Changes in Intestinal Mucosal Microvascular Perfusion Assessed Using Orthogonal Polarisation Spectral Imaging in the Horse





Although several markers for measuring global tissue perfusion are available, there are currently no practical measurements of capillary microvascular perfusion in horses with hypovolaemia. Orthogonal polarisation spectral (OPS) imaging allows assessment of capillary microvascular perfusion by visualisation of mucosal blood flow. This study aims to demonstrate that administration of the α2 adrenoreceptor agonist detomidine, results in measurable changes in mucosal blood flow that can be determined using OPS. We hypothesise that these changes will mirror known aberrations in total peripheral resistance and cardiac output.


Microvascular blood flow was recorded using OPS placed manually, per rectum in 6 normal horses (weighing 603 ± 134 kg) undergoing sedation for a range of clinical procedures. The OPS recordings were made prior to and following sedation (5, 10, 20 min) with detomidine (10 ug/kg bwt) and butorphanol (10 ug/kg bwt) administered by i.v. injection. Microvascular perfusion was determined using standardised methods from OPS recordings including proportion of perfused vessels (PPV), functional capillary density (FCD), microvascular flow index (MFI) and vessel density (VD).


Detomidine had a significant effect on microvascular blood flow as demonstrated by changes in MFI, PPV and FCD 5 min following sedation (P<0.001) and changes in VD 10 min after sedation (P<0.02). Microvasculature had returned to the presedation baseline by 20 min for all criterions.


These data demonstrate that changes in organ perfusion known to be caused by α2 adrenoreceptor agonists result in observable changes in mucosal blood flow. This appears to mirror changes in cardiac output and total peripheral resistance previously demonstrated after administration of detomidine in the horse.

Practical significance

This technique may be a useful marker to use in early goal-directed therapy in horses with systemic inflammatory response syndrome (SIRS) and severe intestinal pathology.


The staff at DAC Melton Mowbray for their assistance with the conduct of the study.

Ethical animal research

This study was approved by the University of Nottingham ethical review committee. Horses were admitted into the DAC veterinary facility for routine veterinary procedures and sedated for routine dental care or orthopaedic investigation. Full consent was given by the DAC for use of these horses in the study. Sources of funding: Student project undertaken at the University of Nottingham. Competing interests: None.