Cases & Commentaries

PCA Overdose

Commentary By D. John Doyle, MD, PhD

The Case

A 49-year-old woman underwent an uneventful total
abdominal hysterectomy bilateral salpingo-oophorectomy.
Postoperatively, the patient complained of severe pain and received
intravenous morphine sulfate in small increments. She remained
alert and oriented and, while in the post-anesthesia care unit
(PACU), she began receiving a continuous infusion of morphine via a
patient-controlled analgesia (PCA) pump.

A few hours after leaving the PACU and arriving
on the floor, she was found pale with shallow breathing, a faint
pulse, and pinpoint pupils. The nursing staff called a
“code” and the patient was resuscitated and transferred
to the intensive care unit on a respirator. A search for reversible
causes was unrevealing and, despite aggressive supportive care, the
patient had no improvement in her mental status. Several days
later, an electroencephalogram result revealed no brain activity.
Based on family wishes, life support was withdrawn and the patient
died. Review of the case by providers implicated a PCA overdose,
though no autopsy was performed to exclude other etiologies. The
precise mechanism of the overdose was never elucidated.

The Commentary

The lack of details available in the
reader-submitted case synopsis limits the already challenging task
of identifying an exact mechanism of death. Even if we presume an
overdose was the cause, it is my experience from past
investigations of similar cases that the exact mechanism of
overdose is often not apparent.

Patient-controlled analgesia (PCA) is a
computer-based medical technology used extensively to treat
postoperative pain via self-administration of analgesic
agents.(1)
Potential benefits include superior pain control, automatic
electronic documentation, and improved utilization of nursing
resources. Unfortunately, however, analgesics also represent a
frequent cause of adverse drug events (ADEs).(2,3)

It is not known exactly how often ADEs are
associated with PCA use, especially because problems with medical
devices tend to be severely under-reported.(4) Nor is it known exactly which patients are at special
risk of ADEs in relation to PCA use, although common sense suggests
that special caution may be warranted in frail or elderly patients,
in patients with obstructive sleep apnea, and in patients with
impaired respiratory function.

A typical PCA machine (Figure) contains an embedded computer programmed to
give a specified amount of opiate intravenously every time the
patient pushes a button. To help prevent excessive drug
administration, the onboard computer ignores further patient
demands until a lockout period (usually set for 5–10
minutes) has passed. In addition, cumulative limits of opiates that
can be administered during specified time intervals also exist in
some models.

Despite such safety features, numerous reports of
respiratory depression and death associated with PCA pumps have
surfaced.(5-10)
A number of adverse outcomes with PCA use have involved particular
models that require manual entering of specific parameters. Easily
misprogrammed by caregivers, such models need a more sensible and
forgiving user interface.(11) A
number of patients have received opiate overdoses because of PCA
errors, such as when the operator has inserted a 5 mg/mL morphine
cartridge when the machine is expecting a concentration of 1 mg/mL
or has accepted the default (initial) drug concentration instead of
scrolling to select the correct value.(12-14)

In 1997, ECRI, a nonprofit health research
organization, documented three deaths that occurred during PCA
use.(12) In
at least two of the cases, the errors that led to the deaths
appeared to be related to the same critical design flaw: the
machine displays the minimal drug concentration as the initial
choice. If nurses mistakenly accept the initially displayed minimal
value (eg, 0.1 mg/mL) instead of changing it to the correct (and
higher) value (eg, 2.0 mg/mL), the machine will “think”
that the drug is less concentrated than it really is. As a result,
it will pump more liquid, and thus more opiate, into the patient
than is desired.

It should be emphasized, however, that other
mechanisms of PCA overdoses may occur. A possible classification
for such overdoses has been proposed.(15) Problems include misprogramming; using the wrong drug
or cartridge; IV flow, triggering, or pump malfunctions; hardware
or software failures; and others.

Under ideal circumstances, the continuous use of
a pulse oximeter and/or other forms of respiratory monitoring would
prevent many of these tragic deaths. In the real world, such
technologies are often too expensive and/or plagued with false
alarm problems for use on ordinary nursing floors. Fortunately, new
signal processing technologies are making pulse oximeter technology
much more reliable. These new oximeters may provide an important
mechanism to better monitor respiratory status and improve safety
when using PCA pumps.

In addition to improved respiratory monitoring
technology, attention to improving the PCA user interface is
desperately required, such as has been carried out at the
University of Toronto.(11,16)
Redesigning PCA pumps to make them more intuitive and easier to
program (using human factors
engineering techniques) will add another important safety
layer.(14) In
the meantime, hospitals should avoid purchasing PCA pumps known to
have design flaws.

Beyond drastically improving the user interface,
a recent article suggested several approaches to improve safety
when using PCA pumps.(14)
One potential safeguard would be to stock only a single
concentration of morphine cartridge (eg, 1 mg/mL). Where this is
not practical in every circumstance (such as in oncology wards),
the hospital should establish special safety measures when
higher-concentration morphine cartridges (eg, 5 mg/mL) are also
available. Another precaution would be to require an independent
check by a second caregiver when a PCA pump is programmed.
Caregivers should report any problems or complications associated
with PCA pumps (as well as all other medical devices) to hospital
authorities and the U.S. Food and Drug Administration (FDA). [To
file an online FDA report, visit https://www.accessdata.fda.gov/scripts/medwatch/].
In addition, there is a critical ongoing need for experts to
formally and informally review medical products in a
“Consumer Reports” fashion. Finally, in the event of an adverse clinical event
possibly related to PCA usage, nothing should be discarded, and an
investigation should begin immediately.

Take-Home Points

  • PCA pumps provide an important mechanism
    for delivering analgesia but can result in respiratory depression;
    routine monitoring of respiratory status may prevent future adverse
    events.
  • Achieving greater safety with the use of
    PCA pumps will require emphasis on improved design, better user
    interfaces, and continued vigilance in reporting existing flaws in
    current systems.

D. John Doyle,
MD, PhD
Staff Anesthesiologist
Department of General Anesthesiology
Cleveland Clinic Foundation

References

1. Ferrante FM, Ostheimer GW, Covino BG.
Patient-Controlled Analgesia. Boston, MA: Blackwell Scientific
Publications; 1990.

2. Classen DC, Pesotnik SL, Evans RS, Burke JP.
Computerized surveillance of adverse drug events in hospital
patients. JAMA. 1991;266:2847-2851.
[
go to pubmed
]

3. Bates DW, Cullen DJ, Laird N, et al. Incidence
of adverse drug events and potential adverse drug events.
Implications for prevention. ADE Prevention Study Group. JAMA.
1995;274:29-34.
[
go to pubmed
]

4. Vicente KJ, Kern S. Problems with medical
devices may be severely under-reported. Can J Nurs Leadersh.
2005;18:82-88.
[
go to pubmed
]

5. Grey TC, Sweeney ES. Patient-controlled
analgesia. JAMA. 1988;259:2240.
[
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]

6. Grover ER, Heath ML. Patient-controlled
analgesia. A serious incident. Anaesthesia. 1992;47:402-404.
[
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]

7. Geller RJ. Meperidine in patient-controlled
analgesia: a near-fatal mishap. Anesth Analg. 1993;76:655-657.
[
go to pubmed
]

8. Etches RC. Respiratory depression associated
patient-controlled analgesia: a review of eight cases. Can J
Anaesth. 1994;41:125-132.
[
go to pubmed
]

9. Baxter AD. Respiratory depression with
patient-controlled analgesia. Can J Anaesth. 1994;41:87-90.
[
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]

10. Kwan A. Overdose of morphine during PCA.
Anaesthesia. 1995;50:919.
[
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]

11. Lin L, Isla R, Doniz K, Harkness H, Vicente
KJ, Doyle DJ. Applying human factors to the design of medical
equipment: patient-controlled analgesia. J Clin Monit Comput.
1998;14:253-263.
[
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]

12. Abbott PCA Plus II patient-controlled
analgesia pumps prone to misprogramming resulting in narcotic
overinfusions. Health Devices. 1997;26:389-391.
[
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]

13. Design flaw predisposes Abbott Lifecare PCA
Plus II pump to dangerous medication errors. ISMP Medication Safety
Alert. May 31, 2000;5:2.

14. Vicente KJ, Kada-Bekhaled K, Hillel G,
Cassano A, Orser BA. Programming errors contribute to death from
patient-controlled analgesia: case report and estimate of
probability. Can J Anesth. 2003;50:328-332.
[
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]

15. Doyle DJ. Programming errors from
patient-controlled analgesia [comment]. Can J Anesth.
2003;50:855-856.
[
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]

16. Lin L, Vicente KJ, Doyle DJ. Patient safety,
potential adverse drug events, and medical device design: a human
factors engineering approach. J Biomed Inform. 2001;34:274-284.
[
go to pubmed
]

Figure

Figure. Patient-Controlled Analgesia (PCA)
Machine.