Comparison of vascular reactivity through infrared spectroscopy between critically ill patients with and without Covid-19 and healthy individuals

<bold>Introduction:</bold> Near-infrared Spectroscopy (NIRS) can be used during a vascular occlusion test (VOT) to assess the rate of decrease in tissue saturation StO2, which is related to oxygen consumption, and the rate of increase, associated with the ability of microvascular hyperemia. <bold>Objectives:</bold> To compare vascular reactivity using VOT in critically ill patients, with or without COVID-19 diagnosis, and healthy individuals; and to analyze the influence of the microcirculatory response on clinical outcomes. <bold>Methods:</bold> This study is prospective and focuses on critically ill patients, comparing them to healthy non-smokers without a diagnosis of asthma, bronchitis, or COPD. During VOT, we verified the desaturation and resaturation curves and compared vascular reactivity (AUC - area under the curve following reperfusion) and baseline StO2 between the groups, and then analysed the outcomes. <bold>Results:</bold> 133 participants were included: 67 critically ill patients (34 COVID-19), with a median age of 62 yrs (29-85, 73% male), and 66 healthy subjects (median age: 39 yrs (18-74), 63% female. StO2 was higher in Covid-19 group (69.3 (64.2 - 73.5)) compared to the non-Covid (62.2 (57.5 - 67.0)), and with control group (66.9 (63.6 - 70.2)) (p< 0.05). The AUC was significantly lower in critically ill patients compared to controls, indicating lower vascular reactivity. Additionally, the AUC was lower for the death outcome compared to the discharge outcome for both COVID-19 and non-COVID ICU patients (p<0.05). <bold>Conclusions:</bold> The AUC of critically ill patients was lower than healthy individuals, and ICU patients that died showed lower values of AUC.