Validation of Bohr dead space measured by volumetric capnography

• Published in: Intensive care medicine Vol. 37; no. 5; pp. 870 - 874
• Main Authors: Tusman, Gerardo, Sipmann, Fernando Suarez, Borges, Joao B., Hedenstierna, Göran, Bohm, Stephan H.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.05.2011; Springer; Springer Nature B.V
• Subjects: Algorithms; Analysis; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Anesthesiology; Animals; Biological and medical sciences; Bohr's dead space; Breath tests; Capnography; Capnography - methods; Carbon dioxide; Carbon Dioxide - blood; Critical Care Medicine; Emergency Medicine; Gas exchange; Gases; Hematology; Intensive; Intensive care medicine; Investigative techniques, diagnostic techniques (general aspects); Mathematical functions; Medical sciences; MEDICIN; MEDICINE; Medicine & Public Health; PACO; Pain Medicine; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Pediatrics; Physiological and Technical Notes; Pneumology/Respiratory System; Pulmonary Gas Exchange; Respiratory Dead Space - physiology; Swine; Tidal volume; Tidal Volume - physiology; Ventilators; Venture capital; Volumetric capnography; Gas exchange; Bohr’s dead space; Volumetric capnography; ACO; Carbon dioxide; Tidal volume; PaCO2; Volumetric analysis; Intensive care; Capnography; Bohr's dead space; PACO; Dead space; Resuscitation
• ISSN: 0342-4642; 1432-1238; 1432-1238
• DOI: 10.1007/s00134-011-2164-x

Purpose Bohr’s dead space (VD Bohr ) is commonly calculated using end-tidal CO 2 instead of the true alveolar partial pressure of CO 2 ( P ACO 2 ). The aim of this work was to validate VD Bohr using P ACO 2 derived from volumetric capnography (VC) against VD Bohr with P ACO 2 values obtained from the standard alveolar air formula. Methods Expired gases of seven lung-lavaged pigs were analyzed at different lung conditions using main-stream VC and multiple inert gas elimination technique (MIGET). P ACO 2 was determined by VC as the midpoint of the slope of phase III of the capnogram, while mean expired partial pressure of CO 2 ( P eCO 2 ) was calculated as the mean expired fraction of CO 2 times the barometric minus the water vapor pressure. MIGET estimated expired CO 2 output ( V CO 2 ) and P eCO 2 by its V/Q algorithms. Then, P ACO 2 was obtained applying the alveolar air formula ( P ACO 2  =  V CO 2 /alveolar ventilation). Results We found close linear correlations between the two methods for calculating both P ACO 2 ( r  = 0.99) and VD Bohr ( r  = 0.96), respectively (both p  < 0.0001). Mean P ACO 2 from VC was very similar to the one obtained by MIGET with a mean bias of −0.10 mmHg and limits of agreement between −2.18 and 1.98 mmHg. Mean VD Bohr from VC was close to the value obtained by MIGET with a mean bias of 0.010 ml and limits of agreement between −0.044 and 0.064 ml. Conclusions VD Bohr can be calculated with accuracy using volumetric capnography.