Orthogonal polarization spectroscopy to detect mesenteric hypoperfusion

Abstract

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.

Cytocam-IDF (incident dark field illumination) imaging for bedside monitoring of the microcirculation

“…Secondly, our data do not deal with the potential influence of intra-observer variability. Although a substantial variability has been reported in the jejunal mucosal microcirculation of pigs [ 29 ], multiple studies have confirmed the excellent reproducibility in the human sublingual area [ 4 , 5 , 26 ].…”

Towards integrative physiological monitoring of the critically ill: from cardiovascular to microcirculatory and cellular function monitoring at the bedside

“…This criticism is based on the fact that these devices have poor reproducibility and image quality [58,59] and require time-consuming off-line analysis of the acquired images. These devices also suffer from pressure artifacts imposed by the weight of the devices [56,57] and from an inability to implement automatic analysis software to process the generated images [60].…”

Microcirculatory assessment in daily clinical practice - not yet ready but not too far!

“…Several measurements can be obtained from these images (24) , including functional capillary density (density of perfused capillaries), total vessel density, and a semi-quantitative estimation of the flow patterns. Although semi-quantitative, these scores have a good reproducibility for flow estimation through different sites (12)(13)(14)(25)(26)(27) , with good agreement of flow measurements with software in experimental conditions (28) , even though the analysis may sometimes be more complex in the gut (29) . Some software for image analysis are currently available, but the technical procedure is somewhat still semiautomatic and allows only measurements of flows lower than 1 mm/sec.…”