Safety application of muscle relaxants and the traditional low-frequency ventilation during the flexible or rigid bronchoscopy in patients with central airway obstruction: a retrospective observational study

The quality of life of the patients is seriously impaired by severe CAO presented as severe dyspnea, stridor, or even respiratory failure. CAO is a potentially life-threatening condition, which has been treated in many ways [1, 2]. For patients amenable to surgery, resection and reconstruction is the best therapeutic option. However, whenever surgery is not feasible, endoscopic therapies are needed [3, 4].

Nowadays, endoscopic treatment has been widely used as an effective method to treat CAO, palliating dyspnea in some cases of malignant obstruction and even be curative in some cases of benign tumor or inflammation [5‐7]. Such procedures are mainly performed using rigid or flexible bronchoscope.

These interventions are high-risky procedures, posing a giant challenge to the anesthesiologists. How to establish adequate gas exchange to maintain the life of patients and allow good surgical access is what should be considered during anesthesia [6, 8]. Furthermore, the choice of ventilation strategy and the use of skeletal muscle relaxants are still significant issues for anesthesiologists to consider.

In this article, we summarized and analyzed our clinical experience in anesthesia management in patients with CAO undergoing flexible or rigid bronchoscopy in general anesthesia from January 2016 to October 2019, including the use of muscle relaxants and the traditional Low-frequency ventilation, to estimate the safety of skeletal muscle relaxants application and the traditional Low-frequency ventilation.

Central airway stenosis is known worldwide as a life-threatening condition with many causes [9‐11]. In this study, we retrospectively reviewed 375 cases with CAO undergoing bronchoscopy with general anesthesia. The causes of CAO were primary tracheal tumors or lung cancer, esophageal cancer, scarring after tracheotomy, post-placement of stenting, mediastinal tumor, pulmonary metastatic tumor, and tracheomalacia etc.. As complications of these diseases, tracheal stenosis can be treated in many ways. Surgery may be the preferred approach, but not all patients are appropriate surgical candidates [4]. Therefore, bronchoscopy treatment remains the best tool for the safest management of airway obstructions, and provides prompt and durable palliation to patients ineligible for surgical treatment [3, 7, 12, 13].

Both rigid and flexible bronchoscopy are now available for the interventional pulmonologists to perform this operation for advanced diagnostic and therapeutic purposes. Flexible bronchoscopy was performed through a laryngeal mask airway or endotracheal tube, which can create auto positive end expiratory pressure and alter airway mechanics with a minimum of sedation. Rigid bronchoscopy relies on the use of a laryngoscope and either a rigid ventilating bronchoscope or Hopkins rod telescope, which can alter the airway by stenting the airway open, and often requires a deeper level of sedation [14]. There are some debates as which one is better than the other, and whether the use of muscle relaxants is safe and indispensable in this procedure [15‐20]. In some articles, the authors are in favor of the non-use of muscle relaxants in rigid or flexible bronchoscopy for the safe factor [17, 21], but a recent research showed that controlled ventilation with muscle relaxants during stenting reduced the incidence of desaturation events, maintaining a favorable respiratory status [22]. A rigid bronchoscope can be placed under deep sedation without muscle relaxants, but that required high doses of analgesic and hypnotic agents, which may lead to cardiovascular instability or residual drug effects harming pulmonary function after the operation, and if the depth of anesthesia is not enough, it may causes the trauma of the vocal cords and larynx, even accidental airway perforation, due to the significant response to tracheal manipulation. The use of topical anesthetics is recommended by the ACCP (American College of Chest Physicians) for both basic and advanced bronchoscopy as it reduces the dose of sedative agents needed and effectively decreases cough [23]. Tracheal reflexes are blunted by incorporating a ‘spray-as-you-go’ technique of topical lidocaine spray via the working channel of the bronchoscope [24]. The use of local anesthetics also can be observed in our research, but with the administration of muscle relaxants, which can provide good surgical conditions, the frequency and dose of local anesthetics were not so high.

In our research, we have observed that the use of muscle relaxants can facilitate the placement of rigid bronchoscope, ensure vocal cord adduction, and prevent life-threatening patient moving and coughing during the procedure, thus to provide the best operating conditions. Although SGA (supraglottic airway) insertion itself may not necessitate muscle paralysis, paralyzed vocal cords facilitates bronchoscopy in adduction position. Furthermore, muscle paralysis could attenuate the risk of patient’s coughing and movements during the operation, as well as lower the chest wall resistance and reduce inspiratory pressures needed to achieve satisfactory tidal volumes [25‐28]. At the beginning, we also did not dare to use muscle relaxants, but with the improvement of anesthesia equipment, visual technology, and anesthesia skills, we began to experiment with muscle relaxants. Approximately 96.5% of the 375 included patients were given skeletal muscle relaxants as recorded in the anesthesia notes, no patients suffered the failure of ventilation, bronchospasm or cough, only 13 patients (8 in flexible, 5 in rigid) suffered the hypoxemia during the procedure, and two patients (0.05%) were reintubated after awakening due to dyspnea after extubating (sent to ICU after adjusting the position of the bracket). In addition, the dosages of muscle relaxants used in rigid bronchoscopy are significantly higher than those used in the flexible bronchoscopy due to the higher degree of irritation, but that didn’t affect the patient’s awakening. The results may illustrate that the muscle relaxants can be safely used both in flexible and rigid bronchoscopy treatments in patients with CAO, and more dose of muscle relaxants should be given in rigid bronchoscopy treatments.

In this process, the way of mechanical ventilation is also a key factor affecting gas exchange for the patients with CAO undergoing flexible or rigid bronchoscopy treatments. In the past years, high-frequency jet ventilation had become the main ventilation method for bronchoscopy in the treatment of central airway stenosis [29]. A previous study has demonstrated no difference in arterial blood gas analysis values between jet ventilation and conventional ventilation during endobronchial laser surgery, yet jet ventilation may be associated with some complications including hypertension, hypoxemia, hypercapnia, and barotrauma [23]. In this study, the traditional Low-frequency ventilation was used in all patients with CAO. We compared ETCO₂, PaCO₂ and PaO₂ between the flexible and rigid bronchoscopy group to assess whether traditional ventilation can provide adequate ventilation. Many patients with CAO already had hypoxia before surgery, and even 98.4% of the patients experienced symptoms of dyspnea [30]. Therefore, most of them inhaled oxygen when they entered the operating room for emergency bronchoscopy surgery. The SpO₂ value of most patients was between 93 and 100%, which couldn’t reflect the true hypoxia. In addition, hypoxemia and hypercapnia may commonly occur during bronchoscopic procedures. During the procedure, we noticed SpO₂ decreased in some patients, despite fraction of inspired oxygen (FIO₂) being kept at 100%, but no patient suffered severe hypoxemia or hypercapnia. For patients undergoing some transient episodes of SpO₂ lowering below 90%, high fresh gas flows are often used to obtain adequate ventilation and compensate for the airway leakage. If it didn’t work, we would remove the placed bronchoscope and then ventilate the patient for several minutes until SpO₂ increased to above 95%, then restart the procedure. PaCO₂ values were significantly higher than preoperative level in both groups, and most patients suffered hypercapnia during the operation (PaCO₂ > 45 mmHg), but there was no correlation between the operation time and EtCO₂ or PaCO₂ after the procedure both in the flexible group and rigid bronchoscopy group. Different from hypoxemia, hypercarbia is generally well tolerated unless severe enough (above 80 to 100 mmHg) to cause obtundation and respiratory arrest, and moderate hypercarbia may be a favorable condition in a number of pathologic situations [31]. Intraoperative hypercapnia caused by insufficient ventilation can be adjusted by hyperventilation soon after the operation completed. So in this study, there was no obvious life-threatening hypercapnia occurred. The results may show that the Low-frequency traditional ventilation also can meet the adequacy of ventilation and gas exchange in patients with CAO undergoing bronchoscopy therapy. Since some cases have been excluded in our study due to the possible advantages of using HFJV in these cases, including bronchopleural, bronchoesophageal and bronchomediastinal fistulae, we still don’t recommend the routine use of jet ventilation in the procedures described.

In this study, most of the patients with CAO who underwent bronchoscopy therapy were safely transferred to the ward (86.7%), while the others were sent to ICU postoperatively due to their poor general condition. Variables identified as increased complication rate predictors for therapeutic bronchoscopy (including both rigid and flexible) include: emergent procedures, ASA physical status scores [23]. We revealed that the grade of ASA and obvious dyspnea or orthopnea were the independent risk factors for postoperative ICU admission. Therefore, ICU admission may be a safe option when an urgent bronchoscopy is carried out in patients with severe dyspnea, or with high ASA scores. Three deaths (2 due to hemoptysis and 1 due to acute myocardial infarction) occurred during the procedures or within 48 h postoperatively, with a mortality rate of 0.8%. The causes of these three deaths were not directly related to the procedures even though they occurred in the perioperative period. The rest of the patients (99.2%) recovered without incidents in the recovery room in the immediate postoperative period.

There are still some limitations in our study. Firstly, we did not have a blank control group to compare the procedures performed without muscle relaxants. Secondly, a lot of blood gas data were missing from the data during the operation. And thirdly, there was a lack of studies investigating the optimal dosages of muscle relaxants, we will design some prospective researches in the future.

The muscle relaxants and low-frequency traditional ventilation can be safely used both in flexible and rigid bronchoscopy treatment in patients with central airway obstruction. Given the rise in the interventional therapy, bronchoscopy treatments of CAO under general anesthesia may turn more frequent in the coming future, and this research may provide a safe anesthesia management option for its implementation.