Plasma Concentrations of Bupivacaine after Spinal Anesthesia with Single Shot Femoral Nerve Block and Periarticular Injection in Total Knee Arthroplasty
Saowaphak Lapmahapaisan MD*, Thitima Chinachoti MD*, Wiriya Maisat MD*, Natthawat Kleebchan MD*, Somruedee Chatsiricharoenkul MD**, Keerati Charoencholvanich MD***, Paweenus Rungwattanakij RN*, Nuchanat Sakulpacharoen RN*, Jureeporn Sri-in MSc**
Affiliation : * Department of Anesthesiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand ** Department of Pharmacology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand *** Department of Orthopedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective : To determine the plasma concentrations of bupivacaine and toxicity after periarticular injection (PAI) combined
with spinal anesthesia and femoral nerve block (FNB).
Material and Method: Forty-three patients scheduled for unilateral total knee arthroplasty (TKA) were enrolled in the
prospective observational study. The dose of bupivacaine for spinal anesthesia was adjusted by the attending anesthesiologist.
The single-shot femoral nerve block (FNB) and periarticular injection (PAI) were performed with 20 ml of 0.5% bupivacaine
and 20 ml of 0.25% bupivacaine respectively. Venous blood samples from antecubital vein were collected at 60 minutes after
femoral nerve block and at the time before periarticular injection, then at 15, 30, 45, and 60 minutes afterwards. Plasma
bupivacaine concentrations were analyzed, using a high performance liquid chromatography with tandem mass spectrometry.
Results : Ten males and 32 females, ASA I-II were included. The highest median plasma concentration was 586.22 ng/ml
(min = 245.39, max = 1,614.36) at 45 minutes after periarticular injection. The maximum plasma bupivacaine concentration
was 1,709.71 ng/ml at 60 minutes after periarticular injection. No clinical toxicity was encountered.
Conclusion : The plasma concentration of bupivacaine in patients performed periarticular injection with 20 ml of 0.25%
bupivacaine after spinal anesthesia and single-shot femoral nerve block with 20 ml of 0.5% bupivacaine is below the plasma
toxic level.
Keywords : Plasma bupivacaine level, Femoral nerve block, Periarticular block
