Ventilator graphics and respiratory mechanics in the patient with obstructive lung disease

Obstruction of the large and small airways occurs in several diseases, including asthma, chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, and bronchiolitis. This article discusses the role of ventilator waveforms in the context of factors that contribute to the development of respiratory failure and acute respiratory distress in patients with obstructive lung disease. Displays of pressure, flow, and volume, flow-volume loops, and pressure-volume loops are available on most modern ventilators. In mechanically ventilated patients with airway obstruction, ventilator graphics aid in recognizing abnormalities in function, in optimizing ventilator settings to promote patient-ventilator interaction, and in diagnosing complications before overt clinical signs develop. Ventilator waveforms are employed to detect the presence of dynamic hyperinflation and to measure lung mechanics. Various forms of patient-ventilator asynchrony (eg, auto-triggering and delayed or ineffective triggering) can also be detected by waveform analysis. Presence of flow limitation during expiration and excessive airway secretions can be determined from flow-volume loops. Abnormalities in pressure-volume loops occur when the trigger sensitivity is inadequate, with alterations in respiratory compliance, or during patient-ventilator asynchrony. Thus, ventilator waveforms play an important role in management of mechanically-ventilated patients with obstructive lung disease.