Comparison of clip and needle electrodes for multifrequency bioimpedance analysis in anesthetized dogs

Multifrequency bioimpedance analysis provides resistance, reactance, and phase angle measurements that are used to characterize body fluid distribution and cellular electrical properties. However, studies reporting on body composition assessment using multifrequency bioimpedance analysis in dogs remain limited. Therefore, we aimed to evaluate the measurement characteristics of trunk multifrequency bioimpedance analysis in dogs and assess the influence of body position and electrode type and placement. We anesthetized seven adult Beagle dogs and performed trunk multifrequency bioimpedance analysis at 5, 50, and 250 kHz using clip and needle electrodes in sternal and left lateral recumbency at three electrode paths. For each condition, 150 repeated measurements were obtained and summarized as a mean value. Repeatability and inter-individual variability were assessed using coefficients of variation. Agreement between electrode types was assessed using Bland-Altman analysis and correlation analysis, and the effects of electrode type and body position were evaluated using linear mixed-effects models with dogs as a random effect. Measurements were feasible under all conditions and showed low intra-individual variability. Inter-individual variability was generally 10-15%, but higher variability was observed for reactance and phase angle at low frequencies. Mean biases between clip and needle electrodes were small for most parameters; however, reactance and phase angle at 5 kHz showed weaker correlations and wider limits of agreement. Across models, between-dog differences accounted for most variability, whereas body position influenced several parameters when the stifle was included in the electrode path. These data indicate that clip electrodes yield measurements with small mean biases relative to those obtained using needle electrodes under controlled conditions in anesthetized dogs; however, the limits of agreement varied among parameters, and wider differences observed at low frequencies suggest that the two electrode types should not be considered fully interchangeable. Accordingly, electrode placement and body position should be standardized for experimental comparison and carefully controlled when monitoring longitudinal changes within individual dogs.