Effect of Hypotension and Dobutamine on Gastrointestinal Microcirculations of Healthy, Anesthetized Horses.

Horses undergoing abdominal exploratory surgery are at risk of hypotension and hypoperfusion. Normal mean arterial pressure is used as a surrogate for adequate tissue perfusion. However, measures of systemic circulation may not be reflective of microcirculation. This study measured the mean arterial pressure, cardiac index, lactate, and four microcirculatory indices in six healthy, anesthetized adult horses undergoing elective laparotomies. The microcirculatory parameters were measured at three different sites along the gastrointestinal tract (oral mucosa, colonic serosa, and rectal mucosa) with dark-field microscopy. All macro- and microcirculatory parameters were obtained when the horses were normotensive, hypotensive, and when normotension returned following treatment with dobutamine. Hypotension was induced with increases in inhaled isoflurane. The horses successfully induced into hypotension did not demonstrate consistent, expected changes in systemic perfusion or microvascular perfusion parameters at any of the three measured gastrointestinal sites. Normotension was successfully restored with the use of dobutamine, while the systemic perfusion and microvascular perfusion parameters remained relatively unchanged. These findings suggest that the use of mean arterial pressure to make clinical decisions regarding perfusion may or may not be accurate.

Longitudinal evaluation of fentanyl concentrations in equine plasma and synovial fluid following application of transdermal fentanyl patches over one carpal joint.

OBJECTIVE: To determine if transdermally delivered fentanyl can achieve greater concentrations of fentanyl in synovial fluid when applied over a synovial structure. STUDY DESIGN: Randomized, experimental study. ANIMALS: Six healthy adult horses. METHODS: Each horse had two 100 µg/h fentanyl matrix patches applied on the dorsal aspect of one, randomly assigned, carpometacarpal joint (CMCJ) for 48 h. Whole blood and bilateral synovial samples from the intercarpal joint were obtained at 0, 2, 6, 12, 24, 36 and 48 h. Fentanyl concentrations were measured with liquid chromatography-mass spectrometry. RESULTS: All subjects achieved detectable concentrations of fentanyl in both plasma and synovial fluid. Time to peak synovial and plasma concentration was 12 h. At 6 h, the synovial concentration in the untreated carpus (0.104 ng/mL ± 0.106) was lower than plasma fentanyl concentrations 0.31 ± 0.27 (p = .036). At 12 h, both treated (0.55 ng/mL ± 0.3) and untreated (0.53 ng/mL ± 0.28) synovial fluid fentanyl concentrations were lower than plasma (0.87 ng/mL ± 0.48) concentrations (p < .001 and p = .001, respectively). Synovial concentrations of fentanyl did not differ between treated and untreated joints (p > 0.608 for all time points). CONCLUSION: Application of fentanyl matrix patches directly over the CMCJ did not result in increased fentanyl concentrations in the synovial fluid of the treated intercarpal joint in normal horses. CLINICAL SIGNIFICANCE: There is likely no analgesic advantage to placing fentanyl patches directly over the affected joint, as it did not result in increased synovial concentrations at the tested site.

Effects of hyaluronate-carboxymethylcellulose membranes on the clinical outcome of horses undergoing emergency exploratory celiotomy.

OBJECTIVE: To determine the influence of hyaluronate-carboxymethylcellulose (HA-CMC) membranes applied to intestinal anastomoses or enterotomies on postoperative complications after emergency exploratory celiotomy. STUDY DESIGN: Multicenter retrospective case-controlled series. ANIMALS: Adult horses (59 in the HA-CMC group and 91 controls). METHODS: Medical records from 4 referral hospitals were searched for horses ≥1 year of age, treated between 2008 and 2014 with emergency exploratory celiotomy, and surviving at least 24 hours postoperatively. Horses receiving repeat celiotomy during the same hospitalization were excluded. Horses who received HA-CMC were matched with controls who did not receive HA-CMC but had similar intestinal lesions and procedures at the same referral hospital. Postoperative complications (colic, nasogastric reflux, fever, incisional infection, and septic peritonitis), duration of hospitalization, and survival were compared between groups. Data were compared between horses by t test, Wilcoxon signed rank test, and χ2 test. RESULTS: The volume of nasogastric reflux at admission (P = .02) and the duration of administration of lidocaine after surgery (P = .02) were greater in horses with HA-CMC membranes than in controls. No difference in postoperative complications or survival was detected between groups: 48 of 59 (81%) horses treated with HA-CMC survived until discharge from the hospital compared with 80 of 91 (88%) horses in the control group (P = .27). Fifteen of 21 horses treated with HA-CMC and 30 of 43 horses in the control group survived >12 months after hospital discharge. CONCLUSION: Application of HA-CMC membranes to anastomoses or intestinal incisions did not influence postoperative complications or survival after emergency celiotomy compared with controls. CLINICAL SIGNIFICANCE: The safety and efficacy of HA-CMC membrane application to intestinal sites during colic surgery in horses is equivocal.

Retrospective Comparison of Gastrosplenic Entrapment of the Small Intestine to Other Strangulating Small Intestinal Lesions in Adult Horses.

OBJECTIVE: To compare clinical data of horses with entrapment of the small intestine by the gastrosplenic ligament (ESIGL) to clinical data of horses with other strangulating small intestinal lesions. STUDY DESIGN: Retrospective case series. METHODS: Medical records (January 2001-December 2011) of horses that had exploratory celiotomy for acute abdominal pain associated with strangulating small intestinal lesions were reviewed. Signalment, physical examination findings, clinicopathologic variables, surgical findings and surgical procedures performed, postoperative data and short-term survival were recorded. RESULTS: Clinical findings included excessive nasogastric reflux and abnormal abdominal fluid. Horses with ESIGL were significantly more likely to require intestinal resection and anastomosis and produced significantly less reflux postoperatively than horses with other strangulating small intestinal obstructions. Geldings were significantly more likely to develop ESIGL than mares or stallions. Quarter Horse or Quarter Horse type breeds were predisposed to ESIGL. Survival to hospital discharge in horses with ESIGL (16/22; 72.7%) was significantly higher than that of horses with other strangulating small intestinal obstructions (92/183; 50%). CONCLUSIONS: ESIGL was more prevalent in this population of horses evaluated for acute abdominal pain than in previous studies, accounting for 10.7% of all horses with strangulating small intestinal lesions. Geldings and Quarter Horse or Quarter Horse related breeds are predisposed to this condition. The prognosis for survival to hospital discharge was fair to good.

A retrospective study comparing the outcome of horses undergoing small intestinal resection and anastomosis with a single layer (Lembert) or double layer (simple continuous and Cushing) technique.

OBJECTIVES: To (1) compare postoperative complications and survival in horses after small intestinal resection and anastomosis using 2 anastomosis techniques (single layer Lembert; double layer simple continuous oversewn with Cushing), and (2) to compare outcome by anastomosis type (jejunoileostomy; jejunojejunostomy). STUDY DESIGN: Retrospective case series. ANIMALS: Horses (n = 53). METHODS: Medical records (July 2006-July 2010) of all horses that had small intestinal resection and anastomosis. Horses were divided into groups based on technique and type of anastomosis. Comparisons of pre- and intraoperative findings (disease severity), postoperative complications, and survival rates were made between groups. RESULTS: There were no differences in disease severity, postoperative complications, or survival between single layer (n = 23) or double layer (n = 31) anastomoses. There were no differences in disease severity or survival between jejunoileostomy (n = 16) or jejunojejunostomy (n = 38). There was a higher incidence of postoperative colic in hospital after jejunoileostomy (13/16) compared with jejunojejunostomy (18/38) (P = .0127). CONCLUSIONS: Postoperative complications and survival are comparable between horses undergoing single layer and double layer small intestinal end-to-end anastomoses. With the exception of increased postoperative colic in the hospital, postoperative complications and survival after jejunoileostomy and jejunojejunostomy are also comparable.

Serial viscoelastic and traditional coagulation testing in horses with gastrointestinal disease.

OBJECTIVE: Objectives of this study were to compare the ability of serial thromboelastography, Sonoclot, and traditional coagulation panels to detect coagulopathies associated with disease category, systemic inflammatory response syndrome (SIRS), complications, and nonsurvival in horses with gastrointestinal disease. DESIGN: Prospective clinical evaluation. SETTING: University referral hospital. ANIMALS: One hundred twenty-one horses admitted as emergencies for gastrointestinal disease and 28 healthy adult horses. INTERVENTION: Blood samples were collected ≤4 times from emergency horses (admission and if surviving and hospitalized on days 2-4) and once from healthy horses. Thromboelastography (with and without tissue factor activation), Sonoclot, and a traditional coagulation panel were performed on each sample. MEASUREMENTS AND MAIN RESULTS: Emergency horses were grouped based on disease category (ie, nonstrangulating medical, nonstrangulating surgical, strangulating, and inflammatory), survival to discharge, SIRS at admission, requirement for exploratory celiotomy, ileus, diarrhea, fever, thrombophlebitis, and laminitis. Changes over time were evaluated individually and compared between disease groups. Horses with gastrointestinal disease had dynamic changes in coagulation and fibrinolysis during the first 4 days of hospitalization that were correlated with disease category, SIRS, complications, and fatality. The multivariate logistic regression model for nonsurvival included activated partial thromboplastin time on day 2 and LY30 on day 3 (overall model significance P < 0.0001). The odds of nonsurvival were 23.75 times higher if activated partial thromboplastin time was >85.6 s on day 2 and 9.38 times higher if LY30 was >1% on day 3. CONCLUSIONS: Horses with gastrointestinal disease have activation of coagulation and fibrinolysis. Magnitude of change in these parameters is small and predictive value moderate, making application of these tests to direct therapy in clinical patients difficult. Effect of specific treatments (eg, surgery) on these tests and coagulation has not been determined. Further studies are required to determine if these tests could be used to help monitor response to treatment in individual animals or specific disease states.

Pharmacodynamics of multi-dose low molecular weight heparin in healthy horses.

OBJECTIVES: To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses. STUDY DESIGN: Randomized cross over study. ANIMALS: Adult mixed breed healthy mares (n = 6). METHODS: LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study. RESULTS: No changes in PCV, platelet count, or AT activity were detected with either frequency of daily LMWH administration. Values for PTT increased throughout the study but never exceeded the normal reference interval. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range (0.1-0.2 U/mL) when LMWH was administered twice daily, but fell below this range ≈ 16 hours after administration when given once daily. For both once and twice daily LMWH administration, the area under the curve was significantly greater after the last dose of LMWH when compared to the first dose. CONCLUSIONS: Administration of LMWH once or twice daily for 3 consecutive days appears to be safe in healthy adult horses. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range for 24 hours with twice daily LMWH administration but not with once daily administration.

In vitro comparison of a single-layer (continuous Lembert) versus two-layer (simple continuous/Cushing) hand-sewn end-to-end jejunoileal anastomosis in normal equine small intestine.

OBJECTIVES: To compare in vitro physical and mechanical characteristics of 1-layer and 2-layer end-to-end jejunoileostomy. STUDY DESIGN: In vitro experimental study. ANIMALS: Adult horses (n = 6). METHODS: Harvested equine jejunum and ileum was used to create 1- and 2-layer end-to-end jejunoileostomy specimens. Construction time, bursting pressure, and relative lumen diameter (anastomosis diameter expressed as a percentage of the lumen diameter of adjacent jejunum and ileum) were compared. Construction time and relative lumen diameters were compared using a paired t-test. Bursting pressure for anastomoses and control jejunal segments were compared using a repeated-measure ANOVA. Statistical significance was set at P < .05. RESULTS: Mean (± SEM) construct completion times were shorter for 1 layer (21 ± 0.91 minutes) than 2 layers (26.71 ± 1.16 minutes; P = .005). Relative lumen diameters (percentage of jejunal diameter) were larger for 1 layer (77.67 ± 4.46%) than for 2 layers (69.37 ± 2.8%; P = .035). There were no significant differences in bursting pressures between the 2 groups and the control jejunum (P =.155) or relative lumen diameters (percentage of ileal diameter; P =.118). CONCLUSIONS: One-layer jejunoileostomy can be created in a shorter time and maintain a larger anastomosis luminal diameter without compromising maximum bursting pressure when compared to 2-layer jejunoileostomy.

Effect of experimentally induced synovitis on amikacin concentrations after intravenous regional limb perfusion.

OBJECTIVES: To determine the effects of experimentally induced synovitis of the radiocarpal joint on the intra-articular pharmacokinetics and pharmacodynamics of amikacin after intravenous regional limb perfusion (IVRLP). STUDY DESIGN: Randomized crossover experimental design. ANIMALS: Adult horses (n = 8). METHODS: Horses were randomly assigned into 2 trials: synovitis and no-synovitis. Radiocarpal joint synovitis was induced with lipopolysaccharide 6 hours before IVRLP. IVRLP (5-mg/kg amikacin qs 60 mL) was performed with a pneumatic tourniquet under general anesthesia. Synovial fluid was obtained before and 0.5, 1, 3, 5, 12, 24, 48 hours after IVRLP. Amikacin concentrations at each time point and pharmacokinetic values were compared between synovitis and no-synovitis trials with Student's t-test. RESULTS: Amikacin synovial fluid concentrations indicated suspected tourniquet failure on 3 occasions (2 synovitis, 1 no-synovitis) on 3 different horses. Data from both trials in these 3 horses were excluded from further analysis. Observed time to maximal concentration (T(max); mean ± SD = 54 ± 13.42 min) was reached earlier in synovitis joints (5/5, 30 min) than in no-synovitis joints (1/5, 30 min and 4/5, 1 h; P = .0476) (P = .0161). Mean observed maximal concentration (C(max)) was higher in synovitis joints (144.48 ± 43.17 µg/mL) than in no-synovitis joints (60.02 ± 28.81 µg/mL; P = .0301). The recommended C(max): minimum inhibitory concentration ratio of 8 was achieved in 3/5 of the successfully perfused joints with induced synovitis, but this ratio was not achieved in any of the clinically normal joints. CONCLUSION: Synovitis of the radiocarpal joint resulted in an earlier observed T(max) and higher observed C(max) of intra-articular amikacin after IVRLP compared with normal joints.

Efficacy of three tourniquet types for intravenous antimicrobial regional limb perfusion in standing horses.

OBJECTIVE: To determine (1) if clinically useful concentrations of amikacin sulfate can be obtained in synovial fluid during regional limb perfusion (RLP) performed above the carpus in standing sedated horses and (2) to determine the efficacy of 3 tourniquet types (narrow rubber [NR], wide rubber [WR], pneumatic [PN]). ANIMALS: Horses (n=9). METHODS: Bilateral forelimb RLP with amikacin sulfate (2.5 g) were administered through the cephalic vein in standing sedated horses. Limbs were randomly assigned to the 3 tourniquet types (NR, WR, PN) applied above the carpus. Metacarpophalangeal synovial fluid was obtained 0.5 hour after perfusion. Amikacin concentration in the synovial fluid was detected using fluorescence polarization immunoassay. RESULTS: Mean synovial concentrations of amikacin in the PN (mean 236 µg/mL; range 23-913 µg/mL) and WR (mean 64.2 µg/mL; range 7-315 µg/mL) were significantly higher (P=.000 and .032, respectively) than the NR tourniquet (mean 2.1 µg/mL; range 0.9-3.3 µg/mL). CONCLUSIONS: The PN tourniquet resulted in the highest synovial fluid amikacin concentrations in all horses, although administration with PN and WR tourniquets achieved adequate amikacin concentrations. NR tourniquet is ineffective and should not be used for RLP above the carpus in the standing horse.

Extraluminal, C shaped polyethylene prostheses in two ponies with tracheal collapse.

OBJECTIVE: To describe the surgical technique, complications, and outcome after use of extraluminal prostheses in 2 ponies with severe tracheal collapse. STUDY DESIGN: Clinical report. ANIMALS: Ponies (n=2) with severe tracheal collapse. METHODS: A ventral median approach was used to expose the trachea from the larynx to the manubrium. Extraluminal, high-density polyethylene, C-shaped prostheses were sutured to the dorsal tracheal membrane and tracheal rings to provide external tracheal support. RESULTS: The surgical approach provided good tracheal access and placement of the rings was uncomplicated. Initial estimates of the tracheal diameter from preoperative radiographs resulted in prostheses that were too small at surgery requiring a 2nd surgical procedure in 1 pony. Postoperative complications were coughing, right laryngeal hemiplegia, seroma formation, and antimicrobial induced colitis. Both ponies had marked resolution of clinical abnormalities after surgery. Recurrent esophageal obstruction resulted in euthanasia of 1 pony 3.5 years after surgery. The other pony was doing well 1 year after surgery. CONCLUSIONS: Extraluminal support of the trachea resulted in rapid resolution of clinical signs in 2 ponies with tracheal collapse. CLINICAL RELEVANCE: Extraluminal tracheal prostheses can resolve clinical abnormalities in ponies with severe tracheal collapse.

Laparoscopic obliteration of the nephrosplenic space using polypropylene mesh in five horses.

OBJECTIVE: To report a laparoscopic technique for insertion of polypropylene mesh in the nephrosplenic space in horses and evaluate outcome. STUDY DESIGN: Descriptive experimental study. ANIMALS: Five healthy mature horses. METHODS: One laparoscope and 2 instrument portals were made on the left side of the horse. The nephrosplenic space was measured and appropriately sized polypropylene mesh was inserted and attached to the dorsolateral splenic capsule and perirenal fascia using helical titanium coils. All horses had repeat laparoscopy 4 weeks later and were necropsied at intervals 4-14 weeks after mesh placement. RESULTS: Mean time for laparoscopic mesh placement was 104 minutes. None of the horses had signs of colic and at 4 weeks all mesh implants were covered by fibrous tissue. One horse had a descending colon mesenteric adhesion to the mesh. At necropsy, the fibrous tissue covering the mesh had adhered to itself and pulled the splenic capsule and perirenal fascia into close apposition. Each mesh implant was firmly adhered to the spleen, nephrosplenic ligament, and perirenal fascia. CONCLUSIONS: Laparoscopic mesh placement was easily performed, well tolerated, and provided excellent fibrous obliteration of the nephrosplenic space. The single important complication observed was a mesenteric adhesion of the descending colon to the mesh in 1 horse. CLINICAL RELEVANCE: Laparoscopic placement of polypropylene mesh leads to obliteration of the nephrosplenic space within 4 weeks and should prevent entrapment of viscera in the nephrosplenic space.