S.L. Freeman

Cardiopulmonary effects and pharmacokinetics of i.v. dexmedetomidine in ponies

REASONS FOR PERFORMING STUDY Currently available sedatives depress cardiopulmonary function considerably; therefore, it is important to search for new, less depressive sedatives. The study was performed to assess duration and intensity of cardiopulmonary side effects of a new sedative, dexmedetomidine (DEX), in horses. OBJECTIVES To study pharmacokinetics and cardiopulmonary effects of i.v. DEX. METHODS Pharmacokinetics of 3.5 microg/kg bwt i.v. DEX were studied in a group of 8 mature (mean age 4.4 years) and 6 old ponies (mean age 20 years). Cardiopulmonary data were recorded in mature ponies before and 5, 10, 20, 30, 45 and 60 mins after administration of DEX 3.5 microg/kg bwt i.v. Data were analysed using ANOVA for repeated measures, and where appropriate Dunnetts t test was used to detect differences from resting values (P < 0.05). RESULTS Within 2 h after DEX administration, plasma levels were beyond limits of quantification (0.05 ng/ml). Mean values for kinetic parameters for mature and old ponies were: Cmax (ng/ml) 4.6 and 3.8, t 1/2 (min) 19.8 and 28.9 and AUC (ng.min/ml) 34.5 and 44.3, respectively. Heart rate, central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure did not change significantly compared to presedation values throughout the 60 min observation period. Compared to presedation values, stroke volume and mixed venous PO2 were reduced for the first 5 mins, paralleled by an increase in systemic and pulmonary vascular resistance. Cardiac index was reduced for the first 10 mins, arterial blood pressures at 20, 30 and 45 mins and respiratory rate throughout the 60 min observation period, but no change in arterial PO2 or PCO2 occurred. CONCLUSIONS DEX administration i.v. causes similar cardiopulmonary changes to those caused by other alpha-2 adrenoceptor agonists, but of very short duration. DEX is redistributed particularly rapidly. POTENTIAL RELEVANCE DEX might be safer for sedation of horses because of its very short-lasting cardiopulmonary side effects. For long duration sedation, its kinetics favour its use as a continuous infusion.

Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography

A technique of transrectal ultrasonography was developed to investigate the effects of romifidine 80 and 120 microg/kg bwt on intestinal motility in the horse. Motility of the small intestine, caecum and left ventral colon were assessed following injection of romifidine and a saline control, using a blinded, cross-over study design in 6 horses. Measurements were taken at 15, 30, 60, 120, 180 and 240 min after drug administration. There was a slight nonsignificant decrease in motility in the control group over the 4 h study period. Both doses of romifidine produced a marked decrease in gastrointestinal motility and were associated with the presence of reduced (nonpropulsive) contractions. Transrectal ultrasonography proved suitable for monitoring changes in the type and frequency of intestinal motility in the horse.

Prevalence of obesity in a population of horses in the UK

OBESITY predisposes to important conditions in horses, such as laminitis and equine metabolic syndrome ([Treiber and others 2006][1]). [Wyse and others (2008)][2] reported a prevalence of obesity of 45 per cent in pleasure riding horses in Scotland, but the prevalence of obesity in the wider UK

Medetomidine-ketamine anaesthesia induction followed by medetomidine-propofol in ponies: infusion rates and cardiopulmonary side effects.

REASONS FOR PERFORMING STUDY To search for long-term total i.v. anaesthesia techniques as a potential alternative to inhalation anaesthesia. OBJECTIVES To determine cardiopulmonary effects and anaesthesia quality of medetomidine-ketamine anaesthesia induction followed by 4 h of medetomidine-propofol anaesthesia in 6 ponies. METHODS Sedation consisted of 7 microg/kg bwt medetomidine i.v. followed after 10 min by 2 mg/kg bwt i.v. ketamine. Anaesthesia was maintained for 4 h with 3.5 microg/kg bwt/h medetomidine and propofol at minimum infusion dose rates determined by application of supramaximal electrical pain stimuli. Ventilation was spontaneous (F(I)O2 > 0.9). Cardiopulmonary measurements were always taken before electrical stimulation, 15 mins after anaesthesia induction and at 25 min intervals. RESULTS Anaesthesia induction was excellent and movements after pain stimuli were subsequently gentle. Mean propofol infusion rates were 0.89-0.1 mg/kg bwt/min. No changes in cardiopulmonary variables occured over time. Range of mean values recorded was: respiratory rate 13.0-15.8 breaths/min; PaO2 29.1-37.9 kPa; PaCO2 6.2-6.9 kPa; heart rate 31.2-40.8 beats/min; mean arterial pressure 90.0-120.8 mmHg; cardiac index 44.1-59.8 ml/kg bwt/min; mean pulmonary arterial pressure 11.8-16.4 mmHg. Recovery to standing was an average of 31.1 mins and ponies stood within one or 2 attempts. CONCLUSIONS In this paper, ketamine anaesthesia induction avoided the problems encountered previously with propofol. Cardiovascular function was remarkably stable. Hypoxaemia did not occur but, despite F(I)O2 of > 0.9, minimal PaO2 in one pony after 4 h anaesthesia was 8.5 kPa. POTENTIAL RELEVANCE The described regime might offer a good, practicable alternative to inhalation anaesthesia and has potential for reducing the fatality rate in horses.

Contact of dog spermatozoa with homologous uterine tube epithelium prolongs flagellar activity in relation to the stage of the estrous cycle

There is scant information about the storage of spermatozoa within the reproductive tract of the bitch. In several species the uterine tube plays a significant role in sperm storage. The present study was performed to investigate the interaction between spermatozoa and the epithelium of the uterine tube, in particular how this interaction might influence the flagellar activity of spermatozoa in relation to the stage of the estrous cycle. Epithelium was harvested from uterine tubes of 24 bitches at various stages of the estrous cycle (estrus, luteal phase or anestrus), and cultured with pooled spermatozoa collected from 6 dogs. Spermatozoa rapidly bound to the epithelial surface by their heads and the majority of attached spermatozoa were motile. The intimate association between spermatozoa and the uterine tube epithelium maintained motility in a manner that was related to the stage of the estrous cycle. Flagellar activity was significantly greater for spermatozoa bound to estrous epithelium than epithelium from the luteal phase or anestrus. On average, approximately 10% of spermatozoa that were attached to the uterine tube epithelium of estrous bitches retained their flagellar activity for 48 h after innoculation. There was no apparent influence of the region of the uterine tube on this effect. These findings suggest that the uterine tube may form a functional spermatozoal reservoir in the bitch.

Follicular Dynamics, Ovulation and Conception Rates in Bitches

Real-time ultrasound imaging was used in a clinical study to estimate the number of follicles of different sizes, ovulation and conception rates, and to study follicle dynamics following oestrus-induction of bitches. Follicles were identified during late anoestrus (between 100 and 60 days prior to the pre-ovulatory LH surge) and there appeared to be a shift in the population from small follicles (1-3 mm in diameter) to large follicles (>4 mm diameter) approximately 2 days prior to the LH surge. Corpora lutea could be reliably identified although the majority were cavitated. High ovulation rates (97-100%) and pregnant rates (86-100%) were detected, and although the conception rate was approximately 70% it varied between 8 and 92%. Within the narrow range of the clinical population studied there were trends relating age to reproduction performance. Oestrus induction with a gonadotrophin regime appeared to result in large numbers of small follicles that did not ovulate, whilst when using cabergoline the number of small and large follicels and the number of copora lutea were similar to those of control cycles.

Treatment of spontaneous pyometra in 22 bitches with a combination of cabergoline and cloprostenol

Twenty-two bitches with ultrasonographically diagnosed spontaneous pyometra were treated with a combination of 5 μg/kg cabergoline per day and 5 μg/kg cloprostenol every third day, and potentiated sulphonamide twice a day. Bitches with either open-cervix or closed-cervix pyometra showed a rapid clinical improvement, associated with a reduction in plasma progesterone concentration, increased vulval discharge and a reduction in the diameter of the uterus. The haematological profiles of 21 of the bitches returned to normal within six days of treatment, and their biochemical profiles returned to normal within nine days; 19 of the bitches were managed successfully by a 10-day period of treatment. Two bitches required a further three days of treatment, and in one bitch with a partial uterine torsion the treatment was not successful. Adverse effects of the treatment were limited to the 60 minutes immediately after the administration of prostaglandin, and included retching, vomiting, mild abdominal straining, diarrhoea and panting. The incidence of adverse effects was reduced after each successive dose of prostaglandin. Eleven of the 21 successfully treated bitches were mated at the next oestrus, and seven became pregnant; their litters were smaller than the published breed averages. In four of the bitches the pyometra recurred after the next oestrus.

Ultrasonography of the equine abdomen: techniques and normal findings

ABDOMINAL ultrasonography is increasingly used in veterinary medicine and has an important role in decision-making in horses with colic. The technique has been used predominantly in foals and smaller horses, where rectal palpation is not possible, but is also a valuable diagnostic aid in the adult horse. It enables the veterinary surgeon to image regions of the abdomen that are inaccessible to rectal palpation, such as the duodenum and stomach. It allows abnormal rectal findings to be confirmed and, in many cases, provides further information. For example, rectal palpation may detect distended loops of small intestine, but ultrasonography will determine the degree of distension, any thickening of the intestinal wall, and the presence or absence of motility. Based on this, features that distinguish between surgical and non-surgical lesions can be identified. This, the first of two articles discussing the use of ultrasonography in the equine acute abdomen, describes the techniques of abdominal ultrasonography, and normal ultrasonographic findings. The second article, to be published in the next issue, will describe ultrasonographic changes occurring in the colic patient.

Ultrasonography of the equine abdomen: findings in the colic patient

RAPID and accurate diagnosis will significantly improve the outcome in horses with acute abdominal pain. This is particularly true of surgical lesions, where swift intervention offers the best chance of survival. However, abdominal surgery is a major procedure in the horse, with a number of potentially severe complications. Therefore, an accurate prediction of the type of lesion and need for surgery is vital to reduce morbidity and mortality. Ultrasonography improves the accuracy of diagnosis in colic patients. In a large study of horses with acute abdominal pain, ultrasonography was more sensitive than rectal palpation in detecting lesions (Klohnen and others 1996); in animals with small intestinal lesions, abnormalities were identified in only 50 per cent of cases by rectal palpation, compared with 100 per cent of cases by ultrasonography. An article in the last issue discussed abdominal ultrasonographic techniques and normal findings in the horse (April 2002, pp 204-211). This article describes the findings in horses with acute gastrointestinal disease, and discusses the differentiation between surgical and non-surgical lesions.

The bitch uterine response to semen deposition and its modification by male accessory gland secretions

Little is known about the response of the bitchs reproductive tract to semen deposition. In this study, an influx of polymorphonuclear neutrophils (PMNs) into the uterus was detected after artificial insemination, but there was normal fertility. Doppler ultrasonography showed that insemination induced an increase in uterine artery blood velocity and a decrease in the resistance index of short duration, indicating vasodilation. Semen that was extended in fluid from the sperm rich fraction of the ejaculate (seminal plasma, SP), or third fraction of the ejaculate (prostatic fluid, PF), produced a similar magnitude of effect but of longer duration. It was hypothesised that vasodilation following insemination was largely induced by SP and PF which, together with PMN influx, was part of a normal uterine response. Physiological concentrations of PMNs in vitro reduced the ability of spermatozoa to attach to uterine epithelium, most likely as a result of spermatozoa becoming attached to PMNs. However, both SP and PF increased attachment of spermatozoa to the uterine epithelium by reducing sperm attachment to PMNs, and potentially by an additional mechanism that did not involve inhibition of sperm binding to PMNs. These are the first canine studies to document an apparent physiological response by the uterus to semen, associated with uterine artery vasodilation and PMN influx. Moreover, these investigations are the first to demonstrate that canine SF and PF are part of the mechanism for increasing uterine perfusion and that both fluids have a modulatory effect on PMN-induced inhibition of spermatozoal attachment to uterine epithelium, most likely mediated by reduced sperm attachment to PMNs.