Peripheral nerve stimulator improves efficacy of the proximal paravertebral block in sheep

The purpose of this study was to compare the efficacy of proximal paravertebral anesthesia in sheep using a peripheral nerve stimulator and compare it to the Cambridge technique. Eight Santa Inês sheep, five females and three males aged 2 years and weighing 13kg were enrolled in the study. Right proximal paravertebral anesthesia was carried out using 2% lidocaine without vasoconstrictor, injected in the spaces between T13-L1, L1-L2 and L2-L3, with and without the aid of a peripheral nerve stimulator in two procedures with an interval of 7 days between treatments, which comprised: ST (stimulator treatment: 3mg kg-1 of lidocaine 2%) and CT (Cambridge control treatment, 6mg kg-1 of lidocaine 2%). Cardiorespiratory variables were recorded before the treatment (baseline, TB) and then at 15, 30, 45 and 60 minutes (T15, T30, T45 and T60, respectively) following local anesthesia. Effectiveness of the regional anesthesia was assessed by means of mechanical skin clamping at a point between the iliac crest and the lowest border of the last rib. Data were tested for normal distribution using the Shapiro-Wilk test and compared using Kruskal-Wallis followed by Dunn post-hoc test. Duration of the blockade was analyzed using a Kaplan-Meyer survival curve. Analyses were performed under 5% significance. ST took significantly longer and had greater success and greater duration. Positive response to skin clamping in CT was obtained in seven animals at T15 and one at T45, whereas in ST, one animal responded to skin clamping at T15, two at T30, four at T45 and one at T60. Duration was significantly longer in ST compared to CT according to the Kaplan-Meyer analysis. No changes were seen in cardiorespiratory variables throughout the study. In conclusion, the peripheral nerve stimulator increases the success of proximal paravertebral anesthesia using a lower dose of 2% lidocaine in healthy sheep.