Effects of intravenous lidocaine, ketamine, and the combination on the minimum alveolar concentration of sevoflurane in dogs

Objective To evaluate the effects of intravenous lidocaine (L) and ketamine (K) alone and their combination (LK) on the minimum alveolar concentration (MAC) of sevoflurane (SEVO) in dogs. Study Design Prospective randomized, Latin-square experimental study. Animals Six, healthy, adult Beagles, 2 males, 4 females, weighing 7.8 - 12.8 kg. Methods Anesthesia was induced with SEVO in oxygen delivered by face mask. The tracheas were intubated and the lungs ventilated to maintain normocapnia. Baseline minimum alveolar concentration of SEVO (MAC(B)) was determined in duplicate for each dog using an electrical stimulus and then the treatment was initiated. Each dog received each of the following treatments, intravenously as a loading dose (LD) followed by a constant rate infusion (CRI): lidocaine (LD 2 mg kg(-1), CRI 50 mu g kg(-1)minute(-1)), lidocaine (LD 2 mg kg(-1), CRI 100 mu gkg(-1) minute(-1)), lidocaine (LD 2 mg kg(-1), CRI 200 mu g kg(-1) minute(-1)), ketamine (LD 3 mg kg(-1), CRI 50 mu g kg(-1) minute(-1)), ketamine (LD 3 mgkg(-1), CRI 100 mu g kg(-1) minute(-1)), or lidocaine (LD 2 mg kg(-1), CRI 100 mu g kg(-1) minute(-1)) + ketamine (LD 3 mg kg(-1), CRI 100 mu g kg(-1) minute(-1)) in combination. Post-treatment MAC (MAC(T)) determination started 30 minutes after initiation of treatment. Results Least squares mean +/- SEM MAC(B) of all groups was 1.9 +/- 0.2%. Lidocaine infusions of 50, 100, and 200 mu g kg(-1) minute(-1) significantly reduced MAC(B) by 22.6%, 29.0%, and 39.6%, respectively. Ketamine infusions of 50 and 100 mu g kg(-1) minute(-1) significantly reduced MAC(B) by 40.0% and 44.7%, respectively. The combination of K and L significantly reduced MAC(B) by 62.8%. Conclusions and clinical relevance Lidocaine and K, alone and in combination, decrease SEVO MAC in dogs. Their use, at the doses studied, provides a clinically important reduction in the concentration of SEVO during anesthesia in dogs.