Cumulative tracheal colonization greater than 10 ( 3 ) cfu/ml at Day 2 was as follows ( median [ interquartile range ] ) : cylindrical polyvinyl chloride , 0.66 ( 0.58-0 .74 ) ; cylindrical polyurethane , 0.61 ( 0.53-0 .70 ) ; conical polyvinyl chloride , 0.67 ( 0.60-0 .76 ) ; and conical polyurethane , 0.62 ( 0.55-0 .70 ) ( P = 0.55 ) .