Augmented renal clearance in the critically ill: how to assess kidney function.

Area of Science:

• Critical Care Medicine
• Nephrology
• Clinical Pharmacology

Background:

• Augmented renal clearance (ARC) in critically ill patients can lead to drug underdosing and treatment failure.
• Accurate assessment of kidney function is crucial for optimizing drug therapy in these patients.
• The validity of formulas for estimating renal function in ARC is not well-established.

Purpose of the Study:

• To evaluate the accuracy of different formulas in estimating kidney function in critically ill patients with ARC.
• To compare measured creatinine clearance (CrCl) with estimated CrCl using the Cockcroft-Gault (CG) method and the Modification of Diet in Renal Disease (MDRD) estimated glomerular filtration rate (eGFR) formula.

Main Methods:

• Observational, retrospective study in a surgical intensive care unit.
• Included adult patients with measured CrCl ≥ 120 mL/min (24-hour urine collection).
• Compared measured CrCl with CrCl(CG) and MDRD-based eGFR; analyzed correlation and agreement using Spearman and Bland-Altman methods.

Main Results:

• ARC was present in 390 out of 1317 screened patients.
• Fair correlation found between measured and estimated clearances (r(s) = 0.343 for CrCl(CG); r(s) = 0.290 for eGFR).
• Significant bias and wide limits of agreement observed for both estimation methods.

Conclusions:

• Formulas like CG and MDRD-eGFR show poor agreement with measured CrCl in critically ill patients with ARC.
• Clinicians must exercise caution when using estimated kidney function equations in this population.
• Measured CrCl via 24-hour urine collection is recommended for patients with suspected ARC.