Ergonomic and Safety Issues in

Patient-Controlled Analgesia

D. John Doyle MD PhDDepartment of General Anesthesiology

Cleveland Clinic Foundation, USA

May 2004

A Continuing Clinical Challenge

Patient Controlled Analgesia (PCA)

• Patient Controlled Analgesia (PCA) is a medical technology used extensively for the treatment of pain.

• A typical PCA machine contains an microcomputer that is programmed to give (for instance) 1 milligram (mg) of intravenous morphine every time the patient pushes the "demand button". (This is a pushbutton on the end of a cable that usually looks and feels much like a nurse call button.)

• To prevent excessive drug administration, which can result in cessation of breathing and even cardiac arrest, the on-board computer ignores further patient until a "lockout period" has passed (usually 5-10 minutes).

Elements of a PCA prescription

• Route of administration (usually IV) • Loading dose (drug quantity) and interval of

administration (e.g. morphine, 4 mg, IV bolus) • Incremental dose administered at patient's discretion

(e.g. morphine, 1.5 mg, IV) • Lock-out interval - time interval after last dose during

which a patient request is denied (e.g., six minutes) • Cumulative dose limit (e.g. maximum dose for a four

hour period; morphine, 30 mg, IV • Background infusion rate (e.g. morphine, 1 mg/hr, IV)

[Many physicians set this to zero for safety reasons]

Advantages of PCA

• Patient can "fine tune" analgesia for preferred trade-off between analgesia, sedation, and mental clouding (for example, patients who are generally resting in bed may choose to use PCA only when getting up to the washroom).

• Little delay between requesting and getting the drug.

• Faster onset of effect than IM injections.

• No needles with their associated pain and complications.

Advantages of PCA

• No need to visit the narcotics cupboard and find the keys every time a patient needs a dose; potential for less associated paperwork.

• Computer in pump keeps a record of everything (including alarms and events).

• Record keeping for narcotics is potentially simplified.

• Reduced overall narcotic requirements (some studies).

Problems with PCA Devices• A number of problems with PCA devices have

been identified in the medical literature.

• For instance, excessive sedation and respiratory depression with PCA often lowers patient oxygen levels to unacceptable levels.

• Many of these problems may be due to programming errors resulting from a hostile interface.

• Some of these problems appear to have resulted in human fatalities.

Other Potential Hazards of PCA

• Wrong drug used

• Wrong concentration cartridge used

• Wrong programming parameters used

• Large ratio of PCA intravenous dead space relative to baseline IV flow (at high ratios drug takes too long to get to patient)

More Potential Hazards of PCA

• Coexisting IM narcotic orders from other physicians unaware that PCA orders have been written

• Relatives pushing PCA button on behalf of patient

• Mechanical failures

• Electrical failures

PCA Patient Interface• While the patient interface is very simple, it can still confuse

some patients.

• Some patients confuse the PCA button with the nurse call button, and give themselves an inadvertent extra dose of morphine when they actually intended to ask the nurse for help getting out of bed.

• Since most designs do not provide an indicator of the patient lockout status (a red/green LED would suffice), patients may not appreciate that their demands are being ignored during a lockout period.

• Some patients just give up, finding the technology to be unsatisfactory. The value of patient feedback in this setting cannot be overemphasized.

The importance of an intuitive interface is exemplified in the following e-letter I received from a frustrated patient:

Dr. Doyle:

I thought you'd be interested my "pain pump" experience I had at Tallahassee Memorial. I hasten to add that ANY hospital could have been at fault.

During my pre-op, no explanation was given about what a "pain pump" was. I went into surgery for removal of my uterus and ovaries, recovered, then was returned to my room -- all pain-free at the time. Gradually, the morphine wore off and my pain was real indeed. However, the effects of the anesthetic had not worn off and I was quite muddle-headed. The "just push this button" for pain relief made no sense to me and could not properly be assimilated by my muddled brain. For well over 5 hrs I suffered while my husband stood by helpless in his efforts to get the hospital to give me something IM or IV (other than the push-button choice). He wasn't allowed to punch that button for me!

I am totally opposed to suicide, by whatever means and for whatever purposes. However, I clearly remember (funny what a muddled brain would remember) thinking that, if I'd had a gun, I'd have shot myself , so extreme was the pain I was in. IM injections were finally initiated and, glad to say, I was out of the hospital in no time.

Please let anyone know that clear instructions about "pain pumps" AND the frequency that they can be administered ought to be given to the patient at their pre-op appointment as well as on the gurney awaiting the actual surgery. I'd bet that I'm not the first to be confused (I was just 40 yrs old at the time--not nearly elderly or slow thinking!).

Additionally, a lighted monitor (4" large letters for the nearsighted please!!!) indicating when the next dose is programmed to be available should be mandatory.

Mrs. T.D. W.

PCA Nurse Interface• The nurse (programming) interface can also be

complex.

• Nurses must correctly enter the drug concentration, dose, lockout period and other information for the unit to operate correctly.

• Unfortunately, medical instruments frequently have poorly designed user interfaces that promote human errors, sometimes with life-threatening consequences. So it is with PCA machines.

Studies of the Nurse Interface• Lin et al studied the nurse interface of a commercially

available PCA system, the Abbott Lifecare 4100 PCA Plus II infuser, using "cognitive task analysis" techniques.

• Based on this analysis, the interface was then redesigned "to include a dialog structure with fewer steps, a dialog overview showing the user's location in the programming sequence, better command feedback, easier error recovery, and clearer labels and messages.”

• Studies of the new interface showed significantly faster programming times, lower mental workload, and fewer errors compared to the manufacturers original interface.

Need for Human Factors Studies

• Human factors studies are obviously needed to ensure safe operation of complex medical equipment.

• Regrettably, such human factors studies on medical equipment are often abandoned in favor of early market penetration.

Drug Overdoses Associated with the Abbott Lifecare 4100 PCA Plus Machine

• In 1997, the ECRI safety watchdog (http://www.ecri.org/) documented deaths while patients were connected to the Lifecare 4100.

• In 2 of these cases, the alleged reasons for the deaths were the same - in the mode of operation used, when nurses program the drug concentration, the unit display shows a particular concentration value (e.g., 0.1 mg/mL).

• Nurses can either accept this initially displayed value or they can modify it using arrow controls.

Drug Overdoses Associated with the Abbott Lifecare 4100 PCA Plus Machine

• The safety-critical flaw in the design is that the Lifecare 4100 offers the minimum drug concentration as the initial choice (in this mode of operation)

• If nurses mistakenly accept the initially displayed minimum value (e.g., 0.1 mg/mL) instead of changing it to the correct value (e.g., 2.0 mg/mL), then the machine will "think" that the drug is less concentrated than it really is.

• As a result, it will deliver more liquid, and thus more narcotic, into the patient (i.e. deliver an overdose).

Drug Overdoses Associated with the Abbott Lifecare 4100 PCA Plus Machine

The Institute for Safe Medication Practices (http://www.ismp.org/) has recommended against purchasing Abbot's PCA machine ("Hospitals and purchasing groups should not contract with vendors of PCA pumps that default to a setting lower than available drug concentrations.")

Twelve Safety-Critical Situations that Apply to PCA Technology

[1] Inadvertent misprogramming

[2] Wrong cartridge insertion

[3] False triggering [for example, due to a short circuit]

[4] False triggering by proxy [relatives pushing the button]

[5] Drug accumulation in IV deadspace

[6] Runaway fluid column due to "siphoning"

Twelve Safety-Critical Situations that Apply to PCA Technology

[7] Anaphylaxis from drug [8] Bad medical judgment in formulating

PCA prescription [9] Coexisting IM or IV or PO narcotic

orders from other physicians unaware that PCA orders have been written

[10] Runaway hardware [not seen in the field?]

[11] Runaway software [not seen in the field?]

[12] Reprogramming with criminal intent [not seen in the field?]

Conclusions

PCA is a valuable clinical modality that presents potential difficulties to patients and nurses alike.

Ergonomic testing is essential to producing a good product.