Influence of Constant Rate Infusions of Fentanyl Alone or in Combination With Lidocaine and Ketamine on the Response to Surgery and Postoperative Pain in Isoflurane Anesthetized Dogs Undergoing Unilateral Mastectomy: A Randomized Clinical Trial.

The aim of this study was to compare the effects of constant rate infusions (CRI) of fentanyl alone or combined with lidocaine and ketamine (FLK), on physiological parameters, isoflurane requirements and the number of postoperative analgesic rescues in dogs undergoing unilateral mastectomy. Twenty-two dogs were premedicated with acepromazine 0.02 mg/kg and morphine 0.5 mg/kg and anesthetized with propofol and isoflurane. Dogs were randomly assigned to 1 of 2 groups: Fentanyl group (fentanyl 5 µg/kg loading dose [LD] and 9 µg/kg/h CRI; n = 11); FLK group (fentanyl [same doses]; lidocaine 2 mg/kg LD and 3 mg/kg/h CRI; ketamine 1.0 mg/kg LD and 0.6 mg/kg/h CRI; = 11). Intraoperative evaluations were performed before the start of surgery and administration of the treatments (T0); three minutes after the LD (T1); during incision and tissue divulsion (T2); during closure of the surgical wound (T3). Meloxicam (0.1 mg/kg) was administered at T3. Blood samples were collected for determination of plasma concentrations of fentanyl, lidocaine and ketamine. Pain scores and the number of postoperative analgesic rescues with morphine (0.5 mg/kg) were evaluated for 24 hours postoperatively using the short form of the Glasgow Composite Measure Pain Scale. Compared to T0, significant decreases in heart rate (from 84 ± 28 to 53 ± 16 bpm in the Fentanyl group and from 93 ± 16 to 63 ± 15 bpm in FLK) and mean arterial pressure (from 61 ± 5 to 49 ± 10 mmHg in Fentanyl and from 59 ± 3 to 38 ± 6 mmHg in FLK) were observed at T1. Arterial hypotension was transient, with normalization of values at T2 and T3. The expired fraction of isoflurane did not differ significantly between the groups. Plasma concentrations of fentanyl, lidocaine and ketamine remained within the therapeutic range. Postoperatively, the number of dogs requiring analgesic rescue was significantly lower in the FLK (0/11, 0%) than in the Fentanyl group (5/11, 45%). In dogs administered morphine and meloxicam as part of the anesthesia protocol, an intraoperative CRI of FLK abolished the requirement for postoperative analgesic rescue for 24 hours in dogs undergoing mastectomy.

Determination of the effective dosage of tiletamine-zolazepam-ketamine-xylazine, with or without methadone, in dogs.

OBJECTIVE: To determine the effective dosage of the combination tiletamine-zolazepam-ketamine-xylazine (TKX), with or without methadone, in dogs. STUDY DESIGN: Prospective, randomized, experimental study. ANIMALS: A total of 29 dogs. METHODS: Dogs were randomly administered TKX (group TKX, n = 13) or combined with 0.3 mg kg-1 of methadone (group TKXM, n = 16) intramuscularly. The TKX solution contained tiletamine (50 mg mL-1), zolazepam (50 mg mL-1), ketamine (80 mg mL-1) and xylazine (20 mg mL-1). The effective dosages for immobility in 50% and 95% of the population (ED50 and ED95) were estimated using the up-and-down method. Approximately 20 minutes after drug administration, a skin incision was performed and the response was judged as positive or negative if the dogs moved or did not move, respectively. The TKX volume for the subsequent dog in the same group was increased or decreased by 0.005 mL kg-1 if the response of the previous dog was positive or negative, respectively. Heart and respiratory rates, and sedation/anesthesia scores (range 0-21) were recorded before and 15 minutes after drug administration. RESULTS: Estimated ED50 and ED95 (95% confidence intervals) were: TKX, 0.025 (0.020-0.029) and 0.026 (0.010-0.042) mL kg-1; TKXM, 0.022 (0.018-0.025) and 0.033 (0.017-0.049) mL kg-1. Median (interquartile range) scores for sedation/anesthesia were 17 (16-18) and 17 (15-20), and times until lateral recumbency were 5 (4-6) and 6 (4-10) minutes in TKX and TKXM, respectively (p > 0.05). In both groups heart and respiratory rates decreased, but values remained acceptable for anesthetized dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The results provide a guide for volumes of TKX and TKXM in dogs requiring restraint for minimally invasive procedures. Inclusion of methadone in the TKX combination did not influence ED50.

Epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing total unilateral mastectomy: a randomized clinical trial.

OBJECTIVE: To investigate the epidural administration of combinations of ropivacaine, morphine and xylazine in bitches undergoing unilateral mastectomy. STUDY DESIGN: Prospective, randomized, blinded, clinical study. ANIMALS: A total of 22 bitches scheduled to undergo unilateral mastectomy for mammary tumor excision. METHODS: Dogs were anesthetized with acepromazine (0.02 mg kg-1) and morphine (0.3 mg kg-1) intramuscularly, propofol intravenously (IV) and isoflurane. Prior to the beginning of surgery, dogs were randomly administered one of three epidural treatments: ropivacaine (0.75 mg kg-1) with morphine (0.1 mg kg-1) (group RM, n = 7); ropivacaine with xylazine (0.1 mg kg-1) (group RX, n = 8); or ropivacaine with morphine and xylazine (group RMX, n = 7). Cardiopulmonary variables and the expired concentration of isoflurane (Fe'Iso) were recorded intraoperatively. Meloxicam (0.1 mg kg-1) was administered IV during skin closure. Postoperative pain scores were evaluated with the Glasgow composite measure pain scale short form for 24 hours, and rescue analgesia with morphine (0.5 mg kg-1) was administered intramuscularly when pain scores were ≥ 6/24. RESULTS: Fe'Iso was significantly higher in group RM than in groups RX and RMX. Heart rate decreased significantly in groups RX and RMX, but blood pressure remained within acceptable values. The number of dogs administered rescue analgesia within 24 hours was significantly higher in group RX (seven dogs, 87.5%) than in groups RM (one dog, 14.3%; p = 0.01) and RMX (two dogs, 28.6%; p = 0.04). Time to standing was significantly longer in group RX than in group RM. CONCLUSIONS AND CLINICAL RELEVANCE: All epidural treatments provided adequate antinociception with minimal cardiovascular adverse effects during mastectomy. The inclusion of morphine (groups RM and RMX) provided the best postoperative analgesia. Owing to the undesirable effect of xylazine on ambulation, the combination ropivacaine-morphine appeared to provide greater benefits in bitches undergoing unilateral mastectomy.