Rationale: Patients with an exacerbation of asthma or chronic obstructive pulmonary
disease (COPD) requiring controlled mechanical ventilation (CMV) on the intensive care
unit (ICU) have a mortality rate between 10 and 20%. This mortality rate is largely
explained by major complications associated with mechanical ventilation e.g.,
pneumothorax, cardiovascular collapse and pneumonia. Complications are the result of
dynamic hyperinflation that forms the cornerstone in the pathophysiology of both
diseases. The diameter of the smaller airways decreases because of inflammation,
bronchospasm, mucus (asthma) and the loss of elastic recoil by emphysema (COPD). This
leads in particular to a high airway resistance during expiration and the residue of
tidal volume in the lung when the next inspiration begins. The result is dynamic
hyperinflation with a continuously increasing lung volume with high pressures,
pneumothorax (barotrauma) and hemodynamic collapse as a result. During CMV (pressure- or
volume controlled ventilation; PCV or VCV) only the inspiration is controlled while
expiration is passive, possibly leading to airway collapse and further dynamic
hyperinflation. Besides, both ventilation modes are accompanied by high flow rates
leading to a further increase in airway resistance and ventilation pressures. Flow
controlled ventilation (FCV) is a mechanical ventilation method that uses a relatively
low and constant flow during both inspiration and expiration, thereby decreasing airway
resistance and preventing airway collapse during expiration. Besides, FCV has shown to
have a higher ventilation efficiency measured by a decrease in minute volume at stable
arterial partial pressures of carbon dioxide (PaCO2). This makes FCV a very interesting
ventilation mode in intubated patients with an exacerbation of asthma or COPD, possibly
decreasing the amount of dynamic hyperinflation and complications in these patients.
Although FCV is widely used for hypoxic respiratory failure on the ICU so far no studies
have been performed in asthma or COPD patients.
We hypothesize that FCV in intubated patients with an exacerbation of asthma or COPD
results in a lower minute volume (MV) and decreased end-inspiratory lung volume (EILV) as
a measurement for dynamic hyperinflation compared to VCV.
Objectives: To study the effect of FCV on the MV and EILV compared to VCV.
Study design: Physiological pilot study with a randomized crossover design comparing FCV
and VCV.
Study population: Patients with an asthma/COPD exacerbation ≥18 years old receiving CMV.
Intervention: Patients are mechanically ventilated with VCV at baseline. Upon inclusion
the EIT-belt and an esophageal balloon are placed to assess the EILV and transpulmonary
pressures respectively. Besides, patients are randomized between the sequence of
ventilation mode, namely 90 minutes of VCV followed by 90 minutes of FCV or 90 minutes of
FCV followed by 90 minutes of VCV. When VCV is switched to FCV the same mechanical
ventilator settings are used as in the VCV mode. After half an hour on FCV the PEEP,
drivingpressure and flow of FCV are optimized based on the highest compliance and lowest
flow matching with a stable PaCO2. VCV is always set according to standard of care. Total
time of measurements / study time is 180 minutes.
Main study parameters/endpoints: Primary endpoint is the difference in minute volume
after 90 minutes on FCV compared to after 90 minutes of VCV. An important secondary
endpoint is the difference in EILV after 30 minutes on FCV compared to after 30 minutes
of VCV.
Nature and extent of the burden and risks associated with participation, benefit and
group relatedness: All patients are sedated and on CMV, therefore there will be no
discomfort for the patient. FCV has been successfully applied during surgery and on the
ICU and the patient will be monitored continuously so the clinical team can act directly
in case of any adverse event. Lung volume is measured with EIT, a non-invasive,
radiation-free monitoring tool. Transpulmonary pressures are measured with an esophageal
balloon that is placed in a similar manor as a nasogastric feeding tube. Therefore,
overall the risks of this study are limited.