Continuous Assessment of Cardiopulmonary Function

Abstract

“Assessment” of oxygenation may entail measurement and calculation of a variety of physiologic variables. However, the oxygen tension of arterial blood (PaO₂) is by far the most common measurement utilized in determining the “adequacy” of oxygenation. Because of the ease of measurement, PaO₂ often is used as a guide to oxygen therapy, ventilator adjustment, and other therapeutic interventions. Some clinicians have suggested a mathematical manipulation of PaO₂, alone or in combination with other variables, to improve diagnostic accuracy and assessment of pulmonary function. The perceived advantage of using the alveolar-arterial O₂ tension difference (AAD), the arterial/alveolar oxygen tension ratio (AAI), the PaO₂/F₁O₂ ratio (PFI), etc., rather than the PaO₂ alone, often is far greater than the actual advantage. It is apparent that the ease and efficiency of measurements and calculations have played a greater role in the determination of monitoring practices than accuracy and efficacy. Because of advances in monitoring technology during the last decade, a reassessment of monitoring techniques is indicated.