Proximal Tubule Function in Septic Patients as Measured by Endogenous Lithium Clearance

Lithium is almost completely reabsorbed in the proximal tubule in parallel with sodium and water. What is not reabsorbed here is assumed to be fully excreted in urine, giving a reasonably accurate measurement of sodium reabsorption in the proximal tubule. Endogenous lithium clearance will be measured by inductively coupled plasma mass spectrometry (ICP-MS). The Gomez equations will be applied to calculate efferent arteriolar resistance, afferent arteriolar resistance, glomerular hydrostatic pressure, glomerular filtration pressure, and glomerular oncotic pressure. N-acetyl-β-D glucosaminidase (NAG) and NGAL, markers of tubular injury, will be measured by a spectrophotometric method using a commercially available kit. Routine blood and urine analyses will be performed at the Diagnostic Clinic Laboratory, University Hospital of North Norway, Tromsø.