Methane Exhalation Can Monitor the Microcirculatory Changes of the Intestinal Mucosa in a Large Animal Model of Hemorrhage and Fluid Resuscitation

Abstract

Background: Internal hemorrhage is a medical emergency, which requires immediate causal therapy, but the recognition may be difficult. The reactive changes of the mesenteric circulation may be part of the earliest hemodynamic responses to bleeding. Methane is present in the luminal atmosphere; thus, we hypothesized that it can track the intestinal circulatory changes, induced by hemorrhage, non-invasively. Our goal was to validate and compare the sensitivity of this method with an established technique using sublingual microcirculatory monitoring in a large animal model of controlled, graded hemorrhage and the early phase of following fluid resuscitation. Materials and Methods: The experiments were performed on anesthetized, ventilated Vietnamese minipigs (approval number: V/148/2013; n = 6). The animals were gradually bled seven times consecutively of 5% of their estimated blood volume (BV) each, followed by gradual fluid resuscitation with colloid (hydroxyethyl starch; 5% of the estimated BV/dose) until 80 mmHg mean arterial pressure was achieved. After each step, macrohemodynamic parameters were recorded, and exhaled methane level was monitored continuously with a custom-built photoacoustic laser-spectroscopy unit. The microcirculation of the sublingual area, ileal serosa, and mucosa was examined by intravital videomicroscopy (Cytocam-IDF, Braedius). Results: Mesenteric perfusion was significantly reduced by a 5% blood loss, whereas microperfusion in the oral cavity deteriorated after a 25% loss. A statistically significant correlation was found between exhaled methane levels, superior mesenteric artery flow (r = 0.93), or microcirculatory changes in the ileal serosa (ρ = 0.78) and mucosa (r = 0.77). After resuscitation, the ileal mucosal microcirculation increased rapidly [De Backer score (DBS): 2.36 ± 0.42 vs. 8.6 ± 2.1 mm-1], whereas serosal perfusion changed gradually and with a lower amplitude (DBS: 2.51 ± 0.48 vs. 5.73 ± 0.75). Sublingual perfusion correlated with mucosal (r = 0.74) and serosal (r = 0.66) mesenteric microperfusion during the hemorrhage phase but not during the resuscitation phase. Conclusion: Detection of exhaled methane levels is of diagnostic significance during experimental hemorrhage as it indicates blood loss earlier than sublingual microcirculatory changes and in the early phase of fluid resuscitation, the exhaled methane values change in association with the mesenteric perfusion and the microcirculation of the ileum.

Keywords: diagnostic significance; exhaled methane; hemorrhage; resuscitation; small intestinal microcirculation.

Copyright © 2020 Bársony, Vida, Gajda, Rutai, Mohácsi, Szabó, Boros, Varga and Érces.

Figures

Figure 1

Experimental protocol (A) and timeline of the measurement period during the experiment (B).

Figure 2

Changes in mean arterial pressure (mmHg) (A), the superior mesenteric artery flow (ml min−1) (B), and exhaled methane levels (ppm) (C) during the hemorrhage and resuscitation phases. The plots demonstrate the median and the 25th (lower whisker) and 75th (upper whisker) percentiles. *p < 0.05 within group vs. baseline values.

Figure 3

Changes in De Backer score (1 mm−1) values (A), the microvascular flow index (B), and the heterogeneity index (C) for the mucosa (black circles) and serosa in the ileum (black triangle) and sublingual area (empty square) during the hemorrhage and resuscitation phases. The plots demonstrate the median values and the 25th (lower whisker) and 75th (upper whisker) percentiles. xp < 0.05 mucosa or sublingual values vs. serosa values; #p < 0.05 serosa or sublingual values vs. mucosa values; *p < 0.05 vs. baseline values.

Figure 4

Correlation between superior mesenteric artery flow (ml min−1) and changes in exhaled methane concentration (ppm) during the whole course of experiments (A; black scatters show the data collected during bleeding, and gray scatters show the data recorded during resuscitation), the hemorrhage (B; black scatters) and resuscitation phases (C; black scatters). The plot demonstrates the regression line (black line) and corresponding r values as indicators of the strength of the linear correlation and p significance values.

Figure 5

Correlation between the De Backer score (1 mm−1) for the serosa and changes in exhaled methane concentration (ppm) during the whole course of experiments (A; black scatters show the data collected during bleeding, and gray scatters show the data recorded during resuscitation), the hemorrhage (B; black scatters) and resuscitation phases (C; black scatters). The plot demonstrates the regression line (black line) and corresponding r and ρ values as indicators of the strength of the linear correlation and p significance values.

Figure 6

Correlation between the De Backer score (1 mm−1) for the mucosa and changes in exhaled methane concentration (ppm) during the whole course of experiments (A; black scatters show the data collected during bleeding, and gray scatters show the data recorded during resuscitation), the hemorrhage (B; black scatters) and resuscitation phases (C; black scatters). The plot demonstrates the regression line (black line) and corresponding r and ρ values as indicators of the strength of the linear correlation and p significance values.

Figure 7

Original tracings representing changes in exhaled methane levels (ppm) (continuous black line), the De Backer score (1 mm−1) for ileal mucosa (black circles) and superior mesenteric artery flow (ml min−1) (gray triangle) of an individual animal.

Figure 8

Correlation between the De Backer score (1 mm−1) for the serosa (A) or mucosa (B) and the De Backer score (1 mm−1) for the sublingual area during the hemorrhage phase. The plot demonstrates the regression line (gray line) and corresponding (black scatters) r values as an indicator of the strength of the linear correlation and p significance values.