Dark-field microscopy in the assessment of large colon microperfusion and mucosal injury in naturally occurring surgical disease of the equine large colon.

This research investigates the use of dark-field microscopy (DFM) for assessing microperfusion–the blood flow through the tiniest vessels in the body–of the colon during surgery in horses. It primarily suggests that this method can be used to predict the severity of histopathological changes due to conditions like colonic volvulus (twisting of the colon).

Research Objectives and Methodology

• The research aimed to measure microvascular perfusion indices (MPI) of the pelvic flexure serosa (a part of the horse’s colon) during surgical interventions and correlate these with macroperfusion indices (MaPI), which measure larger blood vessels, and histomorphometry, which is a study of the form and structure of tissues.
• In this clinical case-control study, horses undergoing surgery for colonic volvulus, displacement, and/or simple obstruction were compared with control horses. Operational videos recorded during these surgeries were used to calculate parameters like total vessel density, perfused vessel density, the proportion of perfusion vessels, and microvascular flow index.
• Alongside these calculations, the arterial blood pressure and heart rate were also recorded as macroperfusion indices.
• A mucosal injury score was determined via histomorphometry method, providing a structural assessment of the tissue.

Results of the Study

• Horses with colonic volvulus exhibited lower blood flow in their microvasculature, as indicated by lower values for perfused vessel density, the proportion of perfusion vessels and flow index, compared to horses with nonstrangulating obstructions and control horses.
• The MPI were found to be correlated with the histomorphometry results, indicating that microvascular perfusion can predict the severity of tissue changes at the pelvic flexure.
• Interestingly, this study revealed no correlation between MPI and MaPI, implying that the blood flow in rather large vessels (macroperfusion) does not necessarily reflect the blood flow in the microvessels.

Conclusion and Future Direction

• The study concluded that dark-field microscopy provides an objective and feasible way to monitor microvascular perfusion during surgery. This method can help to quantify MPI in different colonic lesions, suggesting a correlation between MPI and the severity of tissue changes.
• Macroperfusion indices (large blood vessel indicators) were not found helpful to assess colonic microperfusion. Therefore, MPI can serve as a more reliable indicator of intestinal injury.
• Further research is required to explore whether dark-field microscopy can predict the survival rate in horses suffering from colonic volvulus.