To reduce total cost of care, healthcare providers are increasingly turning toward home and ambulatory infusion pumps to free the patient from the hospital setting. These small, battery powered pumps save thousands of dollars in hospital room and nursing care costs. They also allow the patient to continue therapy while leading a more normal life in the comfort of the home or even on the go. Even within the hospital setting, patients and nurses benefit from the mobility that these smaller pumps provide.
The challenge for a home and ambulatory infusion pump designer is to create pumps that provide mobility and patient comfort while not sacrificing any quality of care (see Figures 1 and 2). Furthermore, the industry faces strong cost pressure, especially in the home market due to lower or nonexistent insurance reimbursement.
Mobility. Traditional bedside hospital pumps remain stationary and often use large and inefficient hybrid stepper motors. Hybrid stepper motors are sufficient in this application because they offer a cost-effective option to achieve the high torque required, and their size and power requirements are not prohibitive because the pumps do not move and primarily remain connected to wall power.
In contrast, home and ambulatory infusion pumps are carried on the patient or on a wheeled pole, and therefore often use higher power density and more efficient coreless DC brushed motors. This allows for a smaller motor and battery to create a much lighter and more compact pump that operates longer between charges. Both are critical for providing freedom to patients who want to resume normal activities (see Figure 3).
Custom integration of the motor into the pump casing can also greatly reduce pump size. For example, if the motor is in line with the pump axle, the motor shaft can be made long enough to double as the pump axle itself, eliminating the price and complexity of multiple mechanical components. Custom connectors and mountings can also help the motor more seamlessly fit the pump design and save valuable space (see Figure 4).
Patient comfort. The ability to receive therapy in the home environment instead of a hospital or clinic significantly improves quality of life. However, the much quieter home setting creates an additional challenge for pump designers in maintaining patient comfort. A gentle whirl that may have gone unnoticed among the chatter and alarms of a hospital may become quite disruptive in the quiet of the home, especially when a patient is sleeping. Additionally, low noise for the sake of discretion is key when administering drug therapy in a public setting.
Selecting the proper motor and gearhead technology is the first step to ensuring a quiet pump. Spur gearheads are naturally quieter than planetary gearheads due to the fewer contact points between gear teeth. If further noise reduction is necessary, plastic or ceramic can be chosen for the gear material, or helical gears can be used. Finally, careful sizing of the motor and gear ratio will ensure that the input speed to the gearhead is as low as possible, which has a significant impact on gearmotor noise.
Cost pressure. Due to the high performance required, the motor is often the most expensive component of a home infusion pump design. Fortunately, motor manufacturers have found ways to make high quality DC coreless motors more cost-effective without sacrificing quality through changes in material, processes, and manufacturing location. Additionally, a resourceful motor designer can devise ways to lower the overall cost of the pump, such as integration to remove redundant components, value-add features to reduce assembly time, and built-in low-resolution feedback systems to replace expensive encoders. For successful implementation of these cost-saving strategies, it is critical to collaboratively engage with a motor designer early in the concept development when all options can be considered.
Optimizing Mini Motors for a Home Infusion Pump
To illustrate the challenge that pump designers face in optimizing these many design criteria, consider a home infusion pump design that utilizes a linear peristaltic pump mechanism. Table 1 provides a look at the motor selection, noise, and feedback in closer detail. Here are some additional details:
The pump casing is plastic, is not sealed, and provides some noise dampening.
The gearmotor is mounted by screws from its front face, but otherwise there is just a thin layer of air between the outside of the motor and the pump case.
The pump is required to last for four years in the field, over which the pump will typically provide a two-hour treatment an average of four times per week for 1,664 hours of total motor run-time.