Correlation between changes in arterial blood oxygen partial pressure, oxygen uptake and carbon dioxide elimination by the lungs with changes in positive end expiratory pressure: a prospective observational study

Abstract

INTRODUCTION: Since mechanical ventilation remains the main tool of respiratory support, ventilatory aspect of lung function fixed researchers’ attention during last decades, which is reflected by open lung concept and lung-protective ventilation strategy. However, it seems logical to assess function of the lung - biphasic mass exchanger with limited capacity - measuring its gas exchange performance, depending upon lung perfusion the same extent as ventilation. Recently clinicians have got routine access to metabolographers, providing figures of lungs oxygen absorption (VO2) and carbon dioxide exhalation (VCO2). OBJECTIVE: To evaluate interchangeability of metabolographer data and arterial blood gases analysis as tools for positive end-expiratory pressure (PEEP) titration by comparison of dynamic VO2 and VCO2 changes with PaO2 shifts after standardized PEEP changing. MATERIALS AND METHODS: A single-center prospective observational study included 41 patients underwent mechanical ventilation during general anesthesia for elective non-cardiothoracic surgery. After anesthesia induction and monitored parameters stabilization, PaO2, VCO2 and VO2 were measured before and after PEEP increasing from 2 to 5 mbar. Correlation was evaluated using Spearman coefficient in R-Studio with ggplot2 visualization package. RESULTS: After PEEP level increase, in 14 patients PaO2 changes were < 5 %, in 15 patients PaO2 increase was observed, and in 12 patients PaO2 has decreased. The Spearman correlation coefficient (rh) between VCO2 and PaO2 was 0.77 (р-value = 3.75 х 10-9), between VO2 and PaO2 - rh = 0.92 (p-value = 2.2 х 10-16). CONCLUSIONS: The VCO2 and VO2 dynamic changes obtained using metabolographer demonstrates high correlation with PaO2 shifts followed PEEP changes, which makes the dynamic analysis of the first two indicators a possible non-invasive alternative for repeated arterial blood gases analysis during РЕЕР level titration. Notable fact is that in significant proportion of observations, PEEP level of 5 mbar, often recommended “by default” for lung-protective ventilation, is excessive from gas exchange performance point of view.