Performance of the Parasympathetic Tone Activity (PTA) index to predict changes in mean arterial pressure in anaesthetized horses with different health conditions.

The parasympathetic tone activity (PTA) index is based on heart rate variability and has been developed recently in animals to assess their relative parasympathetic tone. This study aimed to evaluate PTA index in anaesthetized horses with different health conditions and the performance of PTA variations (∆PTA) to predict changes in mean arterial pressure (MAP). Thirty-nine client-horses were anaesthetized for elective or colic surgery and divided into "Elective" and "Colic" groups. During anaesthesia, dobutamine was administered as treatment of hypotension (MAP <60 mmHg). In both groups, no significant variation of PTA and MAP were detected immediately before and after cutaneous incision. The PTA index increased 5 min before each hypotension, whereas it decreased 1 min after dobutamine administration. Horses of the Colic group had lower PTA values than those of the Elective group, whereas MAP did not differ between groups. 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 specificity of 94.6% for a threshold value of 25%. The PTA index in anaesthetized horses appears to be influenced by the health condition. The shift toward lower PTA values in colic horses may reflect a sympathetic predominance. An increase in PTA of >25% in 1 min showed an acceptable performance to predict 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.

Evaluation of the sublingual microcirculation with sidestream dark field video microscopy in horses anesthetized for an elective procedure or intestinal surgery.

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.

Performance of the Parasympathetic Tone Activity (PTA) index to assess the intraoperative nociception using different premedication drugs in anaesthetised dogs.

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), PTAE (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, PTAE 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 PTAE and HDR. The ΔPTA showed a fair performance in all groups (a mean [95% CI] AUC of 0.73 [0.62-0.82], 0.70 [0.59-0.79] and 0.71 [0.59-0.80] respectively in morphine, morphine + ACP and morphine + medetomidine). Although ΔPTA was rather altered by the premedication drug, it was able to predict, to a certain extent, haemodynamic reactions in all groups.

Effects of esmolol on systemic hemodynamics and heart rate variability measured using the Analgesia/Nociception Index in resuscitated piglets with Pseudomonas aeruginosa septic shock.

OBJECTIVE: To determine the effects of esmolol on hemodynamics and heart rate variability (HRV) in the early stage of sepsis. DESIGN: Prospective, randomized, controlled, parallel trial. SETTINGS: Veterinary research laboratory. ANIMALS: Ten anesthetized piglets. INTERVENTIONS: Septic shock was induced by infusing a suspension of live Pseudomonas aeruginosa IV in 10 anesthetized piglets. The piglets were resuscitated according to a standardized protocol using Ringer's lactate solution, norepinephrine, and milrinone. Once stabilized, the piglets were randomized to receive IV esmolol, titrated to a heart rate <90/min, or control, receiving saline. A pulmonary artery catheter and an arterial catheter were inserted for hemodynamic measurements. The Analgesia/Nociception Index (ANI) and the normalized HRV frequency domain parameters - high-frequency (HF), low frequency (LF), LF/HF ratio - were recorded using a proprietary monitor. MEASUREMENTS AND MAIN RESULTS: A significant decrease in cardiac output and heart rate, and a significant increase in systemic vascular resistance were observed over time in the esmolol group in comparison to the control group. No other differences were observed in hemodynamic parameters. No significant differences were observed in ANI variations or HRV parameters over time between groups. CONCLUSIONS: The administration of esmolol produced significant changes in hemodynamics with no change in ANI values or HRV parameters. Further study is needed to understand the effect of esmolol during sepsis.

Evaluation of the Parasympathetic Tone Activity (PTA) index to assess the analgesia/nociception balance in anaesthetised dogs.

The Parasympathetic Tone Activity (PTA) is an index based on the analysis of heart rate variability that has been recently developed to assess the analgesia/nociception balance in anaesthetised animals. The present study aimed to evaluate its performance in dogs undergoing surgery. Thirty dogs admitted for elective surgeries, were anaesthetised with a standardised protocol. PTA, heart rate (HR), systolic blood pressure (SBP) and HDR (defined as an increase by >20% in HR and/or SBP within 5min) were assessed at the following predefined time-points: TStSt (steady-state, after induction of anaesthesia and before start of surgery), TClamp (clamping of surgical drapes on the skin), TCut (cutaneous incision), TPrePTA (retrospectively assessed 1min before a PTA decline of at least 20%) and TEndIso (isoflurane discontinuation). The dynamic variation of PTA over 1min (∆PTA) was calculated at each predefined time-points and its performance to predict HDR was assessed by building Receiver Operating Characteristics (ROC) curves. A significant decrease of PTA (p<0.002) was detected 1min after TClamp, TCut and TPrePTA followed by a significant increase in HR and/or SBP within 5min after the time points (p<0.01). The ΔPTA was associated with the following performance in predicting HDR: AUC ROC [95% CI]=0.80 [0.71 to 0.88] (p<0.05), with a sensitivity of 77% and a specificity of 72% for a threshold value of -18%. Although encouraging, the performance of the PTA index and its dynamic variation needs to be further evaluated, particularly in different clinical contexts.