EIT Study With COPD and OHS Patients (EIT Step 2)
Condition: OHS; COPD
Study type: Interventional

Summary: 
      Patients with severe respiratory diseases such as chronic obstructive pulmonary disease
      (COPD) or obesity-hypoventilation syndrome (OHS) can benefit from having non-invasive
      ventilation (NIV). NIV consists of a machine (ventilator) that is blowing air inside a
      patient's airway through a mask. NIV provides patients with a bigger breath. Bigger breaths
      help patients to have a more oxygen and less waste gas (or carbon dioxide) in their body.

      These changes can improve outcomes and quality of life. In order to provide appropriate
      ventilation for each patient, the ventilator can generate different types of blowing:

        -  Continuous positive airway pressure (CPAP) which delivers a constant flow of air through
           the mask

        -  Pressure support ventilation (PSV) which delivers a constant flow of air through the
           mask and, on top of that, delivers more flow when the patient begins to inhale

        -  Volume targeted ventilation which delivers a flow of air through the mask that is
           adjusted breath by breath in order to achieve a preset volume.

      These different type of blowing have consequences on patient comfort as well as on the
      improvement of their ventilation.

      To assess the improvement of the ventilation, currently blood tests are used, however, these
      reflect overall output and may miss more subtle changes in breathing that could affect how
      patients feel.

      Electrical impedance tomography (EIT) is a new technology that involves wearing a belt of
      sensors around the chest that provides information on how well the lungs are being filled
      with air by the ventilator. It allows a non-invasive assessment of the effect of NIV on lung
      ventilation in real-time.

      The investigators hope to use the EIT technology to assess in real-time patients lung
      ventilation when they are using the NIV. The investigators hope that EIT will provide
      information on which type of blowing is more effective and more comfortable than the others.
    

Detailed description: 
      Chronic lung disease can sometimes progress to the extent that patients can no longer clear
      the waste gas from their blood. Treatment can be offered with a mask and machine (ventilator)
      that helps people breathe and aims to improve their lung condition. It is common for people's
      lungs to be affected variably, i.e. left more than right or top of lung more than bases of
      lungs. The way in which the ventilator is set may affect how well the machine deals with
      these differences. If the lung is better ventilator patients may find the machine more
      comfortable and it may be more effective.

      Electrical impedance tomography (EIT) is a new technology that involves wearing a belt of
      sensors around the chest that provides information on how well the lungs are being filled
      with air by the ventilator. It allows the assessment of these differences, which previously
      required the use of invasive equipment to obtain.

      Optimising ventilator settings in the administration of non-invasive ventilation (NIV) can be
      improved with the addition of individual physiological data. This approach is limited due to
      the invasive techniques required to obtain this information, often leading to less ideal NIV
      settings promoting patient-ventilator asynchrony. It has been recently demonstrated by our
      group that all patients established on domiciliary NIV have a degree of patient-ventilator
      asynchrony and that the commonest type of asynchrony are triggering issues. Triggering
      asynchrony is promoted by mismatch between a patient's intrinsic positive end-expiratory
      pressure (iPEEP) and applied expiratory positive airway pressure (EPAP) with these
      ineffective efforts contributing to an increased work of breathing and patient discomfort.
      Previous strategies used to optimise patient triggering have involved the placement of
      oesophageal catheters in order to measure neural respiratory drive (NRD) to the diaphragm by
      electromyography (EMG) but again this process is invasive and often poorly tolerated.
      Electrical Impedance Tomography (EIT) is a non-invasive, bedside monitoring technique that
      provides semi-continuous, real-time information about the regional distribution of the
      changes in electrical resistivity of the lung tissue due to variations in ventilation in
      relation to a reference state.

      Information is gained by repeatedly injecting small alternating electric currents (usually 5
      mA) at high frequency of 50 - 80 kHz through a system of skin electrodes (usually 16) applied
      circumferentially around the thorax in a single plane between the 4th and 6th intercostal
      space. While an adjacent pair of electrodes 'injects' the current ('adjacent drive
      configuration'), all the remaining adjacent passive electrode pairs measure the differences
      in electric potential. A resistivity (impedance) image is reconstructed from this data by a
      mathematical algorithm using a two dimensional model and a simplified shape to represent the
      thoracic cross-section.

      The resulting image possesses a high temporal and functional resolution making it possible to
      monitor dynamic physiological phenomena (e.g. delay in regional inflation or recruitment) on
      a breath by breath basis. It is important to realize that the EIT images are based on image
      reconstruction techniques that require at least one measurement on a well-defined reference
      state. All quantitative data are related to this reference and can only indirectly quantify
      (relative) changes in local lung impedance (but not absolute).

      EIT can be used in mechanically ventilated patients to assess recruitment and to optimise
      ventilator settings to reduce risk of iatrogenic ventilator associated lung injury.

      In the supine posture obese patients can generate significant levels of iPEEP that contribute
      to increased levels of neural respiratory drive compared with the upright posture. There has
      been much debate regarding the optimal ventilator strategy in patients with obesity related
      respiratory failure, with uncontrolled trial data to support simple continuous positive
      airway pressure, pressure support (PSV) NIV and volume targeted (VT) NIV. There has been no
      robust evidence to suggest superiority of a single mode but post hoc data suggests superior
      control of sleep disordered breathing in patients in pressure controlled mode. It is unclear
      whether the extended inspiratory time of pressure controlled mode is allowing superior gas
      exchange by maintaining airway distension and preventing regional collapse.

      In COPD, patients' response to treatment can be influenced by disease heterogeneity with some
      patients showing even distribution of lung damage and others marked differences throughout
      the lungs. This variation can lead to significant differences in the lung mechanics in
      different regions with optimal NIV settings for some regions having potentially deleterious
      effects on neighbouring zones. It has been shown that control of hypoventilation and improved
      blood gas exchange is essential in order to improve outcomes with NIV in COPD but is less
      clear if pressure control ventilation as advocated by Windisch and colleagues is required in
      order to achieve this effect. Inappropriate settings of NIV can also lead to dynamic
      distension that results in a decrease of tidal volume and an increase in patient discomfort.
    

Intervention name(s): Treatment Group
Intervention type(s): Other
Intervention description(s): Participants will be established on the randomised mode of ventilation and will have continuous assessment of the following during the assessment period:
Electrical impedance tomography
EMGpara
SpO2
tcCO2
Pneumotachography
End-tidal CO2 monitoring
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: EIT; NIV