A technique to determine the end-expiratory lung volume and dead space in a ventilated patient: Theoretical considerations

Abstract

The term “dead space (VD)” refers to the volume of air/gas in the respiratory tract which does not take part in gas exchange. VD can increase in some pathological settings and has been found to be a prognostic marker in acute lung injury and respiratory distress syndrome. The end-expiratory lung volume (EELV) in a mechanically ventilated patient is the volume in the lungs at the end of passive expiration which is often influenced by disease, atelectasis, airway resistance, shunt, pulmonary vascular resistance, right heart strain, etc. Measuring EELV and VD may allow monitoring of disease state and treatment effect. VD can be derived from the arterial and exhaled CO2 partial pressures. In the intensive care unit, certain ventilators can measure EELV automatically. Unfortunately, there are no means of measuring EELV in the operating room. We herein propose a technique that may theoretically allow for measurement of the EELV and VD in the operating room setting without special equipment or an arterial blood sample.