In this series of 21 patients with various lung comorbidities undergoing laryngo-tracheal surgery for different indications, we show that Tritube in combination with FCV provides good surgical conditions and adequate gas exchange at relatively low minute volumes and global alveolar driving pressures. Our results are in line with earlier publications and suggest this technique to be feasible even in patients with compromised lung mechanics.
Current strategies for airway management during upper airway surgery often require the acceptance of risks related to anesthetic and/or surgical considerations. In contrast, the use of FCV delivered by Tritube may preserve surgical view, while allowing airway protection and adequate gas exchange. First, in our patients, the small OD of Tritube (4.4 mm) allowed easy intubation, even in case of tracheal stenosis, and a spacious working field for the surgeon. Second, no aspiration event occurred, thus minimizing the risk of aspiration pneumonia and atelectasis and aiding in achieving a clean surgical environment. Third, no passive backflow of gases occurred, hence reducing aerosol spread and improved surgical view. This last advantage was recognized by experts in the field of airway management, who recently published recommendations aiming at minimizing the risk of aerosol spread in the setting of upper airway surgery during the COVID-19 pandemic [2]. Furthermore, according to the recent description of surgical tracheotomy using Tritube and FCV, these techniques could increase the safety of patients and medical personnel by avoiding the need for cumbersome cross-field intubations and reducing the aerosol generation, respectively [33]. Fourth, Tritube may be less rigid and traumatic than laser-resistant tubes. While laser resistance is not claimed for Tritube by the manufacturer, we did use it during laser surgery by protecting the cuff with saline-soaked gauze as described earlier [20, 28], which, being located distally to the lesion, did not compromise the surgical exposure. The FiO2 could be easily reduced to 0.3 or lower in our patients.
The practical advantages of Tritube with respect to airway management and surgical conditions are combined with several ventilation benefits.
First, when compared to VCV or PCV, the relatively low and constant inspiratory and expiratory flow during FCV may result in more homogenous lung aeration and recruitment, better gas exchange, and higher ventilation efficiency [15, 29, 34,35,36,37,38]. Moreover, as compared with HFJV, FCV reduces the risk of air-trapping, hyperinflation, and associated barotrauma [28, 39, 40].
Second, since Tritube enables intratracheal pressure measurements and Evone utilizes mass flow controllers, respiratory system mechanics can be precisely determined [41, 42]. This offers the possibility to individually titrate applied flow and pressure based on the dynamic compliance of the patient’s respiratory system [16, 43]. This approach might reduce driving pressure, i.e., the difference between plateau pressure and positive end-expiratory pressure and mechanical power, i.e., the total energy transferred from the mechanical ventilator to the lungs during inflation [17, 42]. In our study, we observed adequate gas exchange and acceptable driving pressures in all patients, except for a post-COVID-19 patient (patient #3) with severely impaired respiratory system mechanics. In this patient, a very high global alveolar driving pressure (23 cmH2O) was required to achieve acceptable oxygenation and normocapnia, while using a minute volume of only 7.4 L/min. In a patient with COVID-19 acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU), Spraider et al. recently found FCV to improve oxygenation, as compared to PCV, while reducing the applied energy of ventilation [43]. Recently, in a small crossover study in 10 patients with COVID-19 ARDS, our group found lower mechanical power and higher ventilation efficiency during FCV compared to VCV [44]. Another recent crossover study comparing FCV with VCV also observed improved ventilation efficiency by FCV [45].
Our study has some limitations. First, the small sample size of our retrospective single-center case series makes our findings exploratory and hypothesis-generating. Importantly, we did not compare FCV delivered by Tritube with other airway management strategies in our patients. Further prospective comparative studies with larger sample sizes are needed to confirm our findings. Second, the achievement of adequate gas exchange could not be confirmed by arterial blood gas analyses, as invasive arterial pressure was not part of our routine intraoperative monitoring. Third, no quantitative assessment of surgical exposure was reported nor imaging aiming at evaluating lung aeration was performed. Fourth, this series of cases was performed by one anesthesiologist (AG), who has 15 years of experience, of which many in airway surgery procedures. The determination of a learning curve was out of scope of this study. Though, in order to gain adequate confidence with the technique, we suggest a minimum of 10 supervised operations.
Some limitations pertaining to FCV and Tritube should also be addressed.
First, FCV represents a novel ventilator mode, requiring specific training.
Second, training is also recommended for the management of Tritube. The small ID of Tritube makes it more susceptible to obstruction by secretions, which may affect or even interrupt ventilation. Therefore, a “plan B” (e.g., hand-held ventilator Ventrain) is always needed, but proper preparation on the forehand can significantly reduce the risk on obstructions. First, it is important to judge on the probability of secretions (e.g., COPD, secretion retention due to obstruction) and to remove these where possible by asking the patient to cough before anesthetizing and to suck away secretions before intubation. Others described to administer glycopyrronium to reduce mucosal secretions [28]. During intubation, Tritube is advanced from its stylet further down the trachea while turning. When the tube is at the right position, it should be slightly pulled back before inflating the cuff to free Tritube’s tip from the tracheal wall. Then, one can flush both the ventilation lumen and pressure lumen with air to ensure the absence of any obstructions. Upon starting FCV ventilation, the machine will also perform a purge with air automatically. During ventilation, irregular pressure curves may indicate the presence of secretions (but may also result from light anesthesia or mispositioning of Tritube). An altered shape of the pressure curve without any other explanation may be solved by flushing the pressure and ventilation lumens using 2–5 cc of saline followed by 15 cc of air. Should the issue persist, one may consider to use the suction catheter to remove secretions from the ventilation lumen after deflating the cuff should be deflated. As mentioned, a mispositioning of Tritube may also affect the shape of the pressure curve. The tube is 45 cm long and may touch the carina or migrate into a bronchus because of surgical manipulations. Furthermore, the higher flexibility of Tritube, when compared to reinforced laser-resistant tubes, makes it more prone to compression during suspension laryngoscopy. Complete obstruction of one of the lumens will be detected by the ventilator, that responds by alarming while purging the lumens. Also, one may use the Jet ventilation mode to purge away an obstruction with a deflated cuff.
Third, as mentioned earlier, Tritube is not laser-safe and its use during laser surgery is not intended by the manufacturer. Indeed, we report the Tritube’s cuff damage during one case. However, given its small OD and the resulting unimpeded surgical view, no complications during laser surgery have been reported by other authors, provided that FiO2 is lowered and the tube and/or its cuff are covered with a wet gauze [20, 28].
Fourth, patients ventilated with FCV should be kept under TIVA with muscle relaxation throughout the procedure to avoid spontaneous breathing efforts and coughing, which may lead to Tritube dislocation and interruption of ventilation [30].