Effects of cardiopulmonary bypass on microvascular reactivity monitored with near-infrared spectroscopy: is there a difference between smokers and non-smokers?
D. Smagghe, K. Lapage, S. De Hert and A. Moerman

Background and goal of the study: Both cardiopulmonary bypass (CPB) and smoking have been linked with a disturbance of vascular microcirculation. The aim of the present study is to evaluate whether the effect of CPB on microvascular reactivity differs between smokers and non-smokers.
Materials and methods: After approval by the local ethics committee and written informed consent, adult patients scheduled for elective coronary artery bypass grafting surgery were recruited prospectively. Twelve actually smoking patients were included. The control group consisted of 18 case-control matched non-smoking patients. Matched variables were gender, age, weight, haemoglobin and PaO2. 
Microvascular reactivity was assessed by the vascular occlusion test (VOT), measured by near-infrared spectroscopy (NIRS) (NIRO 200-NX). VOT was performed before the start of CPB and 10 minutes after weaning from CPB. Baseline, minimum and maximum NIRS values, desaturation rate and resaturation rate were recorded. Data were compared using the Wilcoxon and Mann Whitney U test for within and between group differences, respectively.
Results and discussion: Before CPB, there were no significant differences in NIRS values between smokers and non-smokers. After CPB, baseline and minimum values were significantly lower in the smokers group (66 vs 73%, p=0.01 and 35 vs 48%, p=0.03 for baseline and minimum value, respectively).
Desaturation rate increased significantly in the smokers group from 12.8%/min to 15.3%/min (p=0.008), whereas no significant change was observed in the non-smokers group (11.8 and 11.6%/min pre- and post-CPB, respectively). Resaturation rates did not change significantly (p=0.09 and p=0.16 for the smokers and non-smokers group, respectively).
The use of CPB may cause alterations in the microvascular perfusion and this can lead to impaired tissue oxygenation and organ dysfunction. The results of this study show that these alterations are more pronounced in the smoking population.
Conclusion: Given the lower NIRS values and the higher desaturation rate in the smoking group after CPB, we demonstrated that the effect of CPB on microvascular reactivity is more pronounced in smokers that in non-smokers.

03 / Effects of cardiopulmonary bypass on microvascular reactivity monitored with near-infrared spectroscopy: is there a difference between smokers and non-smokers?