Assessment of the Breathing Workload During Mechanical Ventilation

Abstract

Although “work of breathing (WB) ” is generally understood to relate to patient effort during breathing activity, the term must be carefully defined. An ideal measure of breathing workload would serve as an index of the energy expended by the specific respiratory muscles of interest. Often, however, the clinician or investigator is selectively interested in the inspiratory musculature: diaphragm, external intercostals and the accessory muscles of ventilation. At other times, there is interest in knowing how the stress of breathing adds to total body oxygen consumption (the “oxygen cost of breathing”), regardless of the muscle groups involved. In comparisons of respiratory equipment and in many clinical situations it is not the total energy expenditure of the respiratory system of an individual patient that is in question, but the work done across an external device or a subcomponent of the total breathing impedance (airway, lung or chest wall) under specified airflow conditions.