Effect of Positive End-Expiratory Pressure on the Sonographic Optic Nerve Sheath Diameter as a Surrogate for Intracranial Pressure during Robot-Assisted Laparoscopic Prostatectomy: A Randomized Controlled Trial

Abstract

Background: Positive end-expiratory pressure (PEEP) can increase intracranial pressure. Pneumoperitoneum and the Trendelenburg position are associated with an increased intracranial pressure. We investigated whether PEEP ventilation could additionally influence the sonographic optic nerve sheath diameter as a surrogate for intracranial pressure during pneumoperitoneum combined with the Trendelenburg position in patients undergoing robot-assisted laparoscopic prostatectomy.

Methods: After anesthetic induction, 38 patients were randomly allocated to a low tidal volume ventilation (8 ml/kg) without PEEP group (zero end-expiratory pressure [ZEEP] group, n = 19) or low tidal volume ventilation with 8 cmH2O PEEP group (PEEP group, n = 19). The sonographic optic nerve sheath diameter was measured prior to skin incision, 5 min and 30 min after pneumoperitoneum and the Trendelenburg position, and at the end of surgery. The study endpoint was the difference in the sonographic optic nerve sheath diameter 5 min after pneumoperitoneum and the Trendelenburg position between the ZEEP and PEEP groups.

Results: Optic nerve sheath diameters 5 min after pneumoperitoneum and the Trendelenburg position did not significantly differ between the groups [least square mean (95% confidence interval); 4.8 (4.6-4.9) mm vs 4.8 (4.7-5.0) mm, P = 0.618]. Optic nerve sheath diameters 30 min after pneumoperitoneum and the Trendelenburg position also did not differ between the groups [least square mean (95% confidence interval); 4.5 (4.3-4.6) mm vs 4.5 (4.4-4.6) mm, P = 0.733].

Conclusions: An 8 cmH2O PEEP application under low tidal volume ventilation does not induce an increase in the optic nerve sheath diameter during pneumoperitoneum combined with the steep Trendelenburg position, suggesting that there might be no detrimental effects of PEEP on the intracranial pressure during robot-assisted laparoscopic prostatectomy.

Trial registration: ClinicalTrial.gov NCT02516566.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Study flow diagram.

Patients in the zero end-expiratory pressure (ZEEP) group received mechanical ventilation with a tidal volume 8 ml/kg of ideal body weight without positive end-expiratory pressure (PEEP), and those in PEEP group received mechanical ventilation with a tidal volume 8 ml/kg of ideal body weight with 8 cmH2O PEEP.

Fig 2. Changes in ONSD in the ZEEP group (blue circle) and PEEP group (red circle) during robot-assisted laparoscopic prostatectomy.

Note that the ONSDs during pneumoperitoneum and the Trendelenburg position (T2 and T3) do not significantly differ between the ZEEP and PEEP groups, whereas the ONSD in the PEEP group is significantly higher than that in the ZEEP group during the supine position without pneumoperitoneum (T1). Circles and bars indicate least square means and 95% confidence intervals, respectively. ONSD = optic nerve sheath diameter; ZEEP group = zero end-expiratory pressure with low tidal volume ventilation; PEEP group = positive end-expiratory pressure with low tidal volume ventilation; T0 = 10 min after anesthetic induction in the supine position before random allocation; T1 = 5 min after applying ventilation strategies according to a random allocation; T2 = 5 min after establishing pneumoperitoneum and the steep Trendelenburg position; T3 = 30 min after establishing pneumoperitoneum and the steep Trendelenburg position; T4 = at the end of surgery after desufflation of pneumoperitoneum in the supine position.