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The dynamic variations of the Parasympathetic Tone Activity (PTA) index were evaluated to assess nociception in dogs undergoing anaesthetic protocols with different premedication drugs. Sixty-six dogs, divided into three groups of 22 dogs each, were given different premedication drugs "morphine" (0.2 mg/kg), "morphine + medetomidine (5 μg/kg)", "morphine + acepromazine (0.03 mg/kg)", then similarly induced and maintained under general anaesthesia. The PTA, HR (heart rate) and MAP (mean arterial pressure) were assessed at S (steady-state), Cut (cutaneous incision), PTA E (PTA Event, assessed 1 min before a significant PTA decrease), HDR (Haemodynamic reaction, assessed 5 min before an increase of ≥ 20% in HR and/or MAP). For each group, the dynamic variation of PTA (ΔPTA) was calculated and a Receiver Operating Characteristics (ROC) curve was performed to detect if any of the premedication drugs may alter the performance of PTA index to predict intraoperative haemodynamic reactions. In all groups, a haemodynamic reaction was detected after Cut, PTA E and HDR and was preceded with a significant decrease of PTA, except for "morphine + medetomidine" group which showed a significant drop of PTA only at PTA E and HDR. The ΔPTA showed a fair performance in all groups (a mean [95%

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.