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

Abstract

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: T_StSt (steady-state, after induction of anaesthesia and before start of surgery), T_Clamp (clamping of surgical drapes on the skin), T_Cut (cutaneous incision), T_PrePTA (retrospectively assessed 1min before a PTA decline of at least 20%) and T_EndIso (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 T_Clamp, T_Cut and T_PrePTA 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.

Keywords: Anaesthesia; Analgesia; Dog; Heart rate variability; Monitoring.