Objective: To compare data gathered via four different types of vascular occlusion test (VOT) by using near-infrared spectroscopy. The data may support a standardized method to appropriately measure the postischemic recovery slope, which is currently emphasized as a quantitative marker of the microvascular reserve in septic patients.
Design: Prospective study.
Setting: Medical intensive care unit of a university hospital.
Patients and measurements: In 20 healthy volunteers and in 20 septic shock patients, we measured muscle tissue oxygen saturation at the thenar eminence by using near-infrared spectroscopy and performed four different vascular occlusion tests in a random order. A pneumatic cuff was placed around either the upper arm (A) or the forearm (FA). Cuff inflation was maintained either during 3 mins (VOT(A3min) and VOT(FA3min)) or until muscle tissue oxygen saturation decreased to 40% (VOT(A40%) and VOT(FA40%)).
Results: In volunteers: 1) During VOT(A3min) and VOT(FA3min), the minimal muscle tissue oxygen saturation was significantly higher than 40% (52% ± 10% and 54% ± 6%, respectively), and 2) the muscle tissue oxygen saturation recovery slopes were steeper with VOT(A40%) and VOT(FA40%) than with VOT(A3min) and VOT(FA3min), respectively. Considering the pooled data obtained during VOT(A3min) and VOT(FA3min) (n = 40), recovery slope negatively correlated with minimal muscle tissue oxygen saturation in volunteers (r² = .46, p < .0001) as in septic patients (r² = .34, p = .0001). Considering the pooled data obtained during 40% VOTs, the recovery slope did not correlate with ischemic time in either group. The overlap of recovery slopes between volunteers and septic patients was small for both 40% VOTs but large for both 3-min occlusion VOTs.
Conclusion: The comparison of recovery slopes between volunteers and septic patients and the fact that the recovery slope was influenced by the extent of muscle tissue oxygen saturation decrease during ischemia and not by the ischemic time both support the use of a fixed minimal muscle tissue oxygen saturation target (40%) over the use of a fixed ischemic time (3 mins) for assessing reactive hyperemia by using near-infrared spectroscopy.