Dallas O. Goble

Circulatory and blood gas changes accompanying the development and treatment of induced laminitis

Summary A peripheral vasodilatory agent, isoxsuprine hydro-chloride, was evaluated in a controlled study for its efficacy in the treatment of acute equine laminitis. Eight healthy, adulthorses of variable age and sex were used in the trial. Acute laminitis was induced in 5 of the horses by oral carbohydrate overload. Intravenous isoxsuprine therapy (1.8 mg/kg) was initiated in 3 of the horses receiving carbohydrate overload at first sign of clinical lameness and repeated at 12-hour intervals. Intravenous saline placebos were administered on a similar schedule to 2 control horses which also received a carbohydrate overload. The remaining 3 horses served as further controls. Local and systemic responses to induction of laminitis and isoxsuprine administration were assessed by subjective evaluation of clinical lameness in a double blind trial; nuclear scintigraphy and radiography of the distal forelimbs; and assessment of physical, hematological and biochemical parameters. Pronounced tachycardia, hypotension and sweating accompanied the intravenous infusion of isoxsuprine. The 3 horses treated with isoxsuprine following the induction of laminitis showed a more rapid improvement in soundness than horses receiving saline placebos. No horse developed rotation of the third phalanx in response to the diet Nuclear scintigraphy indicated that blood perfusion patterns within the hoof of laminitic horses altered with isoxsuprine therapy, but an overall increase or decrease in perfusion was not apparent. Alterations in serum enzyme and electrolyte profiles with the onset of laminitis generally concurred with findings previously reported for this model of the disease. No change in coagulation profiles accompanied the onset of laminitis or isoxsuprine administration. Blood gas analysis indicated an increase in median palmar vein oxygen partial pressure (PO 2 ) levels with onset of laminitis. A concurrent decrease in the median palmar arteriovenous oxygen partial pressure difference (AVO 2 ) was significant at the P 2 values between thoseanimals receiving isoxsuprine and those receiving saline placebo therapy. Results of the trialindicated that isoxsuprine may be beneficial in the treatment of acute laminitis. Further controlled studies are appropriate.

Effects of acepromazine maleate, isoxsuprine hydrochloride and prazosin hydrochloride on laminar microcirculatory blood flow in healthy horses

Summary Laser Doppler flowmetry was used to determine the effects of acepromazine maleate, isoxsuprine hydrochloride, and prazosin hydrochloride on laminar microcirculatory blood flow. Five adult horses, weighing 450–500 kg and free of evidence of laminitis or other inflammatory conditions of the lower limb were used. Holes were drilled on the dorsum of each front hoof to the depth of the junction of the sensitive and insensitive laminae. Temperature, pulse rate and respiratory rate were obtained before begining the measurements. Pulse rate was measured at 15-minute intervals throughout the measurement period. A laser Doppler probe was placed in each hole. Baseline Doppler flow measurements were obtained. Following baseline determinations either acepromazine maleate (0.066 mg/kg), isoxsuprine hydrochloride (0.6 mg/kg) or prazosin hydrochloride (0.025 mg/kg) were administered intravenously. Drugs were randomly assigned and repeated 3 times in each horse. Laminar microcirculatory blood flow was then measured continuously for 180 minutes. These data were analyzed using univariate (mixed model) repeated measures analysis. None of the drugs evaluated had any significant effect on laminar microcirculatory blood flow. Acepromazine maleate, isoxsuprine hydrochloride and prazosin hydrochloride have no laminar microcirculatory blood flow effect in standing, healthy horses at dosages used. Efficacy in the use of these 3 drugs for the treatment of laminitis is questionable. However, this study was performed in healthy horses and the results may not be applicable in horses with laminitis.

Medical evaluation of the musculoskeletal system and common integument relevant to purchase.

With recent advances in diagnostic techniques associated with equine lameness, there is a tendency to reduce our reliance on the most important part of purchase evaluation of the horse-the hands-on physical examination. This article stresses the importance of the physical examination and advises less dependence on involved diagnostic procedures.

Hematomyelia in a colt: A post anesthesia/surgery complication

Summary A six-month-old colt was presented for evaluation of chronic joint distention in the tarsocrural joint. Routine arthroscopy and castration were performed on the colt. During recovery, the colt showed signs of difficulty to rise. Differential diagnoses were myopathy, peripheral neuropathy, fracture, and a central neuropathy. The colt was treated with intravenous fluid and anti-inflammatory agents. A complete neurological exam was performed and deficits in the rear consistent with uppermotor neuron damage. The owner elected humane destruction of the colt and a post-mortem exam was performed. A diagnosis of hemorrhagic myelopathy (hematomyelia) was confirmed. Post anesthetic and surgical hemorrhagic myelopathy (hematomyelia) is a rarely encountered neuropathological condition associated with general anesthesia and surgery in the horse. The infrequent occurrence limits opportunities to study contributing factors associated with this complication other than on a retrospective basis. This report details clinical observations, anesthetic protocol, post anesthetic evaluation attempting to provide physiological suggestions that result in the neurological complication. Previously reported cases in the literature are evaluated and compared to this case, documenting common factors present in all reports.