© Borgis - New Medicine 2/2010, s. 66-70
*László Medve1, Emil Préda1, Tibor Gondos2
Acute renal replacement therapy in the intensive care unit: theoretical foundations and terms
1Dr. Kenessey Albert Hospital, Department of Anaesthesiology and Intensive Care Medicine, Balassagyarmat
Head: Dr. Szabó Géza, General Director
2Semmelweis University, Faculty of Health Science, Department of Oxyology and Emergency Care, Budapest
Head: Prof. Dr. Mészáros Judit, Dean of Faculty
The incidence of acute renal failure (ARF) in intensive care units (ICUs) has been continuously on the rise over the years. In the current education system nurses do not receive adequate training to carry out RRT in the ICUs; therefore, in the following, we will provide an overview of the theoretical basics of ARF and will summarize the problems of current treatment modalities. The AKIN Working Group created the concept of acute kidney injury (AKI), replacing the nomenclature of ARF, and set the stages. Recent prospective studies have demonstrated that an early start of RRT is beneficial and increases the patient survival rate. Many factors can affect the completion of treatment and the modality of treatment. RRT needs a well equipped intensive care unit with a well trained staff. During the training process, it is worth for at least one or two specialists to spend a few weeks at a chronic dialysis station, and in an intensive care unit, where haemodialysis is routinely administered. After becoming familiar with the theoretical basis of RRT and after fulfilling the requirements for optimal treatment conditions, our department may begin the introduction and selection of optimal treatment modalities for renal replacement procedures. During the practical application of the chosen treatment method, we may still encounter problems.
The incidence of acute renal failure (ARF) in intensive care units (ICUs) has been continuously on the rise over the years (1, 2, 3, 4). This appears to be primarily related to the increasing number of patients with severe sepsis and multiple organ failure. There are no widely accepted guidelines when to begin the renal replacement therapy (RRT) in these cases; however, there is a consensus to start RRT immediately after early signs of ARF are recognized. There is a reasonable request for the ICUs to carry out RRT, because the technical background, with the new, mobile, easy to use equipment is readily available. In the current education system nurses do not receive adequate training to carry out RRT in the ICUs; therefore, in the following, we will provide an overview on the theoretical basics of ARF and will summarize the problems of current treatment modalities.
The most recent literature data suggest that 1-25% of patients admitted to ICUs have ARF and 72.4% of these patients need renal support therapy (5). Unfortunately, despite the rapidly improving intensive care, the mortality of patients admitted with ARF is still high (15-60%).
In recent years, expert groups have developed a uniform definition of ARF, and grading systems to evaluate its severity (RIFLE and AKIN criteria). These are adopted and used by many intensive care societies worldwide. Both RIFLE and AKIN criteria define ARF as renal impairment when there is a sudden kidney failure (within 48 hours) when the absolute increase of the serum creatinine level exceeds or is equal to 0.3 mg/dl (26.4 mmol/l), which is expressed as an increase of 50% of the baseline value; and the decrease of urine output by 0.5 ml/kg body weight/hour below the baseline value over a period of 6 hours. The criteria above include the level of serum creatinine, absolute and percentage changes, thus eliminating the age, gender, body mass index-related individual differences and the need for basic knowledge of creatinine value. However, this system assumes that at least two serum creatinine measurements are made within 48 hours (7).
Criteria for the classification of the degree of severity of ARF
The Acute Dialysis Quality Initiative (ADQI) at the 2002 Consensus Conference of Vicenza issued the RIFLE criteria to define ARF (5, 6). Evaluating diagnostic and prognostic usefulness of criteria is ongoing; it appears that the nomenclature and definitions are, in general, good, but they need refining. Efforts of refining the criteria resulted in an AKI-network consensus, which modified the RIFLE criteria. Therefore, from 2007 we are no longer talking about ARF, but acute renal impairment. Currently, several multicentre studies have demonstrated that the RIFLE (R = risk, I = injury, F = failure, L = loss, E = end-stage renal disease) classification is valid for assessment of the severity of ARF (tab. 1). The AKIN Working Group created the concept of acute kidney injury (AKI), replacing the nomenclature of ARF, and set the stages (tab. 2). From the point of view of routine practice, the RIFLE and AKIN criteria are almost the same; there are only three subtle differences.
Table 1. Risk, Injury, Failure, Loss, and End-stage Kidney (RIFLE) classification.
|Class||Glomerular filtration rate criteria||Urine output criteria|
|Risk||Serum creatinine × 1.5||< 0.5 ml/kg/hour × 6 hours|
|Injury||Serum creatinine × 2||< 0.5 ml/kg/hour × 12 hours|
|Failure||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|
|Loss||Persistent acute renal failure = complete loss of kidney function > 4 weeks|
|End-stage kidney disease||End-stage kidney disease > 3 months|
Table 2. Classification/staging system for acute kidney injurya.
|Stage||Serum creatinine criteria||Urine output criteria|
|1a||Increase in serum creatinine of more than or equal to 0.3 mg/dl (≥ 26.4 ?mol/l) or increase to more than or equal to 150% to 200% (1.5- to 2-fold) from baseline||Less than 0.5 ml/kg per hour for more than 6 hours|
|2b||Increase in serum creatinine to more than 200% to 300% (> 2- to 3-fold) from baseline||Less than 0.5 ml/kg per hour for more than 12 hours|
|3c||Increase in serum creatinine to more than 300% (> 3-fold) from baseline (or serum creatinine of more than or equal to 4.0 mg/dl (≥ 354 ?mol/l) with an acute increase of at least 0.5 mg/dl (44 ?mol/l))||Less than 0.3 ml/kg per hour for 24 hours or anuria for 12 hours|
|aModified from RIFLE (Risk, Injury, Failure, Loss, and End-stage kidney disease) criteria. The staging system proposed is a highly sensitive interim staging system and is based on recent data indicating that a small change in serum creatinine influences outcome. Only one criterion (creatinine or urine output) has to be fulfilled to qualify for a stage.|
b200% to 300% increase = 2- to 3-fold increase.
cGiven wide variation in indications and timing of initiation of renal replacement therapy (RRT), individuals who receive RRT are considered to have met the criteria for stage 3 irrespective of the stage they are in at the time of RRT.
1. According to the AKIN, a slight increase in serum creatinine values is enough to define ARF.
2. AKIN introduced the time factor because the ARF diagnosis needs an elevated serum creatinine for at least 48 hours.
3. They eliminated the „loss and ESRD” category, because it represents the outcome of kidney disease and not the diagnosis.
Renal replacement indications for treatment of ARF
ARF may require RRT if the patient's glomerular filtration rate (GFR) decreases acutely and the level of toxic material increases significantly and/or there is a fluid overload. In practice, however, conventional indications for the treatment of ARF, the aetiology of which may be renal or non-renal, are accepted (tab. 3). When considering the indications, the rule of thumb is that the existence of one condition provides grounds for consideration of RRT, the presence of two conditions is a clear indication, and the presence of more indications means that RRT has to be initiated even before reaching pathological creatinine levels. The non-renal indication of continuous RRT is not yet sufficiently well established.
Table 3. Renal and non-renal indications of renal replacement therapy.
|RENALIS INDICATION||NON RENAL INDICATION|
|Non obstructív oliguria (urine < 200 mL/12 h) or anuria||Dialysing agent poisoning|
|Progressive azotemia, even without clinical signs (blood urea > 30 mmol/l or blood urea nitrogen > 100 mg ||Hiperthermia (core temperature > 39,5°C)|
|Metabolic acidosis, drug therapy refractory||The need of large quantities of blood in coagulation, in which there is pulmonary edema/ARDS risk|
|The existence of uremic organ symptoms: encephalopathy, myopathy, pericarditis, uremic bleeding diathesises|
|Hyperkalemia, drug therapy, refractory (plasma K +> 6.5 mmol/l or rapidly rising)|
|Progressive severe hyper/hyponatremia (Na +> 160 or <115 mmol/l)|
|Clinically significant organ edema, especially pulmonary edema|
|Intravascular fluid administration which is drug therapy refractory|
The timing of initiation of treatment
In the literature, there is a distinction between early and late start of RRT, taking serum urea, creatinine levels and urine output into consideration (8, 9). Recent prospective studies have demonstrated that an early start of RRT is beneficial and increases the patient survival rate. When considering the potential advantages of early initiation we should always consider the theoretical risk of hypotension, the threat of bleeding as a result of anti-coagulation as well as the mechanical and infectious complications of the central venous input.
The treatment dosage
Previous studies suggested that the increase in the volume of ultrafiltration improved patients' survival, but there were no differences in the improvement of renal function between the groups (18). A recently published multicentre study did not find evidence for this. High-dose haemofiltration did not reduce mortality. It failed to improve the return to good renal function and to reduce the number of multiple organ failures, compared to conventional-dose treatment (10). Another large multicentre study (RENAL study) confirmed these findings (11). Currently, ≥ 20 ml/kg/h is the recommended minimum dose in the case of continuous techniques and 1.2 Kt/V for the daily intermittent dialysis in the intensive care unit.
Timing of treatment completion
Many factors can affect the completion of treatment and the modality of treatment. This includes patient factors (e.g., haemodynamic stability, volume status, urine volume), and other factors (availability of personnel, cost, coagulation of extracorporeal circuit).
The concept of renal replacement therapy
RRT has two basic physical-chemical concepts that we need to be aware of: water and solute removal (12).
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