Although vasopressors have been used extensively in the treatment of hypovolemic shock, convincing evidence of their clinical efficacy is lacking. Many contemporary investigators, recognizing that a deficiency in capillary blood flow is accepted as the basic pathophysiologic defect in shock,1-4 have tried to determine the effect of vasopressors on small vessel flow. However, their efforts have been hindered by the lack of a method for measuring capillary flow. Unfortunately, most related work has dealt with an estimation of capillary flow based on the measurement of large vessel flow in anesthetized animals using operative methods. The hemodynamic variables introduced by anesthesia,5-9 operative manipulation,7 -10 and the frequently resultant hypothermia5,11 and hypovolemia have been overlooked often. Furthermore, these methods fail to differentiate nutritive capillary flow from arteriovenous pathway flow. If we are to evaluate flow changes in the microcirculation, we must use direct methods which eliminate these variables.
Olsen WR. III. Metaraminol and Capillary Flow in the Nonanesthetized and Anesthetized Pig. Arch Surg. 1969;99(5):637-640. doi:10.1001/archsurg.1969.01340170089021