Characterization of infant spinal anesthesia using surface electromyography: An observational study

Background: As the risks of general anesthesia in infants become clearer, pediatric anesthesiologists are seeking alternatives. Though infant spinal anesthesia is one such alternative, its use is limited by its perceived short duration. Prior studies investigating infant spinal anesthesia are open to interpretation and may not have accurately characterized block onset or density. Surface electromyography is a passive, noninvasive modality that can measure the effects of neural blockade.

Aims: To quantitatively describe the onset, density, and duration of infant spinal anesthesia using surface electromyography.

Methods: In this observational study, 13 infants undergoing lower abdominal surgery received spinal anesthesia (0.5% bupivacaine with clonidine). Surface electromyography collected continuous data at T2, right T8, left T8, and L2. Data were processed in MATLAB. Onset, density, and duration were defined as the mean derivative within the first 30 s after block administration, the maximum difference in signal compared with preblock baseline, and the time elapsed between block administration and the return of a persistent signal to 50% above the maximum difference, respectively.

Results: Mean patient age and weight were 7.5 ± 2.6 months and 8.0 ± 2.2 kg, respectively. All patients were male. There was a statistically significant difference in the average rate of spinal anesthesia onset (mean percent decrease per second [95% confidence interval]) between myotomes (F (3, 35) = 7.42, p < .001): T2 = 15.93 (9.23, 22.62), right T8 = 20.98 (14.52, 27.44), left T8 = 17.92 (11.46, 24.38), L2 = 32.92 (26.46, 39.38). There was a statistically significant difference in mean surface electromyography signal (mean decibels, 95% confidence interval) across both pre- and postspinal anesthesia Timepoints between myotomes (F (3, 36) = 32.63, p < .0001): T2 = 45.05 (38.92, 51.18), Right T8 = 41.26 (35.12, 47.39), Left T8 = 43.07 (36.93, 49.20), L2 = 22.79 (16.65, 28.92). Within each myotome, there was statistically significant, near complete attenuation of sEMG signal due to spinal anesthesia: T2 mean (pre-post) difference: mean decibels (95% confidence interval) = 39.53 (28.87, 50.20), p < .0001, right T8 = 51.97 (41.30, 62.64), p < .0001, left T8 = 46.09 (35.42, 56.76), p < .0001, L2 = 44.75 (34.08, 55.42), p < .0001. There was no statistically significant difference in mean (pre-post) differences between myotomes. The mean duration of spinal anesthesia lasted greater than 90 min and there was no statistical difference between myotomes. There were also no statistically significant associations between age and weight and onset or duration.

Conclusions: Surface electromyography can be used to characterize neural blockade in children. Importantly, these results suggest that awake infant spinal anesthesia motor block lasts, conservatively, 90 min. This exploratory study has highlighted the potential for expanding awake infant spinal anesthesia to a broader range of procedures and the utility of surface electromyography in studying regional anesthesia techniques.