• dog
• physiologic covariates
• propofol
• target controlled infusion

Introduction Target Controlled Infusion (TCI) is an anaesthetic technique which is gaining popularity in veterinary practice. Computer controlled infusion devices which are used for propofol TCI in dogs are integrated with a pharmacokinetic model which allows to predict the concentration of propofol at the effect site during administration of the drug. The primary aim of the study was to evaluate the variability in predicted effect site concentrations of propofol during recovery from propofol TCI anaesthesia in a heterogeneous population of dogs. The secondary aim of the study was to explore physiological covariates of patients that act as determinants of the predicted effect site concentration of propofol at different end points during the emergence from propofol TCI anaesthesia in dogs.
Material and Methods Dogs classified as ASA I and II undergoing non-surgical procedures were enrolled in this prospective clinical study. All dogs were premedicated with acepromazine (0.015 mg kg-1) IM and methadone (0.15 mg kg-1) IM. Anaesthesia was induced and maintained with a propofol TCI titrated on clinical requirements. Haemodynamic parameters during infusion and predicted effect site concentrations during recovery were recorded. End points defined during recovery from anaesthesia were: return of palpebral reflex, return of spontaneous ventilation, extubation, head lift, sternal recumbency and the ability to stand up. Variability in predicted effect site concentrations of propofol for each end point was evaluated. Physiological covariates of patients were explored as independent determinants of the predicted effect site concentration for each end point, using a multiple linear regression model.
Results Physiological covariates explored in a population of forty-eight dogs were: age, weight, sex, maximum heart rate during infusion, and pre-induction sedation score. Data processing with a multiple linear regression model showed that physiological covariates which best explain the variability in predicted effect site concentrations of propofol during recovery were weight, pre-induction sedation score and sex, which result to be independent predictors of the ability to stand up.
Conclusions The study introduced for the first time physiological covariates in a clinical context to explain the inter-individual variability in predicted effect site concentrations at recovery end points after propofol TCI anaesthesia in dogs.