Journal article
Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?
Annals of the American Thoracic Society, Vol.14(6), pp.1005-1014
06/2017
DOI: 10.1513/AnnalsATS.201701-034FR
PMID: 28570147
Abstract
The arterial partial pressure of carbon dioxide (Pa
) is an important parameter in critically ill, mechanically ventilated patients. To limit invasive procedures or for more continuous monitoring of Pa
, clinicians often rely on venous blood gases, capnography, or transcutaneous monitoring. Each of these has advantages and limitations. Central venous Pco
allows accurate estimation of Pa
, differing from it by an amount described by the Fick principle. As long as cardiac output is relatively normal, central venous Pco
exceeds the arterial value by approximately 4 mm Hg. In contrast, peripheral venous Pco
is a poor predictor of Pa
, and we do not recommend using peripheral venous Pco
in this manner. Capnography offers measurement of the end-tidal Pco
(Pet
), a value that is close to Pa
when the lung is healthy. It has the advantage of being noninvasive and continuously available. In mechanically ventilated patients with lung disease, however, Pet
often differs from Pa
, sometimes by a large degree, often seriously underestimating the arterial value. Dependence of Pet
on alveolar dead space and ventilator expiratory time limits its value to predict Pa
. When lung function or ventilator settings change, Pet
and Pa
can vary in different directions, producing further uncertainty. Transcutaneous Pco
measurement has become practical and reliable. It is promising for judging steady state values for Pa
unless there is overt vasoconstriction of the skin. Moreover, it can be useful in conditions where capnography fails (high-frequency ventilation) or where arterial blood gas analysis is burdensome (clinic or home management of mechanical ventilation).
Details
- Title: Subtitle
- Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?
- Creators
- Boulos S Nassar - Division of Pulmonary Diseases, Critical Care, and Occupational Medicine, University of Iowa, Iowa City, IowaGregory A Schmidt - Division of Pulmonary Diseases, Critical Care, and Occupational Medicine, University of Iowa, Iowa City, Iowa
- Resource Type
- Journal article
- Publication Details
- Annals of the American Thoracic Society, Vol.14(6), pp.1005-1014
- DOI
- 10.1513/AnnalsATS.201701-034FR
- PMID
- 28570147
- NLM abbreviation
- Ann Am Thorac Soc
- ISSN
- 2325-6621
- eISSN
- 2325-6621
- Publisher
- American Thoracic Society
- Language
- English
- Date published
- 06/2017
- Academic Unit
- Pulmonary, Critical Care, and Occupational Medicine; Internal Medicine
- Record Identifier
- 9984094401302771
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