Orthogonal polarization spectroscopy to detect mesenteric hypoperfusion.
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 (Qsma) reduction.


METHODS
University Animal Laboratory.


METHODS
In eight pigs, Qsma 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.


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% Qsma 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 Qsma reduction, and evaluation of perfused villi revealed blood flow reduction only when Qsma 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.
Department of Intensive Care Medicine, Bern University Hospital and University of Bern, Inselspital, CH-3010 Bern, Switzerland.
Hendrik
H
Bracht
Vladimir
V
Krejci
Luzius
L
Hiltebrand
Sebastian
S
Brandt
Gisli
G
Sigurdsson
Syed Z
SZ
Ali
Jukka
J
Takala
Stephan M
SM
Jakob
D000818:Animals; D007091:Image Processing, Computer-Assisted; D007583:Jejunum / Q000098:blood supply*; D017078:Laser-Doppler Flowmetry; D055806:Microvessels / Q000502:physiology*; D008871:Microvilli / Q000502:physiology; D015588:Observer Variation; D012039:Regional Blood Flow / Q000502:physiology*; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods*; D034421:Sus scrofa