Comparison of non-rebreather face mask and "tusk" mask in delivery of high concentration inspired oxygen

Purpose: In hyporic respiratory failure, where mechanical ventilation is either not readily available or declined by the patient, lifesaving concentrations of inspired oxygen can be delivered by face mask. Conventionally, nonrebreather face masks (NRM) with high oxygen flow rates have been used. We postulated that modifying the partial rebreather mask by inserting two 10 cm pieces of corrugated respiratory tubing ("tusks") into the exhalation ports of a partial rebreather mask would serve as reservoirs for gas entrainment, and should lead to a higher fractional concentration of inspired oxygen (FiO₂) and a higher arterial partial pressure for oxygen (paO₂), compared to the NRM. Methods: We prospectivery studied 19 normal subjects (30.5±6.3 years, percent of predicted forced expiratory volume in 1 second (FEV₁%) 103.2±12.1%; and percent of predicted diffusing capacity for carbon monoxide (D_LCO%) 92.9±17.2% (mean±SD)), and 7 patients with interstitial lung disease (ILD) (63.2± 12 years, FEV₁%=60.2±25.0% and D_LCO%=34.9± 19.4%). Patients were randomized to wear either the NRM or "tusk" mask for 30 minutes, both at a flow rate of 15 L/min, followed by a 60 minute washout period. Then, the other mask was applied for 30 minutes. Arterial blood gas measurements were performed immediately before and at the end of each 30 minute test period. Results: In the normal subjects, paO₂ using the NRM and "tusk" masks increased 263.4±90.1 mmHg and 345.6±77.4 mmHg respectively (p=.014 for the difference between mean values). The paO₂ increased 293.4±38.0 mmHg with the NRM and 378.4±61.7 mmHg with the "tusk" mask (p=.0011) in the patients with ILD. There was no statistically significant change in pH or paCO₂ using either mask in either group. Conclusion: In this group of normal subjects and patients with ILD, the "tusk" mask resulted in a significantly higher mean paO₂ than the conventional NRM at the same flow rate. Clinical Implications: Patients with hypoxemic respiratory failure in whom it is desirable to avoid mechanical ventilation may obtain additional benefit from oxygen delivered via the tusk mask.