Influence of Different PEEP Levels and Tidal Volumes on Regional Lung Function

Influence of Different PEEP Levels and Different Tidal Volumes on Regional Pulmonary Function in Patients Undergoing Robot Assisted Prostatectomy Detected by Electrical Impedance Tomography

Mechanical ventilation is indispensable for most of surgical interventions but can induce lung injury even in pulmonary healthy patients. This can lead to postoperative pulmonary complications. These adverse effects could be prevented by a better monitoring of intraoperative lung function. Electrical impedance tomography is able to visualize aeration within the lung in real time.

The planned study investigates the influence of different levels of positive endexspiratory pressure and different tidal volumes on the aeration.

Available perioperative parameters to set mechanical ventilation parameters represent only global lung function. But to reduce postoperative pulmonary complications induced by mechanical ventilation a better monitoring of intraoperative lung function seems to be crucial, that provides more regional information of lung collapse or over distention.

By application of small currents via electrodes around the thorax and measuring of the resultant resistance the electrical impedance tomography (EIT) can determine the level of aeration of the lung in a cross sectional plane. The EIT device used in this study calculates the percentage of the investigated lung area that can be defined as over distended or collapsed respectively. In these sections the change of resistance within a respiration cycle is reduced compared to well ventilated areas are therefore called silent spaces. Silent spaces located ventral are termed non-dependent (NSS) and silent spaces located dorsal are termed dependent (DSS). Based on this information the clinician is able to set the respirator in a more lung protective manor.

To better understand the influence of positive endexspiratory pressure (PEEP) and tidal volume (Vt) on reginal lung function we are going to carry out the presented study.

40 patients undergoing robot assisted prostatectomy should be enrolled in a study that consists of two phases. In the first phase 20 patients are ventilated with constant PEEP (10mbar) and in ten patients each the Vt is set to 5 or 12ml/kg ideal body weight. In the second phase in further 20 patients the Vt is set to 8ml/ kg ideal bodyweight and the PEEP is 3 or 12mbar in one half of the patients. Under the different ventilation settings the NSS and DSS, the oxygenation index and lung compliance will be investigated.

Inclusion Criteria:

• over 18 years of age
• scheduled for robot assisted prostate ectomy

Exclusion Criteria:

• body mass index >35 kg/m²
• chronic obstructive lung disease (GOLD III or IV)
• obstructive sleep apnoe syndrome
• planned or unplanned admission to intensive care unit for prolonged ventilation
• mechanical ventialtion within the last 30 days
• lung operation in the past
• other lung disease that impairs activity