Effects of anaesthesia induction on microvascular reactivity monitored by near-infrared spectroscopy: is there a difference between smokers and non-smokers?
Willems H., Lapage K., De Hert S., Moerman A.
Ghent University Hospital, Dept of Anaesthesiology, Ghent, Belgium

Background and Aim of Study: 
Recent research has indicated that induction of anaesthesia impairs microvascular reactivity. Also smoking is known to affect microcirculation. The aim of the present study is to evaluate if the effect of anaesthesia on microvascular reactivity is more pronounced in smokers than in 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 12 case-control matched non-smoking patients. Matched variables were gender, age, weight, haemoglobin and PaO2. Microvascular reactivity was assessed by the post occlusive reactive hyperaemia (PORH) response, measured with near-infrared spectroscopy (NIRO-200NX). PORH was performed before and 30 minutes after anaesthesia induction. Oxygen consumption (VO2), recovery times (time from release of cuff to the initial (tR) and to the maximum value (tM)) and rate of recovery (recStO2) were determined. Data were compared using the Wilcoxon and Mann Whitney U test for within and between group differences, respectively.

Results and Discussion: 
Before induction of anaesthesia, only tR was significantly different between smokers and non-smokers (p=0.04). After induction of anaesthesia, all PORH values became significantly different between the smokers and the non-smokers group, except for recStO2. Oxygen consumption (VO2nad) decreased significantly after induction in both groups. The difference between the smokers and non-smokers became significant, with a higher oxygen consumption in the smokers group (94%/min vs 48%/min for smokers and non-smokers respectively, p=0.02). Recovery times (tR and tM) prolonged significantly after induction of anaesthesia in both groups, with significantly longer recovery times in the smokers group (p=0.01 and p=0.05 for tR and tM, respectively). Induction of anaesthesia had a significant effect on the recovery slope (recStO2) in the smokers group (p=0.04).  However, there was no difference between the smokers and the non-smokers .  
Since alterations in microvascular perfusion are known to be associated with impaired tissue oxygenation and organ dysfunction, this finding may have important implications for the anaesthesia management in smoking patients.


Conclusion: 
Given the higher VO2, the longer recovery times and the shortening of the recovery slope in the smoking group after induction of anaesthesia, we demonstrated that the effect of anaesthesia on microvascular reactivity is more pronounced in smokers than in non-smokers.

Effects of anaesthesia induction on microvascular reactivity monitored by near-infrared spectroscopy: is there a difference between smokers and non-smokers?