[Renal protection during surgical procedures on the infrarenal aorta]

Despite the progress in surgical and anaesthetic management, decreased renal function is still observed after abdominal infrarenal aortic surgery and remains an important problem in postoperative period. Although data regarding the efficacy of perioperative renal protection are conflicting, it is widely believed that renal protection before aortic cross-clamping is beneficial and therefore is commonly used. The aim of this study was to evaluate the impact of renal protection in patients undergoing elective infrarenal aortic surgery (1ARS).

We have prospectively studied 80 patients undergoing elective infrarenal aortic surgery from October 1996 to May 1998 in the Clinical Centre of Serbia, because of aorto-occlusive disease or aortic aneurysm. Patients were excluded from the study for three reasons: prior renal dysfunction, suprarenal aortic cross-clamping and ruptured aortic aneurysm. We have randomized the patients in two groups: without renal protection--group A (n = 40) and with renal protection--group B (n = 40). Preanaesthetic medication consisted of midazolam (5 mg i.m.). Anaesthesia was induced with etomidat 0.3 mg/kg, fentanyl 0.05-0.1 mg and succinil-holin Img/kg. Ventilation was controlled using 50% of nitrous oxyde and oxygen. Supplemental anaesthesia consisted of isoflurane and fentanyl, in order to maintain the mean arterial pressure and heart rate +/- 20% regarding preoperative values. In all patients two peripheral vein and radial artery catheters were cannulated before anaesthesia. Central venous catheter and Foley urinary bladder catheter were inserted after the induction of anaesthesia. Two-lead electrocardiograms were recorded. All patients in group B were given intravenously mannitol (0.3 g/kg) before aortic cross-clamping (ACC). After aortic cross-clamping, these patients received furosemide (20-40 mg) or dopamine (1-3 micrograms/kg/min) to the end of surgery (Table 1). In 8 time points (preoperatively, after induction, during ACC, 2 and 8 hours after ACC, on day 1, 2 and 3 postoperatively) haemodynamic parameters (mean arterial and central venous pressure), volume load, urinary output, creatinine and free-water clearance, serum electrolytes, BUN, creatinine, plasma and urine osmolality and ACC time were analyzed in each patient. Renal complications were classified as transient or persistent. Transient renal dysfunction was defined as a greater rise than 20% rise in peak serum creatinine level over baseline serum creatinine level, with a peak of at least 168 mumol/L. Persistent renal insufficiency was defined as a greater rise than 20% rise in discharge serum creatinine level over baseline serum creatinine level, with a peak of at least 168 mumol/L. Moreover, renal insufficiency was defined as a free-water clearance greater than -15 ml/h. Aortic cross-clamping time was defined as a period in which the proximal inflow was occluded. The results were expressed as means +/- SD. Statistical difference detected with Student's t-test, with p < 0.05 being considered significant.

Patients in groups A and B were similar regarding the age (64.32 vs. 62.00), sex (males 35, females vs. males 34, females 6) and preoperative diseases. (Tab. 2) No difference was found between groups regarding any of the parameters (BUN, serum creatinine, electrolytes, volume load, creatinine and free-water clearance, haemodynamic parameters, plasma and urine osmolality). Urinary output was higher in group B during and 2 hours after ACC. (Graph 1.) ACC time was similar in two groups (24.1 min vs 24.5 min). (Graph. 2) Only one patient in group B revealed transitory renal insufficiency, not requiring special treatment. These data indicate that renal protection did not influence renal function. Short ACC time may have impact on the obtained results. Our results suggest that renal protection should not be considered as mandatory for elective infrarenal aortic surgery. Because of the short ACC time observed in this study (in comparison to other studies), further studies of renal protection in patients with longer ACC time are needed.