Continuous monitoring of endotracheal tube obstructions using naturally occurring pressure and flow oscillations

The endotracheal tube resistance dominates the total airway resistance in most intubated patients. Mucus deposition and biofilm formation can rapidly increase tube resistance and thereby contribute to serious ventilatory impairments, including dynamic hyperinflation, intrinsic PEEP build-up, added work of breathing, and patient-ventilator asynchrony. During controlled mechanical ventilation, an increased tube resistance can be inferred from the difference between peak and plateau pressure, but this approach fails during pressure-supported spontaneous breathing.

We present a method that estimates the linear and nonlinear components of tube resistance from naturally occurring airway pressure and flow fluctuations at the airway opening, without a tracheal pressure sensor and without imposed forced oscillations. This is achieved by solving the equation of motion using band-pass filtered airway pressure and flow signals. Band-pass filtering isolates the relevant resistive and inertive pressure losses across the tube by removing slow contributions from muscle pressure and lung elastance as well as high-frequency noise.

Across different ventilation modes, ventilator settings, tube diameters, filters, and breathing patterns, the method recovers both linear and nonlinear tube resistance parameters with < 10% error and < 2% bias. The method can also track progressive tube obstruction on a breath-by-breath basis.

Continuous estimation of the endotracheal tube resistance from naturally occurring, ventilator-induced airway pressure and flow fluctuations enables breath-by-breath detection of tube obstruction and provides the parameters required for automatic tube resistance compensation during spontaneous breathing. This approach may improve patient safety, reduce patient-ventilator asynchrony, and facilitate weaning.