Evidences show the therapeutic uses of nebulized lidocaine in the treatment of intractable cough, asthma and reactive airway dysfunction syndrome [11–13]. In murine model of asthma, it has been investigated that nebulized lidocaine prevents airway inflammation, peribronchial fibrosis, and mucus production, and impaired airway hyperreactivity, possibly by inhibiting allergen-evoked GATA-3 expression and the subsequent up-regulation of proinflammatory cytokines and chemokines . Koirala S reported a case by topical anesthesia of the vocal cords by nebulized lignocaine inhalation to facilitate fiberoptic nasotracheal intubation in a head-size parotid tumor patient, emphasizing the possibility of fiberoptic intubation in a sedated yet spontaneously breathing patient by allowing inhalation of nebulized lidocaine during fiberoptic intubation . And then, nebulized lidocaine combined with fentanyl as a premedication to general anesthesia was a recommended implementation in spontaneously breathing pediatric patients undergoing rigid bronchoscopy .
Aerosol inhalation of nebulized local anesthesia causes fewer trauma to the oropharyngeal and laryngeal tissues and avoids the risk of in advertent injection into a blood vessel as compared to nerve blocks,but requiring a larger dose possibly decreasing the risk of systemic toxicity . Lidocaine plasma concentrations below 6.0 µg/ml are considered safe. And the average dose associated with the occurrence of neurological symptoms in healthy volunteers was about 8 mg/kg, corresponding to a plasma value of about 15 µg/ml . The lidocaine plasma concentration was 0.7 ± 0.3 µg/ml when inhalation of lidocaine was 5 mg/kg . In our study, the time of atomization inhalation lasted 5 min, and the dose of lidocaine was about 300 mg, it was safe as lidocaine plasma concentrations was far below 6.0 µg/ml.
In our study,we used carbonated lidocaine for inhalation. The reason is that surface anesthetic effect of carbonated lidocaine is 4 times more effective than lidocaine hydrochloride . Because the carbon dioxide released following permeation may produce local vasodilatation which increase the rate of absorption. In addition, as the carbon dioxide releases from the site of permeation, there is a resultant increase in pH, which augments formation of free base. The form of the local anesthetic which readily diffuses across biological membranes and facilitates the neural and vascular uptake .
By Adamus M, excellent intubation conditions were observed in 28%, 41% and 54%, while poor conditions were present in 31%, 7% and 3% of patients each receiving sufentanil 0.2, 0.3 or 0.4 µg/kg respectively. Therefore, sufentanil (0.3–0.4 µg/kg in combination with propofol (2 mg/kg) provided clinically acceptable intubating conditions in 93–97% patients . In our study, inhalation aerosol lidocaine was accomplished prior to induction of anesthesia. The intravenous of anesthesia was achieved with propofol, rocuronium 0.9 mg/kg, and combined with adjusting different dose of sufentanil according to the reaction for intubation starting at 0.5 µg /kg. However, it was indicated that inhalation aerosol lidocaine reduced the amount of sufentanil needed for endotracheal intubation, and the EC50 sufentanil with aerosol lidocaine for endotracheal intubation was only found to be 0.232 µg/kg. Twenty-three (55.88%) out of the all 34 patients showed hemodynamic index change < 20% of baseline during endotracheal intubation. It signified that combined with inhalation aerosol lidocaine for endotracheal intubation reduced the dosage of opioids, enhanced hemodynamic stability, and provided better intubation conditions.
For the effect on regional deposition, the significant of particle aerodynamic diameter and inhalation maneuver need to be concerned . Large particles (5–15 µm) are mainly deposited in the upper airways and trachea, intermediate-sized particles (3–5 µm) has tendency to be deposited in the bronchi and bronchioles, and small particles (≤ 3 µm) are flowed into the alveoli . The aerosol characteristics are closely related to the device of atomizer,which depends on the design of pressure swirl, airblast and ultrasonic atomizers . The ultrasonic atomizers operate at different frequencies, which are well with the median droplet size . The piezoelectric part of the ultrasonic atomizer (YUWELL༌402B) produced 35% carbonated lidocaine particle sizes above 5.0 µm, which providing good surface analgesic effect in upper airway and trachea. The maximum rate of aerosol inhalation was more than 3.0 ml/min. And it just took 10 min to prepare and finish the whole process of inhalation.
A major limitation of this study is that each patient routinely received lidocaine for a fixed period of time (5 min) with aerosol inhalation, not according to the patient's individual differences, which might impact the results. Moreover, only 35% of the particle of aerosol inhalation is the ideal size for the upper airways. A more efficient method or medical facilities of aerosol inhalation for surface anesthesia of upper airway is still worthy of further exploration.
The advantages in lidocaine inhalation for airway anesthesia by ultrasonic atomizer are revealed in our study. Inhalation of aerosol carbonated lidocaine is expected to reduce the amount of sufentanil obviously,and then provided stable hemodynamic change which avoiding or reducing the usage of cardiovascular drugs. Therefore, for the patients who are with cardiovascular and cerebrovascular diseases, this clinical application is more suitable that add the key step about aerosol inhalation of lidocaine before endotracheal intubation in anesthesia induction.