Comparison of 4 ml of 1% Lignocaine Versus 2 ml of 2% Lignocaine for Landmark-Guided Superior Laryngeal Nerve Block During Awake Fiberoptic Intubation.

BACKGROUND

Superior laryngeal nerve block is one option for airway topicalization during awake fiberoptic intubation. The optimal balance between injectate volume and lignocaine (lidocaine) concentration remains uncertain.

OBJECTIVE

To compare a larger-volume, lower-concentration regimen (4 mL of 1% lignocaine per side) with a smaller-volume, higher-concentration regimen (2 mL of 2% lignocaine per side). We hypothesized that the larger volume would improve neural spread, increase the proportion of completely relaxed vocal cords, and shorten fiberoptic intubation time without increasing adverse events.

METHODS

In this single-center randomized assessor-blinded trial, 72 adults requiring awake fiberoptic nasotracheal intubation were allocated 1:1 to the 1% group or the 2% group (36 per group). Each regimen delivered 40 mg per side. The primary outcome was completely relaxed vocal cords (Grade 1) during bronchoscope negotiation. Secondary outcomes included fiberoptic intubation time, discomfort assessed 24 hours after extubation, serial hemodynamic variables, oxygen saturation, and bleeding. Categorical outcomes were re-analyzed with exact tests. Fiberoptic intubation time was additionally examined in a post hoc multivariable linear model adjusted for age, sex, and body weight.

RESULTS

Grade 1 vocal-cord status occurred in 32/36 (88.9%) patients in the 1% group and 23/36 (63.9%) in the 2% group (odds ratio 4.52, 95% CI 1.31-15.66; Fisher exact P=0.025). Mean fiberoptic intubation time was 129.3 ± 39.0 seconds versus 161.2 ± 56.8 seconds, respectively (mean difference -31.9 seconds, 95% CI -54.9 to -9.0; P=0.007). The adjusted difference was -29.3 seconds (95% CI -52.9 to -5.6; P=0.015). No discomfort at 24 hours was reported by 32/36 (88.9%) versus 24/36 (66.7%) patients (P=0.045). Bleeding occurred in 2/36 (5.6%) versus 7/36 (19.4%) patients (P=0.151). Serial hemodynamic values were broadly similar; an isolated difference in diastolic pressure at one minute was not interpreted as a sustained treatment effect.

CONCLUSION

For landmark-guided superior laryngeal nerve block, 4 mL of 1% lignocaine per side was associated with more completely relaxed vocal cords and shorter fiberoptic intubation time than 2 mL of 2% lignocaine per side. The findings support further multicenter confirmation using validated airway-anesthesia scales and fully blinded injectate preparation where feasible.