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Jet Ventilation - Principles

In this article, Dr Eleanor Pett, Airway Anaesthesia Fellow and Dr Catriona Ferguson, Consultant Anaesthetist at UCLH, Royal Nose, Throat and Ear Hospital discuss the principles of jet ventilation.

What is Jet Ventilation?

It is a mode of ventilation that uses intermittent, high-pressure jets of gas to deliver inspiratory gas flow and relies on passive expiration. The high-pressure jets can be delivered at low frequency (LFJV) or high frequency (HFJV). It is an advanced airway technique that carries the risk of significant morbidity and even mortality. It is therefore essential that jet ventilation is only performed by experienced clinicians who are familiar with the technique.

When is Jet Ventilation Used?

ENT surgery
Jet ventilation offers multiple benefits over conventional intermittent positive pressure ventilation (IPPV). It can provide the surgeon with a motionless, unobstructed view of the larynx without an endotracheal tube in the surgical field and reduces the risk of airway fire when laser surgery is performed.

Thoracic surgery
Jet ventilation has particular advantages for major conducting airway surgery like carinal resections and tracheal reconstructions. Bronchial and mediastinal excursion and movement is reduced using HFJV compared to conventional IPPV, and fine jet catheters can be passed through the operating field with little obstruction to the surgeon. Because HFJV, by necessity, is an open breathing system, the surgeon can open the trachea with no disruption to the distal delivery of gas.

During one-lung ventilation, HFJV can be applied to the non-dependent lung. The lung is held slightly distended with very minimal excursion and results in superior CO2 removal, oxygenation and shunt reduction compared to PEEP alone. In HFJV, there is an overall reduction in peak and mean airway pressure compared to conventional IPPV. This is useful in the management of bronchopleural fistulae, decreasing the gas leak through the pathological low resistance pathway.

Interventional Radiology
Where precision is paramount (e.g. during interventional procedures), the reduced thoracic and diaphragmatic movement of HFJV compared to conventional IPPV is advantageous.

Emergency airway access
In the emergency ‘can’t intubate, can’t oxygenate’ (CICO) scenario, a trans-tracheal cannula can be placed to deliver LFJV. It is imperative that an expiratory pathway is present and that complete expiration occurs between inspiratory jets to avoid the potential devastating consequences of barotrauma, including pneumothorax and sudden, complete right ventricular failure. It is worth noting that this is not the preferred technique of the Difficult Airway Society in the CICO scenario, whose latest guidelines advocate a surgical cricothyroidotomy.

Low Frequency Jet Ventilation

During LFJV a hand-held device (such as a Manujet or Sanders injector) is usually employed to deliver jets at a frequency of 8 – 10 min-1, with gas exchange primarily achieved by bulk flow in a manner similar to conventional IPPV. A high pressure gas source is needed to overcome the resistance of a narrow bore cannula, but the pressure changes in the trachea during LFJV are similar to conventional ventilation: normal tidal volumes at a relatively low frequency [1], [2]

Manual Jet Vent A Manujet Injector

The primary gas source is pipeline oxygen from wall outlets at 4 bar. This high pressure is then reduced by a series of valves and a regulator that can be adjusted on the handset. Finally, the trigger on the device is operated manually to achieve the desired frequency and chest wall expansion. The device connects to a cannula or bronchoscope/laryngoscope via tubing with a Luer Lock connector. The device is completely manually controlled with no inbuilt safety cut out or means of measuring airway pressures. Safe use relies on meticulous attention of the anaesthetist to ensure that a gas egress pathway exists at all times and that full expiration occurs before the next inspiratory jet is given.

jaw thrust Manujet connected to trans-tracheal cannula. Note that a jaw thrust is being performed to open the airway to create an expiratory pathway.

High Frequency Jet Ventilation

In HFJV high-pressure jets are delivered at supra-physiological frequencies, 60-600 min-1. The jets entrain atmospheric air. The tidal volumes generated are small, often less than the total dead space (anatomical and equipment). Therefore, whilst a minority of alveoli close to the conducting airways may be ventilated via bulk flow, other mechanisms must be at play to maintain effective gas exchange. Whilst detailed explanation of these mechanisms is outside the scope of this article, in brief they include:

  • laminar flow (in which a rapidly moving core of gas travels along the axis of the airway while gas in the margins moves out of the lung)
  • Taylor-type dispersion (enhanced molecular diffusion)
  • pendelluft ventilation (transfer of gas between lung units with different time constants)
  • cardiogenic mixing (mechanical agitation by the beating heart enhances gas exchange in neighboring lung tissue)

HFJV is performed using electrically powered ventilators. A high-frequency flow interrupter cuts continuous pipeline oxygen/air into square wave pressures, thereby generating rapid, discrete pulses of gas.

monsoon Automated Jet Ventilator

The operator can then use the display to alter the composition of the gas jet, driving pressure, frequency and inspiratory time. The pressure should be set just high enough so that chest movement is just visible with each jet delivered (typically between 0.5-2.5 bar).

In this video you can see the chest movements happening during HFJV.

High frequency jet ventilators can measure the pressure within the airways. High-pressure alarms can be set and ventilation automatically stopped (‘paused’) when pressure exceeds the pre-set limits. This ‘pause pressure’ significantly increases the safety profile of HFJV, reducing the risk of pressure-related complications. Newer ventilator models are also able to warm and humidify the gas jets.

Delivery Routes

Jet ventilation can be delivered at various points along the airway; supraglottic, subglottic and trans-tracheal.

Supraglottic jet ventilation:

In this technique, HFJV jet is delivered via a ‘needle’ attached to the surgical suspension laryngoscope.

Supraglottic jet ventilaton equipment
Supraglottic jet ventilaton equipment

Suspension laryngoscope in position
Suspension laryngoscope in position

Ventilation is dependent on the surgeon correctly aligning the jet with the glottic opening, and will be impaired by any obstruction to the glottis (e.g. by surgical swabs/instruments). The supraglottic jet may result in a small degree of vocal cord movement, and there is an inherent risk that debris could be blown into the trachea/bronchi. However, supraglottic jet ventilation facilitates a completely tube-free surgical field.

In this video, you can watch the set up for supraglottic HFJV.

Jet Ventilation can also administered via a tracheal tube or supraglottic airway device, connected to a special connector. Swivel connector, with arm for jet ventilator and anaesthetic circuit
Swivel connector, with arm for jet ventilator and anaesthetic circuit

Subglottic jet ventilation:

Jet ventilation catheters are narrow, non-flammable, laser resistant catheters that can be passed through the glottis. Two brands are in common use: the Hunsaker and the LaserJet catheter. They both have two lumens, enabling continuous CO2 monitoring whilst jetting occurs. They can be inserted using direct or video laryngoscopy.

Hunsaker basket in trachea Hunsaker basket in trachea

Patient with subglottic jet ventilation catheter in situ, attached to both CO2 sampling line and jet ventilator tubing
Patient with subglottic jet ventilation catheter in situ, attached to both CO2 sampling line and jet ventilator tubing

Unlike supraglottic ventilation, delivery of gas in subglottic ventilation doesn’t rely on surgical positioning of the suspension laryngoscope or visualisation of the glottis. Whilst this ensures delivery of inspiratory gas jets, an obstructed expiratory pathway will quickly lead to dangerously high intra-thoracic pressures. It is therefore imperative that an adequate expiratory pathway is established prior to commencing jet ventilation and that the pause pressure alarm on the high-frequency jet ventilator is appropriately set. Subglottic ventilation is not a tubeless technique, and whilst very narrow, jet ventilation catheters can block surgical access, especially to the posterior glottis.

Trans-tracheal jet ventilation

Jet ventilation catheters can be placed directly into the airway via a laryngectomy or tracheostomy stoma. In patients without pre-existing front of neck access, a range of cannulae exist designed for percutaneous insertion, e.g the Ravussin cannula.

Ravussin cannula attached to Luer Lock syringe

Insertion of trans-tracheal catheter

transtracheal JV Trans-tracheal cannula attached to jet ventilator tubing and CO2 sampling line via 3-way tap. Note the suspension laryngoscope maintaining expiratory pathway.

In this last video you can watch the insertion of trans-tracheal cannula for jet ventilation.

What do you think may be the risks associated with the use of jet ventilation? How would the team need to prepare for preventing and managing complications?

Move to the next step to read some tips from Dr Pett and Dr Ferguson.

References

  1. C Patel C, A Diba.
    Measuring tracheal airway pressures during transtracheal jet ventilation: an observational study. Anaesthesia. 2004 Mar;59(3):248-51
  2. TM Cook, JP Nolan, PT Magee, JH Cranshaw. Needle cricothyroidotomy. Anaesthesia. 2007 Mar;62(3):289-90; author reply 290-1

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This article is from the free online course:

Airway Matters

UCL (University College London)