Effects of rapid repetition of a vascular occlusion test on near-infrared spectroscopy-derived variables in healthy subjects and in critically ill patients

Abstract

Introduction Transient ischemia modifies cellular metabolism and microvascular physiology in order to limit damage from future hypoxic episodes, a phenomenon called preconditioning. Near-infrared spectroscopy (NIRS) is a non-invasive technique that, when coupled to a vascular occlusion test (VOT), provides an indirect measurement of muscle oxygen consumption (VO2) and microvascular reactivity. We hypothesized that: rapid repetition of a VOT may alter VOTinduced NIRS-derived variables and these changes could reflect preconditioning; and these alterations would be diff erent in healthy volunteers and critically ill patients. Methods Continuous non-invasive measurements of thenar tissue oxygen saturation (StO2) were performed using NIRS technology (InSpectra 650; Hutchinson, USA). VOTs were performed by inflating a cuff to 50 mmHg above the systolic pressure for 3 minutes. In a group of healthy volunteers, the VOT was repeated after 5 minutes on day 1, after 15 minutes on day 2 and after 30 minutes on day 3. In a group of critically ill patients, the VOT was repeated after 5 minutes. For each VOT, we calculated the StO2 desaturation slope (DescSlope), StO2 resaturation slope (AscSlope) and the NIRS VO2 as the DescSlope×mean total hemoglobin index over the occlusion time. All statistical analyses were performed using SPSS 19.0 (IBM, USA). Results Twenty-one healthy volunteers (age 29 ± 6 years, heart rate 71 ± 6 bpm, mean arterial pressure 82 ± 6 mmHg) and 18 critically ill patients (age 59 ± 14 years, APACHE II score 21 ± 9, norepinephrine use in 10/18, ICU mortality 22%) were included. In the healthy volunteers, repetition of the VOT was associated with a decrease in the DescSlope and in NIRS VO2. This effect was not observed in the critically ill patients Conclusion Rapid repetition of a VOT alters VOT-induced NIRS-derived variables in healthy volunteers but not in critically ill patients. If these alterations reflect preconditioning, our results suggest that this phenomenon may be altered in critically ill patients. (Table Presented).