Stroke volume variation for assessment of the responsiveness to volume loading in canines with hemorrhagic shock: study on the comparison with hemodynamic parameters

Objective

To assess the significance of stroke volume variation and intrathoracic blood volume index on the responsiveness to volume loading in canines with hemorrhagic shock.

Methods

Healthy mongrel canines were studied first to standardize the modified Wiggers' blood loss shock method. The MAP reached 50 mmHg and was maintained for 60 min. Graded volume loading was performed with each volume loading step (VLS) consisting of 7 ml/kg Ringer's given for 2 min. The same VLSs were preformed after a period of 15 min of stability. Successive responsive VLSs were performed (increase in SV >5% after VLS) until a continuous change in SV <5% (nonresponsives) was reached. The values of HR, MAP, CVP, PAWP, ITBI, and SVV were determined immediately before and 5 min after volume loading. The responsives and nonresponsives were identified as two groups.

Results

(1) Responsive of VLS: 14 canines were studied and a total of 134 VLSs were performed. In 94 VLSs, an increase in SV of more than 5% was reached. In 40 VLSs, an increase in SV of less than 5% was reached (nonresponsives). (2) Comparison between the pre-VLS values of hemodynamic variables: the pre-VLS values of MAP, ITBI (79.6 ± 27.6 mmHg, 569.9 ± 341.4 ml/m²) in responsives were less than nonresponsives (98.8 ± 15.2 mmHg, 784.2 ± 407.1 ml/m²). The pre-VLS values of SVV (14.5 ± 4.0%) in responsives were more than nonresponsives (9.0 ± 2.7%), (P < 0.05), but no difference occurred in the values of HR, CVP, and PAWP. (3) Comparison between the change in the values of hemodynamic variables after VLS: the values of HR, CVP, PAWP, ITBI, and SVV in responsives differed from those of nonresponsives (P < 0.05).(4) Correlation between the pre-VLS values of hemodynamic variables and the change in SV after VLS (delta SV): statistically significant correlations were found between delta SV after VLS and the values of ITBI and SVV before fluid loading (r = 0.356 and 0.531, respectively) (P < 0.05). No correlation was found between delta SV and the value of HR, MAP, CVP, and PAWP before fluid loading (P > 0.05). (5) Correlation between the pre-VLS values of hemodynamic variables and delta SV: statistically significant correlations were also found between delta SV and delta CVP, delta PAWP, delta ITBI, and delta SVV after fluid loading (r = -0.371, -0.448, 0.438 and -0.376, respectively) (P < 0.05). (6) Assessment of the volume: using ROC analysis, the area under the curve for SVV was 0.872, and ITBI was 0.689, statistically more than those of HR, MAP, CVP, and PAWP. A SVV value of 9.5% or more will predict an increase in the SV of at least 5% in response to a VLS with a sensitivity of 92.6% and a specificity of 62.5%.

Conclusion

Assessment of SVV and ITBI on the responsiveness to volume loading were more useful indicators than HR, MAP, CVP, and PAWP. It as a functional preload parameter and, for online monitoring, may help to improve the hemodynamic management.