Monitoring of renal venous Po₂and kidney oxygen consumption in rats by a near-infrared phosphorescence lifetime technique

Abstract

Mik EG, Johannes T, Ince C. Monitoring of renal venous PO2 and kidney oxygen consumption in rats by a near-infrared phosphorescence lifetime technique. Am J Physiol Renal Physiol 294: F676-F681, 2008. First published January 9, 2008 doi:10.1152 doi:10. /ajprenal.00569.2007 is an important parameter that has been shown to be influenced by various pathophysiological circumstances. V O2,ren has to be repeatedly measured during an experiment to gain insight in the dynamics of (dys)regulation of oxygen metabolism. In small animals, the classical approach of blood gas analysis of arterial and venous blood samples is only limitedly applicable due to fragile vessels and a low circulating blood volume. We present a phosphorescence lifetime technique that allows nearcontinuous measurement of renal venous PO2 (vPO2) and V O2,ren in rats. The technique does not rely on penetration of the blood vessel, but uses a small reflection probe. This probe is placed in close proximity to the renal vein for detection of the oxygen-dependent phosphorescence of the injected water-soluble near-infrared phosphor Oxyphor G2. The technique was calibrated in vitro and the calibration constants were validated in vivo in anesthetized and mechanically ventilated male Wistar rats. The hemoglobin saturation curve and its pH dependency were determined for calculation of renal venous oxygen content. The phosphorescence technique was in good agreement with blood gas analysis of renal venous blood samples, for both PO2 and hemoglobin saturation. To demonstrate its feasibility in practice, the technique was used in four rats during endotoxin infusion (10 mg ⅐ kg Ϫ1 ⅐ h Ϫ1 during 1 h). Renal vPO2 reduced by 40% upon reduction in oxygen delivery to 30% of baseline, but V O2 remained unchanged. This study documents the feasibility of near-continuous, nondestructive measurement of renal vPO 2 and V O2 by oxygendependent quenching of phosphorescence.oxygen-dependent quenching; Oxyphor G2; time-resolved spectroscopy; Pd-porphyrin THE MEASUREMENT OF OXYGEN in blood within arteries and veins is mandatory for the study of oxygen supply and demand of organs. For example, the oxygen delivery (DO 2 ) to an organ is calculated by the arterial oxygen content of the blood per volume times the blood flow to the organ. To also determine the oxygen utilization (V O 2 ) by an organ, the venous oxygen content has to be known. Another example of a situation where knowledge of the venous oxygenation over time is necessary is monitoring of the "PO 2 -gap," i.e., the discrepancy between capillary PO 2 and venous PO 2 when the capillary PO 2 drops below the venous PO 2 (9,22,23). The latter occurs under certain pathophysiological conditions, such as sepsis and shock (5), and is a valuable parameter when studying resuscitation protocols and treatments.

Effects of Sepiapterin Infusion on Renal Oxygenation and Early Acute Renal Injury After Suprarenal Aortic Clamping in Rats

“…After the surgical protocol (; 60 minutes), one optical fiber was placed 1 mm above the kidney for microvascular PO 2 measurements 11 and another one 1 mm above the renal vein to measure venous oxygenation. 12 Oxyphor G2 (Oxygen Enterprises, Ltd). 13,14 was subsequently infused (6 mg/kg) intravenously for 5 minutes, followed by 30 minutes of stabilization time.…”

“…The S rv O 2 was calculated using the Hill equation with p 50 = 37 Torr (4.9 kPa) and Hill coefficient = 2.7. 12 The renal oxygen extraction ratio was calculated as O 2 ER ren (%) = VO 2ren /DO 2ren 3 100.…”

Microcirculation in Acute and Chronic Kidney Diseases

“…Thus, the heterogeneity of microcirculatory oxygen pressure values can be measured. 79 Blood oxygen level-dependent magnetic resonance. Another noninvasive method to measure tissue oxygenation in vivo is blood oxygen leveldependent (BOLD) magnetic resonance, which determines deoxyhemoglobin levels.…”

The Microcirculation of the Septic Kidney

“…A further refinement of this technique allows noninvasive measurement of venous PO 2 values and, using deconvolution techniques, the analysis of PO 2 histograms where the heterogeneity of microcirculatory oxygen pressure values can be measured. 59 To date, most of the data published with these techniques did not properly explore glomerular circulation in vivo. Thus, it should be kept in mind that most of the published experiments on renal microcirculation only target a limited spectrum of the entire span of renal capillaries.…”