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eExam.11 Pertinent Negative Values
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Joined: 02/29/2012 13:37:55
Messages: 90

Recently one of my developers contacted you to get clarification regarding how to use the pertinent negative values for some of the assessment values. As he and I were going over our database design and trying to understand exactly what is required by NEMSIS, we realized that we may have a conflict between what we see as good database design and what may or may not actually be required. I’ll try to explain as best I can.

For the example, let’s assume that we’re doing an abdominal assessment. Based on our current understanding, we must be able to specify a PN value for zero or more assessment values per finding location. It appears as though we must also be able to specify a PN value without specifying a finding location.
[NEMSIS TAC: ] This is not true. Although the XSD does allow for this (it’s a limitation of XSD) National Schematron rules have been developed to address this and improve overall data quality. How you develop this within your UI is up to you. the XSD and Schematron will only work with a completed ePCR that is generated in XML.

If I am understanding this correctly, by specifying a PN value along with selecting an assessment item, we could say for instance that we assessed the ‘Left Lower Quadrant’ (eExam.10) looking for Gunshot Wound-Entry (eExam.11) but did not find one (eExam.11_PN, 8801005 – Exam Finding Not Present).
[NEMSIS TAC: ] Your understanding is correct. This is exactly how the PN values are intended to be used. It would look like this in the XML file:

<eExam.10>3510003</eExam.10> Left Lower Quadrant
<eExam.11>3511021</eExam.11> Distention
<eExam.11 PN='8801005'>3511029</eExam.11> Exam Finding Not Present >Gunshot Wound-Exit<
<eExam.11>3511051</eExam.11> Tenderness
<eExam.10>3510011</eExam.10> Right Upper Quadrant
<eExam.11>3511025</eExam.11> Guarding
<eExam.11>3511041</eExam.11> Pain
<eExam.11 PN='8801005'>3511029</eExam.11> Exam Finding Not Present >Gunshot Wound-Exit<

According the structure of the schema, it also appears as if we can record a PN value without specifying an actual assessment. In this case, what does that mean exactly? To make it even more confusing, according to the schema, we could specify a finding location and leave out both the assessment value and the PN value.
[NEMSIS TAC: ] As indicated above, although the XSD allows this, the Schematron rules will enforce that proper format is followed based on logic and structural rules.

In the database schema for which NEMSIS supplies scripts to generate, surrogate keys are used to set up the relationships that allow it to be possible for the eExam.11 table for instance, to have a record where only the primary key and foreign key are necessary (all the rest of the columns allow nulls). In our design we try to avoid surrogate keys as much as possible and so our equivalent of the eExam.11 table uses a compound primary key, part of which is the abdomen assessment code. This configuration would not support adding a record with just a PN value. I guess I’m just really trying to fully understand what the intent is here so that I can give NEMSIS what is required while also having our design make sense. I would appreciate any insight you could provide.
[NEMSIS TAC: ] The database scripts follow the same layout as the XSD’s which means each attribute and element get a column. If the element repeats then the element gets its own table.

[NEMSIS TAC: ] The structure of the XSD alone does not enforce what should happen clinically. That’s why the decision was made years ago to adopt Schematron Rules. We’ve had structural Schematron Rules in place to address the issues of NOT values, Pertinent Negatives, Real Values, and Nils. They’ve now been updated with the Version 3.3.4 release in March 2014.

There are numerous documents related to the NEMSIS Version 3 standard on our website. Please review the document listed on the NEMSIS website as “How to Utilize NEMSIS V3 "NOT values/pertinent negatives/nillable” found on the NEMSIS Version 3 >> Resources page. http://nemsis.org/v3/resources.html
Here is the direct link to the document. Please note the schematron national rules enforce the proper clinical use of Pertinent Negatives as well as ensuring data quality by limiting the use of NOT values (NV) when “real” values have also been submitted. Once you review this document it may answer the majority of your questions and concerns.

The NEMSIS Version 3 Schematron Rules can be downloaded from the Version 3 >> Downloads >> Schematron page. Please note there is a section in the documentation / data dictionary version of Schematron NEMSIS v3.3.4 with the section heading “nemSch_consistency_nilNvPn”. This is one of your Schematron Resources. Here is s a link the Schematron page on the NEMSIS website.

This message was edited 1 time. Last update was at 04/22/2014 09:54:58

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