In this study, we found that both ultrasound-guided SLN block combined with transtracheal injection and spray-as-you-go airway topical anesthesia can effectively attenuate cardiovascular responses to DLT tracheal intubation and stabilize hemodynamics. Compared to the FIS group, there was no advantage in ultrasound group. Due to the need for ultrasound equipment and there is a risk of bleeding risks and corresponding contraindications for the invasive operation.
The SLN block can effectively inhibit the sensory nerves of the throat and tongue mucosa. This block effectively reduces the adverse irritation caused by the laryngoscope during intubation and the strong stimulation of the DLT in the throat. The success of SLN block requires accurate anatomical positioning and skilled puncture skills particularly in patients that are obese or have abnormal neck anatomy which increases the difficulty of the block its rate of success. The application of ultrasound in the nerve block improves nerve positioning and guides the injection of puncture needles to effectively improve the success rate of the block.
In this study, the patients experienced abnormal sensations in the base of the tongue and throat after receiving a bilateral SLN block. At the same time, the cough response to transtracheal injection is partially relieved . transtracheal injection is a classic method of intratracheal mucosal anesthesia and is also an effective technique commonly used for conscious intubation . One of the key points of transtracheal injection is accurate positioning. According to previous studies, the success rate of the empirical blind method in locating the cricothyroid membrane is less than 50% and even lower for obese patients. In contrast, the accuracy of ultrasound-assisted positioning can be increased to 100% [20–22]. We used ultrasound positioning to guide the puncture needle to break through the cricothyroid membrane and then draw back air to confirm the success of the puncture. After injecting topical anesthesia, patients often have obvious coughing which is conducive to the spread of liquid in the airway. The SLN block combined with transtracheal injection can improve the anesthetic effect during conscious intubation .
This study confirmed that this method can be used to reduce the stress response of DLT tracheal intubation and stabilize the hemodynamic effects in patients during intubation. The blood pressure and heart rate of the patients remained stable 1 min after intubation and during the stimulation process of body position changes.
Fiberoptic bronchoscopy is an important tool for conscious intubation. It is the gold standard for guiding awake tracheal intubation [23, 24] and is an effective method for airway topical anesthesia. Also, bronchoscopy is often used to judge and adjust the position of the intubation in DLT tracheal intubation . As the bronchoscope has a small diameter, is soft and visible, it can gradually complete surface anesthesia of the entire respiratory mucosa under direct vision through the mouth or nose. In the awake state, topical anesthesia of using the spray-as-you-go technique can result in nausea and coughing. This approach usually requires appropriate sedation and analgesia that is gradually completed with the cooperation of the patient and can be lengthy .
In this study, the FIS group was subjected to the spray-as-you-go technique after induction of anesthesia. As the patient is under anesthesia, the operator can complete the mucosal anesthesia from the throat to the bronchus whilst also avoiding the patient's cough and a bad memory. As the patient received pure oxygen ventilation with a mask before and after the operation, the operation time was completed within 2 min and so all patients did not develop hypoxemia during epithelial anesthesia.
In this study, the purpose of spraying the topical anesthetic solution using an epidural catheter in the working channel of the FIS was to ensure that the drug solution was more evenly distributed on the surface of the airway mucosa. Even if the patient does not redistribute the liquid through a cough reaction, effective results can be achieved. This study confirmed that the use of FIS spray-as-you-go airway mucosal anesthesia to control the stimulation response of DLT intubation is effective. The stress response during tracheal intubation and body position changes were effectively controlled and the hemodynamics were stabilized.
Whilst no significant differences were observed in the blood pressure and heart rate at patients at different times during intubation between the two methods, the number of cases of hypertension and tachycardia in the FIS group were lower than those in the ultrasound group. These data may be explained as follows. In the ultrasound group, transtracheal injection was used to inject drugs into the subglottic main trachea. The distribution of topical anesthesia in the carina and bronchi may be affected by the cough response of the patient. Patients in the FIS group were sprayed directly from the mouth to the bronchus under direct vision and the multiple side holes of the epidural catheter allowed the drug to be more evenly distributed across the entire airway mucosa. Also, the DLT tracheal intubation was longer than the conventional tube. The intubation process spanned from the carina to the bronchus and it directly stimulated the entire trachea including the bronchus. The endotracheal anesthesia of transtracheal injection may be insufficient for the epitracheal anesthesia of the entire trachea and bronchi. The method of increasing the sample size and using topical anesthesia to develop colors will help to further validate these hypotheses.
Since the relevant operations were performed by skilled senior anesthesiologists, and the bronchoscopy was performed after anesthesia, the two methods are not time-consuming. The SLN block and transtracheal injection of patients in the ultrasound group in the awake state, especially the cough of the patient during intratracheal injection, is an important reason for poor memory after surgery. Coughing caused by transtracheal injection can lead to the risk of accidental injection of topical anesthetics into large blood vessels, topical anesthetic poisoning, bleeding, and airway damage. Also, severe coughing has the associated risk of reflux and aspiration [9, 27, 28].
In this study, 4 patients in the ultrasound group had bloodstains on the glottis when the glottis was exposed by the laryngoscopy and all of the patients had recovered at follow-up. Since the bronchoscopy was implemented after anesthesia, the operator can skillfully use the FIS to complete the topical anesthesia of the entire airway mucosa in a short time. Before and after the operation, the mask was fully ventilated with pure oxygen and no adverse reactions such as hypoxia, nausea, and coughing were reported during awake fibreoptic intubation [15, 29]. However, during the operation, an assistant is often required to hold the lower jaw, fix a dental pad, and complete the drug injection.
Lidocaine is an effective topical anesthetic that can be used safely at a dose of 9 mg/kg in airway mucosal anesthesia . Studies have shown that intratracheal use of lidocaine topical anesthesia can effectively reduce the stress response of tracheal intubation and reduce the incidence of postoperative throat discomfort in patients . In this study, no symptoms of lidocaine poisoning were observed. There were no significant differences in the incidence of postoperative sore throat, hoarseness, and the satisfaction score of anesthesia between the two groups.
This study had several limitations including the lack of monitoring of blood catecholamine levels. The blood pressure of the two groups of patients, especially the FIS group, was lower than the baseline values during anesthesia induction intubation. This may be due to the use of conventional intravenous anesthesia induction drugs. Effective airway topical anesthesia can maintain circulatory stability during the induction intubation process and reduce the amount of anesthetics. The optimal anesthesia induction medication regimen combined with the topical anesthesia technique in the process of DLT tracheal intubation requires further investigation.
In summary, the use of topical airway anesthesia during DLT tracheal intubation can effectively inhibit adverse cardiovascular reactions and stabilize hemodynamics during intubation. As a common auxiliary device in the process of DLT tracheal intubation, bronchoscopy can be used to adjust and locate the position of the intubation, and can be combined with the spray-as-you-go airway mucosal anesthesia method of the bronchoscopy working channel.