Extracorporeal Circulation Induced Microvascular Perfusion Injury of the Small Bowel

Abstract

Gastrointestinal complications following cardiopulmonary bypass (CPB) are relatively uncommon, but are associated with a high mortality rate. Impairment of bowel perfusion during and following CPB may serve as a trigger for the development of multiorgan failure. The aim of our study was the development of a new animal model allowing quantitative analysis of small bowel microcirculation during and after CPB. Twelve Landrace pigs served as laboratory animals. A 15-cm loop of the terminal ileum was exteriorized for microscopic observation. In 6 animals, a normothermic, partial left heart bypass (pLHB) was established for 2 h with a flow rate of 2,000 ml/min. Arterioles, collecting venules and the capillaries of the small bowel were recorded for the analysis of the microcirculation. All parameters were recorded prior to, during pLHB and up to 2 h after weaning off the bypass. Six sham operated animals served as controls. Despite unchanged hemodynamics, pLHB leads to microvascular perfusion disturbances of the small bowel. In pLHB animals, blood cell velocity in postcapillary venules (30–70 µm) was significantly decreased during and following bypass. Capillary density was also reduced during bypass and decreased even further after pLHB to only 30% of the control values. With this new large animal model for quantitative assessment of microvascular perfusion of the small bowel during CPB, it could be clearly demonstrated that partial normothermic left heart bypass leads to a significant disturbance of the small bowel microcirculation even under stable hemodynamic conditions.

The impact of selective visceral perfusion on intestinal macrohemodynamics and microhemodynamics in a porcine model of thoracic aortic cross-clamping

“…Relevant factors contributing to damage of the mucosa can also be a reduced functional capillary density of the small bowel and shunting of the microcirculation, as it has been described in septic shock and after mesenteric ischemia/ reperfusion. [25][26][27] Furthermore, that the flow pattern (pulsatile, nonpulsatile) of our artificial organ perfusion system had also an effect on the intestinal microvascular blood flow cannot be excluded. 28,29 Altogether, a detectable injury of the mucosa and muscularis occurred as a result of a prolonged "low-flow ischemia" during SVP caused by a decreased overall intestinal blood flow (CT and SMA).…”

Acute mesenteric ischemia after cardio-pulmonary bypass surgery

“…It is well established that CPB is responsible for mesenteric endothelial dysfunction and microcirculation disturbances even under stable hemodynamic conditions. An increase in the contractile response to alpha1-adrenergic agonist and an early release of pro-inflammatory substances has been observed after CPB [140][141][142] . Nevertheless, the effect of pulseless extracorporeal circulation on bowel hypoperfusion is still under debate [143,144] , and off-pump coronary artery bypass does not prevent subsequent mesenteric ischemia [134,145,146] .…”

A rat model of cardiopulmonary bypass with excellent survival

“…The underlying mechanisms are probably multifactorial, including surgical trauma, anaesthetic effects and muscle paralysis, increase in capillary permeability, and impacts of the CPB apparatus [5,6]. In order to clarify the pathophysiological processes, numerous experimental studies have been developed [7][8][9][10], but most have been performed in larger animal models, such as dogs, sheep, pigs, rabbits, etc. These models have substantial limitations because they are extremely expensive, they utilize very complex instruments, and are labor intensive.…”