Assessing effort and work of breathing.

Abstract

Spontaneous breathing has been shown to induce both positive and negative effects on the function and on injury of lungs and diaphragm during critical illness; thus, monitoring of the breathing effort generated by the patient might be valuable for a better understanding of the mechanisms of disease and to set properly ventilation. The purpose of this review is to summarize the recent findings on the different techniques available to measure the patient's breathing effort, mainly during spontaneous assisted ventilation. Although esophageal pressure measurement remains the solid reference technique to quantitate the breathing effort, other tools have been developed and tested. These include the diaphragmatic electromyogram, whose voltage is linearly related to the pressure generated by the diaphragm, ultrasound, which relies on the measurement of diaphragmatic displacement or thickening, and other approaches, which derive breathing effort solely from the airway flow and pressure tracings. The development of measurement techniques and their introduction in clinical practice will allow us to understand the role of spontaneous breathing effort in the pathophysiology of lung injury and weaning failure, and how to adjust the breathing workload in an individual patient.