Local Anesthetic Administration for Awake Direct Laryngoscopy: Are Glossopharyngeal Nerve Blocks Superior?

After receiving Human Investigation Committee approval and participant written informed consent, we collected complete data on 11 volunteers. Inclusion criteria included American Society of Anesthesiologists physical status classification 1 or 2, Mallampati-Samsoon upper airway class 1 or 2, and anesthesiology resident or faculty appointment. Exclusion criteria included a history of hypersensitivity to amide-type local anesthetics, seizure disorder, bleeding disorder, hypertension, or oropharyngeal disease. A crossover design was used, such that each participant received all three routes of lidocaine local anesthetic administration in a randomized order. Each administration was separated by a minimum of 96 h. An 18-gauge peripheral intravenous cannula was inserted, and 0.2 mg glycopyrrolate (A.H. Robbins, Richmond, VA) was administered as an antisialagogue 30 min before each study. Three routes of lidocaine local anesthetic administration were used.

Fifteen milliliters of 2% viscous lidocaine (Roxane Labs, Columbus, OH) was administered using a swish-and-gargle technique for 2 min. The viscous lidocaine was then expectorated.

Fifteen milliliters of 2% viscous lidocaine was administered using the swish-and-gargle technique. Two minutes later, 100 mg Xylocaine 10% oral spray (Astra Pharmaceutical Products, Westborough, MA) was applied as single sprays bilaterally to the soft palate, posterior oropharyngeal wall, palatopharyngeal arch, and base of the tongue, as well as two sprays to the vallecula region using a disposable spray cannula (for ten sprays in total).

Fifteen milliliters of 2% viscous lidocaine was administered using the swish-and-gargle technique. Two minutes later, a 22-gauge Quincke spinal needle (Becton Dickinson, Franklin Lakes, NJ) was inserted to a depth of 0.5 cm at the base of the anterior tonsillar pillar, where the base of the tongue opposes the palatoglossal fold. After negative aspiration tests, 5 ml 1% lidocaine HCl plain (Abbott Laboratories, Chicago, IL) was slowly injected bilaterally.

When local anesthetic administration was complete, the investigators performing laryngoscopy and taking hemodynamic measurements entered the study area. Both were blinded to the route of local anesthetic administration. Continuity was maintained by having the same investigators provide local anesthetic administration (B.T.S.) and perform laryngoscopy (G.S.L.) and hemodynamic measurements (G.F.R.) for all participants throughout the study. Each participant was fitted with a tooth guard and his or her eyes were covered with a cloth drape. Baseline noninvasive mean arterial blood pressure and heart rate were recorded (Series 7010RA; Marquette Electronics, Milwaukee, WI). Five minutes after anesthetic administration was complete, laryngoscopy was performed using a standard laryngoscope handle and a Macintosh-3 blade. Sufficient force was applied to obtain and sustain a grade 1 to 2 laryngoscopic view for 20 s. [2]Noninvasive hemodynamic measurements were recorded at 1-minute intervals for 5 min after laryngoscopy.

After each laryngoscopic procedure was complete, 10-cm visual analogue scales (VAS) were scored by both participants and the laryngoscopist. Participants assessed their impression of local anesthetic administration with VAS scores ranging from “not unpleasant” to “awful, never again” and their impression of the laryngoscopy with separate VAS scores ranging from “not unpleasant” to “intolerable.” The laryngoscopists assessed ease of laryngoscopy and visualization with VAS scores ranging from “no coughing or gagging” to “severe coughing or gagging making laryngoscopy impossible.” Neither the participants nor the laryngoscopist were aware of each other's scores.

Venous blood samples were obtained from the participants at baseline and 5 and 10 min after lidocaine local anesthetic administration. Serum samples were analyzed for lidocaine concentration (micro gram/ml) by gas chromatography, which has a limit of detection of 0.01 micro gram/ml and a sensitivity of +/- 5%. [13] 

One week after the study (that is, after participants had received all three routes), each participant completed a poststudy questionnaire. They were asked to (1) rank and discuss their impression of the local anesthetic administration route with regard to tolerability of administration and laryngoscopy, and (2) rank and discuss their choice of lidocaine local anesthetic administration route for awake direct laryngoscopy in future patients with anticipated difficult airways (i.e., for use in their clinical practice).

Continuous data are expressed as mean +/- standard error of the mean (SEM) and analyzed using one-way analysis of variance. When overall between group significance was present, multiple pairwise comparisons of means (Tukey's method) were performed. Nominal data are expressed as a proportion and analyzed using the Mantel-Haenszel test. Differences were considered significant at P < 0.05.

Study participants (11 men, 1 woman) were either anesthesiology residents (n = 10) or faculty (n = 2). One withdrew before completion of the study secondary to prolonged unilateral oropharyngeal discomfort after a GPN block. His data are not included in the results. Thus complete data were collected for 11 persons. Participant characteristics included age of 30 +/- 1 y, weight of 77 +/- 4 kg, and height of 177 +/- 3 cm. All participants reported tongue and oropharyngeal numbness after each of the three methods.

There was no significant difference in baseline heart rate between the S&G (72 +/- 5 bpm), S&G/spray (67 +/- 5 bpm), and S&G/block (71 +/- 6 bpm) groups. In addition, there was no significant difference in baseline mean arterial blood pressure between the S&G (91 +/- 3 mmHg), S&G/spray (95 +/- 4 mmHg), and S&G/block (92 +/- 4 mmHg) groups. Hemodynamic changes after the 20-s laryngoscopy were not different among the three local anesthetic administration groups (Figure 1). Only the S&G/block group showed a significant increase in heart rate (P < 0.05) in the first minute after direct laryngoscopy. There were no other significant changes in heart rate or mean arterial blood pressure after direct laryngoscopy.

Serum lidocaine concentrations were very low but significantly greater in the S&G/block group at 5 and 10 min (0.5 +/- 0.1 and 1.0 +/- 0.2 micro gram/ml) than in the S&G group (Figure 2). There were no significant differences between the S&G/spray and the S&G/block groups. No individual local anesthetic concentration exceeded 4 micro gram/ml.

(Figure 3) displays participant and laryngoscopist VAS scores. There were no significant differences in “administration” VAS scores (i.e., subject discomfort with local anesthetic administration) among the three groups. Regarding the participants' impression of discomfort during “laryngoscopy,” the S&G group experienced significantly higher VAS scores (more discomfort) compared with the S&G/spray and S&G/block groups. There was no significant difference between the S&G/spray and S&G/block groups. The laryngoscopist VAS score, assessing ease of laryngoscopy and visualization, revealed a trend (P < 0.08) toward less coughing and gagging with S&G/spray compared with S&G and S&G/block. There were no significant differences among groups with regard to the number of participants unable to complete the full 20-s laryngoscopy (S&G = 3; S&G/spray = 2; S&G/block = 1).

Based on the poststudy questionnaire assessing participants' ability to tolerate local anesthetic at the time of administration and laryngoscopy, 55% of participants ranked S&G/spray as the best method and 18% ranked it as the worst method (Figure 4). Forty-six percent of participants ranked S&G/block as the worst method. Nevertheless, none of these differences were statistically significant.

Oropharyngeal discomfort lasting 24 h or more was reported by 91% of participants after S&G/block, with four persons (36%) reporting discomfort lasting 3 or more days. No participant reported oropharyngeal discomfort after S&G or S&G/spray. Before this study, 91% of participants (P < 0.01) reported GPN blocks as their first choice for use in clinical practice. However, after the study, more participants indicated their preference for S&G/spray (73%) compared with S&G (P < 0.01) and S&G/block (P < 0.05;Figure 4). Prolonged oropharyngeal discomfort after GPN block was the most common reason for this decision.

The poststudy questionnaire also revealed that most participants would modify at least some aspect of their anesthetic practice as a result of participating in this study. Eight of ten participants who ranked S&G/block as their first choice for awake direct laryngoscopy before the study subsequently ranked S&G/spray as their first choice after the study. These persons reported post-GPN block oropharyngeal discomfort as the reason for the change. In addition to their choice for local anesthetic administration in future patients, other changes would involve using an eye drape and less glycopyrrolate. Participants reported a marked antisialagogue effect from 0.2 mg glycopyrrolate given 30 min before laryngoscopy, often lasting 8 h or more.

The key to a successful awake direct laryngoscopy is establishing reliable analgesia. Common routes of oropharyngeal local anesthetic administration include swish and gargle, topical spray, pledgets, nebulization, and nerve blocks (bilateral blockade of the lingual branch of the GPN and the internal branch of the superior laryngeal nerve). [2,14]Methodologic reports and case series have described advantages of using one route of local anesthetic administration over another. [4–7,15,16]However, no study has prospectively compared local anesthetic techniques for awake laryngoscopy in persons who did not receive supplemental opioid or benzodiazepine premedication. Glossopharyngeal blocks have been well described and can be administered through several approaches. [9–11,14]This study used the intraoral, anterior tonsillar pillar technique in which 5 ml 1% lidocaine HCl plain was injected bilaterally, which showed no benefit compared with less-invasive methods to establish topical anesthesia.

Previous studies reported variable effectiveness of lidocaine in blunting the hemodynamic response to direct laryngoscopy and intubation. Most studies used either topical or intravenous lidocaine as an adjunct to general anesthesia. [17–21]Kautto and Heinonen [22]compared viscous lidocaine gargle with aerosolized lidocaine and found that topical anesthesia by either route attenuated the pressor response to direct laryngoscopy and intubation but had no effect on the heart rate response. Beneficial effects of local anesthetic administration have been reported from studies involving awake procedures (laryngoscopy, bronchoscopy, esophagoscopy), although all used supplemental intravenous opioids and benzodiazepines. [4,6,12,16]In this study, the hemodynamic response to direct laryngoscopy in awake unpremedicated persons was significant only in the S&G/block group (with an increase in heart rate 1 min after laryngoscopy). However, the response was clinically modest (<15%) in all three groups, even in the absence of supplemental analgesics and anxiolytics. These results indicate that S&G/block is not superior to S&G or S&G/spray in blunting the hemodynamic response to awake direct laryngoscopy.

Serum lidocaine concentrations 5 and 10 min after S&G/block were significantly higher than after S&G. Nevertheless, mean serum lidocaine concentrations were less than 1 micro gram/ml at 5 min (i.e., immediately before laryngoscopy) and 10 min after lidocaine administration in all three study groups. Although not measured, serum lidocaine concentrations may have been higher at 20 min but were unlikely to have been clinically significant based on previous studies. [18]Our findings are similar to that of Ayuso and colleagues [23]and suggest that attenuation of hemodynamic and pain responses to awake laryngoscopy after oropharyngeal lidocaine is the result of topical analgesia and not the systemic effects of lidocaine.

Participants recorded clinically higher administration VAS scores (i.e., VAS scores higher than 4, suggesting more discomfort) with S&G/block compared with S&G/spray and S&G routes, although this was not statistically significant. No participant reported pain when the 22-gauge spinal needle was first placed. However, several reported intense “pressure” during injection of the 5 ml 1% lidocaine. This pressure probably represents stretching or dissection of pharyngeal tissues in the tonsillar region and is not likely related to the needle gauge.

Participants recorded significantly higher laryngoscopy VAS scores with S&G compared with either S&G/spray or S&G/block. However, opioid or anxiolytic premedication might have diminished this difference. Most importantly, this study shows that there is no difference in laryngoscopy VAS scores between S&G/spray and S&G/block. This indicates that GPN block does not offer an advantage over spray in patients with Mallampati-Samsoon upper-airway classification 1 and 2. However, we cannot state which method is advantageous in patients with higher airway classifications, or if advantages of one method exist during awake tracheal intubation. It is also possible that GPN blocks may be advantageous in patients who have blood or heavy secretions in the oropharynx, which may lessen the effectiveness of spray.

The laryngoscopist's VAS scores revealed a trend (P < 0.08) toward better laryngoscopy and visualization conditions (i.e., less coughing and gagging) after S&G/spray compared with S&G and S&G/block. Several persons in the S&G/block group reported discomfort in the vallecula region during laryngoscopy. Although classic descriptions attribute innervation of the vallecula and anterior surface of the epiglottis to the GPN and innervation of the posterior surface of the epiglottis to the superior laryngeal nerve, there may be considerable sensory overlap in this region. Therefore, it is possible that the 10% lidocaine spray, specifically the two sprays to the vallecula region, provided analgesia to mucosa innervated by the superior laryngeal nerve that was not adequately anesthetized by the GPN block.

Ten of the eleven participants had performed GPN blocks before the study. Ranking local anesthetic administration routes for awake direct laryngoscopy in patients with anticipated difficult airways, 91% of the anesthesiologists reported S&G/block as their first choice before participating in this study. In contrast, after having experienced GPN blocks themselves as a part of this study, 73% of them ranked S&G/spray as their first choice. The main reason for this change in practice was the prolonged oropharyngeal discomfort after GPN block. Although no participant reported oropharyngeal discomfort after S&G or S&G/spray, four (36%) experienced discomfort lasting 3 or more days after S&G/block. Otolaryngologic examination of the one person who withdrew from the study because of prolonged discomfort failed to reveal evidence of abscess or hematoma. We used an injection volume of 5 ml, because this has been suggested to produce a superior laryngeal nerve block as well. [11]Perhaps the use of 5 ml of local anesthetic actually stretched or dissected oropharyngeal tissue. This may not have occurred with smaller volumes of local anesthetic (2 ml). [2,11,14]However, use of 5 ml bilaterally has been recommended by several authors, [9,12,24]none of whom reported prolonged oropharyngeal discomfort as a complication. The lack of discomfort in previous studies may be secondary to the administration of perioperative opioids or the presence of an operative procedure that may mitigate or mask oropharyngeal discomfort. Although more participants might have resulted in more statistically significant differences among groups, we decided to end the study based on the many participants reporting prolonged oropharyngeal discomfort after GPN blocks. In addition, the results of this study revealed no clinical advantage for the administration of S&G/block over S&G/spray before awake direct laryngoscopy, even in the absence of oropharyngeal discomfort.

Using a prospective, randomized, single-blinded, crossover design, we evaluated the effects of three common routes of local anesthetic administration for awake direct laryngoscopy. The results of this study suggest that GPN blocks do not provide a superior route with regard to hemodynamic, gag, and subjective pain responses. In fact, bilateral GPN blocks, as performed in this study, may result in prolonged oropharyngeal discomfort. Two minutes of 2% viscous lidocaine swish and gargle followed by 10% lidocaine spray was the local anesthetic method preferred by participants and the laryngoscopist.

*Woods AM, Lander CW: Abolition of gagging and the hemodynamic response to awake laryngoscopy (abstract). Anesthesiology 1987; 67:A220.