RESULTS	Group 1 had significantly fewer episodes of severe carbon dioxide retention ( rise in PtcCO ( 2 ) > / = 40 mm Hg above baseline ) than group 2 ( 0 of 199 versus 5 of 196 , respectively , p = 0.03 ) , as well a shorter mean duration of procedure discomfort ( 8.3 % of procedure duration rated as `` uncomfortable '' versus 11.5 % , p = 0.04 ) .\