Variability of arterial blood gas values over time in stable medical ICU patients.

The spontaneous variability of arterial blood gas and pH values (ABGs) was examined in a group of 28 typical stable medical ICU patients under a variety of ventilatory conditions. In each patient, 13 ABG specimens were measured at 5-min intervals during a 1-h study period using a new bedside, extravascular fluorescent blood gas monitor. For all patients, the mean coefficient of variation (C) was 6.1 percent for PO2 and 4.7 percent for PCO2. The average SD for pH was 0.012. We conclude that the spontaneous variability for ABG values over a 1-h period is substantial and that this variability should be taken into account when making clinical decisions based on ABG values.