Monitoring of Intensive Care Patients by a Physiology-Related GFR Method

In the intensive care of critically ill patients, accurate and reliable determination of the glomerular filtration rate (GFR) is of utmost importance. We have previously used one of the most established methods for this purpose, iohexol plasma clearance measurement, in combination with a mechanistic model based on mass balances and physiological intercompartmental transport. Here, we apply this method in an intensive care unit setting to investigate its validity for estimating GFR and to interpret data from critically ill patients.

In 86 patients undergoing advanced supportive care for shock, sepsis, or other severe conditions, GFR was estimated using the clearance of iohexol during 24 h after an intravenous injection. Individual iohexol plasma clearance was determined by the mass balance model. Parameters were fitted to each patient's plasma clearance profiles to estimate GFR. The model estimates were compared with estimations using the established Bröchner-Mortensen regression approach and a maximum a posteriori Bayesian estimator.

Iohexol plasma disappearance was stable over the 24-h monitoring period in 80% of patients, while 20% exhibited unstable elimination profiles. In patients with stable profiles, the mechanistic model showed significant correlations with Bröchner-Mortensen estimates and the Bayesian estimator.

This physiology-based model strengthens the determination of GFR by providing interpretable parameters linked to transport and exchange processes between plasma and extracellular volumes and urinary excretion. The model shows that short-term GFR changes can be illustrated during the plasma concentration trajectory of iohexol, and short-term GFRs can be calculated.