RELATIONSHIP BETWEEN BODY-SURFACE AREA AND ARTERIAL CONCENTRATIONS OFBUPIVACAINE FOLLOWING LUMBAR EPIDURAL-ANESTHESIA

Background and Objectives. Most prior studies have shown no relationsh ip between body mass or body surface area (BSA) and maximum plasma con centration of local anesthetic agent (Cmax) following neural block. Me thods. Forty-nine patients, aged 55 or older, undergoing elective tota l hip arthroplasty, had arterial plasma bupivacaine concentrations mea sured (gas chromatography) at 10-minute intervals for the first 60 min utes following lumbar epidural injection of 25 mL 0.75% bupivacaine pl ain. Hemodynamic stability was maintained with either low-dose epineph rine (EPI) or phenylephrine (PHE) intravenous infusions. Results. A si gnificant relationship between arterial bupivacaine concentration and BSA was noted for both EPI and PHE groups at each observation point (P < .05). In addition, Cmax for each group was correlated to both BSA a nd body mass (P < .05). Arterial plasma bupivacaine concentrations wer e significantly higher in patients at 10, 20, 30, and 40 minutes follo wing epidural injection in patients receiving PHE than EPI (P < .05). Conclusions. Between 20% and 40% of the variability in the arterial co ncentrations of bupivacaine following lumbar epidural injection in eld erly patients can be accounted for by differences in BSA.