Published in:
01-10-2008 | Experimental
Orthogonal polarization spectroscopy to detect mesenteric hypoperfusion
Published in: Intensive Care Medicine | Issue 10/2008
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Objective
Orthogonal polarization spectral (OPS) imaging is used to assess mucosal microcirculation. We tested sensitivity and variability of OPS in the assessment of mesenteric blood flow (Q
sma) reduction.
Setting
University Animal Laboratory.
Interventions
In eight pigs, Q
sma was reduced in steps of 15% from baseline; five animals served as controls. Jejunal mucosal microcirculatory blood flow was recorded with OPS and laser Doppler flowmetry at each step. OPS data from each period were collected and randomly ordered. Samples from each period were individually chosen by two blinded investigators and quantified [capillary density (number of vessels crossing predefined lines), number of perfused villi] after agreement on the methodology.
Measurement and results
Interobserver coefficient of variation (CV) for capillary density from samples representing the same flow condition was 0.34 (0.04–1.41) and intraobserver CV was 0.10 (0.02–0.61). Only one investigator observed a decrease in capillary density [to 62% (48–82%) of baseline values at 45% Q
sma reduction; P = 0.011], but comparisons with controls never revealed significant differences. In contrast, reduction in perfused villi was detected by both investigators at 75% of mesenteric blood flow reduction. Laser Doppler flow revealed heterogeneous microcirculatory perfusion.
Conclusions
Assessment of capillary density did not reveal differences between animals with and without Q
sma reduction, and evaluation of perfused villi revealed blood flow reduction only when Q
sma was very low. Potential explanations are blood flow redistribution and heterogeneity, and suboptimal contrast of OPS images. Despite agreement on the method of analysis, interobserver differences in the quantification of vessel density on gut mucosa using OPS are high.