Estimation of renal function in the intensive care unit: the covert concepts brought to light

Frantic efforts have been made up to this date to derive consensus for estimating renal function in critically ill patients, only to open the Pandora's box. This article tries to explore the various methods available to date, the newer concepts, and the uncared issues that may still prove to be useful in estimating renal function in intensive care unit patients. The concept of augmented renal clearance, which is frequently encountered in critically ill patients, should always be taken into account, as correct therapeutic dosage of drugs sounds vital which in turn depends on correctly calculated glomerular filtration rate. Serum creatinine and creatinine-based formulae have their own demerits that are well known and established. While Cockcroft-Gault and 4-variable modification of diet in renal diseases formulae are highly inadequate in the intensive care setup for estimating glomerular filtration rate, employing isotopic methods is impractical and cumbersome. The 6-variable modification of diet in renal diseases formula fairs better as it takes into account the serum albumin and blood urea nitrogen, too. Jelliffe's and modified Jelliffe's equations take into account the rate of creatinine production and volume of distribution which in turn fluctuates heavily in a critically ill patient. Twenty-four-hour and timed creatinine clearances offer values close to reality although not accurate and cannot provide immediate results. Cystatin C is a novel agent that offers a sure promise as it is least influenced by factors that affect serum creatinine to a major extent. Aminoglycoside clearance, although still in the dark area, may prove a simple yet precise way of estimating glomerular filtration rate in those patients in whom these drugs are therapeutically employed. Optic ratiometric method has emerged as the most sophisticated one in glomerular filtration rate estimation in critically ill patients.