Utility of dynamic preload indices of hypovolemia in isoflurane-anesthetized horses.

SPV% and PPV% are useful dynamic preload indices in anesthetized horses; PVI% is not reliable.

This prospective experimental study evaluated three dynamic preload indices—systolic pressure variation (SPV%), pulse pressure variation (PPV%), and plethysmographic variability index (PVI%)—for detecting hypovolemia in eight isoflurane-anesthetized horses. Animals underwent graded hemorrhage (5 mL/kg increments to 25 mL/kg) followed by autotransfusion while hemodynamic parameters and cardiac output were continuously monitored. Baseline values were SPV% 9%, PPV% 14%, and PVI% 12%. At maximal hemorrhage (25 mL/kg), optimal cut-off values were SPV% 16.1% (96% accuracy), PPV% 28.5% (90% accuracy), and PVI% 15.4% (72% accuracy). Inverse correlations with cardiac output were strongest for PPV% (-0.49, p<0.007) and SPV% (-0.34, p=0.131), while PVI% showed weak correlation (-0.20, p=0.253). Accuracy of all indices improved proportionally with blood volume loss. The authors conclude that SPV% and PPV%, but not PVI%, represent useful dynamic preload indices for detecting hypovolemia in anesthetized horses with negative correlation to cardiac output.

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