Electrical Impedance Tomography guided assist levels during Pressure Support Ventilation: A pilot study

From the ARDSnetwork trial we know that controlled mechanical ventilation with
tidal volumes of 6mL/kg improves survival. However, during Pressure Support
Ventilation (PSV) it is unknown which tidal volume is superior. However, we
know that inhomogeneous ventilation of the lung lead to increased stress on the
lung tissue, which increases the risk to develope ventilator induced ling
injury. In recent research we have shown that PSV with lower assist levels
results in more homogeneous ventilation as measured by Electrical Impedance
Tomography (EIT). In addition, we showed that during higher assist levels the
non-dependent lung region is hyperinflated.

Primary objective
- To define the optimal pressure support level for homogeneous lung
ventilation during PSV, based on EIT measurements, in patients with and without
lung disorders.

Secondary objectives
- Improved oxygenation compared to baseline
- Improved dorsal ventilation distribution compared to baseline
- Reduced amount of dead-space compared to baseline
- Improved FRC compared to baseline
- Lower transpulmonary pressure compared to baseline

The study is designed as an intervention study.
The level of ventilatory assist will be titrated based on the intratidal gas
distribution, calculated from EIT measurements. First a baseline EIT
measurement will be performed. Thereafter a pressure support trial will be
performed from 0 to 15 cmH2O. From this support trial the best level of assist
will be defined as the support level leading to homogeneous ventilation of the
lung regions. EIT measurements will be performed twice a day in 3 consecutive
days. After 72 hours the study will end. The level of Positive End-Expiratory
Pressure (PEEP) level will be set according to the standard FiO2/PEEP table,
which is the standard of care on our ICU.

In addition, functional residual capacity, lung compliance, dead-space, blood
gasses and transpulmonary pressures will be measured twice a day.

Pressure Support level will be set based on Electrical Impedance Tomography
measurements, in order to ventilate the lungs homogeneously.

Pressure Support Ventilation (PSV) is the standard of care in our
mechanically-ventilated patients on the Intensive Care Unit. The EIT guided
assist levels could lead to larger tidal volumes. However, during the entire
study the pressure alarms will be kept below 30 cmH2O, which have been shown to
be safe. Therefore patients participating in this study will not be exposed to
additional risk.

An esophagal pressure catheter will replace the standard feeding tube in order
to perform transpulmonary-pressure measurements. This is a special feeding tube
with a small balloon to measure esophageal pressures during the inspiration and
expiration. This special gastric tube can be used to feed the patient. This
tube will be placed following the local protocol for feeding tube placement