Performance of the Parasympathetic Tone Activity (PTA) Index to assess the intraoperative nociception in cats

Abstract

Parasympathetic tone activity (PTA) is an index based on the analysis of heart rate variability that has been recently developed to evaluate the analgesia/nociception balance in anesthetized animals. Detection of nociceptive stimuli responses during general anesthesia remains a challenge. Acute changes of at least 20% in heart rate and arterial blood pressure are clinically used to assess intraoperative nociception. Monitoring nociception is an important objective and allows for reducing the intraoperative stress response far beyond the basic control of hemodynamic responses. The nociception detection allows reducing of patient discomfort at recovery as well as severe postoperative pain, morbidity and mortality. The purpose of this study was to determine the utility of the PTA index for the assessment of analgesia/nociception during the intraoperative period in 49 female cats undergoing ovariectomy. We hypothesized that the PTA index could be used to assess a nociceptive response following a nociceptive stimulus and that its dynamic variation would permit anticipation of hemodynamic responses associated with nociception. Intra-surgical PTAi score, heart rate, respiratory rate and systolic and mean blood pressure were assessed at the following predefined time-points: T0 (basal values before any surgical stimulus of the anesthetized cats), T1 (clamping of surgical field drapes to the animal with Backhaus clamps), T2 (laparotomy of the abdominal cavity), T3 (handling of the right ovary), T4 (handling of the left ovary), T5 (closure of the abdominal cavity). 105 intraoperative “PTA events” (PTA decrease <50) were identified within all subjects, 79% being related to Medium-intensity stimuli. HR mean value was lower in Group 1 (127.84 bpm±20.4 bpm) compared to Group 2 (146.52±18.3 bpm). Regarding PTAi response time, it was longer in Group 1 (79.02±84.5s) than in Group 2 (35.32±32.35s). In Group 2, the mean value of PTAi Time (35.32±32.35s) was lower than the mean value of HR Time (37.50±18.77s). There were statistically significant differences between PTAi Time and HR Time in Group 2 (p≤0.05). There was a moderate negative correlation between PTAi and HR within all subjects exclusively at point T2, meaning that in the presence of nociception, the PTAi value decreases and HR increases. Keywords: analgesia; cats; nociception; ovariectomy; parasympathetic tone activity.