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Lima A, Alamyar M, Bakker J. Int Care Med. 2009;35(Suppl 1):S205.
Introduction: Near-infrared spectroscopy (NIRS) in combination with a vascular occlusion test (VOT) has been proposed to assess and identify metabolic and microcirculatory alterations during sepsis and shock in critically ill patients. For the analysis of changes in the tissue O2 saturation (StO2) during a circulatory stress test, the sphygmomanometer is usually placed on the upper arm and the StO2 is measured over the thenar eminence. However, to automatize repeated measurements at the bedside, this technique can potentially cause discomfort to the patient. Vascular arterial occlusion in the finger may be a more attractive method to perform repeated measurements at the bedside because of patient tolerability.
Objective: To investigate whether vascular occlusion performed in the finger can be used as a surrogate for vascular occlusion in the upper arm to assess the dynamic StO2 response.
Methods: StO2 was non-invasively measured in 11 healthy volunteers during VOTs using two InSpectra Tissue Spectrometers (model 650) equipped with a 15-mm or a 10-mm probe. The 15-mm probe was placed over the thenar eminence and the 10-mm probe was place over the ventral face of the middle finger. We performed in each subject a series of three vascular occlusion tests on the finger (3, 5 and 10 min) followed by one on the arm (3 min). VOT-derived StO2 traces were analyzed for baseline, ischemic and reperfusion parameters.
Results: The general results of VOT in the finger and in the arm are shown in the following table:
DYNAMIC STO2 RESPONSE DURING VOT
|
Measurement site |
Arm |
Finger |
Finger |
Finger |
|
Probe |
15 mm |
10 mm |
10 mm |
10 mm |
|
Vascular occlusion time |
3 min |
3 min |
5 min |
10 min |
|
Baseline (%) |
82 ± 3a |
89 ± 10 |
91 ± 10 |
92 ± 17 |
|
Down-slope (% per min) |
-10 ± 3 |
-8.5 ± 2 |
-8.7 ± 2.6 |
-8.1 ± 2 |
|
Down-slope fit (R2) |
0.98 ± 0.01 |
0.96 ± 0.02 |
0.98 ± 0.01 |
0.98 ± 0.01 |
|
Up-slope (% s) |
4 ± 1.3a |
1.2 ± 0.5 |
1.7 ± 0.9 |
2.3 ± 1.5b |
|
Up-slope fit (R2) |
0.98 ± 0.01 |
0.92 ± 0.04 |
0.96 ± 0.02b |
0.95 ± 0.02b |
|
AUC Ischemic (% per min) |
46 ± 14 |
32 ± 11 |
84 ± 41c |
194 ± 55c |
aP<0.05 versus finger (3, 5, 10 min)
bP<0.05 versus finger 3 min
cP<0.05 versus thenar
StO2 baseline and StO2 up-slope in the finger differed significantly from the arm. No difference in the StO2 down-slope was found between arm and finger. Based on the curve fit (R2) for both StO2 slopes, the best occlusion time in the finger to study NIRS-dynamic variables was 5 min.
Conclusion: Near-infrared spectroscopy can be used on finger to assess the StO2 response to vascular occlusion test. Our results showed that 5 min is an adequate occlusion time to provide the best curve fit for NIRS dynamic variables.