An apparatus for administering fluid into a fluid-filled anatomic space capable of receiving fluid at a lower pressure than tissues surrounding the anatomic space, the apparatus comprising: a disposables assembly comprising: a syringe having a body for containing a fluid to be injected into the anatomic space, the syringe having a plunger movable in one end of the body for dispensing fluid from an opposite end of the body, tubing permanently connected to the opposite end of the body, a needle connected to the tubing and having a point insertable into a subject and movable through tissues surrounding the anatomic space, for seeking the anatomic space, and an in-line pressure transducer for generating a signal corresponding to an instantaneous pressure at the point of the needle; a drive unit mechanically connected to the syringe and electrically connected to the pressure transducer, the drive unit including a controller with a computer, a memory for storing a first selected pressure that is selected to be compatible with injecting fluid into the fluid-filled anatomic space, a motor connected to and controlled by the computer, and a syringe armature connected to the motor and mechanically connected to the syringe for moving the plunger into and out of the body for respectively injecting and aspirating fluid at the point of the needle for injecting and aspirating fluid into and out of the subject; and the computer being programmed to control the motor to move the plunger for a non-continuous fluid flow into the subject until the first selected pressure is detected by the pressure transducer at which time the motor is stopped to stop a flow of additional fluid to the subject, so that as the needle is moved in tissues of the subject surrounding the fluid-filled anatomic space, fluid flow to the tissues stops at instantaneous pressures above the first selected pressure and resumes when the instantaneous pressure falls below the first selected pressure, to indicate the point of the needle is in the anatomic space and to then resume injecting fluid into the anatomic space, wherein said apparatus is characterised in that the memory stores a second selected pressure that is below the first selected pressure by a first selected amount, the computer being programmed to resume operation of the motor to resume moving the plunger to resume flow of fluid to the needle point only when the instantaneous pressure is below P2. a disposables assembly comprising: a syringe having a body for containing a fluid to be injected into the anatomic space, the syringe having a plunger movable in one end of the body for dispensing fluid from an opposite end of the body, tubing permanently connected to the opposite end of the body, a needle connected to the tubing and having a point insertable into a subject and movable through tissues surrounding the anatomic space, for seeking the anatomic space, and an in-line pressure transducer for generating a signal corresponding to an instantaneous pressure at the point of the needle; a syringe having a body for containing a fluid to be injected into the anatomic space, the syringe having a plunger movable in one end of the body for dispensing fluid from an opposite end of the body, tubing permanently connected to the opposite end of the body, a needle connected to the tubing and having a point insertable into a subject and movable through tissues surrounding the anatomic space, for seeking the anatomic space, and an in-line pressure transducer for generating a signal corresponding to an instantaneous pressure at the point of the needle; a drive unit mechanically connected to the syringe and electrically connected to the pressure transducer, the drive unit including a controller with a computer, a memory for storing a first selected pressure that is selected to be compatible with injecting fluid into the fluid-filled anatomic space, a motor connected to and controlled by the computer, and a syringe armature connected to the motor and mechanically connected to the syringe for moving the plunger into and out of the body for respectively injecting and aspirating fluid at the point of the needle for injecting and aspirating fluid into and out of the subject; and the computer being programmed to control the motor to move the plunger for a non-continuous fluid flow into the subject until the first selected pressure is detected by the pressure transducer at which time the motor is stopped to stop a flow of additional fluid to the subject,