Hi Marlene,
You will note that there is the following statement in the âUseâ of the Body weight archetype:
âCan also be used for recording an approximation of body weight measurement in a clinical scenario where it is not possible to measure accurately body weight - for example, weighing an uncooperative child, or estimating the weight of an unborn fetus (where the âsubject of dataâ is the Fetus and recording occurs within the motherâs health record). This is not modelled explicitly in the archetype as the openEHR Reference model allows approximations for any Quantity data type by setting the attribute Magnitude_status to the value â~â. At implementation, for example, an application user interface could allow clinicians to select an appropriately labelled check box adjacent to the Weight data field to indicate that the recorded weight is an approximation, rather than actual.â
There is a similar statement in the Height/Length archetype. The use case driving this statement was an absence of requirement for a formula, maybe even an informal âguesstimateâ.
There is also a statement in the âMisuseâ:
âNot to be used to record a calculated body weight, such as an estimation of the body weight of a person with one or more limbs missing. A calculated body weight may be based on, some or all of, the measured body weight, other body measurements and an algorithm. Use other OBSERVATION archetypes for this purpose.â
The other OBSERVATIONs suggested remain unspecified and unavailable, unfortunately.
The reason for the misuse statement is that a calculated weight can be considered a conceptually different entity to an actual measured weight. For example: in individuals with bilateral lower limb amputations we need a calculated weight for medication dosing based on BSA. In that situation we also clearly need to differentiate between the calculated weight and their actual weight which can still be used for tracking weight change etc.
In the situation with height there are similar issues, for example in paediatrics, contractures due to Cerebral Palsy etc will require a calculated height for tracking growth parameters.
To add to the confusion, the term âEstimatedâ has been used vaguely in many situations - ranging from calculated to vague guesses and we probably need to be explicit in our modelling.
I did some initial modelling on these calculated observations a long time ago, testing how we might specialise these additional concepts for body weight and height/length to support documentation of malnutrition, but it was difficult and it was dropped without a final resolution and no specific user request. However you will note the family of OBSERVATION archetypes for body segments which did arise out of these investigations. For example, Body segment length contains âknee heightâ and âarmspanâ which will support our calculations of other body parameters.
This area clearly needs further consideration and investigation as to the best way to define and model these seemingly simple, yet complex, parameters.
Cheers
Heather