There is a myth in health care that human error can be eliminated altogether, as evidenced by calls to aggressively seek a zero error rate. (Anderson & Ellis, 1999). However, errors are an inevitable consequence of human performance (Reason, 1990, 1997) and are symptoms of broader systems problems, not causes in themselves. Only by viewing errors as sources of information about the "safety health" of an organization can we learn appropriate lessons to improve patient safety.
The "systems approach" to error analysis has been widely adopted in the aviation and nuclear industries, in which a commonly used paradigm of organizational accidents is Reason's Swiss cheese model (Reason, 1990, 1997). This model distinguishes between active failures and latent conditions. Active failures are errors and violations committed by people at the sharp end of the system, i.e. pilots, control room operators and, in this domain, pharmacists, blood bank technicians, nurses, doctors, etc. Active failures have an immediate impact on safety.
Latent conditions arise from fallible decisions made by the higher management in an organization, by regulators, governments, designers, manufacturers and policy makers. Latent conditions lead to weaknesses in the organization's defenses, increasing the likelihood that when active failures occur they will combine with existing preconditions, breach the system's defenses and result in an organizational accident. Latent conditions and active failures lead to windows of opportunity in the system's defenses which, when aligned across several levels of a system, lead to an adverse event (i.e. death or critical incident).
Research on Drug Errors
Adverse drug events (ADEs) are defined as "….injury resulting from a medical intervention relating to a drug (Bates et al, 1995). Drug errors have been estimated to account for over a quarter of causes of ADEs (Bates et al, 1995). Such errors are defined as any preventable event that may cause or lead to inappropriate medication use or patient harm while the drug is in the control of the health care professional, patient or consumer (US Pharmacopeia, 1995). All stages of the drug delivery process (i.e. prescribing, transcribing, dispensing and administration) are susceptible to error.
Errors per stage of the drug delivery process
The landmark Harvard Medical Practice Study reported that adverse events occurred in 3-7% of hospitalized patients (Brennan et al, 1991), with 19% of these events resulting from drug complications (Leape et al, 1991). Four years later, the adverse drug event prevention study analyzed patient records from 4031 adult admissions to two USA hospitals over a 6-month period. Results showed that 49% of errors occurred in the drug ordering stage (i.e. prescribing), 11% in transcription, 14% in dispensing and 26% in administration. The most frequent types of errors in the drug prescribing stage were wrong dose, wrong frequency, wrong choice and known allergy (Bates et al, 1995; Leape et al, 1995).
This study also analyzed error recovery, i.e. the circumstances under which errors were detected and corrected. Errors were more likely to be recovered when they occurred in the early stages of the drug delivery process. Whereas 42% of drug prescribing and 37% of dispensing errors were recovered, none of the administration errors were. Results showed that nurses were most likely to recover errors. Sixteen "systems failures" which led to these drug errors were also identified (Leape et al, 1995). Systems failures are factors pertaining to the organization and its' processes which increase the likelihood that clinicians and nurses will make errors.
Errors per medical speciality
The incidence of drug errors has been shown to increase as more intensive levels of patient care are needed (Vincer et al, 1989; Wilson et al, 1998). An analysis of a pediatric cardiac ward and cardiac intensive care unit (ICU) has shown that drug errors were seven times more likely to occur in the ICU setting than on the ward (Wilson et al, 1998). In a recent study involving a retrospective review of incident reports from a Scottish pediatric hospital, results showed that the highest medication error rates occurred in the Neonatal Intensive Care Unit (NICU) and Pediatric Intensive Care Unit (PICU) (Ross et al, 2000).
The limited value of error counting
Drug administration errors may originate in the prescribing, transcribing or dispensing stages and remain undetected by in-built system checks. Hence, drug administration may often be the final, but not the only point, at which errors occur. Hematology and oncology is often disadvantaged from the outset by error counting studies because many disorders, for example acute lymphoblastic and acute myeloid leukemia, have complex drug protocols issued by the United Kingdom Children's Cancer Study Group.
Health care systems which treat such patients invariably use more drugs, and more complex combinations of drug therapies, than other medical specialities. It is important that these factors are taken into account when making comparisons between hematology and other medical specialities.
It is also important to choose an appropriate denominator. Studies that have used the number of admissions per ward (for example, Ross et al, 2000) may underestimate the magnitude of the denominator because patients may take numerous drugs. It is therefore best to use the number of drugs prescribed, dispensed and administered per 24 h or per week or the number of occasions in which error was possible if cross-speciality comparisons are to be made (for example, Bates et al, 1995; Ridge et al, 1995).
Error counting studies have other important weaknesses. Firstly, definitions of error vary across studies and this invariably influences what is included in the analysis process. Secondly, studies based on the retrospective analysis of patient notes or incident reports are suspect because the data may be unrepresentative. The low incident reporting rate in the study by Ross et al (2000) may say more about the hospital's incident reporting culture than the incidence of errors across specialities.
Types of drugs commonly associated with drug errors
Significant differences have also been found between the classes of drugs associated with prescribing errors. Betablockers, theophyllines and anticonvulsants had the highest error frequencies in one study of a multidisciplinary pediatric intensive care unit (Bodrun & Butt, 1992). Xanthines, cardiovascular agents, antimicrobials and narcotics were the drugs most frequently associated with errors in another study based in a tertiary care teaching hospital (Lesar et al, 1997).
In a more recent study, 56% (109/195 errors) of all reported errors involved intravenous drug administration, with antibiotics/antivirals, parenteral nutrition/intravenous fluids and anticancer drugs being the three categories of drug most frequently involved in intravenous medication errors (Ross et al, 2000).
These findings have to be interpreted cautiously because some types of drugs are intrinsically more harmful than others. The likelihood of detecting an error is a function of its' consequences for the patient. Hence, in the studies cited above, dangerous drugs such as xanthines, anticoagulants and opioids may be over-represented because their harmful effects are more evident than those of other classes of drug.
-- Allard, J., Carthey, J., Cope, J., Pitt, M., & Woodward, S. (2002). MEDICATION ERRORS: CAUSES, PREVENTION AND REDUCTION. British Journal Of Haematology116(2), 255-265. doi:10.1046/j.1365-2141.2002.t01-1-03272.x
Reflection Exercise #3
The preceding section contained information
about causes and prevention of medication errors. Write one case study example
regarding how you might use the content of this section in your practice.
What is the Swiss Cheese Model? Record the letter of the correct answer the