Letters addressing topics of current interest or material

Ventilatory Modes. What’sin a Name?

We have read with great interest the pa-per published by Chatburn et al in RESPIRA-TORY CARE.1 reporting on how familiarhealthcare leaders coming from differentprofessions are with some general technicaland physiological aspects related to mechan-ical ventilation. Even if the survey shows areasonable level of knowledge and agree-ment between both individuals and profes-sions regarding most of the questions sub-mitted, it must be underlined that the targetpopulation consisted mainly of profession-als who had prior skills in the field of me-chanical ventilation. More than 50% of re-sponders were respiratory therapists, whooften have a substantial level of expertiseregarding these issues. Moreover, it is notsure that the same rate of agreement wouldhave been found, even in this specific skilledpopulation, if more detailed questions (ie,as to nomenclature and technical details ofventilator modes proposed by modern ven-tilators) had been raised.2 In fact, as men-tioned by the authors, while mechanical ven-tilation has hugely evolved these lastdecades, what lags behind is a standard clas-sification or taxonomy able to describe thisincreasing complexity.

This issue is still more worrying regard-ing noninvasive ventilation (NIV). Due togrowing evidence of NIV’s effectiveness ina broad range of indications and increasingavailability of user-friendly portable de-vices, the number of patients receiving NIVat home is continuously increasing, For ex-ample, NIV is increasingly applied in dif-ferent settings, such as critical care units,pulmonary, cardiology3 or neurological4 de-partments, pediatrics facilities, weaning cen-ters, sleep labs, in the emergency room,5,6

in pre-hospital care,7 and in general wards.8

As a “victim of its own success” NIV hasbecome a generalized practice, and it is notunusual that it may be carried out by non-specialized healthcare professionals. WhenNIV was introduced, there were a very lim-ited number of modes and types of ventila-tors, with very few possible settings. But asNIV devices were submitted to the samemarket evolution as conventional mechani-cal ventilation, developments in design and

technologies led to the more than 30 modelspresently available, offering numerous op-tions for settings.2

Moreover, there are no marketing regu-lations for ventilators. This leaves manufac-turers free to give different names to iden-tical or very similar ventilators modes andsettings and even “create” new modes thatcorrespond frequently only to minor modi-fications of a previously known mode. Thisexplains why the wide variety of existingterminology describing NIV modes is some-what confusing; it also explains the lack of acommon nomenclature. Clinicians can to-day be confronted with a given acronym thatcorresponds to different modes in differentdevices, and conversely to identical modesthat are called differently in different venti-lators. Bi-level ventilators, for example, wereinitially referred to as BiPAPs (a commer-cial name of the first machine of this type onthe market), but use of this term has causedconflict as the manufacturer claimed forcopyright. Other terms and acronyms wereused such as pressure support ventilation(PSV), IPAP, and EPAP, S/T devices, bi-level pressure assist, CPAP � inspiratorysupport, and PV with PEEP. This can be aproblem in clinical practice, when a nonspe-cialized physician is confronted with this in-comprehensible plethora of names and de-vices.

In this context, proposing a standardizedclassification for a better understanding ofventilation and ventilators seems rather log-ical. But, even if it were possible, this issueinvolves a high level of complexity regard-ing critical care ventilators, because of theoverabundance and complexity of new(supposed) “intelligent modes” that includecomplex closed loops and several differenttargeting algorithms. Furthermore, the clas-sification and terminology applied to inten-sive care respirators does not necessarily ap-ply to the smaller yet very versatilerespirators intended for home use: for thesedevices it seems easier to provide a stan-dardized classification

As ventilators can be categorized by howthey deliver gas flow and how they triggerinspiration and expiration, answers to 3 ba-sic questions may serve as a guide to sim-plify terminology:

• What is the ventilatory mode (pressure orvolume)?

• How is the inspiration triggered (assisted,assisted/controlled, or controlled)?

• How is switching from inspiration to ex-piration (cycling) managed (flow or timedcycling)?

These 3 categories may facilitate a stan-dardizing of NIV taxonomy and clarify thisconfusion. Based on these principles, Cho-pin et al proposed a “physiological” butsomewhat complex categorization of venti-latory modes applied to ICU ventilators.9

Our group proposes a more pragmatic andergonomic approach of this classification,applicable to fewer and more simple modescommonly used to provide NIV by usingportable devices (Table 1).

Even if there is probably no perfect no-menclature, such an attempt at standardiza-tion could provide the basis for a large con-sensus aiming to achieve a morecomprehensive approach to NIV. This mayencourage manufacturers to privilege sim-plicity in their nomenclature instead of orig-inality and confusion. The goal? To makeNIV management easier in clinical practice.

Claudio Rabec MDService de Pneumologie et

Reanimation RespiratoireCentre Hospitalier et Universitaire

de DijonDijon, France

Bruno Langevin MDService de Reanimation Medicale

Centre Hospitalier AlesAles, France

Daniel Rodenstein MD PhDService de Pneumologie

Cliniques Universitaires Saint LucUniversite Catholique de Louvain

Bruxelles, Belgium

Christophe Perrin MDService de Pneumologie

Centre Hospitalier CannesCannes, France

Patrick Leger MDService de Pneumologie

Centre Hospitalier Universitaire Lyon SudLyon, France

2138 RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12

Letters

Letters addressing topics of current interest or material in RESPIRATORY CARE will be considered for publication. The Editors may accept or

decline a letter or edit without changing the author’s views. The content of letters reflects the author’s opinion or interpretation of information;

their publication should not be interpreted as an endorsement by the Journal. Authors of criticized material will have the opportunity to reply

in print. No anonymous letters can be published. Letters should be submitted electronically via Manuscript Central. Log onto RESPIRATORY

CARE’s web site at http://www.RCJournal.com.

Jean-Louis Pepin MD PhDPole Reeducation et Physiologie et

Laboratoire Hopitaux PubliqueInstitut National de la Sante et de la

Recherche MedicaleUniversite Joseph Fourier

Grenoble, France

Jean Paul Janssens MD PhDService de Pneumologie

Hopitaux Universitaires de GeneveGeneva, Switzerland

Jesus Gonzalez-Bermejo MDService de Pneumologie et

Reanimation RespiratoireHopital de la Pitie-Salpetriere

Paris, France

On behalf of the SomnoNIV Group

The authors have disclosed no conflicts of in-terest.

REFERENCES

1. Chatburn RL, Volsko TA, Hazy J, HarrisLN, Sanders S. Determining the basis for ataxonomy of mechanical ventilation. Re-spir Care 2012;57(4):514-524.

2. Gonzalez-Bermejo J, Laplanche V, Hus-seini FE, Duguet A, Derenne JP, SimilowskiT. Evaluation of the user-friendliness of 11home mechanical ventilators. Eur Respir J2006;27(6):1236-1243.

3. Vital FM, Saconato H, Ladeira MT, Sen A,Hawkes CA, Soares B, et al. Non-invasivepositive pressure ventilation (CPAP or bi-level NPPV) for cardiogenic pulmonaryedema. Cochrane Database Syst Rev 2008;(3):CD005351.

4. Atkeson AD, RoyChoudhury A, Har-rington-Moroney G, Shah B, Mitsumoto H,Basner RC. Patient-ventilator asynchronywith nocturnal noninvasive ventilation inALS. Neurology 2011;77(6):549-555.

5. Cabrini L, Antonelli M, Savoia G, Lan-driscina M. Non-invasive ventilation out-side of the intensive care unit: an Italiansurvey. Minerva Anestesiol 2011;77(3):313-22.

6. Davey M. Theme: non-invasive positivepressure ventilation (NiPPV) in the ED.Emerg Med J 2010;27(12):903, 966.

7. Taylor DM, Bernard SA, Masci K,MacBean CE, Kennedy MP, Zalstein S. Pre-hospital noninvasive ventilation: a viabletreatment option in the urban setting. Pre-hosp Emerg Care 2008;12(1):42-55.

8. Plant PK, Owen JL, Elliott MW. Early useof non-invasive ventilation for acute exac-

erbations of chronic obstructive pulmonarydisease on general respiratory wards: a mul-ticentre randomised controlled trial. Lancet2000;355(9219):1931-1935.

9. Chopin C, Chambrin M. An attempt to clas-sify the current positive airway pressuremodes of mechanical ventilation. Reanima-tion Urgences 1998;7:87-99. Article inFrench.

The authors respond:

Rabec et al have supported the concernsmentioned in our paper,1 noting that, “whilemechanical ventilation has hugely evolvedthese last decades, what lags behind is astandard classification or taxonomy able todescribe this increasing complexity.” In ad-dition, they have pointed out the further con-cern that confusion about modes may be aneven greater problem regarding home careventilation, and particularly noninvasiveventilation “when a non-specialized physi-cian is confronted with this incomprehensi-ble plethora of names and devices.” Indeed,they reference a paper that lists no less than24 unique mode names on 11 different homecare ventilators.

Havingstudiedandwrittenabout this sub-ject for over 20 years, and having served asa consultant to committees from the Inter-national Standards Organization and the IHE(Integrating the Healthcare Enterprise,www.ihe.net), I have come to appreciate thecomplexity of addressing this problem. Thesolution requires a level of treatment wellabove simply creating an intuitively pleas-ing nomenclature, such as the “physiologi-cal nomenclature” suggested by Rabec et al.The solution is to create a formal taxon-omy.

Taxonomy is the science of classifica-tion. The most common taxonomies havehistorically been those applied to plants andanimals, in the form of class, family, genus,and species. However, the rapid growth ofthe World Wide Web, and more specifi-cally, the Semantic Web, has created an in-tense need for organized search strategiesthat are based on taxonomies. One wellknown example is the Taxonomy of Edu-cational Objectives, also known as Bloom’sTaxonomy. A taxonomy is typically a hier-archical classification or categorization sys-tem. Anyone who has ever been to the Website www.Amazon.com has used a taxon-omy. The menu along the left hand side ofAmazon’s Web page is an expandable out-line. For example, if you select “books” from

Table 1. “Physiological” Proposed Classification of Noninvasive Ventilation Current Modes

Usual Appellations* “Physiological” Nomenclature

Volume-controlled ventilation (VCV) V-C-TVolume assisted/controlled ventilation V-A/C-TPressure-controlled ventilation, PCV, T mode

(in bi-level devices)P-C-T

Pressure assisted ventilation (PSV, pressure supportventilation (PSV), spontaneous (S) mode(in bi-level devices)

P-A-V

Pressure assisted ventilation � positive end expiratorypressure (PEEP) PSV � PEEP, pressure support �PEEP, CPAP � inspiratory support, S mode(in bi-level devices)

P-A-V (EPAP)

Pressure assisted /controlled ventilation (PAC) P-A/C-TPressure assisted/controlled ventilation (PAC) � PEEP P-A/C-T (EPAP)Spontaneous/timed mode (ST), IPAP/EPAP

(in bi-level devices),P-A-V (EPAP/f)

PACV with volume targeting P-A/C-T (VT)ST mode with volume targeting, AVAPS, IVAPS,

volume assured, PS � PEEP � VT

P-A-V(EPAP/f/ VT)

* Usual appellations correspond to the names devised by the manufacturers for each modality. In the proposed “physiological”nomenclature the first character indicates ventilatory modality (P or V), the second how the inspiration is triggered (A � assisted,A/C � assisted/controlled, C � controlled), and third the mode of switching from inspiration to expiration (V � flow, T � timedcycling).IPAP � inspiratory positive airway pressureEPAP � expiratory positive airway pressureAVAPS � average volume assured pressure supportIVAPS � intelligent volume assured pressure supportVT � tidal volume

LETTERS TO THE EDITOR

RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12 2139

the list of products sold, you will get an-other list lower down on the hierarchy, in-cluding different types of books (eg, audiobooks, business and investing, children’sbooks, cookbooks, et cetera). Clicking anyof these selections brings you to an evendeeper level of the taxonomy. Anothervery good example of a visual display ofa taxonomy can be seen at http://www.accessinn.com:8081/PerfectSearch/navtree/index.html. At this Web site the ex-plicit collapsible levels of the taxonomy’shierarchy are clearly visible. This latter ex-ample is more appropriately called a the-saurus. Most of us are familiar with a the-saurus as a kind of dictionary, such asRoget’s Thesaurus, which contains syn-onyms for each entry. A dictionary-type the-saurus includes all the associated terms thatcould be used in place of the term entry invarious contexts. In contrast, a thesaurusused for information retrieval is designedfor use in all contexts within the domain ofcontent covered, regardless of any specificterm usage or document. A thesaurus of thistype, therefore, is a more structured type ofcontrolled vocabulary that provides infor-mation about each term and its relationshipsto other terms within the same thesaurus.2

National and international standards thatprovide guidance for creating such thesauriinclude:

• International Organization for Standard-ization (www.iso.org/iso/iso_catalogue.htm)- ISO 2788 (1986): Guidelines for the Es-

tablishment and Development of Mono-lingual Thesauri

- ISO 5964 (1985): Guidelines for the Es-tablishment and Development of Mul-tilingual Thesauri

- ISO 2788 and 5964 were replaced in2011 by ISO 25964: Thesauri and In-teroperability With Other Vocabularies

• American National Standards Institute(ANSI) and National Information Stan-dards Organization (NISO) (www.niso.org/kst/reports/standards)- ANSI/NISO Z39.19 (2005): Guidelines

for the Construction, Format, and Man-agement of Monolingual ControlledVocabularies

• British Standards Institution (www.bsig-roup.com)- BS 8723-1 (2005): Structured Vocabu-

laries for Information Retrieval: Defi-nitions, Symbols, and Abbreviations

- BS 8723-2 (2005): Structured Vocabu-laries for Information Retrieval: The-sauri

These standards describe 3 types of re-lationships in a thesaurus: hierarchical(broader term/narrower term), associative(related term), and equivalence (use/usedfor). For simplicity, I will include the the-saurus in the term “taxonomy.”

Taxonomies are not generally created bycommittee. Rather, a trained taxonomistconstructs them from several key compo-nents after becoming sufficiently familiarwith the content of the subject domain (usu-ally with input from end users). In my case,I started as a domain expert who had tolearn about taxonomy: what has been calledan “accidental taxonomist.“2 Either way, thefirst component to create is a “controlledvocabulary,” which is a glossary of pre-defined terms. Choosing appropriate termsis difficult, because there are usually manyways to define key concepts. Priority mustbe given to specificity and logical consis-tency throughout the domain of application.The second component, created using thevocabulary, is the hierarchical structure ofthe taxonomy. There are many logical sys-tems that may work, so priority must begiven to the one that is most useful andmost easily implemented among all groupsof stakeholders. The number of levels in thehierarchy is important; too few and you losethe ability to discriminate among items; toomany and you lose the advantage of group-ing. Creating 3 to 5 levels seems to be aboutright, and this may be related to the humancapacity to store and process only about 4variables at a time.3 Many taxonomies, cre-ated at great expense, have failed becauseof insufficient planning of vocabularies andhierarchies. The third component is the as-sociative and equivalence relationships re-quired to create the finished product. A wellconstructed taxonomy offers these advan-tages4:

• Description

• Reduction of Complexity

• Identification of Similarities

• Identification of Differences

• Comparison of Types

• Explanation of Relationships

These benefits justify the resources re-quired to create and maintain a taxonomy.

According to Hedden,2 “A taxonomy isnever finished. As soon as it is implemented,it undergoes testing and revision, and con-tinued use will dictate further enhancements.All taxonomies require ongoing mainte-nance, and many taxonomies also undergomore significant revisions or restructuringover time.”

Taxonomies serve one of 3 practical func-tions, particularly important in this age ofthe electronic medical record: indexing sup-port; retrieval support; and navigation sup-port. Thus, the taxonomy’s initial purposeis to serve the people doing the indexing,although a second, equally important pur-pose is to serve the end users.2 In the con-text of mechanical ventilation, the “index-ers” are primarily the engineers andmarketing people working for ventilatormanufacturing companies, who must writethe ventilator operators’ manuals. Althoughmanufacturers are responsible for creatingthe chaos related to modes, they are also inthe best position to fix the problem. There isno need for manufacturers to stop creatingnew names for modes, but they must allagree on a standard description of the mode(ie, how it is classified relative to othermodes), and they must use the same vocab-ulary to explain how it performs. Withoutthis, both patient care and device sales willcontinue to be at risk. Until manufacturershave reached such a level of consensus, how-ever, the responsibility for indexing modesof ventilation must fall to the members ofthe other stake-holder groups (ie, clinicians,educators, and researchers).

Recognizing the need for a formal tax-onomy of modes of mechanical ventilationwas the underlying motive of our paper.1

What Rabec et al may not have noticed (dueto recent publication) is the book chapter5

and paper6 from our group demonstratinghow the survey questions of our first paperare developed into a classification system.The first step is to expand the 10 questionsfrom the survey into a set of maxims that,when combined, form the theoretical basisof a taxonomy for modes of ventilation5:

1. A breath is one cycle of positive flow(inspiration) and negative flow (expiration).The purpose of a ventilator is to assist breath-ing. Therefore, the logical start of a taxon-omy is to define a breath. Breaths are de-fined such that during mechanicalventilation, small artificial breaths may besuperimposed on large natural ones or viceversa.



2. A breath is assisted if pressure risesabove baseline during inspiration or fallsduring expiration. A ventilator assistsbreathing by doing some portion of the workof breathing. This occurs by delivering vol-ume under pressure.

3. A ventilator assists breathing usingeither pressure control (PC) or volume con-trol (VC). The equation of motion for therespiratory system is the fundamental modelfor understanding patient-ventilator interac-tion and hence modes of ventilation. Theequation is an expression of the idea thatonly one variable can be predetermined at atime: pressure or volume (flow control isignored for simplicity and for historical rea-sons, and because controlling flow directlywill indirectly control volume and viceversa).

4. Breaths are classified according to thecriteria that trigger (start) and cycle (stop)inspiration. A ventilator must know whento start and stop flow delivery for a givenbreath. Because starting and stopping in-spiratory flow are critical events in synchro-nizing patient-ventilator interaction, and be-cause they involve uniquely differentoperator-influenced factors, they are distin-guished by giving them different names.

5. Trigger and cycle events can be eitherpatient or machine initiated. A major de-sign consideration in creating modes is theability to synchronize breath delivery withpatient demand and at the same time to guar-antee breath delivery if the patient is apneic.Therefore, understanding patient-ventilatorinteraction means understanding the differ-ence between machine and patient triggerand cycle events.

6. Breaths are classified as spontaneousor mandatory, based on both the triggerand cycle events. A spontaneous breatharises without apparent external cause. Thusit is patient triggered and patient cycled.Any machine involvement in triggering orcycling leads to a mandatory breath. Notethat the definition of a spontaneous breathis independent of the definition of an as-sisted breath, and applies to but does notrequire the application of a mechanical ven-tilator. Consistent with common usage, nat-ural breathing is spontaneous.

7. Ventilators deliver only 3 basic breathsequences: continuous mandatory ventila-tion (CMV), intermittent mandatory venti-lation (IMV), and continuous spontaneousventilation (CSV). The 2 breath classifica-tions logically lead to 3 possible breath se-quences that a mode can deliver: CSV im-

plies all spontaneous breaths, IMV allowsspontaneous breaths to occur between man-datory breaths, and CMV does not.

8. There are only 5 basic ventilatory pat-terns: VC-CMV, VC-IMV, PC-CMV, PC-IMV, and PC-CSV. All modes can be cat-egorized by these 5 patterns. This providesenough practical detail about a mode formost clinical purposes.

9. Within each ventilatory pattern thereare several variations that can be distin-guished by their targeting scheme(s). Whencomparing modes or evaluating the capa-bility of a ventilator, more detail is requiredthan just the ventilatory pattern. Modes withthe same ventilatory pattern can be distin-guished by describing the targeting schemesthey use. There are at present only 7 basictargeting schemes: set-point, dual, servo,bio-variable, adaptive, optimal, and intelli-gent, which have been described in detailpreviously.7

10. A mode of ventilation is classifiedaccording to its control variable, breath se-quence, and targeting scheme(s). A practi-cal taxonomy of ventilatory modes is basedon just 4 levels of detail: the control vari-able (pressure or volume), the breath se-quence (CMV, IMV, or CSV), and the tar-geting scheme used for primary breaths(CMV and CSV), and, if applicable, sec-ondary breaths (IMV). This structure is rem-iniscent of the taxonomy of biological or-ganisms, which comprises order, family,genus, and species. Modes in the same “spe-cies” can be further differentiated by de-scribing their “species variety” in term oftheir phase variables (ie, trigger, and cyclevariables plus the within- and between-breath targets and control algorithms). Theadvantage of such a hierarchical structure isthat a mode can be described in any level ofdetail that is required. For example, we cansay that a patient was in volume controlduring surgery but changed to pressure con-trol during recovery, or that he was changedfrom PC-CMV to PC-CSV for a spontane-ous breathing trial, or that Pressure Supportis PC-CSV with set-point targeting, whereasVolume Support is PC-CSV with adaptivetargeting.

One thing I want to emphasize is that thelegacy meaning of the words “assist” and“control” must be abandoned in the forma-tion of a new taxonomy of modes. The mean-ing and importance of these words haveevolved radically since they were coined byanesthesiologists using the first ventilatorsover 60 years ago. The problem is that the

focus of their meanings has shifted subtlyfrom patient physiology to machine func-tion. A prime example is the use of the term“assist/control.” This term focuses on thepatient’s neurological control of breathingand refers to a mode in which the ventilatormay either “control” the breathing patternby triggering inspiration as a substitute forthe patient’s own neurological control, or“assist” the patient’s inspiratory effort afterhe/she has triggered inspiration. These def-initions date back to a time when ventilatorcapabilities were very primitive by today’sstandards.

Ventilators have evolved over at least 5generations in the span of a single humangeneration. As a result, many people whohave been in the field for a long time (ortheir students) cling to the older, patient-centric view of the word “control” and thusfail to appreciate the implications and utilityof the machine-centric view. Manufacturersfeel compelled to perpetuate this inertia be-cause many of these same people make thepurchasing decisions. The result is that theterm “assist/control” continues to be asso-ciated with mode selection on new ventila-tors, even though the meaning of the termhas changed from its historical roots to thepoint of virtual uselessness. Originally, as-sist/control meant volume-controlled con-tinuous mandatory ventilation (CMV). Nowit can also refer to pressure control (espe-cially in the pediatric literature).

In addition to forming the basis for ataxonomy, the 10 constructs listed abovecan be used as the basis of a complete teach-ing system for ventilator technology (ie, howventilators work as opposed to how they areused). Each one can be expanded to perhapsa week’s worth of didactic instruction andlaboratory demonstrations. These constructshave been designed to move progressivelyfrom simple to complex ideas while supply-ing a context for the key definitions in acontrolled vocabulary. They are uniquelysuited to instruction using Bloom’s “learn-ing for mastery” model,8 which has provenan effective learning theory for medical ed-ucation.9

To facilitate the implementation of ataxonomy based on control variables,breath sequences and targeting schemes(ie, for “indexing” or “tagging” modes), Ihave created 4 tools. The first tool is anabbreviated controlled vocabulary for me-chanical ventilation (which appears at theend of this letter). I have included onlythose terms necessary to understand and



use the taxonomy, but many more couldbe added for clarity.

Figure 1 shows the second tool: an algo-rithm for identifying the control variable.Figure 2 shows the third tool: an algorithmfor identifying the breath sequence. Figure 3shows the fourth tool, which provides theinformation necessary to identify the target-

ing schemes used in the design of a mode ofventilation.

To demonstrate the use of these tools,let’s classify 4 modes used for noninvasiveventilation. The simplest example is themode named Pressure Assist/Control. In-spiratory pressure is preset, so the controlvariable is pressure (see Fig. 1). Every breath

is time cycled, so every breath is mandatory(inspiration is machine triggered and/or ma-chine cycled, see the controlled vocabularyand Fig. 2), so the breaths sequence is con-tinuous mandatory ventilation (CMV). Fi-nally, the operator (rather than the ventila-tor) presets the parameters of the pressurewaveform, so the targeting scheme is set-

Fig. 1. Algorithm for determining the control variable when classifying a mode. SIMV � synchronized intermittent mandatory ventilation.(With permission from Mandu Press.)



point (see the controlled vocabulary andFig. 3).7 The mode is thus classified as pres-sure control continuous mandatory ventila-tion with set-point targeting (PC-CMVs).

Now let’s classify a little more complexmode, named Average Volume AssuredPressure Support. Again, inspiratory pres-sure for a given breath is preset, so the con-

trol variable is pressure. All breaths are pa-tient triggered and flow cycled (also knownas a “Pressure Support” breath). Flow cy-cling is a function of patient effort and re-

Fig. 2. Algorithm for determining the breath sequence when classifying a mode. SIMV � synchronized intermittent mandatory ventilation.(With permission from Mandu Press.)



spiratory system mechanics, and hence isconsidered patient cycling. Thus, spontane-ous breaths (patient triggered and patientcycled inspiration; see the controlled vo-cabulary) are possible. However, if the pa-tient does not trigger breaths above the pre-set rate, the ventilator will trigger a breath.A machine triggered breath is defined as amandatory breath. Therefore, spontaneousbreaths may occur between mandatorybreaths, and the breath sequence is classi-fied as intermittent mandatory ventilation(IMV). Finally, the inspiratory pressure is

automatically adjusted between breaths bythe ventilator, to achieve an average tidalvolume equal to the operator set target,which is an example of adaptive targeting.7

The mode is thus classified as pressure con-trol intermittent mandatory ventilation withadaptive targeting for both mandatory andspontaneous breaths (PC-IMVa,a).

Having mentioned Pressure Support(simplycalled“Spontaneous”modeonsomeventilators), we should also classify thiscommon mode. Inspiratory pressure is pre-set, so the control variable is pressure. Ev-

ery breath is spontaneous (ie, patient trig-gered and cycled), so the breath sequence iscontinuous spontaneous ventilation. Finally,the operator sets a fixed inspiratory pres-sure, so the targeting scheme is set-point.7

Thus the mode is classified as pressure con-trol continuous spontaneous ventilation withset-point targeting (PC-CSVs).

The fourth example is a mode namedProportional Pressure Ventilation (anothername for Proportional Assist Ventilation,which was originally developed as an inva-sive mode). Inspiratory pressure is prede-

Fig. 3. Rubric for determining the targeting schemes when classifying a mode. See controlled vocabulary for terms. (With permission fromMandu Press.)



termined, but not to a fixed value. Rather, itis constrained to be proportional to patienteffort, according to the equation of motionfor the respiratory system.7 Hence, the con-trol variable is pressure. Every inspiration ispatient triggered and patient cycled (we ig-nore the backup mode that is activated inthe case of apnea), so the breath sequence iscontinuous spontaneous ventilation (CSV).Finally, the targeting scheme that makes in-spiratory pressure proportional to inspira-tory effort is called servo.7 Thus, the modeis classified as pressure control continuousspontaneous ventilation with servo target-ing (PC-CSVr).

This mode taxonomy is equally usefulfor invasive modes. Indeed, the taxonomyfor classifying the technical capability of aventilator is independent of the ventilator-patient interface (ie, artificial airway vsmask). For example, consider the most com-monly used mode in ICUs: “Volume As-sist/Control.” For this mode, both inspira-tory volume and flow are preset, so thecontrol variable is volume (see Fig. 1). Ev-ery breath is volume cycled, which is a formof machine cycling (see the controlled vo-cabulary). Any breath in which inspirationis machine cycled is classified as a manda-tory breath. Hence, the breath sequence iscontinuous mandatory ventilation (seeFig. 2). Finally, the operator sets the param-eters of the volume and flow waveforms, sothe targeting scheme is set-point (see Fig. 3).Thus, the mode is classified as pressure con-trol continuous mandatory ventilation withset-point targeting.

If carefully applied, the taxonomy hasthepower toclarifyandunmaskhiddencom-plexity in a mode that has a cryptic name.Take, for example, the mode calledCMV�AutoFlow on the Drager Evita XLventilator. While “CMV” on this ventilatoris the same as “Volume Assist/Control” de-scribed above, adding the “AutoFlow” fea-ture changes it to a completely differentmode. For CMV�AutoFlow, the operatorsets a target tidal volume but not inspiratoryflow. Indeed, inspiratory flow is highly vari-able, because the ventilator actually sets theinspiratory pressure within a breath. Thus,the control variable, according to the equa-tion of motion, is pressure (see Fig. 1). Ev-ery inspiration is time cycled, so every breathis mandatory and the breath sequence is con-tinuous mandatory ventilation (CMV). Theventilator adjusts the inspiratory pressure be-tween breaths to achieve an average tidalvolume equal to the preset value, using an

adaptive targeting scheme.7 Thus, the modeis classified as pressure control continuousmandatory ventilation with adaptive target-ing (PC-CMVa).

On the other hand, the taxonomy can un-mask the complexity in an apparently sim-ple mode. A good example is the modenamed simply “Volume Control” on the Ma-quet Servo-i ventilator. As with Volume As-sist/Control on other ventilators, the opera-tor presets both inspiratory volume and flow(inspiratory flow is set indirectly by tidalvolume and inspiratory time settings). FromFigure 1 we see that this indicates volumecontrol, as expected. However, a carefulreading of the operator’s manual indicatesthat whether a breath is mandatory or spon-taneous depends on the level of patient in-spiratory effort. This is because the venti-lator uses dual targeting (see the controlledvocabulary and Fig. 3).7 If the patient makesno inspiratory effort, inspiration is machinetriggered (by a preset ventilatory frequency)and time cycled (by a preset inspiratorytime). Hence, such a breath is classified asmandatory. If the patient makes a moderateinspiratory effort, enough to make inspira-tory pressure fall 3 cm H2O, the ventilatorswitches from volume control to pressurecontrol and delivers as much flow as thepatient demands. If the inspiratory effort isof short duration relative to the preset in-spiratory time, the ventilator switches backto volume control and the breath is volumecycled. The preset tidal volume is still de-livered, but with a shorter inspiratory time,due to the increased average inspiratoryflow. Because inspiration is again machinecycled, this type of breath is also manda-tory. But if the patient makes a large enoughinspiratory effort that lasts beyond the pre-set inspiratory time, the ventilator remainsin pressure control and the breath is flow(ie, patient) cycled. If the breath was alsopatient triggered, it is virtually identical to abreath in the Pressure Support mode and assuch is a spontaneous breath.10

From this analysis we see the possibilityof spontaneous breaths occurring betweenmandatory breaths, and we conclude thebreath sequence is intermittent mandatoryventilation. Finally, as just described, thetargeting scheme is dual and we classify themode as volume control intermittent man-datory ventilation with dual targeting forboth primary and secondary breaths (VC-IMVd,d). In passing, we note that pressurecontrol with dual targeting is also possible,whereby inspiration starts out in pressure

control but switches to volume control ifthe ventilator decides the preset tidal vol-ume will not be delivered before inspirationcycles off. This was originally named Vol-ume Assured Pressure Support.11

Table 1 shows how to classify several ofthe many noninvasive modes, and Table 2applies the taxonomy to common invasivemodes.

In conclusion, the classification of modesof mechanical ventilation is complex enoughto require the full application of the toolsfor building a formal taxonomy, includingboth a controlled vocabulary and a hierar-chical structure of key classification terms.Both the vocabulary and the hierarchy canbe developed from the logical progressionof 10 simple constructs that are familiar tostakeholders, including clinicians, educa-tors, researchers, and manufacturers.1,5

While there may be any number of ways tocreate such a taxonomy, this one empha-sizes the key factors that are important forclinicians to understand in order to optimizethe match between the patient’s needs andthe ventilator’s technological capabilities.6

Abbreviated ControlledVocabulary for Mechanical

Ventilation

Adaptive Targeting SchemeA control system that allows the venti-

lator to automatically set some (or conceiv-ably all) of the targets between breaths inresponse to varying patient conditions. Onecommon example is adaptive pressure tar-geting (eg, Pressure Regulated Volume Con-trol mode on the Maquet Servo-i ventilator)where a static inspiratory pressure is tar-geted within a breath (ie, pressure-controlledinspiration) but this target is automaticallyadjusted by the ventilator between breathsto achieve an operator set tidal volume tar-get.

Assisted BreathA breath during which all or part of in-

spiratory (or expiratory) flow is generatedby the ventilator, doing work on the patient.In simple terms, if the airway pressure risesabove end-expiratory pressure during inspi-ration, the breath is assisted (as in the Pres-sure Support mode). It is also possible toassist expiration by dropping airway pres-sure below end-expiratory pressure (such asAutomatic Tube Compensation on theDrager Evita 4 ventilator). In contrast, spon-taneous breaths during CPAP are unassisted



because the ventilator attempts to maintaina constant airway pressure during inspira-tion.

Bio-variable Targeting SchemeA control system that allows the venti-

lator toautomaticallyset the inspiratorypres-sure or tidal volume randomly to mimic thevariability observed during normal breath-ing.

BreathA positive change in airway flow (inspi-

ration) paired with a negative change in air-way flow (expiration), associated with ven-tilation of the lungs. This definition excludesflow changes caused by hiccups or cardio-genic oscillations. However, it allows thesuperimposition of, for example, a sponta-neous breath on a mandatory breath or viceversa. The flows are paired by size, not nec-essarily by timing. For example, in AirwayPressure Release Ventilation there is a largeinspiration (transition from low pressure tohigh pressure), possibly followed by a fewsmall inspirations and expirations, followedfinally by a large expiration (transition fromhigh pressure to low pressure). These com-pose several small spontaneous breaths su-perimposed on one large mandatory breath.In contrast, during High Frequency Oscil-latory Ventilation, small mandatory breathsare superimposed on larger spontaneousbreaths.

Breath SequenceAparticularpatternofspontaneousand/or

mandatory breaths. The 3 possible breathsequences are: continuous mandatory ven-tilation (CMV), intermittent mandatory ven-tilation (IMV), and continuous spontaneousventilation (CSV).

CMVContinuous mandatory ventilation (com-

monly known as “Assist/Control”). A breathsequence in which mandatory breaths aredelivered at a preset rate and spontaneousbreaths are not possible between mandatorybreaths. Patient-triggered mandatory breathsmay occur between machine-triggeredbreaths (ie, the actual frequency may behigher than the set frequency). In some pres-sure-controlled modes on ventilators withan active exhalation valve, spontaneousbreaths may occur during mandatorybreaths, but the defining characteristic ofCMV is that spontaneous breaths are notpermitted between mandatory breaths, be-cause an inspiratory effort after a manda-tory breath triggers another mandatorybreath.

Control VariableThe variable (ie, pressure or volume in

the equation of motion) that the ventilatoruses as a feedback signal to manipulate in-spiration. For simple set point control, thecontrol variable can be identified as follows:

If the peak inspiratory pressure remains con-stant as the load experienced by the venti-lator changes, then the control variable ispressure. If the peak pressure changes as theload changes but tidal volume remains con-stant, then the control variable is volume.Volume control implies flow control andvice versa, but it is possible to distinguishthe two on the basis of which signal is usedfor feedback control. Some primitive ven-tilators cannot maintain either constant peakpressure or tidal volume and thus controlonly inspiratory and expiratory times (ie,they may be called time controllers).

CSVContinuous spontaneous ventilation. A

breath sequence in which all breaths arespontaneous.

Cycle VariableThe variable (usually pressure, volume,

flow, or time) that is used to end inspiration(and begin expiratory flow).

Cycle (Cycling)To end the inspiratory time (and begin

expiratory flow)Dual Targeting SchemeA control system that allows the venti-

lator to switch between volume control andpressure control during a single inspiration.Dual targeting is a more advanced versionof set-point targeting. It gives the ventilatorthe decision of whether the breath will be

Table 1. Simplified Taxonomy for Classifying Modes for Noninvasive Ventilation

OrderControlVariable

FamilyBreath Sequence

GenusPrimary Breath

Targeting Scheme

SpeciesSecondary BreathTargeting Scheme

Example Mode Names Tag

Volume CMV Set-point NA Volume Controlled Ventilation VC-CMVsSet-point NA Volume Assist/Controlled Ventilation VC-CMVs

Pressure CMV Set-point NA Pressure Control Ventilation PC-CMVsSet-point NA Pressure Assist/Control Ventilation PC-CMVsAdaptive NA Pressure Assist/Control Ventilation with Volume Targeting PC-CMVa

IMV Set-point Set-point Spontaneous/Timed PC-IMVs,sAdaptive Adaptive Intelligent Volume Assured Pressure Support PC-IMVa,aAdaptive Adaptive Average Volume Assured Pressure Support PC-IMVa,a

CSV Set-point NA Pressure Support PC-CSVsServo NA Proportional Pressure Ventilation PC-CSVr

CMV � continuous mandatory ventilationNA � not applicableVC � volume controls � set-pointPC � pressure controla � adaptiveIMV � intermittent mandatory ventilationCSV � continuous spontaneous ventilation.r � servo



volume or pressure-controlled, according tothe operator set priorities. The breath maystart out in pressure control and automati-cally switch to volume control, as in theBird “VAPS” mode or, the reverse, as in theDrager “Pmax” mode. The Maquet Servo-iventilator has a mode called “Volume Con-trol” and the operator presets both inspira-tory time and tidal volume, as would beexpected with any conventional volume con-trol mode. However, if the patient makes aninspiratory effort that decreases inspiratorypressure by 3 cm H2O, the ventilatorswitches to pressure control, and, if the ef-

fort lasts longenough, flowcycles thebreath.Indeed, if the tidal volume and inspiratorytime are set relatively low and the inspira-tory effort is relatively large, the resultantbreath delivery is indistinguishable fromPressure Support. As a result, the tidal vol-ume may be much larger than the expected,preset value. This highlights the need to un-derstand dual targeting. Because both pres-sure and volume may be the control vari-ables during dual targeting, by conventionwe designate the control variable as the onewith which the breath initiates. This is be-cause the other control variable may never

be implemented during the breath, depend-ing on the other factors in the targetingscheme.

Dynamic ComplianceThe slope of the pressure-volume curve

drawn between two points of zero flow (eg,at the start and end of inspiration).

Dynamic HyperinflationThe increase in lung volume that occurs

whenever insufficient exhalation time pre-vents the respiratory system from returningto its normal resting end-expiratory equilib-rium volume between breath cycles. Inap-propriate operator set expiratory time may

Table 2. Simplified Taxonomy for Classifying Modes for Intensive Care

OrderControlVariable

FamilyBreath Sequence

GenusPrimary Breath

Targeting Scheme

SpeciesSecondary BreathTargeting Scheme

Example Mode Names Tag

Volume CMV Set-point NA Assist/Control Volume Control VC-CMVsDual NA Continuous Mandatory Ventilation with

Pressure LimitedVC-CMVd

IMV Set-point Set-point Volume Control SynchronizedIntermittent Mandatory Ventilation

VC-IMVs,s

Dual Dual Volume Control* VC-IMVd,dDual/Adaptive Set-point Mandatory Minute Volume with

Pressure Limited VentilationVC-IMVda,s

Dual Adaptive Automode (Volume Control to VolumeSupport)

VC-IMVd,a

Adaptive Set-point Mandatory Minute Volume Ventilation VC-IMVa,sPressure CMV Set-point NA Pressure Control Assist Control PC-CMVs

Adaptive NA Pressure Regulated Volume Control PC-CMVaIMV Set-point Set-point Airway Pressure Release Ventilation PC-IMVs,s

Adaptive Set-point Adaptive Pressure VentilationSynchronized Intermittent MandatoryVentilation

PC-IMVa,s

Adaptive Adaptive Automode (Pressure Regulated VolumeControl to Volume Support)

PC-IMVa,a

Optimal Optimal Adaptive Support Ventilation PC-IMVo,oOptimal/Intelligent Optimal/Intelligent IntelliVent-ASV PC-IMVoi,oi

CSV Set-point NA Pressure Support PC-CSVsServo NA Proportional Assist Ventilation PC-CSVrServo NA Neurally Adjusted Ventilatory Support PC-CSVrAdaptive NA Volume Support PC-CSVaAdaptive NA Mandatory Rate Ventilation PC-CSVaIntelligent NA SmartCare/PS PC-CSVi

* Servo-i ventilator.CMV � continuous mandatory ventilationNA � not applicableVC � volume controls � set-pointd � dualIMV � intermittent mandatory ventilationa � adaptivePC � pressure controlo � optimalCSV � continuous spontaneous ventilation.r � servoi � intelligent



lead to dynamic hyperinflation, inability ofthe patient to trigger breaths, and an in-creased work of breathing.

ElastanceA mechanical property of a structure such

as the respiratory system; a parameter of alung model, or setting of a lung simulator;defined as the ratio of the change in thepressure difference across the system to theassociated change in volume. Elastance isthe reciprocal of compliance.

Equation of Motion for the Respira-tory System

A relation among pressure difference,volume, and flow (as variable functions oftime) that describes the mechanics of therespiratory system. The simplest and mostuseful form is a differential equation withconstant coefficients describing the respira-tory system as a single deformable com-partment including the lungs and chest wall:

�PTR(t) � �Pmus(t) � EV(t) � RV(t) �autoPEEP

where�PTR(t) � the change in transrespiratory

pressure difference (ie, airway opening pres-sure minus body surface pressure) as a func-tion of time (t), measured relative to end-expiratory airway pressure. This is thepressure generated by a ventilator (�Pvent)during an assisted breath.

�Pmus(t) � ventilatory muscle pressuredifference as a function of time (t); the the-oretical chest wall transmural pressure dif-ference that would produce movementsidentical to those produced by the ventila-tory muscles during breathing maneuvers(positive during inspiratory effort, negativeduring expiratory effort)

E � elastance (inverse of compliance;E � 1/C)

V(t) � volume change relative to end-expiratory volume as a function of time (t)

V(t) � flow as a function of time (t), thefirst derivative of volume with respect totime

autoPEEP � end-expiratory alveolarpressure above end-expiratory airway pres-sure

For the purposes of classifying modes ofmechanical ventilation the equation is oftensimplified to:

Pvent � EV � RVwherePvent � the transrespiratory pressure dif-

ference (ie, “airway pressure”) generated bythe ventilator during an assisted breath

Feedback ControlClosed loop control accomplished by us-

ing the output as a signal that is fed back(compared) to the operator-set input. Thedifference between the two is used to drivethe system toward the desired output (ie,negative feedback control). For example,pressure-controlled modes use airway pres-sure as the feedback signal to manipulategas flow from the ventilator to maintain aninspiratory pressure set-point.

Flow ControlMaintenance of an invariant inspiratory

flow waveform despite changing respiratorysystem mechanics

Flow TriggeringThe starting of inspiratory flow due to a

patient inspiratory effort that generates in-spiratory flow above a preset threshold (ie,the trigger sensitivity setting)

Flow TargetInspiratory flow reaches a preset value

that may be maintained before inspirationcycles off.

Flow CyclingThe ending of inspiratory time due to

inspiratory flow decay below a preset thresh-old (also known as the cycle sensitivity).

Intermittent Mandatory VentilationBreath sequence in which spontaneous

breaths are permitted between mandatorybreaths. For most ventilators, a short “win-dow” is opened before the scheduled ma-chine triggering of mandatory breaths, toallow synchronization with any detected in-spiratory effort on the part of the patient.This is referred to as synchronized IMV (orSIMV). Three common variations of IMVare: mandatory breaths are always deliveredat the set frequency; mandatory breaths aredelivered only when the spontaneous breathfrequency falls below the set frequency;mandatory breaths are delivered only whenthe spontaneous minute ventilation (ie, prod-uct of spontaneous breath frequency andspontaneous breath tidal volume) drops be-low a preset or computed threshold (alsoknown as Mandatory Minute Ventilation).

For some modes (eg, Airway PressureRelease Ventilation), a short window is alsoopened at the end of the inspiratory time.Because spontaneous breaths are allowedduring the mandatory pressure controlledbreath, this window synchronizes the end ofthe mandatory inspiratory time with the startof spontaneous expiratory flow, if detected.With these technological developments, po-tential confusion arises as to whether inspi-ration that is synchronized (either start or

stop) is considered patient triggered/cycledor machine triggered/cycled. If we say syn-chronized breaths are patient triggered andcycled, we have the awkward possibility ofa spontaneous breath occurring during an-other spontaneous breath. This is avoidedby distinguishing between a trigger windowand a synchronization window.

There are some modes where the idea ofIMV may be vague: with Airway PressureRelease Ventilation, relatively high fre-quency spontaneous breaths are superim-posed on low frequency mandatory breaths.However, the expiratory time between man-datory breaths is often set so short that aspontaneous breath is unlikely to occur be-tween them. Other ambiguous modes areHigh Frequency Oscillation, High Fre-quency Jet Ventilation, Interpulmonary Per-cussive Ventilation, and Volumetric Diffu-sive Respiration. With these modes, highfrequency mandatory breaths are superim-posed on low frequency spontaneous breathsand, again, there is no possibility of a spon-taneous breath actually occurring betweenmandatory breaths. Nevertheless, we clas-sify all these modes as forms of IMV be-cause spontaneous breaths can occur alongwith mandatory breaths and because spon-taneous efforts do not affect the mandatorybreath frequency. See machine triggering,patient triggering, synchronization win-dow, and trigger window.

Inspiratory PressureGeneral term for the pressure at the pa-

tient connection during the inspiratoryphase. For pressure control modes, wherethe inspiratory pressure is targeted to a pre-set value, the term is used to designate thissetting. If inspiratory pressure is set relativeto atmospheric pressure, the term “peak in-spiratory pressure” is used. If inspiratorypressure is set relative to PEEP, the term“inspiratory pressure” is used.

Intelligent ControlA ventilator control system that uses ar-

tificial intelligence programs such as fuzzylogic, rule based expert systems, and artifi-cial neural networks. One example is therule based system used by SmartCare(Drager Evita XL ventilator).

Machine CyclingEnding inspiratory time independent of

signals representing the patient determinedcomponents of the equation of motion (ie,Pmus [effort], elastance, or resistance).Common examples of machine cyclingvariables are preset inspiratory time andtidal volume.



Machine TriggeringStarting inspiratory flow based on a sig-

nal (usually time) from the machine, inde-pendent of a signal indicating patient in-spiratory effort. Examples include triggeringbased on a preset frequency (which sets theventilatory period), or based on a preset min-imum minute ventilation (determined bytidal volume divided by the ventilatory pe-riod). If a signal from the patient (indicatingthe need for inspiration) occurs within a syn-chronization window, the start of inspira-tion is defined as a machine trigger eventthat begins a mandatory breath. See inter-mittent mandatory ventilation, patienttriggering, synchronization window, andtrigger window.

Mandatory BreathA breath in which the patient has lost

substantial control over timing. This meansa breath in which the start or end of inspi-ration (or both) is determined by the venti-lator, independent of the patient. That is, themachine triggers and/or cycles the breath.

Mechanical VentilatorAn automatic machine designed to pro-

vide all or part of the work required to gen-erate enough breaths to satisfy the body’srespiratory needs.

Mode of VentilationA predetermined pattern of interaction

between a patient and a ventilator, specifiedas a particular combination of control vari-able, breath sequence, and targeting schemesfor primary and secondary breaths.

Optimum Targeting SchemeA ventilator control system that automat-

ically adjusts the targets of the ventilatorypattern to either minimize or maximize someoverall performance characteristic. One ex-ample is Adaptive Support Ventilation(Hamilton Medical G5 ventilator), in whichthe ventilator adjusts the mandatory tidalvolume and frequency (for a passive pa-tient) in such a way as to minimize the workrate of ventilation.

Patient CyclingEnding inspiratory time based on signals

related to one of the patient determined com-ponents of the equation of motion (ie, Pmus

[effort], elastance, or resistance). Commonexamples of cycling variables are peak in-spiratory pressure and percent inspiratoryflow.

Patient TriggeringStarting inspiratory flow based on sig-

nals representing the patient determinedcomponents of the equation of motion (ie,Pmus [effort], elastance, or resistance). Com-

mon examples of patient trigger variablesare airway pressure drop below baseline andinspiratory flow due to patient effort.

PC-CMVPressure-controlled continuous manda-

tory ventilationPC-IMVPressure-controlled intermittent manda-

tory ventilationPC-CSVPressure-controlledcontinuous spontane-

ous ventilationPressure ControlA general category of ventilator modes

in which pressure delivery is predeter-mined by a targeting scheme such thatinspiratory pressure is either proportionalto patient effort or has a particular wave-form, regardless of respiratory system me-chanics.

Pressure CyclingInspiratory time ends when airway pres-

sure reaches a preset threshold.Pressure TriggeringThe starting of inspiratory flow due to a

patient inspiratory effort that generates anairway pressure drop below end-expiratorypressure larger than a preset threshold (ie,the trigger sensitivity setting).

Pressure TargetInspiratory pressure reaches a preset

value before inspiration cycles off.Primary BreathsMandatory breaths during CMV or IMV,

or spontaneous breaths during CSV.Secondary BreathsSpontaneous breaths during IMV.Servo TargetingA control system in which the output of

the ventilator automatically follows a vary-ing input. For example, the Automatic TubeCompensation feature on the Drager Evita 4ventilator tracks flow and forces pressure tobe equal to flow multiplied by a constant(representing endotracheal tube resistance).Other examples include Proportional AssistVentilation (Covidien Puritan Bennett 840ventilator; pressure is proportional to spon-taneous volume and flow) and Neurally Ad-justed Ventilatory Assist (Maquet Servo-iventilator; pressure is proportional to dia-phragmatic electrical activity). For all 3 ofthese example modes, airway pressure iseffectively proportional to the patient’s in-spiratory effort.

Set-Point TargetingA control system in which the operator

sets all the parameters of the pressure wave-form (pressure control modes) or volume

and flow waveforms (volume controlmodes).

Spontaneous BreathA breath in which the patient retains sub-

stantial control over timing. This means thestart and end of inspiration may be deter-mined by the patient, independent of anymachine settings for inspiratory time andexpiratory time. That is, the patient bothtriggers and cycles the breath. Note that useof this definition for determining the breathsequence (ie, CMV, IMV, CSV) assumesnormal ventilator operation. For example,coughing during VC-CMV may result inpatient cycling for a patient-triggered breath,due to the pressure alarm limit. While inspi-ration for that breath is both patient-triggeredand patient-cycled, this is not normal oper-ation and the sequence does not turn intoIMV.

Synchronized IMV (SIMV)A form of IMV in which mandatory

breath delivery is coordinated with patienteffort. A synchronized breath is consideredto be machine triggered.

Synchronization WindowA short period at the end of the expira-

tory time (eg, based on a preset mandatorybreath frequency and inspiratory time) or atthe end of a preset inspiratory time, duringwhich a patient signal may be used to syn-chronize flow to patient effort. If a signalfrom the patient (indicating the need for in-spiration) occurs during the expiratory timewithin the window, inspiration starts and isdefined as a machine triggered event thatbegins a mandatory breath. This is becausethe mandatory breath would have been timetriggered regardless of whether the patientsignal had appeared or not, and because thedistinction is necessary to avoid logical in-consistencies in defining mandatory andspontaneous breaths, which are the founda-tion of a mode taxonomy. Sometimes a syn-chronization window is used at the end of apressure controlled, time cycled breath. Forexample, during Airway Pressure ReleaseVentilation the patient is free to take spon-taneous breaths during a mandatory breath.If a signal from the patient (eg, the start ofexpiratory flow for a spontaneous breath)occurs during the inspiratory time withinthe window, inspiration stops and is definedas a machine cycled event that ends a man-datory breath. See intermittent mandatoryventilation, machine triggering, patienttriggering, trigger window.



TargetA predetermined goal of ventilator out-

put. Targets can be viewed as the parame-ters of the targeting scheme. Within-breathtargets are the parameters of the pressure,volume, or flow waveform. Examples ofwithin-breath targets include inspiratoryflow or pressure rise time (set-point target-ing), inspiratory pressure, tidal volume (dualtargeting), and the constant of proportion-ality between inspiratory pressure and pa-tienteffort (servo targeting).Between-breathtargets serve to modify the within-breathtargets and/or the overall ventilatory pat-tern. Between-breath targets are used withmore advanced targeting schemes, wheretargets act over multiple breaths. A simpleexample of a between-breath target is tocompare actual exhaled volume to a presetbetween-breath tidal volume in order to au-tomatically adjust the within-breath inspira-tory pressure or flow target for the nextbreath. Examples of between-breath targetsand targeting schemes include average tidalvolume (for adaptive targeting), percentminute ventilation (for optimal targeting),and combined PCO2, volume, and frequencyvalues describing a “zone of comfort” (forintelligent targeting).

Targeting SchemeA model of the relationship between op-

erator inputs and ventilator outputs toachieve a specific ventilatory pattern, usu-ally in the form of a feedback control sys-tem. The targeting scheme is a key compo-nent of a mode description.

Time CyclingInspiratory time ends after a preset time

interval has elapsed. The most common ex-amples are a preset inspiratory time or apreset inspiratory pause time.

Time TriggeringThe starting of inspiratory flow due to a

preset time interval. The most common ex-ample is a preset ventilatory frequency.

Trigger WindowThe period composed of the expiratory

time (minus a short “refractory” period re-quired toreduce theriskof triggeringabreathbefore exhalation is complete). If a signalfrom the patient (indicating the need for in-spiration) occurs within this trigger window,inspiration starts and is defined as a patienttriggered event. See intermittent manda-tory ventilation, machine triggering, pa-

tient triggering, and synchronization win-dow.

Trigger (Triggering)To start inspiration. See machine trig-

gering, patient triggering.Ventilatory PatternA sequence of breaths (CMV, IMV, or

CSV) with a designated control variable(volume, pressure, or dual control) for themandatory breaths (or the spontaneousbreaths for CSV)

Volume ControlA general category of ventilator modes

in which both inspiratory flow and vol-ume delivery are predetermined by a tar-geting scheme to have particular wave-forms independent of respiratory systemmechanics. Usually, flow and tidal vol-ume may be set directly by the operator.Alternatively, the ventilator may deter-mine tidal volume based on operator pre-set values for frequency and minute ven-tilation, or the ventilator may determineinspiratory flow based on operator set tidalvolume and inspiratory time. Note thatthe tidal volume setting refers to the with-in-breath tidal volume, not a between-breath target as used in adaptive pres-sure targeting (see adaptive targetingscheme).

VC-CMVVolume-controlled continuous manda-

tory ventilationVC-IMVVolume-controlled intermittent manda-

tory ventilationVolume TriggeringThe starting of inspiratory flow due to a

patient inspiratory effort that generates an in-spiratory volume signal larger than a presetthreshold (ie, the trigger sensitivity setting)

Volume TargetA preset value for tidal volume that the

ventilator is set toattaineitherwithinabreathor as an average over multiple breaths.

Volume CyclingInspiratory time ends when inspiratory

volume reaches a preset threshold (ie, tidalvolume).

REFERENCES

1. Chatburn RL, Volsko TA, Hazy J, HarrisLN, Sanders S. Determining the basis for ataxonomy of mechanical ventilation. Re-spir Care 2012;57:514-24.

2. Hedden, H. The accidental taxonomist.Medford, NJ: Information Today, 2010.

3. Cowan N. The magical number 4 in short-term memory: a reconsideration of mentalstorage capacity. Behav Brain Sci 2001;24(1):87-114, discussion 114-185.

4. Bailey KD. Typologies and taxonomies: anintroduction to classification techniques.Thousand Oaks, London: Sage Publica-tions; 1994.

5. Chatburn RL. Classification of mechanicalventilators and modes of ventilation. In: To-bin MJ, ed. Principles and practice of me-chanical ventilation, 3rd edition. New York:McGraw-Hill; 2012.

6. Mireles-Cabodevila E, Hatipoglu U, Chat-burn RL. A rational framework for select-ing modes of ventilation. Respir Care 2012.Epub ahead of print.

7. Chatburn RL, Mireles-Cabodevila E.Closed-loop control of mechanical ventila-tion: description and classification of tar-geting schemes. Respir Care 2011;56(1):85-102.

8. Guskey TR. Closing achievement gaps: re-visiting Benjamin S Bloom’s “learning formastery.” J Advanced Academics 2007;19(1):8-31.

9. McGaghie WC, Issenberg B, Cohen ER,Barsuk JH, Wayne DB. Medical educationfeaturing mastery learning with deliberatepractice can lead to better health for indi-viduals and populations. Academic Med2011;86(11):e8–e9.

10. Volsko TA, Hoffman J, Conger A, Chat-burn RL. The effect of targeting scheme ontidal volume delivery during volume con-trol mechanical ventilation. Respir Care2012;57(8):1297-1304.

11. Amato MB, Barbas CS, Bonassa J, SaldivaPH, Zin WA, de Carvalho CR. Volume-assured pressure support ventilation(VAPSV): a new approach for reducingmuscle workload during acute respiratoryfailure. Chest 1992;102(4):1225-1234.

Robert L Chatburn MHHS RRT-NPSFAARC

Respiratory InstituteThe Cleveland Clinic

Cleveland, Ohio

Mr Chatburn has disclosed relationships withthe Alpha-1 Antitrypsin Foundation, BreatheTechnologies, CareFusion, Covidien, Drager,Hamilton, IngMar, Newport, Philips, Radiom-eter America, ResMed, Respironics, StrategicDynamics, and Teleflex.

DOI: 10.4187/respcare.02122



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