Continuous intra-arterial blood gas monitoring is a real-time method of monitoring arterial blood gas status recently introduced to medicine and proven accurate under relatively controlled circumstances. This study was designed to test the effectiveness of intra-arterial blood gas monitoring in performance Thoroughbred horses during incremental exercise testing. Six conditioned male (2 stallions; 4 geldings), Thoroughbred horses, age 4.5 ± 0.3 years (mean ± SEM), weighing 490 kg ± 12.7 kg, were randomly assigned to one of two treatment groups; group 1 horses received placebo and group 2 received albuterol delivered by metered-dose inhaler. Each horse received both placebo and albuterol in a crossover design with a 3 week interval between trials. Horses inspired albuterol (900 g) or placebo over a 5 minute period followed by an incremental, maximal oxygen consumption (VO2max) exercise test.
Facial arteries were cannulated bilaterally. A calibrated Paratrend7® intravascular sensor was inserted into the first artery for continuous arterial blood gas analysis (PaO2, PaCO2, pHa, temperature). Blood was collected from the second catheter and analyzed by a calibrated conventional blood gas analyzer correcting for body temperature (Radiometer ABL 605®). Two methods were applied to assess association and agreement: Intra-class correlation coefficients (ICR) and Bland-Altman analysis of bias and precision. ICR was highly variable, but increased with increasing treadmill speed. Bias (systematic error) and precision (degree of random error with multiple determinations) worsened with increasing treadmill speed. A time constant is associated with the diffusion of gases across membranes of the intravascular sensor. Abrupt changes in acid-base will lead to lag in the intravascular sensor response. In conclusion, the Paratrend7® intravascular sensor functions well in resting Thoroughbred horses, but with less accuracy and reliability when abrupt changes in acid-base associated with incremental VO2max exercise testing occur.
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