Transtracheal oxygenation may be lifesaving in “cannot intubate/cannot ventilate” patients. The French Society of Anesthesiologists has recently published updated guidelines for difficult airway management and recommends the use of dedicated devices for transtracheal oxygen delivery.1 Two devices are available, the ENK Oxygen Flow Modulator™ (ENK) and the Manujet™. Both have been studied in a pig model.2 Both maintain oxygenation, but the ENK seemed to achieve better ventilation because of a continuous flow that provides CO2 washout between insufflations. Very little is known concerning the lung pressures generated with these 2 devices.3 Because it is technically impossible to assess these variables in clinical situations, we conducted this study in an artificial lung to characterize these 2 devices in terms of oxygen flow, tidal volumes, and airway pressures.
The Manujet III™ jet ventilator (VBM®; Vitrolles, France) was connected to a 4-bar oxygen source and the driving pressure was set at 3 bar. Manual activation of the trigger delivered oxygen to a transtracheal catheter. The ENK Oxygen Flow Modulator™ (COOK®, Charenton, France) was connected to an oxygen wall flow regulator set at 15 L/min. Oxygen was delivered when the 5 holes in the ENK's perforated tube were manually occluded.
The 2 devices were evaluated by connecting them to a 15-gauge (2-mm internal diameter, 75-mm length) wire reinforced transtracheal catheter (COOK). The catheter was inserted into the simulated trachea, a 15-cm ringed tube (Intersurgical, Fontenay sous Bois, France) occluded at one end by a plastic cork. The other end of the tube was connected to an IMT Medical Flow Analyzer PF-300™ (IMT Medical®, Buchs, Switzerland) to measure flow rate, tidal volume, peak pressure, mean pressure, and positive end-expiratory pressure. An adult SmartLung™ (IMT Medical) was connected to the analyzer output. The SmartLung settings were as follows: total lung volume = 1000 mL; airway resistance = 5 mbar/L/s; and lung compliance = 30 mbar/mL (Fig. 1).
Two investigators manually delivered 1-second insufflations for 3 minutes at the rate of 4 breaths/min and 12 breaths/min with the plastic cork in place, simulating total upper airway obstruction, and after making a 2-mm hole in the plastic cork, simulating partial upper airway obstruction. A metronome was used to keep the rate and the duration of the insufflations constant. Data were recorded for 3 minutes with an insufflation rate of 4 breaths/min with the Manujet driving pressure set at 0.5, 1.0, 1.5, 2.0, 2.5, and 3 bar. The SmartLung was removed and the gas flow delivery rates were recorded without insufflations (0 breaths/min).
All of the variables were sampled and recorded every 10 milliseconds using Flowlab™ software and transferred to a personal computer as Excel™ files. Statistical analysis was performed using StatPlus® software (AnalystSoft, StatPlus Mac, Version 2008; http://www.analystsoft.com/fr). Continuous data were expressed as the mean ± SD. Data were analyzed using analysis of variance followed by a Fisher exact test. P < 0.05 was considered significant.
The mean duration of the manually delivered insufflations was 1.01 ± 0.06 second at 4 breaths/min and 0.95 ± 0.05 second at 12 breaths/min for the ENK, and 0.97 ± 0.08 second at 4 breaths/min and 0.95 ± 0.08 second at 12 breaths/min for the Manujet. During insufflations, peak flow was 36.0 ± 6.3 L · min−1 with the Manujet and 13.7 ± 2.42 L · min−1 with the ENK. When holes were not occluded, the ENK delivered oxygen at the rate of 0.7 ± 0.1 L · min−1.
Table 1 shows the airway pressure delivered by the ENK during total airway occlusion. With the Manujet, airway pressure was 34 cm H2O after the first insufflation and 136 cm H2O after the second, therefore the experiment was stopped. During total airway occlusion, airway pressures were significantly lower with the ENK.
Table 2 shows tidal volumes, minute volumes, and mean and peak airway pressures during partial upper airway obstruction. Values were significantly higher with the Manujet. Table 3 shows how the Manujet gas flows and tidal volumes increased with an increase in driving pressure.
The Manujet delivers oxygen at a higher peak flow rate than the ENK. As a result, 1-second insufflations with the Manujet result in larger tidal and minute volumes and higher airway pressures than with the ENK. Our results confirm the results of Flint et al.3 The tidal volumes we measured for the Manujet (650 mL) are close to those calculated from the minute volumes reported by Flint et al.3 (627 mL). For the ENK, we measured a 240-mL tidal volume, whereas Flint et al. measured a 156-mL tidal volume. This discrepancy may be explained by the differences in both the model and the methodologies used in the 2 studies.
Yildiz et al.4 found that the oxygen that flows from the ENK between manual insufflations enhances oxygenation, especially at low respiratory rates. Preussler et al.2 found that the constant flow improves CO2 elimination. Because the Manujet generates higher airway pressure, it may result in better alveolar recruitment and better lung ventilation. Both investigators found that decreasing the Manujet driving pressure allows it to deliver higher respiratory rates without excessive airway pressure.2,4
Because the main risk of transtracheal oxygenation is barotrauma, the Manujet should not be used in case of total upper airway obstruction. The ENK seems to be less problematic because it delivers gas at a lower pressure and has a pressure release vent that allows gas to escape between insufflations.5 However, even with the ENK, the peak and mean airway pressures may reach dangerously high levels at high respiratory rates (12 breaths/min) during total airway obstruction. Increasing the respiratory rate results in short expiratory times and, as a consequence, an increase in the volume of the gas trapped in the lung. Our results confirm the absolute necessity of ensuring that the insufflated gas is exhaled during the expiratory period.6 Sufficient exhalation can easily be checked by watching the chest fall before delivering a second tidal volume.
When using the Manujet during partial upper airway obstruction, great attention should be given to delivering insufflations that last <1 second and using low respiratory rates, to avoid excessive airway pressure. The most important goal is to deliver oxygen to the lung, as recommended by Cook and Alexander.7
1. Combes X, Pean D, Lenfant F, Francon D, Marciniak B, Legras A. Difficult airway management devices: establishment and maintenance—question 4. Societe Francaise d'Anesthesie et de Reanimation. Ann Fr Anesth Reanim 2008; 27: 33–40
2. Preussler NP, Schreiber T, Huter L, Gottschall R, Schubert H, Rek H, Karzai W, Schwarzkopf K. Percutaneous transtracheal ventilation: effects of a new oxygen flow modulator on oxygenation and ventilation in pigs compared with a hand triggered emergency jet injector. Resuscitation 2003; 56: 329–33
3. Flint NJ, Russell WC, Thompson JP. Comparison of different methods of ventilation via cannula cricothyroidotomy in a trachea-lung model. Br J Anaesth 2009; 103: 891–5
4. Yildiz Y, Preussler NP, Schreiber T, Hueter L, Gaser E, Schubert H, Gottschalll R, Schwarzkopf K. Percutaneous transtracheal emergency ventilation during respiratory arrest: comparison of the oxygen flow modulator with a hand-triggered emergency jet injector in an animal model. Am J Emerg Med 2006; 24: 455–9
5. Hamaekers A, Borg P, Enk D. The importance of flow and pressure release in emergency jet ventilation devices. Paediatr Anaesth 2009; 19: 452–7
6. Bourgain JL, Desruennes E, Fischler M, Ravussin P. Transtracheal high frequency jet ventilation for endoscopic airway surgery: a multicentre study. Br J Anaesth 2001; 87: 870–7
7. Cook TM, Alexander R. Major complications during anaesthesia for elective laryngeal surgery in the UK: a national survey of the use of high-pressure source ventilation. Br J Anaesth 2008; 101: 266–72