Rectal microcirculatory alterations after elective on-pump cardiac surgery

Hemodynamic changes, related to on-pump cardiac surgery, have been reported to impair intestinal perfusion. However, until recently, direct in vivo observation of the intestinal microcirculation was not clinically feasible, and the concept of altered intestinal blood flow in the setting of cardiac surgery depended on indirect observations from other techniques, such as tonometry and microdialysis. To establish the incidence of intestinal microvascular alterations after cardiac surgery, we performed direct in vivo observation of the microcirculation in a clinically accessible part of the intestinal tract in this setting.

A single-center prospective observational study was conducted in postoperative elective on-pump cardiac surgery patients. Simultaneously, sidestream dark field (SDF) imaging and automated gas tonometry were performed in the rectal pouch within 30 minutes after ICU admission.

The rectal median microvascular flow index was 3(3-3) and the proportion of perfused vessels (PPV) was 85% (72-93). The median rectal-to-arterial partial carbon dioxide pressure difference (ΔPCO(2)) was 1.5 (-1.5-8.3) mmHg; 6 (21%) patients had a ΔPCO(2)> 8.3 mmHg, among them 2 (7%) with values> 10.5 mmHg.

After elective on-pump cardiac surgery, direct in vivo observation of rectal mucosa revealed a PPV <90% in 54% of all patients. At the same time, rectal microcirculatory blood flow appeared to be unaltered. Combining rectal SDF imaging with rectal tonometry revealed a 7% incidence of rectal-to-arterial pCO(2) gap >1.4,kPa, suggesting non-dysoxic perfusion in the majority of patients, despite the observed percentage of non-perfused crypts.