Infusion pumps can administer fluids in ways that would be impractically expensive or unreliable if performed manually by nursing staff. For example, they can administer as little as 0.1 ml per hour injections (too small for a drip), injections every minute, injections with repeated boluses requested by the patient, up to maximum number per hour, or fluids whose volumes vary by the time of day. As they can produce high but controlled pressures, they can inject controlled amounts of fluids subcutaneously (beneath the skin), or epidural (just within the surface of the central nervous system).
In olden days injection pumps are used manually. It is difficult to deliver the liquid in small quantities for us. When we use manually, it may be small decrement or increment in dosage. Exact value is not possible by using manual operation. So to over come these draw backs infusion pumps are used. And exact our required value of dosage will delivered by infusion pump.