The cardiopulmonary effects of romifidine in dogs with and without prior or concurrent administration of glycopyrrolate

Dexmedetomidine combined with etomidate or emulsified isoflurane for induction reduced cardiopulmonary response in dogs

To investigate the effects of etomidate, emulsified isoflurane, and their combination with dexmedetomidine on physiological parameters, electrocardiogram (ECG) results, and the quality of induction and recovery during isoflurane maintenance anaesthesia. 5 mixed-breed dogs received each of four treatments: etomidate (E group); emulsified isoflurane (EI group); both dexmedetomidine and etomidate (DE group); or both dexmedetomidine and emulsified isoflurane (DEI group). All drugs were IV injection administered for induction, followed by 1.5 MAC (minimal alveolar concentration) of isoflurane to maintain anaesthesia. Rectal temperature (RT), respiratory rate (RR), heart rate (HR), mean arterial pressure (MAP), and ECG were measured at baseline, 0, 5, 10, 20, 40, and 60 minutes after intubation. The quality of induction and recovery was evaluated for all dogs. All the anaesthetic procedures provided good conditions for induction of anaesthesia. The quality of induction and recovery in the E group was worse than other groups. The decrease of RR in the E and DE groups was stronger than that in the EI and DEI groups. The dogs in the E group had the most significant prolongation of the Q-T interval and changes in the S-T segment. Deviation and extension of the S-T segment were noted in the El group. The dogs in the DE and DEI groups had fewer changes in the ECG results than those in the E and EI groups. The addition of dexmedetomidine caused less effect on cardiopulmonary parameters and the ECG results than either etomidate or emulsified isoflurane alone. Thus, etomidate or emulsified isoflurane in combination with dexmedetomidine may be useful clinically for the induction of anaesthesia.

Cardiovascular effects of premedication with medetomidine alone and in combination with MK-467 or glycopyrrolate in dogs subsequently anesthetized with isoflurane

OBJECTIVE To compare cardiovascular effects of premedication with medetomidine alone and with each of 3 doses of MK-467 or after glycopyrrolate in dogs subsequently anesthetized with isoflurane. ANIMALS 8 healthy purpose-bred 5-year-old Beagles. PROCEDURES In a randomized crossover study, each dog received 5 premedication protocols (medetomidine [10 μg/kg, IV] alone [MED] and in combination with MK-467 at doses of 50 [MMK50], 100 [MMK100], and 150 [MMK150] μg/kg and 15 minutes after glycopyrrolate [10 μg/kg, SC; MGP]), with at least 14 days between treatments. Twenty minutes after medetomidine administration, anesthesia was induced with ketamine (0.5 mg/kg, IV) and midazolam (0.1 mg/kg, IV) increments given to effect and maintained with isoflurane (1.2%) for 50 minutes. Cardiovascular variables were recorded, and blood samples for determination of plasma dexmedetomidine, levomedetomidine, and MK-467 concentrations were collected at predetermined times. Variables were compared among the 5 treatments. RESULTS The mean arterial pressure and systemic vascular resistance index increased following the MED treatment, and those increases were augmented and obtunded following the MGP and MMK150 treatments, respectively. Mean cardiac index for the MMK100 and MMK150 treatments was significantly greater than that for the MGP treatment. The area under the time-concentration curve to the last sampling point for dexmedetomidine for the MMK150 treatment was significantly lower than that for the MED treatment. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated concurrent administration of MK-467 with medetomidine alleviated medetomidine-induced hemodynamic changes in a dose-dependent manner prior to isoflurane anesthesia. Following MK-467 administration to healthy dogs, mean arterial pressure was sustained at acceptable levels during isoflurane anesthesia.

Hyoscine-N-butylbromide premedication on cardiovascular variables of horses sedated with medetomidine

OBJECTIVE

To evaluate the effects of intravenous (IV) or intramuscular (IM) hyoscine premedication on physiologic variables following IV administration of medetomidine in horses.

STUDY DESIGN

Randomized, crossover experimental study.

ANIMALS

Eight healthy crossbred horses weighing 330 ± 39 kg and aged 7 ± 4 years.

METHODS

Baseline measurements of heart rate (HR), cardiac index (CI), respiratory rate, systemic vascular resistance (SVR), percentage of patients with second degree atrioventricular (2(o) AV) block, mean arterial pressure (MAP), pH, and arterial partial pressures of carbon dioxide (PaCO2 ) and oxygen (PaO2 ) were obtained 5 minutes before administration of IV hyoscine (0.14 mg kg(-1) ; group HIV), IM hyoscine (0.3 mg kg(-1) ; group HIM), or an equal volume of physiologic saline IV (group C). Five minutes later, medetomidine (7.5 μg kg(-1) ) was administered IV and measurements were recorded at various time points for 130 minutes.

RESULTS

Medetomidine induced bradycardia, 2(o) AV blocks and increased SVR immediately after administration, without significant changes in CI or MAP in C. Hyoscine administration induced tachycardia and hypertension, and decreased the percentage of 2(o) AV blocks induced by medetomidine. Peak HR and MAP were higher in HIV than HIM at 88 ± 18 beats minute(-1) and 241 ± 37 mmHg versus 65 ± 16 beats minute(-1) and 192 ± 38 mmHg, respectively. CI was increased significantly in HIV (p ≤ 0.05). Respiratory rate decreased significantly in all groups during the recording period. pH, PaCO2 and PaO2 were not significantly changed by administration of medetomidine with or without hyoscine.

CONCLUSION AND CLINICAL RELEVANCE

Hyoscine administered IV or IM before medetomidine in horses resulted in tachycardia and hypertension under the conditions of this study. The significance of these changes, and responses to other dose rates, requires further investigation.

Romifidine and low doses of tiletamine-zolazepam in dogs

OBJECTIVE

To evaluate clinical effects of romifidine and low doses of tiletamine-zolazepam (TZ) in dogs.

STUDY DESIGN

Randomized "blinded" cross-over study.

ANIMALS

Six healthy beagle dogs (two males, four females).

METHODS

In separate preliminary experiments dogs received intravenous (IV) tiletamine-zolazepam (TZ) at 1 and 2 mg kg(-1). For the main trial, dogs received romifidine (R) followed 5 minutes later by IV at six dose regimens: R40TZ1, R60TZ1, R80TZ1 (Romifidine at 40, 60, 80 μg kg(-1) and TZ at 1 mg kg(-1)), R40TZ2, R60TZ2 and R80TZ2 (Romifidine at 40, 60, 80 μg kg(-1) and TZ at 2 mg kg(-1)). Dogs underwent endotracheal intubation, but breathed room air. Cardiorespiratory variables were measured and arterial blood analyzed. Quality of sedation, duration of anaesthesia and time to recovery (TR) were recorded. Data were analysed by anova or Friedman test as relevant.

RESULTS

Endotracheal intubation was possible with all romifidine/TZ combinations but not with TZ alone. Mean times (minutes) from TZ injection to return of pedal reflex were 1-3 minutes for TZ alone, and 9-17 minutes for romifidine combinations. In the main trial (romifidine combinations) mean time (minutes) to standing increased with increasing dosage (R40TZ1 13; R80TZ2 32). Five minutes after TZ administration, when compared with baseline arterial blood pressures and arterial carbon dioxide had increased, and respiratory rate, pH and arterial oxygen tensions decreased, these changes becoming statistically significant with the higher dose rates. One dog in R60TZ2 and three dogs in R80TZ2 became hypoxaemic.

CONCLUSIONS AND CLINICAL RELEVANCE

Romifidine improves the quality and lengthens the duration of anaesthesia induced by TZ. The combination provides a suitable protocol for induction of or short-term anaesthesia in healthy dogs. However, the higher doses cause cardiovascular stimulation and respiratory depression, and precautions should be taken accordingly.

Sedative effects of three doses of romifidine in comparison with medetomidine in cats

OBJECTIVE

To compare the sedative effects of three doses of romifidine with one dose of medetomidine.

STUDY DESIGN

Prospective blinded experimental cross-over.

ANIMALS

Five adult Domestic Short Hair cats.

METHODS

Cats were administered romifidine at 80, 120 and 160 μg kg(-1) or medetomidine at 20 μg kg(-1) (M20) intramuscularly (IM). Sedative effects were assessed for 3 hours by summing the scores given to posture, auditory response, resistance to positioning, muscular relaxation, and response to noxious stimuli, giving a total sedation score (TS). The area under the curve (AUC) of TS ≥7 (the score considered as clinically useful sedation) was calculated. Times to stages of sedation were determined. Some physiological parameters were measured. Data to compare treatments were analysed by anova or Kruskal-Wallis test as relevant.

RESULTS

All treatments gave a TS considered clinically useful. There were no significant differences between treatments for times to onset of sedation, maximum TS reached, or AUC. Differences between romifidine treatments for other sedation parameters were not significant but the time to maximum TS and to recovery was shortest in M20. Heart rate (HR) fell significantly with all treatments and, although with M20 it recovered at 65 minutes, it remained significantly depressed for 3 hours after all romifidine treatments. Most cats vomited, and/or hypersalivated after all treatments.

CONCLUSIONS

Doses of 80, 120 and 160 μg kg(-1) romifidine IM produce sedation in cats which is similar to that following medetomidine 20 μg kg(-1) . Recovery from sedation and of physiological parameters was quickest after M20.

CLINICAL RELEVANCE

Doses of romifidine considerably lower than those investigated by previous authors give a clinically useful level of sedation, and their use might result in less side effects and a quicker recovery.

Evaluation of cardiorespiratory effects of combinations of dexmedetomidine and atropine in cats

The cardiovascular effects of dexmedetomidine alone or in combination with atropine were studied in six cats. Cats underwent four treatments in a randomized crossover design as follows: DEX15, saline+dexmedetomidine 15microg/kg; DEX30, saline+dexmedetomidine 30microg/kg; ADEX15, atropine+dexmedetomidine 15microg/kg; ADEX30, atropine+dexmedetomidine 30microg/kg. Pulse rate (PR) and systolic arterial pressure (SAP) decreased in DEX15 and DEX30. Premedication with atropine was effective in preventing bradycardia (PR<100 beats/min) and resulted in a biphasic effect in blood pressure. Hypertension was followed by a gradual decrease in SAP. Rate pressure product decreased in DEX15 and DEX30 whereas in ADEX15 and ADEX30 it remained within baseline values for at least 60min. Although premedication with atropine in cats sedated with dexmedetomidine prevents bradycardia, it induces hypertension and increases myocardial oxygen consumption. The magnitude of cardiovascular effects produced by dexmedetomidine in cats does not seem to be dose-related.

Sedative and cardiorespiratory effects of three doses of romifidine in comparison with medetomidine in five cats

This study was designed to compare the effects of three doses of romifidine (200, 400 and 600 microg/kg) with medetomidine (80 microg/kg) administered intramuscularly to five cats. The quality of sedation and the cardiovascular and respiratory effects of each treatment were evaluated, and the onset and duration of the sedation, and the cats' recovery times, were measured. Cardiorespiratory variables were also analysed. The dose of 200 microg/kg romifidine was clinically superior to the other doses of romifidine, providing moderate sedation, with minor cardiorespiratory and other adverse effects. However none of the doses of romifidine induced as deep and reliable sedation as the dose of medetomidine.

Continuous infusion in adult females dogs submitted to ovariohysterectomy with midazolam-xylazine and/or medetomidine pre-treated with methotrimeprazine and buprenorphine

PURPOSE: To compare, by continuous infusion of ketamine or medetomidine combined to methotrimeprazine and buprenorphine, ketamine and midazolam, the degree of hypnosis, myorelaxation, anesthetic quality and surgical feasibility through evaluation of possible parametric alterations and recovery quality. METHODS: 20 healthy adult females dogs, aged 3 to 5 years, body weight between 7 and 15 kg, were assigned randomly and homogenously to 2 groups of 10 animals each (n=10), group 1 (G1) and group 2 (G2), respectively. Animals of G1 were subjected to a pre-treatment with intravenous 1.0 mg/kg methotrimeprazine and or 3ì/kg. After 15 minutes, a 5.0 mg/kg ketamine and 0.2 mg/kg midazolam were intravenously injected. Immediately after induction, an anesthetic combination of 0.4 mg/kg/h midazolam, 20 mg/kg/h ketamine and 1.0 mg/kg/h xylazine, was continuously and intravenously administered for 30 minutes. The same techniques were used in G2 except for the substitution of xylazine for 30ìg/kg/h medetomidine. RESULTS: In G1 there was a 1st and 2nd degree atrioventricular heart block, a longer recovery period and lower quality. In G2 a 1st degree atrioventricular heart block occurred but isolated and ephemeral. CONCLUSIONS: The continuous infusion method, besides reducing drugs utilization, prevented collateral effects allowing a more tranquil recovery with no excitations, both protocols permitted the surgical procedure (ovary-hysterectomy) bringing about a reduction in hypnosis and an accentuated myorelaxation. Xylazine and medetomidine showed a similar pharmacodynamic behavior but with different clinical aspects. The electrocardiographic alterations observed in G2 and in a lower degree in G1 must be well studied. Describers: dogs, ketamine, methotrimeprazine, medetomidine, midazolam and xylazine.

Comparison of Romifidine and Medetomidine Pre-medication in Propofol?Isoflurane Anaesthetised Dogs

The objective of this paper was to evaluate romifidine as a pre-medicant in dogs prior to propofol-isoflurane anaesthesia, and to compare it with medetomidine. For this, eight healthy dogs were anaesthetised. Each dog received three pre-anaesthetic protocols: R40 (romifidine, 40 microg/kg, IV), R80 (romifidine, 80 microg/kg, IV) or MED (medetomidine, 10 microg/kg, IV). Induction of anaesthesia was delivered with propofol and maintained with isoflurane. The following variables were studied before sedative administration and 10 min after sedative administration: heart rate (HR), mean arterial pressure (MAP), systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) and respiratory rate (RR). During maintenance, the following variables were recorded at 5-min intervals: HR, MAP, SAD, DAP, arterial oxygen saturation (SpO(2)), end-tidal CO(2)(EtCO(2)), end-tidal concentration of isoflurane (EtISO) required for maintenance of anaesthesia and tidal volume (TV). Time to extubation, time to sternal recumbency and time to standing were also registered. HR and RR experimented a significantly decreased during sedation in all protocols respect to baseline values. Mean HR, MAP, SAP, DAP, SpO(2), EtCO(2), and TV during anaesthesia were similar for the three protocols. End tidal of isoflurane concentration was statistically similar for all protocols. Recovery time for R40 was significantly shorter than in R80 and MED. The studied combination of romifidine, propofol and isoflurane appears to be an effective drug combination for inducing and maintaining general anaesthesia in healthy dogs.

Sedative, analgesic and cardiorespiratory effects of romifidine in cats

OBJECTIVE

To evaluate the sedative, analgesic, and cardiorespiratory effects of intramascular (IM) romifidine in cats.

STUDY DESIGN

Prospective, randomized experimental trial.

ANIMALS

Ten healthy adult cats.

METHODS

Romifidine (100, 200, and 400 microg kg(-1)) or xylazine (1 mg kg(-1)) was given IM in a cross-over study design. Heart rate (HR), respiratory rate (RR), rectal temperature (RT), hemoglobin saturation, oscillometric arterial pressure, and scores for sedation, muscle relaxation, position, auditory response, and analgesia were determined before and after drug administration. Time to recumbency, duration of recumbency, and time to recover from sedation were determined. Subjective evaluation and cardiorespiratory variables were recorded before and at regular intervals for 60 minutes after drug administration.

RESULTS

Bradycardia developed in all cats that were given romifidine or xylazine. No other significant differences in physiologic parameters were observed from baseline values or between treatments. Increasing the dose of romifidine did not result in increased sedation or muscle relaxation. Cats given xylazine showed higher sedation and muscle relaxation scores over time. Analgesia scores were significantly higher after administration of romifidine (400 microg kg(-1)) and xylazine (1 mg kg(-1)) than after romifidine at 100 or 200 microg kg(-1). Duration of lateral recumbency was not significantly different between treatments; however, cats took longer to recover after administration of 400 micro g kg(-1) romifidine.

CONCLUSIONS AND CLINICAL RELEVANCE

Bradycardia is the most important adverse effect after IM administration of romifidine at doses ranging from 100 to 400 microg kg(-1) or 1 mg kg(-1) of xylazine in cats. The sedative effects of romifidine at 200 microg kg(-1) are comparable to those of 1 mg kg(-1) of xylazine, although muscle relaxation and analgesia were significantly less with romifidine than with xylazine.

The effect of rectal temperature on perianesthetic serum concentrations of transdermally administered fentanyl in cats anesthetized with isoflurane

OBJECTIVES

To determine whether moderate hypothermia during 4 hours of anesthesia with isoflurane substantially affects serum concentrations of transdermally administered fentanyl in the perianesthetic period in cats.

ANIMALS

7 healthy mature cats.

PROCEDURE

A fentanyl patch (25 microg/h) was applied to the shaved thorax 24 hours before induction of anesthesia. Anesthesia was induced at time 0. Each cat received 2 treatments in a random order. Treatments were isoflurane anesthesia with normothermia and isoflurane anesthesia with hypothermia. Cats were intubated, connected to a nonrebreathing circuit, and maintained at 1.3X minimum alveolar concentration for 4 hours. Cats in the hypothermia treatment groups were actively cooled to 35 degrees C following the induction of anesthesia. Serum fentanyl analysis was performed at -24, -12, 0, 1, 2, 3, 4, 4.5, 5, 6, 7, 8, 9, 10, 12, and 24 hours.

RESULTS

Mean +/- SEM serum fentanyl concentration (SFC) for the hypothermia treatment group (0.598 +/- 0.3048 ng/mL) was significantly lower than the baseline concentration (1.834 +/- 0.6393 ng/mL) at 1 hour. This significant reduction persisted for the duration of anesthesia for the hypothermia treatment group. Serum fentanyl concentrations returned to baseline values within 1 hour of the end of anesthesia, regardless of body temperature.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypothermia during inhalant anesthesia induced a significant reduction in SFC obtained with transdermal administration. The impact of this reduction in SFC on the contribution of transdermally administered fentanyl to any reduction in the need for inhalant anesthesia remains to be determined.

Quantitative assessment of nociception in horses by use of the nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation

OBJECTIVES

To evoke and measure the nociceptive withdrawal reflex (NWR) by use of electromyographic recordings and to score the behavioral nociceptive responses to electrical pulses in standing nonsedated horses.

ANIMALS

10 adult horses.

PROCEDURE

The lateral palmar digital nerve of the forelimb was transcutaneously stimulated, and surface electromyographic responses were recorded from the ulnaris lateralis, extensor carpi radialis, and common digital extensor muscles. Stimuli consisted of a 25-millisecond train of 5 constant-current pulses delivered by a computer-controlled stimulator. The 80- to 250-milliseconds poststimulation interval was analyzed to detect the NWR. The current intensity was increased in steps of 0.5 mA until the NWR threshold intensity (lt) was reached. The stimulus at It was repeated twice. Latency and amplitude of the NWR, together with the behavioral reaction of horses, were analyzed. The latter was scored according to a scale from 0 (no reaction) to 5 (vigorous reaction). Finally, 3 suprathreshold stimuli at 1.2 X It were analyzed.

RESULTS

The median It to elicit NWR was 2.5 mA. Median onset latency of the NWR was 96.0 milliseconds at It and 89.6 milliseconds for suprathreshold stimuli. The amplitude of the reflexes was higher for suprathreshold stimulations, and behavioral reactions were slightly stronger when stimulus intensity increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of our study indicate that it is possible to record NWR in conscious standing horses, to define a reflex threshold, and to measure reflexes in response to increasing stimulus intensity.