Effects of four different methods of sampling arterial blood and storage time on gas tensions and shunt calculation in the 100% oxygen test

Abstract

At the present time, plastic syringes are most commonly used for collecting arterial blood. The oxygen tension of the arterial blood (Pa,O2) in these syringes may fall. We studied the effect of the type of syringe, metabolism, and storage time on the arterial oxygen pressures measured and on the pulmonary shunt calculated. In 10 patients, 2-3 h after aortacoronary bypass surgery, a 100% oxygen test was performed. Four arterial blood gas samples were withdrawn from each patient in random order, two in glass syringes and two in plastic syringes. One glass and one plastic syringe were stored at room temperature (RT), and the others were stored in ice-water (IW). Each sample was analysed as soon as possible, and repeated 15, 30, 60 and 120 min after sampling. The Pa,O2 measurement in blood in the glass syringe in IW measured as soon as possible after sampling was considered the "gold standard". Pulmonary shunt calculations were performed using the results of the various blood gas analyses. Compared with the "gold standard", all of the other methods showed significant deterioration in the Pa,O2 measurement. The effect due to diffusion was 0.05 kPa x min(-1), and that due to metabolism 0.11 kPa x min(-1). The Pa,O2 in the glass syringes stored in IW remained stable with time. The pulmonary shunt was significantly overestimated when the "gold standard" blood gas results were not used (range 0.8-9.9%). Glass (not plastic) syringes should be used in the 100% oxygen test. The syringe should be cooled immediately, even when the sample is analysed as soon as possible.

Australian and New Zealand Society of Respiratory Science position statement for arterial blood gas sampling

“…To calculate shunt (the proportion of cardiac output that does not participate in gas exchange), sampling occurs following 15–20 min of breathing a fraction of inspired oxygen of 1.0 (100%O 2 ). At high oxygen concentrations, measured PaO 2 falls at a faster rate, by 9–13 mmHg per min in the first 5–10 min, 21,22 which overestimates shunt calculation by 0.6% per min 22 . Therefore, shunt study samples need to be analysed within 5 min of collection; otherwise, there is significant risk of false positives.…”

Recommendation for the design of stability studies on clinical specimens

“…-Contact with air; diffusion and evaporation. Uncapping the tube during analysis causes evaporation of the solvent, generating an increase in the concentration of most analytes [21] and diffusion of dissolved gases, with loss of carbon dioxide and a subsequent increase in pH [8,22,23].…”

“…Even if the tube is kept closed, these processes must be taken into account as some gases can diffuse through the walls of the container, especially in plastic tubes [22][23][24][25].…”

Pre-analytical validity of arterial blood gas samples: A prospective experimental study on changes derived from time delay and mechanical stress

“…For example, Knowles and Harsten detected changes in partial pressures of respiratory gases (pO 2 and pCO 2 ) 30 and 60 min post-collection. Moreover, Smeenk et al [3] described prolonged stability of pO 2 when using glass syringes or ice-water storage. However, beyond respiratory gases, modern blood gas analyzers measure various clinically relevant analytes, of ionic or organic-small-molecular character (for example, c(sodium), c(potassium), c(calcium), c(glucose), and c(lactate)).…”