Volumetric capnography: lessons from the past and current clinical applications.

Sara Verscheure,Franck Verschuren,Sheldon Magder,Paul B Massion,Pierre Damas

doi:10.1186/s13054-016-1377-3

Abstract

Dead space is an important component of ventilation–perfusion abnormalities. Measurement of dead space has diagnostic, prognostic and therapeutic applications. In the intensive care unit (ICU) dead space measurement can be used to guide therapy for patients with acute respiratory distress syndrome (ARDS); in the emergency department it can guide thrombolytic therapy for pulmonary embolism; in peri-operative patients it can indicate the success of recruitment maneuvers. A newly available technique called volumetric capnography (Vcap) allows measurement of physiological and alveolar dead space on a regular basis at the bedside. We discuss the components of dead space, explain important differences between the Bohr and Enghoff approaches, discuss the clinical significance of arterial to end-tidal CO2 gradient and finally summarize potential clinical indications for Vcap measurements in the emergency room, operating room and ICU.

Highlights

Ventilation dead space (VD) refers to the parts of the lung and airways that do not partake in the clearance of carbon dioxide (CO2) and indicates the inefficient portion of ventilation
In a model of lung injury in pigs, Tusman et al [29] showed that VDalv, VDalv/alveolar tidal volume (VTalv) obtained by volumetric capnography (Vcap) (Enghoff approach) and Pa-end-tidal CO2 in expired gas (ETCO2) gradient are sensitive and specific indicators of the lung’s efficiency of gas-exchange during positive endexpiratory pressure (PEEP) titration conducted after a recruitment maneuver (RM)
Verschuren et al [40] compared Vcap with arterial partial pressure of carbon dioxide (PCO2) (PaCO2)-ETCO2 gradient in patients suspected of having pulmonary embolism (PE) and who had positive D-dimers. They evaluated a number of derived values from the Vcap plot and found that the best indicator was an elevation of what they called "late dead space fraction" (Fdlate), which is defined as (PaCO2-expCO2 at 15 % of total lung capacity)/PaCO2

Summary

Introduction

Ventilation dead space (VD) refers to the parts of the lung and airways that do not partake in the clearance of carbon dioxide (CO2) and indicates the inefficient portion of ventilation. In a model of lung injury in pigs, Tusman et al [29] showed that VDalv, VDalv/alveolar tidal volume (VTalv) obtained by Vcap (Enghoff approach) and Pa-ETCO2 gradient are sensitive and specific indicators of the lung’s efficiency of gas-exchange during PEEP titration conducted after a recruitment maneuver (RM).

Results

Conclusion