Image analysis comparison of nerve staining with food dye, methylene blue or tissue marker.

OBJECTIVE: Novel locoregional techniques use dye studies to confirm successful nerve targeting. The goal was to objectively quantify and compare nerve staining characteristics of dye mixtures commonly reported in the literature using image analysis software. STUDY DESIGN: Prospective, randomized cadaveric study. METHODS: Thirty-six brachial plexus nerves from unpreserved pig cadavers were randomized into three groups of 12: FD (1:10 mixture of blue food dye and bupivacaine 0.5%), MB (methylene blue 1%) and TM (0.1:10 mixture of blue tissue marker and lidocaine 2%). Nerves were immersed in dye for 1, 15, 30 or 60 minutes (n = 3 each). Images of nerves before immersion (baseline) and at each time point with epineurium intact (superficial staining) and after longitudinal bisection (deep staining) were processed using image analysis software. Color saturation values were divided into quartiles (dark, medium-dark, medium-light or light). Percentage of stained nerve area in each quartile was calculated and compared using two-way anova. RESULTS: Superficially, at minute 1, dark saturation covered 40% of nerve area in FD versus 19% in MB (p = 0.04) and 0% in TM (p < 0.0001). In bisected nerves, dark and medium-dark saturations occurred only in FD; medium-light saturation comprised anywhere from 4% to 22.5% over time in FD versus <1% at any time in MB (p = 1.000; p = 0.343; p = 0.383; p = 0.262). Deep staining was not found in TM at any point. CONCLUSION AND CLINICAL RELEVANCE: Food dye rapidly stains superficial and deep nerve layers. Based on these characteristics, investigators can choose the appropriate dye for their study.

Agreement between hematocrits measured with electrical conductivity on the i-STAT analyzer and manual packed cell volume measurements in 148 chelonian patients.

BACKGROUND: Point-of-care (POC) analyzers are increasingly used for diagnostic testing in exotic animals. A few studies with small sample sizes, evaluating agreement between hematocrit (Hct) and packed cell volume (PCV) measurements in chelonians, showed conflicting results. OBJECTIVE: We aimed to assess the agreement between Hct values measured with a POC analyzer and manual PCV measurements in venous samples from 148 chelonians. METHODS: All chelonians that underwent bloodwork for clinical reasons had Hct measured with an analyzer employing electrical conductivity (i-STAT, Abbott), PCVs measured using centrifugation, and total solids (TS) measured with refractometry. Bland-Altman plots were built to assess agreement between the measurements. Generalized linear mixed models were used to determine the effect of different variables on the difference between Hct and PCV. RESULTS: Of 192 chelonians sampled during this period, 148 had Hct, PCV, and TS results. Hct significantly underestimated PCV, with a mean difference between the techniques of -3.8% (95% CI: -4.5 to -3.2; LoA: -11.5 to 3.8). There was a negative correlation between the value of TS and the difference between the methods. Controlling for other factors, the magnitude of the disagreement was not affected by the sex of the chelonian but was smaller in red-eared sliders (Trachemys scripta elegans). CONCLUSIONS: Hct values measured with electrical conductivity in chelonians significantly underestimated manual PCVs by about 4%. This difference should be considered whenever an Hct measured on a POC analyzer using electrical conductance is used in chelonian patient assessments.