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Ventilatory Modes. What’s technologies led to the more than 30 models • What is the ventilatory mode (pressure or in a Name? presently available, offering numerous op- volume)? tions for settings.2 • How is the inspiration triggered (assisted, We have read with great interest the pa- Moreover, there are no marketing regu- assisted/controlled, or controlled)? per published by Chatburn et al in RESPIRA- lations for ventilators. This leaves manufac- TORY CARE.1 reporting on how familiar turers free to give different names to iden- • How is switching from inspiration to ex- healthcare leaders coming from different tical or very similar ventilators modes and piration (cycling) managed (flow or timed professions are with some general technical settings and even “create” new modes that cycling)? and physiological aspects related to mechan- correspond frequently only to minor modi- These 3 categories may facilitate a stan- ical ventilation. Even if the survey shows a fications of a previously known mode. This dardizing of NIV taxonomy and clarify this reasonable level of knowledge and agree- explains why the wide variety of existing confusion. Based on these principles, Cho- ment between both individuals and profes- terminology describing NIV modes is some- pin et al proposed a “physiological” but sions regarding most of the questions sub- what confusing; it also explains the lack of a mitted, it must be underlined that the target somewhat complex categorization of venti- common nomenclature. Clinicians can to- latory modes applied to ICU ventilators.9 population consisted mainly of profession- day be confronted with a given acronym that als who had prior skills in the field of me- Our group proposes a more pragmatic and corresponds to different modes in different ergonomic approach of this classification, chanical ventilation. More than 50% of re- devices, and conversely to identical modes sponders were respiratory therapists, who applicable to fewer and more simple modes that are called differently in different venti- commonly used to provide NIV by using often have a substantial level of expertise lators. Bi-level ventilators, for example, were regarding these issues. Moreover, it is not portable devices (Table 1). initially referred to as BiPAPs (a commer- Even if there is probably no perfect no- sure that the same rate of agreement would cial name of the first machine of this type on have been found, even in this specific skilled menclature, such an attempt at standardiza- the market), but use of this term has caused population, if more detailed questions (ie, tion could provide the basis for a large con- conflict as the manufacturer claimed for as to nomenclature and technical details of sensus aiming to achieve a more copyright. Other terms and acronyms were ventilator modes proposed by modern ven- comprehensive approach to NIV. This may used such as pressure support ventilation tilators) had been raised.2 In fact, as men- encourage manufacturers to privilege sim- (PSV), IPAP, and EPAP, S/T devices, bi- tioned by the authors, while mechanical ven- plicity in their nomenclature instead of orig- level pressure assist, CPAP ϩ inspiratory tilation has hugely evolved these last inality and confusion. The goal? To make support, and PV with PEEP. This can be a decades, what lags behind is a standard clas- NIV management easier in clinical practice. problem in clinical practice, when a nonspe- sification or taxonomy able to describe this cialized physician is confronted with this in- Claudio Rabec MD increasing complexity. comprehensible plethora of names and de- Service de Pneumologie et This issue is still more worrying regard- Re´animation Respiratoire vices. ing noninvasive ventilation (NIV). Due to Centre Hospitalier et Universitaire In this context, proposing a standardized growing evidence of NIV’s effectiveness in de Dijon classification for a better understanding of a broad range of indications and increasing Dijon, France availability of user-friendly portable de- ventilation and ventilators seems rather log- vices, the number of patients receiving NIV ical. But, even if it were possible, this issue Bruno Langevin MD at home is continuously increasing, For ex- involves a high level of complexity regard- Service de Re´animation Me´dicale ample, NIV is increasingly applied in dif- ing critical care ventilators, because of the Centre Hospitalier Ale`s ferent settings, such as critical care units, overabundance and complexity of new Ale`s, France pulmonary, cardiology3 or neurological4 de- (supposed) “intelligent modes” that include Daniel Rodenstein MD PhD partments, pediatrics facilities, weaning cen- complex closed loops and several different Service de Pneumologie ters, sleep labs, in the emergency room,5,6 targeting algorithms. Furthermore, the clas- Cliniques Universitaires Saint Luc in pre-hospital care,7 and in general wards.8 sification and terminology applied to inten- Universite´ Catholique de Louvain As a “victim of its own success” NIV has sive care respirators does not necessarily ap- Bruxelles, Belgium become a generalized practice, and it is not ply to the smaller yet very versatile Christophe Perrin MD unusual that it may be carried out by non- respirators intended for home use: for these Service de Pneumologie specialized healthcare professionals. When devices it seems easier to provide a stan- Centre Hospitalier Cannes NIV was introduced, there were a very lim- dardized classification Cannes, France ited number of modes and types of ventila- As ventilators can be categorized by how tors, with very few possible settings. But as they deliver gas flow and how they trigger Patrick Leger MD NIV devices were submitted to the same inspiration and expiration, answers to 3 ba- Service de Pneumologie market evolution as conventional mechani- sic questions may serve as a guide to sim- Centre Hospitalier Universitaire Lyon Sud cal ventilation, developments in design and plify terminology: Lyon, France

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Table 1. “Physiological” Proposed Classification of Noninvasive Ventilation Current Modes erbations of chronic obstructive pulmonary disease on general respiratory wards: a mul- Usual Appellations* “Physiological” Nomenclature ticentre randomised controlled trial. Lancet 2000;355(9219):1931-1935. Volume-controlled ventilation (VCV) V-C-T 9. Chopin C, Chambrin M. An attempt to clas- Volume assisted/controlled ventilation V-A/C-T sify the current positive airway pressure Pressure-controlled ventilation, PCV, T mode P-C-T modes of mechanical ventilation. Re´anima- (in bi-level devices) tion Urgences 1998;7:87-99. Article in Pressure assisted ventilation (PSV, pressure support P-A-V French. ventilation (PSV), spontaneous (S) mode (in bi-level devices) ϩ Pressure assisted ventilation positive end expiratory P-A-V (EPAP) The authors respond: pressure (PEEP) PSV ϩ PEEP, pressure support ϩ PEEP, CPAP ϩ inspiratory support, S mode Rabec et al have supported the concerns (in bi-level devices) mentioned in our paper,1 noting that, “while Pressure assisted /controlled ventilation (PAC) P-A/C-T mechanical ventilation has hugely evolved Pressure assisted/controlled ventilation (PAC) ϩ PEEP P-A/C-T (EPAP) these last decades, what lags behind is a Spontaneous/timed mode (ST), IPAP/EPAP P-A-V˙ (EPAP/f) standard classification or taxonomy able to (in bi-level devices), describe this increasing complexity.” In ad- PACV with volume targeting P-A/C-T (VT) dition, they have pointed out the further con- ˙ ST mode with volume targeting, AVAPS, IVAPS, P-A-V(EPAP/f/ VT) cern that confusion about modes may be an volume assured, PS ϩ PEEP ϩ V T even greater problem regarding home care

* Usual appellations correspond to the names devised by the manufacturers for each modality. In the proposed “physiological” ventilation, and particularly noninvasive nomenclature the first character indicates ventilatory modality (P or V), the second how the inspiration is triggered (A ϭ assisted, ventilation “when a non-specialized physi- A/C ϭ assisted/controlled, C ϭ controlled), and third the mode of switching from inspiration to expiration (V˙ ϭ flow, T ϭ timed cian is confronted with this incomprehensi- cycling). IPAP ϭ inspiratory positive airway pressure ble plethora of names and devices.” Indeed, EPAP ϭ expiratory positive airway pressure they reference a paper that lists no less than AVAPS ϭ average volume assured pressure support 24 unique mode names on 11 different home IVAPS ϭ intelligent volume assured pressure support VT ϭ tidal volume care ventilators. Having studied and written about this subject for over 20 years, and having served as a consultant to committees from the Inter- Jean-Louis Pepin MD PhD 2. Gonzalez-Bermejo J, Laplanche V, Hus- national Standards Organization and the IHE Pole Reé´ducation et Physiologie et seini FE, Duguet A, Derenne JP, Similowski (Integrating the Healthcare Enterprise, T. Evaluation of the user-friendliness of 11 Laboratoire Hoˆpitaux Publique www.ihe.net), I have come to appreciate the Institut National de la Santeétdela home mechanical ventilators. Eur Respir J 2006;27(6):1236-1243. complexity of addressing this problem. The Recherche Me´dicale 3. Vital FM, Saconato H, Ladeira MT, Sen A, solution requires a level of treatment well Universite´ Joseph Fourier Hawkes CA, Soares B, et al. Non-invasive above simply creating an intuitively pleas- Grenoble, France positive pressure ventilation (CPAP or bi- ing nomenclature, such as the “physiologi- level NPPV) for cardiogenic pulmonary cal nomenclature” suggested by Rabec et al. Jean Paul Janssens MD PhD edema. Cochrane Database Syst Rev 2008; The solution is to create a formal taxon- Service de Pneumologie (3):CD005351. omy. Hoˆpitaux Universitaires de Gene`ve 4. Atkeson AD, RoyChoudhury A, Har- Taxonomy is the science of classifica- Geneva, Switzerland rington-Moroney G, Shah B, Mitsumoto H, tion. The most common taxonomies have Basner RC. Patient-ventilator asynchrony historically been those applied to plants and Je´sus Gonzalez-Bermejo MD with nocturnal noninvasive ventilation in Service de Pneumologie et ALS. Neurology 2011;77(6):549-555. animals, in the form of class, family, genus, Reánimation Respiratoire 5. Cabrini L, Antonelli M, Savoia G, Lan- and species. However, the rapid growth of Hoˆpital de la Pitie´-Salpeˆtrie`re driscina M. Non-invasive ventilation out- the World Wide Web, and more specifi- Paris, France side of the intensive care unit: an Italian cally, the Semantic Web, has created an in- survey. Minerva Anestesiol 2011;77(3): tense need for organized search strategies On behalf of the SomnoNIV Group 313-22. that are based on taxonomies. One well 6. Davey M. Theme: non-invasive positive known example is the Taxonomy of Edu- The authors have disclosed no conflicts of in- pressure ventilation (NiPPV) in the ED. cational Objectives, also known as Bloom’s terest. Emerg Med J 2010;27(12):903, 966. Taxonomy. A taxonomy is typically a hier- 7. Taylor DM, Bernard SA, Masci K, archical classification or categorization sys- REFERENCES MacBean CE, Kennedy MP, Zalstein S. Pre- hospital noninvasive ventilation: a viable tem. Anyone who has ever been to the Web 1. Chatburn RL, Volsko TA, Hazy J, Harris treatment option in the urban setting. Pre- site www.Amazon.com has used a taxon- LN, Sanders S. Determining the basis for a hosp Emerg Care 2008;12(1):42-55. omy. The menu along the left hand side of taxonomy of mechanical ventilation. Re- 8. Plant PK, Owen JL, Elliott MW. Early use Amazon’s Web page is an expandable out- spir Care 2012;57(4):514-524. of non-invasive ventilation for acute exac- line. For example, if you select “books” from

RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12 2139 LETTERS TO THE EDITOR the list of products sold, you will get an- - BS 8723-2 (2005): Structured Vocabu- According to Hedden,2 “A taxonomy is other list lower down on the hierarchy, in- laries for Information Retrieval: The- never finished. As soon as it is implemented, cluding different types of books (eg, audio sauri it undergoes testing and revision, and con- books, business and investing, children’s tinued use will dictate further enhancements. books, cookbooks, et cetera). Clicking any These standards describe 3 types of re- All taxonomies require ongoing mainte- of these selections brings you to an even lationships in a thesaurus: hierarchical nance, and many taxonomies also undergo deeper level of the taxonomy. Another (broader term/narrower term), associative more significant revisions or restructuring very good example of a visual display of (related term), and equivalence (use/used over time.” a taxonomy can be seen at http://www. for). For simplicity, I will include the the- Taxonomies serve one of 3 practical func- accessinn.com:8081/PerfectSearch/ saurus in the term “taxonomy.” tions, particularly important in this age of navtree/index.html. At this Web site the ex- Taxonomies are not generally created by the electronic medical record: indexing sup- plicit collapsible levels of the taxonomy’s committee. Rather, a trained taxonomist port; retrieval support; and navigation sup- hierarchy are clearly visible. This latter ex- constructs them from several key compo- port. Thus, the taxonomy’s initial purpose ample is more appropriately called a the- nents after becoming sufficiently familiar is to serve the people doing the indexing, saurus. Most of us are familiar with a the- with the content of the subject domain (usu- although a second, equally important pur- ally with input from end users). In my case, saurus as a kind of dictionary, such as pose is to serve the end users.2 In the con- I started as a domain expert who had to Roget’s Thesaurus, which contains syn- text of mechanical ventilation, the “index- learn about taxonomy: what has been called onyms for each entry. A dictionary-type the- ers” are primarily the engineers and an “accidental taxonomist.“2 Either way, the saurus includes all the associated terms that marketing people working for ventilator first component to create is a “controlled could be used in place of the term entry in manufacturing companies, who must write vocabulary,” which is a glossary of pre- various contexts. In contrast, a thesaurus the ventilator operators’ manuals. Although defined terms. Choosing appropriate terms used for information retrieval is designed manufacturers are responsible for creating is difficult, because there are usually many for use in all contexts within the domain of the chaos related to modes, they are also in ways to define key concepts. Priority must content covered, regardless of any specific the best position to fix the problem. There is term usage or document. A thesaurus of this be given to specificity and logical consis- no need for manufacturers to stop creating type, therefore, is a more structured type of tency throughout the domain of application. new names for modes, but they must all controlled vocabulary that provides infor- The second component, created using the agree on a standard description of the mode mation about each term and its relationships vocabulary, is the hierarchical structure of (ie, how it is classified relative to other to other terms within the same thesaurus.2 the taxonomy. There are many logical sys- modes), and they must use the same vocab- National and international standards that tems that may work, so priority must be ulary to explain how it performs. Without provide guidance for creating such thesauri given to the one that is most useful and this, both patient care and device sales will include: most easily implemented among all groups of stakeholders. The number of levels in the continue to be at risk. Until manufacturers • International Organization for Standard- hierarchy is important; too few and you lose have reached such a level of consensus, how- ization (www.iso.org/iso/iso_catalogue. the ability to discriminate among items; too ever, the responsibility for indexing modes htm) many and you lose the advantage of group- of ventilation must fall to the members of - ISO 2788 (1986): Guidelines for the Es- ing. Creating 3 to 5 levels seems to be about the other stake-holder groups (ie, clinicians, tablishment and Development of Mono- right, and this may be related to the human educators, and researchers). lingual Thesauri capacity to store and process only about 4 Recognizing the need for a formal tax- - ISO 5964 (1985): Guidelines for the Es- variables at a time.3 Many taxonomies, cre- onomy of modes of mechanical ventilation tablishment and Development of Mul- ated at great expense, have failed because was the underlying motive of our paper.1 tilingual Thesauri of insufficient planning of vocabularies and What Rabec et al may not have noticed (due - ISO 2788 and 5964 were replaced in hierarchies. The third component is the as- to recent publication) is the book chapter5 2011 by ISO 25964: Thesauri and In- sociative and equivalence relationships re- and paper6 from our group demonstrating teroperability With Other Vocabularies quired to create the finished product. A well how the survey questions of our first paper constructed taxonomy offers these advan- are developed into a classification system. • American National Standards Institute tages4: The first step is to expand the 10 questions (ANSI) and National Information Stan- from the survey into a set of maxims that, dards Organization (NISO) (www.niso. • Description when combined, form the theoretical basis org/kst/reports/standards) of a taxonomy for modes of ventilation5: - ANSI/NISO Z39.19 (2005): Guidelines • Reduction of Complexity 1. A breath is one cycle of positive flow for the Construction, Format, and Man- • Identification of Similarities (inspiration) and negative flow (expiration). agement of Monolingual Controlled The purpose of a ventilator is to assist breath- Vocabularies • Identification of Differences ing. Therefore, the logical start of a taxon- • British Standards Institution (www.bsig- • Comparison of Types omy is to define a breath. Breaths are de- roup.com) • Explanation of Relationships fined such that during mechanical - BS 8723-1 (2005): Structured Vocabu- ventilation, small artificial breaths may be laries for Information Retrieval: Defi- These benefits justify the resources re- superimposed on large natural ones or vice nitions, Symbols, and Abbreviations quired to create and maintain a taxonomy. versa.

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2. A breath is assisted if pressure rises plies all spontaneous breaths, IMV allows focus of their meanings has shifted subtly above baseline during inspiration or falls spontaneous breaths to occur between man- from patient physiology to machine func- during expiration. A ventilator assists datory breaths, and CMV does not. tion. A prime example is the use of the term breathing by doing some portion of the work 8. There are only 5 basic ventilatory pat- “assist/control.” This term focuses on the of breathing. This occurs by delivering vol- terns: VC-CMV, VC-IMV, PC-CMV, PC- patient’s neurological control of breathing ume under pressure. IMV, and PC-CSV. All modes can be cat- and refers to a mode in which the ventilator 3. A ventilator assists breathing using egorized by these 5 patterns. This provides may either “control” the breathing pattern either pressure control (PC) or volume con- enough practical detail about a mode for by triggering inspiration as a substitute for trol (VC). The equation of motion for the most clinical purposes. the patient’s own neurological control, or respiratory system is the fundamental model 9. Within each ventilatory pattern there “assist” the patient’s inspiratory effort after for understanding patient-ventilator interac- are several variations that can be distin- he/she has triggered inspiration. These def- tion and hence modes of ventilation. The guished by their targeting scheme(s). When initions date back to a time when ventilator equation is an expression of the idea that comparing modes or evaluating the capa- capabilities were very primitive by today’s only one variable can be predetermined at a bility of a ventilator, more detail is required standards. time: pressure or volume (flow control is than just the ventilatory pattern. Modes with Ventilators have evolved over at least 5 ignored for simplicity and for historical rea- the same ventilatory pattern can be distin- generations in the span of a single human sons, and because controlling flow directly guished by describing the targeting schemes generation. As a result, many people who will indirectly control volume and vice they use. There are at present only 7 basic have been in the field for a long time (or versa). targeting schemes: set-point, dual, servo, their students) cling to the older, patient- 4. Breaths are classified according to the bio-variable, adaptive, optimal, and intelli- centric view of the word “control” and thus criteria that trigger (start) and cycle (stop) gent, which have been described in detail fail to appreciate the implications and utility inspiration. A ventilator must know when previously.7 of the machine-centric view. Manufacturers to start and stop flow delivery for a given 10. A mode of ventilation is classified feel compelled to perpetuate this inertia be- breath. Because starting and stopping in- according to its control variable, breath se- cause many of these same people make the spiratory flow are critical events in synchro- quence, and targeting scheme(s). A practi- purchasing decisions. The result is that the nizing patient-ventilator interaction, and be- cal taxonomy of ventilatory modes is based term “assist/control” continues to be asso- cause they involve uniquely different on just 4 levels of detail: the control vari- ciated with mode selection on new ventila- operator-influenced factors, they are distin- able (pressure or volume), the breath se- tors, even though the meaning of the term guished by giving them different names. quence (CMV, IMV, or CSV), and the tar- has changed from its historical roots to the 5. Trigger and cycle events can be either geting scheme used for primary breaths point of virtual uselessness. Originally, as- patient or machine initiated. A major de- (CMV and CSV), and, if applicable, sec- sist/control meant volume-controlled con- sign consideration in creating modes is the ondary breaths (IMV). This structure is rem- tinuous mandatory ventilation (CMV). Now ability to synchronize breath delivery with iniscent of the taxonomy of biological or- it can also refer to pressure control (espe- patient demand and at the same time to guar- ganisms, which comprises order, family, cially in the pediatric literature). antee breath delivery if the patient is apneic. genus, and species. Modes in the same “spe- In addition to forming the basis for a Therefore, understanding patient-ventilator cies” can be further differentiated by de- taxonomy, the 10 constructs listed above interaction means understanding the differ- scribing their “species variety” in term of can be used as the basis of a complete teach- ence between machine and patient trigger their phase variables (ie, trigger, and cycle ing system for ventilator technology (ie, how and cycle events. variables plus the within- and between- ventilators work as opposed to how they are 6. Breaths are classified as spontaneous breath targets and control algorithms). The used). Each one can be expanded to perhaps or mandatory, based on both the trigger advantage of such a hierarchical structure is a week’s worth of didactic instruction and and cycle events. A spontaneous breath that a mode can be described in any level of laboratory demonstrations. These constructs arises without apparent external cause. Thus detail that is required. For example, we can have been designed to move progressively it is patient triggered and patient cycled. say that a patient was in volume control from simple to complex ideas while supply- Any machine involvement in triggering or during surgery but changed to pressure con- ing a context for the key definitions in a cycling leads to a mandatory breath. Note trol during recovery, or that he was changed controlled vocabulary. They are uniquely that the definition of a spontaneous breath from PC-CMV to PC-CSV for a spontane- suited to instruction using Bloom’s “learn- is independent of the definition of an as- ous breathing trial, or that Pressure Support ing for mastery” model,8 which has proven sisted breath, and applies to but does not is PC-CSV with set-point targeting, whereas an effective learning theory for medical ed- require the application of a mechanical ven- Volume Support is PC-CSV with adaptive ucation.9 tilator. Consistent with common usage, nat- targeting. To facilitate the implementation of a ural breathing is spontaneous. One thing I want to emphasize is that the taxonomy based on control variables, 7. Ventilators deliver only 3 basic breath legacy meaning of the words “assist” and breath sequences and targeting schemes sequences: continuous mandatory ventila- “control” must be abandoned in the forma- (ie, for “indexing” or “tagging” modes), I tion (CMV), intermittent mandatory venti- tion of a new taxonomy of modes. The mean- have created 4 tools. The first tool is an lation (IMV), and continuous spontaneous ing and importance of these words have abbreviated controlled vocabulary for me- ventilation (CSV). The 2 breath classifica- evolved radically since they were coined by chanical ventilation (which appears at the tions logically lead to 3 possible breath se- anesthesiologists using the first ventilators end of this letter). I have included only quences that a mode can deliver: CSV im- over 60 years ago. The problem is that the those terms necessary to understand and

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Fig. 1. Algorithm for determining the control variable when classifying a mode. SIMV ϭ synchronized intermittent mandatory ventilation. (With permission from Mandu Press.) use the taxonomy, but many more could ing schemes used in the design of a mode of is time cycled, so every breath is mandatory be added for clarity. ventilation. (inspiration is machine triggered and/or ma- Figure 1 shows the second tool: an algo- To demonstrate the use of these tools, chine cycled, see the controlled vocabulary rithm for identifying the control variable. let’s classify 4 modes used for noninvasive and Fig. 2), so the breaths sequence is con- Figure 2 shows the third tool: an algorithm ventilation. The simplest example is the tinuous mandatory ventilation (CMV). Fi- for identifying the breath sequence. Figure 3 mode named Pressure Assist/Control. In- nally, the operator (rather than the ventila- shows the fourth tool, which provides the spiratory pressure is preset, so the control tor) presets the parameters of the pressure information necessary to identify the target- variable is pressure (see Fig. 1). Every breath waveform, so the targeting scheme is set-

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Fig. 2. Algorithm for determining the breath sequence when classifying a mode. SIMV ϭ synchronized intermittent mandatory ventilation. (With permission from Mandu Press.) point (see the controlled vocabulary and Now let’s classify a little more complex trol variable is pressure. All breaths are pa- Fig. 3).7 The mode is thus classified as pres- mode, named Average Volume Assured tient triggered and flow cycled (also known sure control continuous mandatory ventila- Pressure Support. Again, inspiratory pres- as a “Pressure Support” breath). Flow cy- tion with set-point targeting (PC-CMVs). sure for a given breath is preset, so the con- cling is a function of patient effort and re-

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Fig. 3. Rubric for determining the targeting schemes when classifying a mode. See controlled vocabulary for terms. (With permission from Mandu Press.) spiratory system mechanics, and hence is automatically adjusted between breaths by ery breath is spontaneous (ie, patient trig- considered patient cycling. Thus, spontane- the ventilator, to achieve an average tidal gered and cycled), so the breath sequence is ous breaths (patient triggered and patient volume equal to the operator set target, continuous spontaneous ventilation. Finally, cycled inspiration; see the controlled vo- which is an example of adaptive targeting.7 the operator sets a fixed inspiratory pres- cabulary) are possible. However, if the pa- The mode is thus classified as pressure con- sure, so the targeting scheme is set-point.7 tient does not trigger breaths above the pre- trol intermittent mandatory ventilation with Thus the mode is classified as pressure con- set rate, the ventilator will trigger a breath. adaptive targeting for both mandatory and trol continuous spontaneous ventilation with A machine triggered breath is defined as a spontaneous breaths (PC-IMVa,a). set-point targeting (PC-CSVs). mandatory breath. Therefore, spontaneous Having mentioned Pressure Support The fourth example is a mode named breaths may occur between mandatory (simplycalled“Spontaneous”modeonsome Proportional Pressure Ventilation (another breaths, and the breath sequence is classi- ventilators), we should also classify this name for Proportional Assist Ventilation, fied as intermittent mandatory ventilation common mode. Inspiratory pressure is pre- which was originally developed as an inva- (IMV). Finally, the inspiratory pressure is set, so the control variable is pressure. Ev- sive mode). Inspiratory pressure is prede-

2144 RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12 LETTERS TO THE EDITOR termined, but not to a fixed value. Rather, it adaptive targeting scheme.7 Thus, the mode control but switches to volume control if is constrained to be proportional to patient is classified as pressure control continuous the ventilator decides the preset tidal vol- effort, according to the equation of motion mandatory ventilation with adaptive target- ume will not be delivered before inspiration for the respiratory system.7 Hence, the con- ing (PC-CMVa). cycles off. This was originally named Vol- trol variable is pressure. Every inspiration is On the other hand, the taxonomy can un- ume Assured Pressure Support.11 patient triggered and patient cycled (we ig- mask the complexity in an apparently sim- Table 1 shows how to classify several of nore the backup mode that is activated in ple mode. A good example is the mode the many noninvasive modes, and Table 2 the case of apnea), so the breath sequence is named simply “Volume Control” on the Ma- applies the taxonomy to common invasive continuous spontaneous ventilation (CSV). quet Servo-i ventilator. As with Volume As- modes. Finally, the targeting scheme that makes in- sist/Control on other ventilators, the opera- In conclusion, the classification of modes spiratory pressure proportional to inspira- tor presets both inspiratory volume and flow of mechanical ventilation is complex enough tory effort is called servo.7 Thus, the mode (inspiratory flow is set indirectly by tidal to require the full application of the tools is classified as pressure control continuous volume and inspiratory time settings). From for building a formal taxonomy, including spontaneous ventilation with servo target- Figure 1 we see that this indicates volume both a controlled vocabulary and a hierar- ing (PC-CSVr). control, as expected. However, a careful chical structure of key classification terms. This mode taxonomy is equally useful reading of the operator’s manual indicates Both the vocabulary and the hierarchy can for invasive modes. Indeed, the taxonomy that whether a breath is mandatory or spon- be developed from the logical progression for classifying the technical capability of a taneous depends on the level of patient in- of 10 simple constructs that are familiar to ventilator is independent of the ventilator- spiratory effort. This is because the venti- stakeholders, including clinicians, educa- patient interface (ie, artificial airway vs lator uses dual targeting (see the controlled tors, researchers, and manufacturers.1,5 mask). For example, consider the most com- vocabulary and Fig. 3).7 If the patient makes While there may be any number of ways to monly used mode in ICUs: “Volume As- no inspiratory effort, inspiration is machine create such a taxonomy, this one empha- sist/Control.” For this mode, both inspira- triggered (by a preset ventilatory frequency) sizes the key factors that are important for tory volume and flow are preset, so the and time cycled (by a preset inspiratory clinicians to understand in order to optimize control variable is volume (see Fig. 1). Ev- time). Hence, such a breath is classified as the match between the patient’s needs and ery breath is volume cycled, which is a form mandatory. If the patient makes a moderate the ventilator’s technological capabilities.6 of machine cycling (see the controlled vo- inspiratory effort, enough to make inspira- cabulary). Any breath in which inspiration tory pressure fall 3 cm H O, the ventilator 2 Abbreviated Controlled is machine cycled is classified as a manda- switches from volume control to pressure Vocabulary for Mechanical tory breath. Hence, the breath sequence is control and delivers as much flow as the continuous mandatory ventilation (see patient demands. If the inspiratory effort is Ventilation Fig. 2). Finally, the operator sets the param- of short duration relative to the preset in- eters of the volume and flow waveforms, so spiratory time, the ventilator switches back Adaptive Targeting Scheme the targeting scheme is set-point (see Fig. 3). to volume control and the breath is volume A control system that allows the venti- Thus, the mode is classified as pressure con- cycled. The preset tidal volume is still de- lator to automatically set some (or conceiv- trol continuous mandatory ventilation with livered, but with a shorter inspiratory time, ably all) of the targets between breaths in set-point targeting. due to the increased average inspiratory response to varying patient conditions. One If carefully applied, the taxonomy has flow. Because inspiration is again machine common example is adaptive pressure tar- the power to clarify and unmask hidden com- cycled, this type of breath is also manda- geting (eg, Pressure Regulated Volume Con- plexity in a mode that has a cryptic name. tory. But if the patient makes a large enough trol mode on the Maquet Servo-i ventilator) Take, for example, the mode called inspiratory effort that lasts beyond the pre- where a static inspiratory pressure is tar- CMVϩAutoFlow on the Dra¨ger Evita XL set inspiratory time, the ventilator remains geted within a breath (ie, pressure-controlled ventilator. While “CMV” on this ventilator in pressure control and the breath is flow inspiration) but this target is automatically is the same as “Volume Assist/Control” de- (ie, patient) cycled. If the breath was also adjusted by the ventilator between breaths scribed above, adding the “AutoFlow” fea- patient triggered, it is virtually identical to a to achieve an operator set tidal volume tar- ture changes it to a completely different breath in the Pressure Support mode and as get. mode. For CMVϩAutoFlow, the operator such is a spontaneous breath.10 Assisted Breath sets a target tidal volume but not inspiratory From this analysis we see the possibility A breath during which all or part of in- flow. Indeed, inspiratory flow is highly vari- of spontaneous breaths occurring between spiratory (or expiratory) flow is generated able, because the ventilator actually sets the mandatory breaths, and we conclude the by the ventilator, doing work on the patient. inspiratory pressure within a breath. Thus, breath sequence is intermittent mandatory In simple terms, if the airway pressure rises the control variable, according to the equa- ventilation. Finally, as just described, the above end-expiratory pressure during inspi- tion of motion, is pressure (see Fig. 1). Ev- targeting scheme is dual and we classify the ration, the breath is assisted (as in the Pres- ery inspiration is time cycled, so every breath mode as volume control intermittent man- sure Support mode). It is also possible to is mandatory and the breath sequence is con- datory ventilation with dual targeting for assist expiration by dropping airway pres- tinuous mandatory ventilation (CMV). The both primary and secondary breaths (VC- sure below end-expiratory pressure (such as ventilator adjusts the inspiratory pressure be- IMVd,d). In passing, we note that pressure Automatic Tube Compensation on the tween breaths to achieve an average tidal control with dual targeting is also possible, Dra¨ger Evita 4 ventilator). In contrast, spon- volume equal to the preset value, using an whereby inspiration starts out in pressure taneous breaths during CPAP are unassisted

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Table 1. Simplified Taxonomy for Classifying Modes for Noninvasive Ventilation

Order Family Genus Species Control Breath Sequence Primary Breath Secondary Breath Example Mode Names Tag Variable Targeting Scheme Targeting Scheme Volume CMV Set-point NA Volume Controlled Ventilation VC-CMVs Set-point NA Volume Assist/Controlled Ventilation VC-CMVs Pressure CMV Set-point NA Pressure Control Ventilation PC-CMVs Set-point NA Pressure Assist/Control Ventilation PC-CMVs Adaptive NA Pressure Assist/Control Ventilation with Volume Targeting PC-CMVa IMV Set-point Set-point Spontaneous/Timed PC-IMVs,s Adaptive Adaptive Intelligent Volume Assured Pressure Support PC-IMVa,a Adaptive Adaptive Average Volume Assured Pressure Support PC-IMVa,a CSV Set-point NA Pressure Support PC-CSVs Servo NA Proportional Pressure Ventilation PC-CSVr

CMV ϭ continuous mandatory ventilation NA ϭ not applicable VC ϭ volume control s ϭ set-point PC ϭ pressure control a ϭ adaptive IMV ϭ intermittent mandatory ventilation CSV ϭ continuous spontaneous ventilation. r ϭ servo

because the ventilator attempts to maintain Breath Sequence If the peak inspiratory pressure remains con- a constant airway pressure during inspira- A particular pattern of spontaneous and/or stant as the load experienced by the venti- tion. mandatory breaths. The 3 possible breath lator changes, then the control variable is Bio-variable Targeting Scheme sequences are: continuous mandatory ven- pressure. If the peak pressure changes as the A control system that allows the venti- tilation (CMV), intermittent mandatory ven- load changes but tidal volume remains con- lator to automatically set the inspiratory pres- tilation (IMV), and continuous spontaneous stant, then the control variable is volume. sure or tidal volume randomly to mimic the ventilation (CSV). Volume control implies flow control and variability observed during normal breath- CMV vice versa, but it is possible to distinguish ing. Continuous mandatory ventilation (com- the two on the basis of which signal is used Breath monly known as “Assist/Control”). A breath for feedback control. Some primitive ven- A positive change in airway flow (inspi- sequence in which mandatory breaths are tilators cannot maintain either constant peak ration) paired with a negative change in air- delivered at a preset rate and spontaneous pressure or tidal volume and thus control way flow (expiration), associated with ven- breaths are not possible between mandatory only inspiratory and expiratory times (ie, tilation of the lungs. This definition excludes breaths. Patient-triggered mandatory breaths they may be called time controllers). flow changes caused by hiccups or cardio- may occur between machine-triggered CSV genic oscillations. However, it allows the breaths (ie, the actual frequency may be Continuous spontaneous ventilation. A superimposition of, for example, a sponta- higher than the set frequency). In some pres- breath sequence in which all breaths are neous breath on a mandatory breath or vice sure-controlled modes on ventilators with spontaneous. versa. The flows are paired by size, not nec- an active exhalation valve, spontaneous Cycle Variable essarily by timing. For example, in Airway breaths may occur during mandatory The variable (usually pressure, volume, Pressure Release Ventilation there is a large breaths, but the defining characteristic of flow, or time) that is used to end inspiration inspiration (transition from low pressure to CMV is that spontaneous breaths are not (and begin expiratory flow). high pressure), possibly followed by a few permitted between mandatory breaths, be- Cycle (Cycling) small inspirations and expirations, followed cause an inspiratory effort after a manda- To end the inspiratory time (and begin finally by a large expiration (transition from tory breath triggers another mandatory expiratory flow) high pressure to low pressure). These com- breath. Dual Targeting Scheme pose several small spontaneous breaths su- Control Variable A control system that allows the venti- perimposed on one large mandatory breath. The variable (ie, pressure or volume in lator to switch between volume control and In contrast, during High Frequency Oscil- the equation of motion) that the ventilator pressure control during a single inspiration. latory Ventilation, small mandatory breaths uses as a feedback signal to manipulate in- Dual targeting is a more advanced version are superimposed on larger spontaneous spiration. For simple set point control, the of set-point targeting. It gives the ventilator breaths. control variable can be identified as follows: the decision of whether the breath will be

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Table 2. Simplified Taxonomy for Classifying Modes for Intensive Care

Order Family Genus Species Control Breath Sequence Primary Breath Secondary Breath Example Mode Names Tag Variable Targeting Scheme Targeting Scheme Volume CMV Set-point NA Assist/Control Volume Control VC-CMVs Dual NA Continuous Mandatory Ventilation with VC-CMVd Pressure Limited IMV Set-point Set-point Volume Control Synchronized VC-IMVs,s Intermittent Mandatory Ventilation Dual Dual Volume Control* VC-IMVd,d Dual/Adaptive Set-point Mandatory Minute Volume with VC-IMVda,s Pressure Limited Ventilation Dual Adaptive Automode (Volume Control to Volume VC-IMVd,a Support) Adaptive Set-point Mandatory Minute Volume Ventilation VC-IMVa,s Pressure CMV Set-point NA Pressure Control Assist Control PC-CMVs Adaptive NA Pressure Regulated Volume Control PC-CMVa IMV Set-point Set-point Airway Pressure Release Ventilation PC-IMVs,s Adaptive Set-point Adaptive Pressure Ventilation PC-IMVa,s Synchronized Intermittent Mandatory Ventilation Adaptive Adaptive Automode (Pressure Regulated Volume PC-IMVa,a Control to Volume Support) Optimal Optimal Adaptive Support Ventilation PC-IMVo,o Optimal/Intelligent Optimal/Intelligent IntelliVent-ASV PC-IMVoi,oi CSV Set-point NA Pressure Support PC-CSVs Servo NA Proportional Assist Ventilation PC-CSVr Servo NA Neurally Adjusted Ventilatory Support PC-CSVr Adaptive NA Volume Support PC-CSVa Adaptive NA Mandatory Rate Ventilation PC-CSVa Intelligent NA SmartCare/PS PC-CSVi

* Servo-i ventilator. CMV ϭ continuous mandatory ventilation NA ϭ not applicable VC ϭ volume control s ϭ set-point d ϭ dual IMV ϭ intermittent mandatory ventilation a ϭ adaptive PC ϭ pressure control o ϭ optimal CSV ϭ continuous spontaneous ventilation. r ϭ servo i ϭ intelligent

volume or pressure-controlled, according to fort lasts long enough, flow cycles the breath. be implemented during the breath, depend- the operator set priorities. The breath may Indeed, if the tidal volume and inspiratory ing on the other factors in the targeting start out in pressure control and automati- time are set relatively low and the inspira- scheme. cally switch to volume control, as in the tory effort is relatively large, the resultant Dynamic Compliance Bird “VAPS” mode or, the reverse, as in the breath delivery is indistinguishable from The slope of the pressure-volume curve Dra¨ger “Pmax” mode. The Maquet Servo-i Pressure Support. As a result, the tidal vol- drawn between two points of zero flow (eg, ventilator has a mode called “Volume Con- ume may be much larger than the expected, at the start and end of inspiration). trol” and the operator presets both inspira- preset value. This highlights the need to un- Dynamic Hyperinflation tory time and tidal volume, as would be derstand dual targeting. Because both pres- The increase in lung volume that occurs expected with any conventional volume con- sure and volume may be the control vari- whenever insufficient exhalation time pre- trol mode. However, if the patient makes an ables during dual targeting, by convention vents the respiratory system from returning inspiratory effort that decreases inspiratory we designate the control variable as the one to its normal resting end-expiratory equilib- pressure by 3 cm H2O, the ventilator with which the breath initiates. This is be- rium volume between breath cycles. Inap- switches to pressure control, and, if the ef- cause the other control variable may never propriate operator set expiratory time may

RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12 2147 LETTERS TO THE EDITOR lead to dynamic hyperinflation, inability of Feedback Control stop) is considered patient triggered/cycled the patient to trigger breaths, and an in- Closed loop control accomplished by us- or machine triggered/cycled. If we say syn- creased work of breathing. ing the output as a signal that is fed back chronized breaths are patient triggered and Elastance (compared) to the operator-set input. The cycled, we have the awkward possibility of A mechanical property of a structure such difference between the two is used to drive a spontaneous breath occurring during an- as the respiratory system; a parameter of a the system toward the desired output (ie, other spontaneous breath. This is avoided lung model, or setting of a lung simulator; negative feedback control). For example, by distinguishing between a trigger window defined as the ratio of the change in the pressure-controlled modes use airway pres- and a synchronization window. pressure difference across the system to the sure as the feedback signal to manipulate There are some modes where the idea of associated change in volume. Elastance is gas flow from the ventilator to maintain an IMV may be vague: with Airway Pressure the reciprocal of compliance. inspiratory pressure set-point. Release Ventilation, relatively high fre- Equation of Motion for the Respira- Flow Control quency spontaneous breaths are superim- Maintenance of an invariant inspiratory posed on low frequency mandatory breaths. tory System flow waveform despite changing respiratory However, the expiratory time between man- A relation among pressure difference, system mechanics datory breaths is often set so short that a volume, and flow (as variable functions of Flow Triggering spontaneous breath is unlikely to occur be- time) that describes the mechanics of the The starting of inspiratory flow due to a tween them. Other ambiguous modes are respiratory system. The simplest and most patient inspiratory effort that generates in- High Frequency Oscillation, High Fre- useful form is a differential equation with spiratory flow above a preset threshold (ie, quency Jet Ventilation, Interpulmonary Per- constant coefficients describing the respira- the trigger sensitivity setting) cussive Ventilation, and Volumetric Diffu- tory system as a single deformable com- Flow Target sive Respiration. With these modes, high partment including the lungs and chest wall: Inspiratory flow reaches a preset value frequency mandatory breaths are superim- ⌬ ϩ⌬ ϭ ϩ ˙ ϩ PTR(t) Pmus(t) EV(t) RV(t) that may be maintained before inspiration posed on low frequency spontaneous breaths autoPEEP cycles off. and, again, there is no possibility of a spon- where Flow Cycling taneous breath actually occurring between ⌬ ϭ PTR(t) the change in transrespiratory The ending of inspiratory time due to mandatory breaths. Nevertheless, we clas- pressure difference (ie, airway opening pres- inspiratory flow decay below a preset thresh- sify all these modes as forms of IMV be- sure minus body surface pressure) as a func- old (also known as the cycle sensitivity). cause spontaneous breaths can occur along tion of time (t), measured relative to end- Intermittent Mandatory Ventilation with mandatory breaths and because spon- expiratory airway pressure. This is the Breath sequence in which spontaneous taneous efforts do not affect the mandatory ⌬ pressure generated by a ventilator ( Pvent) breaths are permitted between mandatory breath frequency. See machine triggering, during an assisted breath. breaths. For most ventilators, a short “win- patient triggering, synchronization win- ⌬ ϭ Pmus(t) ventilatory muscle pressure dow” is opened before the scheduled ma- dow, and trigger window. difference as a function of time (t); the the- chine triggering of mandatory breaths, to Inspiratory Pressure oretical chest wall transmural pressure dif- allow synchronization with any detected in- General term for the pressure at the pa- ference that would produce movements spiratory effort on the part of the patient. tient connection during the inspiratory identical to those produced by the ventila- This is referred to as synchronized IMV (or phase. For pressure control modes, where tory muscles during breathing maneuvers SIMV). Three common variations of IMV the inspiratory pressure is targeted to a pre- (positive during inspiratory effort, negative are: mandatory breaths are always delivered set value, the term is used to designate this during expiratory effort) at the set frequency; mandatory breaths are setting. If inspiratory pressure is set relative E ϭ elastance (inverse of compliance; delivered only when the spontaneous breath to atmospheric pressure, the term “peak in- frequency falls below the set frequency; spiratory pressure” is used. If inspiratory E ϭ 1/C) mandatory breaths are delivered only when pressure is set relative to PEEP, the term V(t) ϭ volume change relative to end- the spontaneous minute ventilation (ie, prod- “inspiratory pressure” is used. expiratory volume as a function of time (t) uct of spontaneous breath frequency and Intelligent Control V˙ (t) ϭ flow as a function of time (t), the spontaneous breath tidal volume) drops be- A ventilator control system that uses ar- first derivative of volume with respect to low a preset or computed threshold (also tificial intelligence programs such as fuzzy time known as Mandatory Minute Ventilation). logic, rule based expert systems, and artifi- ϭ autoPEEP end-expiratory alveolar For some modes (eg, Airway Pressure cial neural networks. One example is the pressure above end-expiratory airway pres- Release Ventilation), a short window is also rule based system used by SmartCare sure opened at the end of the inspiratory time. (Dra¨ger Evita XL ventilator). For the purposes of classifying modes of Because spontaneous breaths are allowed Machine Cycling mechanical ventilation the equation is often during the mandatory pressure controlled Ending inspiratory time independent of simplified to: breath, this window synchronizes the end of signals representing the patient determined ϭ ϩ ˙ Pvent EV RV the mandatory inspiratory time with the start components of the equation of motion (ie,

where of spontaneous expiratory flow, if detected. Pmus [effort], elastance, or resistance). ϭ Pvent the transrespiratory pressure dif- With these technological developments, po- Common examples of machine cycling ference (ie, “airway pressure”) generated by tential confusion arises as to whether inspi- variables are preset inspiratory time and the ventilator during an assisted breath ration that is synchronized (either start or tidal volume.

2148 RESPIRATORY CARE • DECEMBER 2012 VOL 57 NO 12 LETTERS TO THE EDITOR

Machine Triggering mon examples of patient trigger variables and flow waveforms (volume control Starting inspiratory flow based on a sig- are airway pressure drop below baseline and modes). nal (usually time) from the machine, inde- inspiratory flow due to patient effort. Spontaneous Breath pendent of a signal indicating patient in- PC-CMV A breath in which the patient retains sub- spiratory effort. Examples include triggering Pressure-controlled continuous manda- stantial control over timing. This means the based on a preset frequency (which sets the tory ventilation start and end of inspiration may be deter- ventilatory period), or based on a preset min- PC-IMV mined by the patient, independent of any imum minute ventilation (determined by Pressure-controlled intermittent manda- machine settings for inspiratory time and tidal volume divided by the ventilatory pe- tory ventilation expiratory time. That is, the patient both riod). If a signal from the patient (indicating PC-CSV triggers and cycles the breath. Note that use the need for inspiration) occurs within a syn- Pressure-controlled continuous spontane- of this definition for determining the breath chronization window, the start of inspira- ous ventilation sequence (ie, CMV, IMV, CSV) assumes tion is defined as a machine trigger event Pressure Control normal ventilator operation. For example, that begins a mandatory breath. See inter- A general category of ventilator modes coughing during VC-CMV may result in mittent mandatory ventilation, patient in which pressure delivery is predeter- patient cycling for a patient-triggered breath, triggering, synchronization window, and mined by a targeting scheme such that due to the pressure alarm limit. While inspi- trigger window. inspiratory pressure is either proportional ration for that breath is both patient-triggered Mandatory Breath to patient effort or has a particular wave- A breath in which the patient has lost form, regardless of respiratory system me- and patient-cycled, this is not normal oper- substantial control over timing. This means chanics. ation and the sequence does not turn into a breath in which the start or end of inspi- Pressure Cycling IMV. ration (or both) is determined by the venti- Inspiratory time ends when airway pres- Synchronized IMV (SIMV) lator, independent of the patient. That is, the sure reaches a preset threshold. A form of IMV in which mandatory machine triggers and/or cycles the breath. Pressure Triggering breath delivery is coordinated with patient Mechanical Ventilator The starting of inspiratory flow due to a effort. A synchronized breath is considered An automatic machine designed to pro- patient inspiratory effort that generates an to be machine triggered. vide all or part of the work required to gen- airway pressure drop below end-expiratory Synchronization Window erate enough breaths to satisfy the body’s pressure larger than a preset threshold (ie, A short period at the end of the expira- respiratory needs. the trigger sensitivity setting). tory time (eg, based on a preset mandatory Mode of Ventilation Pressure Target breath frequency and inspiratory time) or at A predetermined pattern of interaction Inspiratory pressure reaches a preset the end of a preset inspiratory time, during between a patient and a ventilator, specified value before inspiration cycles off. which a patient signal may be used to syn- as a particular combination of control vari- Primary Breaths chronize flow to patient effort. If a signal able, breath sequence, and targeting schemes Mandatory breaths during CMV or IMV, from the patient (indicating the need for infor primary and secondary breaths. or spontaneous breaths during CSV. spiration) occurs during the expiratory time Optimum Targeting Scheme Secondary Breaths within the window, inspiration starts and is A ventilator control system that automat- Spontaneous breaths during IMV. defined as a machine triggered event that ically adjusts the targets of the ventilatory Servo Targeting begins a mandatory breath. This is because pattern to either minimize or maximize some A control system in which the output of the mandatory breath would have been time overall performance characteristic. One ex- the ventilator automatically follows a vary- triggered regardless of whether the patient ample is Adaptive Support Ventilation ing input. For example, the Automatic Tube signal had appeared or not, and because the (Hamilton Medical G5 ventilator), in which Compensation feature on the Dra¨ger Evita 4 distinction is necessary to avoid logical in- the ventilator adjusts the mandatory tidal ventilator tracks flow and forces pressure to consistencies in defining mandatory and volume and frequency (for a passive pa- be equal to flow multiplied by a constant spontaneous breaths, which are the founda- tient) in such a way as to minimize the work (representing endotracheal tube resistance). tion of a mode taxonomy. Sometimes a syn- rate of ventilation. Other examples include Proportional Assist chronization window is used at the end of a Patient Cycling Ventilation (Covidien Puritan Bennett 840 Ending inspiratory time based on signals ventilator; pressure is proportional to spon- pressure controlled, time cycled breath. For related to one of the patient determined com- taneous volume and flow) and Neurally Ad- example, during Airway Pressure Release Ventilation the patient is free to take spon- ponents of the equation of motion (ie, Pmus justed Ventilatory Assist (Maquet Servo-i [effort], elastance, or resistance). Common ventilator; pressure is proportional to dia- taneous breaths during a mandatory breath. examples of cycling variables are peak in- phragmatic electrical activity). For all 3 of If a signal from the patient (eg, the start of spiratory pressure and percent inspiratory these example modes, airway pressure is expiratory flow for a spontaneous breath) flow. effectively proportional to the patient’s in- occurs during the inspiratory time within Patient Triggering spiratory effort. the window, inspiration stops and is defined Starting inspiratory flow based on sig- Set-Point Targeting as a machine cycled event that ends a man- nals representing the patient determined A control system in which the operator datory breath. See intermittent mandatory components of the equation of motion (ie, sets all the parameters of the pressure wave- ventilation, machine triggering, patient

Pmus [effort], elastance, or resistance). Com- form (pressure control modes) or volume triggering, trigger window.

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Target tient triggering, and synchronization win- 2. Hedden, H. The accidental taxonomist. A predetermined goal of ventilator out- dow. Medford, NJ: Information Today, 2010. put. Targets can be viewed as the parame- Trigger (Triggering) 3. Cowan N. The magical number 4 in short- ters of the targeting scheme. Within-breath To start inspiration. See machine trig- term memory: a reconsideration of mental targets are the parameters of the pressure, gering, patient triggering. storage capacity. Behav Brain Sci 2001; 24(1):87-114, discussion 114-185. volume, or flow waveform. Examples of Ventilatory Pattern 4. Bailey KD. Typologies and taxonomies: an within-breath targets include inspiratory A sequence of breaths (CMV, IMV, or introduction to classification techniques. flow or pressure rise time (set-point target- CSV) with a designated control variable Thousand Oaks, London: Sage Publica- ing), inspiratory pressure, tidal volume (dual (volume, pressure, or dual control) for the tions; 1994. targeting), and the constant of proportion- mandatory breaths (or the spontaneous 5. Chatburn RL. Classification of mechanical ality between inspiratory pressure and pa- breaths for CSV) ventilators and modes of ventilation. In: To- tient effort (servo targeting). Between-breath Volume Control bin MJ, ed. Principles and practice of me- targets serve to modify the within-breath A general category of ventilator modes chanical ventilation, 3rd edition. New York: targets and/or the overall ventilatory pat- in which both inspiratory flow and vol- McGraw-Hill; 2012. 6. Mireles-Cabodevila E, Hatipoglu U, Chat- tern. Between-breath targets are used with ume delivery are predetermined by a tar- burn RL. A rational framework for select- geting scheme to have particular wave- more advanced targeting schemes, where ing modes of ventilation. Respir Care 2012. targets act over multiple breaths. A simple forms independent of respiratory system Epub ahead of print. example of a between-breath target is to mechanics. Usually, flow and tidal vol- 7. Chatburn RL, Mireles-Cabodevila E. compare actual exhaled volume to a preset ume may be set directly by the operator. Closed-loop control of mechanical ventila- between-breath tidal volume in order to au- Alternatively, the ventilator may deter- tion: description and classification of tar- tomatically adjust the within-breath inspira- mine tidal volume based on operator pre- geting schemes. Respir Care 2011;56(1): tory pressure or flow target for the next set values for frequency and minute ven- 85-102. breath. Examples of between-breath targets tilation, or the ventilator may determine 8. Guskey TR. Closing achievement gaps: re- visiting Benjamin S Bloom’s “learning for and targeting schemes include average tidal inspiratory flow based on operator set tidal volume and inspiratory time. Note that mastery.” J Advanced Academics 2007; volume (for adaptive targeting), percent 19(1):8-31. the tidal volume setting refers to the with- minute ventilation (for optimal targeting), 9. McGaghie WC, Issenberg B, Cohen ER, in-breath tidal volume, not a between- and combined PCO2, volume, and frequency Barsuk JH, Wayne DB. Medical education values describing a “zone of comfort” (for breath target as used in adaptive pres- featuring mastery learning with deliberate intelligent targeting). sure targeting (see adaptive targeting practice can lead to better health for indi- Targeting Scheme scheme). viduals and populations. Academic Med A model of the relationship between op- VC-CMV 2011;86(11):e8–e9. erator inputs and ventilator outputs to Volume-controlled continuous manda- 10. Volsko TA, Hoffman J, Conger A, Chat- achieve a specific ventilatory pattern, usu- tory ventilation burn RL. The effect of targeting scheme on tidal volume delivery during volume con- ally in the form of a feedback control sys- VC-IMV Volume-controlled intermittent manda- trol mechanical ventilation. Respir Care tem. The targeting scheme is a key compo- 2012;57(8):1297-1304. tory ventilation nent of a mode description. 11. Amato MB, Barbas CS, Bonassa J, Saldiva Time Cycling Volume Triggering PH, Zin WA, de Carvalho CR. Volume- Inspiratory time ends after a preset time The starting of inspiratory flow due to a assured pressure support ventilation interval has elapsed. The most common ex- patient inspiratory effort that generates an in- (VAPSV): a new approach for reducing amples are a preset inspiratory time or a spiratory volume signal larger than a preset muscle workload during acute respiratory preset inspiratory pause time. threshold (ie, the trigger sensitivity setting) failure. Chest 1992;102(4):1225-1234. Time Triggering Volume Target Robert L Chatburn MHHS RRT-NPS The starting of inspiratory flow due to a A preset value for tidal volume that the FAARC preset time interval. The most common ex- ventilator is set to attain either within a breath or as an average over multiple breaths. Respiratory Institute ample is a preset ventilatory frequency. The Cleveland Clinic Volume Cycling Trigger Window Cleveland, Ohio The period composed of the expiratory Inspiratory time ends when inspiratory time (minus a short “refractory” period re- volume reaches a preset threshold (ie, tidal Mr Chatburn has disclosed relationships with quiredtoreducetheriskoftriggeringabreath volume). the Alpha-1 Antitrypsin Foundation, Breathe Technologies, CareFusion, Covidien, Dra¨ger, before exhalation is complete). If a signal Hamilton, IngMar, Newport, Philips, Radiom- from the patient (indicating the need for in- REFERENCES eter America, ResMed, Respironics, Strategic Dynamics, and Teleflex. spiration) occurs within this trigger window, 1. Chatburn RL, Volsko TA, Hazy J, Harris inspiration starts and is defined as a patient LN, Sanders S. Determining the basis for a triggered event. See intermittent manda- taxonomy of mechanical ventilation. Re- tory ventilation, machine triggering, pa- spir Care 2012;57:514-24. DOI: 10.4187/respcare.02122

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