Effects of Syringe Type and Storage Temperature on Results of Blood Gas Analysis in Arterial Blood of Horses

Background: Results of arterial blood gas analysis can be biased by pre-analytical factors, such as time to analysis, syringe type, and temperature during storage. However, the acceptable delay between time of collection and analysis for equine arterial blood gas remains unknown.

Hypothesis: Dedicated plastic syringes provide better stability of arterial blood gases than multipurpose plastic syringes.

Animals: Eight mares, 1 stallion, and 1 gelding, ages 3 to 10 years old.

Methods: Arterial blood samples were collected in a glass syringe, a plastic syringe designated for blood gas collection, and a multipurpose tuberculin plastic syringe. Blood samples were stored at ambient temperature or in iced water. For each sample, partial pressure of oxygen in arterial blood (PaO2), partial pressure of carbon dioxide in arterial blood (PaCO2), and pH were measured within a few minutes of collection and at 5, 20, 30, 60, 90, and 120 minutes after collection.

Results: Collection into glass syringes stored in iced water provided adequate PaO2 results for up to 117 +/- 35 minutes, whereas blood collected in either of the plastic syringes resulted in a variation >10 mm Hg after 10 +/- 3 to 17 +/- 2 minutes, depending on the storage conditions. Plastic syringes kept at ambient temperature offered more stability for PaCO2 analysis because they could be stored up to 83 +/- 16 minutes without significant variations. Values of pH did not show variations more than 0.02 for the first hour, irrespectively of storage condition.

Conclusions And Clinical Importance: Glass syringes placed on ice are preferable for analysis of PaO2. Blood collected in plastic syringes should be analyzed within 10 minutes, irrespective of the storage temperature, to ensure the accuracy of PaO2 values.