Postoperative TOS levels were higher in the metoprolol group as compared with the carvedilol ( 29.6 vs 24.2 ; P < 0.0001 ) or the carvedilol plus NAC groups ( P < 0.0001 ) , and were also higher in the carvedilol group as compared with the carvedilol plus NAC group ( 24.2 vs 19.3 ; P < 0.0001 ) .