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The number of injections does not influence local anesthetic absorption after paravertebral blockade

[Le nombre d’injections n’influence pas l’absorption d’un anesthésique local après un bloc paravertébral]

Erik Lemay, MD FRCP(C)^*, Joanne Guay, MD FRCP(C)^*, Christiane Côté, RN^*, Marie Claude Boivin, BSc and France Varin, PhD

^* From the Department of Anesthesiology, Maisonneuve-Rosemont Hospital;
and the Faculty of Pharmacy, University of Montreal, Montreal, Quebec, Canada.

Address correspondence to: Dr Joanne Guay, Département d’anesthésie-réanimation, Hôpital Maisonneuve-Rosemont, 5415 boul. L’Assomption, Montréal, Québec H1T 2M4, Canada. Phone: 514-252-3426; Fax: 514-252-3542; E-mail: joanne.guay{at}umontreal.ca

Purpose: The aims of this study are to determine if the injection of a single large dose of local anesthetics into the paravertebral space increases the risks of inducing toxicity compared with multiple small injections and to describe ropivacaine plasma concentrations resulting from paravertebral blockade.

Methods: Paravertebral blockade was performed using a solution of 10 mL ropivacaine 0.75%, 10 mL lidocaine CO₂ 2% plus 0.1 mL epinephrine 1:1000 either by a single injection at T₃ or T₄ (Group S, n = 6) or by five injections of 4 mL each at T₂ to T₆ (Group M, n = 8). Blood samples were taken at zero, five, ten, 15, 20, 30, 45, 60 and 90 min and at two, three, four, five, six and eight hours. Ropivacaine and lidocaine plasma concentrations were measured by high performance liquid chromatography.

Results: Maximal plasma concentrations were comparable for lidocaine: 2.6 ± 1.3 (S) vs 2.6 ± 0.8 µg•mL^-1 (M) and for ropivacaine: 1.3 ± 0.2 (S) vs 1.3 ± 0.1 µg•mL^-1 (M). Area under the plasma concentration-time curve was higher in Group M for lidocaine: 577.6 ± 146.1 vs 401.7 ± 53.2 mg•min^-1•mL^-1 (P = 0.04) but similar for ropivacaine: 381.1 ± 95.4 (M) vs 363.1 ± 85.3 mg•min^-1•mL^-1 (S).

Conclusions: The injection of a single large bolus of local anesthetics into the paravertebral space does not increase its absorption. Maximal ropivacaine plasma concentrations resulting from paravertebral blockade are similar to those reported with equivalent doses of bupivacaine.

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