Background and Goal of Study: Induction of anaesthesia causes significant haemodynamic changes, but little is known about its effects on the microcirculation. Yet, alterations in microvascular perfusion are known to be associated with impaired tissue oxygenation and organ dysfunction.1 Microcirculation can be assessed by measurement of the postocclusive reactive hyperaemia (PORH) response, which is a reproducible transient increase in blood flow after release of an arterial occlusion.2 In the present study, we evaluated the effects of anaesthesia induced physiological changes on microvascular reactivity.
Materials and Methods: After approval by the local research ethics committee and written informed consent, 35 adult patients scheduled for elective coronary artery bypass grafting surgery were recruited. PORH was measured with the use of near-infrared spectroscopy (NIRS), a non-invasive method for assessing tissue oxygenation and microvascular reactivity continuously.2,3 A NIRS sensor (Foresight) was applied on the forearm and arterial occlusion was achieved by inflating a blood pressure cuff. Microvascular reactivity was evaluated with PORH before and 30 minutes after anaesthesia induction. Oxygen consumption, recovery time (time from release of cuff to the maximum value) and rate of recovery were determined. Data were expressed as median [minimum, maximum] and were compared using the Wilcoxon signed rank test. 
Results and Discussion: Tissue oxygen saturation was significantly higher after induction of anaesthesia (70% [54,78] vs 73% [55,94], p=0.015). Oxygen consumption decreased significantly after induction, appreciable by the higher minimum tissue oxygen saturation (45% [29,69] vs 53% [28,81], p<0.001) and the slower oxygen consumption rate (11 %/min [4,18] vs 9 %/min [5,16], p<0.001). After induction of anaesthesia, recovery times were significantly longer (40 sec [20,120] vs 48 sec [24,356], p=0.004) and the rate of recovery was significantly lower (114 %/min [12,497] vs 80 %/min [3,271], p<0.001). 
Conclusion: The longer recovery times and slower rates of recovery indicate impaired microvascular reactivity after induction of anaesthesia. 
References: 
1. Vallet B. Crit Care Med 2002; S229 –S234
2. Futier E et al. Critical Care 2011; 15: R214
3. Moerman A et al. Curr Opin Anaesthesiol. 2015; 28:703-9

Effects of induction of anaesthesia on microvascular reactivity monitored by near-infrared spectroscopy