Abstract

Evaluation and safety of new anesthetic techniques depends on critical physiologic monitoring. Blood pH/gas analysis is critical for physiologic evaluation of anesthetized patients. Literature states regimented handling and rapid processing of blood pH/gas samples is required for valid results.¹ This is problematic in field situations, especially if numerous samples are collected and analyzed a distance from the anesthetized animal.

This study evaluated three storage conditions on stability of PO₂, PCO₂, and pH in blood from eight Grevy’s zebras (Equus grevyi). Arterial and venous samples in heparinized 12-ml plastic syringes were stored in ice (ICE) or at 22°C (RT), or with 2 mg/ml sodium fluoride at 22°C (NaF). One analyzer was used for analysis at average times of 20 (baseline), 79, 144, 204, 365, 326, 385, and 452 min.

Data were analyzed using the generalized estimating equation for sequential measure and ANOVA. Mean baseline P_aO₂ was 81–86 and P_vO₂ was 49–55 mm Hg. Mean PCO₂ and pH in all baseline samples were 61–65 mm Hg and 7.34–7.36 pH units.

Changes in P_aO₂, P_aCO₂, and pHa are shown: Figures 1, 2, and 3.

Zebra blood samples with physiologic blood gases and pH levels are stable in heparin + NaF for up to 7 hr at 22°C.

At RT in heparin alone, PCO₂ increases and pH decreases due to metabolism. The increase in PO₂ in ICE is from leakage into the syringe. Driving pressure in iced samples is higher than at room temperature because of increased solubility of oxygen, and lower P₅₀ of hemoglobin.²

Figure 1. Change in PaO₂ over time

Figure 2. Change in PaCO₂ over time

Figure 3. Change in pHa over time

Literature Cited

1.  Haskins, S.C. 1977. Sampling and storage of blood for pH and blood gas analysis. J. Am. Vet. Med. Assoc. 170: 429–433.

2.  Mahoney, J.J., J.A. Harvey, R.J. Wong, and A.L. Van Kessel. 1991. Changes in oxygen measurements when whole blood is stored in iced plastic or glass syringes. Clin. Chem. 37: 1244–1248.