Impact of Collection Tube Dead Space on the Accuracy of Venous Blood Gas Measures

While arterial blood gases (ABGs) are considered the clinical gold standard for assessment of blood gases and electrolytes, they can be painful, carry more risk and require additional expertise. Venous blood gases (VBGs) are routinely utilized in clinical settings as surrogate measures to assess blood gases, where normative reference values are established. However, there is limited research on the impacts of collection tube (e.g., vacutainer) dead space on the accuracy of VBG measurements, which can range from 2-10mL. We aimed to determine how collection tube dead space affects venous blood gas accuracy. We hypothesized that venous (v) blood obtained directly into a 1mL heparinized syringe (i.e., no dead space) will have PvCO 2 , PvO 2 and SvO 2 values reflective of true venous values, whereas venous blood collected in a heparinized 4mL vacutainer will have a lower PvCO 2 and higher PvO 2 and SvO 2 , due to the effects admixture with increased dead space in the vacutainer tube. Healthy participants (n=16) were instrumented in supine position, and breathed through a custom mouthpiece connected to a pneumotachometer and dual gas analyzer to continuously assess minute ventilation and end-tidal gases (PETCO 2 , PETO 2 ), whereby end-tidal gases and peripheral oxygen saturation (SpO 2 ) measures served as surrogates for arterial blood gases. Venous blood samples were obtained through venipuncture of a superficial antecubital fossa vein while breathing ambient air. Venous blood gases were analyzed using an i-STAT analyzer and G3+ cartridges to quantify PvCO 2 , PvO 2 and SvO 2 . Data were analyzed using paired t-tests, Pearson correlations, and Bland–Altman analysis. Venous blood gas parameters (PvCO 2 , PvO 2 and SvO 2 ) differed significantly between the 4mL vacutainer syringe and 1mL syringe. PvCO 2 was significantly lower in the vacutainer compared to the syringe (40.8±4.1mmHg vs. 43.2±4.7mmHg, respectively; P=0.0023; r=0.8365; Upper LOA = 2.7+2.6mmHg; Lower LOA=-7.4-2.6mmHg; LOA range=10.1±2.6mmHg). PvO 2 was significantly higher in the vacutainer compared to the syringe (40.4±8.8mmHg vs. 33.2±8.2mmHg, respectively; P=0.0001; r=0.7853; Upper LOA=18.2+5.6mmHg; Lower LOA=-3.7-5.6mmHg; LOA range=21.9±5.6mmHg). SvO 2 was significantly higher in the vacutainer compared to the syringe (71.8±12.7% vs. 59.6±15.1%, respectively; P< 0.0001; r=0.8043; Upper LOA=29.9+9.0%; Lower LOA=-5.3-9.0%; LOA range=35.2±9.0%). In summary, the 4mL vacutainer produced artificially lower PvCO 2 values and higher PvO 2 and SvO 2 values compared to the 1mL syringe, likely due to the associated dead space. Our data (a) highlight the importance of standardizing VBG collection procedures in clinical contexts and (b) suggest potential clinical implications regarding the accuracy of VBG samples obtained in vacutainer collection tubes of various sizes, where minimizing dead space likely improves both the accuracy and reliability of VBG values. ACKNOWLEDGEMENT OF FUNDING: Mount Royal University Department of Biology and a Natural Science and Engineering Research Council of Canada Discovery grant This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.