Electronically displayed ventilator waveforms provide a wealth of insight into the physiology of the respiratory system. Pressure and flow values can be independent variables that reflect control by the ventilator or dependent variables that demonstrate the respiratory system’s response to mechanical ventilation. Diagrams of time-based pressure and flow curves may reveal underlying pathophysiology beyond more commonly assessed parameters such as peak airway pressure, respiratory rate, and tidal volume. In this narrative review, we introduce a stepwise approach clinicians can take to diagnose pulmonary pathophysiology by using ventilator waveforms in patients receiving pressure control ventilation or volume control ventilation. Understanding a patient’s pathophysiology (i.e., increased airway resistance) does not distinguish pathology (i.e., kinked endotracheal tube or bronchospasm). A pathology such as pulmonary edema may have more than one pathophysiologic process (i.e., increased airway resistance and low respiratory compliance). To interpret ventilator waveforms, we assume a one-compartment lung model with a linear response to a range of tidal volumes.1 We do not discuss identification of ventilation mode or adaptive ventilation.
Conclusions
Clinicians can use mechanical waveform analysis as a diagnostic tool to identify pulmonary pathophysiology. Flow and pressure waveforms can be interpreted to confirm diagnosis and to optimize ventilator management. This review offers tools for clinicians to use when developing a mental model hypothesis of a patient’s lung pathophysiology and offers a stepwise approach to either accepting or rejecting the hypothesis.
