On the basis of SDNN and high-frequency power values, anesthetic levels between 0.75 and 1.5 MAC within the same anesthetic protocol could be differentiated, but with a large overlap among protocols. Usefulness of standard HRV variables for assessment of anesthetic depth and nociception in dogs is questionable.

Anesthesia with isoflurane alone resulted in the greatest overall EEG depression of all protocols. Use of remifentanil depressed the EEG response to nociceptive stimulation more strongly than did dexmedetomidine. The EEG variables evaluated did not appear useful when used alone as indicators of anesthetic depth in dogs.

Overall, the investigated standard HRV parameters offered no additional information for the monitoring of anaesthetic depths at the investigated, clinically used dose rates.