Objective: To determine the cardiovascular effects of lidocaine infused intravenously (IV) in broiler chickens. Study design: Two phase study: Phase 1, randomized up-and-down study to determine effective dose 50 (ED<inf>50</inf>) for lidocaine; Phase 2, prospective randomized study to determine the cardiovascular effects of lidocaine. Animals: Seventeen Ross-708 broiler chickens (Gallus gallus domesticus) [11 chickens (Phase 1) and 6 chickens (Phase 2)], weighing 2.6-4.3 kg. Methods: After induction of anesthesia with isoflurane and placement of monitoring equipment including invasive blood pressure, chickens were administered lidocaine IV. During Phase 1, using an up-and-down design, each animal received a variable dose selected based on the response of the previous animal. During Phase 2, each animal was administered 6 mg kg<sup>-1</sup> of lidocaine IV over 2 minutes. Clinically irrelevant cardiovascular effects were defined as a relative decrease of heart rate (HR) and mean blood pressure (MAP) <30% subsequent to IV lidocaine administration. The ED<inf>50</inf> was defined as the dose rate that would cause clinically irrelevant cardiovascular depression in 50% of the population. Results: During Phase 1, using an up-and-down study design (n = 11), the ED<inf>50</inf> of lidocaine was determined to be 6.30 mg kg<sup>-1</sup> and 6.22 mg kg<sup>-1</sup> (95% confidence interval, 5.30-7.13 mg kg<sup>-1</sup>), when calculated by Dixon's up-and-down method, and logistic regression, respectively. During Phase 2, following infusion of lidocaine (6 mg kg<sup>-1</sup>), no clinically relevant effects on HR or MAP were detected in any animal. Conclusions and clinical relevance: Previous reports state that the dose of lidocaine used in birds should be ≤4 mg kg<sup>-1</sup>. In this study, 6 mg kg<sup>-1</sup> of lidocaine injected IV was not associated with adverse cardiovascular effects. These results suggest that the dose of 4 mg kg<sup>-1</sup> can be exceeded, at least in chickens, and opens the possibility of other therapeutic uses for lidocaine in birds.
- Local anesthesia
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