Effect of Pneumoperitoneum and Steep Trendelenburg on Autonomic Nervous System

Laparoscopic radical prostatectomy is becoming a widely used surgical procedure because it carries some important advantages over open prostatectomy. This surgical technique requires positioning the patient at 25-40 degree head-down position (steep trendelenburg) for a prolonged time in association with pneumoperitoneum at 12-15 mmHg. The postural change from supine to head down position causes a hydrostatic fluid shift towards the head and the thorax, thus increasing venous return and stimulating the cardiopulmonary baroreceptors. Moreover, there are reports of severe bradycardia and cardiac arrest following pneumoperitoneum in association with steep trendelenburg. A vagal hypertone induced by the combination of these two factors, or sympathetic hyperactivity elicited by pneumoperitoneum insufflation have been alternatively advocated as a cause of such hemodynamic changes. However these speculations are little more than a narrative role because any evidence based demonstration is never been provided.

The aim of this study is to measure the variations of autonomic nervous system modulation induced by steep trendelenburg position at 25 degrees and pneumoperitoneum during laparoscopic radical prostatectomy.

Methods Patients are randomized into two groups. Group A: after induction of general anesthesia, in supine position a pneumoperitoneum is induced with carbon dioxide insufflation through a surgical inserted trocar into the abdominal cavity, then patients are positioned in steep trendelenburg at 25 degrees head down. Group B: after induction of general anesthesia, patients are positioned in steep trendelenburg position at 25 degrees head down, then a pneumoperitoneum is induced with carbon dioxide insufflation through a surgical inserted trocar into the abdominal cavity.

Autonomic nervous system modulation is assessed at four main time: (i) T1 baseline (before the induction of general anesthesia); (ii) T2, 5 min after the induction of general anesthesia, (iii) T3, pneumoperitoneum insufflation (Group A) or steep trendelenburg (Group B); (iv) T4, steep trendelenburg (Group A) or pneumoperitoneum insufflation (Group B).

Autonomic nervous system modulation is studied non invasively by means of heart rate variability (HRV) analysis through both linear and non linear methods. Beat-to-beat intervals are computed detecting the QRS complex on the electrocardiogram and locating the R-apex using parabolic interpolation. The maximum arterial pressure within each R-to-R interval is taken as systolic arterial pressure (SAP). Sequences of 300 values are randomly selected inside each experimental condition.