Sentence:  While my normal practice is to explain the system to the patient preoperatively, it is not necessary to show the <WSD>palliator</WSD> to the patient at this time, and patients can operate PCA satisfactorily where no preoperative instruction has been possible. 
Meaning of the word marked with <WSD> tags:  (medicine) A device that allows a patient to control the amount of pain medication that is added into an intravenous drip; infusion pump.