The sequence for preparation of a programmable pump is more complex because of the internal peristaltic pump motor and its controller. The entire process takes about 20 minutes to complete. The pump model number, reservoir size, and the presence or absence of an access port are noted. The pump is not removed from its sterile packaging until CSF access has been obtained.
When CSF access has been obtained, or if the trial intrathecal catheter is used as the permanent catheter, the pump is interrogated in its sterile container to verify that the calibration constant matches that on the packaging. An error in the calibration constant when downloaded into the programmer will result in faulty readouts of pump performance or calculation of dosing. The pump is then warmed to 35 to 40°C. If this warming step is skipped, the reservoir valve may be activated, preventing infusion.
The pump reservoir is then drained of the fluid supplied by the manufacturer by inserting a Huber-type needle through the refill septum and into the reservoir and allowing the fluid to escape into a 20 mL syringe. The volume removed should be within 20% of the predicted volume after initial interrogation of the pump. If there is more than 20% variation, the pump may be faulty. The initial recommended fill of the reservoir is 10 mL, to avoid overpressurization. However, it has been determined that a full filling of the reservoir to 18 mL of infusate is safe. The advantage of fully filling the reservoir at the time of implantation is that the surgical wound is allowed to heal thoroughly, and any swelling will resolve before the next filling. Each subsequent refill is at 18 mL for safety, although the reservoir volume is 20 mL in the standard pump. A pump with a smaller reservoir (10 mL) is also available. During the pump filling, care must be exercised to avoid allowing air to enter the reservoir, since air in the reservoir chamber could lead to overpressurization and faulty volume estimates.
Using the pump programmer, the implant assistant programs a purge of the reservoir while it is still in the sterile container or on the sterile field after it has been removed. The pump has been placed on the sterile field, the catheter port cover is removed and the port is observed for flow. If after several minutes a drop of fluid is visualized, the pump is submerged in warm saline until the internal purge is completed, about 15 minutes. The pump is then ready for implantation.
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