ALTERATIONS IN RENAL MICROCIRCULATION DURING CARDIOPULMONARY BYPASS

Background. This study was designed to investigate renal microvascular changes during cardiopulmonary bypass. Methods. Kidneys were harveste d from each of four groups of 6 pigs. Group A were anesthetized and he parinized only. The remaining three groups underwent cardiopulmonary b ypass at 28 degrees C, group B for 30 minutes and groups C and D for 1 20 minutes; group D had an additional 30 minutes of normothermic perfu sion at the end of the experiment. Renal cortical blood now was measur ed using radiolabeled microspheres. Microvascular morphology was defin ed by corrosion casting and scanning electron microscopy. Results. In group A, renal vascular resistance was 61 +/- 5.1 mm Hg.mL(-1).min(-1) . This value decreased to 28 +/- 7.8 in group B and 25 +/- 4.0 in grou p C (p < 0.05), and increased in group D to 40 +/- 4.1 (p < 0.05 versu s groups A, B, and C). Cortical thickness, as measured by microvascula r casts in groups A, B, and C, was 33, 34, and 31 mm, respectively, wi th equal distribution of the resin to the superficial and deep cortex but was significantly reduced in group D to 22 mm (p < 0.05 versus gro ups A, B, and C), with failure of the resin to fill the superficial co rtical layer. Diameters of glomeruli as seen on the casts were 111 +/- 10.38 mu m in group A, 100 +/- 9.24 mu m in group B, and 82 +/- 4.4 m u m in group C (p < 0.05 group A versus group C). The glomeruli from g roup D were still significantly smaller than group A (93 +/- 10.35 mu m, p < 0.05). Mean glomerular capillary diameters were 4.65 +/- 0.26 m u m in group A, 3.9 +/- 0.16 mu m in group B, 3.6 +/- 0.19 mu m in gro up C, and 3.65 +/- 0.3 mu m in group D (p < 0.05 group A versus groups B, C, and D). Conclusions. Hypothermic nonpulsatile cardiopulmonary b ypass decreased renal vascular resistance, but the superficial and dee p layers of the cortex were perfused equally. Glomeruli were reduced i n size because of capillary narrowing. This was consistent with divers ion of blood through bypass channels. With restoration of normothermia , underperfusion of the superficial cortex occurred, with potential fo r damage to these nephrons during the increased metabolic demands of r ewarming. (C) 1998 by The Society of Thoracic Surgeons.