Comparison of the cardio-respiratory effects of methadone and morphine in conscious dogs

A comparative analysis of opioid-free and opioid-sparing anaesthesia techniques for laparoscopic ovariectomy in healthy dogs

OBJECTIVE

To compare the perioperative analgesic effects of an opioid-free (OFA) and an opioid-sparing (OSA) anaesthetic protocol in dogs undergoing laparoscopic ovariectomy.

STUDY DESIGN

Prospective, randomized, blinded, clinical trial.

ANIMALS

A group of 28 client-owned dogs.

METHODS

Dogs were allocated to one of two groups. The OFA group was administered intramuscular (IM) dexmedetomidine 5 μg kg-1 and ketamine 1 mg kg-1, followed by two intraoperative constant rate infusions (CRIs) of dexmedetomidine (3 μg kg-1 hour-1) and lidocaine (1 mg kg-1 loading dose, 2 mg kg-1 hour-1). The OSA group was administered IM dexmedetomidine 5 μg kg-1, ketamine 1 mg kg-1 and methadone 0.2 mg kg-1, followed by two intraoperative saline CRIs. In both groups, anaesthesia was induced with intravenous (IV) propofol 2 mg kg-1 and diazepam 0.2 mg kg-1 and maintained with isoflurane. Rescue dexmedetomidine (0.5 μg kg-1) was administered IV if there was a 20% increase in cardiovascular variables compared with pre-stimulation values. Ketorolac (0.5 mg kg-1) was administered IV when the surgery ended. Postoperative analgesia was evaluated using the Short Form-Glasgow Composite Measure Pain Scale and methadone (0.2 mg kg-1) was administered IM if the pain score was ≥ 6/24. Statistical analysis included mixed analysis of variance, Chi-square test and Mann-Whitney U test.

RESULTS

There were no significant differences in the intraoperative monitored variables between groups. The OFA group showed a significantly lower intraoperative rescue analgesia requirement (p = 0.016) and lower postoperative pain scores at 3 (p =0.001) and 6 (p < 0.001) hours. No dogs were administered rescue methadone postoperatively.

CONCLUSIONS AND CLINICAL RELEVANCE

Although both groups achieved acceptable postoperative pain scores with no need for further intervention, the analgesic efficacy of the OFA protocol was significantly superior to that of the OSA protocol presented and was associated with a lower intraoperative rescue analgesia requirement and early postoperative pain scores.

Effects of tasipimidine premedication with and without methadone and dexmedetomidine on cardiovascular variables during propofol-isoflurane anaesthesia in Beagle dogs

OBJECTIVE

To evaluate cardiovascular effects of oral tasipimidine on propofol-isoflurane anaesthesia with or without methadone and dexmedetomidine at equianaesthetic levels.

STUDY DESIGN

Prospective, placebo-controlled, blinded, experimental trial.

ANIMALS

A group of seven adult Beagle dogs weighing (mean ± standard deviation) 12.4 ± 2.6 kg and a mean age of 20.6 ± 1 months.

METHODS

The dogs underwent four treatments 60 minutes before induction of anaesthesia with propofol. PP: placebo orally and placebo (NaCl 0.9%) intravenously (IV); TP: tasipimidine 30 μg kg-1 orally and placebo IV; TMP: tasipimidine 30 μg kg-1 orally and methadone 0.2 mg kg-1 IV; and TMPD: tasipimidine 30 μg kg-1 orally with methadone 0.2 mg kg-1 and dexmedetomidine 1 μg kg-1 IV followed by 1 μg kg-1 hour-1. Isoflurane in oxygen was maintained for 120 minutes at 1.2 individual minimum alveolar concentration preventing motor movement. Cardiac output (CO), tissue blood flow (tbf), tissue oxygen saturation (stO2) and relative haemoglobin content were determined. Arterial and mixed venous blood gases, arterial and pulmonary artery pressures and heart rate (HR) were measured at baseline; 60 minutes after oral premedication; 5 minutes after IV premedication; 15, 30, 60, 90 and 120 minutes after propofol injection; and 30 minutes after switching the vaporiser off. Data were analysed by two-way anova for repeated measures; p < 0.05.

RESULTS

Tasipimidine induced a significant 20-30% reduction in HR and CO with decreases in MAP (10-15%), tbf (40%) and stO2 (43%). Blood pressure and oxygenation variables were mainly influenced by propofol-isoflurane-oxygen anaesthesia, preceded by short-lived alterations related to IV methadone and dexmedetomidine.

CONCLUSIONS AND CLINICAL RELEVANCE

Tasipimidine induced mild to moderate cardiovascular depression. It can be incorporated into a common anaesthetic protocol without detrimental effects in healthy dogs, when anaesthetics are administered to effect and cardiorespiratory function is monitored.

The Outcomes of an Opioid-Free Anaesthetic Plan in Fourteen Dogs Undergoing Enucleation Using an Ultrasound-Guided Supra-Temporal Retrobulbar Block: A Retrospective Case Series

The objective of this retrospective case series is to report the outcomes of an opioid-free anesthetic plan in dogs undergoing enucleation surgery. A total of 14 dogs were admitted for enucleation between March and December 2020. A multimodal approach to perioperative analgesia was used, with a focus on retrobulbar anesthesia. A combination of an ultrasound-guided retrobulbblock with a supratemporal approach in association with ketamine, dexmedetomidine and non-steroidal anti-inflammatory drugs was used in the reported cases. Intraoperative nociception was defined as an increase of 20% from the baseline in one or more of the following parameters: heart rate, respiratory rate or mean arterial pressure. An ultrasound-guided retrobulbar block in an opioid-free anesthesia regime was effective at managing the perioperative analgesia of 13 out of 14 dogs. In only one case, a bolus of fentanyl was administered to treat intraoperative nociception. Recovery was uneventful in all the dogs, and the postoperative pain scores remained below the intervention threshold at all time points. To the authors' knowledge, this is the first reported case series of opioid-free anesthesia for enucleation in dogs.

Comparison of the sedative effects of three nalbuphine doses, alone or combined with acepromazine, in dogs

OBJECTIVE

To compare sedative, cardiopulmonary, and adverse effects of 3 nalbuphine doses, administered alone or in combination with acepromazine, in dogs.

ANIMALS

6 healthy dogs.

PROCEDURES

Dogs were administered nalbuphine (1.0, 1.5, or 2.0 mg/kg, intravenously [IV]) combined with physiologic saline solution (1 mL, IV; treatments SN1.0, SN1.5, and SN2.0, respectively) or acepromazine (0.05 mg/kg, IV; treatments AN1.0, AN1.5, and AN2.0, respectively) in random order, with a 1-week washout interval between treatments. Sedation scores, heart rate, mean arterial pressure, respiratory rate, and rectal temperature were recorded before and 20 minutes after administration of saline solution or acepromazine (T0), and nalbuphine was administered at T0. Measurements were repeated 15, 30, 60, 90, and 120 minutes after nalbuphine administration.

RESULTS

Treatments SN and AN resulted in at least 120 minutes of mild sedation and 60 minutes of moderate sedation, respectively. Sedation scores were greater for treatments AN1.0, AN1.5, and AN2.0 at various times, compared with scores for treatments SN1.0, SN1.5, and SN2.0, respectively. Administration of nalbuphine alone resulted in salivation and panting in some dogs.

CLINICAL RELEVANCE

All nalbuphine doses promoted mild sedation when administered alone, and moderate sedation when combined with acepromazine. Greater doses of nalbuphine did not increase sedation scores. All treatments resulted in minimal changes in heart rate, respiratory rate, rectal temperature, and mean arterial pressure. Nalbuphine alone resulted in few adverse effects.

Is high sensitive-troponin I a reliable biomarker for cardiac injury in methadone toxicity? A prospective cross-sectional study

Background

Methadone is a synthetic opioid mostly used for detoxification therapy, as its use increases; the possibility for methadone-induced cardiotoxicity may rise. The aim of this study was to determine the association of high-sensitivity troponin I levels as a predictor of cardiac injury in methadone toxicity.

Methods

Sixty methadone toxicity patients included in this prospective cross-sectional study from October 2018–November 2020. High-sensitivity troponin I level and electrocardiogram were assessed in patients at admission. All patients underwent echocardiography at admission and 30 days later and compared this finding between two groups based on high-sensitivity troponin I results.

Results

Mean age of the patients was 34.5 ± 11.1 years (males: 67%). Twenty (20%) patients had positive high sensitive-troponin results. Long QT interval and inverted T in precordial leads were mostly observed in individuals with positive high-sensitivity troponin I (75% vs. 35%, P = 0.013 and 83% vs. 16%, P < 0.001, respectively). Patients with elevated troponin had reduced left ventricular ejection fraction in comparison to normal group during admission (43.1 ± 15.4% vs. 55%, P < 0.001) and this left ventricular ejection fraction remained abnormal after 30 days (43.7 ± 21.6%). Patients in positive high-sensitivity troponin I group had higher regional wall motion abnormality frequency both at admission and 30 days later compared to the other group (0 day: 42% vs. 0, P < 0.001, 30th days: 25% vs. 4%, P = 0.020).

Conclusion

Patients with simultaneous methadone toxicity and positive high-sensitivity troponin I had worse cardiac outcomes and this biomarker could be probably used for better implementation of therapeutic interventions and prognosis.

Effects of morphine on histamine release from two cell lines of canine mast cell tumor and on plasma histamine concentrations in dogs with cutaneous mast cell tumor

OBJECTIVE

To determine the effects of morphine on histamine release from 2 canine mast cell tumor (MCT) cell lines and on plasma histamine concentrations in dogs with cutaneous MCTs.

ANIMALS

10 dogs with cutaneous MCT and 10 dogs with soft tissue sarcoma (STS).

PROCEDURES

The study consisted of 2 phases. First, 2 canine MCT cell lines were exposed to 3 pharmacologically relevant morphine concentrations, and histamine concentrations were determined by an ELISA. Second, dogs with MCT or STS received 0.5 mg of morphine/kg, IM, before surgery for tumor excision. Clinical signs, respiratory rate, heart rate, arterial blood pressure, rectal temperature, and plasma histamine concentrations were recorded before and 5, 15, 30, and 60 minutes after morphine administration but prior to surgery. Data were compared by use of a 2-way ANOVA with the Sidak multiple comparisons test.

RESULTS

In the first phase, canine MCT cell lines did not release histamine when exposed to pharmacologically relevant morphine concentrations. In the second phase, no differences were noted for heart rate, arterial blood pressure, and rectal temperature between MCT and STS groups. Plasma histamine concentrations did not significantly differ over time within groups and between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant changes in histamine concentrations were noted for both in vitro and in vivo study phases, and no hemodynamic changes were noted for the in vivo study phase. These preliminary results suggested that morphine may be used safely in some dogs with MCT.

Hemodynamic Effects of Different Combinations of Midazolam and Opioids in Healthy Dogs

The purpose of this study was to compare the hemodynamic effects of four different combinations of midazolam and opioids in healthy dogs. Twenty-four healthy dogs were divided in four groups (n = 6) using intramuscular midazolam 0.3 mg/kg and morphine 0.3 mg/kg (G_MOR), methadone 0.3 mg/kg (G_MET), butorphanol 0.2 mg/kg (G_BUT) or fentanyl 5 ug/kg (G_FEN). Cardiovascular variables were recorded before (T_B) and 20 minutes following drug administration (T₂₀) and comprised arterial blood pressure, heart rate and cardiac index. Subsequently, left ventricular work index and total peripheral resistance index were calculated using the previous variables. At the end of the study, data were compared using analysis of variance followed by Tukey test and Friedman followed by Dunn test, all under 5% significance. No differences were found on cardiovascular variables at all times among the groups, which indicates that all combinations provide hemodynamic stability for clinical sedation of healthy dogs. However, a few animals showed paradoxical excitation in G_BUT. In conclusion, the association of midazolam with morphine, methadone, butorphanol or fentanyl provides cardiovascular stability and can be used to sedate dogs undergoing cardiovascular examination, although caution is warranted with the use of midazolam with butorphanol due to possible paradoxical excitation.

Combined Cardiopulmonary Assessments Using Impedance and Digital Implants in Conscious Freely Moving Cynomolgus Monkeys, Beagle Dogs, and Göttingen Minipigs: Pharmacological Characterization and Social Housing Effects

Respiratory monitoring, using impedance with implanted telemetry in socially housed animals, was not possible until the recent development of digital signal transmission. The objective of this study was to evaluate digital telemetry monitoring of cardiopulmonary parameters (respiratory rate, tidal volume, minute volume, electrocardiography (DII), systemic arterial blood pressure, physical activity, and body temperature) in conscious, single-housed, non-rodent species commonly used in toxicology studies following administration of positive/negative controls (saline, dexmedetomidine, morphine, amphetamine, and doxapram), and also, the effects of various social housing arrangements in untreated female and/or male cynomolgus monkeys, Beagle dogs, and Göttingen minipigs (n = 4 per species). Aggressions were observed in socially housed male minipigs, however, which prevented pair-housed assessments in this species. All tested pharmacological agents significantly altered more than one organ system, highlighting important inter-organ dependencies when analyzing functional endpoints. Stress-related physiological changes were observed with single-housing or pair-housing with a new cage mate in cynomolgus monkeys and Beagle dogs, suggesting that stable social structures are preferable to limit variability, especially around dosing. Concomitant monitoring of cardiovascular and respiratory parameters from the same animals may help reduce the number of animals (3 Rs) needed to fulfill the S7A guidelines and allows for identification of organ system functional correlations. Globally, the data support the use of social housing in non-rodents for safety pharmacology multi-organ system (heart and lungs) monitoring investigations.

Sedative Effects of Intramuscular Dexmedetomidine and Ketamine at Sub-Anesthetic Dose Alone or in Combination with Methadone in Healthy Dogs

The aim of the present study was to compare sedation quality and cardiorespiratory parameters in healthy dogs after intramuscular injection of dexmedetomidine and ketamine with or without methadone. Forty client-owned dogs were randomly divided into two groups and received IM dexmedetomidine (5 µg kg^-1) and ketamine (1 mg kg^-1), associated (DKM group) or not (DK group) with methadone (0.2 mg kg^-1). Sedation, heart rate (HR), respiratory rate (ƒ_R), mucous membrane and rectal temperature were recorded at baseline (T0) and after 5 (T5), 10 (T10) and 20 (T20) minutes. From T10, cardiac rhythm was monitored with a continuous lead II electrocardiogram. Ease of venous catheter placement, total propofol dose and any apnea episodes were recorded. Sedation was significantly greater in the DKM group, and a significant increase from T5 to T20 within DKM (P = .0002) and DK (P = .008) was also observed. Within each group, HR was significantly lower at all time points compared to baseline. No significant differences between groups were found in the number of arrhythmogenic events (atrioventricular blocks). In both group ƒ_R decreased over time. The propofol dose required for anesthesia induction was significantly lower (P = .027) in the DKM group. In conclusion, a good level of sedation was achieved in both groups, although this was greater in DKM. Smooth animal-operator interaction and ease of venous catheter placement showed that DK was a useful sedative protocol in healthy patients.

Laryngeal paralysis secondary to cervical bite injuries in five dogs

CASE HISTORIES

Medical records of a veterinary hospital in Belgium were reviewed for dogs (n = 5) that presented between 2016 and 2019 with laryngeal paralysis secondary to bite wounds to the cervical region received while fighting with other dogs. The time elapsed between the trauma and presentation was from a few hours up to 5 days.

CLINICAL FINDINGS AND TREATMENT

Bilateral laryngeal paralysis was identified in three dogs and unilateral laryngeal paralysis in two dogs via endoscopic assessment of laryngeal function. The primary concomitant lesions included tracheal injury in 3/5 dogs and oesophageal injury in 1/5 dogs. One dog with bilateral laryngeal paralysis was treated medically as no signs of dyspnoea were present. Surgical management was elected in 4/5 dogs based on evaluation of their clinical status and lesions revealed by endoscopic examination of upper gastrointestinal and respiratory tracts. Dogs underwent surgical procedures that were determined to be appropriate for treatment of the lesions identified on clinical examination, diagnostic imaging, and endoscopy. The cervical region was explored through a ventral midline approach in 2/4 cases, to close tracheal perforations. Temporary tracheostomy was performed in 2/4 cases. Procedures to correct brachycephalic airway obstructive syndrome were performed in 2/4 cases. Cricoarytenoid lateralisation was performed in 2/4 dogs. Dogs were hospitalised for 2-10 days and received antimicrobial therapy before surgery and for 2-3 weeks after surgery. Physical examination and respiratory function were normal in 3/5 dogs 4-6 months after discharge. Information regarding outcomes for two cases was obtained from the owners by telephone assessment 1-6 months after surgery. The owner of each dog reported the respiratory function to be excellent.

DIAGNOSIS

Uni- or bilateral, transient or permanent laryngeal paralysis with concomitant oesophageal, tracheal, or laryngeal lesions following cervical dog bite injuries diagnosed by endoscopic examination of upper gastrointestinal and respiratory tracts.

CLINICAL RELEVANCE

This case series describes the diagnosis and management of dogs with laryngeal paralysis secondary to cervical dog bite injuries. To the authors' knowledge, this is the first published report documenting bilateral laryngeal paralysis secondary to cervical dog bite injuries. Clinicians should be aware of this pathology and the importance of investigating laryngeal function in dogs presenting with cervical bites, particularly those with inspiratory dyspnoea. Upper airway and digestive endoscopy are recommended for complete assessment of cervical traumatic injuries.

Evaluation of analgesic interaction between morphine, maropitant and dexmedetomidine in dogs undergoing ovariohysterectomy

ABSTRACTAims: To compare the analgesic effect of morphine combined with maropitant and/or dexmedetomidine to morphine alone but at a higher dose, and to evaluate the pharmacokinetics of the drug combinations, in dogs undergoing ovariohysterectomy (OHE).Methods: Forty client-owned dogs were randomised into four treatment groups (n = 10 per group) each to receive a different analgesic protocol. After premedication with I/M acepromazine, anaesthesia was induced with propofol to effect and maintained with isoflurane in 100% oxygen delivered via a circle system. The heart rate, respiratory rate, blood pressure, haemoglobin oxygen saturation, end-tidal partial pressure of carbon dioxide, electrocardiogram and rectal temperature were monitored during anaesthesia. The test drugs (Mor: 0.6 mg/kg morphine; Maro + Mor: 0.3 mg/kg morphine and 1 mg/kg maropitant; Dex + Mor: 0.3 mg/kg morphine and 10 μg/kg dexmedetomidine; Dex + Maro + Mor: 0.2 mg/kg morphine, 7 μg/kg dexmedetomidine and 0.7 mg/kg maropitant) were administered I/M after induction of anaesthesia and 30 minutes before the expected start time of ovariohysterectomy, which was carried out by veterinary students under veterinary supervision. The short form of the Glasgow composite measure pain scale (CMPS-SF) and visual analogue scale (VAS) were used for pain assessment at 15 and 30 minutes and 1, 2, 3, 6, 9 and 24 hours after extubation. Dogs with CMPS-SF pain score ≥ 6 received rescue analgesia with S/C buprenorphine (0.02 mg/kg). Blood samples were collected before, 15, 30, 60 and 120 minutes after injection of the test drugs and concentration of the test drugs in plasma was determined by liquid chromatography-mass spectrometry.Results: Dogs that received Dex + Mor had significantly lower CMPS-SF (estimate of difference = -1.53 (SE 0.58); p = 0.010) and VAS (estimate of difference = -0.67 (SE 0.25); p = 0.007) scores compared to the dogs that received morphine alone. There was no evidence of a difference in the number of dogs requiring rescue between groups. All dogs that received dexmedetomidine showed cardiac arrhythmia and second-degree heart block. Mean (SD) maximum concentrations (C_max,) of morphine in plasma were 6.8 (4.56), 9.56 (8.29), 9.30 (3.35) and 18.99 (9.41) ng/mL for the groups Dex + Mor, Dex + Maro + Mor, Maro + Mor and Mor respectively. The C_max of morphine was significantly lower in the Dex + Mor (p = 0.004), Dex + Maro + Mor (p = 0.034) and Maro + Mor (p = 0.018) groups compared to the Mor group.Conclusions For dogs undergoing ovariohysterectomy, lower doses of morphine (0.2 and 0.3 mg/kg) combined with dexmedetomidine or maropitant may provide analgesia equivalent to or better than morphine when given alone at a higher dose (0.6 mg/kg).Abbreviations: AUC: Area under curve; C_max: Maximum concentration in plasma; CMPS-SF: Glasgow composite measure pain scale - short form; NK1: Neurokinin-1; OHE: Ovariohysterectomy; T_max: Time to C_max; T_1/2: Half-life of terminal elimination phase; VAS: Visual analogue scale.

Plasma levels of a methadone constant rate infusion and their corresponding effects on thermal and mechanical nociceptive thresholds in dogs

Background

The present study aimed to collect pharmacokinetic data of a methadone continuous rate infusion (CRI) and to investigate its effect on mechanical and thermal nociceptive thresholds. Seven, 47 to 54 months old beagle dogs, weighing 9.8 to 21.2 kg, were used in this experimental, randomized, blinded, placebo-controlled crossover study. Each dog was treated twice with either a methadone bolus of 0.2 mg kg^− 1 followed by a 0.1 mg kg^− 1 h^− 1 methadone CRI (group M) or an equivalent volume of isotonic saline solution (group P) for 72 h. Mechanical and thermal thresholds, as well as vital parameters and sedation were measured during CRI and for further 24 h. Blood samples for methadone plasma concentrations were collected during this 96 h period.

Results

Percentage thermal excursion (%TE) increased significantly from baseline (BL) until 3 h after discontinuation of CRI in M. Within P and between treatment groups differences were not significant. Mechanical threshold (MT) increased in M until 2 h after CRI discontinuation. Bradycardia and hypothermia occurred in M during drug administration and dogs were mildly sedated for the first 47 h. Decreased food intake and regurgitation were observed in M in five and four dogs, respectively. For methadone a volume of distribution of 10.26 l kg^− 1 and a terminal half-life of 2.4 h were detected and a clearance of 51.44 ml kg^− 1 min^− 1 was calculated. Effective methadone plasma concentrations for thermal and mechanical antinociception were above 17 ng ml^− 1.

Conclusion

A methadone CRI of 0.1 mg kg^− 1 h^− 1 for 3 days after a loading dose results in steady anti-nociceptive effects in an acute pain model in healthy dogs. Main side effects were related to gastrointestinal tract, hypothermia, bradycardia and sedation.

Postoperative evaluation of analgesia promoted by the use of dexmedetomidine alone and associated with morphine as an intramuscular pre-anesthetic medication in bitches submitted for ovariohysterectomy

Abstract This study aimed to evaluate the postoperative analgesic efficacy of dexmedetomidine alone and when associated with morphine in patients under general inhalational anesthesia with isoflurane and undergoing elective ovariohysterectomy (OH). Twenty healthy bitches were selected via physical and laboratory examinations. Prior to the study, they underwent a 24-h period of adaptation to the environment and observers. They were then randomly divided into two groups: the dexmedetomidine group receiving a dose of 10 μg/kg, and dexmedetomidine group (10 μg/kg) associated with morphine receiving a dose of 0.3 mg/kg, administered via the intramuscular route. Thereafter, patients were induced with propofol and maintained with isoflurane diluted in 100% oxygen administered through a calibrated vaporizer. To verify postoperative analgesia, pain assessments were performed using the modified Glasgow (EGM) and Melbourne (EM) scales. For sedation assessment, the Dobbins scale was used at different times: before the administration of pre-anesthetic medication (T0) and at another six times in the postoperative period, 1 (T1), 2 (T2), 4 (T3), 8 (T4), 12 (T5), and 24 (T6) h after orotracheal extubation. No statistical differences were observed between groups in the scales according to Dunn’s Kruskal-Wallis post hoc test, and between the times a statistical difference was noticed by the Friedman test (p<0.05) for the EGM and EM scale scores, but there was no need for analgesic rescue. Therefore, we found that isolated dexmedetomidine and morphine produced adequate analgesic effects in the postoperative period of bitches submitted for OH.

Pharmacokinetics and pharmacodynamics of l-methadone in isoflurane-anaesthetized and mechanically ventilated ponies

OBJECTIVE

To evaluate the pharmacokinetics and selected pharmacodynamic effects of a commercially available l-methadone/fenpipramide combination administered to isoflurane anaesthetized ponies.

STUDY DESIGN

Prospective single-group interventional study.

ANIMALS

A group of six healthy adult research ponies (four mares, two geldings).

METHODS

Ponies were sedated with intravenous (IV) detomidine (0.02 mg kg^-1) and butorphanol (0.01 mg kg^-1) for an unrelated study. Additional IV detomidine (0.004 mg kg^-1) was administered 85 minutes later, followed by induction of anaesthesia using IV diazepam (0.05 mg kg^-1) and ketamine (2.2 mg kg^-1). Anaesthesia was maintained with isoflurane in oxygen. Baseline readings were taken after 15 minutes of stable isoflurane anaesthesia. l-Methadone (0.25 mg kg^-1) with fenpipramide (0.0125 mg kg^-1) was then administered IV. Selected cardiorespiratory variables were recorded every 10 minutes and compared to baseline using the Wilcoxon signed-rank test. Adverse events were recorded. Arterial plasma samples for analysis of plasma concentrations and pharmacokinetics of l-methadone were collected throughout anaesthesia at predetermined time points. Data are shown as mean ± standard deviation or median and interquartile range (p < 0.05).

RESULTS

Plasma concentrations of l-methadone showed a rapid initial distribution phase followed by a slower elimination phase which is best described with a two-compartment model. The terminal half-life was 44.3 ± 18.0 minutes, volume of distribution 0.43 ± 0.12 L kg^-1 and plasma clearance 7.77 ± 1.98 mL minute^-1 kg^-1. Mean arterial blood pressure increased from 85 (±16) at baseline to 100 (±26) 10 minutes after l-methadone/fenpipramide administration (p = 0.031). Heart rate remained constant. In two ponies fasciculations occurred at different time points after l-methadone administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of a l-methadone/fenpipramide combination to isoflurane anaesthetized ponies led to a transient increase in blood pressure without concurrent increases in heart rate. Pharmacokinetics of l-methadone were similar to those reported for conscious horses administered racemic methadone.

Acute right ventricular failure: a novel presentation of methadone-induced cardiotoxicity

As methadone use increases, the potential for methadone-induced cardiotoxicity (MIC) may rise. We describe a case of acute right ventricular (RV) failure leading to cardiogenic shock after methadone overdose. This presentation was followed by full RV recovery. This previously undescribed presentation highlights the challenges involved with MIC, its diagnosis and its management.

Effect of combinations of morphine, dexmedetomidine and maropitant on the electroencephalogram in response to acute electrical stimulation in anaesthetized dogs

This study was conducted to compare the efficacy of combinations of morphine, dexmedetomidine and maropitant in preventing the changes in electroencephalographic (EEG) indices of nociception in anaesthetized dogs subjected to a noxious electrical stimulus. In a crossover study, eight healthy adult dogs were randomly allocated to four groups: Mor: morphine 0.6 mg/kg; Dex + Mor: morphine 0.3 mg/kg + dexmedetomidine 5 μg/kg; Maro + Mor: morphine 0.3 mg/kg + maropitant 1 mg/kg; and Dex + Maro + Mor: morphine 0.2 mg/kg + dexmedetomidine 3 μg/kg + maropitant 0.7 mg/kg. Following intramuscular administration of test drugs in a minimal anaesthesia model, a supramaximal electrical stimulus (50 V at 50 Hz for 2 s) was applied and the EEG data were recorded. There were significant increases (p < .05) in the poststimulus median frequency (F50) only in groups Mor and Maro + Mor. Dex + Mor group had a significantly lower change in F50 and F95 compared to all other treatment groups. There was no correlation of the changes in EEG frequencies with blood plasma concentration of the drugs during and after noxious stimulation. Combination of dexmedetomidine and morphine was most effective in abolishing the changes in EEG indices in response to a noxious stimulus indicating a supra-additive interaction between these two drugs.

Pharmacokinetics and analgesic efficacy of intranasal administration of tramadol in dogs after ovariohysterectomy

OBJECTIVE

To assess analgesic efficacy and the pharmacokinetics of intranasal (IN) tramadol in dogs following ovariohysterectomy.

STUDY DESIGN

Randomized, blinded clinical study.

ANIMALS

A total of 30 bitches undergoing elective ovariohysterectomy.

METHODS

Dogs were randomly assigned to one of three experimental groups (10 dogs per group): IN tramadol 4 mg kg^-1 (group T-IN), intravenous (IV) tramadol 4 mg kg^-1 (group T-IV) and IV methadone 0.2 mg kg^-1 (group M). Drugs were administered at extubation. At established time points (before surgery and up to 8 hours after drug administration) analgesia was assessed using the Italian version of the Glasgow Composite Measure Pain Scale Short Form and physiological variables were recorded. To determine the pharmacokinetics of IN tramadol, blood samples were collected at predetermined time points. Shapiro-Wilk test was used to assess whether data were normally distributed and consequently parametric or non parametric tests were applied. A p value < 0.05 was considered significant.

RESULTS

No significant intergroup differences were observed in the dogs that were administered rescue analgesia and time of its administration. Excluding dogs that were administered rescue analgesia, no significant intergroup differences emerged in pain scores and physiological variables, except for a lower rectal temperature in group M compared with the tramadol groups. After IN administration, tramadol was rapidly absorbed into the systemic circulation, reaching its maximum concentration (range 74.74-200.29 ng mL^-1) within 30-60 minutes, it then decreased rapidly and was detectable in plasma for up to 2 hours after treatment in all dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

IN tramadol administration appears to be as effective as IV tramadol and methadone treatments in pain management of dogs after elective ovariohysterectomy. Given its low concentrations and short detection time in plasma after the IN route, systemic tramadol action appears unlikely.

Pharmacokinetics of morphine in combination with dexmedetomidine and maropitant following intramuscular injection in dogs anaesthetized with halothane

The purpose of this study was to evaluate the pharmacokinetics of morphine in combination with dexmedetomidine and maropitant injected intramuscularly in dogs under general anaesthesia. Eight healthy dogs weighing 25.76 ± 3.16 kg and 3.87 ± 1.64 years of age were used in a crossover study. Dogs were randomly allocated to four groups: (1) morphine 0.6 mg/kg; (2) morphine 0.3 mg/kg + dexmedetomidine 5 μg/kg; (3) morphine 0.3 mg/kg + maropitant 1 mg/kg; (4) morphine 0.2 mg/kg + dexmedetomidine 3 μg/kg + maropitant 0.7 mg/kg. Blood samples were collected before, 15 and 30 min, and 1, 2, 3 4, 6 and 8 hr after injection of the test drugs. Plasma concentration of the drugs was determined by liquid chromatography-mass spectrometry. The elimination half-life (T_1/2 ) of morphine was higher and the clearance rate (CL) was lower when combined with dexmedetomidine (T_1/2  = 77.72 ± 20.27 min, CL = 119.41 ± 23.34 ml kg^-1  min^-1 ) compared to maropitant (T_1/2  = 52.73 min ± 13.823 ml kg^-1  min^-1 , CL = 178.57 ± 70.55) or morphine alone at higher doses (T_1/2  = 50.53 ± 12.55 min, CL = 187.24 ± 34.45 ml kg^-1  min^-1 ). Combining morphine with dexmedetomidine may increase the dosing interval of morphine and may have a clinical advantage.

Opioid-sparing effect of a medetomidine constant rate infusion during thoraco-lumbar hemilaminectomy in dogs administered a ketamine infusion

OBJECTIVE

To evaluate the perioperative opioid-sparing effect of a medetomidine (MED) infusion compared to a saline (SAL) infusion in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery.

STUDY DESIGN

Randomized, partially blinded, clinical study.

ANIMALS

A total of 44 client-owned adult dogs.

METHODS

All dogs were administered a 1 μg kg^-1 MED loading dose, followed by a 1.7 μg kg^-1 hour^-1 constant rate infusion (CRI) intravenously or equivalent volumes of SAL. Infusions were started 10-15 minutes before surgical incision and continued throughout the surgical procedure. All dogs were administered a standardized anaesthetic and analgesic protocol (including a ketamine CRI). Multiparametric monitoring, including invasive arterial blood pressure, was performed. A trained investigator, unaware of the treatment, performed pain scores for 4 hours postoperatively. Rescue analgesia consisted of fentanyl administered intraoperatively and methadone postoperatively. Data were tested for normality and analysed with Fisher's exact test, Mann-Whitney U-test, analysis of variance and Kaplan-Meier survival analysis. Data are shown as median (interquartile range) and p-value was set at < 0.05.

RESULTS

The total dose of fentanyl was significantly lower with MED 0 (0-0.8) μg kg^-1 hour^-1 compared to SAL 3 (1.8-5.3) μg kg^-1 hour^-1 (p = 0.004). In the MED group, one dog compared to 12 dogs in the SAL group required a fentanyl CRI (p = 0.001). There were no statistically significant differences between groups regarding the total dose of methadone administered.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of a low-dose medetomidine CRI to the anaesthetic protocol decreased the need for a fentanyl CRI in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery during administration of a ketamine CRI.

Effect of three doses of nalbuphine on reversal of sedation and cardiopulmonary effects of morphine-acepromazine in healthy dogs

OBJECTIVE

To evaluate the efficacy of three doses of nalbuphine in reversing sedative and cardiopulmonary effects of morphine-acepromazine in dogs.

STUDY DESIGN

Prospective, randomized experimental trial.

ANIMALS

A group of eight healthy Beagle dogs, aged 5-6 years and weighing 12.5 ± 2.1 kg.

METHODS

Dogs were administered morphine (0.5 mg kg^-1) and acepromazine (0.05 mg kg^-1) intravenously (IV). After 20 minutes, dogs were administered one of four treatments IV: saline (control); or nalbuphine (0.3 mg kg^-1; treatment N0.3), (0.6 mg kg^-1; treatment N0.6) or (1.0 mg kg^-1; treatment N1.0), in random order separated by 1 week. Sedation was scored using a numeric descriptive scale (NDS) and simple numerical scale (SNS). Heart rate, systolic arterial pressure (SAP), respiratory rate (f_R) and rectal temperature (RT) were recorded before (BL), 20 minutes after morphine-acepromazine (T0), then 10 (T10), 30, 60 and 90 minutes after saline or nalbuphine. Arterial blood gases were measured at BL, T0 and T10. Values were compared with BL, T0 and among treatments using anova (p < 0.05) and the Bonferroni correction (p < 0.008).

RESULTS

NDS for N0.6 and SNS for N0.6 and N1.0 at T30, and both scores for all nalbuphine treatments at T60-T90 were lower compared with T0 (p < 0.05). Sedation scores were not different among nalbuphine treatments. SNS scores were lower than control at T10 for N0.3 and N0.6 (p < 0.05). SAP and f_R were lower than BL for all treatments at some time points (p < 0.05). RT was higher than control at T60 in the nalbuphine treatments (p < 0.001). PaO₂ was lower in N0.3 at T0 compared with BL (p = 0.036).

CONCLUSIONS AND CLINICAL RELEVANCE

All nalbuphine doses decreased the degree of sedation, without differences among them. Administration of nalbuphine resulted in minimal changes in measured cardiopulmonary variables.

Efeitos adversos da morfina, metadona e tramadol no pós-operatório de cães submetidos à cirurgia da coluna vertebral: 180 casos (2011-2016)

RESUMO: A dor pós-operatória em cães que são submetidos a cirurgias da coluna vertebral é considerada severa e seu manejo inadequado pode influenciar no tempo de recuperação do paciente, na qualidade de vida e no resultado cirúrgico. Dentre os analgésicos indicados para uso no pós-operatório dessas cirurgias tem-se os opioides, que podem apresentar inúmeros efeitos adversos que requerem atenção. Devido à escassez de estudos clínicos acerca desse assunto em se tratando do pós-operatório de cães, objetivou-se com o presente estudo retrospectivo apresentar os efeitos adversos da morfina, metadona e tramadol utilizados no pós-operatório de cirurgias da coluna vertebral. Foram revisadas e avaliadas as fichas de 180 cães e anotadas as alterações observadas no pós-operatório e decorrentes do uso de opioides. Os principais efeitos adversos observados foram anorexia, hiporexia, vômito, salivação, vocalização, bradicardia, hipotermia, ofegação e sedação. Também foi observada persistência da dor em alguns cães mesmo com o uso de analgésicos. Houve diferença na ocorrência de anorexia nos cães tratados com morfina e nos tratados com metadona em relação aos tratados com tramadol. Ocorreu diferença também entre a observação de dor dos grupos morfina e tramadol. A associação de dipirona com morfina e com metadona não revelou diferença com relação à ocorrência de efeitos adversos, bem como a variação de doses. Conclui-se que a morfina, a metadona e o tramadol apresentam efeitos adversos quando empregados para tratamento da dor pós-operatória em cães submetidos à cirurgia da coluna vertebral; a anorexia, a hiporexia e o vômito foram os efeitos adversos frequentes com o uso de morfina e de metadona e, mesmo que o tramadol apresente menor ocorrência desses efeitos, seu uso, na dose estudada, pode não ser vantajoso quando se leva em consideração o grau de dor para cirurgias da coluna vertebral.

A comparison between methadone and buprenorphine for perioperative analgesia in dogs undergoing ovariohysterectomy

OBJECTIVE

To investigate whether preoperative methadone provides superior perioperative analgesia compared to buprenorphine in dogs undergoing ovariohysterectomy.

METHODS

Eighty female dogs were recruited to an assessor-blinded, randomised, clinical trial. Dogs received a premedication dose of 0·05 mg/kg acepromazine or 10 μg/kg medetomidine combined with either 0·3 mg/kg methadone or 20 μg/kg buprenorphine intramuscularly. Anaesthesia was induced with propofol and maintained with isoflurane. Pain was assessed using two scoring schemes (a dynamic interactive visual analogue scale and the short form of the Glasgow Composite Pain Scale) before premedication, 30 minutes later and every hour for 8 hours after premedication. If indicated, rescue analgesia was provided with methadone. Meloxicam was administered after the final assessment. The area under the curve for change in pain scores over time and the requirement for rescue analgesia were compared between groups.

RESULTS

Groups premedicated with buprenorphine had significantly higher pain scores than those premedicated with methadone. There was no interaction between opioid and sedative for any outcome measure. Rescue analgesia was required by significantly more dogs premedicated with buprenorphine (45%) than that of methadone (20%).

CLINICAL SIGNIFICANCE

At the doses investigated, methadone produced superior postoperative analgesia compared to buprenorphine in dogs undergoing ovariohysterectomy.

Food engorgement in 35 dogs (2009-2013) compared with 36 dogs with gastric dilation and volvulus

The clinical features and management of food engorgement (FE) in dogs have not been previously described. This retrospective observational study describes characteristics and outcome of 35 dogs with FE, and compares features on presentation to 36 dogs with gastric dilation and volvulus (GDV). Cases were retrospectively reviewed for history, clinical findings and outcome. Gastric distension was measured by caudal gastric margin (CGM), level with lumbar vertebrae, on a lateral abdominal radiograph. Frequent characteristics of dogs with FE included tachycardia, tachypnoea, hyperproteinaemia, increased base excess (BE), mild hypernatraemia and hyperlactataemia. There was overlap in CGM between dogs with GDV (CGM range L3 to >L6) and dogs with FE (CGM range <L2 to L5-L6). In contrast to dogs with GDV, lactate concentration in dogs with FE was not associated with CGM or BE. Dogs with FE mostly received medical intervention consisting of fluid therapy and analgesia, and all dogs survived to discharge. In conclusion, dogs with FE frequently presented with acid-base and electrolyte derangements, including hyperlactataemia. While dogs with FE can have gastric distension as severe as that seen with GDV, outcome with supportive care only is excellent.

Refluxo gastroesofágico em cadelas durante ovário-histerectomia convencional submetidas a diferentes medicações pré-anestésicas

RESUMO A doença do refluxo gastroesofágico decorre do fluxo de conteúdo gastroduodenal para o esôfago e/ou para os órgãos adjacentes, o que leva à ampla gama de sinais e implicações clínicas. É desconhecida a incidência de refluxo gastroesofágico transoperatório em caninos. O objetivo deste trabalho foi, por meio da endoscopia flexível, avaliar a presença do refluxo gastroesofágico em cadelas submetidas a ovário-histerectomia com base nos fármacos analgésicos utilizados na medicação pré-anestésica (morfina, tramadol ou metadona). Concluiu-se que não houve diferença na incidência de refluxo gastroesofágico transoperatório, não tendo os fármacos testados influenciado de forma diferente esse comportamento; porém, alguns animais do grupo morfina apresentaram êmese pré-operatória. A gravidade dos refluxos foi maior nas cadelas submetidas ao uso da metadona, de acordo com o método de avaliação utilizado para esta pesquisa.

The Effect of Acepromazine Alone or in Combination with Methadone, Morphine, or Tramadol on Sedation and Selected Cardiopulmonary Variables in Sheep

The sedative and selected cardiopulmonary effects of acepromazine alone or in combination with methadone, morphine, or tramadol were compared in sheep. Six ewes were randomly assigned to treatments: A (0.05 mg/kg acepromazine), AM (A plus 0.5 mg/kg methadone), AMO (A plus 0.5 mg/kg morphine), and AT (A plus 5 mg/kg tramadol). Parameters were assessed before sedative drug administration (baseline) and every 15 minutes thereafter, for two hours. Treatments A and AM were associated with increases in sedation score for 60 minutes and treatments AMO and AT for 30 minutes; however, there were no significant differences between treatments. There was a decrease in mean arterial pressure compared to baseline values in treatment A at 15, 45, 60, and 90 minutes, in treatment AM at 15 minutes, and in treatment AT from 45 to 120 minutes. Arterial blood carbon dioxide pressure increased at all time points in all treatments. Arterial oxygen pressure decreased in treatment AMO at 15, 30, and 120 minutes and in treatment AT at 15–45, 105, and 120 minutes, compared to baseline. Acepromazine alone causes a level of sedation similar to that observed when it is coadministered with opioids methadone, morphine, and tramadol. These combinations did not cause clinical cardiopulmonary changes.

Perioperative Blood Pressure Control and Management

Blood pressure monitoring and management is a vital part of the perianesthetic period. Disturbances in blood pressure, especially hypotension, can have significant impacts on the well-being of small animal patients. There are a variety of mechanisms present to control blood pressure, including ultra-short-, short-, and long-term mechanisms. Several conditions can contribute to decreased blood pressure, including anesthetics, tension pneumothorax, intermittent positive pressure ventilation, hypoxemia, hypercapnia, surgical positioning, and abdominal distension. If hypotension is encountered, the initial response is to provide appropriate fluid therapy. If this is inadequate, other interventions can be used to increase blood pressure and thereby increase perfusion.

A systematic review of the cardiotoxicity of methadone

Methadone is one of the most popular synthetic opioids in the world with some favorable properties making it useful both in the treatment of moderate to severe pain and for opioid addiction. Increased use of methadone has resulted in an increased prevalence of its toxicity, one aspect of which is cardiotoxicity. In this paper, we review the effects of methadone on the heart as well as cardiac concerns in some special situations such as pregnancy and childhood.

METHODS

We searched for the terms methadone, toxicity, poisoning, cardiotoxicity, heart, dysrhythmia, arrhythmia, QT interval prolongation, torsade de pointes, and Electrocardiogram (ECG) in bibliographical databases including TUMS digital library, PubMed, Scopus, and Google Scholar. This review includes relevant articles published between 2000 and 2013. The main cardiac effects of methadone include prolongation of QT interval and torsade de pointes. Other effects include changes in QT dispersion, pathological U waves, Taku-Tsubo syndrome (stress cardiomyopathy), Brugada-like syndrome, and coronary artery diseases. The aim of this paper is to inform physicians and health care staff about these adverse effects. Effectiveness of methadone in the treatment of pain and addiction should be weighed against these adverse effects and physicians should consider the ways to lessen such undesirable effects. This article presents some recommendations to prevent heart toxicity in methadone users.

The effect of morphine on regional cerebral blood flow measured by 99mTc-ECD SPECT in dogs

To gain insights into the working mechanism of morphine, regional cerebral blood flow (rCBF) patterns after morphine administration were assessed in dogs. In a randomized cross-over experimental study, rCBF was estimated with ^99mTc-Ethylcysteinate Dimer single photon emission computed tomography in 8 dogs at baseline, at 30 minutes and at 120 minutes after a single bolus of morphine. Perfusion indices (PI) in the frontal, parietal, temporal and occipital cortex and in the subcortical and cerebellar region were calculated. PI was significantly decreased 30 min after morphine compared to baseline in the right frontal cortex. The left parietal cortex and subcortical region showed a significantly increased PI 30 min after morphine compared to baseline. No significant differences were noted for the other regions or at other time points. In conclusion, a single bolus of morphine generated a changing rCBF pattern at different time points.

Population pharmacokinetics of methadone hydrochloride after a single intramuscular administration in adult Japanese sika deer (Cervus nippon nippon)

OBJECTIVE

To assess the population pharmacokinetics of methadone in deer.

STUDY DESIGN

Prospective non-randomized experimental trial.

ANIMALS

Twelve healthy adult sika deer (nine males and three females).

METHODS

Deer received intramuscular administration of racemic methadone hydrochloride at 0.5 mg kg(-1) or 1 mg kg(-1) . Plasma methadone and its metabolite 2-Ethylidene-1,5-Dimethyl-3,3-Diphenyl-Pyrolidine (EDDP) concentrations were determined by validated liquid chromatography coupled to tandem mass spectrometry methods, at times 0, 30 minutes, 1, 2, 3, 4, 5, 6, 8, 12 and 24 hours. Population pharmacokinetics analysis was undertaken using a non-linear mixed effects modelling (NONMEM).

RESULTS

A two-compartment linear disposition model best described observed time-concentration profiles of methadone and EDDP. Population parameter estimates of methadone were elimination clearance (17.3 L hour(-1) ), metabolic clearance (34.6 L hour(-1) ), volume of distribution of compartment 1 (216.0 L) and volume of distribution of compartment 2 (384.0 L). Population parameter estimates of EDDP were elimination clearance (121.0 L hour(-1) ), volume of distribution of compartment 3 (1.08 L) and volume of distribution of compartment 4 (499.5 L). The total clearance and total volume of distribution of methadone and EDDP were 51.9 L hour(-1) , 121.0 L hour (-1) , 600.0 L and 500.6 L, respectively. The methadone terminal elimination half-life was 8.19 hours. No adverse effects were observed after methadone administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Following intramuscular injection, methadone was characterized by a large total volume of distribution, high systemic clearance and intermediate terminal half-life in sika deer.

Cardiorespiratory, sedative and antinociceptive effects of dexmedetomidine alone or in combination with methadone, morphine or tramadol in dogs

OBJECTIVE

To evaluate the cardiorespiratory, sedative and antinociceptive effects of dexmedetomidine alone or in combination with methadone, morphine or tramadol in dogs.

STUDY DESIGN

Experimental, blinded, randomized, crossover study.

ANIMALS

Six mixed breed dogs (two males and four females) weighing 10 ± 4 kg.

METHODS

The animals were randomly divided into four treatments: D (10 μg kg(-1) of dexmedetomidine), DM (dexmedetomidine 10 μg kg(-1) and methadone 0.5 mg kg(-1)); DMO (dexmedetomidine 10 μg kg(-1) and morphine 0.5 mg kg(-1)), and DT (dexmedetomidine 10 μg kg(-1) and tramadol 2 mg kg(-1)). The combinations were administered intramuscularly in all treatments. The variables evaluated were heart rate (HR), respiratory rate (f(R)), rectal temperature (RT), systolic arterial pressure (SAP), sedation scale and pedal withdrawal reflex. These variables were measured at T0 (immediately before the administration of the protocol) and every 15 minutes thereafter until T105.

RESULTS

A decrease in HR and f(R) occurred in all the treatments compared with T0, but no significant difference was observed between the treatments. The RT decreased from T45 onward in all the treatments. The SAP did not show a difference between the treatments, but in the DT treatment, the SAP was lower at T30 and T45 compared with T0. The D treatment had lower scores of sedation at T15 to T75 compared with the other treatments, and the DMO and DM treatments showed higher scores at T60 and T75 compared with DT.

CONCLUSIONS AND CLINICAL RELEVANCE

The treatments with morphine and methadone added to the dexmedetomidine showed higher sedation scores than the control treatment and the treatment with tramadol added to the dexmedetomidine showed no relevant differences in any of the variables evaluated in the study.

The effects of an intravenous bolus of dexmedetomidine following extubation in a mixed population of dogs undergoing general anaesthesia and surgery

An observer blinded, placebo controlled study evaluated the effects of 62.5 μg/m(2) dexmedetomidine administered IV on recovery from isoflurane anaesthesia in dogs. Forty-four healthy dogs, weighing 1.8-19.95 kg, presented for surgery that was expected to cause mild to moderate pain were studied. All were premedicated with 125 μg/m(2) dexmedetomidine and 20 μg/kg buprenorphine IM. Anaesthesia was induced with propofol and maintained with isoflurane. Non-steroidal anti-inflammatory drugs and local anaesthetics were administered as appropriate. Immediately prior to extubation dogs were treated with dexmedetomidine 62.5 μg/m(2) (group D) or an equivalent volume of heparinised saline (S). Assessments of heart rate, respiratory rate, pain (short form Glasgow composite pain scale [SF-GCPS], dynamic interactive visual analogue scale [DIVAS]), sedation (simple descriptive scale [SDS], DIVAS) and mechanical nociceptive threshold (MNT) were performed immediately before premedication, 20 min later, at the time of test drug administration (T0) and at 15-30 min intervals for four hours (T240 min). Recovery quality was scored 0 - 3 (SDS). Data were analysed with Student's t and Mann-Whitney U tests, two-way ANOVA and Fisher's exact test. Significantly fewer poor quality recoveries were observed in group D (D 2 [1-3]; S 2 [0-3]; P=0.02), however, sedation was increased in group D compared to group S from T15 to T150 min (P=0.0001). Pain scores were lower in group D compared to group S from T15 to T120 min (P=0.001), but the requirement for additional analgesia in the first 4h following extubation was not different between groups. Dexmedetomidine may decrease the incidence of poor quality anaesthetic recoveries in dogs.

Cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in healthy Beagle dogs

OBJECTIVE

To determine the cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in dogs.

STUDY DESIGN

Prospective, randomized, experimental crossover study.

ANIMALS

Five adult healthy Beagle dogs (one male and four females, weighing 12.8-16.4 kg).

METHODS

Dogs were instrumented for haemodynamic measurements whilst anaesthetized with isoflurane. Three hours after recovery dogs received 0.025 mg kg(-1) acepromazine (AP) or saline (SP) IM followed by 0.5 mg kg(-1) L-methadone/ 0.025 mg kg(-1) fenpipramide IV after 30 minutes. Cardiac output using thermodilution, heart rate, mean arterial pressure (MAP), central venous pressure (CVP), mean pulmonary artery pressure (MPAP), pulmonary artery occlusion pressure (PAOP), haemoglobin concentration, arterial and mixed-venous blood gas analysis were measured and sedation evaluated at baseline (BL), 30 minutes after acepromazine or saline IM (A/S), 5 minutes after L-methadone/fenpipramide IV application (35), every 15 minutes for 1 hour (50, 65, 80, 95 minutes) and every hour until baseline cardiac output was regained. Standard cardiovascular parameters were calculated. Data were analyzed by repeated measures anova and paired t-tests with p < 0.05 considered significant.

RESULTS

Baseline measurements did not differ. Cardiac index decreased after acepromazine administration in treatment AP (p = 0.027), but was not significantly influenced after l-methadone/fenpipramide injection in either treatment. In both treatments heart rate did not change significantly over time. Stroke volume index increased after A/S in both treatments (p = 0.049). Systemic vascular resistance index, MAP, CVP, MPAP, and pulmonary vascular resistance index did not change significantly after either treatment and did not differ between treatments. Dogs were deeply sedated in both treatments with a longer duration in treatment AP.

CONCLUSIONS AND CLINICAL RELEVANCE

In healthy dogs the dose of l-methadone/fenpipramide used in this study alone and in combination with acepromazine induced deep sedation without significant cardiovascular changes.

Cardiorespiratory and neuroendocrine changes induced by methadone in conscious and in isoflurane anaesthetised dogs

The aim of this study was to compare the cardiorespiratory and neurohormonal effects of methadone in conscious and in isoflurane anaesthetised dogs. Six mature dogs (28.0 ± 3.8 kg bodyweight) received intravenous (IV) methadone (1mg/kg) three times, once when conscious and twice during isoflurane anaesthesia (with a wash-out period of 1 week). The vasopressin antagonist relcovaptan (0.1mg/kg IV) was administered before the methadone either during the first or second (selected randomly) isoflurane anaesthesia to evaluate the contribution of vasopressin to methadone-associated vasoconstriction. Cardiorespiratory data, plasma catecholamines and serum vasopressin were recorded before (baseline) and for 90 min after methadone. Methadone induced dysphoria in all conscious dogs and significantly (P<0.05) increased mean arterial pressure (MAP), catecholamines, and vasopressin concentrations. During anaesthesia, in addition to significantly greater decreases in heart rate (HR) and cardiac index (CI) than during the conscious state, methadone induced apnoea and mechanical ventilation was necessary in all dogs. In anaesthetised animals, methadone administration significantly increased vasopressin concentrations and systemic vascular resistance index (SVRI), while MAP did not differ from baseline. Relcovaptan administration did not modify the increase in SVRI associated with methadone injection during anaesthesia. Increases in plasma catecholamines may account for the slight decreases in HR and CI seen after methadone administration in conscious dogs. In contrast, isoflurane enhanced the intensity of the cardiorespiratory changes induced by methadone. Vasoconstrictive responses associated with methadone did not appear to be induced by vasopressin.