Development of application and studies of volume-capnography in critical patients

Abstract

Background Volume PETCO2 is a sigal-wave plot based on the expired carbon dioxide fraction,which is the standard tool for understanding carbon dioxide elimination and the dead space. Objective The basic principles and clinical significance of normal and abnormal waveform of v-PETCO2 is introduced. Content v-PETCO2 wave morphology depends on production, transport (pulmonary perfusion) and diffusion of the carbon dioxide, as well as any changes in respiratory pathophysiology, v-PETCO2 can be used to study the dynamics of CO2. This plot yields three parts: first phase is carbon dioxide free;phase Ⅱ represents the transition between gas from the airways and alveolar gas, and phase Ⅲ represents alveolar gas. The respiratory dysfunction reduces ventilation in some units more than others, causing an increased scatter of ventilation/perfusion (V/Q)ratios and thus of the range of alveolar PCO2 values. They results in increased slope of phase 3 and three dead space estimates derived from the v-capnogram, including the anatomical dead space, alveolar dead space and physiological dead space. This can differentiate a patient with a pulmonary embolism from a healthy patient or a COPD, ARDS or asthma patients. Trend v-PETCO2 is the standard tool for understanding carbon dioxide elimination and the dead space concept. Key words: PETCO2; Capnography; Volume-capnogram; Ventilation