Exercise-induced Pulmonary Hemorrhage: Is It Important and Can It Be Prevented?

Exercise-induced pulmonary hemorrhage (EIPH) occurs commonly in horses undergoing strenuous exercise. Reported risk factors include racing in cold temperatures and wearing of bar shoes. In horses with documented moderate to severe EIPH, increasing the interval between races and adopting a negative race pace strategy may reduce the severity of EIPH in subsequent races. EIPH seems to have an impact on performance only when moderate to severe. This occurs in a small number of starters, approximately 6%. EIPH often is erratic in severity from race to race, although across a population it is weakly progressive over increasing race starts.

Agreement between invasive blood pressure measured centrally and peripherally in anaesthetized horses.

OBJECTIVE: To determine the agreement of invasive blood pressure measured in the facial, metatarsal and carotid arteries, and evaluate the effects of two haemodynamic conditions on agreement. STUDY DESIGN: Prospective randomized study. ANIMALS: A group of eight horses aged 7 (4-23) years with a body weight of 493 ± 33 kg. METHODS: Horses were anaesthetized and positioned in dorsal recumbency. Invasive blood pressure was measured simultaneously via catheters placed in the facial, metatarsal and carotid arteries. Cardiovascular function and agreement between arteries was assessed before and during administration of phenylephrine and sodium nitroprusside. These were administered until carotid mean pressure (MAPc) increased or decreased from baseline (65 ± 5) to >90 or <50 mmHg, respectively. Data recorded at each sample time included systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures for carotid (c), facial (f) and metatarsal (m) arteries as well as cardiac output (Q˙t) and systemic vascular resistance (SVR). Bland-Altman analysis was used to assess agreement between peripheral and central sites, and regression analysis to determine influence of Q˙t and SVR. RESULTS: The largest difference was observed in SAPc and SAPm with a bias and limits of agreement (LOA) of 2 (-15 to 19) mmHg. The bias (LOA) for MAPc and MAPf was 2 (-4 to 9) mmHg and for MAPc and MAPm was 5 (-4 to 14) mmHg. The best agreement for DAP was seen between DAPc and DAPf with bias (LOA) of 1 (-3 to 5) mmHg. Regression analysis indicated marginal influence on agreement by Q˙t on MAPc and MAPf. CONCLUSIONS AND CLINICAL RELEVANCE: MAP and DAP of the carotid artery were higher than those of the peripheral arteries, which may lead to overzealous treatment of hypotension, albeit maintaining central pressures. Q˙t and SVR did not largely influence the difference between sites.

Agreement between invasive blood pressures measured in three peripheral arteries in anaesthetized horses under clinical conditions.

OBJECTIVE: To determine agreement between invasive blood pressures measured in three peripheral arteries in anaesthetized horses undergoing elective surgery. STUDY DESIGN: Prospective balanced incomplete block design. ANIMALS: A total of 18 client-owned horses. METHODS: Invasive blood pressure (IBP) was measured simultaneously in one of the following three combinations: 1) transverse facial and facial artery; 2) transverse facial and metatarsal artery; and 3) facial and metatarsal artery. The agreement in blood pressure measured for each combination was performed in six horses. At each sample time, systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures were measured concurrently in each artery, and the mean of three consecutive measurements was recorded. The position of horse, heart rate and use of dobutamine were also recorded. Bland-Altman analysis was used to assess agreement between sites. RESULTS: A total of 54 paired measurements were obtained, with 18 paired measurements from each combination. All paired measurements showed poor and haphazard (nonsystematic) agreement. The widest limit of agreement was 51 mmHg for SAP measured in the facial artery and metatarsal artery, with a bias of -11 mmHg. The smallest limit of agreement was 16 mmHg for MAP measured in the transverse facial and metatarsal artery, with a bias of 1 mmHg. CONCLUSIONS AND CLINICAL RELEVANCE: There was poor and haphazard agreement for SAP, MAP and DAP measured in each pair of peripheral arteries in this study. These results show that blood pressure measured in different peripheral arteries cannot be used interchangeably. This has implications for studies that use IBP as an outcome variable and studies determining agreement between noninvasive blood pressure and IBP measurements in horses under general anaesthesia.

Effects of dobutamine hydrochloride on cardiovascular function in horses anesthetized with isoflurane with or without acepromazine maleate premedication.

OBJECTIVE To determine the effects of acepromazine maleate premedication on cardiovascular function before and after infusion of dobutamine hydrochloride for 30 minutes in isoflurane-anesthetized horses. ANIMALS 6 healthy adult horses. PROCEDURES Each horse was anesthetized once following premedication with acepromazine (0.02 mg/kg, IV) administered 30 minutes prior to anesthetic induction (ACP+ treatment) and once without premedication (ACP- treatment). Anesthesia was induced with IV administration of xylazine hydrochloride (0.8 mg/kg), ketamine hydrochloride (2.2 mg/kg), and diazepam (0.08 mg/kg). Horses were positioned in right lateral recumbency, and anesthesia was maintained via inhalation of isoflurane delivered in oxygen. End-tidal isoflurane concentration was adjusted to achieve a target mean arterial blood pressure of 60 mm Hg (interquartile range [25th to 75th percentile], 57 to 63 mm Hg) for at least 15 minutes. Cardiac index, oxygen delivery index, and femoral arterial blood flow indices were determined 60 minutes after anesthetic induction (baseline). Dobutamine was then infused to achieve a target mean arterial blood pressure of 80 mm Hg (interquartile range, 76 to 80 mm Hg). Data collection was repeated 30 minutes after the start of dobutamine infusion for comparison with baseline values. RESULTS Complete data sets were available from 5 of the 6 horses. Dobutamine administration resulted in significant increases in oxygen delivery and femoral arterial blood flow indices but no significant change in cardiac index for each treatment. However, at baseline or 30 minutes after the start of dobutamine infusion, findings for the ACP+ and ACP- treatments did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized horses, dobutamine administration increased oxygen delivery and femoral arterial blood flow indices, but these changes were unaffected by premedication with acepromazine.

Effects of leukotriene C4 on the bioelectric properties and ion transport of equine tracheal epithelium.

OBJECTIVE: To determine effects of leukotriene (LT) C(4) on ion transport across equine tracheal epithelium. Sample-Tracheal epithelium from cadavers of 24 horses considered free of respiratory tract disease. PROCEDURES: Mucosae were mounted into Ussing chambers, and short-circuit current (I(sc)) was monitored over time. Effects of LTC(4) were examined for various conditions, including addition of amiloride (10µM) to the mucosal bath solution, addition of bumetanide (10µM) to the serosal bath solution, addition of barium (1mM) to the serosal bath solution, and substitution of gluconate for chloride and HEPES for bicarbonate in bath solutions. Electrolyte transport was assessed via (22)Na and (36)Cl isotope fluxes. RESULTS: Addition of LTC(4) (50nM) to the serosal bath solution caused an increase in I(sc) for basal conditions and a larger increase after pretreatment with amiloride. The increase was negated in part by the addition of bumetanide to the serosal bath solution and further reduced by substitution of HEPES for bicarbonate in bath solutions. Remaining current was reduced to values less than those before treatment with LTC(4) by the addition of barium to the serosal solution. There was a small increase in I(sc) after the addition of amiloride and substitution of gluconate for chloride. Radioisotope flux indicated that addition of LTC(4) to the serosal bath solution increased chloride secretion and reduced sodium absorption. CONCLUSIONS AND CLINICAL RELEVANCE: LTC(4) stimulated chloride secretion through a predominately bumetanide-sensitive pathway, with a smaller contribution from a bicarbonate-dependent pathway. Thus, LTC(4) appears to be a potential mediator of airway hypersecretion in horses.

An ex vivo biomechanical study comparing strength characteristics of a new technique with the three-loop pulley for equine tenorrhaphy.

OBJECTIVE: To test single cycle to failure tensile strength characteristics of 6 suture material-pattern combinations in equine superficial digital flexor (SDF) tenorrhaphy, specifically to compare a 10-strand modification of the Savage core suture technique with the 3-loop pulley technique. STUDY DESIGN: Ex vivo mechanical experiment comparing 3 different suture patterns with 2 different materials. SAMPLE POPULATION: Forelimb and hindlimb SDF tendons (n=48) harvested from adult Thoroughbred and Standardbred horses of mixed age and gender. METHODS: Six suture material-pattern combinations were evaluated: (1) 10-strand Savage, size 2 polydioxanone (PDS); (2) 10-strand Savage, size 2 polyglactin 910 (PG910); (3) 10-strand Savage, size 2 PDS with Lin-locking epitenon suture, size 2-0 PDS; (4) 10-strand Savage size 2 PG910 with Lin-locking epitenon suture, size 2-0 PDS; (5) 3-loop pulley, size 2 PDS; and (6) 3-loop pulley, size 2 PG910. Maximum load at failure (N), gap at failure (mm), and mode of failure (suture breakage or pull through) were evaluated for each of the 6 suture material-pattern combinations and underwent statistical analysis to determine significance of differences and interactions of the measured data. RESULTS: The 10-strand Savage technique failed at a mean load of 872 (804-939, 95% CI). The 10-strand Savage with Lin-locking failed at a significantly greater mean load of 998 (930-1065, 95% CI). The 3-loop pulley pattern failed with a mean load of 337 (270-405, 95% CI). There were significant interactions between the technique and suture material used. CONCLUSION: The 10-strand Savage technique for repair of transected cadaver SDF tendons has superior strength characteristics with or without the epitenon suture when compared to the 3-loop pulley. Suture material and pattern interactions were observed with PG 910 conferring higher strength for the 10-strand Savage whereas PDS did so for the 3-loop pulley.

Evaluation of the secretory response to endogenous and exogenous prostaglandins in mucosa from the proximal and distal portions of the colon of dogs.

OBJECTIVE: To compare secretory responses to prostaglandin (PG) E(2) in mucosa obtained from the proximal and distal portions of the colon of dogs. SAMPLE: Colonic mucosa from cadavers of 18 clinically normal adult dogs. PROCEDURES: Short-circuit current (I(SC)) and maximum change in I(SC) (ΔI(sc)) in response to administration of 1µM PGE(2) were measured across mucosa obtained from the proximal and distal portions of the colon. Responses were evaluated in mucosa (n = 6 dogs) incubated in Ussing chambers with or without 1 mM amiloride or without chloride in the Ringer's bathing solution. Responses were also evaluated in mucosa (n = 9 dogs) incubated with or without pretreatment with 1 µM indomethacin, with or without amiloride in the subsequent bathing solution. Histologic changes in mucosa from 3 dogs were assessed over time. RESULTS: I(SC) and ΔI(SC) were significantly reduced when chloride was removed from, but not when amiloride was added to, the bathing solution and were significantly reduced after pretreatment with indomethacin. The ΔI(SC) was significantly greater in mucosa from the distal portion of the colon than in the proximal portion of the colon. Histologic changes after incubation for 3 hours were minimal. CONCLUSIONS AND CLINICAL RELEVANCE: I(SC) and ΔI(SC) resulted from electrogenic chloride secretion. Chloride secretion was reduced when release of PGs was prevented by indomethacin and was induced by administration of PGE(2). Chloride secretion in response to PGE(2) was greater in mucosa from the distal portion of the colon than in mucosa from the proximal portion of the colon.

Factors associated with survival of neonatal foals with bacteremia and racing performance of surviving Thoroughbreds: 423 cases (1982-2007).

OBJECTIVE: To identify factors associated with short-term survival in bacteremic neonatal foals, evaluate the racing performance of Thoroughbred survivors, and evaluate changes in causative organisms and their antimicrobial susceptibility. DESIGN: Retrospective case series. ANIMALS: 423 bacteremic foals. PROCEDURES: Medical records of foals that were hospitalized in 1982 through 2007 were reviewed, and those with bacteremia were included in the study. Data retrieved included signalment, physical examination and clinicopathologic findings at admission, localized infections, concurrent illnesses, duration of hospitalization, and outcome (survival to discharge from the hospital vs nonsurvival). The number, identity, and antimicrobial susceptibility of organisms isolated from blood samples were also obtained. Racing records for surviving Thoroughbred foals and maternal siblings were examined. RESULTS: Of 423 bacteremic foals, 254 survived. Odds of survival were negatively associated with age at admission, septic arthritis, band neutrophil count, and serum creatinine concentration and positively associated with year of admission, diarrhea, rectal temperature, neutrophil count, and arterial blood pH. Overall, microbial culture of blood samples yielded 554 isolates; Escherichia coli was consistently isolated most frequently. Percentage of isolates susceptible to enrofloxacin, but no other antimicrobial, decreased over time. Surviving Thoroughbred foals did not differ from siblings with regard to percentage of starters, percentage of winners, or number of starts; however, surviving foals had significantly fewer wins and total earnings. CONCLUSIONS AND CLINICAL RELEVANCE: During the study period, microbial resistance to antimicrobials commonly used to treat bacteremic foals did not develop. Surviving bacteremic Thoroughbred foals were as likely to start races as their siblings but earned less money.

Effects of treatment with omeprazole or ranitidine on gastric squamous ulceration in racing Thoroughbreds.

OBJECTIVE: To compare the effects of oral administration of omeprazole and ranitidine on gastric squamous ulceration in Thoroughbreds in race training. DESIGN: Modified crossover study. ANIMALS: 60 Thoroughbreds in race training with gastric squamous mucosal ulceration. PROCEDURE: Horses were randomly allocated into 3 groups. Group 1 received no treatment for 28 days followed by administration of omeprazole (4 mg/kg [1.8 mg/lb], PO, once daily) for 28 days; group 2 received omeprazole (4 mg/kg, PO, once daily) for 28 days followed by no treatment for 28 days; and group 3 received ranitidine (6.6 mg/kg [3.0 mg/lb], PO, q 8 h) for 28 days followed by administration of omeprazole (4 mg/kg, PO, once daily) for 28 days. Ulceration was assessed endoscopically at days 0, 28, 42, and 56. Lesions were scored from 0 (no ulceration) to 3 (severe ulceration). RESULTS: After the initial 28 days of treatment, the decrease in ulcer severity was significantly greater after omeprazole treatment than after ranitidine treatment. Ulcer severity decreased significantly in group 3 horses after 14 days of treatment with omeprazole. Discontinuation of omeprazole resulted in worsening of ulcer scores; however, ulcer scores at completion of the study were less than at day 0. Horses that received omeprazole after 28 days of ranitidine treatment had a further reduction in ulcer severity. CONCLUSIONS AND CLINICAL RELEVANCE: Omeprazole was more effective than ranitidine in healing gastric squamous ulcers in Thoroughbreds in race training. Improvement was detected by 14 days and persisted in most of the group 2 horses for at least 28 days after omeprazole treatment was discontinued.

Maturity of the neonatal foal.

The immature foal frequently represents a significant management challenge to even the most experienced clinician. The clinical course typically involves complications to a range of body systems,including the musculoskeletal, respiratory, and gastrointestinal systems. Before the commencement of treatment, it is important to provide the owner with an estimation of short-term and long-term survival, expected costs, and possible complications. Formulation of an accurate prognosis can be a difficult task but is aided by knowledge not only of normal maturation but of the factors that affect this process.

Evaluation of risk factors associated with development of postoperative ileus in horses.

OBJECTIVE: To determine factors associated with development of postoperative ileus (POI) in horses undergoing surgery for colic. DESIGN: Prospective case-control study. ANIMALS: 251 horses undergoing colic surgery, of which 47 developed POI. PROCEDURE: Signalment, history, clinicopathologic data, pre- and postoperative treatments, lesions, complications, costs, and outcome were recorded for all horses during hospitalization. RESULTS: Variables associated with increased odds of POI included small intestinal lesion, high PCV, and increased duration of anesthesia. There was modest evidence that pelvic flexure enterotomy and intraoperative administration of lidocaine may have reduced the odds of developing POI. CONCLUSIONS AND CLINICAL RELEVANCE: Findings during the preoperative and intraoperative periods can be used to identify horses at increased risk of POI. Reducing surgical and anesthetic duration should decrease the incidence of POI.

Prevalence of anthelmintic resistant cyathostomes on horse farms.

OBJECTIVE: To determine prevalence of anthelmintic resistance in cyathostome nematodes of horses in the southern United States. DESIGN: Cross-sectional study. ANIMALS: 786 horses on 44 farms and stables in Georgia, South Carolina, Florida, Kentucky, and Louisiana. PROCEDURE: Fecal egg count (FEC) reduction tests were performed on 44 large farms and stables. Horses on each farm were treated with an oral paste formulation of fenbendazole, oxibendazole, pyrantel pamoate, or ivermectin at recommended label dosages. A mixed linear model was fitted to the percentage reduction in FEC, accounting for differences among farms, states, ages, treatments, and treatment by state interactions. RESULTS: By use of a conservative measure of resistance (< 80% reduction), the percentage of farms with anthelmintic-resistant cyathostomes was 97.7%, 0%, 53.5%, and 40.5% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Mean percentage reductions in FEC for all farms were 24.8%, 99.9%, 73.8%, and 78.6% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Pairwise contrasts between states for each treatment revealed that in almost all instances, there were no significant differences in results between states. CONCLUSIONS AND CLINICAL RELEVANCE: The prevalence of resistance found in this study was higher than that reported previously, suggesting that anthelmintic resistance in equine cyathostomes is becoming a major problem. Furthermore, data from these 5 southern states, which are geographically and physiographically distinct, were remarkably similar. This suggests that drug resistance in cyathostomes is highly prevalent throughout the entire southern United States and probably nationwide.

Diagnostic contribution of thoracic ultrasonography in 17 foals with Rhodococcus equi pneumonia.

The aim of this retrospective study was to determine the clinical usefulness of thoracic ultrasonography compared to thoracic radiography in evaluation of Rhodococcus equi pneumonia. Criteria for patient inclusion in this study were: (1) isolation of R. equi from transtracheal aspirate, (2) radiographic evaluation of the pulmonary parenchyma, and (3) sonographic evaluation of the pulmonary parenchyma. Seventeen foals met this criteria and their medical records were reviewed. Pyogranulomatous pneumonia was identified radiographically in 13 foals. Severe consolidative pneumonia with no detectable abscessation was identified radiographically in three others. Both consolidation and abscessation were identified radiographically in one. In this foal only consolidation was ultrasonographically identified. Ultrasonographically, pulmonary abscessation was identified in 12 foals and pulmonary consolidation with no detectable abscessation was identified in three others. Sonographic examination allowed detection of only pleural irregularities in one foal, which was subsequently found to have pyogranulomatous pneumonia radiographically. Results indicate that ultrasonography may be an accurate alternative imaging modality for detection of pulmonary pathology attributed to R. equi pneumonia in foals when thoracic radiography is not available.

West Nile virus encephalomyelitis in horses: 46 cases (2001).

OBJECTIVE: To determine signalment, clinical findings, results of diagnostic testing, outcome, and postmortem findings in horses with West Nile virus (WNV) encephalomyelitis. DESIGN: Retrospective study. ANIMALS: 46 horses with WNV encephalomyelitis. PROCEDURE: Clinical data were extracted from medical records of affected horses. RESULTS: On the basis of clinical signs and results of serologic testing, WNV encephalomyelitis was diagnosed in 46 of 56 horses with CNS signs. Significantly more males than females were affected. Increased rectal temperature, weakness or ataxia, and muscle fasciculations were the most common clinical signs. Paresis was more common than ataxia, although both could be asymmetrical and multifocal. Supportive treatment included anti-inflammatory medications, fluids, antimicrobials, and slinging of recumbent horses. Results of the IgM capture ELISA and the plaque reduction neutralization test provided a diagnosis in 43 horses, and only results of the plaque reduction neutralization test were positive in 3 horses. Mortality rate was 30%, and 71% of recumbent horses were euthanatized. One horse that had received 2 vaccinations for WNV developed the disease and was euthanatized. Follow-up communications with 19 owners revealed that most horses had residual deficits at 1 month after release from the hospital; abnormalities were resolved in all but 2 horses by 12 months after release. CONCLUSIONS AND CLINICAL RELEVANCE: Our findings were similar to those of previous WNV outbreaks in horses but provided additional clinical details from monitored hospitalized horses. Diagnostic testing is essential to diagnosis, treatment is supportive, and recovery rate of discharged ambulatory horses is < 100%.

Evaluation of a method to experimentally induce colic in horses and the effects of acupuncture applied at the Guan-yuan-shu (similar to BL-21) acupoint.

OBJECTIVE: To evaluate the reliability of a method for inducing colic via small intestinal distention in horses and to examine the analgesic potential of bilateral electroacupuncture (EAP) at the Guan-yuan-shu (similar to BL21) acupoint. ANIMALS: 5 healthy adult horses, each with a gastric cannula. PROCEDURE: A polyester balloon connected to an electronic barostat was introduced into the duodenum via the gastric cannula. At 2 specified intervals (before and after commencement of EAP), the balloon was inflated to a barostat-controlled pressure that induced signs of moderate colic. Each inflation was maintained for 10 minutes. Heart and respiratory rates were continuously recorded. Frequency of various clinical signs of colic was recorded by 2 trained observers during various combinations of balloon inflation and EAP. Each horse received each of 5 treatment protocols (EAP at 20 Hz, sham EAP at 20 Hz, EAP at 80: 120 Hz dense:disperse, sham EAP at 80: 120 Hz dense:disperse, no treatment). Sham EAP was at a point located 2 cm lateral to the Guan-yuan-shu acupoint. RESULTS: Duodenal distention consistently induced a significant increase in frequency of signs of colic. None of the EAP protocols caused a significant reduction in frequency of these clinical signs during distention. CONCLUSIONS AND CLINICAL RELEVANCE: The method described is reproducible and highly controllable method for inducing colic that involved duodenal distention that should be useful in evaluating the efficacy of various analgesic strategies. Bilateral EAP at the Guan-yuan-shu acupoint was ineffective in reducing signs of discomfort induced by this method.

Effect of hydrochloric acid, pepsin, or taurocholate on bioelectric properties of gastric squamous mucosa in horses.

OBJECTIVE: To determine the effect of pH with or without pepsin or taurocholic acid on the bioelectric properties of gastric squamous mucosa in horses. SAMPLE POPULATION: Gastric tissues obtained from 16 adult horses that did not have evidence of gastric disease. PROCEDURE: Bioelectric properties of squamous mucosa were determined, using modified Ussing chambers. Tissues then were exposed to mucosal pepsin (1 mg/ml) or taurocholic acid (2.5 mM) under neutral (pH 74) or acidic (pH 1.7) conditions. RESULTS: Exposure of mucosal sheets to an acidic pH resulted in an immediate and sustained decrease in transmembrane potential difference and calculated tissue resistance. Pepsin or taurocholic acid did not significantly affect bioelectric variables when added to a mucosal bath solution of pH 7.4. A synergistic effect between pepsin or taurocholic acid and mucosal acidification was not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Mucosal acidification with or without pepsin or taurocholic acid resulted in reduced tissue resistance. These data support the contention that squamous erosions or ulcers in horses are mediated, in part, by prolonged exposure of gastric squamous mucosa to luminal acid.