A comparative study of medetomidine/ketamine and xylazine/ketamine anaesthesia in dogs

The anaesthetic and physiological effects of a combination of 40 micrograms medetomidine with 2.5 ketamine, 5.0 or 7.5 mg/kg administered intramuscularly were compared with the effects of a combination of 1 mg/kg xylazine and 15 mg/kg ketamine. All the combinations rapidly induced an anaesthetic state that permitted endotracheal intubation, with the absence of the pedal reflex and with good muscle relaxation, and induced bradycardia that was less pronounced as the dose of ketamine was increased. All the combinations produced a decrease in respiratory rate. Increasing the dose of ketamine combined with medetomidine resulted in a very significant prolongation of the duration of anaesthesia, the duration of muscle relaxation and the arousal time. The duration of the anaesthetic effects of 40 micrograms/kg medetomidine with 5 mg/kg ketamine was comparable to that provided by the recommended xylazine/ketamine combination but the period of muscle relaxation was significantly longer. The recovery from medetomidine/ketamine took longer than recovery from xylazine/ketamine but there were fewer side effects.     

A comparison of propofol infusion and propofol/isoflurane anaesthesia in dexmedetomidine premedicated dogs

The effects of propofol infusion were compared with propofol/isoflurane anaesthesia in six beagles premedicated with 10 microg/kg intramuscular (i.m.) dexmedetomidine. The suitability of a cold pressor test (CPT) as a stress stimulus in dogs was also studied. Each dog received isoflurane (end tidal 1.0%, induction with propofol) with and without CPT; propofol (200 microg/kg/min, induction with propofol) with and without CPT; premedication alone with and without CPT in a randomized block study in six separate sessions. Heart rate and arterial blood pressures and gases were monitored. Plasma catecholamine, beta-endorphin and cortisol concentrations were measured. Recovery profile was observed. Blood pressures stayed within normal reference range but the dogs were bradycardic (mean heart rate < 70 bpm). PaCO2 concentration during anaesthesia was higher in the propofol group (mean > 57 mmHg) when compared with isoflurane (mean < 52 mmHg). Recovery times were longer with propofol than when compared with the other treatments. The mean extubation times were 8 +/- 3.4 and 23 +/- 6.3 min after propofol/isoflurane and propofol anaesthesia, respectively. The endocrine stress response was similar in all treatments except for lower adrenaline level after propofol infusion at the end of the recovery period. Cold pressor test produced variable responses and was not a reliable stress stimulus in the present study. Propofol/isoflurane anaesthesia was considered more useful than propofol infusion because of milder degree of respiratory depression and faster recovery.     

Total intravenous anaesthesia in the horse with propofol

The use of propofol, solubilised in a non-ionic emulsifying agent, for the induction and maintenance of anaesthesia in experimental ponies was assessed. Pilot studies revealed that premedication with xylazine (0.5 mg/kg bodyweight [bwt]) intravenously (iv) followed by propofol (2.0 mg/kg bwt) iv provided a satisfactory smooth induction. Two infusion rates (0.15 mg/kg bwt/min and 0.2 mg/kg bwt/min) were compared for maintenance of anaesthesia. An infusion rate of 0.2 mg/kg/min produced adequate anaesthesia in these ponies. Cardiovascular changes included a decrease in arterial pressure and cardiac output during maintenance. Respiratory depression was manifested by a decrease in rate and an increase in arterial carbon dioxide tension. Recovery after 1 h anaesthesia was rapid and smooth. In conclusion, induction and maintenance of anaesthesia with propofol in premedicated ponies proved a satisfactory technique.     

Effects of medetomidine premedication on propofol infusion anaesthesia in dogs

Observations of cardiovascular and respiratory parameters were made on six dogs anaesthetized on two separate occasions for 120 minutes with a propofol infusion, once without premedication and once following premedication with 10 μg kg-¹ of intramuscular medetomidine. During anaesthesia the heart rate and cardiac index tended to be lower following medetomidine premedication, while the mean arterial pressure was significantly greater (p<0.05). Although the differences were not statistically significant, the systemic vascular resistance, pulmonary vascular resistance and stroke volume index were also greater in dogs given medetomidine. The mean arterial oxygen and carbon dioxide tensions were similar under both regimens, but in 2 dogs supplementary oxygen had to be administered during anaesthesia to alleviate severe hypoxaemia on both occasions they were anaesthetized. Minute and tidal volumes of respiration tended to be greater in dogs not given medetomidine but medetomidine premedication appeared to have no effect on venous admixture. Dogs given medetomidine received intramuscular atipamezole at the end of the 120 min. propofol infusion; the mean time from induction of anaesthesia to walking without ataxia was 174. min in the unpremedicated dogs and 160 min. in the dogs given atipamezole. The mean blood propofol concentration at which the dogs walked without ataxia was higher in the unpremedicated animals (2.12 ± 0.077 μg. ml-¹ compared with 1.27 ± 0.518 μg. ml-¹ in the premedicated dogs). The oxygen delivery to the tissues was lower after medetomidine premedication (p = 0.03) and the oxygen consumption was generally lower after medetomidine premedication but the difference did not achieve statistical significance. No correlation could be demonstrated between blood propofol concentration and cardiac index, systemic or pulmonary vascular resistance indices, systolic, diastolic or mean arterial blood pressures.     

Comparative study of propofol or propofol and ketamine for the induction of anaesthesia in dogs

The effects of propofol alone or propofol and ketamine for the induction of anaesthesia in dogs were compared. Thirty healthy dogs were premedicated with acepromazine and pethidine, then randomly allocated to either treatment. Anaesthesia was induced with propofol (4 mg/kg bodyweight intravenously) (group 1), or propofol and ketamine (2 mg/kg bodyweight of each intravenously) (group 2). Anaesthesia was maintained with halothane, delivered in a mixture of oxygen and nitrous oxide (1:2) via a non-rebreathing Bain circuit. Various cardiorespiratory parameters were monitored at two, five, 10, 15, 20, 25 and 30 minutes after induction, and the animals were observed during anaesthesia and recovery, and any adverse effects were recorded. During anaesthesia, the heart rate, but not the systolic arterial pressure, was consistently higher in group 2 (range 95 to 102 beats per minute) than in group 1 (range 73 to 90 beats per minute). Post-induction apnoea was more common in group 2 (11 of 15) than in group 1 (six of 15). Muscle twitching was observed in three dogs in each group. Recovery times were similar in both groups. Propofol followed by ketamine was comparable with propofol alone for the induction of anaesthesia in healthy dogs.     

Dexmedetomidine or medetomidine premedication before propofol-desflurane anaesthesia in dogs

The objective of this study was to evaluate dexmedetomidine as a premedicant in dogs prior to propofol-desflurane anaesthesia, and to compare it with medetomidine. Six healthy dogs were anaesthetized. Each dog received intravenously (i.v.) five preanaesthetic protocols: D1 (dexmedetomidine, 1 microg/kg, i.v.), D2 (dexmedetomidine, 2 microg/kg, i.v.), M1 (medetomidine, 1 microg/kg, i.v.), M2 (medetomidine, 2 microg/kg, i.v.), or M4 (medetomidine, 4 microg/kg, i.v.). Anaesthesia was induced with propofol (2.3-3.3 mg/kg) and maintained with desflurane. The following variables were studied: heart rate (HR), mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, respiratory rate (RR), arterial oxygen saturation, end-tidal CO2, end-tidal concentration of desflurane (EtDES) required for maintenance of anaesthesia and tidal volume. Arterial blood pH (pHa) and arterial blood gas tensions (PaO2, PaCO2) were measured during anaesthesia. Time to extubation, time to sternal recumbency and time to standing were also recorded. HR and RR decreased significantly during sedation in all protocols. Cardiorespiratory variables during anaesthesia were statistically similar for all protocols. EtDES was significantly different between D1 (8.1%) and D2 (7.5%), and between all doses of medetomidine. Desflurane requirements were similar for D1 and M2, and for D2 and M4 protocols. No statistical differences were observed in recovery times. The combination of dexmedetomidine, propofol and desflurane appears to be effective for induction and maintenance of general anaesthesia in healthy dogs.     

Anaesthesia with midazolam/medetomidine/fentanyl in chinchillas (Chinchilla lanigera) compared to anaesthesia with xylazine/ketamine and medetomidine/ketamine

We studied four different drug regimes for anaesthetic management in chinchillas and evaluated and compared their cardiovascular and respiratory effects. In this randomized, cross-over experimental study, seven adult chinchillas, five females, two males [515 +/- 70 (SD) g] were randomly assigned to one of the following groups: group 1 [midazolam, medetomidine and fentanyl (MMF), flumazenil, atipamezole and naloxone (FAN); MMF-FAN] received 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m., and for reversal 0.1 mg/kg flumazenil, 0.5 mg/kg atipamezole and 0.05 mg/kg naloxone s.c. after 45 min; group 2 (MMF) 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m.; group 3 [xylazine/ketamine (X/K)] 2.0 mg/kg xylazine and 40.0 mg/kg ketamine i.m.; and group 4 [medetomidine/ketamine (M/K)] 0.06 mg/kg medetomidine and 5.0 mg/kg ketamine i.m. Reflexes were judged to determine anaesthetic stages and planes. Anaesthesia with X/K and M/K was associated with a prolonged surgical tolerance and recovery period. By reversing MMF, recovery period was significantly shortened (5 +/- 1.3 min versus 40 +/- 10.3 min in MMF without FAN, 73 +/- 15.0 min in X/K, and 31 +/- 8.5 min in M/K). Without reversal, MMF produced anaesthesia lasting 109 +/- 16.3 min. All combinations decreased respiratory and heart rate but compared with X/K and M/K, respiratory and cardiovascular complications were less in the MMF groups. Focussing on the clinical relevance of the tested combinations, completely reversible anaesthesia showed two major advantages: anaesthesia can be antagonized in case of emergency and routinely shortens recovery. In small animals particularly these advantages lead to less complications and discomfort and thus often can be lifesaving. As all analgesic components (medetomidine and fentanyl) are reversed, postoperative analgesia should be provided before reversal of anaesthesia.     

Postinduction apnoea in dogs premedicated with acepromazine or dexmedetomidine and anaesthetized with alfaxalone or propofol

Objective

To compare incidence and duration of postinduction apnoea in dogs after premedication with methadone and acepromazine (MA) or methadone and dexmedetomidine (MD) followed by induction with propofol (P) or alfaxalone (A).

Continuous infusion of propofol in dogs premedicated with methotrimeprazine

Objective To evaluate the cardiopulmonary and clinical effects of three different infusion rates of propofol in dogs premedicated with methotrimeprazine. Study design Randomized experimental trial. Animals Ten healthy adult mixed‐breed male and female dogs, weighing from 14 to 20 kg. Methods Dogs were premedicated with methotrimeprazine [1 mg kg^?1 intravenously (IV)] followed by induction of anesthesia with 4.5 mg kg^?1 of propofol IV and maintenance with propofol for 60 minutes as follows: T1, 0.2 mg kg^?1 minute^?1; T2, 0.3 mg kg^?1minute^?1; and T3, 0.4 mg kg^?1minute^?1. Heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP), end‐tidal CO₂ (P_ETCO₂), arterial hemoglobin O₂ saturation, arterial blood gases, and pedal and cutaneous reflexes were measured before and 5, 10, 20, 30, 45 and 60 minutes after the beginning of the propofol infusion. Statistical analysis was performed using an anova . Results Heart rate increased during anesthesia in all cases and arterial blood pressure decreased only in dogs in the T3 category. Respiratory depression was proportional to the infusion rate of propofol. Muscle relaxation was satisfactory, but analgesia was inadequate in the three treatments. Conclusions The infusion of 0.2–0.4 mg kg^?1 minute^?1 of propofol produced a dose‐dependent respiratory depression. The presence of a pedal withdrawal reflex and marked cardiovascular responses to this noxious stimulus suggests that anesthesia may not be of sufficient depth for surgery to be carried out. Clinical relevance Although several studies have been performed using propofol in animals, few studies have investigated the cardiopulmonary and analgesic effects with different doses. The determination of an adequate propofol infusion rate is necessary for the routine use of this intravenous anesthetic for the maintenance of anesthesia during major surgical procedures in dogs.     

Effects of vatinoxan in dogs premedicated with medetomidine and butorphanol followed by sevoflurane anaesthesia: a randomized clinical study

ObjectiveTo investigate effects of vatinoxan in dogs, when administered as intravenous (IV) premedication with medetomidine and butorphanol before anaesthesia for surgical castration.Study designA randomized, controlled, blinded, clinical trial.AnimalsA total of 28 client-owned dogs.MethodsDogs were premedicated with medetomidine (0.125 mg m^?2) and butorphanol (0.2 mg kg^?1) (group MB; n = 14), or medetomidine (0.25 mg m^?2), butorphanol (0.2 mg kg^?1) and vatinoxan (5 mg m^?2) (group MB-VATI; n = 14). Anaesthesia was induced 15 minutes later with propofol and maintained with sevoflurane in oxygen (targeting 1.3%). Before surgical incision, lidocaine (2 mg kg^?1) was injected intratesticularly. At the end of the procedure, meloxicam (0.2 mg kg^?1) was administered IV. The level of sedation, the qualities of induction, intubation and recovery, and Glasgow Composite Pain Scale short form (GCPS-SF) were assessed. Heart rate (HR), respiratory rate (f_R), mean arterial pressure (MAP), end-tidal concentration of sevoflurane (Fe′Sevo) and carbon dioxide (Pe′CO₂) were recorded. Blood samples were collected at 10 and 30 minutes after premedication for plasma medetomidine and butorphanol concentrations.ResultsAt the beginning of surgery, HR was 61 ± 16 and 93 ± 23 beats minute^?1 (p = 0.001), and MAP was 78 ± 7 and 56 ± 7 mmHg (p = 0.001) in MB and MB-VATI groups, respectively. No differences were detected in f_R, Pe′CO₂, Fe′Sevo, the level of sedation, the qualities of induction, intubation and recovery, or in GCPS-SF. Plasma medetomidine concentrations were higher in group MB-VATI than in MB at 10 minutes (p = 0.002) and 30 minutes (p = 0.0001). Plasma butorphanol concentrations were not different between groups.Conclusions and clinical relevanceIn group MB, HR was significantly lower than in group MB-VATI. Hypotension detected in group MB-VATI during sevoflurane anaesthesia was clinically the most significant difference between groups.     

Recovery characteristics following maintenance of anaesthesia with sevoflurane or isoflurane in dogs premedicated with acepromazine

A standard anaesthetic protocol was used to anaesthetise 40 dogs for intravenous urography and a retrograde urethrogram or vaginourethrogram. The dogs were allocated by blocked randomisation to receive either isoflurane or sevoflurane for maintenance of anaesthesia after they had been premedicated with acepromazine and pethidine, and anaesthesia induced with propofol. An observer who was unaware of which agent had been used assessed ataxia 30 and 60 minutes after discontinuation of administration of the anaesthetic and assigned an overall recovery score. No complications occurred during anaesthesia of either group of dogs. The scores for ataxia were significantly lower after 60 minutes than after 30 minutes, but there was no significant difference between the groups. The quality of recovery was significantly better in the dogs that received sevoflurane than in those that received isoflurane, but the recovery times were similar.     

Propofol infusion anaesthesia in dogs pre-medicated with medetomidine

Ten laboratory beagles pre-medicated with medetomidine (40 μg/kg bodyweight [bwt]) were anaesthetised using a rapid injection of propofol, followed by propofol infusion. A loading dose of 4 mg/kg bwt of propofol was administered intravenously (iv) as a bolus and, immediately after, a 60 min iv propofol infusion (150 μg/kg bwt/min) was initiated. After a transient increase, mean arterial blood pressure decreased significantly below the pre-propofol level. However, the lowest values recorded (115 ± 11 mmHg) remained within the physiological limits. Heart rate increased significantly (from 41 ± 7.3 to 58 ± 11 beats/min) after initiation of the propofol infusion. No significant changes were seen in respiratory frequency; pO₂ decreased transiently; minimum values (10 ± 2.3 kPa) recorded 5 mins after initiation of the propofol infusion differed significantly from the starting level. pCO₂ increased significantly and the highest values recorded were 6.1 ± 0.35 kPa. Accordingly, pH decreased reaching the lowest level (pH 7.29) 15 mins after initiation of the propofol infusion. The analgesic effect of the present combination was not studied, but the absence of the palpebral and pedal reflexes suggested a surgical stage of anaesthesia. Therefore, propofol infusion in beagles pre-medicated with medetomidine proved to be a promising anaesthetic regimen but, if used clinically, oxygen-enriched inspired air should be used.     

The use of propofol for induction of anaesthesia in dogs premedicated with acepromazine, butorphanol and acepromazine-butorphanol

Cardiovascular, pulmonary and anaesthetic-analgesic responses were evaluated in 18 male and female dogs to determine the effect of the injectable anaesthetic propofol used in conjuction with acepromazine and butorphanol. The dogs were randomly divided into three groups. Dogs in Group A were premeditated with 0.1 mg/kg of intramuscular acepromazine followed by an induction dose of 4.4 mg/kg of intravenous propofol; Group B received 0.2 mg/kg of intramuscular butorphanol and 4.4 mg/kg of intravenous propofol; dogs in Group AB were administered a premeditation combination of 0.1 mg/kg of intramuscular acepromazine and 0.2 mg/kg of intramuscular butorphanol, followed by induction with 3.3 mg/kg of intravenous propofol. The induction dose of propofol was given over a period of 30-60 seconds to determine responses and duration of anaesthesia. Observations recorded in the dogs included heart and respiratory rates, indirect arterial blood pressures (systolic, diastolic and mean), cardiac rhythm, end-tidal CO, tension, oxygen saturation, induction time, duration of anaesthesia, recovery time and adverse reactions. The depth of anaesthesia was assessed by the response to mechanical noxious stimuli (tail clamping), the degree of muscle relaxation and the strength of reflexes. Significant respiratory depression was seen after propofol induction in both groups receiving butorphanol with or without acepromazine. The incidence of apnea was 4/6 dogs in Group B, and 5/6 dogs in Group AB. The incidence of apnea was also correlated to the rate of propofol administration. Propofol-mediated decreases in arterial blood pressure were observed in all three groups. Moderate bradycardia (minimum value > 55 beats/min) was observed in both Groups B and AB. There were no cardiac dysrhythmias noted in any of the 18 dogs. The anaesthetic duration and recovery times were longer in dogs premeditated with acepromazine/butorphanol.     

Pharmacokinetics of propofol infusions, either alone or with ketamine, in sheep premedicated with acepromazine and papaveretum

The pharmacokinetics of propofol were investigated in two groups of five Scottish blackface sheep undergoing surgery for the implantation of subcutaneous tissue pouches. After premedication with acepromazine and papaveretum, anaesthesia was induced with either propofol at 4 mg kg⁻¹ intravenously (group 1) or with a mixture of propofol at 3 mg kg⁻¹ and ketamine at 1 mg kg ⁻¹ intravenously (group 2). Anaesthesia was maintained with a variable infusion rate of either propofol alone (group 1) or propofol and ketamine (group 2). Both regimens produced satisfactory conditions for superficial surgery of the body surface. The mean (SD) duration of anaesthesia was 64·8 (3·1) minutes for group 1 and 60 (0) minutes for group 2; the mean total dose of propofol given to the sheep in group 1 was 801 (84) mg, and the sheep in group 2 received 470 (46) mg of propofol and 267 (30) mg of ketamine. The mean elimination half-life of propofol was 56·6 (13·1) minutes in group 1 and 50·3 (21·4) minutes in group 2; the mean volume of distribution at steady state was 1037 (0480) litre kg⁻¹ in group 1 and 1·515 (0939) litre kg⁻¹ in group 2; the mean body clearance was 85·4 (28·0) ml kg⁻¹ min⁻¹ in group 1 and 1280 (35·0) ml kg⁻¹ min⁻¹ in group 2; the mean residence time corrected for a bolus injection was 12·1 (4·2) minutes in group 1 and 11·9 (6·6) minutes in group 2; for the infusion, the mean residence time was 72·1 (4·2) minutes in group 1 and 69·9 (7·9) minutes in group 2. There were wide variations in the blood propofol concentrations reached in individual sheep by using this standard dosing regimen. All the sheep recovered quickly from anaesthesia; the mean times to extubation, sternal recumbency and standing for the animals in group 1 were 2·8 (0·4) 6·3 (1·2) and 10·9 (1·6) minutes from the end of the infusion, and the times for group 2 were 5·3 (0·9), 11·2 (1·7) and 15·1 (2·2) minutes.