There was little difference in the incidence of post-LP headache between the two needle sizes ( 22-gauge 7.2 % , 95 % CI 3.8 to 12.2 ; 25-gauge 4.6 % , 95 % CI 2.0 to 8.9 , p = 0.3 ) or in the incidence of any headache ( 22-gauge 18 % 95 % CI 12.5 to 24.6 ; 25-gauge 15 % , 95 % CI 10.0 to 21.1 , p = 0.4 ) .