Continuous arteriovenous hemodiafiltration: predicting the clearance of drugs

Influence of renal replacement therapy on pharmacokinetics in critically ill patients

Critical illness has a great impact on many pharmacokinetic parameters. An increased volume of distribution often results in drug underdosing, whereas organ impairment may lead to drug accumulation and overdosing. Renal replacement therapy (RRT) in critically ill patients with renal failure may significantly increase drug clearance, requiring drug-dosing adjustments. Drugs significantly eliminated by the kidney are likely to experience substantial removal during RRT, and a supplemental dose--corresponding to the amount of drug removed by RRT--should be administered. Mechanisms of drug removal during RRT are reviewed together with methods for measuring or estimating RRT drug clearances. Approaches for drug-dosing adjustments are suggested and, at the end, the pharmacological principles for antibiotic prescription in the critically ill are discussed.

Pharmacokinetics and drug dosing adjustments during continuous venovenous hemofiltration or hemodiafiltration in critically ill patients

Continuous renal replacement therapy (CRRT) in critically ill patients with renal failure may significantly increase drug clearance, requiring drug dosing adjustments. Drugs significantly eliminated by the kidney often undergo substantial removal during CRRT, and a supplemental dose corresponding to the amount of drug removed by CRRT should be administered. Clearance by CRRT can either be measured or estimated. The high-flux membranes used in CRRT make no filtration barrier to most drugs, and the filtrate concentration can be estimated by the unbound fraction of the drug in plasma. When adding dialysis to filtration, this approach overestimates drug clearance, and a correcting factor should be used. A method for estimating drug clearance as a function of creatinine clearance is also suggested, but it has the same limitations in overestimating drug clearance when dialysis is combined with filtration. For non-toxic drugs, doses can safely be increased 30% above actual estimates to ensure adequate dosing. For drugs with a narrow therapeutical margin, monitoring plasma concentrations are mandatory. When appropriate, the use of a readily available reference for drug dosing is recommended.

Continuous renal replacement therapy for critically ill patients: an update

Despite continuous progress in intensive care during the last decades, the outcome of critically ill patients in whom acute renal failure (ARF) develops is still poor. This outcome may be explained partially by the frequent occurrence of ARF as part of multiple organ systems failure (MOSF). In this complex and unstable patient population, the provision of adequate renal support with either intermittent hemodialysis or peritoneal dialysis may pose major problems. Continuous renal replacement therapy (CRRT) is now increasingly accepted as the preferred treatment modality in the management of ARF in these patients. The technique offers adequate control of biochemistry and fluid balance in hemodynamically unstable patients, thereby enabling aggressive nutritional and inotropic support without the risk of exacerbating azotemia or fluid overload. In addition, experimental and clinical data suggest that CRRT may have a beneficial influence on hemodynamics and gas exchange in patients with septic shock and (nonrenal) MOSF, independent of an impact on fluid balance. We review both technical and clinical aspects of various continuous therapies, including their impact on serum drug levels and nutrient balance. In addition, an attempt is made to clarify the possible beneficial role of CRRT in reducing patient morbidity and mortality in the ICU.

A review of continuous renal replacement therapy

Patients in the Intensive Care Unit commonly develop acute renal failure (ARF). The kidneys are rarely the only organs failing in these patients. Frequently ARF is part of multiple organ dysfunction syndrome. The choice of dialytic therapy should consider, not only the efficacy of the therapy, but also the undesirable effects such therapy may have on the other failing organs. Intermittent Haemodialysis and Peritoneal Dialysis were the conventional forms of dialysis available. Both are associated with complications which may make them unsuitable for use in the haemodynamically unstable, hypercatabolic patients, seen in the Intensive Care setting. Continuous Renal Replacement Therapy (CRRT) has been introduced in many Intensive Care Units to provide a more stable, flexible form of dialysis. The purpose of this article is to give an overview of the various forms of CRRT and to discuss the advantages of this form of therapy.

Acute continuous hemodiafiltration: a prospective study of 110 patients and a review of the literature

One hundred ten critically ill patients with acute renal failure receiving acute continuous hemodiafiltration (ACHD) in our intensive care unit were studied prospectively. Acute continuous hemodiafiltration consisted either of continuous arteriovenous hemodiafiltration or of continuous veno-venous hemodiafiltration, and was used for 17,817 hours (mean duration of patient treatment, 161.9 hours), resulting in a fall from a mean pre-ACHD urea of 35.7 mmol/L to a plateau value of 16.8 mmol/L at 72 hours of treatment. The mean urea clearance achieved was 24.9 mL/min. Eighty of these patients (72.7%) were receiving artificial ventilation at the time of ACHD and 45 (40.9%) had more than four failing organs. The mean APACHE II score was 27.7. Despite the degree of illness severity, 42 patients (32.2%) survived to discharge from hospital. The use of ACHD was associated with hemodynamic stability, rapid normalization of electrolytes, and the ability to freely administer drugs, blood, and/or blood products. It also allowed for maintenance of an aggressive, nitrogen-rich, nutritional regimen. Support of these critically ill patients with acute renal failure using ACHD was achieved safely and without the employment of additional dialysis-trained nursing staff. Our own experience and a review of the available literature strongly suggest that the advantages associated with the use of ACHD therapies are clinically significant and support the view that ACHD is a modality of renal replacement most suited to critically ill patients with acute renal failure.