Pill-pushing cart ensures patient safetyPill-pushing cart ensures patient safety

Here's a cause of death you probably haven't considered: According to the National Academy of Sciences' Institute of Medicine, around 7,000 Americans die each year from errors in administration of prescription medicines-exceeding deaths from workplace injuries. And thousands of others suffer from allergic reactions to medication. Add to that a shortage of pharmacists (only a 5% increase annually) and an increasing volume of prescriptions (expected to double by 2005) and the prognosis might seem to be guarded.

But modern pick-and-place robots are beginning to allow automation of the prescription-filling process at pharmacies across the country. These systems allow pharmacists to double-check the robot's barcode-selected prescription before being administered to the patient.

While automation appears to be gaining on the problem in general, until recently there remained a gap at nursing homes. Here, nurses usually make rounds to administer medication to patients in each room, completing the necessary paperwork after each round. But, according to Dennis Murdock, design engineer for Pearson Medication Technologies (PMT; Alexandria, LA), there are several potential problems with this arrangement that a robotic system could alleviate:

The time lag between dispensing medication and filling out the paperwork relies on memory for accuracy. Also a two-hour round/two-hour paper-work cycle means the nurse is not doing what she or he is trained to do half of the time.

If a patient has an allergic reaction, regulations often require that the rest of the prescription be discarded, at extra cost to the healthcare system.

With nurses having to carry prescription containers, there is potential for pilferage of drugs.

While seemingly a simple solution, development of a practical portable, secure robotic dispenser for nursing homes had its unique design challenges, according to Murdock, team leader for developing PMT's RX ⁵ medication cart (see sidebar).

Pick-and-place precision. At the heart of the RX ⁵ is a miniature robot that delivers the prescription drugs to the nurse, who administers them to the patient. The computerized system also automatically does the paperwork for the nurse, accounting for each item dispensed.

Rexroth Star (Charlotte, NC) specifically designed the cart's 35-lb, three-axis (x, y, and z) gantry robot for PMT and, according to Murdock, "It's built with an aluminum frame like we used on the cart itself, rigid in the x-y plane." He notes that, "other suppliers wanted to use off-the-shelf systems" which require four times the power and weigh up to 60 lb. Some also have excessive vibration and noise. "Rexroth sent their engineers down here and they custom built it for one third the cost," Murdock adds.

In use, the nurse confirms the patient's name using the RX ⁵ touch screen. The system displays a digital image of the patient, allowing for validation that the correct person is actually receiving the medication. The robot then positions a vacuum-pump, pick-and-place head to within an accuracy of 0.030 inches over any one of 126 medication containers in a tray at the bottom of the cart. Each container is barcoded and read by the robot to ensure all proper drugs for a given patient are retrieved. The system generates the individual container barcodes directly from the bulk containers supplied by the drug company, further reducing the chance for errors. As a final safeguard, the tray is loaded and locked by a pharmacist who can spot any labeling errors.

The system creates a bill for only pills retrieved, not for any larger supply, as with a usual prescription that may be discarded after an allergic reaction. "What's slick," says Murdock, "is the pharmacist can put the containers in the tray in any order. The system scans and makes its own look up table for the medication." The vacuum head next picks up a pill or capsule. Linked to the barcode is a data base so the system knows how much vacuum to draw to retrieve only one pill, ranging in size from "pinheads" of 50 mg to "horse chokers" coming in at 2,000 mg. An infrared LED and sensor confirm that the pill has been grasped, and the robot deposits it in a vertical conveyor to lift it to the top of the cart so the nurse will not be stooping all day long.

If a patient requires only a half dose, the computer notifies the nurse so the other half of a tablet can be returned to a secure container and inventoried. A similar routine is done if a patient is unable to swallow a pill. Such tight inventory control also aids in avoiding pilferage of controlled substances.

With prescription errors estimated to run about 17% of all of those filled, and the high cost of prescription waste ($7 million in Louisiana, PMT's home state, alone), such computerized dispensing systems should aid in reducing injuries, deaths, and health care expenses.

Lightening the load

A major design challenge was keeping the RX ⁵ medication cart's weight below 200 lb so that a nurse half that weight could move it. For starters, the PMT team went to an aluminum frame for lightness and low cost. They built in stiffness by tailoring the frame members to have high cross-sectional moments of inertia. The resulting cart dimensions are 28 inches wide, by 41 inches long, and 42.5 inches high.

But design Engineer Dennis Murdock says, "The biggest problem was battery power." Other products on the market use two 80A-hr, lead-acid batteries that hefted in at 60 lb each-clearly unacceptable, along with issues of acid fumes. The PMT designers found a sealed 32A-hr, 40-lb gel/acid hybrid cell made by Hawker Energy Products (Warrensburg, MO) that lasts up to three times as long (6 hr) without a recharge, and can be charged to full capacity in 20 min. Murdock adds that the key to getting longer life with the lower capacity battery is proprietary control architecture and circuitry (along with low electrical resistance and power consumption) which allow "using the lower end of the battery" to still put 12V into the system when battery output is between 6 and 12V.

Even with weight on target, Murdock says the requirement to easily start and stop the cart, on tile or carpet, dictated low-friction operating castors. Engineers selected twin, large wheel (5-inch diameter), ball-bearing castors from Darcor (Toronto, Ontario) to spread the weight, which he adds have proved smooth and trouble free.