Continuous renal replacement therapy in acute renal failure: membranes for CRRT

Intermittent versus continuous renal replacement therapy: a matter of controversy

BACKGROUND

Acute Renal Failure (ARF) requiring some form of replacement therapy is a frequent complication in the critically ill patient. Despite potential therapeutic advantages the expectation of an improvement in patient outcomes using Continuous Renal Replacement Therapy (CRRT) compared to conventional Intermittent Haemodialysis (IHD) remains controversial.

AIMS AND METHOD

This article will review the literature on the issues surrounding the use of IHD versus CRRT in the management of the critically ill patient. Articles were selected according to level of evidence with priority given to meta-analyses and randomised controlled trials.

DISCUSSION

Several operational features of CRRT allow this technique to be tolerated more easily in critical illness than IHD. The gradual removal of fluid reduces the incidence of hypotension and the risk of volume overload. Decreased variability in the concentration of solutes enables greater azotemia control. However, CRRT is required to operate uninterrupted to achieve a treatment dose that is equivalent to a conventional IHD treatment schedule. In the absence of definitive evidence to validate superior patient survival and return of renal function there is disagreement as to the most appropriate form of Renal Replacement Therapy (RRT) for the critically ill patient. The introduction of 'hybrid' therapies offers a further alternative treatment strategy, which combine favourable aspects of IHD and CRRT.

CONCLUSION

The decision to use IHD or CRRT should be guided by the therapeutic needs of the patient rather than the operational differences between the two techniques. The resources and expertise available at the organisation are also important in determining the mode best able to manage the critically ill patient at any stage and may change according to the severity of illness. The emergence of hybrid therapies provides a compromise option which encompasses many of the features of both systems, but does not embrace all options of either approach.

Maintaining the CRRT circuit: non-anticoagulant alternatives

Prevention of clotting is an important factor in continuous renal replacement therapy (CRRT) to ensure that solute clearance, electrolytes and acid base and fluid balance are controlled. This article will focus attention on the components and design of the CRRT circuit, identifying strategies in the literature which may promote circuit life. It is important that the CRRT circuit incorporates biocompatible materials and is designed in a way which limits turbulent blood flow. Premature clotting is also more likely to occur when blood flow through the circuit is interrupted or sluggish as a result of poor vascular access, or when there is increased resistance or obstruction in the circuit. The pre-dilution method of fluid replacement reduces blood viscosity inside the haemofilter and assists in delaying the onset of blood clots by limiting the potential for haemoconcentration. The monitoring and adjustment of the blood level inside the venous bubble or air trap can lessen the effect of blood-air contact and protect the site from excessive clotting. A number of other factors are also considered important as predictors of circuit life in the operation and management of the circuit. They include the choice of access site and design configuration of the catheter device, and the level of competency of nursing staff preparing and monitoring circuit function. Whilst the value of intermittent saline flushing has not been proven to be of benefit in promoting circuit life, it remains to be determined whether the choice in the CRRT mode affects circuit life differently. In conclusion, specific measures in the application of CRRT besides anticoagulation therapy can influence the development of blood clots and the duration of circuit life. This requires the development of evidence-based practice guidelines which include strategies that are known to promote circuit life.

The diagnosis of acute renal failure in intensive care: mongrel or pedigree?

Acute renal failure is common in the intensive care unit; it is well recognised that patients who develop acute renal failure have a high mortality rate. While there have been improvements in the management of acute renal failure, the mortality remains high. Acute renal failure is easily diagnosed biochemically and clinically but it is not a single disease entity. It is a syndrome that affects a very heterogeneous population. Studies of acute renal failure and of the impact of renal replacement therapy in intensive care are usually inconclusive, which may be the natural consequence of studying a syndrome. This article focuses on the more uncertain features of acute renal failure, the problems of investigating acute renal failure as a disease and the difficulties of applying the results of a study of a heterogeneous population to the management of individuals.