Personal Health Device Implementation Guide
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Personal Health Device Implementation Guide, published by HL7 International / Health Care Devices. This guide is not an authorized publication; it is the continuous build for version 1.0.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/HL7/phd/ and changes regularly. See the Directory of published versions

PHD BITs Coded Enumeration Observation Profile

The BITs Enumeration Observation Profile is used when the PHD metric measurement is an integer where each bit represents an event or a state. PHDs typically send this kind of measurement when more than one event or state can occur simultaneously. If the event or states are mutually exclusive, the coded form of the measurement is typically used instead.

The measurement is a BITs state and/or event set when the PHD metric contains one of the following attributes:

Attribute Value Additional Information
Enum-Observed-Value-Simple-Bit-Str 32-bit value Each bit in the 32-bit integer signifies some item
Enum-Observed-Value-Basic-Bit-Str 16-bit value Each bit in the 16-bit integer signifies some item
Enum-Observed-Value 32-bit term code when a BITs When this complex attribute is used the only option is for the 32-bit BITs field

The Enum-Observed-Value-Simple/Basic-Bit-Str attribute is used when the measurement reports one or more events or states. Each bit in the 16 or 32-bit number may represent some state or event. The most common use of this type of measurement is for reporting device status events that influence the measurement. It is also used extensively in the Independent Living specialization to report states such as ‘door open’, ‘door closed’ or ‘patient in room’, ‘patient out of room’, etc. The measurement is generally used when there is the potential for more than one event or state to be set at the same time.

The Enum-Observed-Value attribute is a complex attribute and can be any one of the three possible enumeration measurements. There is an element in the structure which indicates which type of enumeration it is. If it is a ‘BITs’ type it reports only the 32-bit version. The attribute also has its own metric-id value telling what it is and status value. The metric-id value replaces the term code given by the Type attribute for the type of measurement and the status value replaces the Measurement-Status attribute.

The structure definition for this profile is given here

Mapping BITs Enumerations to FHIR

FHIR has no data type that corresponds to this kind of measurement. Consequently Continua has developed a code system which maps the BITs measurement to a set of codes. The details of the mapping and how these codes are generated from data received from the PHD are given in ASN1 BITS Code System. These codes are reported in the component element; one component per reported bit setting. Thus similar to the compound numerical measurement, there is no Observation.value[x] element. There may still be an Observation.dataAbsentReason element if a measurement status indicates a measurement failure in which case no component elements representing the BITs setting are reported.

In the following table, N is the bit position being reported. M is the component element number in the Observation. Since not all bits may be reported, M is always <= N. The notation “Type” is the 32-bit code reported in Observation.code.coding.code used in the ASN1 mapping to HL7 codes. Note that the term code of this value will come from the metric-id element when an Enum-Observed-Value attribute is reported.

Recall that only set bits of type ‘event’ need to be reported. If of type ‘state’ both set and cleared states need to be reported. Undefined bits are not reported. Unsupported bits (only available in the later versions of the 20601 spec) may be indicated.

Attribute FHIR coding
Enum-Observed-Value-Basic-Bit_str.bitN
where 0 <= N <= 15		 Observation.componentM.code.coding.code=”Type.N“
where M is the Mth setting being reported
Observation.componentM.code.coding.system=”http://hl7.org/fhir/uv/phd/CodeSystem/ASN1ToHL7”
where M is the Mth setting being reported
Observation.componentM.valueCodableConcept.coding.code=”Y/N” if bit N is set/cleared</br>Observation.componentM.valueCodableConcept.coding.system=”http://terminology.hl7.org/CodeSystem/v2-0136”
where M is the Mth setting being reported
Enum-Observed-Value-Simple-Bit_str.bitN
where 0 <= N <= 31		 Observation.componentM.code.coding.code
where M is the Mth setting being reported
Observation.componentM.code.coding.system=”http://hl7.org/fhir/uv/phd/CodeSystem/ASN1ToHL7”
where M is the Mth setting being reported
Observation.componentM.valueCodableConcept.coding.code=”Y/N” if bit N is set/cleared</br>Observation.componentM.valueCodableConcept.coding.system=”http://terminology.hl7.org/CodeSystem/v2-0136”
where M is the Mth setting being reported
Enum-Observed-Value.bitN

where 0 <= N <= 31
Enum-Observed-Value.metric-id
Enum-Observed-Value.status		 Observation.componentN.code.coding.code=”Type.N” where M is the Mth setting being reported
Observation.componentM.code.coding.system=”http://hl7.org/fhir/uv/phd/CodeSystem/ASN1ToHL7”
where M is the Mth setting being reported
Observation.componentM.valueCodableConcept.coding.code=”Y/N” if bit N is set/cleared
Observation.componentM.valueCodableConcept.coding.system=”http://terminology.hl7.org/CodeSystem/v2-0136”
where M is the Mth setting being reported

effects the Observation.component.code.coding.code “Type” see Obtaining the Observation.code
see Measurement Status in Phd Base Observation Profile
If reporting an unsupported bit N Observation.componentM.dataAbsentReason=”unsupported”

Below is an example of one Observation.component element containing one of the perhaps several bit settings from a pulse oximeter device and sensor status measurement:

component": [
    {
        "code": {
            "coding": [
                {
                    "system": "http://hl7.org/fhir/uv/phd/CodeSystem/ASN1ToHL7",
                    "code": "150604.2"
                }
            ],
            "text": "sensor-displaced"
        },
        "valueCodeableConcept": {
            "coding": [
                {
                    "system": "http://terminology.hl7.org/CodeSystem/v2-0136",
                    "code": "Y"
                }
            ],
            "text": "Sensor is incorrectly placed on user"
        }
}

There would be one such component element for every bit setting to be reported. Of one examines the ASN1ToHL7 code system here one will see that the code 150604.2 means “Sensor is incorrectly placed on user”.

Meta Data Profile

The uploader shall populate the Observation.meta.profile with “http://hl7.org/fhir/uv/phd/StructureDefinition/PhdBitsEnumerationObservation” indicating this resource is generated following the PHD Implementation Guide.

Conditional Create Identifier Generation

For a general description of the PHD Observation Identifier see the “PHD Observation Identifier” section in PHD Base Observation Profile. The table below lists the items that make up the identifier.

Entry value Additional information
device “PHD Device.identifier.value” This value is the PHD IEEE EUI-64 system identifier
patient “Patient.identifier.value-Patient.identifier.system” or
provided logical id		 The dashes are part of the identifier.
When the service provider gives the PHG a pre-determined patient logical id the PHG creates no Patient resource and has no patient information. In that special case the provided logical id is used
type “Observation.code.coding.code” See Obtaining the Observation.code
value The raw 16-bit or 32-bit integer delivered by the PHD  
reported PHD timestamp “timestamp” See Generating the PHD Reported Time Stamp
supplemental types “Supplemental-Types.N-“ A sequence of 32-bit MDC codes separated by a dash

The final identifier is made by concatenating the entries above as follows:

  • “device-patient-type-value-reported PHD timestamp-supplemental types”

Additional Enumeration Measurement Information

There are no additional descriptive attributes that are unique to the Enumeration type of measurement.

Examples:

A BITs observation example from a pulse oximeter is shown in Device Sensor Issues. This observation results when the pulse oximeter is having difficulty obtaining the measurement, perhaps due to motion or position of the finger in the sensor, a bad signal, etc.

The Other Profiles