Effects on Respiratory Mechanics of Two Different Ventilation Strategies During Robotic-Gynecological Surgery

The ventilation protocol consisted in volume-controlled mechanical ventilation through Ventilator, inspiratory to expiratory ratio of 1:2, and a respiratory rate adjusted to normocapnia (end-tidal carbon dioxide partial pressure between 30 and 40 mmHg). The were randomly assigned to Standard (SV) or Protective (PV) group.

participants in the SV group received a Tidal Volume (Vt) of 10 ml/kg of Ideal Body Weight (IBW) and a PEEP of 5 cmH2O, the participants in the PV group a Vt of 6 ml/kg of IBW and a PEEP of 8-10 cmH2O, associated to recruitment maneuvers (RMs).

RMs were performed only in hemodynamic stable conditions and at pre-set moments: after the induction of anesthesia, after any disconnection from the mechanical ventilator, each hour during the surgical procedures and immediately before extubation. RMs were performed in Pressure Control mode as follows: the limit of peak inspiratory pressure was set at 45 cmH2O and the pressure control was set at 30 cmH2O, therefore three consecutive thirty seconds lasting inspiratory pauses were performed. At the end of RMs, respiratory rate, inspiratory to expiratory ratio, inspiratory pause, and Vt were set back at values preceding the RMs.

Air Flow (V') was measured with a heated pneumotachograph, inserted between the Y-piece of the ventilator circuit and the endotracheal tube. The pneumotachograph was linear over the experimental range of flow. Volume was obtained by numerical integration of the flow signal. Airway pressure (Paw) was measured proximal to the endotracheal tube with a pressure transducer with a differential pressure of ± 100 cm H2O. The end-inspiratory and end-expiratory occlusions were performed through specific maneuver of ventilator.

Following end-inspiratory occlusion there is an immediate drop of the airway pressure from a maximal value (Pmax) to airway pressure at zero flow (P1), followed by a further decrease to plateau pressure (P2). The plateau pressure usually arrived within 3 seconds. Therefore, airway pressure 3 seconds after occlusion was taken as the static end-inspiratory elastic recoil pressure (P2) of the respiratory system. The use of the interrupter method for the measurement of respiratory mechanics allows possible quantification of the airway and viscoelastic properties of the respiratory system. The difference between Pmax and P1 divided by flow provides major information about minimal airway resistance (Rmin), while the difference between P1 and P2 (ΔP) divided by flow stands for viscoelastic resistance or Pendelluft effect of the respiratory system (ΔR). Maximal respiratory resistance (Rmax) is the sum of Rmin and ΔR. The inspiratory volume divided by P2- Total PEEP yields respiratory system compliance. Mechanical respiratory measurements and arterial blood gases were performed immediately after intubation, after pneumoperitoneum (AP), every hour during the procedure and before extubation (Ext). A further arterial blood gas sample was analyzed 1 hour after extubation.