Induction of anaesthesia with remifentanil after bolus midazolam administration in Landrace/Large White swine.

OBJECTIVE: To investigate an alternative combination for anaesthesia induction in swine.

STUDY DESIGN: Randomized, 'blinded' experimental study.

ANIMALS: Forty-five Landrace/Large White swine weighing 20.0±1.5 kg.

METHODS: Pulse oximetry, heart rate (HR) and blood pressure were measured after premedication with ketamine, midazolam and atropine as well as after intubation following induction with a fixed dose of 0.2 mg kg-1 midazolam combined with 1, 2, 3, 4 or 5 μg kg-1 remifentanil (groups R1, R2, R3, R4 and R5, respectively). Intubation was evaluated using a numerical scoring system assessing jaw relaxation, resistance to the laryngoscope, vocal cord position, vocal cord movement and response to intubation. The time required to intubate and necessity for an additional midazolam dose were recorded. Baseline and post-intubation variables were compared with paired t tests, whereas for differences between the remifentanil groups the Spearman's rank correlation coefficient was estimated. Multivariate regression analysis was performed to disentangle the effect of remifentanil dose and the additional midazolam.

RESULTS: Higher dose of remifentanil was associated with better vocal cord position (p<0.001), better response to intubation (p<0.001), shorter time required for intubation (p=0.030) and less frequent necessity for additional administration of midazolam (p=0.004). In total, 39.5% of the animals required additional midazolam. In groups R1, R4 and R5, there were decreases in HRs (p=0.009, p=0.008 and p=0.032, respectively) between baseline and post-intubation phase; in groups R3 and R4, there were decreases in systolic blood pressure (p=0.040 and p=0.019, respectively). In the multivariate analysis, remifentanil dose was not associated with the observed changes in haemodynamic variables. One animal developed apnoea and four electrocardiographic anomalies; all resolved without pharmaceutical interventions.

CONCLUSIONS AND CLINICAL RELEVANCE: A combination of 0.2 mg kg-1 midazolam with 4 or 5 μg kg-1 remifentanil may provide an alternative method of anaesthesia induction for swine.