Non-invasive evaluation of cardiac index by impedance cardiography in patients undergoing percutaneous nephrolithotomy

Percutaneous nephrolithotomy (PNL) is an endoscopic treatment of renal lithiasis. It is usually two-staged: it begins in the lithotomy position for ureteral catheter placement and retrograde pyelography, and subsequently an optimal renal access is obtained in the prone position. Some patients under epidural anesthesia do not tolerate the prone position and the PNL cannot be continued. This may be related to changes occurring within the circulatory system. The aim of this prospective randomized double-blind study was to evaluate the changes of the cardiac index (CI) during PNL.

In a group of 50 patients, with ASA physical status grade 1-2, epidural anesthesia with either 0.2% ropivacaine or 0.25% bupivacaine was performed and then the CI was evaluated by impedance cardiography.

Forty-five patients were included in the analysis; all tolerated the PNL well. After turning prone, a decrease in the CI was always recorded, a maximum after 10-15 min - 22.58 ±11.47%. There was significant variability of recorded values. The average CI dropped from 2.96 ±0.42 l/min/m² to 2.28 ±0.39 l/min/m². In 7 patients the decrease in the CI was greater than 35%. No correlation was observed with the arterial blood pressure or the heart rate. The decrease in the CI occurred irrespective of the type of local anesthetic used (p = 0.91).

A decrease in the CI was observed in every case, and it should be taken into consideration during qualification for PNL in the prone position.