In this course, we show you how analysis of the PaO2 in the context of the A-a gradient can help you avoid critical errors in clinical practice. In order to adopt this approach to arterial blood gas (ABG) analysis, certain concepts must first be understood. We begin by explaining how, in response to CO2 produced during metabolism, brainstem centres control the level of alveolar ventilation. We explain how this establishes a strict relationship between the fraction of inspired oxygen (FiO2), the PaO2, the arterial partial pressure of CO2 (PaCO2) and the partial pressure of oxygen in the alveoli (PAO2). We show you how the relationship between these key parameters is described by the alveolar gas equation. We teach you how to use this equation to calculate the PAO2 and the actual A-a gradient present in a patient based on values reported on the ABG. We explain the nature of, and factors contributing to the normal A-a gradient. You will learn how to calculate the predicted appropriate A-a gradient for a patient of a given age on a given level of inspired oxygen. In a series of case studies, we then illustrate how an understanding of the A-a gradient helps us avoid misdiagnosis in practice and allows us to detect problems in patients on oxygen therapy. We also explain two important, commonly misused terms in respiratory medicine, hypoventilation and hyperventilation. We explain the difference between, and the identification of type I and type II respiratory failure.
Planner and Author: Dr John Seery MB PhD
Planner: Dr Karen Strahan PhD (University of Cambridge), Head of Editorial
Planner: Tommy O'Sullivan, CME Manager
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Dempsey JA and Smith CA. Pathophysiology of human ventilatory control. Eur Respir J. 2014;44(2):495-512.
Sue DY. Treating hypoxemia with supplemental oxygen. Same game, different rules. Ann Am Thorac Soc. 2016;13(12): 2266-71.
Sue DY. Treating Hypoxemia with Supplemental Oxygen. Same Game, Different Rules. Ann Am Thor Soc. 2016;13(12):2266-71.
Acadoodle, Ltd is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.
Acadoodle, Ltd designates this enduring material activity for a maximum of 2.0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.