Can a change in pH and pCO2 be used to monitor progress in patients undergoing noninvasive ventilation? A prospective cohort study

Abstract

The aim of this study was to compare changes in arterial and venous pH and pCO2 in patients undergoing noninvasive ventilation and having serial blood gases to assess ventilatory function. This was a prospective observational study of patients with acute respiratory distress. The outcome of interest was agreement in change in pH and pCO2 between arterial and venous specimens [mean difference; 95% limits of agreement (LoA)]. The average difference between the change in pH (v-a) was 0.001 pH units (LoA -0.7 to +0.7). The average difference between the change in pCO2 (v-a) was 0.04 mmHg (LoA -17.3 to +18.2). For both pH and pCO2, in the majority of cases, the direction of change was the same, although the magnitude was variable. The agreement between absolute change is reasonable for pH but not for pCO2. The direction of change agreed in most cases. Changes in venous pH and pCO2, in combination with clinical assessment, may be useful for assessing progress in patients undergoing noninvasive ventilation.