Role of Lignocaine Nebulization as an Adjunct to Airway Blocks for Awake Fiber-Optic Intubation: A Comparative Study.

CONTEXT: Airway management is a crucial skill and area of concern for the anesthesiologist. Awake fiber-optic intubation (AFOI) remains the gold standard in managing difficult airway. Anaesthetizing the airway along with psychological assurance is the mainstay for Preparation of AFOI. Different topical and regional techniques have been developed to subdue reflexes and facilitate AFOI. AIM: This randomized controlled study was performed to evaluate the effectiveness of using lignocaine nebulization in addition to specific airway blocks for AFOI.
METHODOLOGY: This was a comparative study conducted in 60 patients with difficult airway (LEMON score >2) and randomly allocated into two groups of 30 each. Group LB and Group NB received nebulization of 2% lignocaine 4 mL and 0.9% normal saline 4 mL, respectively. Both groups were then given airway blocks as bilateral superior laryngeal (2% lignocaine 1-2 mL each) and transtracheal (2% lignocaine 4 mL) block. Two puffs of 10% lignocaine to nose and postnasal space on each side were given in both groups. Fiber-optic bronchoscopy (FOB)-guided tracheal intubation was Performed. Vital parameters, side effects, bronchoscopy-guided intubation time and other parameters as intubation grading scale, patient comfort score, satisfaction score were recorded. Chi-square test and unpaired t-test were used for statistical analysis.
RESULTS: Statistically, no significant differences were found in hemodynamic parameters, demographics, intubation time, and intubation grading scale in both groups. However, overall patient comfort and satisfaction score was better in Group LB.
CONCLUSION: Upper airway blocks provide adequate anesthesia for awake FOB, but when lignocaine nebulization is added to these blocks, it improves the quality of anesthesia and patient satisfaction.

INTRODUCTION

Airway management is an integral part of general anesthesia, allowing ventilation, oxygenation, preventing aspiration, and working as a mode for delivering anesthetic gasses. It is a crucial skill and area of concern for the anesthesiologist because sometimes it becomes very much difficult to maintain or manage an airway which may result in life-threatening conditions.

Handling of difficult airway with precaution, use of modern techniques such as fiber-optic bronchoscopy (FOB), and supraglottic airway devices are the mainstay. The transtracheal jet ventilation, mini cricothyrotomy, and tracheostomy are alternative methods.[1]

The incidence of difficult intubation depends on the degree of difficulty encountered showing a range of 1%–18% of all intubations.[1]

In patients with difficult airway, giving anesthesia for fiber-optic intubation can be further detrimental, so it is a usual practice to have awake fiber-optic intubation (AFOI). Many techniques have been applied for difficult airway, but AFOI remains the gold standard.[2]

AFOI is a technique which provides clear visualization of vocal cords through oral or nasal pathway and subsequent passage of an endotracheal tube under direct vision.[3]

Various studies indicated that AFOI is successful in 88%–100% of difficult airway patients.[4567] Preparation for AFOI is a challenge which includes, anesthetizing the airway with topical application of local anesthetics, airway nerve blocks along with psychological assurance.[38]

Successful performance of the procedure requires not only patient's cooperation but also the adequate physiological anesthesia of the whole airway from nostril to bronchus.

Different techniques are being used to achieve these objectives such as airway blocks in the form of glossopharyngeal nerve block, superior laryngeal nerve (SLN) block, and transtracheal block to abate gag reflex, glottis closure, and cough reflex.[910] These blocks are sometimes inadequate because of improper technique, lack of expertise, and anatomical challenges and not anesthetizing the whole airway from nostrils to bronchus which can hamper the patient cooperation that will further compromise the ease of doing FOB and intubation.[11121314]

Nebulization of lignocaine can achieve highly effective anesthesia from the oral cavity up to trachea for intubation. Simplicity and lack of discomfort is the major advantage of this technique. In addition, very little working knowledge of the anatomy of concern region is sufficient for its successful implementation.[9]

Topicalization alone may be inadequate for awake intubation in some patients because the stretch receptors present at the base of tongue causing gag reflex are submucosal. These receptors are not easily blocked by topical method so have to be supplemented by specific airway bocks.[10]

A combination of techniques is better to adequately anesthetize upper airway structures for AFOI. Inhalational technique provides the widest coverage, but this technique, however, does not provide a dense enough level of anesthesia.[9] Supplementation of this technique with specific nerve blocks can be an excellent way to accomplish efficacious anesthesia for AFOI.[915]

Many studies have been done previously to compare lignocaine nebulization/spray technique with airway block technique, but there is a paucity of enough literature to get the combined benefits of both techniques. Hence, we hypothesize that by combining both techniques, not only we can achieve more suitable condition for AFOI but also better patient cooperation during the procedure.

This prospective randomized study was conducted to evaluate the effectiveness of using lignocaine nebulization for topical anesthesia in addition to airway blocks for AFOI in a patient whom we have assessed a predicted difficult airway.

METHODOLOGY

After approval by the institutional ethics committee, this double-blinded randomized prospective study was conducted in 60 patients in 3-month duration. Patients were divided into two groups of 30 each of either sex, age 20–60 years, weighing 40–80 kg, and American Society of Anesthesiologists (ASA) physical status Classes I and II having LEMON score of >2 with written informed consent for surgery and emergency tracheostomy. Consolidated flow diagram showing patient progress through the study is shown as CONSORT [Figure 1].

Figure 1

Consolidated flow diagram showing patient progress through the study phases (CONSORT)

We have taken LEMON airway assessment method which is having high index of sensitivity and specificity with a maximum of 10-point score and calculated by assigning 1 point for each of the LEMON criteria. Patients falling in the difficult intubation group have higher LEMON scores.[1617]

Patients with nasal problems (fractures and trauma), fracture base of the skull, hypersensitivity (asthma and bronchitis), allergy to drugs used in the procedure (lignocaine), epileptics, bleeding tendency, obesity, and other comorbid diseases were excluded from the study.

After checking preanesthetic report, consent, identity, and fasting, the patients were explained about the awake FOB-guided intubation during preoperative assessment.

In preoperating room after securing an intravenous (i.v.) line, injection ranitidine 50 mg, injection ondansetron 4 mg i.v., and injection glycopyrrolate 0.2 mg i.v. were given.

Nasal xylometazoline drops (2 in each nostril, two times at a gap of 10 min) instilled.

Inside the operating room, electrocardiography (ECG), noninvasive blood pressure (NIBP), pulse oximetry (SpO2) and end tidal carbon di oxide (EtCO2) applied for monitoring.

The patients were randomly allocated into two groups of 30 patients in each group after calculating sample size on the basis of the time taken to perform FOB-guided intubation[10] as presuming confidence level of 95% at α error 0.05 for two-tailed test and taking power of the study 90%.

Airway block was supplemented either with lignocaine nebulization in Group LB or with placebo (normal saline) nebulization in Group NB.

A nebulizer with the oxygen flow rate of 8–10 L/min is used to deliver up to 4 mL of 2% lignocaine (80 mg of which 25% is typically absorbed –20 mg)[3] into the naso-oro-pharynx in Group LB and 4 mL of 0.9% normal saline in Group NB.

Patients were encouraged to inhale deeply through their nose and mouth to facilitate entrainment of nebulized drug into their airway over 10 min.

After nebulization, airway blocks were given in both groups as the SLNs are blocked bilaterally by infiltrating 2% lignocaine 1–2 mL (10–40 mg) at the lateral and inferior aspect of the hyoid. Finally, 2% lignocaine 4 mL (80 mg) was injected through the cricothyroid membrane into the trachea.

Trained nurses who have not participated in the study prepared the drugs and placed them in numbered and sealed envelopes. Randomization was done by computer-generated random number tables.

Four puffs of 10% lignocaine to nose and postnasal space (two puffs on each side – 40 mg) were given in each group patients.

After recording the baseline heart rate (HR), BP, and SpO2, injection midazolam (1–2 mg) and fentanyl 1.5 μg/kg i.v. slowly were given during the procedure (AFOI).

Adequate effect of local anesthesia was confirmed by heaviness in the oral cavity and by hoarseness of voice.

FOB-guided intubation was performed by the anesthesiologist who was blinded to the study groups. Size 7.5 mm internal diameter endotracheal tube for male and 7 mm for female patients were used. Supplemental O2 was given through FOB throughout the procedure.

Vital parameters such as HR, BP, and oxygen saturation (SpO2) were recorded immediately after intubation and 5 min postintubation and at every 10 min during surgery.

Supplemental local Anaesthetic (LA) was given if required as 1 mL aliquots of 2% lignocaine through the working port of FOB, by spray-as-you-go technique.[23] The total dose of lignocaine administered was recorded. Total dose of lignocaine used in our study is lesser than the maximum recommended dose.[318]

Bronchoscopy-guided intubation time (from insertion of the fiber-optic bronchoscope in the nostril to confirmation of tracheal intubation) and any hypoxic episode (SPO2 <90%) during intubation were recorded.

Other parameters such as gag/cough reflex, vocal cord visibility (relaxed, partially relaxed, or adducted on fiberscope view), patient comfort score,[19] satisfaction score postoperatively,[19] and intubation grading scale[20] were recorded for comparison [Tables 1 and 2].

Table 1

Intubation grading scale[20]

Table 2

Patients comfort score intraoperatively and satisfaction score postoperatively[19]

Postoperative adverse events of hoarseness and sore throat, any signs of lignocaine toxicity such as ECG changes, seizures, and bronchoconstriction were noted.

After securing the airway, general anesthesia was given with propofol 2 mg/kg and vecuronium 0.1 mg/kg. For maintenance, O2, N2O, isoflurane, and vecuronium 0.015 mg/kg as muscle relaxant were used. Injection neostigmine with glycopyrrolate was used in standard doses for reversal. The methodology of the study is shown in flow chart 1. Confidentiality of patient's data maintained.

Flow chart 1

Flow Chart to show the study in brief

Statistical analysis

All data were tabulated and analyzed. Parametric values were reported as mean ± standard deviation. Chi-square test was used for comparing nonparametric data such as sex and ASA class. Hemodynamic variables, intubation grades, and various scores were compared using unpaired Student's t-test. P < 0.05 was considered as statistically significant.

RESULTS

Analysis showed no significant differences in the demographic data between the two groups [Table 3]. Statistically, no significant difference was found regarding hemodynamic variables such as HR or mean arterial pressure at any interval between both groups [Figure 2]. There was a slight decrease in SpO2 during the bronchoscopy in both the groups, but the lowest SpO2 recorded was 90%.

Table 3

Demographic data and time taken for fiber-optic bronchoscopy-guided intubation

Figure 2

Comparison of hemodynamic variables (mean arterial pressure, heart rate)

All the patients of both the groups well participated and were sufficiently cooperative with the procedure so that awake FOB intubation was accomplished in all patients and none of the patients showed any evidence of lignocaine toxicity.

There was no statistically significant difference in the time required to perform FOB-guided intubation (110.57 ± 16.65 in Group NB and 108.27 ± 16.05 in Group LB).

The number of patients who experienced gag and cough reflex according to intubation grading scale also showed no statistically significant difference between the two groups [Figure 3].

Figure 3

Intubation grading scale

The highest quantity of supplemental lignocaine used by spray-as-you-go technique was 2 mL in Group LB (n = 1) and 2 mL in Group NB (n = 3).

The mean supplemental lignocaine volume used was also insignificant in both groups.

There was no statistical difference between the two groups regarding the intubating conditions and vocal cord visibility.

Patient comfort score was recorded during bronchoscopy to see patient reaction which was better in Group LB as compared to Group NB but statistically insignificant (P = 0.07) [Figure 4].

Figure 4

Patient comfort score during bronchoscopy

Patient behavior score recorded immediately after intubation to see patient response. Most of the patients were cooperative in both the groups (18 patients in Group NB and 21 patients in Group LB). Only one patient showed severe resistance in Group NB which was managed with proper counseling and local anesthetic instillation through the fiber-optic channel (P = 0.325) [Figure 5].

Figure 5

Patient behaviour score immediately after intubation

When patients were asked about the satisfaction score postoperatively, 23 patients reported excellent/good experience in Group LB as compared to only 16 patients in Group NB which is statistically significant (P = 0.045) [Figure 6].

Figure 6

Patient satisfaction score postoperatively

DISCUSSION

There are many independent predictors of difficult intubation such as previous history of difficult intubation, Mallampati scoring, restricted neck movements, and short thyromental and sternomental distance.[2122]

Single airway test cannot provide a high index of sensitivity and specificity for prediction of difficult airway. Therefore, it has to be a combination of multiple tests.[22] Several multivariate scores for assessing difficult airway have been described such as Wilson score, M-TAC, Simplified Airway Risk Index, and LEMON score.[2223]

AFOI is in use since 1967 when it was first used by Murphy, who used a choledochoscope for intubation.[24] Numerous techniques have been emerged now to facilitate awake intubation.

It offers the advantages of securing the airway with preserving spontaneous respiration without any significant complications in patients with difficult airway.[19]

It is necessary to anesthetize the airway in such a way that awake FOB-guided intubation can be successful and comfortable for the patients with minimal sequels. Many techniques are described like topical anesthesia with nebulized LA, lozenges, sprays, gargles, airway blocks, and LA through working channel of a bronchoscope. Selection of technique depends not only on patient's characteristics but also on the expertise of the anesthesiologist.

Many studies have been done to compare the different techniques of awake FOB intubation, but this RCT was performed to evaluate the effectiveness of using lignocaine nebulization in addition to airway blocks.

Lignocaine nebulization is already proven to decrease the discomfort of nasopharyngeal instrumentation (Cullen et al.[25]). Airway blocks provide good airway anesthesia to facilitate the performance of awake FOB intubation (Gupta et al.[2]).

Techanivate et al.[26] found adequate upper airway anesthesia for fiber-optic intubation using 2% lignocaine in the form of nebulization and topical cocaine application in the nose.

In our study, vocal cord visibility, intubation grading scale, and time taken to perform FOB-guided intubation were similar in both groups.

This might be the result of airway blocks (bilateral SLN and transtracheal block) given in both groups.

These results are similar to the randomized study conducted in 1995 by Reasoner et al.[5] They also found no significant difference in the time to perform intubation between the topical anesthesia and nerve block group. The topical anesthesia group received 20 mL of 4% lignocaine through nebulization along with a transtracheal injection of 3 mL lignocaine. The nerve block group received bilateral glossopharyngeal, SLN blocks and trans-tracheal injection of lignocaine. A similarity of the result was probably due to patients in topical anesthesia group and also received transtracheal injection of lignocaine with nebulization, which further improved the quality of anesthesia.

Blockade of the glossopharyngeal nerve is also a part of effective block combinations.[9] Glossopharyngeal nerve block was not given in our study because of its anatomic limitation. Most of the patients were of limited mouth opening, so intraoral approach was not feasible. Accidental vascular injection and bleeding are risk factors due to high vascularity of palatoglossal arch which may hinder the fiber-optic view. In addition, local anesthetic drug can be significantly absorbed in this region.

Further local anesthetic can be trickled down to nasopharynx and base of the tongue from nostrils during nasal puff administration and patients can be instructed to cough immediately after transtracheal block so that local anesthetic is sprayed even up to oropharynx to abate cough reflex more smoothly.

Chatrath et al.[19] suggested that a proper technique of AFOI under combined regional nerve blocks provides good intubating conditions and increases patient comfort, satisfaction, and safety with minimal hemodynamic changes.

In our study, patient comfort score during bronchoscopy, behavior score immediately after intubation, and satisfaction score postoperatively were recorded and compared. Patients in both groups were given airway blocks, but addition of lignocaine nebulization increased the patient comfort and satisfaction in Group LB.

Topical anesthesia in the form of nebulization (4 mL of 2% lignocaine) facilitated the distribution of local anesthetic to pharynx, epiglottis, larynx, and trachea and provided the anesthesia for successful AFOI.[26]

Gupta et al.,[2] in 2014, showed better patient comfort in the nerve block group as compared to the nebulization group. Vocal cord visibility and ease of intubation were also better in nerve block group as compared to the nebulization group.

Kundra et al.[27] compared two methods of anaesthetizing airway for AFOI. One group received 4 mL of 4% lignocaine through nebulization and the other group received airway blocks (translaryngeal, bilateral superior laryngeal, and lignocaine soaked cotton swabs in the nose).

Intubation time was almost similar in both the groups. Patients in the nebulization group had to undergo higher stress during the intubation because the grimace scores as well as the mean HR and BP were significantly higher during intubation in the nebulization group.

However, in our study, both groups were given airway blocks and one group was supplemented with lignocaine nebulization, and hence, cough reflex in the form of intubation grading scale, bronchoscopy time, and vocal cord visibility was same in both groups.

The total dose of lignocaine used in our study was maximum 240 mg in both groups. Such dose of lignocaine is far less than maximum recommended dose for FOB. The British Thoracic Society in 2001 recommended that the total dose of lignocaine during bronchoscopy should be limited to 8.2 mg/kg.[18]

Anesthesia tutorial of the week 201 by World Federation of Societies of Anaesthesiologists 2010 recommended a dose of maximum 9 mg/kg of lignocaine, based on lean body weight, for topical anesthesia in adults.[3]

Parkes et al.[28] in 1997 done fiber-optic intubation using 6 mg/kg of 10% lignocaine through nebulization. The serum lignocaine levels remained below the threshold of 5 mg/l at all times (highest levels obtained were 0.45 mg/l).

Similarly, Langmack et al.[29] measured the serum lignocaine levels in asthmatic patients undergoing FOB with the use of topical lignocaine. Average total dose used was 600 mg (8.2 mg/kg), which was found to be safe in near all patients as measured by serum lignocaine concentrations.

However, in 1993, Wu et al.[30] reported seizures in a patient during FOB after administration of a total dose of 300 mg of topical lignocaine.

Large doses such as14.77 mg/kg of lignocaine, which were administered by a spray-as-you-go method, were reported to have experienced involuntary movement symptoms. This probably indicates cortical irritability leading to convulsion. Although, in 1990, Webb J. measured serial plasma lignocaine concentrations during a similar protocol for topical lignocaine nebulizer and reported very low systemic absorption of topical lignocaine and minimal cardiovascular effect.

Gal[31] reported that lignocaine nebulization can cause airway irritation as evidenced by coughing; however, later, it results in bronchodilatation due to its membrane stabilizing action. No such adverse effects caused by lignocaine mist were noted in our study.

The lignocaine concentrations used in our study were well below the acceptable toxic limits. But still, a constant lookout for signs and symptoms of lignocaine toxicity is mandatory.

Limitation of our study was to have an invasive technique in terms of airway blocks and not having the facility to measure serum lignocaine level.

CONCLUSION

Upper airway blocks (bilateral superior laryngeal and transtracheal nerve block) provide adequate anesthesia for performance of awake FOB.

Furthermore, when 4 mL of 2% lignocaine through nebulization is added with airway blocks, it improves the quality of anesthesia by increasing overall comfort and satisfaction of patients, thus providing more acceptable condition for awake FOB.

More studies are required to find out the ideal technique for airway anesthesia with lesser or no pain and minimum or no invasion with the achievement of best intubating condition along with better patient satisfaction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.