the recent study by burri and colleagues examined the usefulness of arterial blood gases ( abg ) in the diagnosis and prognosis of 530 dyspneic patients with abg drawn upon presentation to the emergency department .
the study was a retrospective analysis of prospectively collected data performed at a single center .
they concluded that abg can not be used to distinguish between pulmonary and other causes of dyspnea .
prior to the introduction of automated blood gas analyzers , blood po2 and pco2 could be obtained only by laborious and often inaccurate laboratory methods , such as gas tonometry and van slyke manometric extraction of plasma total carbon dioxide .
improvements in electrode technology came with the development of the astrup ph electrode , the stow / severinghaus - type pco2 electrode   and the polarographic oxygen clark electrode .
although pulse oximetry has largely superseded the use of arterial po2 ( pao2 ) , the ease by which abg can now be measured has made this test de rigueur in the workup of dyspneic patients .
we agree with burri and colleagues in that pao2 values serve mainly to triage and to guide treatment , rather than to differentiate among the causes of dyspnea . except for anxiety hyperventilation , it is difficult to rely solely on abg to identify a specific clinical syndrome .
the poor predictive value of pao2 in diagnosing patients with pulmonary embolism is well known . in the pioped
i study of patients with angiographically proven pulmonary embolism and no prior cardiopulmonary disease , 26% had pao2 > 80 mmhg .
the probability of diagnosing an acute pulmonary embolism based on changes in pao2 did not achieve statistical significance .
burri and colleagues also report that arterial ph was a significant predictor of short - term and long - term outcome .
multiple physiological buffers act to preserve the concentration of hydrogen ions in blood within a relatively small range .
decreases in arterial ph are likely to reflect severe impairments or even exhaustion of systemic compensatory mechanisms in patients with acute dyspnea .
the predictive value of the arterial ph in dyspneic patients noted by burri and colleagues supports this hypothesis .
burri and colleagues propose the use of venous blood ph in the initial evaluation of acute dyspnea , based on data from several single - center studies reporting relatively close limits of agreement ( -0.11 to + 0.04 ) between arterial ph and venous blood ph .
one must keep in mind , however , that muscular activity or regional microcirculatory alterations could result in misleadingly low regional ph values in septic or agitated patients . substituting venous blood ph for arterial ph in the evaluation of dyspneic patients
is an appealing notion , but one that requires testing in multicenter , prospective clinical studies .
until these studies corroborate the equivalence between arterial and peripheral venous blood gases , or until non - invasive techniques to monitor arterial pco2 and ph become available , we shall continue to support the use of abg in the initial evaluation and treatment of patients with acute dyspnea .
abg : arterial blood gases ; icu : intensive care unit ; paco2 : arterial partial pressure of carbon dioxide ; pco2 : partial pressure of carbon dioxide ; po2 : partial pressure of oxygen .
 arterial blood gases ( abg ) are obtained commonly in dyspneic persons presenting to emergency departments . 
 the study by burri and colleagues found that the information contained in abg fails to distinguish between pulmonary and other causes of dyspnea . on the other hand , 
 arterial ph was highly predictive of icu admission and outcome . 
 until large clinical studies show equivalence between peripheral venous and abg , we will continue to advocate the use of abg in the evaluation of acute dyspnea . 
None
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