Jet Ventilation - Safety Aspects
In this article Dr Eleanor Pett and Dr Catriona Ferguson continue their exploration of jet ventilation and will now discuss safety aspects of the technique as well as sharing their top tips when using it.
Complications of Jet Ventilation
Complications are mainly due to an increase in airway pressure leading to:
- Subcutaneous emphysema
- Right heart failure
- Mucosal trauma
- Necrotising tracheo-bronchitis
- Airway soiling
Practicalities, hints, tips and pitfalls!
Jet ventilation in the CT scanner
The decision to use jet ventilation should be discussed with the whole theatre team at the team brief. All necessary equipment should be checked and a back up airway plan should be made.
Anaesthesia and paralysis
Total intravenous anaesthesia (TIVA) is the obvious anaesthetic technique of choice, uncoupling ventilation from anaesthesia. Ensure that the patient is adequately paralysed.
After induction, a supraglottic airway device or high flow nasal oxygen can be used to oxygenate the patient until the surgeon is ready to insert the suspension laryngoscope.
Although some high frequency jet ventilators can warm and humidify the gas jet, this is not always the case. Patients can lose heat very quickly from the cold dry gas jets causing rapid evaporation and heat loss. Ensure all patients are warmed with a hot air blanket, even for short procedures. Give nebulized saline in the recovery room to compensate for the drying effect of the jet ventilation.
Be mindful of CO2
During supraglottic jet ventilation CO2 measurement is not possible. Subglottic HFJV catheters do have a lumen that can facilitate capnography, although in such an open system, with high flows and small tidal volumes, the reading will not reflect the true arterial CO2. One solution is to temporarily interrupt jet ventilation and physically compress the chest to cause a tidal expiration. Alternatively jet ventilation can be paused to deliver a standard tidal volume inflation. Other means of monitoring CO2 include transcutaneous CO2 monitoring and arterial sampling. In the event of hypercapnia, reducing the inspiratory time and frequency will increase the time available for passive expiration and therefore may help. Equally increasing the driving pressure may also improve the CO2 clearance by increasing the tidal volume.
Desaturation: what to do?
Ensure that the jet catheter is in the correct position. If supraglottic jetting, ensure that the surgeon has the jet needle on the suspension laryngoscope optimally aligned with the glottic opening and that there is no obstruction to the jet’s path. Increasing the oxygen fraction of the jet may help, although bear in mind that this will not be the fraction delivered to the patient due to the significant entrainment of atmospheric gas that occurs. With this in mind, applying nasal oxygen will increase the oxygen fraction of the entrained gas and increase the oxygen fraction delivered to the patient. Positioning the patient in a reverse Trendelenberg position may help to improve chest wall compliance, as will ensuring the patient is adequately paralysed. Finally a cautious increase in the driving pressure will increase the tidal volume and hopefully improve oxygenation. If desaturation is still a problem, then it may be necessary to resort to alternating periods of jet ventilation with traditional IPPV.
Always ensure there’s an adequate expiratory pathway
Without a gas egress pathway, intrathoracic pressure can climb extremely quickly. For this reason, it is paramount that complete expiratory excursion occurs after each jet, and that when using a high frequency jet ventilator the pause pressure is appropriately set.
Are you experienced in using jet ventilation? Do you feel comfortable with the technique? How do you ensure the patient remains safe? Please do discuss how you use jet ventilation in the comments section before you move onto the next step to learn about the use of LASER in airway surgery.