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Splenic Doppler Resistance Index for Detection of Circulatory Shock in Dogs

Pablo Alejandro Donati, Pablo E. Otero, Lisa Tarragona, Marcela Tunesi, Manuel Martín Flores, Santiago D´alotto, Arnaldo Dubín

Background
Circulatory shock in dogs leads to compromised tissue perfusion and organ dysfunction, often with early hypoperfusion in the splanchnic circulation. The splenic Doppler resistance index (RI), which reflects arteriolar resistance, has been shown in human studies to detect occult hemorrhagic shock before systemic hemodynamic changes appear. Given the dog spleen’s significant role in blood storage and response to shock, this study aimed to assess the utility of splenic RI in identifying circulatory abnormalities and evaluating response to fluid therapy in dogs.

Methods
A prospective clinical study was conducted on 18 hospitalized adult dogs: nine with circulatory shock and nine controls without hemodynamic abnormalities. Splenic RI was measured using Doppler ultrasonography, along with velocity–time integral (VTI) and left ventricular internal dimensions. Dogs with shock received a 30 mL/kg IV fluid bolus of isotonic crystalloid, after which measurements were repeated. Splenic RI was calculated as (peak systolic velocity − end-diastolic velocity)/peak systolic velocity. Statistical analysis included AUROC, sensitivity, specificity, and correlation assessments. Inter- and intraobserver variability were evaluated using ICC and coefficient of variation.

Results
Dogs with circulatory shock had significantly higher splenic RI values than controls (median: 0.64 vs. 0.54). The optimal RI cutoff for distinguishing shock was 0.61, yielding an AUROC of 1.00 with 100% sensitivity and specificity. Following fluid resuscitation, median RI significantly decreased (from 0.64 to 0.57), and VTI increased, suggesting improved cardiac output. A strong negative correlation was observed between VTI and splenic RI. Measurement reproducibility was good, with intraobserver ICC of 0.83 and interobserver ICC of 0.76, both with 14% variability.

Limitations
Limitations include a small and heterogeneous sample size, potential operator bias (as the ultrasonographer was not blinded to the group), and the exclusion of dogs when high-quality images could not be obtained within five minutes. Some control dogs had conditions potentially affecting intra-abdominal pressure, which was not measured. Furthermore, the inclusion of dogs with splenic pathology necessitated a sensitivity analysis to validate findings.

Conclusions
The splenic Doppler resistance index is a promising noninvasive tool for detecting circulatory shock and monitoring response to fluid therapy in dogs. The significant correlation with VTI and its responsiveness to fluid expansion underscore its clinical potential. However, further studies are needed to validate its broader application and ease of use in varied clinical settings.

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