Pulmonary function changes after interscalene brachial plexus anesthesia with 0.5% and 0.75% ropivacaine: A double-blinded comparison with 2% mepivacaine

The purpose of this investigation was to compare, in a prospective, double- blinded fashion, 0.5% and 0.75% ropivacaine with 2% mepivacaine to determin e their effects on respiratory function during interscalene brachial plexus (IBP) anesthesia. With ethical committee approval and written, informed co nsent, 30 healthy patients presenting for elective shoulder capsuloplastic or acromioplastic procedures were randomized to receive IBP anesthesia by 2 0 mL of either 0.5% ropivacaine (n = 10), 0.75% ropivacaine (n = 10), or 2% mepivacaine (n = 10). Block onset time, pulmonary function variables, ipsi lateral hemidiaphragmatic motion (ultrasonographic evaluation), and first r equirement of postoperative analgesic were evaluated. Surgical anesthesia ( loss of pinprick sensation from C4 to C7 and motor block of the shoulder jo int) was achieved later with 0.5% ropivacaine than with either 0.75% ropiva caine or 2% mepivacaine (P < 0.05), whereas the first pain medication was r equested later with both ropivacaine concentrations than with mepivacaine ( P < 0.0005). No differences in quality of the block or patient acceptance w ere observed in the three groups. All 30 patients had ipsilateral hemidiaph ragmatic paresis and large mean decreases in forced vital capacity (ropivac aine 0.5%: 40% +/- 17%, ropivacaine 0.75%: 41% +/- 22%, mepivacaine 2%: 39% +/- 21%) and forced expiratory volume at 1 s (ropivacaine 0.5%: 30% +/- 19 %, ropivacaine 0.75%: 38% +/- 26%, mepivacaine 2%: 40% +/- 10%). We conclud e that, when performing IBP anesthesia, 0.5% ropivacaine does not decrease the incidence of ipsilateral paresis of the hemidiaphragm compared with 0.7 5% ropivacaine and 2% mepivacaine. Implications: During the first 30 min af ter placing interscalene brachial plexus anesthesia, 0.5% ropivacaine does not provide clinically relevant advantages in terms of pulmonary function c hanges compared with either 0.75% ropivacaine or 2% mepivacaine. However, 0 .75% ropivacaine allows a short onset, similar to that of mepivacaine, with long postoperative analgesia.