The SNOMED RT Procedure Model

Robert H. Dolin, MDl (Robert.H.Dolin~kp.org); Kent Spackman, MD, PhDi2'3; AlanAbilla, RN'; Carol M. Correia, MS, RN'; Bruce Goldberg, MD, PhD'; Debra Konicek,

RN, BSN2; Jonathan Lukoff, MD'; Cynthia B. Lundberg, RN'

'Kaiser Permanente; 2College ofAmerican Pathologists; 3Oregon Health SciencesUniversity

Background: SNOMED R7* represents afundamental change from prior versions ofSNOMED. The logic-based structure ofSNOMED RT enables concepts to be definedmore explicitly, providing an opportunity toaddress inconsistencies and ambiguities presentin prior SNOMED concept definitions.Objectives: Create a unifying organizationalstrategy for all SNOMED RT procedures, andremove ambiguities in procedure conceptdefinitions. Methods: A comprehensive model ofprocedures was developed, based on a set ofguiding principles and a review of knownexisting models. Results: All SNOMED RTprocedures are categorized by a common set of"root procedures" (high level atomic actions),and are more explicitly defined by a shared setofdefining relationships. Conclusions: While theobjectives have largely been met, open issuescontinue to be addressed. The similarity betweenprocedure models of SNOMED RT and theU.K 's Clinical Terms Version 3 is proving togreatly facilitate the full integration of the twoterminologies into a merged vocabulary to beknown as SNOMEDO Clinical Terms (SNOMEDCT), slated to be released in the nearfuture.

Introduction

The objective of this document is to describe theSNOMED RT Procedure Model, along with theprinciples underlying its inception. Just asSNOMED RT represents a fundamental changefrom prior editions of SNOMED, so too has theorganization of procedures undergone a majorre-thinking.

The SNOMED RT procedure hierarchy includesall clinical actions and healthcare services, suchas surgical and invasive procedures, non-invasive interventions, referrals, counseling,teaching, planning, regimens, courses of therapy,history taking, physical examinations, tests of allkinds, monitoring, administrative and financialservices.

The stimulus for this work was to addressinconsistencies and ambiguities present in therepresentation of procedures in SNOMED 3.x.Prior editions of SNOMED grouped proceduresinto chapters [Table 1]. These chapters clusteredprocedures based in part on the performingprovider, even though many of the procedurescould potentially be performed by a range ofproviders. For instance, Gait-evaluation (P7-20130) was classified as a Physical-medicine-and-physiotherapy-procedure, Blood-pressure-education (PA-60180) was classified as aNursing-procedure.

Table 1: Organization of Procedures in

PO-00000 Administrative procedures and physicianservices

P1-00000 Operations and anesthesia proceduresP2-0000 Medical proceduresP3-00000 Laboratory proceduresP5-00000 Radiology, radiotherapy, nuclear medicine

and ultrasound proceduresP7-00000 Physical medicine and physiotherapy

proceduresP8-00000 Dental proceduresP9-00000 Psychologic and psychiatric proceduresPA-00000 ,,Nursing procedures

SNOMED 3.x lacked definitions for procedures,leading to ambiguous concepts andinconsistently structured hierarchies. Forinstance, what is a Manipulation (Pl-OE000),and are Massage-physiotherapy (P7-01050) orDigital-palpation-of-pharynx (P2-20230) kindsof Manipulation? What distinguishes a Medical-procedure-on-bladder (P2-70050) from anOperative-procedure-on-bladder (P1-740H8)?

The various chapters sub-organize their conceptsalong different and overlapping principles. Forinstance, operations are organized by rootprocedure (e.g. Excisions, Incisions) andtopography; radiology procedures are organizedby equipment (e.g. Nuclear medicine,

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Ultrasound) and topography; laboratoryprocedures are organized by lab fimctional units(e.g. Hematology, Chemistry) and measuredcomponents. A Pulpectomy (P8-60240) in theDental-procedure chapter is classified as anEndodontic-procedure (P8-60000), while in theOperations chapter would be classified as anExcision.

The objective with SNOMED RT was to create aconsistent organizational strategy, and removeambiguities.

Introduction to SNOMED RT

SNOMED RT represents several fundamentalenhancements over prior editions of SNOMED12. These enhancements were crucial in enablingexplicit definitions to be created for SNOMEDRT procedures. In particular:

* Hierarchies in SNOMED RT represent strictsupertype-subtype relationships. Therefore, achild concept is necessarily always a kind ofthe parent concept. (Thus, it would be correctto classify Blood-pressure-education as a kindof Nursing-procedure only if Blood-pressure-education is ALWAYS a kind of Nursing-procedure.)

* Concepts are defined by their placement in a(poly)hierarchy and by additional propertiescalled "Relationship Types" or "Roles", whosetarget values are also SNOMED concepts. Forexample, Appendectomy (P1-57450) has an"ASSOCIATED-TOPOGRAPHY" role,whose value is Appendix (T-59200).

* SNOMED RT contains textual definitions,which are especially valuable when theunderlying description logic is unable to definea procedure fillly.

* A fully-specified (a.k.a. context-free) name isprovided in SNOMED RT for each concept

SNOMED RT "Root Procedures"

The primary organizational approach toprocedures in SNOMED RT is both bytopography (e.g., "Procedure-on-chest","Procedure-on-abdomen"), and by "rootprocedure" (e.g., "Excision-procedure","Education-procedure"). A root procedure is oneof the basic acts of a performed procedure. Root

procedures aren't themselves performed - theylack specification of other necessary qualifiers.As such, root procedures are typically neutralwith respect to: providers and recipients;administered substances and administeredenergy; equipment; procedure approach;topography; and procedure goal or intent.

The "root procedure" represents the main deed oraction of the procedure. These root proceduresare segregated into a "clinical action" hierarchy,and SNOMED RT procedures use the HAS-ACTION role to indicate the specific rootprocedure (e.g., Repair-of-tendon HAS-ACTION Repair-action; Closure-of-jejunal-fistula HAS-ACTION Closure-action).

SNOMED RT procedures are organized by theirroot procedures. As such, it was criticallyimportant that the root procedure hierarchy beunambiguous. A subset of SNOMED RT rootprocedures is shown in [Table 2]. Guidingprinciples used in the construction of the rootprocedure hierarchy included:

* A single SNOMED Root Procedure hierarchywill organize all SNOMED RT procedures.

* SNOMED Root Procedures must be:UNDERSTANDABLE: Each SNOMEDRoot Procedure will have a precise textualdefinition. The sum total of all definitions willbe internally consistent; REPRODUCIBLE:Each SNOMED Root Procedure must be usedconsistently by independent SNOMEDterminology modelers; and USEFUL:SNOMED Root Procedures are created tosupport the categorization of real SNOMEDprocedures. New root procedures are addedonly when new procedures require them.

* SNOMED Root Procedure hierarchy anddefinitions are based on a thorough review ofmajor standards and references (such asCTV334, ICD-10-PCS5, HL7 ReferenceInformation Model (RIM) 67, InternationalClassification of Nursing Practices"9, CEN'0,and standard clinical textbooks anddictionaries). Although there are oftenconflicting definitions of root procedure termswithin these references, SNOMED RT assignsa single best definition to each root procedure,and bases all subsequent modeling on thatdefinition.

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Table 2: Subset of SNOMED RT Root Procedures

* EductIon-action (P0-02023) Providing kno tosomeon.* Training-action (P0-02024) An education that includes hands-on practice by the recipient of

the education.* Introduction-action (P0-02067) IntWducon of obect or substance Into or onto body.

. Administrafton-acton (P0-02198) Introducftin of a substance Into the body.*Injecton-action (P0-02068) Administatlion usin psve pressure and a needle or other

_ equipment to drive a subs nce into te body.* implantation-action (P0-02079) Intduction of a nonilc device.

* Removal-action (P0-02045) To take somethin2g off or out, to get rid of, to eliminate.* Evacuation-action (PO-02034) Removal of the contents of a body cavity or container.

* Drainage-action (P0-02031) Evacuation of liquid ontents.by gravity.* Expulsion-action PO-02049) Ecpositive pressure.

Expression-action (P0-02167 _ An e*pulsion done by manipulation.Excision-action (P0-02046 Removal done wth a ctting Instrment

* Extraction-action (PO-021P64) R al pulin* Aspirafton-action (P0-02058) Extracton usingnaesage

* Where the differences between two conceptsare subtle or cannot be adequately defined(e.g. "insertion" vs. "implantation"), createonly one SNOMED Root Procedure and listthe subtly different concept as a synonym

* Roles can be constrained based on the rootprocedure. For instance, the INTRODUCESand INTRODUCES-TO roles are used only tofurther define procedures that have HAS-ACTION Introduction-action. The REMOVESand REMOVES-FROM roles are used onlywhere HAS-ACTION is Removal-action.

SNOMED RT Procedure RelationshipTypes

SNOMED RT procedures are defined using theroles shown in [Table 3]. Laboratory LOINCconcepts have been merged with SNOMED RTlaboratory observations'112; as a result,SNOMED RT laboratory observations use adistinct set of roles that mirror those used byLOINC. Note that while these relationship typesare used in the pre-coordinated definition ofSNOMED RT procedures, they can also be usedin the post-coordinated construction of newprocedure concepts. A sample of SNOMEDprocedures are shown in [Figure 1].

Comments on SNOMED RTProcedures

How do you remove ambiguity and re-organizeprocedures without invalidating legacy dataencoded with SNOMED 3.x? The approachtaken was to best understand how an ambiguousconcept was typically used, and then model that

concept explicitly. This was achieved by (1)examining the lexical string as expressed in theSNOMED Preferred Term; (2) exam ning theplacement of a concept within the SNOMEDhierarchy; (3) consulting SNOMED users; (4)having independent modelers work in parallel onoverlapping concepts, then resolving inter-modeler discrepancies . In some cases,clarification could be achieved by simply addinga new defining characteristic (for instance,Pulpectomy was clarified with the addition ofHAS-ACTION Excision-action). In some cases,the vague provider-specific concepts were re-organized. For example, Blood-pressure-education was defined as a Nursing-procedure,but is now defined as an Education-procedure. Inother cases broader categories were created tosubsume the provider-specific concepts. Forinstance, Amniotomy-by-nurse remains aNursing-procedure but is now also defined as akind of Amniotomy. In many cases textualdefinitions were created - for instance, aManipulation is now defined as a "skilleddexterous action of the hands directly applied toa body part". Concepts remaining hopelesslyvague were retired, and now make reference tonew explicit concepts.

This isn't to say that SNOMED RT procedureconcepts are modeled perfectly. There is someoverlap in the various relationship types, and as aresult there may be some inconsistencies in howthe relationships were applied. For instance, theADMINISTERED-SUBSTANCE andINTRODUCES relationships overlap somewhat,although the intent is to use onlyADMINISTERED-SUBSTANCE where the rootprocedure is not a kind of Introduction.

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Table 3: SNOMED RT Procedure relatshi Cs.

ADMINISTERED- Names the dcheical placed Into the body or the non-inert material placed onto the body that isSUBSTANCE meant to Interact chemically with the Intent of achieving a therapeutic, prophylactic, protetve,

diagnostic, nutritional and/or physiological goal.* Peritoneal-dIalyis ADMINISTERED-SUBSTANCE Perltoneal-dialylsi-solution

ADMINISTERS- Names th energy applied t, placed Into, or transmitted through the body with the Intent ofENERGY achieving a therapeutic, prophylactic, protective, diagnostic, nutritional, and/or physiological

goal. The domain for this role Is mainly the Physical Agents, Activities, and/or Forces hierarchy.* Lpser-rurfadng-of-skin ADMINISTERS-ENERGY Laser-generated -radiation

ASSOCIATED- Names the anatomical site affected by a procedure.TOPOGRAPHY * Excsinof-csto ddney ASSOCIATED-TOPOGRAPHY KidneyHAS-ACTION Names the root procedure or maln deed or action of the procedure.____. ___ .___ * Repalr-of-tendon-by-direct-suture HAS-ACTION Repair-action.HAS-OBJECT Names the anatomy, pathology, substance or physical object toward which HAS-ACTION is

directed.* Closure-ofjejunal-fstula HAS-OBJECT Fistula* Reduction-of-fracture-o-tibIa HAS-OBJECT Fracture

INTRODUCES Names the material, substance, prosthesis or other entity that Is placed Into or on the body.* Insertion-of rod-through-fracture INTRODUCES Orthopedic-intemal-fixation-device

INTRODUCES-TO Names the device or structire to which an entity Is Introduced.* Cathetierization-of-pancreatic-cyst INTRODUCES-TO Cyt

PROCEDURE- Names the directional, spatial, or relational access to the topographic site of a procedure.APPROACH Abdominal-hysterectonjy PROCEDURE-APPROACH Trans-abdominal-approachREMOVES Names the material, substance, tissue, prosthesis: or other entity that Is removed from the body.REMOVES_____ * euseom oalanges-of-hand REMOVES SequestrumREMOVES-FROM Names the device or structure from which an entity Is removed.

_* 4piration-ofdivertculum-of-phax REMOVES-FROM DiverticulumUSES-EQUIPMENT Names the equipment used to accomplish a procedure.

* Arthroco y USES-EQUIPMENT Endo-.....

HAS-MEASURED- Names the substance, entity, physiological function or physical property being measured.COMPONENT * l-Weeding-time HAS-MEASURED-COMPONENT Hemostatio-functionHAS-METHOD Names the method by-which a procedure Is perfmed (e.g., India ink preparation).

.________* He.moglobin A HAS-METHOD ElectrophoresisHAS-PROPERTY Names the kind of quantity belng measured (e.g., concentration).

* 24-hour-urine-steroids HAS-PROPERTY Mass rateHAS-SCALE-TYPE Names the scale of the result of an observation of a diagnostic test (e.g., quantitative, qualitative).

* Serum-sodiuHmeasurement HAS-SCALE-TYPE QuantitativeHAS-SPECIMEN Names the specimen used for a measurement.

* Serum-sodium-measurement HAS-SPECIMEN Serum-specmenHAS-SUBJECT-OF- Distinguishes observations or actions on the patient (or samples taken from the patent) ftrnOBSERVATION observations or actions on non-patient materials that relate to the patient

* ADO-typing-of-patfent HAS-SUBJECT-OF-OBSERVATION Patient* ABO-typfn -fdonor HAS-SUBJECT-OF-OBSERVATION Blood-donor

HAS-TIME-ASPECT Names definitional temporal relationships for a procedure.24-hour-urine-creatinine HAS-TIME-ASPECT 24-hours

The HAS-OBJECT relationship has proven to bethe most difficult to apply consistently. TheREMOVES, REMOVES-FROM,INTRODUCES, and INTRODUCES-TO roleswere created to supplant its ambiguity.

It turned out to be quite challenging to craftcertain definitions, such as "surgical procedure",which seems straightforward until one attemptsto make a cleanly define those procedures thatare always and necessarily surgical. Although thefollowing definition is still a work in progress, itis the result of a significant amount of discussionand thought by the contributors to SNOMED,and seems to be reproducible. It largely defines a

surgical procedure by enumerating those rootprocedures that are surgical.

A surgical procedure (a.lca. an operation oroperative procedure) involves planned alterationofthe structure ofthe body, ordinarily requiringthe disruption of some body surface, usuallythrough an incision. Root procedures that arenecessarily surgical include: construction,closure, open reduction, dissection, avulsion,open biopsy, debridement, decortication,enucleation, excision, scraping, stripping,exteriorization, fixation, incision, ligation,plastic repair.

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* Introduction (HAS-ACTION Introduction-action]Administration [HAS-ACTIONAdministration-action]* Administration-of-medication (HAS-ACTION Administration-action;INTRODUCES Drug]

* Injection [HAS-ACTION Injection-action]* Intramuscular injection [HAS-ACTION Injection-action;ASSOCIATED-TOPOGRAPHY Muscle]

* Injection of diaphragm [HAS-ACTION Injection-action;ASSOCIATED-TOPOGRAPHYDiaphragm]

* Implantation [HAS-ACTIONImplantation-action]* Implantation of joint prosthesis

(HAS-ACTION Implantation-action;ASSOCIATED-TOPOGRAPHY Joint;INTRODUCES Joint prosthesis]

Figure 1: A small subset of the SNOMED RTProcedure hierarchy.

Conclusion

The objective with SNOMED RT was to create aconsistent organizational strategy, and to removeambiguities. This objective has largely been met.A single set of root procedures serves as aunifying organizational principle for allprocedures, and all procedures are moreexplicitly defined using multiple parents and acommon set of relationship types. Open issuesremain, some of which are noted in the sectionabove, and these are continuing to be addressed.

The similarity between the SNOMED RT andthe UK's Clinical Terms, Version 3 proceduremodels is proving to greatly facilitate theintegration of the two terminologies into amerged vocabulary known as SNOMED ClinicalTerms (SNOMED CT), slated to be released bythe College of American Pathologists in the nearfuture. The similarities between the SNOMEDRT and SNOMED CT procedure modelsfacilitates migrating from one edition to the next.

Acknowledgments

Special thanks to John Mattison, MD and KeithCampbell, MD, PhD for their vision andleadership in Kaiser Permanente's participationwith the College of American Pathologists in thedevelopment of SNOMED RT. Thanks also goto other Kaiser Permanente modelers: Aaron

Snyder, John Fedack, Robert Clements, EnriqueHernandez, Gerry Lazzareschi, Steven Lester,David Levy, Jim Resneck, Chris Zingo; and tothe College of American Pathologists' SNOMEDmodelers, Julia Kim, Marjorie Rallins; whonever let a relationship type or proceduredefinition into SNOMED without close scrutiny.

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