Assessment of Regional Lung Ventilation Distribution During Supraglottic and Subglottic Jet Ventilation by EIT.
Condition: Respiratory Physiological Phenomena
Study type: Interventional

Summary: 
      Objective: To estimate regional lung volume changes by electrical impedance tomography (EIT)
      during supra- and subglottic jet ventilation via the jet laryngoscope and LaserJet catheter
      for performing laryngotracheal surgery.

      Design: A monocentric, prospective, randomized study. Patients: Patients who require elective
      micro laryngo-tracheal surgery under jet ventilation.

      Interventions: Patients undergoing elective micro laryngeal surgery will be assigned to
      subglottic JV via the new LaserJet catheter and supraglottic JV via the jet laryngoscope vice
      versa. The sequence of JV modes will be randomized (subglottic followed by supraglottic or
      supraglottic followed by subglottic JV). Hemodynamic and ventilation parameters will be
      monitored. Arterial blood gas samples will be drawn and the regional ventilation distribution
      assessed, using the EIT.

      Outcomes measures: Reported EIT data of regional ventilation distribution, values of
      oxygenation and carbon dioxide elimination during the application of supra- and subglottic JV
      via jet laryngoscope and LaserJet catheter in patients undergoing laryngo-tracheal surgery.
      The purpose of this study is to investigate the influence of supraglottic and subglottic JV
      compared to standardized, controlled mask ventilation on measurements of pulmonary regional
      ventilation distribution by EIT, blood gas analyses and serological biomarkers.
    

Detailed description: 
      Surgical procedures of the larynx and trachea present special challenges for surgeons and
      anesthesiologists. To enable an unrestricted view of the operating field, ventilation of the
      patient is not performed over an endotracheal tube but instead over a steel laryngoscope or a
      thin catheter with Jet ventilation (JV). This enables precision surgical work, good
      visibility of the operating area and the safe use of various laser types. Over the last
      decades, different modalities of JV for laryngo-tracheal surgery have been developed. The
      former techniques of the supraglottic approach were improved with simultaneously applied
      low-frequency jet ventilation additionally to the high-frequency jet ventilation, called
      superimposed high-frequency jet ventilation (SHFJV). The SHFJV was developed in 1990 and was
      applied in several clinical trials [1-4] In recent years, a number of new catheters have been
      developed for the trans laryngeal subglottic approach of JV, like the translaryngeal Hunsaker
      MonJet Ventilation catheter and its successor, the LaserJet catheter. These catheters though
      can be used only with the HFJV. They provide less vocal cord movement and precise surgical
      manipulation are possible on one side, but on the other the risk of barotrauma may result in
      cases of proximal obstruction of the catheter.

      [5, 6] Although jet ventilation is an established method to replace patients breathing during
      otorhinolaryngeal surgery, research is still required on efficient lung protective
      ventilation in order to provide adequate carbon dioxide (CO2) elimination, adequate
      oxygenation and in preventing ventilator induced lung injury. Jet ventilation techniques and
      access routes The TwinStream jet ventilator (C. Reiner Corp, Vienna, Austria) is routinely
      used for high-frequency jet ventilation (HFJV) or SHFJV in case of tubeless jet laryngoscopy
      (laryngeal micro- and laser surgery) and tracheoscopy. The device consists of two
      simultaneously operating ventilation units which can be adjusted separately. The driving
      pressure of the device is 1.5-3 bar and respiratory rates of 10-900 per min can be provided.
      Supraglottic jet laryngoscope In SHFJV, jet ventilation of normal frequency and high
      frequency is conducted simultaneously and enables ventilation at two different pressure
      levels through the steel jet laryngoscope. It is equipped with two jet nozzles, which are
      placed at the distal end of the jet laryngoscope, with the low-frequency jet stream passing
      the distal cannula, and the high-frequency jet stream at the proximal cannula. A third
      cannula at the tip of the laryngoscope allows ventilation pressure monitoring. The jet
      laryngoscope is introduced by the surgeon, for examining and operating structures within the
      laryngotracheal system. Supraglottic JV causes more laryngeal movement induced by
      disturbances through the high frequent inspiratory air passing the operating field compared
      to the subglottic jet ventilation. [9] Furthermore it leads to greater dryness of the vocal
      cords. During supraglottic SHFJV the escaping exhaled gases vent blood and secretion outward,
      reducing the risk of fluid aspiration and of displacing cells of any entity down to the
      tracheobronchial tree.

      Advantages of SHFJV with the supraglottic inserted steel laryngoscope:

        -  Unlimited surgical access and vision of the operating field

        -  Laser resistant

        -  Protection of the airway through the inherent 'auto-PEEP (positive endexpiratory
           pressure)' effect

        -  Prevention of CO2 retention, lung alveolar collapse and improvement of the oxygen index
           Subglottic LaserJet Catheter Through the LaserJet catheter ventilation is performed only
           with HFJV. It is characterized by the delivery of small tidal volumes from a high
           pressure jet at very high frequencies (100-400) followed by passive expiration for a
           very short period before delivering the next jet, creating an "auto-PEEP".

      The LaserJet catheter (C. Reiner Corp, Vienna, Austria) is made of polyterafluoroethylene and
      is non inflammable and provides a good micro anatomical overview of the operating structures
      [7,8,9] However, the LaserJet catheter is not laser resistant in regards of deformation
      damage (perforation) under direct exposure to a continuous laser beam. The use of the new 445
      nm wavelength laser, the 'blue laser' eases the surgical performance by securing important
      laryngeal functionality even in advanced disease [3,4,10] While the exposure of the complete
      pathology is visualized and treated, the surrounding tissue is not dislocated or deformed.

      [11] The LaserJet catheter has the advantage of minimizing movements of the larynx and vocal
      cords and facilitates the precise use of the blue laser without affecting healthy tissue.

      Electrical impedance tomography (EIT) When evaluating different JV devices and techniques,
      tidal volume and minute ventilation are difficult to assess because SHFJV and HFJV are
      applied in an open airway system. Air entrainment occurs to a varying extent depending on the
      route of JV administration, anatomical factors and jet alignment with the airway. [13] A
      standard intraoperative monitoring does not provide accurate predictions about changes in
      regional lung ventilation. The use of electrical impedance tomography (EIT) (SentecTom BB2,
      Landquart, Switzerland) allows the investigators to obtain a visual and quantitative
      representation of the areas of ventilation and aeration of the lung. The fundamental
      principle of lung EIT relies on the application of small alternating electrical currents into
      the thorax and voltage measurements using electrodes on the skin surface generating
      cross-sectional images representing impedance change in a slice of the thorax. It is a
      radiation-free imaging method which has the advantage to reveal real-time information.

      An array of electrodes (textile belt with 32 integrated electrocardiographic electrodes) has
      to be placed around the thorax to inject currents and to measure the resulting voltages on
      the thoracic surface. Analyzing EIT measurements during ongoing mechanical JV is a useful
      tool to detect imbalances in regional lung ventilation and in further consequence enables to
      optimize ventilator setting during surgery. The investigators will assess changes in regional
      lung ventilation distribution during supra- and subglottic JV compared to controlled mask
      ventilation. EIT, as a non-invasive method, may become a useful tool for adjustment of
      optimal positioning of the JV devices and for decision-making of the optimal type of the JV
      device (supraglottic laryngoscope versus subglottic jet catheter) by detecting atelectasis as
      "silent spaces" or over distension. This additional source of information could help fine
      tune the jet ventilator. Its intraoperative use could provide the basis for individual
      optimization of jet ventilator settings, especially in patients at risk for
      ventilation-perfusion mismatch and impaired gas exchange. Serological biomarkers of lung
      damage and inflammation It is still an open question whether the type of specific mechanical
      ventilation like HFJV and SHFJV have an influence on changes in serological biomarkers for
      lung damage and inflammation like Surfactant proteins (SP)-D [14-16], Krebs van den Lungen
      (KL)-6 [17, 18], Clara cell protein (CC16) [19, 20], Adrenomedullin (ADM) [21] or Interleukin
      6 (IL-6) and 8 (IL-8). Studies revealed that in patients with normal lungs, relatively short
      periods of mechanical ventilation induce lung inflammation and that these changes depend on
      the ventilatory parameters applied. [22-25] The investigators will study the influence of JV
      on these serum levels in patients undergoing elective laryngotracheal surgery. Specific aims
      and hypotheses The objective of this study is to compare regional ventilation distribution,
      blood gas oxygenation, CO2 elimination and serum biomarkers with different jet ventilatory
      techniques and access routes.

      Our primary aim is to determine whether supraglottic JV with the jet laryngoscope leads to a
      shift of the Center of Ventilation (COV) towards the ventral lungs compared to mask
      ventilation.

      The secondary objective of the study is to investigate changes in ventro-dorsal ventilation
      distribution, measured as ventro-dorsal COV shift, under subglottic JV compared to
      standardized, controlled mask ventilation. Further study objectives are the comparison of
      ventilation distribution parameters between the two JV techniques, supra- and subglottic JV,
      and the analysis of oxygenation and CO2 elimination during these two ventilation modes over
      time. Furthermore, special serum biomarkers of pulmonary lung damage are determined after JV
      application. Primary hypothesis The primary hypothesis is that during the use of supraglottic
      jet ventilation, the COV is shifted to more ventrally located (non-dependent) lung sections
      compared to controlled mask ventilation.

      Secondary hypothesis The secondary hypothesis is that subglottic JV ventilation leads to a
      ventral displacement of the COV compared to controlled mask ventilation and that this occurs
      to a greater extent than during supraglottic JV. Null hypothesis There is no significant
      displacement of COV into ventrally located lung sections under supraglottic jet ventilation
      compared to controlled mask ventilation.
    

Intervention name(s): EIT-measurement
Intervention type(s): Device
Intervention description(s): The use of electrical impedance tomography (EIT) (SentecTom BB2, Landquart, Switzerland) allows the investigators to obtain a visual and quantitative representation of the areas of ventilation and aeration of the lung. The fundamental principle of lung EIT relies on the application of small alternating electrical currents into the thorax and voltage measurements using electrodes on the skin surface generating cross-sectional images representing impedance change in a slice of the thorax. It is a radiation-free imaging method which has the advantage to reveal real-time information.
An array of electrodes (textile belt with 32 integrated electrocardiographic electrodes) has to be placed around the thorax to inject currents and to measure the resulting voltages on the thoracic surface.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Patients undergoing elective micro laryngeal surgery will be assigned to subglottic JV via the new LaserJet catheter and supraglottic JV via the jet laryngoscope vice versa. The sequence of JV modes will be randomized (subglottic followed by supraglottic or supraglottic followed by subglottic JV).
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: jet ventilation; electroimpedance tomography; supraglottic jet ventilation; subglottic jet ventilation