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Wednesday, February 16, 2011

On The IHE Model for Exchange

Fred Trotter wrote a post about the Patient Centered Health Internet back in December.  In it, he describes what he calls the IHE model of exchange, and then describes the NWHIN model of exchange which uses IHE profiles.  He also combines this model with a number of committees who "believe they are in charge of interoperability".  I commented on this post, and @ePatientDave asked for more information (even though he spelled my handle wrong), so here it is.

IHE has defined a number of different interoperability specifications that can be used to support healthcare exchange.  They include:
XDS - Cross Enterprise Document Sharing
XDR - Cross Enterprise Document Sharing via Reliable Messaging (Point to Point)
XDM - Cross Enterprise Document Sharing via Media (Stick, CD or e-Mail)

Supporting profiles include:
ATNA - Audit Trails and Node Authentication
BPPC - Basic Patient Privacy Consent
XUA - Cross Enterprise User Authentication
PIX/PDQ - Patient Identifier Cross Referencing
XCA - Cross Community Access
XCPD - Cross Community Patient Discovery

Other capabilities include:
DSUB - Document Subscription
MPQ - Multipatient Query

These profiles are building blocks upon which one can develop a number of architectures.  The NWHIN architecture that Fred describes is one such architecture.  It uses XCA, XUA, BPPC, XDS and PIX/PDQ or XCPD to federate HIEs at various levels.  This is akin to the distributed DNS architecture of the internet, or the architecture used to federate organizational directories using LDAP.  It is, like the internet, complex, fault tolerant, but subject to multiple points of local failure.

The NHIN Direct architecture that he describes is what IHE Patient Care Coordination considered as one possible architecture when we created the IHE XPHR (Exchange of Personal Health Records) content profile.  The Direct Project includes references to both XDM and XDR in it, and can be used to exchange the HITSP C32 specification.  XDR is an alternate messaging backbone for Direct which can be entered through an SMPT gateway.  XDM is the specification that should be used with Direct when sending multiple documents in one message.

The IHE XPHR profile is a specification built over the HL7 CCD, and upon which the HITSP C32 is built.  That profile is intended to support the exchange of information between the physician and the patient, putting the patient at the center of care.

IHE supports both models Fred presented; we build the lego blocks, and someone else figures out how to put them into an architecture for health information exchange.  We design these lego blocks to be reusable and to support a number of different configurations, so there is no single IHE model.  XDS was designed to support national, regional and local or institutional architectures by tying together health information systems containing clinical information with a single index.  XDR is designed for point to point communication.  XCA is designed to connect indices from multiple sources.  PIX/PDQ is designed to be an interface to a Master Patient Index, which could be at the national, regional, local or institutional level.  XCPD is designed to support location of patients across identity boundaries at any of several levels.  BPPC is designed to support the recording of patient consents to policies established at any level.  Because we address requirements at multiple levels, a wide variety of architectures is supported.

If you want to assign responsibility for the NWHIN architecture, please don't assume it was IHE.  You'll have to look elsewhere.  I'd start with the committee responsible for it.

     Keith

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