Hypotension during fluid-restricted abdominal surgery: effects of norepinephrine treatment on regional and microcirculatory blood flow in the intestinal tract.

Vasopressors, such as norepinephrine, are frequently used to treat perioperative hypotension. Increasing perfusion pressure with norepinephrine may increase blood flow in regions at risk. However, the resulting vasoconstriction could deteriorate microcirculatory blood flow in the intestinal tract and kidneys. This animal study was designed to investigate the effects of treating perioperative hypotension with norepinephrine during laparotomy with low fluid volume replacement. Twenty anesthetized and ventilated pigs were randomly assigned to a control or treatment (norepinephrine) group. Both groups received 3 ml · kg⁻¹ · h⁻¹ Ringer's lactate solution. In addition, the norepinephrine group received norepinephrine to stepwise increase blood pressure to 65 and 75 mmHg. Regional blood flow was measured in the splanchnic arteries. In the small bowel and colon, microcirculatory blood flow was measured using laser Doppler flowmetry. Intestinal tissue oxygen tension was measured with intramural Clark-type electrodes. Hepatosplanchnic and kidney blood flow remained unchanged after reversal of arterial hypotension to a mean arterial pressure of 75 mmHg with norepinephrine. For the norepinephrine group versus the control group, the mean ± SD microcirculatory blood flow in the jejunum (96 ± 41% vs. 93 ± 18%) and colon (98 ± 19% vs. 97 ± 28%) and intestinal tissue oxygen tension (jejunum, 45 ± 13 vs. 43 ± 5 mmHg; colon, 50 ± 10 vs. 45 ± 8 mmHg) were comparable. In this model of abdominal surgery in which clinical conditions were imitated as close as possible, treatment of perioperative hypotension with norepinephrine had no adverse effects on microcirculatory blood flow or tissue oxygen tension in the intestinal tract.