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BACKGROUND: Arterial blood sampling is subject to numerous pre-analytical errors, one of which is inadvertent venous blood sampling. Especially when assessing oxygenation and titrating ventilation, accidental venous blood sampling may lead to inappropriate respiratory care and repeated percutaneous punctures. OBJECTIVE: To determine the effects of mean systemic blood pressure and needle size on vented arterial sampler filling times, to distinguish venous and arterial sampling. METHODS: We constructed an extracorporeal laboratory model to circulate whole blood at 4 L/min. We used hemostats to create 6 pressures: 57 mm Hg (representing a patient in shock), 70 mm Hg (representing a patient with low-normal blood pressure), 93 mm Hg (normal), 107 mm Hg (high-normal), 133 mm Hg (severe hypertension), and 14 (peripheral venous pressure). We simulated percutaneous punctures with vented arterial samplers preset to 2 mL, with 2 common sampling needles. We compared the filling times of each pressure/needle combination and determined the correlation between the mean pressure and filling time. RESULTS: For all the tested arterial pressures combined, the mean SD sampler filling time was 15.8 0.4 s; for venous pressures the time was 51.4 1.4 s (P < .001). With the 22-gauge/1.5-inch needles the sampler filling time was 22.2 14.9 s. With the 23-gauge/1-inch needle the time was 21.4 13.1 s (difference not significant). The Pearson correlation coefficient between the mean blood pressures and the sampler filling times was r2 0.86 (P .01). CONCLUSIONS: Lower blood pressure increased the sampler filling time. Measuring the filling time may enable therapists to confirm successful arterial puncture in adult patients. Confirming successful arterial puncture prior to blood analysis would expedite appropriate patient care decisions. [ABSTRACT FROM AUTHOR]