Effect of dose of furosemide on plasma tCO2 changes in standardbred horses

Total Carbon Dioxide (TCO2) Concentrations in Thoroughbred and Quarter Racehorses in Louisiana

The TCO₂ (total carbon dioxide) test is performed on the blood of racehorses as a means of combatting the practice of administering alkalizing agents. This study evaluated serum TCO₂ concentrations and factors influencing concentration of TCO₂ in Thoroughbred and Quarter Horses. The normality of data were evaluated with a Shapiro-Wilk test. Mann-Whitney tests and Kruskal-Wallis tests were used against different effects. When a fixed effect was detected, Dunn's post-hoc comparisons were performed. The median pre-race serum TCO₂ concentration (32.20 mmol/L (interquartile range (IQR): 30.80-33.50)) was higher than that of post-race samples (26.70 mmol/L (IQR: 24.55-29.25)) (P < .0001). The median TCO₂ concentrations in pre-race samples were different between Thoroughbred (32.40 mmol/L (IQR: 30.90-33.60)) and Quarter Horses (31.30 mmol/L (IQR: 30.00-32.50)) (P < .0001). The median pre-race TCO₂ concentrations were 32.75 (IQR: 31.40-33.90), 31.40 (IQR: 29.80-32.80), 32.50 (IQR: 31.20-33.88), and 31.60 (IQR 30.00-32.70) mmol/L in racehorses at Fair Grounds, Louisiana Downs, Delta Downs, and Evangeline Downs racetracks, respectively (P < .0001). The total serum TCO₂ concentrations in Thoroughbred and Quarter Horse racehorses were affected by seasonal temperature variation (P < .0001). A smaller sample size was available for post-race samples (n = 205) and Quarter Horse pre-race samples (n = 351). The results of this study indicated that the breed, seasonal temperature variation, pre-race or post-race sampling, and track location are strongly correlated to total TCO₂ concentrations. It was not clear whether the statistically significant differences in TCO₂ levels among racetracks in Louisiana were due to location of racetracks and/or seasonal temperature variation.

Prerace venous blood gases and acid-base values in Standardbred horses: effects of geography, season, prerace furosemide, gender, age, and trainer using big data analytics

OBJECTIVE

A retrospective study was conducted to establish the prerace venous acid-base and blood gas values of Standardbred horses at rest using big data analytics.

SAMPLES

Venous blood samples (73,382) were collected during seven racing seasons from 3 regional tracks in the Commonwealth of Pennsylvania. Horses were detained 2 hours prior to race time.

PROCEDURES

A mixed-effects linear regression model was used for estimating the marginal model adjusted mean (marginal mean) for all major outcomes. The interaction between age and gender, track, and the interaction between month, treatment (furosemide), and year were the major confounders included in the model. Random effects were set on individual animal nested within trainer. Partial pressure of venous carbon dioxide (PVCO2), partial pressure of oxygen (PVO2), and pH were measured, and base excess (BE), total carbon dioxide (TCO2), and bicarbonate (HCO3-) were calculated.

RESULTS

Significant (P < .001) geographical differences in track locations were seen. Seasonal reductions in acid-base values started in January with significant (P < .001) decreases from adjacent months seen in June, July, and August followed by a gradual return. There were significant increases (P < .001) in BE and TCO2 and decreases in PVO2 with age. Significant differences (P < .001) in acid-base values were seen when comparing genders. A population of trainers were significantly different (P < .001) from the marginal mean and considered outliers.

CLINICAL RELEVANCE

In a population of horses, big data analytics was used to confirm the effects of geography, season, prerace furosemide, gender, age, and trainer influence on blood gases and the acid-base profile.

Total Carbon Dioxide in Adult Standardbred and Thoroughbred Horses

The TCO2 (total carbon dioxide) test is performed on the blood of racehorses as a means of combatting the practice of administering alkalizing agents for the purpose of enhancing performance. The purposes of this review are to present an overview of the factors contributing to TCO2 and to review the literature regarding TCO2 in adult Standardbred and Thoroughbred horses to demonstrate the range of variability of TCO2 in horses. Most of the research published on the topic of TCO2 or bicarbonate measurement in racehorses was accessed and reviewed. PubMed and Google Scholar were the primary search engines used to source the relevant literature. The main physicochemical factors that contribute to changes in TCO2 in horses at rest are changes in strong ions concentration, followed by changes in weak acid (i.e. plasma albumin) concentrations. There is a wide normal distribution of TCO2 in horses ranging from 23 mmol/L to 38 mmol/L. Independent of administration of alkalizing agents, blood TCO2 is affected mainly by feeding, time of day (diurnal variation), season and exercise. There are few studies that have reported hour-by-hour changes in TCO2. Racehorse population studies suffer from lack of validation regarding whether or not a horse was administered an alkalizing agent. It is concluded that the normal range of TCO2 in non-alkalized Standardbred and Thoroughbred horses is significantly wider than has been appreciated, that periods of elevated TCO2 appear to be normal for many horses at rest, and that a TCO2 test alone is not definitive for the purposes of determining of an alkalizing agent has been administered to a horse.

The effect of sodium bicarbonate and validation of beckman coulter AU680 analyzers for measuring total carbon dioxide (TCO2) concentrations in horse serum

This study evaluated the usage of Beckman Coulter AU680 analyzers for measurement of TCO 2 in horse serum, and the effect of sodium bicarbonate administrations on serum TCO 2 levels in resting horses. Treatment of horses with sodium bicarbonate did not result in any adverse events. Mean TCO 2 concentration was significantly higher from 1 to 8 h in the sodium bicarbonate-treated horses compared to the untreated controls. Within an hour, administration of sodium bicarbonate increased the TCO 2 level from 31.5 ± -2.5 (SD) to 34.0 ± 2.65 (SD) mmol/L and at 2-8 h post-administration, the TCO 2 level was above the 36 mmol/L cut-off level. In all quality control analysis of Australian standard by Beckman Coulter AU680 analyzer, the instrument slightly over estimated the TCO 2 level but the values were in close agreement with mean TCO 2 level being 38.03 with ± 0.87 mmol/L (SD). Expanded uncertainty was calculated using different levels of confidence interval. Based on 99.5% confidence interval using 0.805% expanded uncertainty using mean measured concentration of 38.05 mmol/L, it was estimated that any race samples TCO 2 level higher than 38.5 mmol/L will be indicative of sodium bicarbonate administration using Beckman Coulter AU680 analyzer in Louisiana.

Cross Validation of HS-GC/MS to Quantify Total Carbon Dioxide in Horse Plasma

The use of alkinizing agents by trainers to counteract the accumulation of lactic acid in racehorses has been well documented. A by-product of this administration is elevated total carbon dioxide (tCO2) concentrations. Most regulatory authorities have set the threshold for tCO2 in plasma at 37 mM. The quantification of tCO2 often presents a challenge to laboratories due to the instrumentation required, which can be expensive to use and maintain. The Beckman DxC 600 (Brea, CA) is currently used in our laboratory for tCO2 quantification. The goal of this research was to determine if another analytical method could be used for this procedure. We report the use of headspace gas chromatography-mass spectrometry (HS-GC/MS) as an acceptable alternative to the use of the Beckman DxC 600. A six-point calibration curve ranging from 10 to 60 mM was analyzed along with controls at 15, 25 and 45 mM. Imprecision was found to be <3% at all concentrations. Inaccuracy was measured at <4% at all concentrations. Measurement of uncertainty was determined using the Simplified GUM approach and was found to be 3% at 99.7% confidence level with eight measurements at a tCO2 concentration of 45 mM. Furthermore, the HS-GC/MS was cross-validated according to international protocols with all parameters being met. During cross validation, a standard at a known concentration was analyzed by both instruments. The average difference using 25 replicates in calculated concentrations was <0.1 mM. Also, plasma samples from four untreated horses were analyzed by both instruments. The difference in calculated concentrations between the two instruments was <0.6 mM for all horses. The results show that the use of HS-GC/MS is an acceptable alternative to the use of the Beckman DxC 600 for the quantification of tCO2 in horse plasma.

Comparison of two analyzers for measurement of plasma total carbon dioxide concentration in horses

OBJECTIVE

To determine the degree of agreement between 2 analyzers for measurement of total CO₂ concentration (ctCO₂) in equine plasma.

ANIMALS

6 healthy untrained horses, 6 trained Standardbreds undergoing a simulated race protocol, and 135 trained Standardbreds at a racetrack.

PROCEDURES

Jugular venous blood samples were obtained from all horses. Two analyzers (commonly used analyzer A and less expensive analyzer B) were used to measure plasma ctCO₂ in each sample. Validation of both analyzers was conducted in accordance with guidelines established by the Clinical and Laboratory Standards Institute and involved characterization of linearity, total analytic error, and bias estimation.

RESULTS

Total analytic error (instrument SD) was 0.58 mmol/L (coefficient of variation, 1.6%) and 0.49 mmol/L (coefficient of variation, 1.4%) for analyzers A and B, respectively, when measuring an aqueous standard containing 36.0 mmol of CO₂/L. A 1 g/L decrease in plasma protein concentration corresponded to an increase in ctCO₂ measured with analyzer B of 0.065 mmol/L. A difference plot indicated that analyzer B produced values 2.7% higher than analyzer A for 103 samples from the 6 trained and exercised Standardbreds (mean plasma protein concentration, 67 g/L).

CONCLUSIONS AND CLINICAL RELEVANCE

Analyzer B provided adequate precision and linearity for measurement of ctCO₂ from 5 to 40 mmol/L and was therefore suitable for measuring ctCO₂ in equine plasma, provided allowances are made for changes in plasma protein concentration.

Alkalinizing effects of oral sodium bicarbonate and sodium acetate in sedentary horses

Equimolar solutions of sodium bicarbonate (NaHCO3) or sodium acetate (NaC2H3O2), or deionised water (as a negative control) were administered by nasogastric intubation randomly to each of 12 sedentary mares every 2 weeks. Anaerobic samples of jugular venous blood were obtained hourly until 7 h after administration and were analysed for pH, pCO2, and concentrations of tCO2, HCO3−, Na+, K+, Cl−, and Ca++. Measured strong ion difference (SIDm), anion gap (AG), and estimated strong ion gap (SIGest) were calculated. Least square means differences for each variable were determined using ANOVA for repeated measures. Significance level was set at P<0.05. Treatment with NaHCO3increased pH, pCO2, [tCO2], [HCO3−], [Na+], and SIDm within 1 h of intubation (P<0.05). Peaks were reached at 2 (pH and [Na+]) and 3 h (pH, pCO2, [tCO2], [HCO3−], and SIDm) after NaHCO3 treatment. Sodium acetate increased [Na+] within 1 h of intubation; pH, [tCO2], and [HCO3−] within 2 h; and pCO2 and SIDm within 3 h (P<0.05). Peaks in pCO2, [tCO2], and [HCO3−] (4 h) and in pH and SIDm (5 h) were later with NaC2H3O2 when compared with NaHCO3. Changes in AG, SIDm, and SIGest were delayed after NaC2H3O2 treatment, corresponding to the lags in venous pH, pCO2, [tCO2], and [HCO3−]. Serum [K+] decreased from 3 through 6 h for both treatments when compared to H2O control (P<0.05). Serum [Cl−] was decreased only for NaHCO3 at 3 h (P<0.05). Serum [Ca++] was decreased for NaHCO3 at 2, 3, 4, and 7 h and for NaC2H3O2 only at 3 h (P<0.05). It was concluded that oral NaC2H3O2in horses caused a metabolic alkalosis similar to that caused by oral NaHCO3, but that the peaks in pH, pCO2, [tCO2], [HCO3−], SIDm, AG, and SIGest were delayed after NaC2H3O2 treatment.