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Background and goal of the study: The aim was to: (1) to determine the changes in gastric intramucosal pH (pHi) and partial pressure of gastric mucosal carbon dioxide (PrCO2) which are early indicators of circular failure during coronary artery bypass grafting (CABG); and (2) to elucidate the contribution of bronchial flow to the recorded laser Doppler (LD) perfusion signal during CABG. LD technique allows to record local pulmonary blood perfusion (LPBP).
Materials and methods: We studied eight consecutive patients (ASA III) scheduled for elective cardiac surgery requiring CABG. A standardized anaesthetic technique was used. The pump flow rate was set at 4.0 L min−1 m−2 at mild hypothermia (32.8°C). The tonometer catheter was inserted nasally after induction of anaesthesia and connected to an automated gas analyser (Tonocap TM, Datex, Finland). Angled endoscopic LD probe in the instrument channel of bronchoscope was introduced through the orifice of 3d segmental bronchus until wedging into small bronchus. Regional pulmonary vascular resistance at the site of the LD probe (LPVR) was calculated as a proportion between LD perfusion and the difference between pulmonary artery and pulmonary wedge pressure. Regional resistance of bronchial vascular bed (LBVR) was calculated as the proportion between LD perfusion and the difference between systemic arterial and central venous pressure.
Results: pHi decreased to the lowest value (7.25 ± 0.06) and PrCO2 increased to the highest value (58 ± 10) at the period of renewal of spontaneous circulation. Before patients transfer to ICU pHi and PrCO2 started to improve, but returned to normal 24 h after admission to ICU. Initial LPBP varied in different subjects from 32 PU to 144 PU (perfusion units) and LPVR - from 0.06 to 0.75 RU (resistance units). During CABG, when pulmonary perfusion was supported only by bronchial artery, LPBP dropped to the range from 1.0 to 18.5 PU, contributing 2.5-32.1% of initial perfusion, while LBVR was from 1.52 to 69 RU. Pulmonary reperfusion led to the increase of LPBP from 75 to 334% of initial and to corresponding drop of resistance from 0.14 to 0.3 RU.
Conclusions: pHi and PrCO2 (an indicator of splanchnic perfusion) changes during CABG were rather similar, but pulmonary perfusion, substantially supported from bronchial circulation, varied widely among patients.
