Cardiopulmonary effects of continuous intravenous infusion of guaifenesin, ketamine, and xylazine in ponies

Eight ponies were anesthetized with a solution containing 50 mg of guaifenesin, 1 mg of ketamine, and 0.5 mg of xylazine X ml-1 of 5% dextrose in water. Anesthesia was induced by IV injection (1.1 ml X kg-1), followed by continuous IV infusion at 2.75 ml X kg-1 X hr-1. Heart rate, rate-pressure product, mean pulmonary artery pressure, and standard bicarbonate were not significantly changed throughout the study. Systolic, diastolic, and mean arterial pressures and left ventricular stroke work index were significantly decreased at 5 and 15 minutes after a bolus of the anesthetic solution was injected. Systolic blood pressure returned to within the base-line range at 30 minutes, but diastolic and mean arterial pressures were significantly decreased throughout the study. Cardiac index and arterial pH were decreased at 5 minutes only. Systemic vascular resistance was significantly decreased 60 minutes after bolus injection was given. Hypoventilation, as indicated by increased PaCO2, occurred 5 minutes after bolus injection was given.     

Cardiopulmonary responses of swine to intravenous infusion of guaifenesin, ketamine, and xylazine

Swine were anesthetized with a 5% solution of dextrose in water containing 50 mg of guaifenesin, 1 mg of ketamine, and 1 mg of xylazine X ml-1 (G-K-X) infused IV at a rate of 2.2 ml X kg-1 X hr-1. Mean arterial blood pressure and systemic vascular resistance were significantly increased from base-line values throughout the 2 hours of G-K-X infusion. Cardiac index decreased significantly initially, but returned to near base line at 30 minutes. Fifteen minutes after G-K-X infusion was discontinued, cardiac index was not significantly different from base line. Heart rate decreased significantly from base line 90 minutes after infusion of G-K-X began and remained so throughout the study. However, the mean heart rate remained within the acceptable range for swine. Rate-pressure product was not significantly altered. The PaCO2 decreased, and arterial pH increased significantly from base line, supporting our clinical impression that pigs breathe well when anesthetized with G-K-X. We conclude that G-K-X is a satisfactory combination of drugs for induction and maintenance of surgical anesthesia in healthy swine for a period of 2 hours.     

Continuous intravenous anesthesia in dogs using a combination of xylazine, ketamine and guaifenesin]

The tested anaesthesia through a permanent infusion of a xylazine, ketamine and guaifenezine (XKG) mixture was used in ten experimental dogs without clinical signs of a disease and in fifty two patients during different surgical interventions. After joint i.m. atropine (0.05 mg/kg) and xylazine (2 mg/kg) premedication, anaesthesia in dogs was induced by an i.v. administration of 1% ketamine at a dose of 2 mg/kg, and the XKG was infused instantly after the previous treatment. The mixture contained 2.0 ml of 5% ketamine and 1.25 ml of 2% xylazine added to 100 ml of 5% guaifenezine. The infusion was applied at a rate of 3.3 ml/kg for the first five minutes and then it was maintained at constant values of 2.2 ml/kg during the whole surgical intervention (Tab. I). The induction and course of anaesthesia, and waking up and recovery from anaesthesia were evaluated in all dogs, and the trias values were also followed. These additional parameters were followed in the test group: breathing volumes, ECG values and acid-base balance parameters were determined from the collected blood samples. The observation of measurable parameters (Figs. 1 to 5) and ECG analysis did not demonstrate any large departures from the starting values, and the changes in the acid-base balance (Tab. II) suggest the partly compensated respiratory acidosis. On the basis of our results, we can recommend this tested method for general anaesthesia particularly of dogs of larger breeds and for longer-lasting operations. This method is suitable to be used first of all in the veterinary establishments where inhalation anaesthesia is not practicable.     

Cardiopulmonary effects of xylazine in dogs.

Effects of the drug xylazine were determined on arterial pH, arterial oxygen pressure (PaO2), arterial carbon dioxide pressure (PaCO2), aortic blood pressure, aortic flow, heart rate, pulse pressure, stroke volume, and peripheral resistance of dogs. The drug was given intravenously (IV) with and without atropine and was given intramuscularly (IM) without atropine. After IV administration of xylazine (1.1 mg/kg), arterial pH, PaO2, and PaCO2 values were not changed from control values. However, the drug did produce a statistically significant decrease in heart rate, decrease in aortic flow, initial increase in blood pressure followed by decrease, and increase in peripheral resistance. Stroke volume and pulse pressure were not significantly changed. Atropine (0.02 mg/kg, IV) did not significantly change any of the effects produced by xylazine. Intramuscular administration of xylazine (2.2 mg/kg) did not produce significant changes in arterial pH, PaO2, or PaCO2. Heart rate and aortic flow decreased significantly, but statistically significant changes did not occur in aortic blood pressure or peripheral resistance; however, the changes in these last 2 values were in the same direction and were of similar magnitude as those which occurred afger IV administration of xylazine.     

Cardiopulmonary effects of administration of a combination solution of xylazine, guaifenesin, and ketamine or inhaled isoflurane in mechanically ventilated calves

OBJECTIVE: To compare the cardiopulmonary effects of administration of a solution of xylazine, guaifenesin, and ketamine (XGK) or inhaled isoflurane in mechanically ventilated calves undergoing surgery. ANIMALS: 13 male calves 2 to 26 days of age. Procedures-In calves in the XGK group, anesthesia was induced (0.5 mL/kg) and maintained (2.5 mL/kg/h) with a combination solution of xylazine (0.1 mg/mL), guaifenesin (50 mg/mL), and ketamine (1.0 mg/mL). For calves in the isoflurane group, anesthesia was induced and maintained with isoflurane in oxygen. The rates of XGK infusion and isoflurane administration were adjusted to achieve suitable anesthetic depth. All calves received 100% oxygen and were mechanically ventilated to maintain end-tidal carbon dioxide concentrations from 35 to 40 mm Hg and underwent laparoscopic bladder surgery through an abdominal approach. Cardiopulmonary variables were measured before induction and at intervals up to 90 minutes after anesthetic induction. RESULTS: The quality of induction was excellent in all calves. The XGK requirements were 0.57 +/- 0.18 mL/kg and 2.70 +/- 0.40 mL/kg/h to induce and maintain anesthesia, respectively. Heart rate was significantly lower than baseline throughout the anesthetic period in the XGK group. Systolic arterial blood pressure was significantly higher in the XGK group, compared with the isoflurane group, from 5 to 90 minutes. Cardiac index was lower than baseline in both groups. Differences between groups in cardiac index and arterial blood gas values were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of XGK resulted in excellent anesthetic induction and maintenance with cardiopulmonary alterations similar to those associated with isoflurane in mechanically ventilated calves.     

Cardiopulmonary effects of a xylazine and ketamine combination in pigs

The carotid and pulmonary arteries were catheterised in six pigs anaesthetised with thiopentone sodium and halothane. A minimum of five days was allowed to elapse before the investigation. The carotid artery pressure, pulmonary artery pressure, cardiac output, arterial pH, PO2, PCO2, plasma glucose and lactate were measured before and after intravenous injection of xylazine (1 mg kg-1) and ketamine 10 mg kg-1). Complete analgesia was produced for 10 minutes in all pigs but by 25 minutes all animals responded to a painful stimulus. The cardiac output and arterial PO2 were significantly decreased for 30 minutes and 10 minutes, respectively. The total vascular resistance was significantly increased. No statistically significant changes occurred in the other variables measured.     

Cardiopulmonary and anesthetic effects of ketamine and its enantiomers in dogs

Dogs were used to determine cardiopulmonary and chemical restraining effects of racemic ketamine and its enantiomers. Levorotatory ketamine induced the shortest duration of unconsciousness and recumbency when compared with effects of dextrorotatory and racemic ketamine. Administration of racemic ketamine or either of its enantiomers (30 mg/kg of body weight, IV) to dogs recovering from isoflurane anesthesia induced transient, but significant (P less than 0.05), decreases in arterial blood pressure, left ventricular contractility, cardiac output, and total peripheral vascular resistance. Arterial blood pressure and left ventricular contractility significantly (P less than 0.05) increased at later times after ketamine administration. Arterial pH and the PO2 values decreased after IV administration of racemic ketamine or its enantiomers. Significant differences in cardiopulmonary variables were not observed between groups given ketamine or its enantiomers.     

Alfaxalone compared with ketamine for induction of anaesthesia in horses following xylazine and guaifenesin

ObjectiveTo compare anaesthesia induced with either alfaxalone or ketamine in horses following premedication with xylazine and guaifenesin.Study designRandomized blinded cross-over experimental study.AnimalsSix adult horses, five Standardbreds and one Thoroughbred; two mares and four geldings.MethodsEach horse received, on separate occasions, induction of anaesthesia with either ketamine 2.2 mg kg^?1 or alfaxalone 1 mg kg^?1. Premedication was with xylazine 0.5 mg kg^?1 and guaifenesin 35 mg kg^?1. Incidence of tremors/shaking after induction, recovery and ataxia on recovery were scored. Time to recovery was recorded. Partial pressure of arterial blood oxygen (PaO₂) and carbon dioxide (PaO₂), arterial blood pressures, heart rate (HR) and respiratory rates were recorded before premedication and at intervals during anaesthesia. Data were analyzed using Wilcoxon matched pairs signed rank test and are expressed as median (range).ResultsThere was no difference in the quality of recovery or in ataxia scores. Horses receiving alfaxalone exhibited a higher incidence of tremors/shaking on induction compared with those receiving ketamine (five and one of six horses respectively). Horses recovered to standing similarly [28 (24–47) minutes for alfaxalone; 22 (18–35) for ketamine] but took longer to recover adequately to return to the paddock after alfaxalone [44 (38–67) minutes] compared with ketamine [35 (30–47)]. There was no statistical difference between treatments in effect on HR, PaO₂ or PaCO₂ although for both regimens, PaO₂ decreased with respect to before premedication values. There was no difference between treatments in effect on blood pressure.Conclusions and clinical relevanceBoth alfaxalone and ketamine were effective at inducing anaesthesia, although at induction there were more muscle tremors after alfaxalone. As there were no differences between treatments in relation to cardiopulmonary responses or quality of recovery, and only minor differences in recovery times, both agents appear suitable for this purpose following the premedication regimen used in this study.     

Cardiopulmonary effects of diazepam/ketamine/isoflurane or xylazine/ketamine/isoflurane in foals undergoing abdominal surgery

The purpose of this study was to evaluate the cardiopulmonary effects of anesthetic induction with diazepam/ketamine or xylazine/ketamine with subsequent maintenance of anesthesia using isoflurane in foals undergoing abdominal surgery. Seventeen foals underwent laparotomy at 7–10 days of age and a laparoscopy 7–10 days later. Foals were randomly assigned to receive xylazine (0.8 mg kg^?1)/ketamine (2 mg kg^?1) (X/K)(n = 9) or diazepam (0.2 mg kg^?1)/ketamine (2 mg kg^?1) (D/K)(n = 8) for induction of anesthesia for both procedures. In all foals, anesthesia was maintained with isoflurane in oxygen with the inspired concentration adjusted to achieve adequate depth of anesthesia as assessed by an individual blinded to the treatments. IPPV was employed throughout using a tidal volume of 10 mL kg^?1 adjusting the frequency to maintain eucapnia (PaCO₂ 35–45 mm Hg, 4.7–6.0 kPa). Cardiopulmonary variables were measured after induction of anesthesia prior to, during, and following surgery. To compare the measured cardiopulmonary variables between the two anesthetic regimes for both surgical procedures, results were analyzed using a three‐way factorial anova for repeated measures (p < 0.05). During anesthesia for laparotomy, mean CI and MAP ranged from 110 to 180 mL kg^?1 minute^?1 and 57–81 mm Hg, respectively, in the D/K foals and 98–171 mL kg^?1 minute^?1 and 50–66 mm Hg in the X/K foals. Overall, CI, HR, SAP, DAP, and MAP were significantly higher in foals in the D/K group versus the X/K group during this anesthetic period. During anesthesia for laparoscopy, mean CI and MBP ranged from 85 to 165 mL kg^?1 minute^?1 and 67–83 mm Hg, respectively, in the D/K group, and 98–171 mL kg^?1 minute^?1 and 48–67 mm Hg in the X/K group. Only HR, SAP, DAP, and MAP were significantly higher in the D/K group versus X/K group during this latter anesthetic period. There were no significant differences between groups during either surgical procedure for end‐tidal isoflurane, PaO₂, PaCO₂, or pH. In conclusion, anesthesia of foals for laparotomy and laparoscopy with diazepam/ketamine/isoflurane is associated with less hemodynamic depression than with xylazine/ketamine/isoflurane.     

Cardiopulmonary effects of romifidine/ketamine or xylazine/ketamine when used for short duration anesthesia in the horse

The cardiovascular changes associated with anesthesia induced and maintained with romifidine/ketamine versus xylazine/ ketamine were compared using 6 horses in a cross over design. Anesthesia was induced and maintained with romifidine (100 microg/kg, IV)/ketamine (2.0 mg/kg, IV) and ketamine (0.1 mg/kg/min, IV), respectively, in horses assigned to the romifidine/ ketamine group. Horses assigned to the xylazine/ketamine group had anesthesia induced and maintained with xylazine (1.0 mg/kg, IV)/ketamine (2.0 mg/kg, IV) and a combination of xylazine (0.05 mg/kg/min, IV) and ketamine (0.1 mg/kg/min, IV), respectively. Cardiopulmonary variables were measured at intervals up to 40 min after induction. All horses showed effective sedation following intravenous romifidine or xylazine and achieved recumbency after ketamine administration. There were no significant differences between groups in heart rate, arterial oxygen partial pressures, arterial carbon dioxide partial pressures, cardiac index, stroke index, oxygen delivery, oxygen utilization, systemic vascular resistance, left ventricular work, or any of the measured systemic arterial blood pressures. Cardiac index and left ventricular work fell significantly from baseline while systemic vascular resistance increased from baseline in both groups. The oxygen utilization ratio was higher in the xylazine group at 5 and 15 min after induction. In conclusion, the combination of romifidine/ketamine results in similar cardiopulmonary alterations as a xylazine/ketamine regime, and is a suitable alternative for clinical anesthesia of the horse from a cardiopulmonary viewpoint.     

Effects of ketamine, xylazine, and a combination of ketamine and xylazine in Pekin ducks

Effects of ketamine, xylazine, and a combination of ketamine and xylazine were studied in 12 male Pekin ducks (7 to 12 weeks old; mean [+/- SD] body weight, 3.1 +/- 0.3 kg). After venous and arterial catheterization and fixation of a temperature probe in the cloaca, each awake duck was confined, but not restrained, in an open box in a dimly lit room. Blood pressure and lead-II ECG were recorded. Three arterial blood samples were collected every 15 minutes over a 45-minute period (control period) and were analyzed for pHa, PaCO2 and PaO2. After the control period, each duck was assigned at random to 1 of 3 drug groups: (1) ketamine (KET; 20 mg/kg of body weight, IV), (2) xylazine (XYL; 1 mg/kg, IV), and (3) KET + XYL (KET 20 mg/kg and XYL, 1 mg/kg; IV). Measurements were made at 1, 5, 10, 15, 30, 45, 60, and 90 minutes after drug administration. All ducks survived the drug study. Cloacal temperature was significantly (P less than or equal to 0.05) increased above control cloacal temperature at 90 minutes after the administration of ketamine, and from 10 through 90 minutes after administration of ketamine plus xylazine. In ducks of the KET group, pHa, PaCO2, and PaO2, remained unchanged after administration of the drug. In ducks of the XYL group, pHa and PaO2 decreased significantly (P less than or equal to 0.05) from control values for all time points up to and including 15 minutes after drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Prolongation of anesthesia with xylazine, ketamine, and guaifenesin in horses: 64 cases (1986-1989)

On 74 occasions, 54 horses and 6 foals were anesthetized with xylazine and ketamine or xylazine, guaifenesin, and ketamine, with or without butorphanol. On 64 occasions, anesthesia was prolonged for up to 70 minutes (34 +/- 15 min) by administration of 1 to 9 supplemental IV injections of xylazine and ketamine at approximately a third the initial dosage. All horses except 5 were positioned in lateral recumbency, and oxygen was insufflated. In adult horses, the time from induction of anesthesia to the first supplemental xylazine and ketamine injection was 13 +/- 4 minutes and the time between supplemental injections was 12.1 +/- 3.7 minutes. These results were consistent with predicted plasma ketamine concentration calculated from previously published pharmacokinetic data for ketamine in horses. Respiratory and heart rates and coccygeal artery pressure remained consistent for the duration of anesthesia. The average interval between the last injection of ketamine and assumption of sternal position was approximately 30 minutes, and was the same regardless of the number of supplemental injections. The time to standing was significantly longer (P less than 0.05) in horses given 2 supplemental injections, compared with those not given any or only given 1, but was not longer in horses given 3 supplemental injections. Recovery was considered unsatisfactory in 5 horses, but did not appear to be related to prolongation of anesthesia.     

Evaluation of xylazine and ketamine for total intravenous anesthesia in horses

OBJECTIVE: To evaluate the use of xylazine and ketamine for total i.v. anesthesia in horses. ANIMALS: 8 horses. PROCEDURE: Anesthetic induction was performed on 4 occasions in each horse with xylazine (0.75 mg/kg, i.v.), guaifenesin (75 mg/kg, i.v.), and ketamine (2 mg/kg, i.v.). Intravenous infusions of xylazine and ketamine were then started by use of 1 of 6 treatments as follows for which 35, 90, 120, and 150 represent infusion dosages (microg/kg/min) and X and K represent xylazine and ketamine, respectively: X35 + K90 with 100% inspired oxygen (O2), X35 + K120-(O2), X35 + K150-(O2), X70 + K90-(O2), K150-(O2), and X35 + K120 with a 21% fraction of inspired oxygen (ie, air). Cardiopulmonary measurements were performed. Response to a noxious electrical stimulus was observed at 20, 40, and 60 minutes after induction. Times to achieve sternal recumbency and standing were recorded. Quality of sedation, induction, and recovery to sternal recumbency and standing were subjectively evaluated. RESULTS: Heart rate and cardiac index were higher and total peripheral resistance lower in K150-(O2) and X35 + K120-air groups. The mean arterial pressure was highest in the X35 + K120-air group and lowest in the K150-(O2) group (125 +/- 6 vs 85 +/- 8 at 20 minutes, respectively). Mean Pa(O2) was lowest in the X35 + K120-air group. Times to sternal recumbency and standing were shortest for horses receiving K150-(O2) (23 +/- 6 minutes and 33 +/- 8 minutes, respectively) and longest for those receiving X70 + K90-(O2) (58 +/- 28 minutes and 69 +/- 27 minutes, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Infusions of xylazine and ketamine may be used with oxygen supplementation to maintain 60 minutes of anesthesia in healthy adult horses.     

Cardiovascular effects of a continuous rate infusion of lidocaine in calves anesthetized with xylazine,midazolam, ketamine and isoflurane

ObjectiveTo assess the cardiovascular changes of a continuous rate infusion of lidocaine in calves anesthetized with xylazine, midazolam, ketamine and isoflurane during mechanical ventilation.Study designProspective, randomized, cross-over, experimental trial.AnimalsA total of eight, healthy, male Holstein calves, aged 10 ± 1 months and weighing 114 ± 11 kg were included in the study.MethodsCalves were administered xylazine followed by ketamine and midazolam, orotracheal intubation and maintenance on isoflurane (1.3%) using mechanical ventilation. Forty minutes after induction, lidocaine (2 mg kg^?1 bolus) or an equivalent volume of saline (0.9%) was administered IV followed by a continuous rate infusion (100 μg kg^?1 minute^?1) of lidocaine (treatment L) or saline (treatment C). Heart rate (HR), systolic, diastolic and mean arterial pressures (SAP, DAP and MAP), central venous pressure (CVP), mean pulmonary arterial pressure (mPAP), pulmonary arterial occlusion pressure (PAOP), cardiac output, end-tidal carbon dioxide (Pe’CO₂) and core temperature (CT) were recorded before lidocaine or saline administration (Baseline) and at 20-minute intervals (T20-T80). Plasma concentrations of lidocaine were measured in treatment L.ResultsThe HR was significantly lower in treatment L compared with treatment C. There was no difference between the treatments with regards to SAP, DAP, MAP and SVRI. CI was significantly lower at T60 in treatment L when compared with treatment C. PAOP and CVP increased significantly at all times compared with Baseline in treatment L. There was no significant difference between times within each treatment and between treatments with regards to other measured variables. Plasma concentrations of lidocaine ranged from 1.85 to 2.06 μg mL^?1 during the CRI.Conclusion and clinical relevanceAt the studied rate, lidocaine causes a decrease in heart rate which is unlikely to be of clinical significance in healthy animals, but could be a concern in compromised animals.     

Effects of changing body position on oxygenation and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine

ObjectiveTo investigate the impact of a change in body position on blood gases and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine.Study designProspective, randomized experimental study.AnimalsTwelve Quarter Horse foals, age of 5.4 ±0.9 months and weighing 222 ± 48 kg.MethodsFoals were anesthetized with guaifenesin, ketamine, and xylazine for 40 minutes in lateral recumbency and then assigned to a change in lateral recumbency after hoisting (Group 1, n = 6), or no change (Group 2, n = 6). Oxygen 15 L minute^?1 was insufflated into the endotracheal tube throughout anesthesia. Arterial blood pressure, heart rate, respiratory rate (f_R), inspired fraction of oxygen (FiO₂), and end-tidal carbon dioxide (Pe’CO₂) were measured every 5 minutes. Arterial pH and blood gases [arterial partial pressure of oxygen (PaO₂), arterial partial pressure of carbon dioxide (PaCO₂)] were measured at 10, 30, and 40 minutes after induction, and 5 minutes after hoisting. Alveolar dead space ventilation and PaO₂/FiO₂ were calculated. Two repeated measures models were used. All hypothesis tests were two-sided and significance level was α = 0.05. All values are presented as least square means ± SE.ResultsValues at time-matched points from the two groups were not significantly different so they were combined. Arterial partial pressure of oxygen decreased significantly from 149 ± 14.4 mmHg before hoisting to 92 ± 11.6 mmHg after hoisting (p=0.0013). The PaO₂/FiO₂ ratio decreased from 275 ± 30 to 175 ± 24 (p=0.0055). End-tidal carbon dioxide decreased significantly from 48.7 ± 1.6 to 44.5 ± 1.2 mmHg (p=0.021). Arterial partial pressure of carbon dioxide, blood pressures and heart rates measured 5 minutes after hoisting were not different from measurements obtained before hoisting.Conclusion and clinical relevanceHoisting decreased PaO₂ in anesthetized healthy foals. Administration of supplemental oxygen is recommended to counter the decrease in oxygenation and PaO₂ measurement is necessary to detect early changes.     

Pharmacokinetics of midazolam administered concurrently with ketamine after intravenous bolus or infusion in dogs

Brown, S.A., Jacobson, J.D., Hartsfield, S.M. Pharmacokinetics of midazolam administered concurrently with ketamine after intravenous bolus or infusion in dogs. J. vet. Pharmacol. Therap. 16 , 419–425. Midazolam, a water-soluble benzodiazepine tranquilizer, has been considered by some veterinary anaesthesiologists to be suitable as a combination anaesthetic agent when administered concurrently with ketamine because of its water solubility and miscibility with ketamine. However, the pharmacokinetics of midazolam have not been extensively described in the dog. Twelve clinically healthy mixed breed dogs (22.2–33.4 kg) were divided into two groups at random and were administered ketamine (10 mg/kg) and midazolam (0.5 mg/kg) either as an intravenous bolus over 30 s (group 1) or as an i.v. infusion in 0.9% NaCl (2 ml/kg) over 15 min. Blood samples were obtained immediately before the drugs were injected and periodically for 6 h afterwards. Serum concentrations were determined using gas chromatography with electron-capture detection. Serum concentrations were best described using a two-compartment open model and indicated a t_½α of 1.8 min and t_½β.p of 27.8 min after i.v. bolus, and t_½α f 1–35 min and t_½β of 31.6 min after i.v. infusion. The calculated pharmacokinetic coefficient B was significantly smaller after i.v. infusion (429 ± 244 ng/ml) than after i.v. bolus (888 ± 130 ng/ml, P = 0.004). Furthermore, AUC was significantly smaller after i.v. infusion (29 800 ±6120 ng/h/ml) than after i.v. bolus (42 500 ± 8460 ng/h/ml, P < 0.05), resulting in a larger Cl_B after i.v. infusion (17.4 ± 4.00 ml/min/kg than after i.v. bolus (12.1 ± 2.24 ml/min/kg, P < 0.05). No other pharmacokinetic value was significantly affected by rate of intravenous administration.     

Cardiopulmonary and sedative effects of intravenous or epidural methadone in conscious dogs

Cardiopulmonary and sedative effects of intravenous or epidural methadone were compared. Six beagles were randomly assigned to group MIV (methadone 0.5 mg/kg IV + NaCl 0.9% epidurally) or MEP (methadone 0.5 mg/kg epidurally + NaCl 0.9% IV). Cardiopulmonary, blood gas and sedation were assessed at time (T) 0, 15, 30, 60, 120, 240 and 480 min after drug administration. Compared to T0, heart rate decreased at T15–T120 in MIV (p < .001) and T15–T240 in MEP (p < .05); mean arterial pressure was reduced at T15–T60 in MEP (p < .01); respiratory rate was higher at T15 and T30 in both groups (p < .05); pH was lower at T15–T120 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .05); PaCO₂ was higher at T15–T60 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .01); sedation scores were higher at T15 and T30 in MIV and T15–T60 in MEP (p < .05). At T120 and T240, sedation score was higher in group MEP compared with group MIV (p < .01) In conclusion, cardiopulmonary and sedative effects of identical methadone doses are similar when administered IV or epidurally to conscious healthy dogs.     

Cardiopulmonary effects of xylazine sedation in the foal

Six healthy foals underwent instrumentation for measurement of the cardiopulmonary effects of sedation with 1.1 mg/kg bodyweight xylazine hydrochloride given intravenously. Responses to xylazine in foals at 10 and 28 days of age were not significantly different. Foals became sedate and markedly ataxic, and four of the six foals became recumbent. Heart rate decreased significantly but no arrhythmias were detected. Arterial blood pressure increased initially and then fell significantly below pre-injection values. Changes in respiratory airflow, upper airway obstruction and respiratory noise were noted in the initial 20 mins of sedation, after which respiratory rate fell, tidal volume increased, and minute volume decreased gradually. Arterial blood gas tensions and pH did not change significantly during the 120 mins following xylazine administration. Control studies showed no significant changes. All foals recovered uneventfully.