Aim: Determine the capability of a new nasal cannula system (Silhouette, Parker Instrument, Hatfield, PA) to reliably deliver predictable concentrations of nitrous oxide for dental sedation and deliver 100% O2 following the procedure as required by the ADA and AAPD. Methods: 24 volunteers, 12 male, 12 female, 26-61 y/o, took part. Body weight and actual corresponding resting respiratory minute volume (MV) were recorded for each subject. As per manufacturer's instructions, the system was properly fitted, nasal cannula in the right nostril, hood over nose, sealed with attached adhesive and flowmeter set to 6 LPM, which is the maximum safe flow rate [1]. N2O was set at 70% for 10 minutes followed by 100% O2 for 5 minutes. Max N2O concentration was measured during the N2O application and max O2 concentration following the washout of N2O. Results: Females showed significantly lower respiratory minute volumes (MV) and significantly higher max N2O and max O2. Spearman's rank correlation coefficients (rho) were as follows: Total (n=24) MV/N2O: rho -0.93, p0.001, MV/02: rho -0.60, p=0.002. Male (n=12) MV/N2O: rho -0.83, p0.001, MV/O2: rho -0.55, p=0.064. Female (n=12) MV/N2O: rho -0.86, p0.001, MV/O2: rho -0.58 p=0.047. Conclusion: Nasal cannulas have been used to administer low concentrations of oxygen for many years but are known to deliver unpredictable gas concentrations [2]. This study shows similarly unpredictable results for nitrous oxide using a new nasal cannula system. Lower MV causes an unpredictable increase in inhaled N2O and the system is not capable of delivering 100% O2 at the conclusion of N2O sedation. 1. Ward, J.J., High-flow oxygen administration by nasal cannula for adult and perinatal patients. Respir Care, 2013. 58(1): p. 98-122. 2. O'Reilly Nugent, A., et al., Measurement of oxygen concentration delivered via nasal cannulae by tracheal sampling. Respirology, 2014. 19(4): p. 538-43. Keywords: porter silhouette, nitrous oxide, sedation, complications