Evaluation of an in-shoe pressure measurement system in horses

OBJECTIVE: To develop an objective, accurate method for quantifying forelimb ground reaction forces in horses by adapting a human in-shoe pressure measurement system and determine the reliability of the system for shod and unshod horses. ANIMALS: 6 adult Thoroughbreds. PROCEDURE: Horses were instrumented with a human in-shoe pressure measurement system and evaluated at a trot (3 m/s) on a motorized treadmill. Maximum force, stance time, and peak contact area were evaluated for shod and unshod horses. Three trials were performed for shod and unshod horses, and differences in the measured values were examined with a mixed model ANOVA for repeated measures. Sensor accuracy was evaluated by correlating measured variables to clinically observed lameness and by a variance component analysis. RESULTS: 4 of 6 horses were determined to be lame in a forelimb on the basis of clinical examination and measured values from the system. No significant differences were observed between shod and unshod horses for maximum force and stance time. A significant decrease in peak contact area was observed for shod and unshod horses at each successive trial. Maximum force measurements provided the highest correlation for detecting lameness (r = 0.91, shod horses; r = 1.0, unshod horses). A variance component analysis revealed that 3 trials provided a variance of 35.35 kg for maximum force (+/- 5.78% accuracy), 0.007 seconds for stance time (+/- 2.5% accuracy), and 8.58 cm2 for peak contact area (+/- 11.95% accuracy). CONCLUSIONS AND CLINICAL RELEVANCE: The in-shoe pressure measurement system provides an accurate, objective, and effective method to evaluate lameness in horses.     

Repeatability, reproducibility, and effect of head position on central venous pressure measurement in standing adult horses

Background: Central venous pressure (CVP) is a used as an estimation of intravascular volume status in various species. Techniques for measuring CVP in horses have been described, but the repeatability of these readings at a single time point or over time has not been established. Hypothesis: That CVP measurements in healthy adult horses would be repeatable at each time point, that these readings would be reproducible over time, and that alteration in head position relative to the heart would alter CVP. Animals: Ten healthy adult research horses. Methods: In an experimental study, horses were instrumented with a central venous catheter. Readings were taken in triplicate q6h for 2 days by water manometry, and twice daily with the head in neutral, elevated, and lowered positions by electronic manometry. Results: Variation in the “neutral” measurements obtained at each time point was <0.1 ± 1.0 cmH₂O (P= .718). There was a significant decrease in CVP over time (P= .015), which was eliminated when results were controlled for acute decrease in body weight of ?1.35% (presumed hypohydration because of lack of acclimatization and decreased water intake). Head height had a significant and directional effect on CVP in that the elevated head position decreased CVP ?2.0 ± 6.5 cmH₂O (P < .001) while the lowered head position increased CVP by 3.7 ± 5.5 cmH₂O (P < .001). Conclusions and Clinical Importance: CVP values obtained by water manometry were repeatable in adult horses, but were reproducible only when controlled for changes in hydration. Care should be taken to maintain consistency in head position to prevent erroneous readings.     

A technique for central venous pressure measurement in normal horses

Objective – To investigate a technique of central venous pressure (CVP) measurement using a newly developed catheter in healthy adult horses. Design – Prospective experimental study. Setting – University research facility. Animals – Twenty healthy adult horses. Interventions – An equine central venous catheter was inserted into the jugular vein to a length of approximately 80 cm from the mid‐cervical region in an attempt to catheterize the pulmonary artery. Pulmonary arterial catheterization was confirmed by echocardiography. Insertion distance and pressure were measured at this location with a disposable manometer. The catheter was then withdrawn until presence in the right atrium was confirmed by echocardiography. Insertion distance and pressure were also measured at this location. The catheter was then withdrawn in 5 cm increments until exiting the jugular insertion site with pressure measured at each location. All pressure measurements were taken with the manometer zero position at the point of the shoulder. Measurements and Main Results – Pulmonary artery catheterization was successful in 16 of 20 horses. Mean pulmonary arterial pressure was 23.8 cm H₂O (17.5 mm Hg) (95% confidence interval [CI] 20.9–26.7 cm H₂O [15.4–19.6 mm Hg]). Mean right atrial pressure was 8.3 cm H₂O (6.1 mm Hg) (95% CI 7.1–9.4 cm H₂O [5.2–6.9 mm Hg]). Right atrial pressure was compared with pressures recorded at sequential insertion distances and resulted in a recommendation for catheter insertion of at least 40 cm for CVP measurement in adult horses. Jugular venous pressure measurement was statistically different from CVP measurement. Conclusions – This catheter measurement technique is well tolerated in normal horses. Routine clinical use of this equine central venous catheter may improve our ability to monitor patients and improve patient care and outcomes of ill horses in hospital.     

Papers and articles measurement of central venous pressure in horses.

Central venous pressure measurements were made in 74 horses and ponies free from clinical evidence of cardiopulmonary disease. Using the sternal manubrium as the zero reference point, the mean value obtained was 12 cm H2O (S.D. +/- 6). There was a significant correlation with body weight (r=0.6, p less than 0.001) but there was none with age, sex, breed or type. During halothane anaesthesia, using the same reference point, the mean value was 24.5 cm H2O (S.D. +/- 6) in 28 animals in right lateral recumbency, 29 cm H2O (S.D. +/- 8) in 17 animals in left lateral recumbency and -6 cm H20 (S.D. +/- 4) IN 27 supine animals. The use of the sternal manubrium as zero reference point did not allow comparison of values in standing and recumbent animals and it was considered that serial measurements were of more value than isolated determinations in assessing the circulatory state of an animal.     

Comparison of water manometry to 2 commercial electronic pressure monitors for central venous pressure measurement in horses

Background: Central venous pressure (CVP) customarily has been measured in veterinary patients with water manometry. However, many institutions are now using stallside electronic monitors in both anesthesia and intensive care units for many aspects of patient monitoring. Hypothesis: Electronic stall side monitoring devices will agree with water manometry for measurement of CVP in horses. Animals: Ten healthy adult horses from the university research herd. Methods: Central venous catheters were placed routinely, and measurements were obtained in triplicate with each of the 3 methods every 12 hours for 3 days. Data were analyzed by a Lin concordance correlation coefficient and modified Bland‐Altman limits of agreement, with all devices compared pairwise. Results: Compared with water manometry, agreement (bias) of the Passport was ?1.94 cmH₂O (95% limits of agreement, ?8.54 to 4.66 cmH₂O) and of the Medtronic was ?1.83 cmH₂O (95% limits of agreement, ?8.60 to 4.94 cmH₂O). When compared with the Passport, agreement of the data obtained with the Medtronic was 0.27 cmH₂O (95% limits of agreement, ?4.39 to 4.93 cmH₂O). Conclusions and Clinical Importance: These data show that both electronic monitors systematically provide measurements that are approximately 2 cmH₂O lower than water manometry, but differences between the 2 electronic devices are small enough (< 0.5 cmH₂O) to be considered clinically unimportant. This discrepancy should be taken into account when interpreting data obtained with these monitoring devices.     

The effects of hypohydration on central venous pressure and splenic volume in adult horses

Background: Central venous pressure (CVP) is used in many species to monitor right‐sided intravascular volume status, especially in critical care medicine. Hypothesis: That hypohydration in adult horses is associated with a proportional reduction in CVP. Animals: Ten healthy adult horses from the university teaching herd. Methods: In this experimental study, horses underwent central venous catheter placement and CVP readings were obtained by water manometry. The horses were then deprived of water and administered furosemide (1 mg/kg IV q6h) for up to 36 hours. Weight, CVP, vital signs, PCV, total protein (TP), and serum lactate were monitored at baseline and every 6 hours until a target of 5% decrease in body weight loss was achieved. The spleen volume was estimated sonographically at baseline and peak volume depletion. Linear regression analysis was used to assess the association of CVP and other clinical parameters with degree of body weight loss over time. Results: There was a significant association between CVP and decline in body weight (P < .001), with a decrease in CVP of 2.2 cmH₂O for every percentage point decrease in body weight. Other significant associations between volume depletion and parameters measured included increased TP (P= .007), increased serum lactate concentration (P= .048), and decreased splenic volume (P= .046). There was no significant association between CVP and vital signs or PCV. Conclusions and Clinical Importance: These findings suggest that CVP monitoring might be a useful addition to the clinical evaluation of hydration status in adult horses.     

Septic arthritis in adult horses

Septic arthritis in horses is a serious disease which can become life-threatening. In case the infection can be eliminated before irreversible joint damage occurs, complete recovery is possible. This article gives an overview of the literature concerning etiology, diagnosis and strategies of therapy in cases of septic arthritis in adult horses, with special reference to novel options of treatment.     

Pharmacokinetics of acyclovir in adult horses

Objective: To determine the pharmacokinetics of acyclovir administered intravenously (IV) and orally to healthy adult horses. Design: Random cross‐over with an approximate 1‐week washout period between trials. Setting: University veterinary medical teaching hospital. Animals: Six healthy adult research herd horses. Interventions and main results: Acyclovir was administered IV (10 mg/kg in 1 L isotonic crystalloid solution over 60 minutes) and orally (20 mg/kg) to healthy adult horses. Plasma samples were obtained and acyclovir concentrations were determined by high‐pressure liquid chromatography. Peak concentration (mean±SD) for IV acyclovir was 13.74±5.88 μg/mL at the completion of the 1‐hour infusion. The half‐life of the distribution phase (α) was 0.16 hours while the half‐life of the elimination phase (β) was 9.6 hours. The steady‐state volume of distribution was 3.93±1.21 L/kg. We were unable to measure pharmacokinetics after PO acyclovir as plasma concentrations were below the lower limits of detection in all 6 horses. Conclusions: IV administration of acyclovir to healthy adult horses achieves concentrations within the sensitivity range described for equine herpes virus‐type 1. The oral bioavailability of acyclovir in horses is low and additional studies are required.     

Development of a neurosurgical operating table for adult cattle and changes in intracranial pressure and blood pressure in adult cattle undergoing long-time isoflurane anesthesia

We developed a neurosurgical operating table for restraining adult cattle in the sternal recumbent position during long-time inhalation anesthesia, and examined intracranial pressure (ICP), blood pressure and blood gases during isoflurane anesthesia. We confirmed that the maintenance of inhalation anesthesia, the restraint of cattle in the sternal recumbent position and bringing the cattle out of anesthesia could all be carried out safely using the operating table we produced. For the purposes of the present experiment, the cattle were divided into 2 groups: the SR group, which underwent sternal recumbency for 8 hr under isoflurane anesthesia using the neurosurgical operating table, and the RR group, which underwent right lateral recumbency for 3 hr under isoflurane anesthesia on a standard operating table. The mean ICP was found to be significantly lower in the SR group than in the RR group during anesthesia, and PaO2 was significantly higher in the SR group. In the SR group, no complications such as regurgitation or ruminal tympany occurred for 8 hr after the induction of anesthesia, and recovery from anesthesia was uneventful. In contrast, all RR cattle showed ruminal tympany and regurgitated ruminal fluid at 3 hr after the induction of anesthesia. Thus, the neurosurgical operating table developed in the present study may be useful for long-time anesthesia and neurosurgery of adult cattle.     

Clinical nutrition of adult horses

Horses suffering from trauma, sepsis, and severe burns need 12% to 16% of protein (dry matter basis) in their diet. Since reduced appetite may be a problem, relatively energy dense (greater than 2 Mcal DE/kg) feeds should be offered. In hepatic failure, maintenance protein requirements (8% on a dry matter basis for adult horses) should be met with feeds that are high in short branched-chain amino acids and arginine but low in aromatic amino acids and tryptophan (for example, milo, corn, soybean, or linseed meal) in addition to grass hay. Vitamins A, C, and E should also be supplemented. In cases with renal failure, protein, calcium, and phosphorus should be restricted to maintenance or lower levels. Grass hay and corn are the best feeds for horses with reduced renal function. Do not offer free-choice salt to horses with dependent edema from uncompensated chronic heart failure. Following gastrointestinal resection, legume hay and grain mixtures are the feeds of choice. Horses with diarrhea should not be deprived or oral or enteral alimentation for prolonged periods of time. Liquid formulas may be used if bulk or gastrointestinal motility are a problem. Apple cider vinegar and a high grain diet may reduce the incidence of enteroliths in horses prone to this problem. Pelleted feeds will reduce fecal volume and produce softer feces for horses that have had rectovaginal lacerations or surgery. Horses with small intestinal dysfunction or resection should be offered low residue diets initially, but long-term maintenance requires diets that promote large intestinal digestion (alfalfa hay, vegetable oil, restricted grain). Geriatric horses (greater than 20 years old need diets similar to those recommended for horses 6 to 18 months old.     

Intra-abdominal hypertension in two adult horses

Objective – To describe the clinical and pathological findings in 2 adult horses with documented increases in intra-abdominal pressure (IAP), and to describe the direct puncture technique used to measure this pressure.
Series Summary – Two adult horses developed increases in IAP secondary to large-volume abdominal effusion. A 9-year-old Quarter Horse cross gelding was presented for evaluation of urinary and neurologic signs. Abdominal ultrasonographic examination showed a hepatic abscess along with abdominal effusion. A 4-year-old Quarter Horse gelding was presented for evaluation of castration complications. A castration site infection extended into surrounding tissues, resulting in peritonitis, abdominal effusion, and severe cellulitis of the limbs. IAP measured in both horses was increased relative to reported equine reference values. Changes in hemodynamic parameters in both horses, notably increased central venous pressure, were consistent with those seen in other species in which intra-abdominal hypertension (IAH) and its sequellae have been documented.
New or Unique Information Provided – Extensive research and clinical literature guides management of humans with IAH and abdominal compartment syndrome. Knowledge of these conditions in companion animal and large domestic species is less well developed. Recent research has established reference values for standing, sedated and recumbent, anesthetized horses. Detailed reports of equine clinical cases of IAH have not been reported in the literature. This report provides information on the clinical, hemodynamic, and pathologic characteristics of 2 horses with measured increases in IAP, and describes the direct puncture technique used to perform these measurements.     

Pharmacokinetics of potassium bromide in adult horses

OBJECTIVE: To determine the pharmacokinetics of potassium bromide (KBr) in horses after a single and multiple oral doses. ANIMALS: Twelve adult Standardbred and Thoroughbred mares. PROCEDURE: Horses were randomly assigned into two treatment groups. In Part 1 of the study, horses were given a single oral dose of 120 mg/kg KBr. Part 2 of the study evaluated a loading dose of 120 mg/kg KBr daily by stomach tube for 5 days, followed by 40 mg/kg daily in feed for 7 days. Serum concentrations of bromide were determined by colorimetric spectrophotometry following drug administration to permit determination of concentration versus time curves from which pharmacokinetic parameters could be calculated. Treated horses were monitored twice daily by clinical examination. Serum concentrations of sodium, potassium and chloride ions and partial pressures of venous blood gases were determined. RESULTS: Maximum mean serum bromide concentration following a single dose of KBr (120 mg/kg) was 284 +/- 15 microg/mL and the mean elimination half-life was 75 +/- 14 h. Repeated administration of a loading dose of KBr (120 mg/kg once daily for 5 days) gave a maximum serum bromide concentration of 1098 +/- 105 microg/mL. The administration of lower, maintenance doses of KBr (40 mg/kg once daily) was associated with decreased serum bromide concentrations, which plateaued at approximately 700 microg/mL. Administration of KBr was associated with significant but transient changes in serum potassium and sodium concentrations, and possible changes in base excess and plasma bicarbonate concentrations. High serum concentrations of bromide were associated with an apparent increase in serum chloride concentrations, when measured on an ion specific electrode. CONCLUSIONS AND CLINICAL RELEVANCE: A loading dose of 120 mg/kg daily over 5 days and maintenance doses of approximately 90-100 mg/kg of KBr administered once daily are predicted to result in serum bromide concentrations consistent with therapeutic efficacy for the management of seizures in other species. The clinical efficacy of this agent as an anticonvulsant medication and/or calmative in horses warrants further investigation.     

Comparison of direct and indirect methods of intra‐abdominal pressure measurement in normal horses

Objectives – To develop a direct method for measuring intra‐abdominal pressures in the standing horse, identify a reference interval for direct intra‐abdominal pressures, compare these pressures to indirect intra‐abdominal pressures measured from the bladder, and determine the optimal bladder infusion volume for indirect pressure measurement. Design – Prospective, experimental study. Setting – A university‐based equine research facility. Animals – Ten healthy adult horses, 5 males and 5 females. Interventions – Direct intra‐abdominal pressures were measured through an intraperitoneal cannula and zeroed at the height midway between the height of the tuber ishii and point of the shoulder. Indirect measurements of intra‐abdominal pressure were performed by measuring intravesicular pressures through a transurethral catheter zeroed at the tuber ishii. Measurements and Main Results – Direct pressure measurements obtained in the standing horse were subatmospheric (mean, ?1.80 cm H₂O; SD, 1.61 cm H₂O; 95% CI, ?2.80 to ?0.80) and were shown to decrease as the horse's weight increased (Pearson's r=?0.67, P=0.04), with no effect of head position (P=0.15). Mean baseline indirect pressure measurements (mean, ?8.63 cm H₂O; SD, 4.37 cm H₂O; 95% CI, ?13.05 to ?4.21) were significantly different from the pressures measured directly from the abdomen (P<0.001). Indirect pressure measurements were noted to increase with increasing volumes infused into the bladder, and were statistically different at a volume of 100 mL (P=0.004). There was low to moderate correlation between direct and indirect pressure measurements of intra‐abdominal pressure over a range of fluid volumes infused into the bladder (Pearson's correlation range ?0.38 to 0.58). Conclusion – Pressures measured directly in the standing horse were subatmospheric, and increased as the horse's weight increased. Indirect pressures measured were altered by increasing volumes infused in the bladder. There was no significant correlation between the 2 methods of intra‐abdominal pressure measurement.     

Disposition of levetiracetam in healthy adult horses

Nine horses received 20 mg/kg of intravenous (LEV_IV ); 30 mg/kg of intragastric, crushed immediate release (LEV_CIR ); and 30 mg/kg of intragastric, crushed extended release (LEV_CER ) levetiracetam, in a three‐way randomized crossover design. Crushed tablets were dissolved in water and administered by nasogastric tube. Serum samples were collected over 48 hr, and levetiracetam concentrations were determined by immunoassay. Mean ± SD peak concentrations for LEV_CIR and LEV_CER were 50.72 ± 10.60 and 53.58 ± 15.94 μg/ml, respectively. The y ‐intercept for IV administration was 64.54 ± 24.99 μg/ml. The terminal half‐life was 6.38 ± 1.97, 7.07 ± 1.93 and 6.22 ± 1.35 hr for LEV_CIR , LEV_{CER ,} and LEV_IV , respectively. Volume of distribution at steady‐state was 630 ± 73.4 ml/kg. Total body clearance after IV administration was 74.40 ± 19.20 ml kg^?1 hr^?1. Bioavailability was 96 ± 10, and 98 ± 13% for LEV_CIR and LEV_CER , respectively. A single dose of Levetiracetam (LEV ) was well tolerated. Based on this study, a recommended dosing regimen of intravenous or oral LEV of 32 mg/kg every 12 hr is likely to achieve and maintain plasma concentrations within the therapeutic range suggested for humans, with optimal kinetics throughout the dosing interval in healthy adult horses. Repeated dosing and pharmacodynamic studies are warranted.     

Pharmacokinetics of potassium bromide in adult horses

OBJECTIVE: To determine the pharmacokinetics of potassium bromide (KBr) in horses after single and multiple oral doses. ANIMALS: Twelve adult Standardbred and Thoroughbred mares. PROCEDURE: Horses were randomly assigned to two treatment groups. Group 1 horses were given a single oral dose of 120 mg/kg potassium bromide. Part 2 of the study evaluated a loading dose of 120 mg/kg KBr daily by stomach tube for 5 days, followed by 40 mg/kg daily in feed for 7 days. Serum concentrations of KBr were measured to construct concentration versus time curves and to calculate pharmacokinetic parameters. Treated horses were monitored twice daily by clinical examination. Serum concentrations of sodium, potassium and chloride ions and partial pressures of venous blood gases were determined. RESULTS: Maximum mean serum concentration following a single dose of KBr (120 mg/kg) was 423 +/- 22 microg/mL and the mean elimination half-life was 75 +/- 14 h. Repeated administration of a loading dose of KBr (120 mg/kg once daily for 5 d) gave a maximum serum concentration 1639 +/- 156 microg/mL. The administration of lower, maintenance doses (40 mg/kg once daily) was associated with decreased serum bromide concentrations, which plateaued at approximately 1000 microg/mL. Administration of KBr was associated with significant but transient changes in serum potassium and sodium concentrations, and possible changes in base excess and plasma bicarbonate concentrations. High serum concentrations of bromide were associated with an apparent increase in serum chloride concentrations, when measured on an ion specific electrode. CONCLUSIONS: and clinical relevance Loading doses of 120 mg/kg daily over 5 d and maintenance doses of approximately 90 mg/kg of KBr administered once daily resulted in serum bromide concentrations consistent with therapeutic efficacy for the management of seizures in other species. The clinical efficacy of this agent as an anticonvulsant medication and/or calmative in horses warrants further investigation.     

Pharmacokinetics of oral terbinafine in adult horses

The primary study objective was to compare the pharmacokinetics of p.o. terbinafine alone to p.o. terbinafine administered with p.o. cimetidine in healthy adult horses. The second objective was to assess the pharmacokinetics of terbinafine when administered per rectum in two different suspensions at 30 mg/kg to adult horses. Six healthy adult horses were included in this crossover study. Plasma terbinafine concentrations were quantified with liquid chromatography and mass spectrometry. The half‐life (geometric mean) was 8.38 and 10.76 h, for p.o. alone and p.o. with cimetidine, respectively. The mean maximum plasma concentrations were 0.291 μg/mL at 1.54 h and 0.418 μg/mL at 1.28 h for p.o. alone and p.o. with cimetidine, respectively. Terbinafine with cimetidine had an average C_MAX 44% higher and the relative F was 153% compared p.o. terbinafine alone, but was not statistically different (P > 0.05). Terbinafine was infrequently detected when administered per rectum in two different suspensions (water or olive oil). Minor adverse effects included oral irritation, fever, and colic. All resolved spontaneously. More pharmacokinetic studies are indicated assessing drug–drug interactions and using multiple dosing intervals to improve our knowledge of effective oral dosing, the potential for drug accumulation, and systemic adverse effect of terbinafine in horses.     

Pulmonary artery wedge pressure measurement in healthy warmblood horses and in warmblood horses with mitral valve insufficiencies of various degrees during standardised treadmill exercise

In 12 healthy warmblood horses and 10 horses with mitral valve insufficiencies (MVI) of various degrees heart rate and pulmonary artery wedge pressure (PWP) was measured at rest and during standardised exercise on a high speed treadmill. There was a significant increase in PWP with each change in speed of the treadmill (p < 0.01). The PWP of horses with mild mitral valve regurgitation under working conditions was not significantly different compared to the healthy horses. The horses with moderate mitral valve regurgitation showed a significant higher pulmonary artery wedge pressure at rest and during exercise compared to the healthy horses (p < 0.01) at rest and during treadmill velocity. The tendencies were seen that mild mitral valve regurgitation results only in mild hemodynamic changes during exercise, while moderate MVI have an important influence on haemodynamics.