In R4 Device could be associated with a single patient. This works for implantable devices and other devices that are permanently associated with a patient. Many devices can be associate with multiple patients over time, e.g. a wheelchair, and that association may need to be tracked for, e.g. recall purposes.

To address this, R5 Device changes that patient element to association[0..*].humanSubject. There are several issues with this approach: there is no time period associated with the association (FHIR-38637), and we end up with Device  resource containing data about multiple patients. The latter issue is particularly relevant because Device is in the patient compartment, and thus would leak PHI about other patients.

A different approach is needed, such as: creation of a new "DeviceAssociation" resource, or updates to or profiling of DeviceDispense (e.g. adding an end date, or potentially using a List for each Device of Patient assignments, including of the end date of the assignment).

This issue was discussed during the 2022-09 WGM, and several points were brought forth:

• Are reassign-able devices within the 80% or is this extension territory (and thus we should revert back to the single patient in Device)?
• Should we have a simple solution for single permanent assignment, and a different solution for more complex cases?
• Any approach that differs from the R4 Device, including the current R5-ballot approach, has an impact on US Core Implantable Devices
• Do we need a broader solution for "assignments over time" (what else can be assigned, and to whom)? Is there a pattern for "history" type records, such as the new EncounterHistory? We may need to establish a list of "assignable" or "history" resources, and work with other WGs to devise suitable resources/patterns.
• There may be benefits a smaller scope solution that we can get into R5 to play with; rather than delaying for a more robust solution in R6.
• General consensus that resource history isn't a "good" solution.
• We need to review PHI/access control implications of any solution.
• What is the defining characteristic of this association? Is it different from some item being assigned to a practitioner, or assigned to a location, etc.? Is this a way of tracking blood products assigned to a fridge? 
• Do we need to include Transport in the list of "assignments"?
• Is there a need to similarly track association of a Device to a Organization? (Is this in lieu of a patient, or in addition?)
• DeviceDispense is the act of dispensing. The need here is a record of who had the device after the dispense and for how long. (The change of state has characteristics different from the resulting state.) We may also know that a patient has/had a device, but don’t have a record of it being dispensed. Need to distinguish from DeviceUseStatement which is a (patient) claim of use, which is different from a clinician or system assertion of association.
• Consider if we need to track a period of use different (longer or shorter) from when the device was assigned. (i.e., the patient had the device from March 1, but didn’t do anything with it until April 15, etc.)
• Why are AuditEvent and Provenance not appropriate? (AuditEvent is really around security, etc. decisions; neither resource is typically exchanged between systems.) Is EpisodeOfCare with a period aligned to the assignment appropriate? (Might be able to use for patient-assigned devices, but not for other assignments.) Can the association of a Practitioner to an Organization via PractitionerRole provide insight into the association of a Patient to a Device?
• Do we track more than just the patient assignment? E.g., who operated a device during a procedure; when and by whom the device was maintained.
• Need to be clear on boundaries between this and existing resources (may need to adjust).
• Are there similarities with curated medication lists, and could the approach to one be used for the other?
• Do we track association between devices/products, e.g. blood in a centrifuge. Review GenomicStudy for overlap or patterns, and adjust both resources appropriately.
• Where are the device settings for a particular assignment recorded? Is that in here?

If nothing else is done, we need to either remove Device from the patient compartment, or change the cardinality back to 0..1.