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SUMMARY

The ultrastructural injury that develops sequentially in the ascending colon during experimentally induced ischemia was examined in 6 halothane-anesthetized horses. Colonic ischemia was created by 2 types of vascular occlusion 24 cm proximal and distal to the pelvic flexure.

In all horses, transmural vascular compression was created. The colonic venous circulation was obstructed in 3 horses, whereas in the other 3 horses, arterial and venous circulation was obstructed. Two additional horses were anesthetized as controls for determination of any morphologic alterations associated with the experimental protocol.

Full-thickness colonic biopsy specimens were obtained from the antimesenteric border of the pelvic flexure at 0, 0.25, 0.5, 1, 1.5, 1.75, 2, 2.25, 2.5, 3, 3.5, 4, 4.5, and 5 hours during occlusion, and were studied by light and transmission electron microscopy. Morphologic alterations did not develop in the colon of control horses. Mucosal congestion was observed by light microscopy in the colon of horses with experimentally induced ischemia, but congestion developed early in those with obstructed colonic venous circulation, compared with those having arterial and venous obstruction. Inter- and intracellular vacuolation and loss of staining initially resulted in groups of 3 to 5 superficial luminal epithelial cells. Alterations in the glandular epithelium lagged behind those in the superficial epithelium, but were observed in both groups by 2 hours of obstruction. These changes progressed to 100% sloughing of all epithelium by 4.5 to 5 hours.

The initial cellular alterations, which were observed by transmission electron microscopy, developed at 0.25 hour in horses with colonic venous obstruction and was characterized by inter- and intracellular edema. By 1 hour in horses with colonic venous obstruction, vacuoles were observed within the basal lamina and some vacuoles contained intracellular organelles. These cellular changes were followed by increases in the intercellular gap and breaks between degenerating and more normal-appearing superficial epithelium, which led to sloughing of the epithelium. Endocrine cells by 1 hour also had evidence of ischemic injury.

Injury to the vascular circulation, including congestion and platelet accumulations within the mucosal capillaries was apparent by 0.25 hour in horses with venous obstruction. By 1 to 1.5 hours in both groups of horses with experimentally induced ischemia, loss of vascular integrity and leukocyte migration frequently were observed. Platelets, proteinaceous material, and cellular debris continued to accumulate, and by 2.25 hour capillary plugging frequently was observed. These results indicated that the initial ultrastructural injury in the ischemic colon consisted of degenerative changes in epithelial cells, which led to sloughing of degenerating and necrotic cells. Although injury between the 2 types of vascular obstruction differed, end results were similar. Ischemic vascular injury may lead to further vascular thrombosis and necrosis, resulting in an irreversible injury or contribute to difficulty in medically managing horses with natural ischemia during the perioperative period.

Free access
in American Journal of Veterinary Research

SUMMARY

Conventional fluid resuscitation is unsatisfactory in a small percentage of equine emergency surgical cases because the large volumes of fluids required cannot be given rapidly enough to adequately stabilize the horse. In anesthetized horses, the volume expansion and cardiopulmonary effects of a small volume of highly concentrated hypertonic saline-dextran solution were evaluated as an alternative initial fluid choice. Seven halothane-anesthetized, laterally recumbent, spontaneously ventilating, normovolemic horses were treated with a 25% NaCl-24% dextran 70 solution (hsd) at a dosage of 1.0 ml/kg of body weight, iv, infused over 10 minutes, and the effects were measured for 120 minutes after infusion. Plasma volume expansion was rapid and significant (from 36.6 ± 4.6 ml/kg to 44.9 ± 4.8 ml/kg), and remained significantly expanded for the duration of the experiment. Packed cell volume, total blood hemoglobin, and plasma protein concentrations significantly decreased, confirming rapid and sustained volume expansion with hemodilution. Cardiac index and stroke index immediately increased and remained high for the entire study (from 69.6 ± 15.3 ml/min/kg to 106.6 ± 28.4 ml/min/kg, and from 1.88 ± 0.49 ml/beat/kg to 2.50 ± 0.72 ml/beat/kg, respectively). Systemic vascular resistance significantly decreased immediately after hsd infusion and remained decreased for the duration of the study (from 1.41 ± 0.45 mm of Hg/ml/min/kg to 0.88 ± 0.22 mm of Hg/ml/min/kg). Arterial and venous blood oxygen content decreased significantly because of hemodilution, but actual oxygen transport transiently increased at the 10-minute measurement before returning toward baseline. Plasma osmolality and sodium significantly increased and remained high for the entire 120 minutes (from 293 ± 2 osm/L to 326 ± 9 mosm/L, and from 142.8 ± 3.3 mM/L to 159.0 ± 6.2 mM/L, respectively). Urine output increased in 5 of 7 horses within minutes of hsd infusion, but the mean increase was not statistically significant.

Three horses developed transiently severe, clinically apparent intravascular hemolysis and hemoglobinuria. One horse developed multiple single premature ventricular contractions during the infusion with no persistent ecg changes after infusion. The potential benefit of using hsd as a rapid volume expander in anesthetized horses was documented because infusion of 1 ml of hsd/kg rapidly increased plasma volume by approximately 8 ml/kg. Substantial side effects developed in these normovolemic horses, however, and this solution requires further investigation before it can be recommended in hemodynamically unstable horses.

Free access
in American Journal of Veterinary Research

Summary

Intramural vascular patterns of the jejunum and colon were evaluated during ischemic strangulation obstruction (iso, 70 minutes) and subsequent reperfusion (60 minutes) in 7 adult anesthetized horses. Microvasculature of experimental and control segments was described by comparison of results from microangiography, light microscopy, and scanning electron microscopy of vascular replicas. Experimental and control segments with isolated vascular arcades were removed either immediately after the experimental period or after 60 minutes of reperfusion. Blood was flushed from the vascular system by use of isotonic NaCl, and the segments were divided. Half of each segment was perfused with a modified radiopaque medium for microangiographic evaluation, and half was perfused with dilute methylmethacrylate to create a vascular replica to be studied by scanning electron microscopy. Microangiographic section also were evaluated for histologic changes.

Microvasculature of jejunal control segments and all colon segments was similar to described normal microvasculature of the equine jejunum and ascending colon. In jejunal iso segments, intramural perfusion was redistributed away from the mucosa. In the villi, the central arteriole was short and convoluted and the subepithelial capillaries were not filled. The submucosal vessels and crypt capillaries were congested, compared with those of controls, and the serosal vessels were not filled in the ischemic segments. Histologic grade II-III mucosal lesion was seen in jejunal iso segments. Reperfused jejunal segments had a transmural hyperemic response, and previously unfilled capillaries were observed in all intestinal layers. After reperfusion, the mucosal lesion progressed to grade III-IV and a cellular infiltrate and edema formation were observed in the serosa.

The intramural vasculature of the ischemic and reperfused colon remain unchanged. Minimal histologic damage was observed in the colon after 70 minutes of iso or after 60 minutes of reperfusion.

Free access
in American Journal of Veterinary Research

Summary

Effects of intraluminal distention (25 cm of H2O, 120 minutes) and subsequent decompression (60 minutes) on intramural vascular patterns of the small intestine was evaluated in 7 anesthetized horses. Intraluminal distention (25 cm of H2O, 120 mintutes) was created in 2 jejunal segments in each horse. Experimental and control segments were removed either immediately after the experimental period or after 60 minutes of decompression. The vascular system of experimental and control jejunal segments was lavaged with NaCl, then was injected with a blue-colored radiopaque medium for microangiography or with a diluted methyl methacrylate for scanning electron microscopy of microcorrosion vascular casts. After angiographic evaluation, tissue sections were prepared for light microscopic evaluation to assess vascular filling and tissue morphology. The distended segments had short villi, which were separated by expanded crypts, and had mesothelial cell loss, neutrophil infiltration, and edema in the seromuscular layer. The number of perfused vessels was significantly (P < 0.05) decreased in the seromuscular layer and, to a lesser extent, in the mucosal layer of the distended segments, compared with controls. After decompression, the morphologic lesions progressed in mucosal and serosal layers and the number of observed vessels increased in all intramural layers; however, vascular density did not return to the predistention state. These results identify altered intramural vascular patterns in the equine jejunum during luminal distention and subsequent decompression.

Free access
in American Journal of Veterinary Research

Objective

To determine whether peritoneal fluid pH, glucose concentration, and lactate dehydrogenase activity can be used to differentiate horses with septic peritonitis from those with nonseptic peritonitis.

Design

Prospective study.

Animals

46 horses, including 10 healthy horses, 15 horses with septic peritonitis, and 21 horses with nonseptic peritonitis.

Procedure

Peritoneal fluid and blood samples were analyzed for pH, glucose concentration, and lactate dehydrogenase activity. Complete blood cell counts were performed, and peritoneal fluid samples were submitted for bacterial culture.

Results

Horses with septic peritonitis had significantly lower peritoneal fluid pH and glucose concentrations than horses with nonseptic peritonitis and healthy horses. Compared with other tests, serum-to-peritoneal fluid glucose concentration differences > 50 mg/dl had the highest diagnostic use for detection of septic peritonitis. Peritoneal fluid pH < 7.3, glucose concentration < 30 mg/dl, and fibrinogen concentration > 200 mg/dl were also highly indicative of septic peritonitis.

Clinical Implications

Peritoneal fluid pH and glucose concentration can be used to assist in the identification of horses with septic peritonitis. These measurements can provide an early indication of sepsis, especially if cytologic evaluation of peritoneal fluid is unavailable or results are equivocal and peritoneal fluid bacterial culture results are pending. (J Am Vet Med Assoc 1999;214: 1032–1036)

Free access
in Journal of the American Veterinary Medical Association

Objective

To identify breed, age, sex, physical findings, history, and outcome of treatment in horses and other equids with enterolithiasis.

Design

Retrospective study.

Animals

900 equids with enterolithiasis.

Procedure

Medical records from equids with enterolithiasis admitted between 1973 and 1996 were reviewed. Data on signalment, history, physical examination and clinicopathologic findings, surgical findings, and outcome were compiled from records and from telephone interviews with owners. Sex and breed predilections were determined by comparison of the study population with the general hospital population of equids during the same time period.

Results

Equids with enterolithiasis represented 15.1% of patients admitted for treatment of colic, and 27.5% of patients undergoing celiotomy for treatment of colic. Arabian and Arabian crosses, Morgans, American Saddlebreds, and donkeys were significantly overrepresented, and Thoroughbreds, Standardbreds, warmbloods, and stallions were significantly underrepresented in the study population, compared with the hospital population. The mean age of equids with enterolithiasis was 11.4 years. The most common historic findings were signs of intermittent colic (33.3%) and passage of enteroliths in the feces (13.5%). Physical examination findings were similar to those found in equids with other forms of nonstrangulating large colon obstructive disease. Fifteen percent (131) developed gastrointestinal tract rupture caused by an enterolith that necessitated euthanasia. Short-term and 1-year survival rates for equids undergoing celiotomy for treatment of enterolithiasis and recovering from anesthesia were excellent (96.2 and 92.5%, respectively), and postoperative complications were uncommon. Recurrence of enterolithiasis was identified in 7.7% of the study population.

Clinical Implications

Results indicated that short-term and 1-year survival rates for equids undergoing surgery for enterolithiasis are excellent. Identification of signalment, history, and management factors may help identify equids with a high risk for development of enterolithiasis. (J Am Vet Med Assoc 1999;214;233–237)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To compare the strength of the sutured linea alba, in vitro, using 2 suture patterns.

Animals

12 clinically normal llamas.

Procedure

2 incisions in the linea alba of 12 llamas were closed with a simple continuous or inverted cruciate pattern, and tissue was harvested after 10 days. In 6 llamas, the simple continuous line was intact; the inverted cruciate specimens contained 6 sutures. In 6 llamas, 1 knot was excised in the simple continuous pattern to simulate a failed line; the cruciate pattern contained 5 knots. Tissue sections were taken from cranial, between, and caudal to the linea alba incisions to compare fascial thickness. The sutured specimens were mounted in a mechanical testing system and tested to failure. A mixed-model ANOVA was used to evaluate the effects of suture pattern and incisional position on mechanical properties.

Results

Significant differences were not found between suture patterns or between location for yield force, failure force, or yield strain, whereas failure strain was lower for the intact simple continuous pattern than the inverted cruciate pattern (P = 0.003). From histomorphometric analysis, the caudal tissue specimens were significantly thinner than the middle tissue specimen cranial to the umbilicus (P = 0.006).

Conclusion

There was no significant difference in monotonic breaking strength of the linea alba sutured with the simple continuous or inverted cruciate pattern.

Clinical Relevance

These results justify the use of the simple continuous pattern over the cruciate pattern for ventral midline closure in llamas because of the ease of placement and speed. (Am J Vet Res 1996;57:938–942)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To provide an accurate and detailed description of the laparoscopic anatomy of the abdomen of horses positioned in dorsal recumbency and to compare those observations with laparoscopic anatomy of standing horses. The effects of laparoscopy and positional changes on arterial blood pressure and blood gas values also were investigated.

Design

Descriptive anatomic study.

Sample Population

Laparoscopy was performed on 6 horses (2 mares, 2 geldings, and 2 stallions) to record the normal laparoscopic anatomy of the abdomen in dorsal recumbency.

Procedure

Feed was withheld from all horses for 36 hours. Horses, under general anesthesia, were examined in horizontal and inclined positions (head-up and head-down). Intermittent positive-pressure ventilation was used, arterial blood pressure was continuously monitored, and samples for arterial blood gas measurements were taken at intervals.

Results

The main structures of diagnostic relevance observed in the caudal region of the abdomen were the urinary bladder, mesorchium and ductus deferens (left and right), left and right vaginal rings, insertion of the pre-pubic tendon, random segments of jejunum and descending colon, pelvic flexure of the ascending colon, body of the cecum, and cecocolic fold. The main structures observed in the cranial region of the abdomen were ventral surface of the diaphragm, falciform ligament and round ligaments of the liver, ventral portion of the left lateral, left medial, quadrate, and right lateral lobes of the liver, spleen, right and left ventral colons, sternal flexure of the ascending colon, apex of the cecum, and stomach.

Conclusions

Alterations in cardiovascular and respiratory function in response to pneumoperitoneum and various positional changes indicated the need for continuous and throrough anesthetic monitoring and support. Comparison of anatomic observations made in dorsally recumbent, inclined horses with those reported for standing horses should enable practitioners to make patient positioning decisions that best suit access to specific visceral structures. Development of special instrumentation for manipulation of the viscera in horses, particularly the intestinal tract, would increase the diagnostic and therapeutic capabilities of laparoscopy during dorsal recumbency. (Am J Vet Res 1996;57:923–931)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To evaluate the role of nitric oxide (NO), vasoactive intestinal peptide (VIP), and a transmitter acting through an apamin-sensitive mechanism in mediating inhibitory transmission in the equine jejunal circular muscle, and to determine the distribution of VIP-and NO-producing nerve fibers in the myenteric plexus and circular muscle.

Procedure

Circular muscle strips were suspended in tissue baths containing an oxygenated modified Krebs solution and attached to isometric force transducers. Responses to electrical field stimulation (EFS), tetrodotoxin, the NO antagonists l-N-nitro-arginine-methyl-ester (L-NAME) and N-nitro-l-arginine, apamin, VIP, authentic NO, and the NO donar sodium nitroprusside were tested. Immunostaining for VIP-like and NADPH diaphorase histochemical staining were performed on paraformaldehyde-fixed tissue.

Results

Subpopulations of myenteric neurons and nerve fibers in the circular muscle were positive for NADPH diaphorase and VIP-like staining. EFS caused a frequency-dependent inhibition of contractile activity. Tetrodotoxin prevented the EFS-induced inhibition of contractions. L-NAME (200 μM) and apamin 0.3 μM) significantly (P < 0.01) reduced EFS-stimulated inhibition of contractile activity at most frequencies tested. The effects of L-NAME and apamin were additive. In their combined presence, EFS induced excitation instead of inhibition (196.7% increase at 5 Hz, n = 28, P < 0.01). Inhibition of contractile activity by EFS was mimicked by sodium nitroprusside. Authentic NO (3-6 μM) abolished contractile activity. VIP induced a dose-dependent inhibition of contractile activity (89.1 ± 6.3% reduction at approximately 0.3 μM, n = 16). Antagonism of NO synthesis did not alter the response to VIP.

Conclusion

NO, VIP, and a substance acting through an apamin-sensitive mechanism appear to comediate inhibitory transmission in the equine jejunal circular muscle.

Clinical Relevance

These findings may suggest new therapeutic targets for motility disorders, such as agents that inhibit the synthesis or actions of NO. (Am J Vet Res 1996;57:1206-1213)

Free access
in American Journal of Veterinary Research

Summary

A review of medical records was used to identify 10 horses in which stringhalt developed subsequent to trauma to the dorsal metatarsus. Six horses developed stringhalt within 3 months after injury, 3 horses developed stringhalt > 3 months after injury, and time from injury to stringhalt was unknown for 1 horse. Horses were treated with exercise, including daily hand-walking with pasture turnout, followed by lunging; or surgically, using lateral digital extensor myotenectomy. Of the horses treated with exercise, 1 had resolution of stringhalt, 2 improved but had residual stringhalt, and 1 had no change. Two of the horses having lateral digital extensor myotenectomy had resolution of stringhalt. Two of the remaining 3 horses treated surgically had varying degrees of improvement, and in 1 horse there was no change. Stringhalt is a potential complication following trauma to the dorsal metatarsal region. Potential causes include tendon adhesions enhancing tarsocrural joint flexion or abnormalities in the myotatic reflex caused by tendon injury that result in abnormal flexion of the tarsocrural joint.

Free access
in Journal of the American Veterinary Medical Association