Effects of lung hyperinflation and presence of positive end-expiratory pressure on arterial and tissue oxygenation during endotracheal suctioning

PURPOSE: To explore the effects of endotracheal suctioning on mixed venous oxygen tension and other measures of arterial and tissue oxygenation, to determine if these would be clinically useful outcome measures of endotracheal suctioning. BACKGROUND: Measuring arterial oxygenation only as an outcome of endotracheal suctioning can be misleading in that it may appear adequate in the presence of marked decreases in mixed venous oxygen tension, a good indicator of the adequacy of tissue oxygenation. METHODS: Eighteen instrumented and oleic acid-injured animal models of acute respiratory failure undergoing closed-system endotracheal suctioning were studied according to a 2 x 2 factorial design to measure the effects of oxygen inflations at tidal volume or 135% of tidal volume either in the presence or absence of positive end-expiratory pressure. RESULTS: Using multivariate analysis of variance for repeated measures, protocol by time effects for mixed venous oxygen tension, arterial oxygen saturation, arterial oxygen tension, oxygen delivery and oxygen extraction ratio were statistically significant. Changes in mixed venous oxygen tension and arterial oxygen saturation were parallel. CONCLUSIONS: Continuous measurement of mixed venous oxygen tension allows the calculation of oxygen delivery and oxygen extraction ratio, which provide a better estimation of the effects of endotracheal suctioning on tissue oxygenation than arterial oxygen tension alone.