Amendment History

Review Timetable

© International Health Terminology Standards Development Organisation 2016. All rights reserved.

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Glossary

Domain Terms

Introduction

Purpose

The purpose of this project is to consider templates for the representation of concepts currently subsumed by 46680005 | Vital sign (observable entity) | as SNOMED CT Observable entities using the draft Observable entity and Investigation procedure model.

Audience and stakeholder domain

The audience for this document includes all standards terminology leaders, implementers and users. Investigations including vital signs, i.e. heart rate, respiratory rate, core body temperature and (systemic arterial systolic and diastolic) blood pressure, are frequently used in diagnostics and follow-up of treatment

A further significant audience is the community of SNOMED authors that may be requested to implement the recommended specification.

The IHTSDO Observable and Investigation Model Project is a stakeholder, and specifically the LOINC mapping subproject as the approximately 500 LOINC vital signs terms are to be mapped to the Observables model eventually.

Input from stakeholders 

Initially, the project has been worked on within the Observables project group and, specifically, a parallel modeling effort was performed with four modelers representing a (random) subset of existing vital signs observables.

In 2016 a renewed project continued the work from the Observables project group with a focus of implementing the vital signs observables in a SNOMED CT International Release.

On 2016-09-27 the issue with 46680005 | vital sign (observable entity) | subsuming all blood pressures, body temperatures, heart rates, and respiratory rates was discussed at the Anesthesia SIG meeting. The SIG would look in to the possibility of identifying more specific concepts which could replace the broad subclass axioms in observables definitions, e.g. core body temperature as opposed to just body temperature. The Nursing SIG also volunteered to review this issue. The groups were also invited to review the full document and the accompanying OWL ontology. Results of this process are recorded on this Confluence page: True vital signs.

At the 2016-10-24 Observables project group meeting it was proposed to retire the vital signs concept as it cannot be reproducibly understood. A refset-based approach was proposed to replace the concept to specify lists of vital signs per use case. The creation of such refsets is outside the scope of this project. 

Degree of consensus on the statement of problem

Some controversy has been identified around the distinction of that which is being observed from how that is observed. An example is the core body temperature observables where there have been different opinions about how to use the two attributes 704319004 | Inheres in (attribute) | and 704327008 | Direct site (attribute) |. However, the proposed solution is following the observables inception/elaboration document and allows for fully defined concepts to infer a hierarchy mostly identical to the current manually maintained hierarchy. No alternative solution with the same properties has been identified.

Statement of the problem or need

Summary of problem or need, as reported

This document does not directly correspond to a IHTSDO content tracker artifact, other than the general artf6283 : Observables and investigation procedures redesign tracker item.

Vital signs is in scope of the LOINC mapping project.

Summary of requested solution

No requested solution.

Statement of problem as understood

To develop guidance for representation of SNOMED CT vital signs concepts (subsumed by 46680005 | vital sign (observable entity) |). While there are other concepts in other SNOMED CT hierarchies related to the vital signs observables, such as procedures and findings, these are considered out of scope of this project (see Table 1).

Table 1 Examples of related SNOMED CT concepts

Detailed analysis of reported problem, including background

Vital signs observables current status

There are 138 SNOMED CT concepts subsumed by 46680005 | vital sign (observable entity) | in the 2016-07-31 release. 46680005 | vital sign (observable entity) | directly subsumes the five concepts 78564009 | pulse rate (observable entity) |, 86290005 | respiratory rate (observable entity) |, 386725007 | body temperature (observable entity) |, 75367002 | blood pressure (observable entity) |, and 431314004 | Peripheral oxygen saturation (observable entity) |. All concepts are, as in the rest of the Observable entity hierarchy, primitive. Further, there is, separate from the 46680005 | vital sign (observable entity) | hierarchy, the concept 405016003 | Vital signs status (observable entity) | is subsuming the concept 363814008 | Temperature associated observable (observable entity) | which also includes the 386725007 | body temperature (observable entity) | concepts.

It should be noted that 46680005 | vital sign (observable entity) | is a grouper of the five specific observables based on convention and cannot reasonably be fully defined. It should be considered whether or not a primitive grouper is the best way of representing such clinical conventions. Currently, due to the grouping, all current temperatures of the body, including e.g. 364511004 | ankle joint temperature (observable entity) |, are vital signs. Also, due to the primitive status of the grouper, body temperatures which do not explicitly or implicitly include an IS A relationship to 46680005 | vital sign (observable entity) | will not be subsumed by any modeled body temperature observables.

Figure 1 Vital sign observables

Although the five specific vital signs listed in SNOMED CT are generally agreed upon, there are also additional vital signs. E.g. the US PHIN, Public Health Information Network, lists 3 additional vital signs including head circumference, height, and weight and the HITSP Consolidated CDA template for vital signs further lists an additional two: body surface area and BMI, thus including a total of 10 vital signs, although not all would be considered vital signs according to the definition used in this document.

Due to the variability of what is included in the list of vital signs between different users, specialties, etc. it is proposed to retire the vital signs grouper concept and to use a refset-based approach for representing the list of vital signs.

Each of the more specific kinds of observable will be described separately below.

Process observables

The current Observables model contains a specific set of attributes for representing observables about processes (see Table 2). 

Table 2 Process observables attributes

Heart rate

In the 2016-07-31 release there are 8 heart rate observable concepts. Currently in SNOMED CT 78564009 | pulse rate (observable entity) | is the top concept among the heart rate observables and subsumes 364075005 | heart rate (observable entity) |. According to the definitions in the glossary “heart rate” would be the broader term.

The concept 713982009 | Ability to achieve target heart rate (observable entity) | does not belong among the other heart rate concepts. "Ability..." observables are typically about volitional acts, e.g. movement, daily living activities and not about physiological processes, possible exceptions being <<363832008 | Sensation observable (observable entity) |. 

Respiratory rate

In the 2016-07-31 release there are 3 respiratory rate observable concepts. In addition to the generic respiratory rate concept, there are two respiratory rate observables related to ventilator treatment.

Body temperature

In the 2016-07-31 release there are 36 body temperature observable concepts plus the concept 248458005 | comparative temperature in limbs (observable entity) | not subsumed by 386725007 | body temperature (observable entity) |. The concept 431807005 | temperature taken with digital thermometer (observable entity) | may be interpreted as a kind of body temperature observable as it is subsumed by 363816005 | Body temperature measure (observable entity) |, although in the fully specified name it is not explicitly stated what the temperature inheres in.

There is a group of body temperature observables which aim to observe the core body temperature at different direct sites, e.g. the axilla (or the axillary pit), the mouth (or the sublingual space), tympanic membrane, etc. Among the body temperature concepts 9 are subsumed by 276885007 | core body temperature (observable entity) | while debatably 415922000 | forehead temperature (observable entity) | is often also an indirect measure of the core body temperature.

Two concepts 248430002 | pattern of fever (observable entity) | and 248431003 | phase of fever (observable entity) | are not considered body temperature observables and thus considered out of scope of this work.

Blood pressure

In the 2016-07-31 release there are 88 concepts subsumed by 75367002 | Blood pressure (observable entity) | plus an additional 29 concepts subsumed by 165077006 | intracardiac pressure (observable entity) | but not currently subsumed by 75367002 | blood pressure (observable entity) |. It should be considered whether blood pressure observables should include both pressures inside blood vessels and the heart or only the blood vessels. From a clinical perspective, the boundary may not always be clear. E.g. the central venous pressure, measured in the superior vena cava close to the right atrium, is often an estimate of right atrial pressure.  

There are some missing stated IsA relationships, for example, 72313002 | Systolic arterial pressure (observable entity) | does not have an IsA relationship to 386534000 | Arterial blood pressure (observable entity) |. 

It is here assumed that blood is the fluid that flows in the spaces of the cardiovascular system or, alternatively, that “blood pressure” would be the pressure exerted by any fluid, e.g. a resuscitation fluids or blood substitute, on the walls of the spaces of the cardiovascular structures.

It has been discussed what blood pressures inhere in: the vessels and the heart, the endothelium, the inner surface of the hollow cardiovascular structures, the fluid, typically the blood, or the spaces or lumens of the cardiovascular structures, or any combination of those entities.

Blood pressure observables are typically specified in terms of points in time in relation to the cardiac cycle, or as an aggregate over the cardiac cycle: mainly systolic pressure (max arterial pressure over a cycle) and diastolic pressure (min arterial pressure over a cycle), but also a wave, v wave, x trough, and y trough. Further, blood pressures are often aggregated over several cardiac cycles, e.g. minimum/maximum/average 24 hour systolic blood pressure. Thus, there are two levels of process where one aggregate process may consist of specified parts of underlying cardiac cycles (see Figure 2).

Figure 2 Heart beating processes

Often the term “blood pressure” is used to only refer to systemic arterial pressure, and cases where this is clear, for example as used in data capture forms, such blood pressure concepts should not subsume other kinds of blood pressure.

Systemic arterial pressure

The phrase "systemic arterial pressure" has a literal interpretation of "blood pressure in systemic artery" and would thus subsume all blood pressures in any systemic artery. Systemic arterial pressure is also used as a synonym of other kinds of blood pressure.

Ankle brachial pressure index

The hierarchy subsumed by 75367002 | blood pressure (observable entity) | includes a number of concepts which are not pressures. One of these is 446841001 | Ankle brachial pressure index (observable entity) |, being a ratio of the ankle systolic pressure and the brachial systolic pressure.

Segmental pressure

Segmental pressure is a procedure during which blood pressure is measured in the limbs at several different locations, together with ultrasound Doppler flow measurements. Thus, 251079001 | Segmental pressure (blood pressure) (observable entity) | is not a blood pressure observable. Possibly a panel including multiple blood pressure observables.

Invasive and non-invasive blood pressure

Some existing blood pressure observables have invasiveness specified in the FSN, e.g. 386533006 | Invasive blood pressure (observable entity) | or 251074006 | Non-invasive mean arterial pressure (observable entity) |. However, those do not subsume other blood pressure concepts which are necessarily invasive, such as the wedge pressure observables, e.g. 37087001 | Arterial wedge pressure (observable entity) |.

Peripheral oxygen saturation

In the 2016-07-31 release the existing concept 431314004 | Peripheral oxygen saturation (observable entity) | (with a synonym | SpO2 - saturation of peripheral oxygen | ) was added as a child to 46680005 | Vital sign (observable entity) |. However, there are 10 other oxygen saturation observables subsumed by 103228002 | Hemoglobin saturation with oxygen (observable entity) |. 431314004 | Peripheral oxygen saturation (observable entity) |  is the only one of these which is subsumed by 46680005 | Vital sign (observable entity) |. This is a sibling of 442476006 | Arterial oxygen saturation (observable entity) | with the synonym | SaO2 - Arterial oxygen saturation |. Further, there is at least one evaluation procedure with overlapping meaning 250554003 | Measurement of oxygen saturation at periphery (procedure) |.

Target observables

Among the 46680005 | Vital sign (observable entity) | observables, there are a few "target" observables: 428420003 | Target heart rate (observable entity) |, 315612005 | Target systolic blood pressure (observable entity) |, and 315613000 | Target diastolic blood pressure (observable entity) |. These concepts would not be considered vital signs according to the definition used in this document. While the representation of such targets have not yet been elaborated on, it is clear that a target observable is distinct from a "ordinary" observable, particularly true for e.g. 390734006 | Target weight (observable entity) | and 27113001 | Body weight (observable entity) |. There are related JIRA tickets: IHTSDO-457, PCP-5, IHTSDO-39 and also some potentially related tickets: IHTSDO-356, IHTSDO-308.

Terming

Textual definitions should be collected and added to the concepts that will remain primitive.

Synonyms need to be reviewed and will be examined during modeling, e.g. Mean blood pressure is not the same as Mean Arterial Pressure, 271649006 | Systolic blood pressure (observable entity) | has a synonym "SAP - Systolic arterial pressure". Any questionable descriptions will be brought to the relevant project groups for discussion and resolution. 

Subsidiary and interrelated problems

artf6283 : Observables and investigation procedures redesign

LOINC mapping project

Risks / Benefits

Project Risk Profile

The project risk profile is determined using the project risk profile assessment instrument as described in the “Guide to Stakeholder Engagement in Content Development” document.

Controversy level is assumed to be medium-low, a score of 1.

According to the project risk profile instrument the project is of low risk. The proposed project stakeholder engagement approach is indirect consultation of a larger number (> 10) of users/groups.

Risks of not addressing the problem

Not modeling these concepts will preclude automated comparison with LOINC terms mapped to SNOMED CT expressions in the same domain.

Risks of addressing the problem

A potential result of applying a model to the vital signs content in SNOMED CT is that existing concepts could be re-classified. Users assuming the current structure of vital signs content will have to adopt to those changes.

Requirements: criteria for success and completion

Criteria for success/completion

Consistent meaning, modeling and editorial policy

The criteria for success/completion for this project will be:

To address the issues outlined in this document with respect to modeling and naming existing vital sign observable entity content

To provide clear editorial guidance for the modeling of new vital signs content

To review all concepts that are descendants of Vital sign (observable entity) for validity

To remove descendants of Vital sign (observable entity) which are not considered to be vital signs in clinical practice. 

To determine whether the concept Vital sign (observable entity) can be reliably defined and should remain as a concept in the International Release, or if vital signs should be included in a refset instead.

Strategic and/or specific operational use cases

This project is a part of a pilot of scalable authoring of observables content using the new model.

Fit with IHTSDO strategy

In the document Strategic content projects justification the following is stated:

• Observable Entity (fundamental) 8,500 concepts currently

• • Required to support recording and transmission of clinical observations unambiguously
  • Currently a primitive hierarchy
  • Provides the model for specifying functioning and laboratory content

Solution Development

Initial Design

Outline of initial design

The solution applies the existing draft observables model for currently existing SNOMED CT observables.

Process observables (Heart rate and Respiratory rate)

Process observables are observables which are about process qualities, qualities that inhere in processes according to BioTopLite. Both heart rate and respiratory rate are number rates, i.e. the number of entities, here cardiac and ventilation cycles, “produced” by the process per unit of time.

Figure 3 Definition of Heart rate (observable entity), stated view

Here, the concept | Entire cardiac cycle (qualifier value) | represents one cycle of heart contraction and relaxation, i.e. a heart beat (see Figure 3).

This definition of heart rate is similar to, at least one perspective of, other process observables having specific output, such as excretion observables. The difference here is that an excretion process has continuant material entities as output while these processes have certain types of process parts as output.

Figure 4a Heart rate classification results (prototype ontology)

Figure 4b Heart rate classification results

A Heart rate observable is defined as any observable which observes this process quality and a Pulse rate observable is defined as any observable which observes this process quality at the direct site of a specific systemic artery (see Figure 4a, 4b).  

713982009 | Ability to achieve target heart rate (observable entity) | is different compared to the sibling heart rate concepts and is proposed to be moved up to 364072008 | Cardiac feature (observable entity) |, which is a subsumer of the current concept. While other representations could be explored, it is considered out of scope of this project. Particularly, the function observables hierarchy needs further work.

The pulse rate FSNs should follow the pattern "Heart rate measured at <artery> (observable entity)" and have existing FSNs as synonyms (see Figure 4b). 

Figure 5 Definition of Respiratory rate (observable entity), stated view

A Respiratory rate observable is defined likewise, with ventilationCycle replacing cardiacCycle (see Figure 5).

Figure 6 Respiratory rate classification result

The two observables Rate of spontaneous respiration and Total breath rate, both relating to ventilator treatment, are primitive.

Body temperature

Body temperature is defined as any temperature that inheres in any (anatomical or acquired) body structure (see Figure 7).

Figure 7 Definition of Body temperature (observable entity), stated view

There are two kinds of body temperature observable: core body temperature observable and specific anatomy temperature observable. The core body temperature inheres in 278826002 | body internal region (body structure) | representing the non-superficial parts of the body. The ‘direct site’ attribute specifies the site of measurement (see Figure 8). However, 278826002 | body internal region (body structure) | is a leaf node in SNOMED CT and does not subsume any of the structures considered to be contained in the body internal region, such as e.g. the viscera. Thus, temperatures of specific internal body parts are not automatically classified as core body temperatures. There are no current plans to define body structures as internal or peripheral in SNOMED CT.

Figure 8 Definition of Core body temperature, measured at tympanic membrane (observable entity), stated view

The specific anatomy temperature observables are more straight-forward. The temperature qualities inhere in the specific body structure, as e.g. in Figure 9.

Figure 9 Definition of Knee joint temperature (observable entity), stated view

There are two primitive concepts among the body temperature observables: Basal body temperature and Peripheral body temperature. Basal body temperature is the minimum “normal” core body temperature during rest, i.e. not related e.g. to hypothermia or other non-normal conditions. Thus, basal body temperature cannot just be defined as an aggregate minimum temperature. Peripheral body temperature cannot be fully defined, unlike core body temperature, because there is no single SNOMED CT concept corresponding to ‘peripheral body region’.

Figure 10 Body temperature classification results

Blood pressure

75367002 | Blood pressure (observable entity) | currently has 88 descendants and 165077006 | Intracardiac pressure (observable entity) | has an additional 29 descendants.

All blood pressure observables have a property type of pressure, they inhere in cardiovascular system structures, and they characterize the cardiac cycle. Note here that the process observable attribute 'characterizes' is used for a quality observables.  By defining blood pressure as inhering in the cardiovascular system, the blood pressure will subsume both pressures in blood vessels and intracardiac pressures.

Figure 11 Blood pressure observable, stated view

The characterizes attribute is used to distinguish blood pressures by which part of the cardiac cycle (process) they are characterizing, e.g. the systolic phase.

Figure 12 Systolic blood pressure, stated view

A set of cardiac processes have been created to allow definition of the cardicac cycle phase-specific pressure observables currently in SNOMED CT.

Figure 13 Cardiac process hierarchy

There are two kinds of aggregation blood pressure observables: those that aggregate over the whole or part of the cardiac cycle, e.g. mean arterial blood pressure, or those that aggregate over a set of cardiac cycles, e.g. average 24 hour systolic blood pressure. Note that systolic blood pressure is also an aggregated quantity as it is the maximum pressure of the systolic phase. To represent these various aggregation blood pressures, and to avoid using features not currently in SNOMED CT description logic, a number of primitive concepts were used or introduced.

The concept 6797001 | Mean blood pressure (observable entity) | is made into a primitive child of 75367002 | Blood pressure (observable entity) | (i.e. as it is today). Likewise, new concepts representing Average, Minimum, and Maximum pressure needs to be added as they do not currently exist. All those blood pressure observables with aggregation will then have stated IsA relationshiops to those primitive concepts. E.g. 252077001 | Venous mean pressure (observable entity) | would be defined by reference to the primitive concept 6797001 | Mean blood pressure (observable entity) |. This pattern could also possibly be reused for other aggregate observables, e.g. 252082008 | Venous mean flow (observable entity) |

Note that mean pressure refers to the average over a cardiac cycle whereas average pressures refers to an average over multiple cardiac cycles, e.g. over 24 hours.

Figure 14 Mean blood pressure, stated view

Blood pressure and time aspect

Currently, blood pressure observables without a specific time aspect stated in the FSN (e.g. 24 H) have not been assigned a single-point-in-time time aspect. It is assumed that blood pressure observables without specific time aspect could subsume both aggregate/time-specified observables and non-aggregate/single-point-in-time observables. If a blood pressure observable always, i.e. 100 % of the time, represents a single-point-in-time measurement, then a time aspect could be added.

Invasive and non-invasive blood pressure

To avoid having to create the concepts "invasive technique" and "non-invasive technique" and the problems associated with maintaining any such concepts, e.g. in terms of which other techniques should be subsumed by "invasive technique" and "non-invasive technique", it was decided to make the most generic concepts primitive, i.e. 386533006 | Invasive blood pressure (observable entity) | and 251076008 | Non-invasive arterial pressure (observable entity) |. Note that the "non-invasive" concept is more specific compared to the invasive one.

446841001 | Ankle brachial pressure index (observable entity) |

Ankle-brachial pressure index is the ratio between the systolic blood pressure in the ankle arteries and the brachial artery. For each leg, the highest of the systolic pressures in posterior tibial and dorsalis pedis arteries is divided by the highest systolic pressure in left or right brachial artery [Aboyans, V., et al. (2012). Measurement and interpretation of the ankle-brachial index. Circulation, 126(24), 2890-2909]. There is no single concept which subsumes only those two artery concepts. The most specific common subsumer of 13363002 | Structure of posterior tibial artery (body structure) | and 86547008 | Structure of dorsalis pedis artery (body structure) | is 312333002 | Distal lower limb artery (body structure) |, which is too generic. Thus, the concept needs to be primitive. Possibly, a "ankle brachial pressure measurement technique" could be added to fully define the concept.

The concept is defined as follows:

Figure 15 Ankle brachial pressure index, stated view

431314004 | Peripheral oxygen saturation (observable entity) |

Oxygen saturation (in blood) is the fraction of the amount of oxyhemoglobin to the total mount of oxy- and deoxyhemoglobin. Peripheral oxygen saturation (SpO₂) is the oxygen saturation measured with a pulse oximeter. [Nitzan, M., et al. (2014). Pulse oximetry: fundamentals and technology update. Medical Devices (Auckland, NZ), 7, 231.] 

However, the concept 709451001 | Deoxyhemoglobin + oxyhemoglobin (substance) | is defined as the conjunction of 80873004 | Oxyhemoglobin (substance) | and 9865006 | Deoxyhemoglobin (substance) |. 

The site of measurement can be e.g. a finger, ear lobe, forehead [Tokuda, K., et al. (2007). A comparison of finger, ear and forehead SpO2 on detecting oxygen desaturation in healthy volunteers. Anesthesiology, 107, A1544], nostril, or toe. Thus, for the generic peripheral oxygen saturation concept the site cannot be specified, as there is no single concept subsuming all possible peripheral measurement sites.

The generic concept 118596002 | Quantity fraction (property) (qualifier value) | has been used in order to allow the 431314004 | Peripheral oxygen saturation (observable entity) | concept to subsume e.g. both mass fraction and substance fraction peripheral oxygen saturation observables.

Figure 16 Peripheral oxygen saturation, stated view

Target observables

Currently, there is no proposed pattern for representing target (or goal, parameter, setting, etc.) observables. The target observables are left primitive being directly subsumed by the different children of 46680005 | Vital sign (observable entity) |, e.g. 428420003 | Target heart rate (observable entity) | is subsumed by 364075005 | Heart rate (observable entity) |. According to the definition of vital sign used in this document, these are not considered vital signs.

Terming

The FSNs and preferred descriptions will be updated to follow the Editorial Guidelines for Observable entities when appropriate and when doing so will make the name of concepts more clear rather than create additional confusion. For example, "Temperature of ear" is more clear than "Ear temperature" whereas "Pressure of blood" may be less clear than "Blood pressure."

Specifically, FSNs of concepts subsumed by 276885007 | Core body temperature (observable entity) | will be renamed using the this pattern: "Core body temperature measured at <location>".

Significant design or implementation decisions / compromises

A number of concepts were made primitive in order to avoid non-RF2 compliant representation (reflexive attributes). Further, a number of concepts were made primitive to avoid having to maintain qualifier values hierarchies, for example specifically stated invasive/non-invasive observables were made primitive to avoid having to represent hierarchies of invasive/non-invasive techniques in the techniques hierarchy, as well as the expectations around such a techniques hierarchy. Further, "at home" and "on admission" observables were represented as primitives.

Evaluation of Design

The design was evaluated by the Observable and Investigation Model Project, IHTSDO Terminologists, and the IHTSDO Head of terminology.

Exceptions and Problems

Design Strengths

The specific vital signs observables model has allowed a high number of fully defined concepts.

Design Weakness

Design Risks

Recommendation

Quality program criteria

Quality metrics

Quality metric 1

Quality metric 2

Project Resource Estimates

Scope of construction phase

Skills required:

• Knowledge of new Observables model
• Skills with modeling content in SCA Authoring Tool and/or preparing batch upload file to import into SCA Authoring Tool
• Ability to review concepts in SCA Authoring Tool

Solution Specification (Elaboration)

Implementation

• Work will be implemented using the SCA Authoring Tool

Preventing recurrence of problem

• If any new vital sign observables content are included in SNOMED CT, ensure that they are modeled properly
• Update SNOMED CT Editorial Guidance document with guidelines for modeling the content

Division of project into stages

• Authoring will likely be performed in stages:
  • Body temperature observables
  • Heart rate observables
  • Respiratory rate observables
  • Blood pressure observables

Projection of remaining overall project resource requirements

Expected project resource requirement category

The project requires project management.

Expected project impact and benefit

This project will enable modeling and full definition of almost all of the existing vital sign Observable entity content, thus allowing for enhanced utilization and streamlined maintenance of the content. This will also allow the newly modeled content to be compared to the LOINC vital signs Terms, identifying equivalencies which can result in a mapping between a LOINC Term and a pre-coordinated SNOMED CT concept and creating a hierarchy between LOINC Terms and SNOMED CT concepts which allows for enhanced analysis of the modeling of both LOINC and SNOMED CT.

Indicative resource estimates for construction, transition and maintenance:

Modeling existing content and review of modeling:

We estimate around 60 hours will be required to manually model and review the existing observable entity concepts using the SCA Authoring Tool. We estimate an additional 20 hours of a separate reviewer's time will be needed. An additional 20 hours is included to correct any issues identified in the final review. An additional 10 hours will be required to validate and promote the tasks and project to main.

Reviewing synonyms and adding text definitions:

We estimate around 20 hours to review potentially problematic descriptions, discuss with the review team, and update the descriptions as needed.

We estimate around 10 hours to author and include text definitions for the ~10 primitive concepts in the project scope (e.g., noninvasive blood pressure (observable entity), venous ambulatory pressure (observable entity)).

Project resource estimate

The project resource requirement is therefore classed as SMALL – less than 6 person months.

Although the work is presently available in a format suitable for batch upload of modeling, the necessary infrastructure on the back end of the SCA Authoring Tool is not ready at this time.

Construction and transition phase:  ca 130 concepts to be modeled, 10-15 new concepts to be authored

Maintenance phase: given the cooperative agreement between RII and IHTSDO, it is unlikely that any new Observable entity vital signs content will be added.