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© Borgis - New Medicine 3/2010, s. 102-106
*László Medve1, Emil Préda1, Tibor Gondos2
The practice of renal replacement therapy in the intensive care unit
1Dr. Kenessey Albert Hospital, Department of Anesthesiology 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
Summary
Little information is available regarding current practice in renal replacement therapy (RRT) for the treatment of acute kidney injury (AKI) and the possible clinical effect of practice variation. Over the last three decades the treatment options for patients with AKI requiring renal replacement therapy (RRT) have expanded from basic acute peritoneal dialysis and intermittent hemodialysis (IHD), to now include a variety of continuous modalities (CRRT), ranging from hemofiltration to dialysis and/or hemodiafiltration, and a variety of hybrid therapies, variously described as extended daily dialysis and/or hemodiafiltration. There is also disagreement on clinical practice for RRT including the best timing to start, vascular access, anti-coagulation, membranes, equipment and finally, if continuous or intermittent techniques should be preferred. This study surveyed the availability and current practice of renal replacement therapy in adult general intensive care units.
Introduction. After having learned the theoretical basis of renal replacement therapy (RRT) and after having established the objective conditions and appropriate environment, acute RRT may be initiated in the ICU. However, during the practical application of the chosen treatment modality, problems still can emerge. To solve these problems it is necessary to assess and manage practical issues arising during RRT.
Treatment modalities
Hemodialysis (HD): primarily diffusion-based treatment modality, where the water and dissolved substances are transported through a semipermeable membrane to the dialysis solution.
Hemofiltration (HF): primarily based on convective transport, where water and dissolved substances are transported through a semipermeable membrane. Substitution fluid must be administered in order to maintain liquid balance.
Hemodiafiltration (HDF): a method that combines high ultrafiltration rate and diffusion through a high permeability membrane. In other words, the method combines the benefits of hemodialysis and hemofiltration. The blood and the dialysis solution flow in opposite directions in the hemodialysis filter, but at the same time ultrafiltration takes place for fluid removal purposes. Substitution fluid should be given to ensure water balance.
Modality of RRT
The management of acute kidney injury (AKI) with renal support includes peritoneal dialysis, intermittent dialysis and continuous renal replacement techniques (1-4) (tab. 1).
Table 1. The management of acute kidney injury (AKI) with renal support.
Peritoneal dialysisIntermittent treatmentsContinuous treatment
Every second dayVeno-venous hemofiltration
Every dayVeno-venous hemodialysis
Prolonged daily treatmentVeno-venous hemodiafiltration
New therapy guidelines 
Continuous low efficiency hemodialysis"High flux" dialysis
High volume hemofiltration
Acute peritoneal dialysis in developing countries remains an important form of treatment, but nowadays there are other modern procedures to be considered.
Intermittent hemodialysis treatments (IHD)
Daily Intermittent Hemodialysis:
– 4-6 hours per day of hemodialysis treatment
– blood flow from 300 to 350 ml/min
– target urea reduction ratio of at least 0.65
Extended Daily Dialysis
– 6-10 hours daily treatment
Alternate Daily Hemodialysis is performed every other day
– Typically 3-4 times a week with at least 4 hours treatment at a time.
Continuous Renal Replacement Therapy (CRRT)
Continuous Renal Replacement Therapy is carried out continuously (24 hours per day) using a veno-venous catheter in which the blood flow is significantly lower than during IHD. The most commonly used modalities of CRRT are continuous veno-venous hemofiltration (CVVH), continuous veno-venous hemodialysis (CVVHD) and continuous veno-venous hemodiafiltration (CVVHDF). CRRT has a slower solute clearance compared to IHD, but the 24-hour full-clearance balance is higher than that of IHD, particularly for high molecular weight substances, e.g. cytokines. During CRRT the fluid elimination is much slower, and the treatment usually requires continuous anticoagulation with the potential risk of bleeding. The extracorporeal system also removes other substances with the possible risk of electrolyte and nutrient imbalance and antibiotic concentration below therapeutic levels (5).
Continuous veno-venous hemofiltration (CVVH)
– ultrafiltrate is produced, which must be replaced with a substitution solution,
– the removal of excess ultrafiltrate may result in volume loss of the patient,
– the solute removal takes place through convective transport.
Continuous veno-venous hemodialysis (CVVHD)
– the dialysis solution flows opposite to the blood in the dialysis filter,
– the speed of blood flow is 100-200 ml/min,
– speed of the dialysis solution is 1-2 l/h,
– fluid administration is not routine,
– solute removal takes place through diffusion.
Continuous veno-venous hemodiafiltration (CVVHDF)
– the dialysis solution flows opposite to the blood in the dialysis filter,
– speed of blood flow is 100-200 ml/min,
– speed of the dialysis solution is 1-2 l/h,
– the ultrafiltration rate should be optimized in accordance with the volume loss and the convective transport of dissolved substances,
– the fluid can be replaced with substitution solution,
– solute removal takes place simultaneously by convection and diffusion.
New therapeutic procedures (6-9)
Long-term, low-efficiency dialysis (Slow Low Efficiency Dialysis)
– blood flow 150 to 200 ml/min,
– dialysis flow 100 to 200 ml/min,
– treatment duration: 10-24 hours.
Continuous High Flux Dialysis (CAVHFD/CVVHFD)
– using high-permeability membrane in which the blood flows opposite to the dialysis solution,
– the production of ultrafiltered substance is controlled by a blood pump,
– it is important to balance between filtration and back-filtration: the ultrafiltrate is produced in the proximal part of the filter, while, because the back-filtration occurs in the distal part, there is no need for substitution fluid.
Continuous High Volume Hemofiltration (HVCVVH)
– a form of CVVH in which the hemofilter surface is large; therefore it is suitable to achieve> 35 ml/kg/h ultrafiltration rate.
The acute renal replacement protocol
Vascular access selection
Intermittent techniques require high blood flow (250-400 ml/min); the continuous techniques need lower blood flow (150-200 ml/min).
In renal replacement, the venous catheterization possibilities include the subclavian vein, the internal jugular vein and the femoral vein (10-14). The optimal input depends on the risk of thrombosis, the risk of infection, the insertion and the suitability of simpler sets. The catheter insertion depends on the patient (status of blood vessels, coagulation status), and the physician's experience. In general, the femoral vein is the fastest way to insert a central cannula, and may be best for bedridden, ventilated patients, or for patients with central nervous system trauma. The catheter length should be at least 25-30 cm and it usually should not be left in place for more than 2 weeks. The main risk of puncturing the subclavian vein is the possibility of venous stenosis/thrombosis of the efferent blood vessels. That is why the use of the subclavian vein is recommended just as a second option.
Recently, jugular vein puncture became favored. The main risk is infection, especially because of tracheostoma, and the proximity of the ear.
Many clinicians avoid the use of the subclavian vein, because of the risk of late stenosis, which can reach 50%. In contrast, late stenosis does not occur after internal jugular vein puncture: Altogether, the complication after using the internal jugular vein is around 10%, while after using the subclavian vein the complication rate is 19.6% (11).
However, when using the jugular vein we must take into consideration a higher risk of bleeding and thrombosis, compared to the use of the femoral vein.
When deciding the insertion site, most clinicians do not take the risk of infection into consideration, although after using the femoral catheter, infection is often observed. Special attention must always be paid to maximally comply with rules of hygiene.
In double lumen hemodialysis catheters the output and input blood gates are relatively close to each other and a certain amount of filtered blood is recirculated into the extracorporeal system. In order to reduce the recirculation, the most important issue is the proper positioning of the catheter. It is generally expected that, if a femoral catheter is used, then the tip of it should be in the inferior cava vein. For the other two inputs (internal jugular and subclavian vein) the best catheter position for the tip of the catheter is in the right atrium or the cava/atrium opening.
With the help of ultrasound we can enhance the security of the procedure and reduce the frequency of complications.
Choosing the treatment modality

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Piśmiennictwo
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otrzymano: 2010-07-15
zaakceptowano do druku: 2010-08-04

Adres do korespondencji:
*László Medve
3100. Salgótarján Kemping út 2
phone: +36 20 4006168
e-mail: dr. medve. laszlo@chello.hu

New Medicine 3/2010
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