Local Anaesthesia for Fiberoptic Intubation : A Comparison of Three Techniques

Abstract

Background

The successful conduct of fiberoptic aided intubation is dependent upon effective local anaesthesia. The aim of the study was to compare three different methods of anaesthetizing the airway.

Methods

60 adult patients (American Society of Anaesthesiologists status I-III and Mallampati class III & IV), scheduled for elective surgery, received sedation followed by spraying of the nares and posterior pharyngeal wall with 4% lignocaine. Thereafter the patients received 4 ml of 4% lignocaine either by transtracheal injection (n=20, group A), via intubating fiberscope (Pentax F1-10P2) using ‘spray as you go’ technique (n=20, group B) or by nebulizer (Devilbiss 5610W) 20 min before intubation, (n=20, group C). Patients were asked to score the procedure using visual analog scale (VAS) and severity scores. Episodes of coughing, choking, stridor, extra / total local anaesthetic used and intubation times were recorded. Patients were monitored continuously for vital parameters.

Results

Group B patients showed better VAS scores with shorter intubation times and had a lower incidence of coughing and choking. The endoscopists’ VAS scores also showed a preference for group B.

Conclusion

In conclusion the ‘spray as you go’ technique was safe, provided effective local anaesthesia and was preferred by both patients and endoscopists.

Introduction

Awake fiberoptic aided intubation is now an accepted technique for managing the difficult airway. However it is often an unpleasant procedure. The principal patient complaints include sensation of passage of the instrument through the nose and larynx, pain and coughing while endoscopists usually ascribe difficulty in laryngeal visualization to secretions and inadequate local anaesthesia [1, 2, 3]. Inevitably the patient's tolerance and the success of fiberoptic-assisted intubation depends on the effectiveness of topical anaesthesia and obtundation of pharyngeal, laryngeal and tracheobronchial reflexes [3, 4].

Prior to endoscopy, while the upper airway is commonly anaesthetized by local lignocaine spray or gel, the modalities of applying local anaesthetic to the larynx and lower respiratory tract include injection via the fiberoptic bronchoscope and transtracheal injection delivery via a nebulizer [5].

The aim of this study was to compare the three techniques of local anaesthesia using VAS and severity scale for patients undergoing awake intubation. It was also proposed to study the acceptability and suitability of these techniques to the patient with objective measurement of cough, stridor, intubation time and total dose of anaesthetic used.

Methods

Sixty adult patients in American Society of Anaesthesiologists (ASA) status I-III between the age group of 18 to 60 years were included in the study. All the patients had an anticipated difficult airway with Mallampati Class III and IV, and were to undergo elective fiberoptic intubation. After informed consent and approval by the Hospital Ethics Committee, patients were randomized into three groups, each receiving 4 ml of 4% lignocaine with either of three different methods: group A (n=20) via transcricoid injection (cricothyroid puncture); group B (n=20) via intubating fiberscope; group C (n=20) via nebulizer.

A common standard anaesthetic regimen was followed for all the patients which included overnight fasting and premedication in the form of tablet diazepam 10 mg the night before surgery and 10 mg in the morning 2 hours before surgery. In the theatre, they received injection glycopyrrolate 0.2 mg, pethidine 50 mg and phenergan 25 mg intramuscularly 45 minutes before the start of the procedure. Further 0.1% xylometazoline drops were instilled in both the nostrils 15 minutes later. Thereafter, both the nasal passages were lubricated with 2 ml of 2% lignocaine jelly. Posterior pharynx was then anaesthetized with 4 sprays of 4% lignocaine and the patient was asked to gargle with the excess solution trickling down the throat.

Inside the theatre an intravenous access was established and monitoring instituted viz electrocardiogram (ECG), oxygen saturation (SaO₂), and non-invasive blood pressure (NIBP). The next step was aimed at achieving laryngo-tracheal anaesthesia prior to intubation of trachea. Group A patients had 4 ml of 4% lignocaine injected through the cricothyroid membrane in two aliquots using 22 G catheter over needle. Group B patients had the intubating fiberscope (Pentax F1-10P2) inserted transnasally until just above the cords and 4 ml of 4% lignocaine was administered through an 18G epidural catheter which was passed through the suction channel. This was done in two steps: the first onto the vocal cords and the second into the trachea during inspiration. Group C patients had 4 ml of 4% lignocaine delivered by nebulizer (Devilbiss 5610W) starting 20 minutes before the procedure and taking 10 minutes to complete. In each group additional 1-2 ml aliquots of 2% lignocaine were administered if required.

The lubricated endotracheal tube (Mallinckrodt flexometallic) was passed through the nares. The fiberscope was manoeuvred through the tube beyond the vocal cords and into the trachea. The endotracheal tube was then slid off the fiberscope and mid-tracheal placement was confirmed under direct vision. During this entire procedure that is, from the passage of the tube into the nares and the manipulation of the scope till placement of the tube in the trachea, the following observations were made:

• a)Intubation time (i.e. time from introduction of the fiberscope till the first measurement of end-tidal carbon dioxide was recorded) and number of attempts
• b)Pulse, NIBP, SaO₂, ECG and complications such as arrhythmias, bleeding or sore throat.
• c)Incidents of cough (abrupt expiratory sounds) and stridor (musical inspiratory sounds)

To assess the severity of symptoms, a 10 cm VAS ranging through ‘not pleasant to ‘intolerable’ was used to assess the patients’ symptoms and affirm the endoscopists’ appraisal. A severity scale ranging from 1 to 5 [6] (Table 1) was also employed to assess the patients’ quality of anaesthesia (nasal & laryngeal) and intubation (fiberoptic & endotracheal). In addition, the endoscopist was asked to grade the overall ‘scope inserting and intubating’ conditions in each case. The defining criteria are described (Table 2). All the patients were interviewed post operatively to comment about discomfort if any in the form of coughing, choking and pain.

Table 1.

Severity scale (as reported by the patient)

Not unpleasant	1
Uncomfortable	2
Unpleasant	3
Most unpleasant	4
Intolerable	5

Table 2.

Grading of overall intubating conditions (as assessed by the endoscopist)

I	No adverse events, cough or stridor, co-operative and well tolerated
II	Coughed once or twice, co-operative with reassurance, tolerated the tube well.
III	Coughed repeatedly, no stridor, tube accepted
IV	Coughed repeatedly, stridor present, unco-operative, did not allow scope to be passed beyond glottis

The study was terminated when these recordings pertaining to VAS and severity scores were completed at the end of fiberoptic endoscopy. Additional amount of lignocaine used (in mg) was also recorded. The results were analysed statistically using Student's t test and chi square test and probability values p<0.05 were taken as significant.

Results

All the three groups were similar demographically (Table 3) without any significant difference. There were no adverse/untoward incidents like desaturation or arrhythmias. The types of surgery are displayed (Table 4).

Table 3.

Demographic data

	Group A	Group B	Group C
Age (years)	38 ± 2.1	37 ± 1.6	39 ± 1.1
Weight (kg)	56.8 ± 1.5	55 ± 2.3	58.1 ± 1.3
Sex (M:F)	12:8	13:7	11:9

Table 4.

Types of surgery

Head and neck malignancy	32
Dental tumours and TM joint ankylosis	20
Burns contractures (face and neck)	8
Total	60

Subjective Assessment

The patients’ VAS for symptoms and the endoscopists’ assessment showed a significant overall preference for group B (Fig. 1) with lower scores for coughing and choking. The severity scores (Table 5 and Fig. 2) recorded by the patients showed no significant difference in nasal anaesthesia (mean scores of 2.2, 1.8, 2.0). However, the quality of laryngeal anaesthesia was significantly better in group B as evidenced by significantly lower scores (p<0.05). Similarly fiberoptic intubation of the larynx (mean scores of 2.2,1.0, 2.3) and endotracheal intubation (2.0, 1.2, 2.7) displayed significantly lower scores for group B (p<0.05).

Fig. 1.

VAS scores

Table 5.

Quality of anaesthesia (severity scores – mean)

	Group A	Group B	Group C
Nasal anaesthesia	2.2	1.8	2.0
Laryngeal anaesthesia	2.8	1.5	2.6
Fiberoptic intubation of the larynx	2.2	1.0	2.3
Endotracheal intubation	2.0	1.2	2.7

Fig. 2.

Severity scores

Objective Measurement

The cough counts during the procedure were recorded as the mean count per procedure. The total number of coughs was significantly less in the ‘spray as you go’ technique compared with group A and group C (p<0.05). 12 patients in group B coughed whereas 18 patients in group A and all patients in group C coughed (Table 6 and Fig. 3). Stridor was uncommon during nasal and laryngeal passage of the fiberscope in all the groups. However, immediately following endotracheal intubation, 3 patients in group A had stridor (mean of 2 stridors per patient), 2 patients in group B had stridor (mean of 2 episodes) while 10 patients in group C (mean of 4 episodes) experienced stridor, significantly more than group A and B (p<0.01).

Table 6.

Complications and mean extra lignocaine dose

	Group A	Group B	Group C
Cough count	18	12	20
Stridor	3	2	10
Mean lignocaine dose (mg)	20	60	120
Time taken (asec)	82 (30-255)	64 (25-104)	85 (34-174)

Fig. 3.

Objective measurement

The time taken (mean) for intubation was significantly less in group B (64 seconds) as compared to group A (82 seconds) and group C (85 seconds). There was no significant difference in the number of intubation attempts between the three groups. The mean amount of extra lignocaine used in group A was 20 mg (2 patients), in group B was 60 mg (8 patients) and in group C was 120 mg (12 patients) respectively. Scope inserting and intubating conditions were graded by the endoscopist to be significantly better in group B (p<0.01) as compared with group A and group C (Table 7).

Table 7.

Intubating conditions

	Group A	Group B	Group C
Grade I (best)	10	16	6
Grade II	4	2	2
Grade III	3	1	4
Grade IV (Worst)	3	1	8

Discussion

This study was undertaken to compare three different methods of instituting local anaesthesia for fiberoptic aided intubation. Subjective assessment by patients and endoscopists using VAS and severity scores were compared with objective measurements of cough, stridor and extra / total quantity of local anaesthetic used besides time taken for each endoscopy.

Pain and coughing are among the most distressing aspects of bronchoscopy and fiberoptic intubation [1, 2, 3]. This is borne out in the present study as the patients’ VAS showed a significant preference for the ‘spray as you go’ technique. The severity scores showed that fiberoptic and endotracheal intubation in group B patients was the least distressing. The endoscopists’ assessment also showed a preference for the ‘spray as you go’ technique.

Both patients and endoscopists reported a significantly reduced tendency to cough with the ‘spray as you go’ technique which was exemplified by the reduced cough counts. Group C patients had significantly greater incidence of stridor than group A and B, which is a reflection of inadequate laryngotracheal anaesthesia with the nebulizer technique.

Although group B patients had least amount of coughing and choking the amount of extra lignocaine used (60 mg mean) was more than group A (20 mg mean) but less than group C (120 mg mean). Although none of the patients displayed any adverse effects, there is a potential for the safe upper dose of lignocaine viz 4 mg/kg [7] to be exceeded in case of nebulization. However most authors now recommend higher safe doses for topical lignocaine viz 7-8 mg/kg, except in the elderly or those with hepatic or cardiac impairment [8]. The contention is that lignocaine is only partially absorbed across mucous membranes and some amount is reaspirated or swallowed during bronchoscopy. Peak systemic concentrations of lignocaine have been reported as early as 15 minutes following topical application [9] while tissue bound lignocaine acts for 30-45 minutes [7].

A comparison with other studies yields similarities and certain differences. In a series of 200 patients [10] undergoing transtracheal injection of lignocaine 94% of patients coughed and 48% had severe coughing. In the present study majority of patients in group A and group C coughed. In the former the injection itself is a strong stimulus for coughing while in the latter inadequate laryngeal anaesthesia is causal. Webb et al [11] found transcricoid injection of lignocaine produced less cough than ‘spray as you go’ technique. However one third of patients found the cricothyroid puncture to be unpleasant which was also reflected in the present study by better patient acceptance of the ‘spray as you go’ technique.

Graham et al [6] using phonopneumography found that the transtracheal method produced less cough and stridor during bronchoscopy as compared to ‘spray as you go’ and nebulization techniques. However they used 4 ml of 2.5% cocaine, a drug which is not available for routine clinical use. In the present study we employed lignocaine which is undoubtedly a safer local anaesthetic than cocaine [5]. The precise deposition of the local anaesthetic viz on the cords and in the trachea would also have a bearing on the efficacy of reflex obtundation obtained. The authors [6] found the nebulization method, with its imprecise and unpredictable local anaesthetic deposition, to be the least satisfactory method of local anaesthesia. This was also borne out in the present study.

The time taken for intubation was significantly less in group B (64 seconds) as compared to group A (82 seconds) and group C (85 seconds) which is a reflection of the better quality of local anaesthesia and intubating conditions afforded. The fiberoptic intubation times compare favourably with other authors [3, 12, 13].

Although no major complications were encountered in the present study, the transtracheal route has more potential complications than the other techniques [5]. These include paroxysms of severe coughing, (with concomitant rise of heart rate, blood pressure, intracranial pressure), intralaryngeal bleeding, pain, cellulitis, oesophageal penetration, paratracheal abscess and subcutaneous emphysema. Thus the inherent safety of ‘spray as you go’ technique is an important advantage. In fact a postal survey of fiberoptic bronchoscopy in the UK [14] and recent reviews [8] show that the majority of bronchoscopists spray the upper airways with local anaesthetic and inject local anaesthetic (usually lignocaine) via the suction channel of the bronchoscope.

Conclusion

Subjective and objective measurements in this study show that 4 ml of 4% lignocaine sprayed onto the larynx and trachea during fiberoptic intubation produced excellent local anaesthesia and was the method preferred by both patients and endoscopists.