Venous circulation from cerebral area is further aggravated by the inspiratory subatmospheric pressure during spontaneous ventilation , but such mechanism is being offset by the positive pressure ventilation . In addition , the obstruction on inner jugular veins can block the cerebral venous drainage , most especially during head-on-neck flexion . Meanwhile , in Abrams and Nottage 's (2003 ) experimental study of controlled respondents who have had shoulder arthroscopy , the findings of complications are conflictingly low (accounts to 5 .8 to 5 .9 ) compared to the...