[Minimum anesthetic volumes for extraconal retrobulbar block: comparison between 0.5% racemic bupivacaine, levobupivacaine and enantiomeric mixture S75/R25 bupivacaine].
OBJECTIVE
Minimum anesthetic volume (MAV) of local anesthetics corresponds to the effective volume for regional anesthesia in 50% of patients. In this study, MAV of 0.5% racemic bupivacaine, 0.5% levobupivacaine and enantiomeric S75/R25 bupivacaine were calculated and compared.


METHODS
This study involved two series of patients undergoing cataract extraction. Series 1 patients received either 0.5% racemic bupivacaine (n = 9) or 0.5% levobupivacaine (n = 11). Series 2 patients received either 0.5% racemic bupivacaine (n = 11) or 0.5% enantiomeric S75/R25 bupivacaine (n = 10). Blockades were achieved by single-injection and inferior-lateral approach. Motility of each rectus muscle was assessed 10 minutes later as: 0 (absent), 1 (decreased) or 2 (normal). Total muscle scores represented total eye motility score (TMS). Local anesthetic volume administered to the first patient of each group was 7.4 mL. Subsequent patients received volumes corresponding to 0.1 higher natural logarithm unit (if TME > 2) or lower (if TME < 2) as compared to natural logarithm of preceding volume. Massey and Dixon's formulae were used for MAV calculations.


RESULTS
MAVs of bupivacaine in both series were 6 mL and 6.2 mL, respectively. MAVs of levobupivacaine and enantiomeric S75/R25 bupivacaine were 5.7 mL and 5.8 mL, respectively. There were no differences between groups in effective anesthetic volumes.


CONCLUSIONS
Similar volumes of 0.5% racemic bupivacaine, 0.5% levobupivacaine and enantiomeric S75/R25 bupivacaine are needed for extraconal retrobulbar anesthesia.
Soares
Luiz Fernando
LF
CET, SBA Integrado de Anestesiologia, SES-SC, Brazil.
Barros
Ana Claudia de Melo
AC
Almeida
Gustavo Paiva
GP
Boos
Gustavo Luchi
GL
Oliveira Filho
Getúlio Rodrigues de
GR