Introduction
Providing intravenous (IV) therapy is a complex health care technology and patients are at risk of experiencing adverse events such as medication errors. Increasingly, human error theory is used to investigate adverse events such as these.

Objective
To identify the incidence of IV medication errors in hospital and explore their causes using human error theory.

Method
IV medication errors were defined as a deviation in preparation or administration of IV medication from the doctor's prescription, the hospital's IV policy and the manufacturer's instructions with the potential to adversely affect the patient. Data was collected using non participant observation of nurses preparing and administering IV medication in hospital and causes of errors were explored during conversations with nurses preparing medication. The researcher spent between 6 and 10 consecutive days on each of 6 ward specialities in a university teaching hospital in London between June and December 1999.

Results
In 253 cases IV drug preparations and administrations were observed, in a further 42 cases only drug preparations were observed and in a further 6 cases only drug administrations were observed. Forty nine (17%) preparation errors and 111 (43%) administration errors were identified. Preparation errors included using the wrong volume to dissolve the drug (25), preparation of the wrong dose (9) and omitting medication (3). The majority of administration errors were bolus doses administered in less than 3 minutes through a peripheral vein (61). Furthermore, there were 11 administrations of potentially incompatible IV drugs and 6 with the wrong infusion rate. Preliminary analysis of causes of errors suggested that both active and latent failures contributed towards IV medication errors. Active failures included not following hospital guidelines regarding drug administration and slips such as not reading the labels on medication vials. Examples of latent failures were communication problems between nurses and pharmacists and complex design of drug vials. Further analysis will quantify these issues.

Conclusion
This observation study identified a high incidence of IV medication errors. Causes of errors included active and latent failures and this analysis will indicate ways to improve the safety of IV drug therapy.