Biomedical subjects

G M Baxter

Publications and source records attributed to G M Baxter.

84 records · Page 5Linked to original sources

PubMedDate not supplied

Reactivity of equine palmar digital arteries and veins to vasodilating agents.

Palmar digital arteries and veins removed surgically from healthy horses under general anesthesia were cut into 4 mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for continuous measurement of vascular tension. In vitro vascular responses were determined for acetylcholine, acepromazine, isoxsuprine hydrochloride (isoxsuprine), prostaglandin E2 (PGE2), and prostaglandin I2 (prostacyclin). After preconstriction with norepinephrine hydrochloride (norepinephrine), or prostaglandin F2 alpha (PGF2 alpha), the concentrations needed to produce 50% maximum relaxation (EC50) and the maximum percentage of relaxation were determined for each drug. Acetylcholine was the most potent arterial vasodilator (smallest EC50 value) and PGE2 was the least potent. Prostacyclin was the least potent venodilator (highest EC50 value); there were no differences between acetylcholine, acepromazine, isoxsuprine, and PGE2. Isoxsuprine produced greater arterial relaxation than all other agents. Isoxsuprine and acepromazine produced significantly greater venous relaxation than did acetylcholine and PGE2. Prostacyclin produced minimal vasodilation of arteries or veins. Acepromazine and isoxsuprine relaxed the veins significantly more than the arteries. When PGF2 alpha was used instead of norepinephrine to preconstrict the arteries and veins, the potency and effectiveness of acepromazine and isoxsuprine to produce vasodilation were significantly decreased. Results indicate that acepromazine and isoxsuprine can relax the equine digital vasculature but their effectiveness varies depending on the origin of the constriction.

Animals↗

PubMedDate not supplied

Abdominal adhesions after small intestinal surgery in the horse.

One hundred thirteen of 172 horses (66%) undergoing exploratory celiotomy for a small intestinal lesion survived 4 or more days after surgery. Intra-abdominal adhesions causing clinical problems requiring additional surgery or euthanasia were documented in 25 horses (22.1%). Problems developed in significantly more males than females. The most common initial small bowel lesion was ileal impaction (12 horses); 21 horses underwent small intestinal resection or bypass. However, there was no significant difference in the incidence of intra-abdominal adhesions between horses that underwent intestinal resection or bypass and those that did not. Only 4 of the 25 horses (16%) with problems associated with postoperative adhesions survived. The mean interval between surgical procedures or between the initial procedure and euthanasia for all horses was 84 days (range, 7-512 days; median, 25 days). However, 70% of the subsequent celiotomies were performed within 60 days of the previous surgery. The mean interval between celiotomies was 221 days (range, 9-512 days) for the survivors and 61 days (range, 7-358 days) for the nonsurvivors. These results indicated that most of the problems related to postoperative intra-abdominal adhesions occurred within 2 months of the initial small intestinal surgery. Furthermore, the earlier development of postoperative adhesions was associated with a poorer prognosis for survival.

Age Factors↗

PubMedDate not supplied

Mid-metacarpal deep digital flexor tenotomy in the management of refractory laminitis in horses.

Deep digital flexor tendon transection at the mid-metacarpus was performed in 20 horses with severe acute or chronic laminitis that was not responsive to conventional treatment. Sixteen horses improved within 72 hours, one horse worsened, and two horses were unaffected by the surgery. Eleven horses survived less than 1 month after surgery and six horses survived longer than 6 months. Three horses surviving longer than 6 months have remained lame and no horse has returned to athletic performance. Transection of the deep digital flexor tendon at the mid-metacarpus may decrease the pain associated with the acute refractory stage of laminitis and may be useful as an immediate salvage procedure; however, despite the early clinical improvement observed after tenotomy, the survival rate of affected horses may not be altered.

Acute Disease↗

PubMedDate not supplied

Sutured end-to-end and stapled side-to-side jejunal anastomoses in the horse.

Hand sutured end-to-end (EE) and stapled side-to-side (SS) small intestinal anastomoses were performed in 10 healthy adult horses. In five SS anastomoses, staple lines on the blind ends of the jejunum were inverted (SSI) and in five they were not (SSNI). Five EE anastomoses were sutured with polydioxanone and five were sutured with polyglyconate. All horses were euthanatized on day 30. Intra-abdominal adhesions were graded (0-4), and stomal areas were calculated from contrast radiographs made with the bowel distended. Histopathology scores for the anastomoses were based on the degree of inflammation (0-3), fibrosis (0-3), and alignment and healing of intestinal layers (0-3). Mean surgery times +/- standard deviations for EE, SSI, and SSNI techniques were 33.9 +/- 5.4, 36.2 +/- 5.6, and 29.6 +/- 5.9 minutes, respectively. Mean and median stomal areas were 9.4 +/- 5.5 and 8.9 cm2 for EE anastomoses and 17.2 +/- 16.5 and 12.1 cm2 for SS anastomoses. Intra-abdominal adhesions developed in three horses, one of which had clinical signs of colic. Mean histopathology scores for EE and SS anastomoses were 4.8 +/- 2.0 (median = 5) and 4.4 +/- 1.8 (median = 4), respectively. There were no statistically significant differences in surgery times, intra-abdominal adhesion scores, stomal areas, or histopathology scores between small intestinal EE and SS anastomoses in these horses.

Abdominal Pain↗

PubMedDate not supplied

Complete excision of a fractured fourth metatarsal bone in eight horses.

Proximal open comminuted fractures of the fourth metatarsal bone (Mt IV) in eight horses were treated by complete removal of the affected bone and antimicrobial therapy. Two horses had concurrent septic arthritis of the tarsocrural or distal tarsal articulations, and five horses had radiographic evidence of osteomyelitis and sequestration of the affected bone. Five horses became athletically sound for their intended use, two horses with septic arthritis had residual lameness but were pasture sound, and one horse was lost to follow-up. Excision of the entire bone appears to be an acceptable treatment of open comminuted fractures of the proximal one-third of Mt IV that do not respond to more conservative modes of therapy.

Animals↗

PubMedDate not supplied

Palmar digital neurectomy in horses. 57 cases (1984-1990).

The medical records of 57 horses that had palmar digital neurectomy performed between 1984 and 1990 were reviewed. Neurectomies were performed either by transection and electrocoagulation (47 horses) or by the guillotine technique (10 horses). Middle-aged geldings, Quarter Horses, and Thoroughbreds were significantly over-represented when compared with the hospital population. Horses used as hunter/jumpers also appeared to be over-represented. Complications occurred in 17 (34%) of the 50 horses for which follow-up information was obtained. Recurrence of heel pain was the most common complication (14 horses). Palpable painful neuromas were detected in three horses. One year after neurectomy, 74% of the horses were sound; this decreased to 63% after 2 years.

Animals↗

PubMedDate not supplied

Failure of calcium channel blockade to prevent intra-abdominal adhesions in ponies.

Intra-abdominal adhesions were created by localized serosal trauma in 11 adult ponies at three locations on the small intestine. Six ponies received verapamil hydrochloride (0.2 mg/kg) subcutaneously every eight hours for three days, and five ponies received an equal volume of saline solution at the same intervals. The investigators were not informed which treatments the ponies received. Systolic, diastolic, and mean carotid arterial pressures and heart rates were measured six hours before surgery, and then 0.5, 1, 1.5, and 8 hours after the first treatment on each day for three days. One pony was euthanatized on day 13 because of colic, and the other 10 ponies were euthanatized 14 days after surgery. Scoring methods were used to assess the severity of adhesion formation and to grade the histologic appearance of the abraded sites. No significant differences were found for rectal temperature, packed cell volume, total plasma proteins, heart rate, and systolic, diastolic, or mean arterial pressures between control and verapamil-treated ponies. No significant differences were detected between the treatment groups for adhesion scores per abraded site, total adhesion scores per pony, the total number of adhesions per pony, or in the histologic scores.

Animals↗

PubMedDate not supplied

Hemodynamic responses of horses to anesthesia and surgery, before and after administration of a low dose of endotoxin.

Seven horses, which were part of an investigation of the effect of endotoxin administration on vascular reactivity, were anesthetized on two separate occasions for surgical excision of 4-cm sections of palmar digital artery and vein. On the first occasion, the horses were given an infusion of 1 L 0.9% NaCl solution intravenously (i.v.) just before induction of anesthesia (control); on the second occasion, the horses received an infusion of 1 L 0.9% NaCl containing Escherichia coli endotoxin, 0.1 microgram/kg (endotoxin). On both occasions, anesthesia was induced with xylazine, guaifenesin, and ketamine, and maintained with halothane in oxygen. Hemodynamic measurements were made with the horses under anesthesia immediately before beginning surgery (period 1), during skin incision (period 2), during dissection and excision of the vessels (period 3), during skin suturing (period 4), and after completion of surgery during bandaging (period 5). Hemoglobin concentration and mixed venous oxygen content were greater at all periods in horses that received endotoxin. Otherwise, there were no significant differences in hemodynamic parameters between control horses and horses administered endotoxin before beginning surgery (period 1). During surgery and bandaging, horses administered endotoxin had significantly higher heart rate (periods 3, 4, and 5), cardiac index (periods 3, 4, and 5), and oxygen delivery (periods 2, 3, 4, and 5) than did control horses, and mean arterial blood pressure (period 2) and systemic vascular resistance (periods 2, 3, 4, and 5) were less than in control horses. Compared with period 1, surgical stimulation in control horses was associated with increased mean arterial blood pressure and systemic vascular resistance (periods 2, 3, 4, and 5), but cardiac index and oxygen delivery were decreased (periods 3, 4, and 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗

PubMedDate not supplied

Alterations of endothelium-dependent digital vascular responses in horses given low-dose endotoxin.

Low doses of endotoxin cause vasoconstriction and hypoperfusion of the digit, small intestine, and cecum in horses. To determine the potential cause of these vascular alterations, in vitro vascular responses of palmar digital arteries and veins were determined in 8 horses after intravenous (IV) infusion of 1 L 0.9% NaCl (control) and 0.1 microgram/kg Escherichia coli 055:B5 endotoxin in 1 L of 0.9% NaCl (endotoxin-treated). Vessels were surgically removed under general anesthesia, cut into 4-mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for measurement of vascular tension. Cumulative concentration response curves to acetylcholine, bradykinin, nitroprusside, norepinephrine, 5-hydroxytryptamine (serotonin), and endothelin were determined. Maximal relaxation or contraction and the concentrations needed to produce 50% maximal relaxation or contraction were determined. Palmar digital arteries from endotoxin-treated horses relaxed significantly less in response to acetylcholine and bradykinin (endothelium-dependent), but not to nitroprusside (endothelium-independent) when compared with arteries from control horses. Digital arteries from endotoxin-treated horses also contracted significantly more with norepinephrine but less with serotonin. Digital veins responded less than digital arteries. In another study, vascular reactivity experiments documented that acetylcholine and bradykinin were endothelium-dependent vasodilators (endothelium-denuded vessels relaxed less than control vessels) in palmar digital vessels. Additionally, maximal relaxations for both vasodilators were significantly inhibited by N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide antagonist, suggesting that acetylcholine and bradykinin cause relaxation through the nitric oxide pathway. The data from these studies indicate that low dose endotoxin impairs endothelium-dependent relaxation and augments adrenergic contraction of palmar digital arteries in horses.

Acetylcholine↗

PubMedDate not supplied

Bacterial culturing of ventral median celiotomies for prediction of postoperative incisional complications in horses.

OBJECTIVE: The purpose of this study was to determine whether detection of bacterial contamination of ventral midline incisions was predictive of postoperative incisional complications in horses undergoing exploratory celiotomy for colic. STUDY DESIGN: Prospective study. ANIMAL OR SAMPLE POPULATION: Horses that had ventral median celiotomies for colic at Colorado State University between May 1, 1991 and April 30, 1993 were studied prospectively. Complete information was obtained on 66 horses. METHODS: Bacterial cultures were obtained from ventral midline incisions at surgery. Information regarding the type of surgery performed (celiotomy vs celiotomy plus enterotomy or enterectomy), preoperative total nucleated cells and presence of a left shift, postoperative fever (> 38.5 degrees C), incisional drainage, incisional herniation, and outcome were obtained from medical records. Additional information concerning incisional drainage, herniation, and survival was obtained at a minimum of 18 months after surgery. RESULTS: Examination of odds ratio (ORs) and confidence intervals (CIs) revealed that a celiotomy plus enterotomy or enterectomy was positively, but not significantly, associated (OR > 1) with positive culture results, presence of incisional drainage and incisional herniation. A significant association between incisional drainage and hernia formation was found; odds of incisional herniation were 62.5 times greater in horses that had incisional drainage. Incisional drainage and herniation were negatively associated with patient survival. The later association was significant (OR = 0.18, P = .04). CONCLUSIONS: This study indicated that detection of bacterial contamination at incisional closure by the swab culture technique was not beneficial in the prediction of postoperative incisional problems in horses undergoing colic surgery. Incisional drainage or infection appeared to be associated with hernia formation. CLINICAL RELEVANCE: Immediate treatment of incisional drainage or method to prevent incisional infections may decrease hernia formation.

Abdomen↗

PubMedDate not supplied

Acute gastrointestinal disease in 27 New World camelids: clinical and surgical findings.

OBJECTIVE: To describe clinical and surgical findings from New World camelids with acute gastrointestinal disease. STUDY DESIGN: Retrospective study. ANIMAL POPULATION: 20 llamas and 7 alpacas. METHODS: Camelids were grouped based on surgical lesions. Clinical and surgical findings were compared between groups and between surviving and nonsurviving camelids. RESULTS: Twelve of 27 initial celiotomies and 3 of 4 repeat celiotomies were successful. Death occurred from euthanasia during surgery (nine camelids), peritonitis or sepsis (five), aspiration pneumonia (one), and respiratory distress (one). Survival was lowest after celiotomy for proximal obstruction (3 of 10 camelids), ruptured viscus (0 of 4), and necrotizing enteritis (0 of 2) and highest after celiotomy for distal obstruction (10 of 13) and septic peritonitis without ruptured viscus (2 of 2). Before surgery, camelids with proximal obstruction had significantly lower (P < .05) serum chloride concentrations (median, 97 mEq/L) than those with distal obstruction (median, 109 mEq/L) or ruptured viscus (median, 117 mEq/L). Serum bicarbonate concentration also was highest (median, 34.6 mEq/L) and often greater than 28 mEq/L in camelids with proximal obstruction. Camelids with distal obstruction had significantly lower (P < .05) nucleated cell counts in peritoneal fluid (median, 700 cells/microL) than those with ruptured viscus (median, 20,600 cells/microL) or septic peritonitis (median, 88,300 cells/microL). CONCLUSIONS: Camelids with proximal obstruction often had hypochloremic metabolic alkalosis. Camelids with distal obstruction had less metabolic derangement and tissue compromise and a higher survival rate. CLINICAL RELEVANCE: Awareness of the characteristics of the various types of acute gastrointestinal disease in camelids will augment veterinarians' ability to diagnose and treat these disorders.

Acute Disease↗

PubMedDate not supplied

Endoscopy of the calcaneal bursa in horses.

OBJECTIVE: To describe endoscopic approaches to the calcaneal bursa and clinical findings in 2 horses with calcaneal bursitis. STUDY DESIGN: Cadaver evaluations and retrospective case reports. ANIMALS: 12 cadavers and 2 adult horses. METHODS: Cadaver specimens of the calcaneal bursa were evaluated with a rigid arthroscope and gross dissection to determine the endoscopic appearance of anatomic structures located within the bursa. The site(s) for placement of the arthroscope and instrument(s) was determined based on cadaver dissection and endoscopic examination. RESULTS: Placement of the arthroscope 1 cm dorsal to the superficial digital flexor tendon (SDFT) and 1 cm distal to the medial or lateral aspect of the SDFT retinaculum allowed consistent examination of the tuber calcis, proximal aspect of the long plantar ligament, calcaneal tendon of the gastrocnemius muscle inserting on the tuber calcis, SDFT and the proximal and distal extent of the bursa. Lesions observed and treated with use of endoscopy included local bone necrosis of the proximoplantar aspect of the tuber calcis and damage of the origin of the long plantar ligament in one horse. Mild disruption of the superficial digital flexor tendon and long plantar ligament were observed and debrided in another horse. CONCLUSIONS: Endoscopic exploration of the calcaneal bursa is clinically feasible to treat infectious and noninfectious bursitis and to help identify the cause(s) of undiagnosed bursitis or lameness associated with the calcaneus, superficial digital flexor tendon, tendon of the gastrocnemius muscle, and the long plantar ligament. CLINICAL RELEVANCE: An endoscopic approach to the calcaneal bursa is recommended whenever possible to decrease complications associated with surgery in this region and improve the diagnosis of infectious and non-infectious calcaneal bursitis.

Animals↗