Abstract: A PCA pump has a fluid reservoir connected via a capillary and a gas vent filter to a cylinder having a piston urged outwardly by a spring to draw fluid into the cylinder. A button can be pressed by the user to press in the piston and dispense fluid. After actuation, the piston moves out to fill the cylinder with fluid and the button is disconnected from the piston until it has moved back to its outer position.

Abstract: PCA apparatus has a container with a movable piston dividing the container into a lower chamber for medication liquid and an upper, air-filled chamber. A manually-actuated air pump is connected to the upper chamber so that air can be supplied to the upper chamber to displace the piston and discharge the liquid through a catheter. The air pump has a cylinder containing a plunger with a capillary inlet, to limit the rate at which air can flow into the cylinder and hence be pumped to the upper chamber. The lower chamber is filled through a removable inlet spike connector by pulling up the piston with an actuating rod projecting from the upper end of the container. The rod is frangible so that it can be removed after filling the lower chamber.