A syringe assembly comprising: a cylinder (120) that includes a cylindrical side wall (110) having an inner surface defining a chamber (128) for retaining fluid, an open proximal end (129) and a distal end (121 ) which includes a distal wall (122) having an opening (111) through a fluid communication with said chamber (128)； an elongated piston rod (140) including a proximal end (149), a distal end (141) and a main body (148) extending between the proximal and distal end, the piston rod (140) being distal and proximally movable within said chamber (128), including the proximal end (149) a thumb press (300) having a proximal end (309), a distal end (301) and a diameter, including the distal end (141) from the piston rod (140) a plug coupling part (146)； an annular extension (400) projecting proximally from the proximal end (129) of the cylinder (120) having a diameter greater than the diameter of the thumb press (300)； and a plug (160) having a proximal end (169) and a distal end (161), the plug (160) attached to the coupling part (146) of the plunger rod plug (140) characterized in that, said cap is distal and proximally movable with respect to the coupling portion (146) of the cap for a preselected axial distance, so that when the distal end (161) of the cap (160) is in contact with the distal wall (122) of the cylinder (120), the thumb press (300) is allowed to advance distally in the annular extension (400) and the annular extension (400) at least partially envelops a portion of the thumb press (300) to prevent the user access the thumb press (300) and move the piston rod (140) in a proximal direction, the plug coupling part (146) comprising a visual indicator (510) that is fully visible when the part (146) of plug coupling moves proximally relative to the plug (160 ).Un conjunto de jeringa que comprende: un cilindro (120) que incluye una pared lateral cilíndrica (110) que tiene una superficie interior que define una cámara (128) para retener fluido, un extremo p
