Effects of perfusion pressure on microcirculatory perfusion of gastric tubes in pigs

Abstract

Introduction: It is known that formation of a gastric tube after esophagectomy impairs microcirculatory perfusion in the anastomotic region. The impaired microcirculatory perfusion is caused by poor arterial inflow and insufficient venous drainage, due to ligation of three of the four gastric arteries. We therefore hypothesized that improving venous drainage by giving nitroglycerin (NTG) and titrating norepinephrine (NE) to increasing levels of mean arterial pressure (MAP) would improve microcirculatory perfusion of the distal part of the gastric tube. Methods: Five pigs, bodyweight 30.5 +/- 0.5 kg (mean +/- SD) were anaesthesized and instrumented for continuous hemodynamic monitoring. A median laparotomy was performed and a gastric tube was reconstructed. Laser speckle imaging was used to measure the microcirculatory blood flow (MBF) in the gastric tube. Laser speckle imaging is a laser-based technique that measures MBF in a macroscopic field at a video frame rate. NTG was titrated to in order to achieve a central venous pressure below 10 mmHg. MBF was measured at the base and at the distal site of the gastric tube at MAP increasing stepwise from 50 to 110 mmHg. For this purpose the MAP was decreased with infusion of propofol and increased with infusion of NE. We determined the flow at the distal site for each step compared with flow at the base of the gastric tube (fraction of flow) in percentages. Results: Hemodynamic values: MAP was increased in steps of 10 mmHg. The heart rate and cardiac output remained constant at around 123 +/- 28 bpm and 4.2 +/- 1.0 l/min, respectively. Central venous pressure and pulmonary artery occlusion pressure did not change throughout the experiment. MBF results: at MAP below 70 mmHg the fraction of flow at the distal part was 23.49 +/- 3.47%. This increased significantly to 31.12 +/- 9.15% at MAP between 70 and 90 mmHg. The fraction of flow for MAP above 90 mmHg was 29.42 +/- 6.84%. See Figure 1. Conclusions: Hypotension impairs flow in the distal part compared with the base of the gastric tube. Normotension significantly improves flow in this region. MBF in the distal part does not benefit from increasing MAP to supranormal values.