To prevent updating stale data - which can lead to data loss, we recommend the usage of ETag. Resources returned by Metriport’s Medical API include an eTag property, which can later on be sent back to the API when performing an update on said data. The API will then compare that ETag with the one on the repository: if they don’t match it means data was updated by another process and the server will abort the update and respond with 412 - Precondition Failed; otherwise it will proceed updating the resource. To send the ETag to an update endpoint, you can use the If-Match HTTP header, or include an eTag property on the request body. The header takes precedence if both are informed. The SDK implements this automatically, as long as the data obtained from a get or list function is updated and sent to the respective update function. Example: 
const await patient = metriportClient.getPatient("...");
// logic that updates the patient
...
// this update will automatically send the ETag if present on patient
await metriportClient.updatePatient(patient, facilityId);
If no ETag is provided the API will perform updates without checking for mid-air collisions. This technique is also called Optimistic Locking. Note that currently we only support ETag to prevent mid-air collisions, not for caching purposes.