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Correspondence |
Cleveland, Ohio
To the Editor:
The recent case report by Vicente et al.1 concerning a patient-controlled analgesia (PCA)-related opiate overdose demonstrates some of the potential safety hazards of complex medical technology. It is sometimes helpful to consider the various means by which hazards involving such technologies may occur. In this context, I would like to offer the following taxonomy of PCA safety hazards. I hope this classification will be useful to both designers and users of PCA systems.
[1] Use of wrong drug or wrong cartridge (e.g., insertion of a 5-mg•mL-1 morphine cartridge when a 1-mg•mL-1 cartridge is required).
[2] Accidental misprogramming, sometimes as a consequence of a hostile user interface.2–4
[3] False triggering, for example, due to a short circuit in the PCA button5 or for other reasons.6,7
[4] False triggering by proxy (e.g., relatives pushing the PCA button because Granny is too sleepy to do it herself).
[5] Drug accumulation in iv deadspace.8 This may occur with large iv deadspaces under low flow conditions.
[6] Runaway fluid column due to "siphoning".9 (Should a crack occur in the PCA drug cartridge, entrainment of air into the system may lead to a free-flow of drug into the patient. Some manufacturers incorporate anti-siphon valves into their designs to prevent this).
[7] PCA machine malfunction due to hardware failure.10
[8] PCA machine malfunction related to software design error.11,12
[9] Retrograde flow of PCA analgesic drug into a secondary iv set (e.g., for administering antibiotics) due to a temporarily blocked iv catheter.13 When the iv catheter is subsequently unblocked, the PCA drug that has accumulated in the secondary iv bag is then suddenly released into the patient. (The use of a one-way valve on the secondary iv set will prevent this).
[10] Bad medical judgment in formulating PCA prescription, or opiate orders from other physicians unaware that PCA orders have been written.
[11] Anaphylaxis (either de novo or despite knowledge of risk of reaction).
[12] Extraordinary sensitivity to opiates resulting in unexpected respiratory depression.
In addition to these situations, there is one safety situation that, while theoretically possible, is unlikely to be encountered in real life.
[13] Reprogramming with criminal intent.
References
1 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: 328–32.
2 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: 253–63.[Medline]
3 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: 274–84.[Medline]
4 Doyle DJ, Vicente KJ. Patient-controlled analgesia (Letter). CMAJ 2001; 164: 620.
5 Doyle DJ, Vicente KJ. Electrical short circuit as a possible cause of death in patients on PCA machines: report on an opiate overdose and a possible preventive remedy (Letter). Anesthesiology 2001; 94: 940.
6 Chan S, Chen PP, Chui PT, Ma M. Unintentional bolus with Graseby 9300 pump (Letter). Anaesth Intensive Care 1998; 26: 117.
7 Christie L, Cranfield KA. A dangerous fault with a PCA pump (Letter). Anaesthesia 1998; 53: 827.
8 Doyle DJ, Nebbia S. Intravenous deadspace and patient safety in patient-controlled analgesia (Letter). Can J Anaesth 1995; 42: 658.
9 Grey TC, Sweeney ES. Patient-controlled analgesia (Letter). J Am Med Assoc 1988; 259: 2240.
10 Youngs PJ. A problem with a PCA pump (Letter). Anaesthesia 1993; 48: 829.
11 Ma M, Chen PP, Chan S, Chung D. A potential PCA hazard (Letter). Anaesthesia 1998; 53: 314.
12 White E. A problem with the Graseby 3300 PCA pump (Letter). Anaesthesia 1993; 48: 1013–4.
13 Notcutt W. Overdose of opioid from patient controlled analgesia pumps (Letter). Br J Anaesth 1992; 68: 450.
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  D. J. Doyle and A. Keebler Another failure mechanism leading to patient-controlled analgesia overdoses Can J Anesth, May 1, 2008; 55(5): 319 - 320. [Full Text] [PDF]
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S. Syed, J. E. Paul, M. Hueftlein, M. Kampf, and R. F. McLean Morphine overdose from error propagation on an acute pain service: [Une surdose de morphine resultant de multiples erreurs dans un service de douleur aigue]. Can J Anesth, June 1, 2006; 53(6): 586 - 590. [Abstract] [Full Text] [PDF]
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