Monitoring microvascular blood flow during hemorrhage and resuscitation

Abstract

Blood flow through the microvascular (arterioles, capillaries, venules) is critical to survival. Until recently, microvascular responses to cardiovascular events, such as hemorrhage and resuscitation, have been difficult to assess. Macrovascular responses (blood pressure, heart rate, large artery flow) have generally been easier to monitor, but aren’t always indicative of microvascular responses. While monitoring macrovascular reactions, we used orthogonal polarization spectral imaging (OPSI) to monitor microvascular responses to hemorrhage, low-pressure stabilization, and resuscitation. Methods: 8 anesthetized, ventilated dogs were hemorrhaged (H, 90min mean arterial pressure [MAP]=35-40mmHg or MAP<30mmHg>10min or MAP<25mmHg>1min), hypotensively stabilized (S, 120min enalaprilat 0.01mg/kg/hr + hemoglobin based oxygen carrier [HBOC] or 7.8% hypertonic saline dextran 70 [HSD] for MAP=40-45mmHg), resuscitated (60min lactated Ringer’s for MAP=75-80mmHg), then only monitored (60min no fluids), and euthanized. Sublingual and jejunal mucosal microvascular blood flow, visualized by OPSI, was recorded every 10 minutes. Results: 2 early non-survivors: NS1 (1 of 5 HBOC, died 117min into S) and NS2 (1 of 3 HSD, died 9min into S). Cardiac output, carotid blood flow, and systemic arterial blood pressure decreased during bleeding, were variably affected by low-pressure stabilization, and increased during resuscitation. Sublingual and jejunal mucosal microvascular blood flow video was collected, but motion and focus issues were extremely prevalent. Microvascular blood flow was decreased by hemorrhage and increased during resuscitation, but the microvascular effects of the low-pressure stabilization were difficult to analyze. Conclusion: Microvascular blood flow responses can be monitored, but motion and focus issues can make analysis quite difficult.