Plunger activated vacuum release mechanism for a syringe

1. 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.

2. The syringe of claim 1 further comprising a proximal seal disposed between the plunger shaft and the syringe body forming an airtight seal between the plunger shaft and the syringe body, and wherein the proximal seal, distal seal and syringe body define the variable vacuum compartment.

3. The syringe of claim 1 wherein the through hole extends between an outer surface of the shaft and the thumb platform.

4. The syringe of claim 3 wherein an entrance of the through hole is centrally positioned on the thumb platform.

5. The syringe of claim 3 wherein an entrance of the through hole is laterally positioned on the thumb platform.

6. The syringe of claim 1 wherein the through hole is configured to be blocked by the placement of a finger over an entrance of the through hole.

7. The syringe of claim 1 further comprising a shut off valve configured to block the through hole.

8. The retractable safety syringe of claim 7 , wherein the shutoff valve is located external to the syringe body.

9. The syringe of claim 1 wherein the through hole extends from a distal portion of the shaft to the thumb platform.

10. The retractable safety syringe of claim 1 , wherein the through hole is selectively blockable externally to the syringe body.

11. A method of injecting fluid into a patient, the method comprising:

inverting a syringe having a needle attached to a needle holder so as to point the needle upward, the syringe having a tubular syringe body, a variable liquid 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 liquid 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; a piston disposed within the syringe body forming a variable fluid chamber between the piston, the needle, and the inner surface of the syringe body, the syringe also containing a proximal seal disposed within the syringe body near a proximal end of the syringe body, the proximal seal, piston, and inner surface forming a variable vacuum compartment, a through hole selectively blockable by a user independently of the position of the plunger in the syringe body, the through hole passing from the interior of the variable vacuum compartment to the outside of the syringe, the through hole configured to provide air communication between the variable vacuum compartment and an environment external to the 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;

leaving the through hole open while moving the piston of the syringe toward the needle to remove trapped air from the variable fluid chamber, allowing air into the variable vacuum compartment via the through hole to equalize pressure within the variable vacuum compartment with ambient pressure;

inserting the needle into the patient;

blocking the through hole while traversing the piston to inject a fluid into the patient, preventing air from entering the variable vacuum compartment and reducing the pressure within the variable vacuum compartment below the ambient pressure such that the variable vacuum compartment creates a retraction force while the through hole is blocked;

engaging the piston with the needle holder; and

allowing the retraction force to move the piston, the needle holder, and the needle into the syringe body.

12. The method of claim 11 further comprising:

leaving the through hole open while moving the piston away from the needle, removing air from the variable vacuum compartment via the through hole while filling the variable fluid chamber with fluid.

13. The method of claim 11 wherein blocking the through hole further comprises placing one of a user's digits over an entrance of the through hole.

14. The method of claim 11 wherein blocking the through hole further comprises traversing a vane of a shut off valve from an open position to a closed position.

15. The method of claim 14 , wherein the shutoff valve is located external to the syringe body.

16. The method of claim 11 , wherein the through hole is blocked externally to the syringe body.

17. 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 a the variable vacuum compartment, and

a through hole formed through the shaft, the through hole selectively blockable by a user, 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, so that, while the through hole is unblocked, air is introduced the variable vacuum compartment for a substantial distance while the plunger is traversed to an engaged position and air is removed from the variable vacuum compartment while the plunger is traversed to a retracted position;

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.

18. The syringe of claim 17 wherein the through hole extends between an outer surface of the shaft and the thumb platform.

19. The syringe of claim 18 , wherein an entrance of the through hole is laterally positioned on the thumb platform.

20. The retractable safety syringe of claim 17 , wherein the through hole is selectively blockable externally to the syringe body.