Acknowledgements in HL7V2.x

HL7V2.x messaging standard indicates that Acknowledgements (ACK’s) are messages sent by a receiving system to the sending system in response to a transaction from the sending application. In a setup where HL7 is implemented the sending system will assume that the message sent by it is not received till it receives an ACK from the receiver. So in summary Acknowledgements are used to confirm the receipt of the message. Acknowledgements are implemented at two levels transport level and application level. In this post we will have a look at both the options.

Transport Level Acknowledgements: Sending systems open a connection to send messages to the receiving messages, mostly through the interface engine which act as broker for communications between different systems in a healthcare setup. If a message is acknowledged on the same connection which is used to send a message they are termed as transport level acknowledgements.

The connections can be transient or persistent in nature. Transient connections are those where the connections are closed after an acknowledgement is received. Each time a message is sent a new connection is made. Persistent connections are those where the connections are kept open and messages are sent over the same connection in a sequence, in sense sending a next message over the same connection after an acknowledgement is received for the previous sent message. Persistent connections are generally configurable where the connections can be closed after a certain period of inactivity. There are different factors which determine the choice of connection. The factors include message throughput, latency, sequencing, fail over, high availability and general infrastructure of the organisation.

Transport Level Acknowledgements also indicate that the ownership of the message is passed to the receiving system after it has received a acknowledgment. The transport level acknowledgement also informs the transport and reception error.

If a message is received and accepted by the receiver then it sends a ACK and performs one of the following

•Validates and persists the message successfully, generating the functional response message with a value of AA (Application Accept) in MSA-1-acknowledgment code field.

Or

•Send an error response, providing error information in functional segments to be included in the response message with a value of AE (Application Error) in MSA-1-acknowledgment code field.

Or

•Fail to process (reject) the message for reasons unrelated to its content or format (system down, internal error, etc.). For most such problems it is likely that the receiving system will be able to accept the same message at a later time. The sending system must decide on an application-specific basis whether the message should be automatically sent again. The response message contains a value of AR (Application Reject) in MSA-1-acknowledgment code.

Application Level Acknowledgement: A sending system may require an application level acknowledgment from the receiving system if confirmation of successful processing is required. This can take the form of an HL7v2 ACK message (e.g. to indicate a successful processing of order it received) or a business response.

Generally the transport acknowledgment only confirms the receipt of messages but does not convey any confirmation of processing of the message. The need for these interfaces needs to be decided by the business processes. They are transmitted in the same way as any other message

In HL7 terminology the above two types of ACK's are termed as follows

•Original Mode Acknowledgement - a "Receive" ACK and majority of the ACKs used in HL7 communications; indicates that a message has been received but not necessarily processed yet

•Enhanced Mode Acknowledgement - an "Application" ACK that is a resultant status return rather than a communication response (i.e. query results, order response, etc.)

ICP's and EHR

An ICP determines locally agreed, multidisciplinary practice based on guidelines and evidence where available, for a specific patient/client group. It forms all or part of the clinical record, documents the care given and facilitates the evaluation of outcomes for continuous quality improvement".

National Pathway Association (1998)

ICP’s have their origin in providing coordinated care to patients by different specialist teams within a healthcare organisation. Each team records their interventions on a patient for a specific health condition in the organisation’s Electronic Patient Record (EPR) system and other teams intervene accordingly based on the notes provided. This paved the way to define electronic ICP’s (e-ICP) in EPR systems.

The advent of Electronic Health Records (EHR) brought the possibility of extending ICP’s across multiple healthcare organisations from different care settings. EHR's facilitate flow of information across different care setting boundaries even to agencies outside healthcare (e.g. social care) who are involved in the care of a patient.

Benefits of Electronic Care Pathways over EHR's:

• Allows care pathways to be built around patients and not institutions by providing real time recording and allowing different organisations involved in the patient care to have the same view
• e-ICP’s provide quick access to information(instead of browsing though bundles of paper for which each organisation has different format and different recording styles) and provide multiple views – high level summary view from different organisations as well as detailed view of each organisation in a chronological fashion
• e-ICP’s allow faster remodelling and review of business processes to suite each patient

However the difficulties in deploying e-ICPS’ through EHR is not a technological one but cultural and business one involving the need for agreeing common data formats and sharing the data owned by an organisation across different care settings and agencies.