The effects of ice-water storage on blood gas and acid-base measurements

Objective: To determine the effects of storage of arterial and venous blood samples in ice water on blood gas and acid-base measurements.Design: Prospective, in vitro, laboratory study.Setting: School of veterinary medicine.Subjects: Six healthy dogs.Measurements and main results: Baseline measurements of partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), pH, hemoglobin concentration (tHb), oxyhemoglobin saturation, and oxygen content (ContO(2)) were made. Bicarbonate (HCO3) and standard base excess (SBE) were calculated. Arterial and venous blood samples were separated into 1 and 3 mL samples, anaerobically transferred into 3 mL plastic syringes, and stored in ice water for 6 hours. Measurements were repeated at 15, 30 minutes, and 1, 2, 4, and 6 hours after baseline measurements. Arterial (a) PO2 increased significantly from baseline after 30 minutes of storage in the 1 mL samples and after 2 hours in the 3 mL samples. Venous (v) PO2 was significantly increased from baseline after 4 hours in the 1 mL samples and after 6 hours in the 3 mL samples. The pHa significantly decreased after 2 hours of storage in the 1 mL samples and after 4 hours in the 3 mL samples. In both the 1 and 3 mL samples, pHv decreased significantly only after 6 hours. Neither the arterial nor the venous PCO2 values changed significantly in the 1 mL samples and increased only after 6 hours in the 3 mL samples. No significant changes in tHb, ContO(2), SBE, or HCO3 were detected.Conclusions: the PO2 of arterial and venous blood increased significantly when samples were stored in plastic syringes in ice water. These increases are attributable to the diffusion of oxygen from and through the plastic of the syringe into the blood, which occurred at a rate that exceeded metabolic consumption of oxygen by the nucleated cells

Use of the oxygen content-based index, fshunt, as an indicator of pulmonary venous admixture at various inspired oxygen fractions in anesthetized sheep

Objective-To evaluate the use of the oxygen content-based index, Fshunt, as an indicator of venous admixture (Qs/Qt) at various fractions of inspired oxygen (FIO2s) in anesthetized sheep undergoing 1-lung or 2-lung ventilation. Animals-6 healthy adult female sheep. Procedures-Sheep were anesthetized and administered 5 different FIO2s (0.21, 0.40, 0.60, 0.80, and 1.00) in random order during 2-lung mechanical ventilation. Arterial and mixed venous blood samples were obtained at each FIO2 after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used FIO2 sequence was reversed for sample collection during 1-lung ventilation. Blood samples were analyzed for arterial, pulmonary end-capillary, and mixed venous oxygen content and partial pressure and for hemoglobin concentration. Oxygen hemoglobin saturation, Qs/Qt, Fshunt, and oxygen tension-based indices (OTIs; including PaO2:FIO2, alveolar-arterial difference in partial pressure of oxygen [PAO2 -PaO2], [PAO2 -PaO2]:FIO2, [PAO2 -PaO2]:PaO2, and PaO2:PAO2) were calculated at each FIO2; associations were evaluated with linear regression analysis, concordance, and correlation tests. Intermethod agreement between Qs/Qt and Fshunt was tested via Bland-Altman analysis. Results-Strong and significant associations and substantial agreement were detected between Fshunt and Qs/Qt. Relationships between OTIs and Qs/Qt varied, but overall correlations were weak. Conclusions and Clinical Relevance-Whereas OTIs were generally poor indicators of Qs/Qt, Fshunt was a good indicator of Qs/Qt at various FIO2s, regardless of the magnitude of Qs/Qt, and could be potentially used as a surrogate for Qs/Qt measurements in healthy sheep