RESULTS	With blood propofol concentrations increasing from 2 to 7.3 microg/ml , the C ( 50 ) of remifentanil decreased from 3.8 ng/ml to 0 ng/ml for laryngoscopy , from 4.4 ng/ml to 1.2 ng/ml for intubation , and from 6.3 ng/ml to 0.4 ng/ml for intraabdominal surgery .\