A needle assembly includes an outer cannula having a distal end portion, the distal end portion comprising a sharp bevel facilitating insertion of the needle assembly into a subject. The needle assembly further includes an inner cannula slidably disposed coaxially in the lumen of the outer cannula and movable between an extended position and a retracted position, the inner cannula having a blunt distal end portion extending beyond the sharp bevel of the outer cannula whenever the inner cannula is in the extended position. The needle assembly further includes a bias coupled to the inner cannula in a manner favoring automatic positioning of the inner cannula at the extended position. The needle assembly includes a valve located in fluid communication with the lumen of the inner cannula to allow fluid to exit the subject through the inner cannula, and to prevent ingress of fluid into the subject.