K. R. Koko1, J. P. Gaughan1, B. McCauley1, M. W. Fromer1, A. L. Hagaman1, N. S. Ryan1, S. S. Brown1, J. P. Hazelton1 1Cooper University Hospital,Trauma,Camden, NJ, USA
Introduction: Spectral analysis of continuous blood pressure and heart-rate variability provides a quantitative assessment of autonomic response to hemorrhage. This may reveal markers of mortality as well as endpoints of resuscitation.
Methods: 28 Yorkshire swine, ranging in weight from 35kg-40kg were included in the analysis. Four groups of animals were compared. Normothermic pigs who survived [S] and did not survive [NS], and coagulopathic pigs who survived [C-S] and did not survive [C-NS.] Hypothermia and coagulopathy was achieved by exchanging 20% of estimated blood volume with refrigerated normal saline solution. All pigs underwent a laparotomy and then sustained a standardized retrohepatic IVC injury Animals were then allowed to progress to class III hemorrhagic shock and where then treated with abdominal sponge packing followed by 6 hours of crystalloid resuscitation. Fast Fourier transformation calculations were used to convert the components of blood pressure and heart-rate variability into corresponding frequency classifications. Autonomic tones are represented as the following: HF=parasympathetic tone, LF=Sympathetic, VLF=Renin-angiotensin aldosterone system. The relative sympathetic to parasympathetic tone was expressed as LF/HF ratio.
Results: Baseline hemodynamic parameters were equal for the Survival [S](n=11), Non-Survival [NS](n=3), coagulopathic survival [C-S](n=11), and coagulopathic non-survival [C-NS](n=3) groups. LF/HF ratio decreased during initial laparotomy and bowel manipulation in the non-survival group ([S]1.3 vs [NS]0.3 p<0.05). LF/HF ratio increased significantly before death compared to corresponding times in survival groups (e.g. [S]2.3 vs [NS]0.8 p<0.05). Baseline sympathetic tone was increased during induction of coagulopathy and hypothermia compared to non-coagulopathic pigs; however, pigs who were able to recover to a lower sympathetic to parasympathetic ratio survived to complete the 6-hour resuscitation. Lastly, the non-survival group had significantly lower VLF signal during the hemorrhage and resuscitation period (e.g. [S]29.8±2.5 vs [NS]5.6±3.9 p<0.05).
Conclusion: An increased LF/HF ratio, indicative of sympathetic predominance following injury and during resuscitation was a marker of impending death. Spectral analysis of heart rate variability can also identify autonomic lability in hypothermic coagulopathic pigs, with implications for first responder triage. Furthermore, a decreased VLF signal during resuscitation indicates an additional marker of hemodynamic instability and death. These data indicate that continuous quantitative assessment of autonomic response can be a predictor of mortality and potentially guide resuscitation of patients in hemorrhagic shock.
