Table 4 Mean values ± standard deviation of the pharmacokinetic parameters of ketamine and fentanyl in plasma samples of dogs treated with ketamine (GK: bolus 0.5 mg kg−1; CRI 20 µg kg−1 min−1 in intra- and postoperative periods), fentanyl (GF: bolus 5 µg kg−1; intraoperative CRI 5 µg kg−1 h−1 and postoperative CRI 2 µg kg−1 h−1), or combination of ketamine-fentanyl (GKF: aforementioned doses)