Bedside Assessment of Pulmonary Mechanics: Instruments, Techniques, and Application

Abstract

The major function of the respiratory system is gas exchange. Respiratory muscles exert the force necessary to move air into alveolar sacs, where gas exchange takes place by diffusion. Under resting conditions, alveolar gas passively exits the lung during expiration. Because of the respiratory system's large reserve capacity, gas exchange is usually accomplished with little noticeable effort in a normal person. This capacity can be severely reduced or inadequate to handle the load when respiratory mechanics are impaired by disease processes, however. When workload exceeds capacity, respiratory muscles fatigue and respiratory failure may ensue. Many patients require ventilatory support while waiting for improved respiratory mechanics. It is therefore important to assess respiratory mechanics routinely in critically ill patients. It allows the physician to determine the physiological effects of the disease process, and it helps to assess the efficacy of therapy. In this chapter, we will discuss the equipment and techniques needed to obtain lung mechanic measurements. Later, their clinical use will be considered.