The Role of Transtracheal Jet Ventilation

Abstract

Transcutaneous transtracheal jet ventilation (TTJV) is a minimally invasive ventilatory modality that uses a catheter to insufflate oxygen or air at high pressure (0.5–4.0 bar, or 8–60 psi) into the tracheal lumen. To perform TTJV, one can use an automatic jet ventilator or a manual trigger-activated device.

Appendices

Appendix: Approximate Measures of Pressure

$$ 1\;\mathrm{atm}\;(1\;\mathrm{bar}) = 1\;\mathrm{kg}/\mathrm{c}{{\mathrm{m}}^{2}}(1.033\;\mathrm{kg}/\mathrm{c}{{\mathrm{m}}^{2}}) = 100\;\mathrm{kPa}\;(101.3\;\mathrm{kPa}) = 15\;\mathrm{psi}\;(14.69\;\mathrm{psi}) = 1,000\;\mathrm{cm}\;{{\mathrm{H}}_{2}}\mathrm{O} = 760\;\mathrm{mmHg} $$

1 atm (1bar) = 1 kg/cm2 (1.033 kg/cm2) = 100 kPa (101.3 kPa) = 15 psi (14.69 psi) = 1000 cmH2O = 760 mmHg

Physiology and Mechanism of Action

Tidal volume (V _t), is the sum of the volume of the jet of gas (V _j) that is insufflated from the catheter and the volume of gas entrained by the venturi effect (V _e), minus the gas which escapes from the airway or “spilt volume” (V _s). So, V _t  =  (V _j  +  V _e)  −  V _s (see Figure 13.33).

Figure 13.33.

Schematic view of the trachea, lung, and transtracheal catheter during inspiration. V _j jet volume; V _e entrainment volume; V _s spilt volume or backflow gas.

Generally speaking, V _j increases as driving pressure increases. Manual ventilation at high pressure (>3 bar or 45 psi) using a 14 or 16G catheter can result in flows that exceed 500 cc/s.

V _e is generated by the gas flow that escapes from the catheter at high velocity. This results in negative tracheal pressure relative to the surrounding atmosphere (Venturi effect), which in turn “entrains” or drags adjacent gasses into the airway. V _e theoretically could add significantly to the volume of inspiration contributed by V _j, but in practice, aspiration and entrainment of gas are thought to be minimal with TTJV52.

V _s results from the increase in intrathoracic pressure that occurs as gas enters the chest during inspiration. This volume of gas is subtracted from the volume that reaches the respiratory tree (V _j  +  V _e) because ventilation occurs in a system that is open proximally. The more compliant the chest wall and/or the lungs, as well as the less resistance offered by the airway, the smaller V _s will be.

The inspiratory phase of TTJV occurs via insufflation of oxygen or air under pressure. Expiration is passive, a function of the elastic recoil of the lungs, pleura, and tracheal wall. Tidal volumes and peak inspiratory pressures observed during manual TTJV or LFJV are similar to those observed with intermittent positive pressure ventilation through an endotracheal tube. In contrast, HFJV administers low tidal volumes with lower corresponding peak inspiratory pressures than LFJV (see Figure 13.34).

Figure 13.34.

This chart shows the U-shaped relationship between frequency of jet insufflation and peak airway pressure (Paw), holding other variables constant. With low frequencies, Paw values are similar to those observed during conventional positive pressure ventilation. With higher frequencies Paw falls, but it increases again when frequency is extremely high.

Peak inspiratory pressure depends on various factors that are amenable to manipulation by the clinician’s adjustments to the jet ventilator. These include driving (or working) pressure and inspiratory time, which determine the volume insufflated with each triggering of the ventilator. This pressure is also determined by “fixed” patient and equipment related factors. These include the diameter of the trachea, the diameter and length of the catheter that one has inserted, any obstruction to efflux of gas from the airway, and, as with V _s, pulmonary and chest wall compliance. For example, the pediatric tracheal diameter is smaller than the adult and this predisposes children to having higher tracheal pressures.

The generation of auto-PEEP is often associated with insufficient expiratory time, a function of respiratory rate (see Figure 13.35) and I:E ratio, particularly if it coexists with tracheal, or proximal laryngeal stenosis that limits expiratory flow and gives rise to intrapulmonary gas entrapment. This situation predisposes patients to barotrauma and decreases systemic venous blood return to the heart17,53–55.

Figure 13.35.

This chart shows the relationship between frequency of jet insufflation and end-expiratory pressure (EEP), holding other variables constant. End-expiratory pressure (EEP) rises progressively with as frequency rises.

Maintaining One’s Skills

When a technique is not incorporated into one’s normal practice, it is very improbable that one will be able to employ it correctly in a situation with maximum risk, maximum urgency, and a great deal of psychological stress. In addition, TTJV is unsafe in inexpert hands. The need to resort to the cricothyroid approach is unusual, but it may save a life. Because we are authorized to induce apnea, we are also obliged to prepare ourselves to use TTJV to rescue patients if that becomes necessary.

The first set of recommendations concerns equipment. We must familiarize ourselves with the equipment described above, and have certified, not improvised ventilators, catheters, and tubing. Any ventilator must be equipped with a pressure regulator.

The second set of recommendations relates to training. Airway managers should arrange regular practice, timing the procedure and noting any failures or obstacles to mastering the procedure that arise. We must also bear in mind that procedural skills decay with the passage of time56,57 so that any skills gained in practice must be periodically refreshed. To this end, training may be carried out in a variety of airway models, including manikins58, improvised laryngotracheal simulators, pig or goat tracheas, or in the best existing model: human cadavers59.

The third set of recommendations concerns different ways to maintain one’s skills by performing related procedures when indicated. Patients who are to be intubated awake benefit from transcricoid administration of local anesthetic. Anesthesiologists and other airway managers often have the opportunity to assist surgeons during OR tracheotomies, particularly when it is not emergent. Finally, in the ICU or PACU, there are frequent opportunities to practice the tracheal approach by performing dilatational tracheostomy.

The fourth set of recommendations is the most accessible of all: routinely practice identifying the anatomic structures of the anterior neck. During the preoperative airway assessment, or even before performing intubation in the ICU or ED, we typically acquaint ourselves with the anatomy that we will soon manage, becoming familiar with any difficulties that may present themselves. Identifying the landmarks relevant to TTJV and to cricothyroidotomy will make us that much more ready to act in the event that we need to perform these life-saving procedures.