Patent ID: 8152762

Claim:
A retractable safety needle syringe, the syringe comprising: a syringe body defining a distal end, a proximal portion and an inner surface; a variable fluid compartment located within the syringe body and in fluid communication with the distal end of the syringe, the variable fluid compartment configured to receive a liquid for injection into a patient through the distal end of the syringe; a variable vacuum compartment located proximally from the variable fluid compartment within the syringe body, the distal end of the variable vacuum compartment sealed on the distal end to prevent fluid communication from the variable vacuum compartment with the distal end of the syringe and with the variable liquid compartment, the variable vacuum compartment configured to produce a retraction force when the a plunger is depressed; the plunger having a piston slideably disposed within the syringe body, a shaft extending through the proximal portion of the syringe body, a thumb platform attached to the shaft for traversing the piston between an engaged position and a retracted position, wherein the piston, the inner surface of the syringe body and the proximal portion of the syringe body define the variable vacuum compartment, and a through hole formed through the shaft, the through hole selectively blockable by a user independently of the position of the plunger within the syringe body, the through hole configured to provide air communication between the variable vacuum compartment and an environment external to the safety syringe when unblocked and to prevent air communication between the variable vacuum compartment and the environment when blocked, the variable vacuum compartment being otherwise sealed from the external environment; a distal seal disposed between the plunger piston and the syringe body forming a fluid tight and air-tight seal between the plunger piston and the syringe body; and a needle holder disposable at the distal portion of the syringe body, the needle holder being removeably engageable to the distal portion of the syringe body and engageable to the piston; wherein the vacuum compartment is configured to increase in volume when the piston moves toward the distal end of the syringe body, the increase in volume creating a retraction force when the through hole is blocked but not when the through hole is unblocked; and wherein the retraction force created is greater than a retaining force engaging the needle holder with the distal portion of the syringe body such that the retraction force moves the piston, the needle holder, and the needle toward the proximal portion of the syringe body when the injection is complete.