A novel approach to assess hemorrhagic shock severity using the arterially determined left ventricular isovolumic contraction period

Recently, the ventilatory variation in pre-ejection period (Delta PEP) was found to be useful in the prediction of fluid-responsiveness of patients in shock. In the present study we investigated the behavior of the ventilation-induced variations in the systolic timing intervals in response to a graded hemorrhage protocol. The timing intervals studied included the ventilatory variation in ventricular electromechanical delay (Delta EMD), isovolumic contraction period (determined from the arterial pressure waveform, Delta AIC), pulse travel time (Delta PTT), and Delta PEP. Delta AIC and Delta PEP were evaluated in the aorta and carotid artery (annotated by subscripts Ao and CA) and were compared with the responses of pulse pressure variation (Delta PPAo) and stroke volume variation (Delta SV). The graded hemorrhage protocol, followed by resuscitation using norepinephrine and autologous blood transfusion, was performed in eight anesthetized Yorkshire X Landrace swine. Delta AIC(Ao), Delta AIC(CA), Delta PEPAo, Delta PEPCA, Delta PPAo, Delta PPCA, and Delta SV showed significant increases during the graded hemorrhage and significant decreases during the subsequent resuscitation. Delta AIC(Ao), Delta AIC(CA), Delta PEPAo, and Delta PEPCA all correlated well with Delta PPAo and Delta SV (all r >= 0.8, all P <0.001). Delta EMD and Delta PTT did not significantly change throughout the protocol. In contrast with Delta PEPAo, which was significantly higher than Delta PEPCA (P <0.01), Delta AIC(Ao) was not different from Delta AIC(CA). In conclusion, ventilation-induced preload variation principally affects the arterially determined isovolumic contraction period (AIC). Moreover, Delta AIC can be determined solely from the arterial pressure waveform, whereas Delta PEP also requires ECG measurement. Importantly, Delta AIC determined from either the carotid or aortic pressure waveform are interchangeable, suggesting that, in contrast with Delta PEP, Delta AIC may be site independent.