An error is defined as " an unintended act (either of omission or commission) or one that does not achieve its intended outcome" (Leape, 1991). In the Harvard Medical Practice Study, 69 % of the injuries were due to errors. However, since most errors do not lead to patient injury, the incidence of error in medical practice is likely to be much higher than the rate of adverse events. The incidence of medication errors, for instance, are high in patients admitted to hospitals, but most do not result in injury (Bates et al., 1995). McL Wilson et al (1995) argue that adverse events in health care "seldom arise from a single human error or the failure of one item of equipment, but are usually associated with complex interactions between management, organisational, technical and equipment problems". They found that system errors accounted for 16 % of adverse events, errors of omission were judged to have occurred in 52 % of them, and errors of commission in 27 %. The type of error could not be determined in 21 % of adverse events.
In the few studies (e.g. autopsy studies, house officers mistakes) that have looked specifically at errors, errors have been found to be very common. For instance, in a review of 50,000 autopsies of patients dying from one of 11 specific diseases (Anderson et al., 1989), the accuracy of a high number of medical diagnoses was found to be erroneous. Rates of 35 to 40 % of missed diagnoses causing death were discovered (Anderson et al., 1989; Goldman et al., 1983 ; Cameron and McGoogan , 1981). Anderson et al (1989) states that it is often "physician factors rather than patient factors that account for the great majority of missed diagnoses... with the misdiagnoses approximately evenly divided among errors of
Chapter 3: Errors and adverse events in health care
omission and errors of judgement...", the most common cause of diagnostic errors being lack of awareness or alertness on the part of the physician.
In the autopsy studies, it was also observed that improvement in diagnostic technologies had not had an apparent impact on the accuracy of diagnosis. In fact, several studies have shown that doctors have problems in interpreting particular tests or using certain types of diagnostic procedures. Cooper, Newbower and Kitz (1984) claim that the increased sophistication and complexity of medical technology have made errors more likely to occur in its operation. Even with frequently used and relatively more mundane diagnostic technique such as X-rays, junior doctors working in accident and emergency department were unable to detect 35 % of radiographic abnormalities (Vincent et al., 1988). They also reported high rates of error in detecting signs of cyanosis, interpreting electrocardiograms, and assessing biopsy specimens. The most startling findings of errors in assessing biopsy specimens is the revelation that 42 patients in a bone tumour unit in a Birmingham hospital were misdiagnosed and received extensive unnecessary treatment (Milhill, 1993). Errors in cytology tests have also been widely reported in the press in recent months (e.g. The Times,
1998).
In a study of house officers' mistakes involving 254 house officers (Wu et al, 1991), it was found that the most common types of reported errors were errors of diagnosis (33%), prescribing (29%), evaluation (21%), communications (5%) and procedural complications (11%). The findings also revealed that there was serious outcomes in 90 % of reported cases of errors, 31 % of which were death.
3.3.1 Factors relating to errors in medicine.
Adverse drug events (Brennan et al., 1991; Leape et al., 1991; Bates et al., 1993 ; Leape et al., 1995) and cardiac arrests are two major complications of iatrogenic
illness (Steel et aL, 1981 ; Bedell et al., 1991). The type and frequency of identifiable factors associated with these iatrogenic injuries will now be examined as they might help us to understand the cause of errors in the care of hospitalised patients and also suggest interventions to reduce their frequency in the future.
The overall medication prescribing error rate over a 1-year study period in a 631- bed teaching hospital in New York was 3.99 per 1000 orders, giving a total of 2103 confirmed clinically significant medication errors (Lesar et al., 1997). The most common types of errors detected accounting for 81 % of all medication prescribing errors were dosing errors (both overdoses and underdoses), prescribing medications to which the patient was allergic and errors involving the prescribing of inappropriate dosage forms.
A large number of these errors were found to be due to lack of knowledge, inadequate access to patient's information, miscalculation of medication doses, mental slip and memory lapse (Lesar et al., 1997). In a study of errors causing adverse drug events, Leape et al (1995) also found that lack of knowledge, lack of information about the patient, slips and lapses were major proximal causes of errors, accounting for 22 % and 14 % of the 334 errors respectively. However, Lesar et al (1997) argue that is not always easy to identify the true underlying cause of a medication error as identical errors may be caused by any proximal and underlying causes or by a number of causes. But, by focusing efforts on the factors which have been found to be associated with medication prescribing errors, the problematic areas of medication prescribing could be identified and the risk to patients from prescribing errors should be reduced.
In a study of 203 cardiac arrests in which resuscitation was attempted, 14 % of the arrests followed an iatrogenic complication (Bedell et al., 1991), which was defined as an "arrest that resulted from therapy or from clearly identified error of
Chapter 3: Errors and adverse events in health care
omission". They found that the main causes of iatrogenic cardiac arrests were medications, procedures, and sub optimal attention to clinical signs and symptoms. Bedell et al (1991) suggest that 64 % of the iatrogenic cardiac arrests might have been prevented if the physicians paid more attention to the laboratory and clinical data prior to the arrest.