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This Article Full Text Full Text (PDF) All Versions of this Article: 586/15/3675    most recent jphysiol.2008.154716v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Ito, S. Articles by Fisher, J. A. PubMed PubMed Citation Articles by Ito, S. Articles by Fisher, J. A. Related Collections Respiratory

¹ Department of Anaesthesiology, University Health Network, Toronto Canada
² Department of Physiology, University of Toronto, Toronto, Canada
³ Biostatistical Consulting Service, Centre for Addiction and Mental Health, Toronto, Canada
⁴ Department of Anaesthesiology and Medical Crisis Management, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan

Accurate measurements of arterial P_CO2 (P_a,CO2) currently require blood sampling because the end-tidal P_CO2 (P_ET,CO2) of the expired gas often does not accurately reflect the mean alveolar P_CO2 and P_a,CO2. Differences between P_ET,CO2 and P_a,CO2 result from regional inhomogeneities in perfusion and gas exchange. We hypothesized that breathing via a sequential gas delivery circuit would reduce these inhomogeneities sufficiently to allow accurate prediction of P_a,CO2 from P_ET,CO2. We tested this hypothesis in five healthy middle-aged men by comparing their P_ET,CO2 values with P_a,CO2 values at various combinations of P_ET,CO2 (between 35 and 50 mmHg), P_O2 (between 70 and 300 mmHg), and breathing frequencies (f; between 6 and 24 breaths min^–1). Once each individual was in a steady state, P_a,CO2 was collected in duplicate by consecutive blood samples to assess its repeatability. The difference between P_ET,CO2 and average P_a,CO2 was 0.5 ± 1.7 mmHg (P = 0.53; 95% CI –2.8, 3.8 mmHg) whereas the mean difference between the two measurements of P_a,CO2 was –0.1 ± 1.6 mmHg (95% CI –3.7, 2.6 mmHg). Repeated measures ANOVAs revealed no significant differences between P_ET,CO2 and P_a,CO2 over the ranges of P_O2, f and target P_ET,CO2. We conclude that when breathing via a sequential gas delivery circuit, P_ET,CO2 provides as accurate a measurement of P_a,CO2 as the actual analysis of arterial blood.

(Received 3 April 2008; accepted after revision 11 June 2008; first published online 19 June 2008)
Corresponding author J. A. Fisher: The Toronto General Hospital 7EN-242, 200 Elizabeth Street, Toronto, Canada, M5G 2C4.   Email: joe.fisher{at}utoronto.ca