Comparison of Two Bandage Splint Constructs in an Ex Vivo Equine Metacarpal Fracture Model.

OBJECTIVES: The aim of this study was to compare the deflection distance, deflection angle and pre-loading sub-bandage pressure of a transverse, mid-metacarpal fracture in an equine cadaver limb when loaded in bending while stabilized with either a Robert Jones Bandage (RJB) or a single-stack bandage (SS), each containing two orthogonal splints. STUDY DESIGN: In an ex vivo experimental study, forelimb pairs from eight horses were collected, and one forelimb from each pair was assigned to either the SS or RJB groups. A transverse osteotomy was performed at the midpoint of the metacarpus. After bandaging, the limbs were loaded in bending. Pre-loading sub-bandage pressure, pre- and post-loading radiographs and post-loading deflection distance measurements were taken. Dorsopalmar radiographs were used to measure the loaded deflection angle. RESULTS: There was no significant difference between RJB and SS constructs in change in deflection angle (10.7 ± 3.0 degrees vs. 9.8 ± 2.6 degrees; p = 0.5) or deflection distance (13.1 ± 2.6 cm vs. 11.4 ± 3.1 cm; p = 0.2). Sub-bandage pressures were significantly greater for the SS than the RJB both dorsally and laterally. CONCLUSION: The SS splint construct resists bending forces similarly to the RJB splint construct in an ex vivo transverse, metacarpal fracture model. The SS splint construct may be a useful alternative to the RJB splint construct in field situations for metacarpal fracture stabilization.

Measurement of distal limb sub-bandage pressure over 96 hours in horses.

REASONS FOR PERFORMING STUDY: Currently, there is no objective information quantifying pressures exerted by distal limb bandages. OBJECTIVES: To quantify the pressure exerted by each compression layer, a polo wrap (DLP), a compression bandage (DLC), and to measure the effect of time on sub-bandage pressure. STUDY DESIGN: Longitudinal observational experiment. METHODS: A DLC construct included a cotton roll compressed with brown gauze and elastic layers and the DLP construct included a pillow pad compressed by a cloth wrap. Dorsal and lateral sensors were placed on the mid-metacarpus. In healthy horses, sub-bandage pressures were recorded during application (n = 8) and at scheduled time points over the 24 (n = 9) and 96 h periods (n = 8). A generalised linear model was used to evaluate associations between pressure and sensor location, bandage type and time (P<0.05). RESULTS: For the DLC, dorsal and lateral sensor pressures were 187 mmHg (95% CI 185-189 mmHg) and 142 mmHg (95% CI 133-151 mmHg). Combined sensor pressure after application of the brown gauze was 80 mmHg (95% CI 75-85 mmHg) and rose to 165 mmHg (95% CI 160-170 mmHg) after the elastic layer. Combined pressure at the end of the 96 h period was 135 mmHg (95% CI 123-147 mmHg). For the DLP bandage, location but not time was significant. Combined pressures ranged between 75 mmHg (95% CI 53-97 mmHg) and 85 mmHg (95% CI 63-107 mmHg). CONCLUSIONS: Pressure distribution was not uniform. The DLP pressures were maintained for a 24 h period. The DLC maintained high pressures for 96 h, but a significant decrease in pressure occurred between 6 and 12 h. Providing there are no other reasons to change a bandage, a 4 day interval between bandages may be appropriate if maintaining distal limb compression is the principal indication.

Comparison of sub-bandage pressures achieved by 3 abdominal bandaging techniques in horses.

REASONS FOR PERFORMING STUDY: Clinicians frequently place post operative abdominal bandages on horses undergoing laparotomies. Presently, no information exists on the amount of incisional support provided by these bandages. Determination of sub-bandage pressure provides a means of comparing the ability of different bandages to support incisions. OBJECTIVES: Determination of sub-bandage pressure over a 24 h period using 3 bandaging techniques. STUDY DESIGN: A randomised, crossover design using 9 healthy horses. METHODS: Horses were randomly assigned to a treatment regimen consisting of placement of 3 abdominal bandage types, namely an elastic bandage (ELA), the CM(TM) Hernia Heal Belt (CM) or a nylon binder (NYL). The sub-bandage pressures for each bandage were measured with the Picopress® compression-measuring system at 0, 2, 4, 6, 8, 12, 16, 20 and 24 h after application. RESULTS: No time and treatment interactions were observed, and bandage pressures were maintained within each treatment group over the 24 h period. Mean sub-bandage pressures were different between all treatment groups (P < 0.001) at 39 (95% confidence interval, 36.7-40.5 mmHg), 25 (95% confidence interval, 23.9-27.7 mmHg) and 5 mmHg (95% confidence interval, 4.1-7.8 mmHg) for CM, ELA and NYL bandages, respectively. Horses were more likely to lie down with the CM (P = 0.02) and ELA treatments (P = 0.0002) when compared with the NYL treatment. The ELA bandages were more likely to displace caudally compared with both CM and NYL bandages. CONCLUSIONS: The CM bandage was superior to both ELA and NYL bandages with regard to measured sub-bandage pressure over the 24 h period. The clinical significance of the differences in sub-bandage pressure between treatments cannot be determined by this study.

Effect of orally administered sodium bicarbonate on caecal pH.

REASONS FOR PERFORMING STUDY: Caecal acidosis is a central event in the metabolic cascade that occurs following grain overload. Buffering the caecal acidosis by enterally administered sodium bicarbonate (NaHCO3 ) may be beneficial to affected horses. OBJECTIVES: To determine the effect and duration of enterally administered NaHCO3 on caecal pH in healthy horses. STUDY DESIGN: Experimental study using horses with caecal cannulas. METHODS: Nine horses had been previously fitted with a caecal cannula. Six horses received 1.0 g/kg bwt NaHCO3 and 3 control horses were given 3 l of water via nasogastric tube. Clinical parameters, water consumption, venous blood gases, caecal pH, faecal pH and faecal water content were measured at 6 h intervals over a 36 h study period. RESULTS: Horses that received enterally administered NaHCO3 had significantly increased caecal pH that lasted the duration of the study. Treated horses increased their water intake, and developed metabolic alkalaemia, significantly increased plasma sodium concentrations and significantly decreased plasma potassium concentrations. CONCLUSIONS: Enterally administered NaHCO3 may be beneficial in buffering caecal acidosis.

A comparative study of proximal hindlimb flexion in horses: 5 versus 60 seconds.

REASONS FOR PERFORMING STUDY: The flexion test is routinely used in lameness and prepurchase examinations. There is no accepted standard for duration of flexion or evidence that interpretation of results would differ with different durations of flexion. HYPOTHESIS: There will be no difference in interpretation of proximal hindlimb flexion for 5 or 60 s. METHODS: Video recordings of lameness examinations of 34 client-owned horses were performed that included: baseline lameness, proximal hindlimb flexion for 60 s, and flexion of the same limb for 5 s. Videos were edited to blind reviewers to the hypothesis being tested. The baseline lameness video from each horse was paired with each flexion to make 2 pairs of videos for each case. Twenty video pairs were repeated to assess intraobserver repeatability. Fifteen experienced equine clinicians were asked to review the baseline lameness video followed by the flexion test and grade the response to flexion as either positive or negative. Potential associations between the duration of flexion and the likelihood of a positive flexion test were evaluated using generalised linear mixed models. A kappa value was calculated to assess the degree of intraobserver agreement on the repeated videos. Significance level was set at P<0.05. RESULTS: Proximal hindlimb flexion of 60 s was more likely to be called positive than flexion of 5 s (P<0.0001), with the likelihood of the same interpretation 74% of the time. The first flexion performed was more likely to be called positive than subsequent flexions (P = 0.029). Intra-assessor agreement averaged 75% with κ= 0.49. CONCLUSIONS: Proximal hindlimb flexion of a limb for 5 s does not yield the same result as flexing a limb for 60 s. POTENTIAL RELEVANCE: Shorter durations of flexion may be useful for clinicians that have good agreement with flexions of 5 and 60 s.

Technical note: a 2-stage cecal cannulation technique in standing horses.

Cecal cannulation is necessary for sampling of intestinal contents for a variety of nutritional or digestive physiology studies. This report describes a 2-stage technique for permanent cecal cannulation in standing horses. For the first procedure, a right flank laparotomy is performed and a small pouch of the cecal base exteriorized and sutured to the body wall. The second procedure is performed approximately 1 wk later. During the second procedure, the exposed cecal pouch is removed and the cannula inserted. Ten horses were cannulated using this technique. After the first procedure, 1 horse developed a cecal impaction unresponsive to medical therapy and ruptured its cecum, whereas 2 other horses developed mild transient colic that responded to medical management. Insertion of the cecal cannula after creation of the stoma in the second procedure resulted in transient colic in 4 of 9 horses, but they responded to analgesic therapy in less than 24 h in all instances. The time to complete healing of the cannula site was approximately 30 d. The technique described in this report decreases the risk of peritonitis due to intestinal leakage and is technically easier to perform than previously described techniques.

The effect of uterine torsion on mare and foal survival: a retrospective study, 1985--2005.

REASONS FOR PERFORMING STUDY: Anecdotal speculation suggests that prognosis for survival of mares and foals following correction of uterine torsion has improved over the past 30 years. OBJECTIVES: To determine statistically the outcome of uterine torsion according to duration of clinical signs, stage of gestation, parity, physical examination findings, method of correction, prognosis for survival and reproductive health of the mare, and prospects for the foal within the neonatal period. METHODS: This retrospective study combined cases from 4 equine referral hospitals. RESULTS: The stage of gestation at which uterine torsion occurred was a risk factor for survival of mare and foal. Overall mare survival was 53/63 (84%); when uterine torsion occurred at < 320 days gestation, 36/37 (97%) of mares survived compared to 17/26 (65%) survival rate when uterine torsion occurred at > or = 320 days gestation. Overall foal survival was 54% (29/54). When uterine torsion occurred at < 320 days gestation, 21/29 (72%) foals survived compared to 8/25 (32%) when uterine torsion occurred at > or = 320 days gestation. Thirty mares were discharged from the hospital carrying a viable fetus following uterine torsion correction and 25/30 (83%) of these mares delivered live foals that survived beyond the neonatal period. CONCLUSIONS: Prognosis for survival for mares and foals following uterine torsion is good and improves if torsion occurs < 320 days compared to > or = 320 days gestation. CLINICAL RELEVANCE: Gestational timing of uterine torsion should be considered when advising clients about the prognosis for survival of the mare and foal. The prognosis for a mare delivering a live foal is good if the mare is discharged from the hospital following uterine torsion correction with a viable fetus.

Ureteral ligation prevents the haemodynamic effect of frusemide in pentobarbitol anaesthetised horses.

Frusemide reduces pulmonary vascular pressures in resting horses and attenuates exercise-induced increases in these pressures in exercising horses. The mechanism underlying these effects of frusemide is unclear. We tested the hypothesis that the haemodynamic effects of frusemide are dependent on diuresis by examining the effect of frusemide in anaesthetised horses in which diuresis was prevented by ligation of ureters. Twenty four horses were assigned randomly to one of 4 treatments: 1) frusemide (1 mg/kg bwt i.v.) and intact ureters; 2) frusemide and ligated ureters; 3) saline placebo and ligated ureters; and 4) frusemide and phenylbutazone (4.4 mg/kg bwt i.v. 12 h and 15 min before frusemide) and ligated ureters. Frusemide administration to anaesthetised horses with intact ureters increased plasma total protein concentration and reduced mean right atrial, pulmonary artery and aortic pressures. There was no significant effect of frusemide administration on haemodynamic variables or plasma total protein concentration in horses with ligated ureters. The combination of frusemide and phenylbutazone increased mean right atrial, pulmonary artery and aortic pressures in horses with ligated ureters. This study demonstrates that, in anaesthetised horses, the haemodynamic effect of frusemide is dependent upon diuresis. We interpret these results as providing further evidence that the haemodynamic effect of frusemide in horses is attributable to a reduction in plasma and blood volume.

Partial orbital rim resection, mesh skin expansion, and second intention healing combined with enucleation or exenteration for extensive periocular tumors in horses.

Ocular and periorbital sarcoids and squamous cell carcinoma are common in equine practice. Extensive involvement of periorbital tissues often necessitates removal of the globe if the function of the eyelids can not be maintained with tumor removal alone. This report describes a modification of the standard enucleation or exenteration technique for cases in which there is insufficient skin to achieve primary closure following complete surgical excision. The caudal portion of the dorsal orbital rim is protuberant; partial excision with an osteotome facilitates skin closure by decreasing the size of the wound. Mesh expansion of skin via multiple rows or parallel stab incisions can also be used as an adjunct to facilitate closure. Four horses underwent enucleation or exenteration using the orbital rim resection and mesh skin expansion techniques for extensive periocular tumors that were unresponsive to prior treatments. Follow-up intervals ranged from 6 to 42 months and no horses had tumor regrowth.

Esophagomyotomy and esophagopexy to create a diverticulum for treatment of chronic esophageal stricture in 2 horses.

We report use of esophagomyotomy and esophagopexy to create a diverticulum for relief of chronic type I esophageal stricture in 2 horses. After esophagomyotomy, the mucosa was dissected free from the muscularis for approximately 180 degrees around the myotomy. Then, the tunica muscularis of esophagus was sutured to the sternocephalicus muscle ventrally and the periesophageal tissues dorsally to create a diverticulum without disruption of the esophageal mucosa. Clinical signs of esophageal stricture were relieved, and the horses were fed normal diets without further esophageal obstruction.

Effect of a tongue-tie on upper airway mechanics during exercise following sternothyrohyoid myectomy in clinically normal horses.

OBJECTIVE: To determine the effect of a tongue-tie on upper airway mechanics in clinically normal horses exercising on a treadmill following sternothyrohyoid myectomy. ANIMALS: 6 Standardbreds. PROCEDURE: Upper airway mechanics were measured with horses exercising on a treadmill at 5, 8, and 10 m/s 4 weeks after a sternothyrohyoid myectomy was performed. Pharyngeal and tracheal inspiratory and expiratory pressures were measured by use of transnasal pharyngeal and tracheal catheters connected to differential pressure transducers. Horses were fitted with a facemask and airflow was measured by use of a pneumotachograph. Horses underwent a standardized exercise protocol on a treadmill at 5, 8, and 10 m/s with and without a tongue-tie in a randomized cross-over design. Inspiratory and expiratory airflow, tracheal pressure, and pharyngeal pressure were measured, and inspiratory and expiratory resistances were calculated. RESULTS: We were unable to detect an effect of a tongue-tie on any of the respiratory variables measured. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that a tongue-tie does not alter upper airway mechanics following sternothyrohyoid myectomy in clinically normal horses during exercise.

Transarterial coil embolization of the internal and external carotid and maxillary arteries for prevention of hemorrhage from guttural pouch mycosis in horses.

OBJECTIVES: To develop a transarterial coil embolization technique for occlusion of the internal carotid artery (ICA), external carotid artery (ECA), and maxillary arteries (MA) in normal horses and to evaluate this technique for prevention of hemorrhage in horses affected with guttural pouch mycosis. ANIMALS: Ten adult, normal horses and 4 horses with guttural pouch mycosis. METHODS: All horses had transarterial coil embolization of the rostral and caudal ICA, caudal MA, and rostral ECA. In 1 affected horse, an aberrant actively bleeding branch of the ECA was also occluded. Normal horses had a premortem angiogram, and were killed either at 1 or 2 weeks or 1, 2, or 3 months after the procedure. Specimens from the ICA, ECA and MA were evaluated by light microscopy. RESULTS: No surgical complications were observed, except 1 horse that developed laryngeal hemiplegia and 1 pilot horse that had embolization of the cerebral arterial circle. In normal horses, premortem angiography confirmed complete occlusion of all vessels, and coils were positioned as intended. All normal horses had partially maturing to mature, continuous thrombi occluding at the coils. In affected horses, no further episodes of epistaxis were observed. By day 60, all mycotic plaques had resolved without further treatment. Ophthalmic complications were not observed. CONCLUSION: Transarterial embolization provided a safe, rapid, and effective method for ICA, ECA, and MA occlusion in normal and affected horses. In affected horses, the technique was possible despite active bleeding, allowing adequate identification and occlusion of all sources of hemorrhage.

Nephrosplenic entrapment in the horse: a retrospective study of 174 cases.

The clinical findings and outcome of 161 horses diagnosed with 174 episodes of nephrosplenic entrapment (NSE) were reviewed retrospectively. The median age at presentation was 5 years (9 months to 24 years), and duration of colic was 2-92 h. Nasogastric reflux was present in 49 of 113 horses (43.4%) and was significant (> or = 21) in 32 (28.3%) horses. The recurrence rate was 13/161 (8.1%). Thirteen horses (13/174, 7.5%) had other lesions including small intestinal obstruction (4), 360 degrees large colon torsion (5), gastric rupture (2), thromboembolic colic (1) and small colon infarction (1). Of 115 cases, in 107 horses treated by surgery alone, 2 horses required a large colon resection, and 8 (8/107, 7.5%) horses died or were subjected to euthanasia. Twenty-six of 35 horses (74%) were successfully corrected by rolling under general anesthesia and, of the 9 horses taken to surgery after rolling, 4 had other lesions and 2 were corrected at surgery. Phenylephrine was used in 20 of 35 horses that were rolled and 2 horses required surgery after rolling with phenylephrine. Five horses were jogged after phenylephrine administration and all were successfully corrected. Eleven horses presented with the left colon located between the spleen and the body wall were treated successfully by fasting and/or i.v. fluids. One horse had a gastric rupture after rolling. The overall success rate was 92.5%. In conclusion, NSE is a condition associated with a good prognosis for medical or surgical correction. A small number of horses may have additional gastrointestinal lesions, which may affect outcome.

Fractures of the rostral portion of the mandible and maxilla in horses: 89 cases (1979-1997).

OBJECTIVE: To compare fracture locations, repair methods, complications, and outcomes of horses with fractures of the rostral portions of the mandible and maxilla. DESIGN: Retrospective study. ANIMALS: 89 horses with fractures of the rostral portions of the mandible and maxilla. PROCEDURE: Medical records and radiographs were reviewed. Fractures were categorized by fracture location and stability. Postoperative complications and long-term outcome were determined by clinical examination and telephone interviews with horse owners. RESULTS: 4 fracture types were recognized. Fractures involving just the alveolar plate (33%) and those involving the alveolar plate and the body of the bone (32%) were most common and were often repaired by interdental wiring. Unilateral fractures of the mandible (11%) were managed without surgery if stable. Unstable fractures were repaired with wires, a U-shaped bar (U-bar), or a bone plate. Bilateral fractures (24%) were often repaired with orthopedic wires in foals or with a U-bar, acrylic splint, wires, or bone plate in adult horses. In 2 horses, bilateral fractures were managed conservatively. Short-term complications developed in 24 of 89 (27%) horses. Soft tissue infections and wire loosening or failure were the most common short-term and long-term complications. Wire replacement was not required in any horses after release from hospital. Persistent draining tracts were most often associated with bone sequestration. Long-term functional and cosmetic outcomes were favorable for all fracture types and repair methods. CLINICAL IMPLICATIONS: Although complications in horses with fractures of the mandible and maxilla are common, long-term prognoses for functional and cosmetic outcome are favorable.

Effect of combined staphylectomy and laryngotomy on upper airway mechanics in clinically normal horses.

OBJECTIVE: To investigate the effect of combined staphylectomy and laryngotomy on upper airway mechanics in clinically normal horses running on a treadmill. ANIMALS: 6 Standardbreds. PROCEDURE: Upper airway mechanics were measured with horses trotting or pacing on a treadmill at 5, 8, and 10 m/s before and 6 weeks after combined staphylectomy and laryngotomy. Pharyngeal and tracheal inspiratory and expiratory pressure were measured by use of transnasal tracheal and pharyngeal side hole catheters connected to differential pressure transducers. A pneumotachograph mounted on the rostral end of an airtight face mask was used to measure airflow. RESULTS: Upper airway and translaryngeal inspiratory impedances were higher, respiratory rate was decreased, and inspiratory time was longer (P < 0.05) at all speeds after staphylectomy and laryngotomy. CONCLUSION: Combined staphylectomy and laryngotomy significantly affects upper airway mechanics in clinically normal horses. CLINICAL RELEVANCE: Because combined staphylectomy and laryngotomy exerts a potentially adverse effect on upper airway mechanics in clinically normal horses, the procedure should only be performed when it is clearly indicated.

Open peritoneal drainage in horses with experimentally induced peritonitis.

Peritonitis was induced in 12 horses by median celiotomy and 1 hour of small intestinal ischemia. Six horses had primary closure of the incision, whereas six horses had a plastic mesh sutured to the ventral abdominal wall leaving the abdomen open for ventral drainage. The mesh was removed after 5 days and the abdominal wall was closed by apposition of the linea alba and subcutaneous tissues and approximation ef the skin edges. Peritoneal fluid was collected and analyzed for nucleated cell count and total protein concentration on days 0 and 5. Serum biochemical profiles, serum electrolyte concentrations, and complete blood counts were performed on days 0, 1, 2, 5, 6, 10, and 14. Body weight, rectal temperature, and physical examination findings were recorded daily for 30 days, then horses were euthanatized and the abdominal cavity was examined for the presence of adhesions. Histological examination was performed to assess the inflammatory response of the healing body wall; inflammation scores were significantly lower in horses that had primary closure of the incision. The mesh was well tolerated by all horses and allowed egress of peritoneal fluid for 5 days. Adhesions were present in four control horses and in two horses that had open peritoneal drainage. All horses that had open drainage developed incisional infections after mesh removal. Abdominal wall herniation did not occur in any of the horses. The mild peritonitis induced in this study was insufficient to establish the efficacy of open peritoneal drainage for an established peritonitis in horses; however, the results of this study indicate that open peritoneal drainage is feasible in horses.

Effect of a mask and pneumotachograph on tracheal and nasopharyngeal pressures, respiratory frequency, and ventilation in horses.

OBJECTIVE: To investigate the effect of a mask and pneumotachograph on ventilation, respiratory frequency, and tracheal and nasopharyngeal pressures in horses running on a treadmill. DESIGN: Six horses ran at 50, 75, and 100% of the speed that resulted in maximum oxygen consumption, with and without a mask and pneumotachograph. Tracheal and pharyngeal inspiratory and expiratory pressures, respiratory frequency, and arterial blood gases were measured. ANIMALS: Six Standardbred horses. PROCEDURE: Oxygen consumption was measured during an incremental exercise test to determine the speed that resulted in maximal oxygen consumption for each horse. Tracheal and pharyngeal pressures were measured, using transnasal tracheal and pharyngeal side-hole catheters connected to differential pressure transducers. Carotid arterial blood samples were collected and PAO2, PaCO2, and pH were measured with a blood gas analyzer. RESULTS: Peak tracheal and pharyngeal inspiratory pressures were significantly more negative, peak tracheal and pharyngeal expiratory pressures were significantly more positive, and respiratory frequency was significantly lower (all P < 0.05) at all speeds when horses wore a mask. The PaCO2 was higher and arterial pH and PaO2 were lower (P < 0.05) when horses wore a mask. CONCLUSIONS: The mask and pneumotachograph altered upper airway pressures, respiratory frequency, and ventilation in horses running on a treadmill.

Systemic and colonic venous plasma eicosanoid and endotoxin concentrations, and colonic venous serum tumor necrosis factor and interleukin-6 activities in horses during low-flow ischemia and reperfusion of the large colon.

Twenty-four horses were randomly allocated to 3 groups. Horses were anesthetized, subjected to a ventral midline celiotomy, and the large colon was exteriorized and instrumented. Group-1 horses served as sham-operated controls. Group-2 horses were subjected to 6 hours of low-flow colonic arterial ischemia, and group-3 horses were subjected to 3 hours of ischemia and 3 hours of reperfusion. Baseline (BL) samples were collected, then low-flow ischemia was induced by reducing ventral colonic arterial blood flow to 20% of BL. All horses were monitored for 6 hours after BL data were collected. Blood samples were collected from the colonic vein and main pulmonary artery (systemic venous [SV]) for measurement of plasma endotoxin, 6-keto prostaglandin F1 alpha (6-kPG), thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) concentrations. Tumor necrosis factor and interleukin-6 activities were measured in colonic venous (CV) serum samples. Data were analyzed, using two-way ANOVA, and post-hoc comparisons were made, using Dunnett's and Tukey's tests. Statistical significance was set at P < 0.05. Endotoxin was not detected in CV or SV plasma at any time. There was no detectable tumor necrosis factor or interleukin-6 activity in CV samples at any time. There were no differences at BL among groups for CV or SV 6-kPG, PGE2, or TXB2 concentrations, nor were there any changes across time in group-1 horses.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dimethyl sulfoxide, allopurinol, 21-aminosteroid U-74389G, and manganese chloride on low-flow ischemia and reperfusion of the large colon in horses.

Thirty horses were randomly assigned to 1 of 5 groups. All horses were anesthetized and subjected to ventral midline celiotomy, then the large colon was exteriorized and instrumented. Colonic arterial blood flow was reduced to 20% of baseline (BL) and was maintained for 3 hours. Colonic blood flow was then restored, and the colon was reperfused for an additional 3 hours. One of 5 drug solutions was administered via the jugular vein 30 minutes prior to colonic reperfusion: group 1, 0.9% NaCl; group 2, dimethyl sulfoxide: 1 g/kg of body weight; group 3, allopurinol: 25 mg/kg; group 4, 21-aminosteroid U-74389G: 10 mg/kg; and group 5, manganese chloride (MnCl2): 10 mg/kg. Hemodynamic variables were monitored and recorded at 30-minutes intervals. Systemic arterial, systemic venous (SV), and colonic venous (CV) blood samples were collected for measurement of blood gas tensions, oximetry, lactate concentration, PCV, and plasma total protein concentration. The eicosanoids, 6-keto prostaglandin F1 alpha, prostaglandin E2, and thromboxane B2, were measured in CV blood, and endotoxin was measured in CV and SV blood. Full-thickness biopsy specimens were harvested from the left ventral colon for histologic evaluation and determination of wet weight-to-dry weight ratios (WW:DW). Data were analyzed, using two-way ANOVA for repeated measures, and statistical significance was set at P < 0.05. Heart rate, mean arterial pressure, and cardiac output increased with MnCl2 infusion; heart rate and cardiac output remained increased throughout the study, but mean arterial pressure returned to BL values within 30 minutes after completion of MnCl2 infusion. Other drug-induced changes were not significant. There were significant increases in mean pulmonary artery and mean right atrial pressures at 2 and 2.5 hours in horses of all groups, but other changes across time or differences among groups were not observed. Mean pulmonary artery pressure remained increased through 6 hours in all groups, but mean right atrial pressure had returned to BL values at 3 hours. Mean colonic arterial pressure was significantly decreased at 30 minutes of ischemia and remained decreased through 6 hours; however, by 3.25 hours it was significantly higher than the value at 3 hours of ischemia. Colonic arterial resistance decreased during ischemia and remained decreased throughout reperfusion in all groups; there were no differences among groups for colonic arterial resistance.(ABSTRACT TRUNCATED AT 400 WORDS)