Blood Gas Analysis Clinical Guide

Development of a deep understanding of arterial blood gas, or ABG, analysis is very much based on a solid appreciation of the underlying pulmonary physiology of gas exchange. This chapter of our Clinical Guide reviews the basic physics of gases in a way that’s intuitive and visually engaging. So, dive right in and lay the foundation for anything that’s to come in later chapters.

Arterial blood gas values reflect the efficiency of diffusion of gases, in particular, oxygen and carbon dioxide, across the alveolar-capillary membrane. Do you know that the major clinical manifestations of many lung diseases are a direct consequence of their effects on diffusion in the lung? The articles in this chapter review the critically important concept of gas diffusion across the alveolar-capillary membrane and look at relevant factors that affect it.

The extent to which the body can use oxygen and eliminate carbon dioxide depends not only on the efficiency of gas exchange in the lungs, but also on how well these gases are transported to and from metabolizing tissues. Many important clinical factors affect these transport mechanisms. This chapter addresses the movement of oxygen into and out of red blood cells and its distribution between hemoglobin and the rest of the red cell.

Do you recall that oxygen delivery to peripheral tissues depends not only on how much oxygen is loaded into the blood in the lungs but also on the amount of blood pumped out of the left ventricle? The articles in this chapter address the determinants of oxygen delivery to peripheral tissues, including oxygen content of the blood and cardiac output.

While it’s easy to think about gas exchange by treating the lungs as a single homogeneous unit, the lungs are very heterogeneous in their structure and function. The heterogeneity has profound effects on gas exchange in health and disease. The articles of this chapter address the relationship between regional lung ventilation and perfusion. We’ll review the effect of alterations in these relationships on gas exchange in various disease states.

It’s appropriate to focus on arterial blood gas analysis to understand how effectively the lungs oxygenate the blood. But equally important is the test’s value in assessing the elimination of the principal metabolic product of aerobic metabolism—carbon dioxide. The arterial carbon dioxide level is a critical parameter in the other major application of arterial blood gas testing—the analysis of your patient’s acid-base status. The articles in this chapter of our Blood Gas Analysis Clinical Guide, review the principal determinants of arterial PCO₂.

Looking at arterial oxygen tension is just one aspect of blood gas analysis. In addition to its valuable role in assessing respiratory function, arterial blood gas analysis is vitally important in evaluating acid-base balance. The articles in this chapter describe the relationship between arterial PCO₂ and ventilation, in particular, alveolar ventilation. The relationship between arterial PCO₂ and pH is reviewed, as are the roles of ventilation and alterations in arterial PCO₂ in adjusting arterial pH.