Analgesia and side effects of the addition of 10 or 20 µg fentanyl to articaine in spinal anesthesia for knee arthroscopy: a randomized and observer-blinded study.

OBJECTIVES: Articaine, a popular and rapidly acting local anesthetic in dentistry, has been also found to be beneficial in ambulatory spinal anesthesia. Analgesia in the intraoperative and immediate postoperative period may be further improved by adding fentanyl to the local anesthetic solution for spinal anesthesia. The aim was to evaluate dose-dependency of analgesia and side effects associated with intrathecal fentanyl additive to articaine for spinal anesthesia in knee arthroscopy patients. METHODS: In this randomized, observer- and patient-blinded study, 90 adult patients scheduled for elective ambulatory knee arthroscopy under spinal anesthesia were randomized into three groups: plain articaine 60 mg with saline (group AF0), articaine 60 mg with fentanyl 10 µg (group AF10) or 20 µg (group AF20) in a total volume of 1.9 ml. The blinded observer tested the sensory and the motor block, and performed telephone interviews on the first and seventh postoperative days. RESULTS: The median (IQR) duration of sensory block at the dermatomal level of T10 was significantly longer in groups AF10, 69 min (56) and AF20, 69 min (45) than in group AF0, 41 min (35) (p = 0.013). Motor block duration was similar in all groups (median 120 min). Group AF20 patients experienced pruritus significantly more often than patients in the other groups (p = 0.039). No acute or late anesthetic side effects occurred, and satisfaction with the anesthetic technique was the same in all groups (97% satisfied). CONCLUSIONS: Fentanyl 10 or 20 µg as additive to articaine for spinal anesthesia prolonged the duration of sensory block significantly and similarly. Fentanyl 20 µg was more often associated with pruritus than fentanyl 10 µg.

Pharmacokinetics of ropivacaine in uremic and nonuremic patients after axillary brachial plexus block.

Reports on the efficacy and pharmacokinetics of local anesthetics in uremic patients have been controversial. Our study involved 29 uremic and 28 nonuremic patients. We performed axillary block with ropivacaine 300 mg (50 mL). Venous blood samples were drawn for 24 h for assay of total and unbound plasma ropivacaine, 3-hydroxyropivacaine, pipecoloxylidide (PPX), and serum alpha(1)-acid glycoprotein (AAG). Block quality was similar in both groups. No toxicity occurred. Plasma clearance of ropivacaine was smaller and the area under the concentration-time curve of ropivacaine, 3-hydroxyropivacaine, and PPX larger in the uremic patients. The plasma concentration of PPX increased until 24 h in uremic patients whose AAG concentrations were also larger throughout the study. The free fraction of ropivacaine in plasma was smaller in the uremic group when measured 60 min and 12 h after the block, but the unbound concentration of ropivacaine was larger in the uremic group at 12 h. Enhanced absorption of ropivacaine into circulation, increased binding to AAG, and probably reduced urinary excretion of the metabolites lead to larger total plasma concentrations of ropivacaine and its main metabolites in uremic patients.