Assessment of Atelectasis by Electrical Impedance Tomography during General Anesthesia for Surgery

Mechanical ventilation is mandatory in patients under general anesthesia.
Mechanical ventilation has the potential to aggravate or even initiate lung
injury, causing overdistention of the non-dependent lung regions and repetitive
collapse and re-expansion of dependent lung regions (e.g. atelectasis). Various
modesof mechanical ventilation are employed during general anesthesia for
surgery in an effort to minimize atalectasis and prevent lung injury caused by
mechanical ventilation.
Electrical Impedance tomography (EIT) is a real-time, non-invasive, bed-side,
radiation-free continuous imaging technique able to detect changes of regional
lung aeration that could be used to guide mechanical ventilation settings.

Our longstanding goal is to assess the clinical applicability of EIT in
intubated and mechanically ventilated patients. We aim to observe changes in
regional lung ventilation during alterations of mechanical ventilation
strategies in clinical situations. EIT will be applied in existing
interventional trials in the operation room (e.g., PROVHILO; MEC 10/251),
assessing regional lung ventilation in non-injured lungs during the
interventions (see research protocol of PROVHILO). Moreover, the effects of
different strategies on regional lung ventilation in other patient populations
can be determined during mechanical ventilation strategies as performed
according to standard clinical care.

The main research questions include:
1. Technical feasibility of EIT registration during mechanically ventilation in
patients under general anesthesia for surgery.
2. Assessment of changes in regional lung aeration during mechanical
ventilation in the interventional trial PROVHILO (MEC 10/251), and future
trials comparing different ventilation strategies.
3. Assessment of changes in regional lung aeration during changes in mechanical
ventilation therapy according to standard clinical care.
4. Assessment of correlation of changes in regional lung aeration with observed
gas exchange and radiological assessments.

This study concerns non-invasive observations in intubated and mechanically
ventilated patients with non-injured lungs in the operation room.

This is a observational study; electrical impenance tomography will be used to
observe regional lung aeration changes during interventions in existing
interventional trials and in ventilation strategy changes according standard
clinical care.

Prior to EIT registration 16 electrocardiographic electrodes will be placed
around the thoracic cage at the 5th or 6th intercostal space and connected with
an EIT device. EIT data are generated using an electrical current of 5 mA at 50
kHz (equal to ECG registration).
As data analysis of the EIT registrations are presently performed off-line,
after the measurements, the ventilator settings applied by the clinician can
and will not be influenced.

In this observational study there are no risks involved for participating
patients. Patient burden is minimal to none, and comprises of painless
placement of an electrical impedance belt around the lower thorax
pre-operatively. The patient will not experience any burden of the
measurements.