Changes in microcirculation variables in an acute endotoxaemic equine model.

Abstract

Background: Microcirculation is the essential link between macrocirculation and cellular metabolism.

Objectives: To test our hypotheses that microcirculation variables will show a heterogeneous flow pattern during experimental endotoxaemia, and that fluid therapy and noradrenaline (NA) infusion will normalise altered microcirculation variables.

Study design: In vivo experiments.

Methods: Six healthy adult horses were anaesthetised with dexmedetomidine, ketamine, and diazepam and were mechanically ventilated under isoflurane anaesthesia. Endotoxaemia was induced with 30 ng kg^-1 Escherichia coli lipopolysaccharide intravenously. One hundred and twenty minutes later fluid bolus and noradrenaline (NA) infusion were administered to produce normotension. Pulse rate (PR) and mean arterial blood pressure (MAP) were measured and microcirculation variables were obtained by side-stream darkfield technique (de Backer density (DBD), perfused de Backer density (PDBD), proportion of perfused vessels, microvascular flow index (MFI), heterogeneity index (HI)), laser Doppler flowmetry (blood flow) and white light spectrometry (tissue oxygen saturation (tSO₂)) in sublingual, jejunal and genital area. Measurements were obtained at baseline, after endotoxin, at 60 and 120 min and during the normotensive phase. Data were analysed by mixed model variance analysis and Tukey-Kramer.

Results: The PPV decreased significantly over time by 30% (p < 0.001) at the jejunum. MFI decreased from baseline to ET60 and from baseline to ET120 in sublingual and genital mucosa (2.9 vs. 1.4, p < 0.001 and 2.8 vs. 1.9, p < 0.01), respectively. The sublingual HI increased from baseline to ET60, ET120 and NA (0.1 vs. 0.9, p = 0.02; vs. 0.6, p = 0.01; vs. 0.3, p = 0.01), respectively. The genital HI increased from baseline to ET120 (0.2 vs. 1.1, p ≤ 0.01) and NA (0.16 vs. 0.53, p < 0.05, respectively). Moderate agreement between observers for MFI assessment was present (kappa = 0.4). The PR significantly increased, and MAP significantly decreased from baseline over time.

Main limitations: The obtained data could be influenced by secretions, pressure artefacts, the experience of the examiner and the sampling location. Blood flow was not quantified and there was no control group.

Conclusions: Overall, short-term experimental endotoxaemia did negatively alter MFI and HI; however, it did not alter tSO₂, blood flow, DBD, PDBD or proportion of perfused vessels. Intravenous fluid therapy and NA did not restore MFI and HI to baseline values.