Intensive Care Medicine

, Volume 37, Issue 5, pp 870–874 | Cite as

Validation of Bohr dead space measured by volumetric capnography

  • Gerardo Tusman
  • Fernando Suarez Sipmann
  • Joao B. Borges
  • Göran Hedenstierna
  • Stephan H. Bohm
Physiological and Technical Notes

Abstract

Purpose

Bohr’s dead space (VDBohr) is commonly calculated using end-tidal CO2 instead of the true alveolar partial pressure of CO2 (PACO2). The aim of this work was to validate VDBohr using PACO2 derived from volumetric capnography (VC) against VDBohr with PACO2 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). PACO2 was determined by VC as the midpoint of the slope of phase III of the capnogram, while mean expired partial pressure of CO2 (PeCO2) was calculated as the mean expired fraction of CO2 times the barometric minus the water vapor pressure. MIGET estimated expired CO2 output (VCO2) and PeCO2 by its V/Q algorithms. Then, PACO2 was obtained applying the alveolar air formula (PACO2 = VCO2/alveolar ventilation).

Results

We found close linear correlations between the two methods for calculating both PACO2 (r = 0.99) and VDBohr (r = 0.96), respectively (both p < 0.0001). Mean PACO2 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 VDBohr 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

VDBohr can be calculated with accuracy using volumetric capnography.

Keywords

Volumetric capnography PACO2 Bohr’s dead space Carbon dioxide Tidal volume Gas exchange 

Supplementary material

134_2011_2164_MOESM1_ESM.doc (456 kb)
Supplementary material 1 (DOC 455 kb)

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Copyright information

© Copyright jointly held by Springer and ESICM 2011

Authors and Affiliations

  • Gerardo Tusman
    • 1
  • Fernando Suarez Sipmann
    • 2
  • Joao B. Borges
    • 3
  • Göran Hedenstierna
    • 3
  • Stephan H. Bohm
    • 4
  1. 1.Department of AnesthesiologyHospital Privado de ComunidadMar del PlataArgentina
  2. 2.Department of Critical Care MedicineFundación Jiménez Díaz-UTEMadridSpain
  3. 3.Department of Medical Sciences, Clinical PhysiologyUniversity HospitalUppsalaSweden
  4. 4.CSEM Centre Suisse d’Electronique et de Microtechnique SAResearch Centre for NanomedicineLandquartSwitzerland

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