Bupivacaine with and without adrenaline in interscalene brachial plexus blockade. Studies in patients with rheumatoid arthritis.

The action of adrenaline on the pharmacokinetics of bupivacaine has been tested during two successive interscalene brachial plexus blocks in 10 patients with rheumatoid arthritis. The mean venous serum Cmax of bupivacaine after using it with or without adrenaline 1:200000 were 1.49 +/- 0.41 micrograms ml-1 and 2.46 +/- 0.85 micrograms ml-1, respectively. In spite of relatively high total serum concentrations, we could not detect any evidence of toxicity from bupivacaine. Significant tachycardia was seen after bupivacaine with adrenaline, but systolic and diastolic arterial pressures did not change significantly in any session. Marked subjective side effects were noticed only after bupivacaine with adrenaline (shivering twice and palpitations once). The serum protein bound fraction of bupivacaine was higher in rheumatic patients than in our healthy controls: 97.1 +/- 2.4% and 91.3 +/- 3.6%, respectively. Thus bupivacaine as a local anaesthetic agent seems to be even safer in patients with rheumatoid arthritis than in normal healthy volunteers, because of lower free fraction in the former.