In the DeviceUseStatement resource for FHIR dstu2 , the whenUsed attribute identifies the
"whenUsed":
"timingPeriod":
"whenUsed":
"timingTiming":
"notes":
"recordedOn":
"timingDateTime":
"indication":
"device":
"bodySiteCodeableConcept":
"identifier":
"bodySiteReference":
"subject":