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

[O estimulador de nervo periférico melhora a eficácia do bloqueio paravertebral proximal paravertebral proximal em ovelhas]

ABSTRACT

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, T_B) 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.

Keywords: regional anesthesia; large animals; ruminant; lidocaine