N2 gas egress from patients' airways during LN2 spray cryotherapy

- Fluid mechanics simulations of gaseous flow completed for first 4 bronchial generations.
- N2 Egress flow rates > 0.64 L/s for gen 0-3 with inserted endotracheal tube and bronchoscope.
- Measured typical LN2 spray cryotherapy generates N2 input rates 0.24 L/s.
- Airway N2 pressure maintained < 40 cm H2O with passive venting areas > 20 mm2.
- Bench and Porcine studies confirm safe airway pressures during LN2 spray cryotherapy.

Spray cryotherapy using liquid nitrogen (LN2) is a general surgical tool used to ablate benign or malignant lesions. Adequate egress of the gaseous nitrogen (N2) generated during this process must be provided for safe use when LN2 is used within the body rather than topically. When delivered to either the gastrointestinal tract (requiring active venting via a suction tube) or body cavities open to room barometric pressure (such as lung airways) allowing for passive venting, the N2 gas generated from the boiling process must be evacuated. This work will examine the egress of N2 during procedures requiring passive venting from human airways undergoing liquid nitrogen spray cryotherapy. Venting characteristics for safe N2 egress will be presented and discussed based on analytical modeling using fluid mechanics simulations and experimental studies of N2 venting with laboratory and porcine models.