Time Variable Models of Severe Hemorrhagic Shock in Rats

Background: Classical teaching dictates that damage control resuscitation is ideally implemented within the first or ‘golden’ hour after trauma-related hemorrhage. Given the heterogeneity of trauma, varied models must be utilized to guide ongoing investigation. We sought to determine exactly what happens during the ‘golden hour’ by varying hemorrhage and down times and mimicking venous or arterial bleeding while varying oxygen therapy, a readily available pre-hospital intervention, on survival in a small-animal rodent model. Methods: Rats were bled by 40% of their blood volume over 30 or 60 min, with varied ‘down-times’ of 30, 45, or 60 min. FiO2 was administered at 21% or 40%, mimicking nasal cannula. Multiple linear regression was performed between the independent variables and each measured outcome. Sub-group analyses were stratified by survival. Results: There was no statistically significant variation in end-organ insult (lactate), cardiac functioning (cardiac output or left ventricle fractional area of change), mean arterial pressure at end experiment, survival, or survival times among the groups. Conclusions: This study adds to the data against an all-encompassing golden hour, as even a rapid hemorrhage with long down time did not decrease survival. Furthermore, we add to the body of literature in this field by examining cardiac markers of injury with transthoracic echocardiography.