RESUMO
This study explores the application of electric impedance tomography (EIT) to estimate tidal volume (VT) by measuring impedance change per breath (∆Zbreath). Seventeen healthy horses were anaesthetised and mechanically ventilated for elective procedures requiring dorsal recumbency. Spirometric VT (VTSPIRO) and ∆Zbreath were recorded periodically; up to six times throughout anaesthesia. Part 1 assessed these variables at incremental delivered VT of 10, 12 and 15 mL/kg. Part 2 estimated VT (VTEIT) in litres from ∆Zbreath at three additional measurement points using a line of best fit obtained from Part 1. During part 2, VT was adjusted to maintain end-tidal carbon dioxide between 45-55 mmHg. Linear regression determined the correlation between VTSPIRO and ∆Zbreath (part 1). Estimated VTEIT was assessed for agreement with measured VTSPIRO using Bland Altman analysis (part 2). Marked variability in slope and intercepts was observed across horses. Strong positive correlation between ∆Zbreath and VTSPIRO was found in each horse (R2 0.9-0.99). The agreement between VTEIT and VTSPIRO was good with bias (LOA) of 0.26 (-0.36-0.88) L. These results suggest that, in anaesthetised horses, EIT can be used to monitor and estimate VT after establishing the individual relationship between these variables.
RESUMO
OBJECTIVE: To compare the peribulbar injectate distribution and probability of regional anaesthesia of four peribulbar anaesthetic techniques in equine cadavers. STUDY DESIGN: Prospective experimental cadaver study. ANIMALS: A total of 12 isolated equine cadaver heads and 24 eyes. METHODS: The 24 orbits underwent one of four injection techniques (six orbits each) with a mixture (1:4) of contrast medium and saline (CM): 20 mL ventrolateral peribulbar injection (V-20), 20 mL dorsolateral peribulbar injection (D-20), combined ventrolateral and dorsolateral peribulbar injections 10 mL each (VD-20) or 20 mL each (VD-40). To evaluate and score CM distribution at the base of, within the extraocular muscle cone (EOMC), and around the optic nerve (before and after pressure application to the periorbital area), computed tomography was performed. To assess the probability of achieving locoregional anaesthesia, two criteria were applied and both scored as 'likely', 'possible' or 'unlikely'. To compare CM distribution scores between injection techniques, Kruskal-Wallis analysis of variance was used. Mann-Whitney U test was used for post hoc comparisons between groups when needed. A p value < 0.05 was considered significant. RESULTS: The CM distribution within the EOMC and around the optic nerve circumference was detected as 'possible' only after pressure application in seven out of 24 orbits (V-20, 3; D-20, 1; VD-40, 3). It was never considered 'likely' either before or after pressure application. The CM distribution at the EOMC base was considered 'likely' to provide regional anaesthesia in 50% (V-20), 0% (D-20), 33% (VD-20), 100% (VD-40) and in 66% (V-20), 16% (D-20), 50% (VD-20), 100% (VD-40) before and after applying pressure, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Complete regional anaesthesia seems more likely using the VD-40 technique, although the authors advise caution due to the risk of potential complications. Future studies are necessary to evaluate the efficacy of the technique in vivo.
