Airway ventilation pressures during bronchoscopy, bronchial blocker, and double-lumen endotracheal tube use: an in...

To quantify inspiratory flow resistance of instrumented single-lumen and double-lumen endotracheal tubes.

Bench-top in vitro experiments.

Laboratory of a university hospital.

In vitro lung simulator.

A lung simulator was ventilated mechanically via several single- and double-lumen endotracheal tubes (ETT) that were instrumented with adult and pediatric bronchoscopes as well as bronchial blockers. While ventilating with a square-flow wave and increasing peak inspiratory flow from 10-100 L/min, the pressures proximal and distal to the instrumented ETT were measured. Flow (Q) and the pressure loss (∆P) were related with regression of the quadratic equation: ∆P=k1Q+k2Q2.

With all combinations of single-lumen endotracheal tubes, double-lumen endotracheal tubes, bronchial blockers, and adult and pediatric bronchoscopes, ∆P was accurately related to Q using the quadratic equation with excellent fit, R2>0.99 for all combinations. The regression parameters k1 and k2 were statistically significant for all combinations except k1 with a bronchoscope through 37-Fr double-lumen endotracheal tube. Parameter k2 was dominant at flows above 10 L/min for uninstrumented airways and 20 L/min for instrumented airways. ∆P increased dramatically with flow, and increased with decreasing endotracheal tube size or addition of instrumentation in a quantitatively predictable manner.

Pressure loss across instrumented endotracheal tubes follows a predictable flow-dependant quadratic pattern. Using the quantitative in vitro results of this study, a clinician can maximize inspiratory ventilation pressures during these situations without delivering excessive airway pressures to the patient.