Preliminary evaluation of the effects of a 1:1 inspiratory-to-expiratory ratio in anesthetized and ventilated horses.

OBJECTIVE: To describe some cardiorespiratory effects of an inspiratory-to-expiratory (IE) ratio of 1:1 compared with 1:3 in ventilated horses in dorsal recumbency. STUDY DESIGN: Randomized crossover experimental study. ANIMALS: A total of eight anesthetized horses, with 444 (330-485) kg body weight [median (range)]. METHODS: Horses were ventilated in dorsal recumbency with a tidal volume of 15 mL kg-1 and a respiratory rate of 8 breaths minute-1, and IE ratios of 1:1 (IE1:1) and 1:3 (IE1:3) in random order, each for 25 minutes after applying a recruitment maneuver. Spirometry, arterial blood gases and dobutamine requirements were recorded in all horses during each treatment. Electrical impedance tomography (EIT) data were recorded in four horses and used to generate functional EIT variables including regional ventilation delay index (RVD), a measure of speed of lung inflation, and end-expiratory lung impedance (EELI), an indicator of functional residual capacity (FRC). Results were assessed with linear and generalized linear mixed models. RESULTS: Compared with treatment IE1:3, horses ventilated with treatment IE1:1 had higher mean airway pressures and respiratory system compliance (p < 0.014), while peak, end-inspiratory and driving airway pressures were lower (p < 0.001). No differences in arterial oxygenation or dobutamine requirements were observed. PaCO2 was lower in treatment IE1:1 (p = 0.039). Treatment IE1:1 resulted in lower RVD (p < 0.002) and higher EELI (p = 0.023) than treatment IE1:3. CONCLUSIONS AND CLINICAL RELEVANCE: These results suggest that IE1:1 improved respiratory system mechanics and alveolar ventilation compared with IE1:3, whereas oxygenation and dobutamine requirements were unchanged, although differences were small. In the four horses where EIT was evaluated, IE1:1 led to a faster inflation rate of the lung, possibly the result of increased FRC. The clinical relevance of these findings needs to be further investigated.

Investigation of associations between preoperative acepromazine or dexmedetomidine administration and development of arterial hypotension or bradycardia in dogs undergoing ovariohysterectomy.

OBJECTIVE To evaluate potential associations between preanesthetic administration of acepromazine or dexmedetomidine and development of arterial hypotension or bradycardia in isoflurane-anesthetized dogs undergoing ovariohysterectomy. ANIMALS 341 dogs. PROCEDURES Medical records were searched to identify dogs that underwent ovariohysterectomy between January 2009 and December 2010 and received hydromorphone with acepromazine or dexmedetomidine as preanesthetic agents. Demographic data, sedative and anesthetic drugs, duration of anesthesia, average vaporizer setting, positive pressure ventilation, occurrence of hypotension (mean arterial pressure < 60 mm Hg) or bradycardia (> 50% reduction in heart rate, compared with the preanesthetic value), time to first occurrence and duration of hypotension, and treatment with dopamine or anticholinergic agents were recorded. Data were compared between dogs that received acepromazine and dexmedetomidine. Logistic regression was used to investigate associations between the treatments of interest (and other putative risk factors) and development of hypotension or bradycardia. RESULTS For dogs that received acepromazine, the odds of developing hypotension were 2.61 times those for dogs that received dexmedetomidine. Hypotension occurred earlier and lasted longer in dogs that received acepromazine, and this group was treated with dopamine more frequently than the group that received dexmedetomidine. Lower body weight was associated with increased odds of hypotension. Odds of developing bradycardia were greater for dogs sedated with dexmedetomidine (vs acepromazine) and for dogs that underwent anesthetic induction with propofol or a ketamine-benzodiazepine combination (vs thiopental). CONCLUSIONS AND CLINICAL RELEVANCE Anesthetic complications differed between isoflurane-anesthetized dogs undergoing ovariohysterectomy after premedication with acepromazine or dexmedetomidine in this study; future prospective investigations are warranted to investigate these effects in other, less homogenous populations of dogs.

The effects of a post-exercise carbohydrate and protein supplement on repeat performance, serum chemistry, insulin and glucagon in competitive weight-pulling dogs.

The physiological demands of weight-pulling dogs have yet to be investigated. Two groups of competitive weight-pulling dogs both underwent two identical pull series 3 h apart. The control group (n 8) was compared with a group fed a rapidly digestible carbohydrate and protein supplement after the first pull series (n 9). Blood was drawn before and after each pull series as well as at 15 and 30 min after the first pull series finished. Biochemistry values remained unremarkable throughout the study in both groups regardless of supplementation or exercise over time. Lactic acid showed mild significant increases post-exercise (2·1 (sd 1·2) mmol/l) compared with baseline (1·4 (sd 0·3) mmol/l; P = 0·03) after the initial pull series. When examining the effects of time there was a significant increase in insulin from baseline (median of 10·8 (range 6·8-17·4) µIU/ml) compared with 30 min after supplementation (17·0 (range 8·1-33·0) µIU/ml) and at 3 h after supplementation (19·2 (range 9·7-53·4) µIU/ml). In the treatment group there was also a time effect, with glucagon being elevated from baseline (median of 100 (range 79-115) pg/ml) compared with 30 min after supplementation (114 (range 90-183) pg/ml) and after the second pull series (131 (range 107-152) pg/ml). Evaluation of each dog's ability to pull the same or greater amount of weight on the second pull series revealed no significant differences. In conclusion, weight-pulling dogs have mild elevations in lactate reflecting little anaerobic metabolism compared with other canine sprinting athletes; hormonal changes associated with carbohydrate absorption are reflected within the treatment group, and supplementation had no effect on performance.