| Indications for jet ventilation |
| Elective airway or thoracic surgery |
| Elective vocal cord surgery |
| Elective use in the anticipated difficult airway |
| Emergency use via trans-tracheal cannula |
| Application to non-dependent lung in one-lung ventilation |
Jet Ventilation
Jet Ventilation
This topic fulfils the curriculum requirement to 'recall/explain the principles of jet ventilation'.
Resources
- Both manual jet ventilation and high-frequency jet ventilation (HFJV) are modes of high-pressure source ventilation
- HFJV is a specialised ventilation modality designed to achieve gas exchange via high-frequency, low tidal volume breaths
Manual jet ventilation
- Manual jet ventilation be achieved by using:
- Sanders-type injector: fixed 4atm pressure
- Manujet device: controlled 0 - 4atm pressure
- The lowest driving pressure should be used to limit pressure-related complications
- The devices lack the ability to monitor airway pressure or EtCO2
Automated jet ventilation
- HFJV may be achieved with devices such as the Monsoon or Mistral devices
- HFJV devices are generally superior, as they include:
- FiO2 control
- EtCO2 measurement
- Airway pressure monitoring with automatic cessation if it is escalating beyond set limits
- Potential for humidification
- Ability to alter driving pressure
- Ability to alter ventilatory frequency
| Advantages of HFJV | Disadvantages of HFJV |
| Reduced Ppeak | Barotrauma and its sequelae |
| Reduced haemodynamic compromise (vs. IPPV) | Malposition of the catheter can cause gastric distension ± rupture, or dysrhythmia |
| Good in low-resistance but large-volume airway leak | Inadequate gas exchange (hypoxia, hypercapnoea), especially if restrictive lung disease |
| Improved visibility / surgical field access | Risk of necrotising tracheo-bronchitis (and increased risk of NEC in neonates) |
| No fuel for ignition during LASER surgery | Potential for airway soiling |
| Life-saving manoeuvre in CICO situation | Inhalational anaesthesia impractical, or contaminates operating theatre air if used |
| EtCO2 monitoring only intermittent | |
| Airway pressure measurements may be unreliable | |
| High gas flow required |
- High frequency jet streams are generated
- These entrain air at the jet nozzle via the Venturi principle
Gas exchange
- Gas exchange does not depend primarily on bulk flow of gas to the alveoli, as tidal volumes are less than dead space volume
- Gas exchange instead occurs due to:
- Pendelluft ventilation - Movement of gas between lung units with different time constants
- Enhanced molecular diffusion - Enhanced kinetic activity of gas molecules increases their diffusion across the alveolocapillary membrane
- Cardiogenic mixing - Cardiogenic oscillations are transmitted through the lung parenchyma, which augments gas mixing
- Co-axial flow - Gas inflow is confined to the centre of the airway, while outflow occurs circumferentially along the periphery
Supraglottic
- Allows a fully tubeless surgical field
- Can be provided by a rigid bronchoscope with jet ventilator attachment
- Issues:
- Requires surgeon to maintain airway patency whilst concurrently operating
- Quality of ventilation dependent on alignment of jet and airway
- Safety features including airway pressure and EtCO2 monitoring are not reliable
- Rapid increase in airway pressures can occur due to entrainment of air via the Venturi effect at the glottis
Subglottic
- Trans-glottic catheters tend to be LASER-resistant, narrow-bore (external diameter ∽4mm) catheters
- The trans-glottic approach confers several benefits, including:
- Minimal vocal cord displacement as ventilation occurs below the glottis
- Expiratory flow displaces blood/debris outwards (rather than into tracheo-bronchial tree)
- Minimal air entrainment and therefore more consistent FiO2
- Better monitoring of airway pressure and EtCO2
- Risks include tracheal mucosal trauma, either from the jet stream or 'baskets' on the catheters designed to maintain their position within the trachea
Transtracheal
- The trans-tracheal approach benefits from not relying on adequate/unimpeded oral access to the glottis
- A cricothyroid cannula is sited either awake or under GA
- Tidal volume target is 1 - 3ml/kg
- Adjustable settings include:
- Driving pressure: 0.3-3 Bar (= 30-300kPa, or 300-3,000cmH2O)
- Ventilation frequency: typically 1-10Hz (60-600 impulses/minute)
- Inspiratory time
- FiO2
- Responses to adjustments in settings are different to standard ventilation, and counter-intuitive
- E.g. increased ventilation frequency will worsen CO2 by impeding passive exhalation
Hypercapnoea
- If there is hypercapnoea and air trapping, it is recommended to reduce the ventilatory rate
- If there is hypercapnoea without air trapping, increasing the driving pressure will increase tidal volumes and alveolar ventilation
- Increasing the expiratory time will not improve CO2 clearance in the absence of gas trapping
Hypoxia
- Increase the FiO2
- Increasing the inspiratory time will improve oxygenation, though may impair passive exhalation and cause hypercapnoea
- Barotrauma
- Hypercapnoea
- Gas trapping
- Hypoxia