Evaluation of thoracic mechanics in the ventilated patient part 1: Primary measurements

In ambulatory patients, the respiratory system can be evaluated by voluntary tests of pulmonary function, as well as by physical examination, roentgenography, and arterial blood sampling. Unfortunately, although data regarding thoracic mechanics and muscle strength are often key to the scientific management of critically ill patients receiving mechanical ventilation, patient cooperation is often impaired. This review focuses on techniques for assessing effort intensity, the pattern and rhythm of the breathing cycle, and the physical properties of the lung and chest wall during mechanical ventilation. In the first portion of this two-part review, the discussion centers on five primary measurements that underlie all derived indices of mechanics, drive, and effort: airway and esophageal pressures, flow, volume, and breathing pattern. Detailed discussion of applied mechanics, including ventilatory drive, muscle strength, work of breathing and energy expenditure, will be addressed in the second segment.