Clinical decision support rules play a key role in the overall delivery of CDS. CDS rules typically follow a common pattern, which has been modeled in several healthcare standards formalisms. The Event-Condition-Action1 model, as used in the HL7 community, is described below.
A CDS event is the clinical situation in which a decision support rule will be applied. First something must happen before the rule can be utilized. Examples of CDS events include:
A CDS condition defines the question(s) that must be answered to determine the outcome of the rule. Examples of conditions include:
The CDS action describes what should be done if the condition evaluates to true. Examples of actions include:
An informal representation or rule template which captures the Event-Condition-Action pattern is shown below. This pattern can be read as "ON event IF condition THEN action".
Rules may reference both EHR data and reference data such as terminology to determine whether or not a specific condition is true. This topic will be explored in more detail the section Inference Engine.