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OBJECTIVE To compare the sublingual microcirculation between healthy horses anesthetized for elective procedures and horses with colic anesthetized for abdominal surgery and to determine the effect of mean arterial blood pressure (MAP) on the microcirculation. ANIMALS 9 horses in the elective group and 8 horses in the colic group. PROCEDURES Sublingual microcirculation was assessed with sidestream dark field video microscopy. Videos were captured at 3 time points during anesthesia. Recorded microvasculature parameters were De Backer score (DBS), total density of perfused vessels (PVD) and small vessels (PVD-S), total proportion of perfused vessels (PPV) and small vessels (PPV-S), vascular flow index (MFI), and heterogeneity index (HI). Blood pressure during hypotensive (MAP < 60 mm Hg) and normotensive (MAP ≥ 60 mm Hg) episodes was also recorded. RESULTS During normotensive episodes, the elective group had significantly better PPV and PPV-S versus the colic group (median PPV, 76% vs 50%; median PPV-S, 73% vs 51%). In both groups, PPV decreased during anesthesia (elective group, −29%; colic group, −16%) but significantly improved in the elective group 15 minutes before the end of anesthesia (59%). During hypotensive episodes, PVD-S was better preserved in the colic group (11.1 vs 3.8 mm/mm2). No differences were identified for the microcirculatory parameters between normo- and hypotensive episodes in the colic group. CONCLUSIONS AND CLINICAL RELEVANCE Sublingual microcirculation was better preserved in healthy horses anesthetized for elective procedures than in horses with colic anesthetized for abdominal surgery despite resuscitation maneuvers. Results indicated that the macrocirculation and microcirculation in critically ill horses may be independent.

Background: The parasympathetic tone activity (PTA) index is based on heart rate variability recently and has been developed in animals to assess their relative parasympathetic tone and their analgesia nociception balance. The present study aimed to evaluate the variation of PTA in anaesthetized horses according to haemodynamic status and health conditions and to determine the performance of dynamic variations of PTA (∆PTA) to predict mean arterial pressure (MAP) variations.Results: Thirty-nine client-horses admitted to the Veterinary Campus of Lyon were anaesthetized for elective or emergency surgery and divided into "Colic" and "Elective" groups. During anaesthesia, dobutamine was administered as treatment of hypotension (MAP < 60 mmHg). No signi cant variation of PTA and MAP were detected immediately before and after the time of cutaneous incision. PTA increased 5 min before each hypotension (+15% in Elective and +11.4% in Colic group), conversely, PTA decreased 1 min after the administration of dobutamine (-12.7% in Elective and -9% in Colic group). Horses of the Colic group had lower PTA values than those in Elective group, whereas MAP didn't differ between groups. Globally, to predict a 10% increase in MAP, ΔPTA performance was associated with: AUC ROC [95% CI] = 0.77 [0.70 to 0.83] (p<0.0001), with a sensitivity of 88.2% and a speci city of 57.7% for a threshold value of −1%. Besides, to predict a 10% decrease in MAP, ΔPTA performance was associated with: AUC ROC [95% CI] =0.80 [0.73 to 0.85] (p<0.0001), with a sensitivity of 62.5% and a speci city of 94.6% for a threshold value of 25%.Conclusions: The PTA index in anaesthetized horses appears to be in uenced by the haemodynamic status and the health condition. The shift toward lower PTA values in colic horses may potentially re ects a sympathetic tone predominance. Of clinical signi cance, a PTA increase of >25% in 1 min showed an acceptable performance to predict a MAP decrease of >10% within 5 min. Even though these results require further evaluation, this index may thus help to predict potential autonomic dysfunctions in sick animals.