creatinine × 3, or serum creatinine ≥ 4 mg/dl with an acute rise > 0.5 mg/dl
< 0.3 ml/kg/hour × 24 hours, or anuria × 12 hours
Persistent acute renal failure = complete loss of kidney function > 4 weeks
End-stage kidney disease
End-stage kidney disease > 3 months
For conversion of creatinine expressed in conventional units to SI units, multiply by 88.4. RIFLE class is determined based on the worst of either glomerular filtration criteria or urine output criteria. Glomerular filtration criteria are calculated as an increase of serum creatinine above the baseline serum creatinine level. Acute kidney injury should be both abrupt (within 1–7 days) and sustained (more than 24 hours). When the baseline serum creatinine is not known and patients are without a history of chronic kidney insufficiency, it is recommend to calculate a baseline serum creatinine using the Modification of Diet in Renal Disease equation for assessment of kidney function, assuming a glomerular filtration rate of 75 ml/min/1.73 m2. When the baseline serum creatinine is elevated, an abrupt rise of at least 0.5 mg/dl to more than 4 mg/dl is all that is required to achieve class Failure.
The RIFLE classification has now been prospectively assessed in clinical practice and a recent modification has been suggested by Acute Kidney Injury Network.
Hoste EA, Kellum JA.
Incidence, classification, and outcomes of acute kidney injury.
Contrib Nephrol 2007;156:32-8.
Focus on biomarkers for Acute Kidney Injury
The development of the RIFLE criteria to define AKI has led to the study of potential biomarkers to detect acute renal injury. A large number of biomarkers are currently being studied and include neutrophil gelatinase associated lipocalin. Currently, these biomarkers are more specific in paediatric practice due to the fact that many adults develop AKI on the background of pre-existing renal damage. However, the potential of defining AKI in adults by biomarkers is an exciting field as serum creatinine remains a poor marker of AKI in this population.
Askenazi DJ, Bunchman TE.
Pediatric acute kidney injury: The use of the RIFLE criteria.
Kidney Int 2007 71 (10):963-4.
Mori K, Nakao K.
Neutrophil gelatinase-associated lipocalin as the real-time indicator of active kidney damage.
Kidney Int 2007 71 (10):967-70.
Focus on Renal Replacement Therapy (RRT)
There are three main questions pertaining to RRT for ARF on the ICU:
- When should RRT be commenced?
- What modality of RRT should be used?
- What dose of RRT should be delivered?
Probably earlier rather than later:
These questions are best addressed by reflecting on recent literature:
1. When should RRT be commenced?
Probably CVVH rather than IHD but there appears to be little difference:
Demirkilic U, Kuralay E et al.
Timing of replacement therapy for acute renal failure after cardiac surgery.
J Card Surg 2004 19(1):17-20.
Mehta et al.
Spectrum of acute renal failure in the intensive care unit: the PICARD experience.
Kidney Int 2004 66 (4):1613-21.
Gettings et al.
Outcome in post-traumatic acute renal failure when continuous renal replacement therapy is applied early vs. late.
Intensive Care Med 1999 Aug;25(8):805-13.
2. What modality of RRT should be used?
Vinsonneau C, Camus C et al.
Continuous venovenous haemodiafiltration versus intermittent haemodialysis for acute renal failure in patients with MODS: a multicentre randomised trial.
Lancet 2006; 368: 379-85.
Uehlinger DE, Jakob SM, Ferrari P et al.
Comparison of continuous and intermittent renal replacement therapy for acute renal failure.
Nephrol Dial Transplant 2005 20(8):1630-7.
Kellum JA, Angus DC, Johnson JP, Leblanc M, Griffin M et al.
Continuous versus intermittent renal replacement therapy: a meta- analysis.
Intensive Care Medicine 2002; 28: 29-37.
3. What dose of RRT should be delivered?
Probably at least 35ml/kg/hr:
Ronco C, et al.
Effects of different doses in continuous veno-venous haemofiltration on outcomes of acute renal failure: a prospective randomised trial.
Lancet 2000 356 (9223) 26-30
Schiffl H, Lang SM, Fischer R.
Daily hemodialysis and the outcome of acute renal failure.
N Engl J Med 2002 31;346(5):305-10.