Evaluation of athletic performance in horses with jugular vein thrombophlebitis: 91 cases (1988–2005)

Peggy Moreau Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 7C6, Canada.

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Jean-Pierre Lavoie Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC J2S 7C6, Canada.

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Abstract

Objective—To evaluate effects of thrombophlebitis of 1 or both jugular veins on athletic performance of horses.

Design—Retrospective case series.

Animals—91 horses with jugular vein thrombophlebitis.

Procedures—Medical records of horses with jugular vein thrombophlebitis examined between 1988 and 2005 were reviewed for signalment, history, clinical signs, diagnosis, and treatment. Performance was evaluated in 2 ways. A questionnaire was used to obtain a subjective assessment from the owner or trainer of the horse's performance after thrombophlebitis, compared with the performance before thrombophlebitis. Racing records from before and after thrombophlebitis were also evaluated.

Results—Thrombophlebitis was diagnosed in 37 horses at the time of admission (group 1), and 54 horses developed thrombophlebitis during hospitalization for an unrelated medical condition (group 2). Twenty-seven of 81 (33%) owners answered the questionnaire, and racing records were available for 31 horses. Performance data were available for 48 horses. Owners reported that all nonracing horses, except 1, had equivalent or better performances after discharge. Twenty-six of 31 (84%) Standardbreds resumed racing; in these horses, there was no significant difference between racing times before and after thrombophlebitis. No significant difference in performance was detected regardless of the primary disease, whether a horse had unilateral or bilateral thrombophlebitis, or the treatment administered.

Conclusions and Clinical Relevance—Results suggested that the athletic performance of horses used for nonracing events was not affected by thrombophlebitis. Thrombophlebitis in racing Standardbreds was associated with a decreased chance of return to racing; however, performance was not impaired in those that resumed racing.

Abstract

Objective—To evaluate effects of thrombophlebitis of 1 or both jugular veins on athletic performance of horses.

Design—Retrospective case series.

Animals—91 horses with jugular vein thrombophlebitis.

Procedures—Medical records of horses with jugular vein thrombophlebitis examined between 1988 and 2005 were reviewed for signalment, history, clinical signs, diagnosis, and treatment. Performance was evaluated in 2 ways. A questionnaire was used to obtain a subjective assessment from the owner or trainer of the horse's performance after thrombophlebitis, compared with the performance before thrombophlebitis. Racing records from before and after thrombophlebitis were also evaluated.

Results—Thrombophlebitis was diagnosed in 37 horses at the time of admission (group 1), and 54 horses developed thrombophlebitis during hospitalization for an unrelated medical condition (group 2). Twenty-seven of 81 (33%) owners answered the questionnaire, and racing records were available for 31 horses. Performance data were available for 48 horses. Owners reported that all nonracing horses, except 1, had equivalent or better performances after discharge. Twenty-six of 31 (84%) Standardbreds resumed racing; in these horses, there was no significant difference between racing times before and after thrombophlebitis. No significant difference in performance was detected regardless of the primary disease, whether a horse had unilateral or bilateral thrombophlebitis, or the treatment administered.

Conclusions and Clinical Relevance—Results suggested that the athletic performance of horses used for nonracing events was not affected by thrombophlebitis. Thrombophlebitis in racing Standardbreds was associated with a decreased chance of return to racing; however, performance was not impaired in those that resumed racing.

Thrombophlebitis is defined as an inflammation of the vein wall in conjunction with thrombosis. Thrombophlebitis most commonly affects the jugular veins in horses because they are the site most commonly used for collection of blood samples, IV injection, and catheterization.1,2 The classic triad that predisposes an animal to develop intravascular thrombosis includes blood vessel trauma (eg, puncture, injection, administration of irritant drugs, or catheterization), stasis of blood flow (eg, head in a low position), and a hypercoagulable state.2–5 Clinically, thrombophlebitis of a jugular vein is recognized as a palpably hard, cord-like vein with decreased blood flow.

Ultrasonography allows for confirmation of the diagnosis of thrombophlebitis and determination of the extent and severity of lesions.6,7 Signs of septic thrombophlebitis may include heat, swelling, signs of pain, fever, suppuration, and hyperechoic intraluminal material. Bilateral jugular vein thrombophlebitis can lead to edema of the head with lingual, pharyngeal, or laryngeal edema that can result in dysphagia and dyspnea.6,8

The long-term outcome for a thrombus is variable. Recanalization of the vein may take place; the thrombus may undergo fibrous organization without recanalization, which restricts the venous return; or collateral circulation may develop.6,8 Jugular vein thrombophlebitis is encountered relatively frequently in equine practice and develops secondary to IV injection or, commonly, after gastrointestinal diseases and other debilitating conditions. Impaired venous drainage of the head and neck, particularly when bilateral, is suspected to limit athletic performance; thus, the objective of the study reported here was to evaluate the impact of jugular vein thrombophlebitis on the athletic performance of horses.

Materials and Methods

Case selection—Medical records of horses with jugular vein thrombophlebitis examined at the Veterinary Medical Teaching Hospital of the Université de Montréal between 1988 and 2005 were reviewed. Horses with phlebitis, periphlebitis, or subcutaneous abscesses were excluded.

Jugular vein thrombophlebitis was diagnosed clinically or via ultrasonographic examination. A clinical diagnosis of jugular vein thrombophlebitis was made on the basis of an indurated (hard and cord-like) jugular vein and variable degrees of swelling, heat, signs of pain, and a decrease in blood flow. Congestion of the facial veins, facial edema, and abscesses were also recorded. Ultrasonographic findings of thrombophlebitis included a dilated and incompressible vein, no increase in intraluminal volume of the vein after applying gentle compression at the base of the jugular furrow, a thickening of the vessel wall indicative of phlebitis, and intraluminal echoic or hyperechoic material suggestive of a thrombus, with or without hypoechoic areas in the lumen of the vein that partially or completely occluded the vessel.7,8

Medical record review—Data obtained from medical records included signalment, the jugular vein or veins affected, clinical signs associated with thrombophlebitis, ongoing disease processes, history of catheterization of a jugular vein or veins, hematologic abnormalities, ultrasonographic findings, and treatment.

At our hospital, 2 types of catheters were used in the jugular veins of horses. An over-the-needle polypropylene cathetera was used as a short-term catheter; these catheters were allowed to remain in place for up to 48 hours before they were removed or replaced. For long-term treatment, an over-the-wire polyurethane catheterb was used. These catheters were removed only when there was a suspected problem or when they were no longer needed. All catheters were monitored every 6 hours or more frequently; catheters were removed as soon as a problem was suspected. Once thrombophlebitis developed, the affected vein ceased to be manipulated, catheterized, or punctured for blood collection or IV injection.

Horses were assigned to 1 of 2 groups. Group 1 consisted of horses with thrombophlebitis at the time of admission to our veterinary hospital. Group 2 consisted of horses that developed thrombophlebitis while hospitalized for treatment of a primary medical condition.

Ultrasonographic results were obtained from the records. Size of the thrombus, degree of obstruction (partial or complete) of the vein, and echogenicity were recorded. Doppler ultrasonography (when performed) served to detect flow changes secondary to the thrombus and was used to determine the percentage of occlusion of the vein.9 The side affected and whether the thrombophlebitis was unilateral or bilateral were also recorded.

Performance evaluation—Performances were subjectively evaluated through the use of a questionnaire (mailed or completed via telephone conversation) by the owner or trainer after a horse was discharged from the hospital. This information was obtained during 2006. Owners and trainers were asked to compare the athletic performance of the horse after the episode of thrombophlebitis with that before thrombophlebitis (performance was assessed as better, the same, or worse).

Racing records were obtained from Standardbred Canada. Mean race time before and after an episode of thrombophlebitis, interval from the end of hospitalization to the first race, and the number of races before and after thrombophlebitis were analyzed. The mean of 15 race times both before and after thrombophlebitis was compared. Racing performance was considered decreased when the mean race time after thrombophlebitis was increased by > 1 second.

Statistical analysis—Associations between group, side of the affected jugular vein, and use of antimicrobials or aspirin with performance were evaluated by use of the exact χ2 test. A nonparametric Wilcoxon signed rank test was used to compare the mean racing time before and after thrombophlebitis. Breed distribution of horses with jugular vein thrombophlebitis was compared with that of the general hospital population during the study period by use of a goodness-of-fit χ2 test. All statistical tests were conducted with a commercially available program.c For all statistical tests, significance was set at P < 0.05.

Results

Sample population—Review of the medical records identified 120 horses with jugular vein thrombosis or a similar condition. Ninety-one horses met the inclusion criteria and were included in the study. Twenty-six horses (11 with periphlebitis, 10 with phlebitis, 3 with subcutaneous abscesses, and 2 with a hematoma) were excluded because they did not have evidence of venous thrombosis. Three other horses were excluded because their medical records were incomplete.

Of the 91 horses included, there were 47 (52%) Standardbreds, 16 (18%) Quarter Horses or Paint Horses, 7 (8%) draft horses, 6 (7%) ponies, 3 (3%) Trakehners, 3 (3%) warmblood-type horses, 2 (2%) Arabians, 2 (2%) Thoroughbreds, and 1 (2%) horse for each of 5 other breeds. The distribution differed significantly (P < 0.001) from that of the general hospital population, with ponies being overrepresented in groups 1 and 2. Standardbred was the predominant breed of horses in group 1.

Age of horses at the time of admission ranged from 1 day to 17 years (mean, 5 years; median, 3 years). Affected horses included 44 (48%) females, 26 (29%) sexually intact males, and 21 (23%) geldings. Racehorses (n = 50 [55%]) included 47 Standardbreds and 3 racing ponies. Nonracing horses (n = 41 [45%]) were used for pleasure riding (17 [19%]), western riding (10 [11%]), jumping (6 [7%]), dressage (3 [3%]), driving competitions (3 [3%]), and pulling competitions (2 [2%]).

Group 1—Thirty-seven (41%) horses had thrombophlebitis at the time of admission; 26 (70%) were racing Standardbreds and racing ponies. Fifteen (41%) horses were brought to our veterinary hospital for evaluation of thrombophlebitis, 9 (24%) because of exercise intolerance, and 13 (35%) for various medical problems, which included diarrhea (4 [10%]), fever (4 [11%]), edema of the head (3 [8%]), dysphagia (1 [3%]), and weight loss (1 [3%]).

Thrombophlebitis was the only medical problem identified in the 9 horses examined because of exercise intolerance. Ancillary tests used to rule out other causes for exercise intolerance included CBCs and serum biochemical analyses (n = 8 horses), endoscopy of the upper airways (ie, nasal cavities, pharynx, and larynx; 9), thoracic radiography (5), evaluation of bronchoalveolar lavage fluid (6), ECG (3), and treadmill exercise tests (3).

In 22 (59%) horses, thrombophlebitis had not been noticed by the horse's owner prior to admission to our veterinary hospital. Four horses had no history of IV injections. However, 33 (89%) horses in group 1 had a history of IV injections, which included NSAIDs (7 [21%]), vitamins (3 [9%]), iron (2 [6%]), fluids (2 [6%]), or other unspecified agents (19 [58%]).

Group 2—Fifty-four (59%) horses (21 [39%] of which were Standardbreds) developed thrombophlebitis while hospitalized for treatment of a primary medical condition (Table 1). Colic, diarrhea, and neonatal diseases (primarily septicemia and prematurity) were the conditions most commonly associated with the development of thrombophlebitis. Hypoproteinemia was detected in 25 (46%) horses. Endotoxemia was suspected in 20 (37%) horses on the basis of clinical signs compatible with the condition (eg, lethargy, tachycardia, fever, and congested mucous membranes) in horses with a primary gastrointestinal condition (eg, colic, colitis, or diarrhea) and neutropenia. Thrombophlebitis was associated with short-term polypropylene and long-term polyurethane catheters (27 [50%] and 19 [35%] horses, respectively); the catheter type at the time of thrombophlebitis development was not recorded in 8 (15%) horses. Polypropylene catheters had been in a jugular vein for 1 to 2.5 days (mean, 1.8 days) and polyurethane cathers had been in a jugular vein for 3 to 12 days (mean, 6 days) when thrombophlebitis was diagnosed.

Table 1—

Primary medical conditions in horses that developed jugular vein thrombophlebitis while hospitalized for treatment of a primary medical condition (group 2).

Primary conditionNo. (%) of horses
Diarrhea19 (35)
Colic12 (22)
Neonatal diseases11 (20)
   Septicemia8
   Prematurity4
   Pneumonia3
   Diarrhea1
   Bladder rupture2
Respiratory diseases6 (11)
   Pleuropneumonia4
   Lung abscess2
Abortion2 (4)
Myonecrosis1 (2)
Weight loss1 (2)
Elective surgeries2 (4)
Total54 (100)

Clinical data and ultrasonography—Clinical signs associated with thrombophlebitis were summarized (Table 2). Of the 91 horses with thrombophlebitis, only 1 jugular vein was affected in 62 (68%; 21 [34%] affected the right jugular vein, and 41 [66%] affected the left jugular vein). Thrombophlebitis was bilateral in 29 (32%) horses. In group 1, 29 of 37 (78%) horses had unilateral thrombophlebitis, whereas 33 of 54 (61%) horses in group 2 had unilateral thrombophlebitis.

Table 2—

Clinical signs associated with jugular vein thrombophlebitis in horses at the time of admission to a veterinary medical teaching hospital (group 1; 37 horses) and horses that developed jugular vein thrombophlebitis while hospitalized for treatment of a primary medical condition (group 2; 54 horses).

Clinical signGroup 1Group 2Total
Indurated vein20 (54)27 (50)47 (52)
Indurated catheter siteNA15 (28)15 (16)
Swelling7 (19)6 (11)13 (14)
Impaired blood flow6 (16)11 (20)17 (19)
Subcutaneous abscess10 (27)7 (13)17 (19)
Congestion of facial veins6 (16)0 (0)6 (7)
Facial edema4 (11)4 (7)8 (9)
Signs of pain5 (13)4 (7)9 (10)
Heat2 (5)5 (9)7 (8)
Fever5 (13)9 (17)14 (15)
Laryngeal hemiplegia1 (3)0 (0)1 (1)
Difficulty swallowing1 (3)0 (0)1 (1)

Values reported are number (%) of horses. Within columns, values total to > 37 (100%) horses (group 1), > 54 (100%) horses (group 2), and > 91 (100%) horses (total) because some horses had > 1 clinical sign.

NA = Not applicable.

Ultrasonographic findings were available for 73 (80%) horses. Thrombosis affected the entire length of the vein in 15 horses, whereas a third of the vein (or less) was thrombosed in 19 horses and two-thirds of the jugular vein was affected in 7 horses. Extent of the thrombus was not recorded for the remaining 32 horses. The degree of luminal obstruction was reported in 57 horses (32 horses had partial luminal obstruction of the vein, and 25 horses had complete luminal obstruction). Hyperechoic and hypoechoic areas in the thrombus, which were suggestive of infection, were reported for 7 and 3 horses, respectively.

Hematologic examination—Neutrophilia (n = 13 [35%] horses), hyperfibrinogenemia (6 [16%]), hypoproteinemia (6 [16%]), hyperproteinemia (5 [14%]), anemia (2 [5%]), and neutropenia (2 [5%]) were detected in horses of group 1. For group 2, neutropenia (n = 25 [46%] horses), neutrophilia (24 [44%]), hypoproteinemia (20 [37%[), hyperfibrinogenemia (15 [28%]), and hyperproteinemia (3 [6%]) were detected.

Treatment—Treatments administered for thrombophlebitis were summarized (Table 3). The underlying diseases were treated on a case-by-case basis by the attending clinician. Ten (11%) horses died or were euthanized because of the severity of the ongoing primary disease (eg, pleuropneumonia, septicemia, or myonecrosis), and 2 (2%) horses died of unrelated causes after being discharged from the hospital.

Table 3—

Treatment of horses with jugular vein thrombophlebitis at the time of admission (group 1; 37 horses) and horses that developed jugular vein thrombophlebitis while hospitalized for treatment of a primary medical condition (group 2; 54 horses).

TreatmentGroup 1Group 2Total
DiarrheaColicOthers
Antimicrobials21 (57)16 (84)9 (75)10 (43)56 (61)
Aspirin*17 (46)16 (84)9 (75)10 (43)52 (57)
Other NSAIDs3 (8)10 (53)4 (33)0 (0)14 (15)
Heparin2 (5)0 (0)0 (0)0 (0)2 (2)
Dimethyl sulfoxide2 (5)0 (0)0 (0)0 (0)2 (2)
Poultice5 (13)0 (0)0 (0)0 (0)5 (5)
Hydrotherapy3 (8)0 (0)0 (0)0 (0)3 (3)
Flush abscess7 (19)0 (0)0 (0)0 (0)7 (8)
No treatment13 (35)3 (16)0 (0)3 (13)19 (21)

Values reported are number (%) of horses. Within columns, values total to > 37 (100%) horses (group 1), > 54 (100%) horses (group 2), and > 91 (100%) horses (total) because some horses received > 1 treatment.

Aspirin was administered at a dosage of 17 mg/kg (7.7 mg/lb), PO, q 48 h.

Flunixin meglumine was administered at a dosage of 1.1 mg/kg (0.5 mg/lb), IV or PO, q 12 h, and phenylbutazone was administered at a dosage of 2.2 mg/kg (1.0 mg/lb), IV or PO, q 12 h.

Performance outcome determined from questionnaires—Twenty-seven of 81 (33%) owners contacted responded to questions about performance. Time elapsed between discharge of the horse from the hospital and the owner's response ranged from 4 months to 14 years (median, 5 years). A subjective assessment of the athletic performance outcome was available for 7 of 47 (15%) racing Standardbreds, 10 of 17 (59%) horses used for pleasure riding, and 7 of 26 (27%) horses used in other performance events. Three horses had died (mean time after discharge from the hospital was not known). Sixteen of 17 (94%) owners of nonracing horses (eg, used for shows and competitions, western riding, dressage, jumping, or pleasure riding) considered that the performance of their horse had not been decreased by the thrombophlebitis and met their expectations.

Performance outcome from racing records—No racing records were available for 10 Standardbreds (6 were registered at Standardbred Canada but never raced, and 4 were not registered), and 6 Standardbreds had died during hospitalization as a result of the severity of the primary disease. Data for these horses were not used for performance analyses. In addition, racing data were not available for the 3 racing ponies. Thus, racing records from 31 horses were used.

Age of the 31 racehorses ranged from 1 day to 10 years (mean, 5 years; median, 4 years). Twenty-six of the 31 (84%) horses raced after the episode of thrombophlebitis. Twenty-one horses had recorded race times for before and after thrombophlebitis. In these, there was no significant (P = 0.08) difference between the median race time recorded before (121 seconds; mean ± SD, 121.0 ± 4.9 seconds) and after (121 seconds; mean, 120.8 ± 4.2 seconds) thrombophlebitis, irrespective of whether the horses were examined because of exercise intolerance or another reason. Seventeen of the 21 (81%) horses that resumed racing had equal or better performances, with 6 of them having better race times after thrombophlebitis (decrease in race time of 2 to 4 seconds). Elapsed time between the end of hospitalization and the first race ranged from 4 days to 3 years (mean, 9 months; median, 4 months). Of the 5 horses treated for thrombophlebitis as foals, only 2 subsequently had race times (1 died, 1 was not recorded in the Standardbred Canada database, and 1 was registered but never raced).

Influence of reason for examination on performance—When considering both methods of evaluation (owner or trainer perception of performance and data from the racing records), performances of 48 horses (31 racehorses and 17 nonracing horses) could be assessed. This represented 22 horses (19 racehorses and 3 nonracing horses) and 26 horses (12 racehorses and 14 nonracing horses) of groups 1 and 2, respectively. Overall, horses that developed thrombophlebitis when hospitalized (group 2) had significantly (P = 0.47) better athletic performance than those with thrombophlebitis at the time of admission (group 1). Indeed, 14 of 22 (64%) horses in group 1 had performances after thrombophlebitis similar to or better than those before thrombophlebitis, compared with 22 of 26 (85%) horses in group 2 with similar or better performances after thrombophlebitis. However, there was not a significant (P = 0.66) difference in athletic performances on the basis of race times between the 2 groups when only racehorses were considered because 12 of 19 racehorses in group 1 and 8 of 12 racehorses in group 2 raced at an equivalent or faster speed after thrombophlebitis.

Influence of primary disease, ultrasonographic findings, or treatment on performance—We did not detect a significant (P = 0.18) association between performance and type of primary disease (eg, colic, diarrhea, neonatal diseases, or respiratory disease) for group 2 horses. Similarly, we did not detect a significant association between performance and whether thrombophlebitis was unilateral or bilateral (P = 0.86), use of antimicrobials (P = 1.00), degree of luminal obstruction of the vein (P = 0.50), or aspirin administration (P = 1.00).

Discussion

Results of the study reported here suggested that thrombophlebitis did not affect athletic performances of horses used for pleasure riding and other nonracing activities. Similarly, racing performance was only slightly negatively affected because 26 of 31 (84%) horses raced again after developing thrombophlebitis. However, those that resumed racing performed adequately as indicated by the mean race times before and after thrombophlebitis. When both likelihood of racing and performances were evaluated concurrently, only 17 of 26 (65%) Standardbreds treated performed at the same level after thrombophlebitis as before thrombophlebitis; however, the relative contribution of thrombophlebitis and concurrent medical conditions to the racing performance in these horses could not be assessed. Although these results provide novel information regarding the athletic performance of horses with thrombophlebitis, they must be interpreted cautiously because of the relatively small sample size (n = 31 horses).

Thrombophlebitis may possibly decrease the performance of horses because of pain, impaired venous drainage of the head that leads to brain congestion or edema and impaired thermoregulation, or congestion or edema of the nasal, pharyngeal, or laryngeal mucosa that causes airway obstruction and airflow limitations. These factors are more likely to cause problems during intense exercise and thus could have explained the better performance of nonracing horses. Also, the methods used for performance comparison in this study differed between the 2 groups of horses because performance of nonracing horses was determined by the subjective assessment of the owners or trainers, whereas the assessment of racing performance was objective and based on racing records. The assessment of performance for nonracing horses was based on each owner's or trainer's subjective evaluations because of a lack of better methods. Moreover, time elapsed between discharge of the horse and the study may have led to recall bias for some horses. The finding that the performances of nonracing horses were not affected by thrombophlebitis was not surprising but must be interpreted cautiously because it was possible that only satisfied owners or trainers responded to the questionnaire and because of the low number of nonracing horses. Nevertheless, the intensity of work required by nonracing horses was small, compared with that of racehorses, because only a few of the nonracing horses were involved in highly competitive activities.

Possible biases of the use of race times to evaluate performance include variability attributable to age of the horses, whether the horse was a pacer or trotter, conditions related to climatic conditions for the racetracks, or other causes of a decrease in performance. To overcome these limits, each horse served as its own control animal and the mean of 15 racing times both before and after thrombophlebitis was used to assess racing performance. In this study, age effects may have biased our results because horses generally raced faster during their second and third year of racing than during their first year. However, most of the horses in our study were in the second or third year of racing (median age, 4 years) when thrombophlebitis was diagnosed, and most of them returned to racing within a median of 4 months after discharge. Finally, performance assessments were limited to the 15 races before and the 15 races after thrombophlebitis to limit a potential additional time effect.

In this study, jugular vein thrombophlebitis was believed to be secondary to IV injection or a complication of catheterization of a jugular vein associated with an underlying disease. Intravenous injections may cause jugular vein thrombosis as a result of perivenous drug administrations or direct endothelial damage attributable to trauma or injection of irritant drugs.1,5 The predominance of Standardbred and racing ponies in group 1 was expected because medications are commonly administered via the IV route. The overrepresentation of ponies used for pleasure riding in our general hospital population was unclear; however, sick ponies often receive dextrose-containing fluids to prevent or treat hyperlipemia. Dextrose administration could have contributed to thrombophlebitis because of hyperosmolarity-induced endothelial damage.

In agreement with findings in horses of other studies,1,4,10–12 a catheter was present in most of the horses at the time thrombophlebitis developed in hospitalized horses. The catheter acts as the nidus for clot formation, and a fibrin sheath begins to form at the site of entry within 30 minutes after catheter placement. Additionally, the catheter tip may cause endothelial damage and disrupt venous flow, which further increases clot formation.12 Several factors, such as catheter material, catheter length, type of fluid (commercially available vs locally produced), catheter placement technique, and amount of time the catheter remains in a vein,4,10,13 may increase the risks of thrombophlebitis. However, the primary disease, rather than the catheter, appears to be the most important factor for development of jugular vein thrombosis.3,4,6 Horses with diseases associated with hypercoagulable states, such as colic, protein-losing diseases, sepsis, fever, and diarrhea, are prone to develop complications associated with a venous catheter.1,3,4,13 In agreement with results of another study,4 clinical signs suggestive of endotoxemia and hypoproteinemia were common in horses of our study that developed thrombophlebitis while hospitalized. Loss of anticoagulant proteins (such as antithrombin III, protein C, and protein S) concurrent with loss of other plasma proteins may contribute to the hypercoagulable state, whereas endotoxins contribute to endothelial cell damage and the initiation of the intrinsic and extrinsic coagulation pathways.4 Lower head carriage in debilitated horses reduces blood flow to the jugular veins and may also promote thrombus formation.

Horses that developed thrombophlebitis while hospitalized had significantly better performances than those of horses with thrombophlebitis at the time of admission. However, there were no differences between groups when only racehorses were compared, which indicated that the horse population (subset of horses with thrombophlebitis and exercise intolerance), rather than the initiating cause of thrombophlebitis, contributed to these differences. Surprisingly, there were no significant differences in performance between horses with unilateral or bilateral thrombophlebitis. Recanalization of the veins or development of collateral circulation may have allowed adequate venous drainage of the head. It would have been interesting to monitor the clinical and ultrasonographic outcome of jugular veins in this study and to correlate that data with athletic performance. Unfortunately, little information was provided by owners about progression of clinical signs, and too few horses were returned for reevaluation at our veterinary hospital to provide sufficient clinical and ultrasonographic follow-up data.

In horses, complications associated with thrombophlebitis include pleuropneumonia, bacterial endocarditis, pulmonary thromboembolism, septicemia, and other conditions associated with metastasis of septic thrombi.6,7,10,14–16 Interestingly, none of these complications were recognized in the horses of the study reported here.

Treatments used for horses with thrombophlebitis in this study (antimicrobials, aspirin, or both) had no impact on subsequent athletic performance. In general, antimicrobials were used when septic thrombophlebitis was suspected (as determined on the basis of clinical, hematologic, and ultrasonographic findings; 56/91 [62%] horses). However, in most horses, the infectious process was not confirmed, although abscesses formed in 17 (19%) horses. Thus, it was likely that the number of infectious thrombi was overestimated. Alternatively, the process may have been self-limiting, or the antimicrobials did not penetrate the thrombus and influence the outcome.

Similarly, administration of aspirin, an inhibitor of platelet function, had no effect on performance. Because platelets are important early in thrombus formation, administration of aspirin once thrombosis is established may not be an effective treatment. Moreover, platelets play a greater role in the formation of arterial thrombi than they do in venous thrombi.17 Finally, absorption of aspirin may be erratic in horses with gastrointestinal disease, and its efficacy in inhibiting endotoxin-enhanced platelet aggregation has been questioned.2,9,18

Results of this retrospective case series suggested that the athletic capacity of horses used for nonracing activities was not affected by thrombophlebitis, even when the horses had bilateral thrombophlebitis. However, thrombophlebitis in racing Standardbreds was associated with a decreased chance of return to racing. For those that resumed racing, performance was not impaired.

a.

NB Angiocath, 14 gauge, Becton Dickinson Infusion Therapy Systems Inc, Sandy, Utah.

b.

Arrow, 14 gauge, Arrow International Inc, Reading, Pa.

c.

SAS, version 9.1, SAS Institute Inc, Cary, NC.

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    Bayly WM, Vale BH. Intravenous catheterization and associated problems in the horse. Compend Contin Educ Pract Vet 1982;4:S227S237.

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    Spurlock SL, Spurlock GH. Risk factors of catheter related complications. Compend Contin Educ Pract Vet 1990;12:241245.

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    Traub-Dargatz JL, Dargatz DA. A retrospective study of vein thrombosis in horses treated with intravenous fluids in a veterinary teaching hospital. J Vet Intern Med 1994;8:264266.

    • Crossref
    • Search Google Scholar
    • Export Citation
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    Ryu SH, Kim JG, Bak UB, et al. A hematogenic pleuropneumonia caused by postoperative septic thrombophlebitis in a Thoroughbred gelding. J Vet Sci 2004;5:7577.

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    • Search Google Scholar
    • Export Citation
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    Deem DA. Complications associated with the use of intravenous catheters in large animals. Calif Vet 1981;6:1924.

  • 16.

    Norman TE, Chaffin MK, Perris EE, et al. Massive pulmonary thromboembolism in six horses. Equine Vet J 2008;40:514517.

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    Cambridge H, Lees P, Hooke RE, et al. Antithrombotic actions of aspirin in the horse. Equine Vet J 1991;23:123127.

  • 18.

    Jarvis GE, Evans RJ. Platelet-activating factor and not thromboxane A2 is an important mediator of endotoxin-induced platelet aggregation in equine heparinised whole blood in vitro. Blood Coagul Fibrinolysis 1996;7:194198.

    • Crossref
    • Search Google Scholar
    • Export Citation

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