Resp 3030: Respiratory Research

Chapter 4

Evaluating Introductions and Literature Reviews

Does the Researcher Begin by Identifying a Specific Problem Area?

Does the Researcher Establish the Importance of the Problem Area?

Are any Underlying Theories Adequately Described?

Does the Introduction Move from Topic to Topic Instead of from Citation to Citation?

Are Very Long Introductions Broken into Subsections, Each with its Own Subheading?

Has the Researcher Provided Adequate Conceptual Definitions of Key Terms?

Has the Researcher Cited Sources for “Factual” Statements?

Do the Specific Research Purposes, Questions, or Hypotheses Logically Flow from the Introductory Material?

Overall, is the Introduction Effective and Appropriate?

Chapter 5

A Closer Look at Evaluating Literature Reviews

Has the Researcher Avoided Citing a Large Number of Sources for a Single Point?

Is the Literature Review Critical?

Is the Literature Review Critical?

Has the Author Cited any Contradictory Research Findings?

Has the Researcher Distinguished between Opinions and Research Findings?

Has the Researcher Noted any Gaps in the Literature?

Has the Researcher Interpreted Research Literature in Light of the Inherent Limits of Empirical Research?

Has the Researcher Avoided Overuse of Direct Quotations from the Literature?

After Reading the Literature Review, Does a Clear Picture Emerge of What the Previous Research has Accomplished and Which Questions Still Remain Unresolved?

Overall, is the Literature Review Portion of the Introduction Appropriate and Effective?

Chapter 6

Evaluating Samples when Researchers Generalize

Was Random Sampling Used?

If Random Sampling was Used, was it Stratified?

If Some Potential Participants Refused to Participate, Was the Rate of Participation Reasonably High?

If the Response Rate Was Low, Did the Researcher Make Multiple Attempts to Contact Potential Participants?

Is There Reason to Believe that the Participants and Nonparticipants are Similar on Relevant Variables?

If a Sample is Not Random, Was it at Least Drawn from the Target Group for the Generalization?

If a Sample is Not Random, Was it Drawn from Diverse Sources?

If a Sample is Not Random, Does the Researcher Explicitly Discuss This Limitation and How it May Have Affected the Generalizability of the Study Findings?

Has the Author Described Relevant Characteristics (Demographics) of the Sample?

Is the Overall Size of the Sample Adequate?

Is the Number of Participants in Each Subgroup Sufficiently Large?

Has Informed Consent Been Obtained?

Has the Study Been Approved by an Ethics Review Agency (Institutional Review Board, or IRB, if in the United States or a Similar Agency if in Another Country)?

Overall, is the Sample Appropriate for Generalizing?

Chapter 7

Evaluating Samples when Researchers Do Not Generalize

Has the Researcher Described the Sample/Population in Sufficient Detail?

For a Pilot Study or Developmental Test of a Theory, Has the Researcher Used a Sample with Relevant Demographics?

Even if the Purpose is Not to Generalize to a Population, Has the Researcher Used a Sample of Adequate Size?

Is the Sample Size Adequate in Terms of its Orientation (Quantitative Versus Qualitative)?

If a Purposive Sample Has Been Used, Has the Researcher Indicated the Basis for Selecting Participants?

If a Population Has Been Studied, Has it Been Clearly Identified and Described?

Has Informed Consent Been Obtained?

Has the Study Been Approved by an Ethics Review Committee?

Overall, is the Description of the Sample Adequate?

From Novice to Expert
Author(s): Patricia Benner
Source: The American Journal of Nursing, Vol. 82, No. 3 (Mar., 1982), pp. 402-407
Published by: Lippincott Williams & Wilkins
Stable URL: http://www.jstor.org/stable/3462928
Accessed: 19-12-2016 19:11 UTC
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American Journal of Nursing
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long-term and ongoing career de- opment of a skill, one passes through
velopment. This, in turn, requires five levels of proficiency:
* novice
an understanding
Nursing in acute-care settings
hasof the differences
* advanced beginner
experienced nurse and
grown so complex that itbetween
is no the
longthe routinize,
novice.
* competent
er possible to standardize,
By Patricia Benner
The Dreyfus
and delegate much of what
theModel of Skill Ac-
nurse does.
quisition offers a useful tool for
doing this. of
This model was inducIn the past, formalization
tively derived by two University of
nursing care and interchangeability
of nursing personnel were
considCalifornia,
Berkeley, professors–
* proficient
* expert
The levels reflect changes in
two general aspects of skilled per-
formance. One is a movement from
Stuart
Dreyfus, a mathematician
ered easy answers to nurse
turnover.
and systemsof
analyst, and Hubert
The discretionary responsibility
Dreyfus, a philosopher-from
their
nursing care for patient welfare
was
reliance on abstract principles to the
lots(1,2).and repaid to providing incentives
myclinistudies, I have found
wards for long-term careersInin
thatThis
the model
be generalized to
cal nursing in hospitals.
iscan
no
nursing. It takes into account increlonger tenable.
ments of
in skilled
performance based
Increased acuity levels
patients, decreased length of
upon
hospitaliexperience as well as education. It also provides
zation, and the proliferation
ofa basis for clinical knowledge
development and
health care technology and
specialization have increased the need for
career progression in clinical nurs-
of a demand situation so that the sit-
study of was
chess players and piignored, and little attention
highly experienced nurses. The
complexity and responsibility of
use of past, concrete experience as
paradigms. The other is a change in
the perception and understanding
uation is seen less as a compilation
of equally relevant bits and more as
a complete whole in which only certain parts are relevant(2).
To evaluate the practicality of
applying the Dreyfus model to nursing and to clarify the characteristics
of nurse performance at different
stages of skill acquisition, interviews
ing.
Briefly, the Dreyfus model pos-
nursing practice today requires its that, in the acquisition and devel-
and participant observations were
conducted with 51 experienced
402 American Journal of Nursing/March 1982
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and output, temperature,
blooding graduate
clinicians,
11 new
rules legislates against successful
pulse, and other
such ob- task performance
and 5pressure,
senior
nursing
students
because no rule
tasks are
different
hospitals-two
prijectifiable, measurable
parameterscan tell a novice which
nurses,
in
six
mosttwo
relevant in a comreal situation or
vate community
of the patient’s
hospitals,
condition.
when
an
exception
to the rule is in
Novice practitioners
are also
munity teaching
hospitals,
one university medical
taught rules
center,
to guide actionand
in order. one inrespect to different
attributes. The
ner-city general
teaching
hospital.
Much
confirming
following is an example
and
of suchno
aLevel II:
disconAdvanced Beginner
context-free rule:
firming evidence
was found for use
of the Dreyfus
Skill
AcquiThe advanced
beginner is one
To Model
determine fluidof
balance,
sition
tice(3,4).
Level I: Novice
in
check the patient’snursing
morning
clinical
pracwho can demonstrate
marginally
weights and daily intake and out-
put for the past three days. Weight
gain in addition to an intake that is
consistently greater than 500 cc
Beginners have no experiencecould indicate water retention; in
with the situations in which they are
that case, fluid restriction should
be started until the cause of the
expected to perform tasks. In order
imbalance can be determined.
to give them entry to these situa-
acceptable performance. This person is one who has coped with
enough real situations to note (or to
have them pointed out by a mentor)
the recurrent meaningful situational
components, called aspects.
In the Dreyfus model, the term
“aspects” has a very specific mean-
The heart of the difficulty that ing. Unlike the measurable, contexttions, they are taught about them in
terms of objective attributes. Thesethe novice faces is the inability to free attributes of features that the
attributes are features of the task
use discretionary judgment. Since inexperienced novice uses, aspects
that can be recognized without situ- novices have no experience with the are overall, global characteristics
ational experience.
situation they face, they must usethat require prior experience in acCommon attributes accessible
these context-free rules to guide tual situations for recognition.
to the novice include weight, intake their task performance. But followFor example, assessing a pa-
American Journal of Nursing/March 1982 403
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The advanced beginner, or inindicative of pulmonary edema and
structor of the advanced beginner,those indicative of pneumonia. But
similar situations and similar teachcan formulate guidelines for actions
in practice areas, where the cliniing-learning needs. An expert clini- in terms of attributes and aspects.
cian has already attained competencian describes her assessment of a
These action guidelines integrate ascy, aspect recognition will probably
patient’s readiness to learn about his
many attributes and aspects as possibe redundant; the competent clinician will focus on the more adcontinent ileostomy this way:
ble, but they tend to ignore the difEarlier, I thought he was feel- ferential importance. In other
vanced clinical skill of judging the
relative importance of different aspects of the situation.
The major implication for both
tient’s readiness to learn depends on
experience with previous patients in
“Novices and advanced beginners
can take in little of the situation-it
is too new, too strange.”
preservice and inservice education
is that the advanced beginner needs
support in the clinical setting. Ad-
vanced beginners need help in setting priorities since they operate on
general guidelines and are only being helpless about the operation he
had just had. He looked as though
he felt crummy-physically, sort of
stressed-looking, nervous-looking.
Furthermore, he was treating the
wound physically very gingerly. He
didn’t need to be that gentle with
it. But, on this morning, it was different, he began to ask questions.
An instructor or mentor can
words, they treat all attributes and
aspects as equally important. The
ginning to perceive recurrent meaningful patterns in their clinical prac-
following comment about advanced
beginners in an intensive care nursery illustrates this.
nurses to ensure that important pa-
tice. Their patient care must be
backed up by competent level
I give very detailed and expli- tient needs do not go unattended
cit instructions to the new grad- because the advanced beginner canuate: When you come in and first not yet sort out what is most imporsee the baby, take the vital signs tant.
and make the physical examina-
provide guidelines for recognizingtion. Then, check the IV sites,
such aspects as readiness to learn; check the standby ventilator and
Level III: Competent
for example, “Notice whether or not make sure that it works, and check
the patient asks questions about the the monitors and alarms. When I
Competency, typified by the
nurse who has been on the job two
surgery or the dressing change.”say this to new graduates, they do to three years, develops when the
“Observe whether or not the patient exactly what I tell them to do, no nurse begins to see his or her actions
looks at or handles the wound.” But
matter what else is going on…. in terms of long-range goals or
the guidelines are dependent onThey can’t choose one to leave out. plans. The nurse is consciously
knowing what these aspects soundThey can’t choose which is more aware of these plans, and the goal or
like and look like in a patient careimportant…. They can’t do for plan dictates which attributes and
situation.
one baby the things that are most aspects of the current and contem-
While aspects may be made important, then go to the next baby
explicit, they cannot be made com- and do the things that are most
pletely objective. It makes a differ- important and leave out the things
ence in the way that the patient asks that can be left until later.
plated future situation are to be con-
about the surgery or the dressing
tive, and the plan is based on consid-
Novices and advanced begin-
change. You have to have some ners can take in little of the situa-
experience with prior situations be-
tion-it is too new, too strange.
Aspect recognition is dependent on
prior experience.
remembering the rules they have
fore you can use the guidelines. Besides, they have to concentrate on
PATRIC(:IA BENNER, RN. MS, has been involved in
studies to identify the competencies of new
graduates for over 10 years. When this was
prepared, Ms. Benner was director of the
Achieving Methods of Intraprofessional Con-
sensus, Assessment, and Evaluation (AMI-
CAE) Project at the University of San Francisco. This article is based on material to be
published by the National Commission on
Nursing of the American Hospital Associa-
tion in a monograph, From’ Novice to Expert:
Promoting Excellence and Career Develop-
ment in Clinical Nursing Practice. The
study reported in the monograph was sup-
ported by a Department of Health and
Human Services Division of Nursing grant.
sidered most important and which
can be ignored. For the competent
nurse, a plan establishes a perspecerable conscious, abstract, analytic
contemplation of the problem. A
preceptor describes her own evolu-
tion to the stage of competent,
been taught. As the expert clinician
planned nursing from her earlier
quoted above adds,
If I say, you have to do these
stimulus-response level of nursing:
eight things, they do those things.
They don’t stop if another baby is
I had four patients. One
needed colostomy teaching, the
others needed a lot of other things.
Instead of thinking before I went
into the room, I got caught up….
Someone’s IV would stop, and I’d
needs attention, they’re like mules
work on that. Then I’d forget to
between two piles of hay.
Much time is spent by precep- give someone their meds, and so
would have to rush around and do
tors and new graduates on aspect
that. And then someone would feel
recognition. For example, in mak-
screaming its head off. When they
do realize that the other child
ing physical assessments, aspect rec-nauseated and I’d try to make
them feel better while they were
ognition is an appropriate learning
goal. The nurse will practice dis-sick. And then the colostomy bag
criminating between breath soundswould fall off when I wanted to
404 American Journal of Nursing/March 1982
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start teaching. And, all of a sudden
the morning was gone, and no one
had a bed bath.
Now I come out of report and
I know I have a couple of things
that I have to do. Before I go in the
room, I write down the meds I’m
supposed to give for that day, and
then walk in there and make sure
terms of aspects, and performance situation.
is
They can mean one thing
at one time and quite another at
guided by maxims.
another time. But once one has a
Experience teaches the profi-
cient nurse what typical events deep
to
understanding of the situation,
the maxim provides directions as to
expect in a given situation and how
what is important to take into conto modify plans in response to these
sideration. This is revealed in the
events. There is a web of perspectives, and as Dreyfus notes,
experienced nurse clinicians’s ac-
Except in unusual circum-count of how she weans a patient
that everybody’s IV is fine…. I stances, the performer will be expefrom a respirator:
know what I have to do, and I am
much more organized.
Competence is evidenced by
the fact that the nurse begins to see
his or her actions in terms of longrange goals or plans. The competent
nurse lacks the speed and flexibility
riencing his current situation as Well, you look at vital signs to
similar to some brain-stored, expesee if there is anything significant
there. But even here you need to do
rience-created, typical situation
little guessing. You have to decide
(complete with its saliences) due ato
recent past history of events….
if the patient is just anxious be-
cause he’s so used to the machine
Hence the person will experience
breathing for him. And if he does
of the nurse who has reached the
through a perspective, but ratherget anxious, you don’t really want
proficient level, but the competencythan consciously calculating this to medicate him, because you’re
stage is characterized by a feeling ofperspective or plan, it will simply
afraid he will quit breathing. But
mastery and the ability to cope withpresent itself to him or her(5).
on the other hand, he may really
and manage the many contingenBecause of the experience- need to calm down a bit. It just
his or her situation at all times
cies of clinical nursing. The compe- based ability to recognize whole sit-depends on the situation…. You
tent nurse’s conscious, deliberateuations, the proficient nurse canhave your groundwork from what
planning helps achieve a level of now recognize when the expectedyou have done in the past, and you
efficiency and organization. Nurses normal picture does not present know when you are going to get
at this stage can benefit from deci-itself-that is, when the normal is
sion-making games and simulations absent. The holistic understanding
that give them practice in planningof the proficient nurse improves his
and coordinating multiple, com- or her decision making. Decision
plex, patient care demands.
making is now less labored since the
The competent level is sup-nurse has a perspective about which
ported and reinforced institutional-of the many attributes and aspects
ly, and many nurses may stay at thispresent are the important ones.
level because it is perceived as the
Whereas the competent person
ideal by their supervisors. The stan-does not yet have enough experidardization and routinization of
ence to recognize a situation in
into trouble.
Proficient performers are best
taught by use of case studies where
their ability to grasp the situation is
solicited and taxed. Providing proficient performers with context-free
principles and rules will leave them
somewhat frustrated and will usually stimulate them to give examples
of situations where, clearly, the
principle or rule would be contra-
procedures, geared to manage the
terms of an overall picture or in
dicted,
high turnover in nursing, most often
terms of which aspects are most salireflect the competent level of perent and most important, the profi-
Level V: Expert
“Experience teaches the proficient
nurse what typical events to expect
in a given situation and how to modify
plans in response to these events.”
formance. Most inservice education
cient performer now considers few-
is aimed at the competent level of er options and hones in on an accuachievement; few inservice offer- rate region of the problem. Aspects
ings are aimed at the proficient or stand out to the proficient nurse as
expert level of performance.
Level IV: Proficient
With continued practice, the
competent performer moves to the
proficient stage. Characteristically,
the proficient performer perceives
situations as wholes, rather than in
being more or less important to the
situation at hand.
Maxims are used to guide the
proficient performer, but a deep
understanding of the situation is required before a maxim can be used.
At the expert level, the performer no longer relies on an analy-
tical principle (rule, guideline,
maxim) to connect her/his under-
standing of the situation to an
appropriate action. The expert
nurse, with her/his enormous background of experience, has an intuitive grasp of the situation and zeros
in on the accurate region of the
problem without wasteful consideration of a large range of unfruitful
possible problem situations.
It is very frustrating to try to
capture verbal descriptions of expert performance because the expert operates from a deep under-
standing of the situation, much like
the chess master who, when asked
Maxims reflect what would appear why he made a particularly masterto the competent or novice perform- ful move, will just say, “Because it
er as unintelligible nuances of the felt right. It looked good.”
American Journal of Nursing/March 1982 405
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The problem experts have telling all they know is evident in the
following excerpt from an interview
with an expert psychiatric nurse
clinician. She has worked in psychiatry for 15 years and is highly
respected by both nurse and physician colleagues for her clinical judgment and ability.
When I say to a doctor, “The
patient is psychotic,” I don’t always know how to legitimize that
statement. But I am never wrong
because I know psychosis from the
inside out. And I feel that, and I
know it, and I trust it.
This nurse went on to describe
a specific situation in which she
knew that a patient was being mis-
diagnosed as psychotic when the
patient was extremely angry. The
physician was convinced that the
embedded in the expert’s practice
clinical situation in the same way. It
is not that proficient nurses have
becomes visible.
This is not to say that the internalized the rules and formulas
expert never uses analytical tools. learned during the earlier stages of
Highly skilled analytical ability is skill acquisition; they are no longer
necessary for novel or new situa- using rules and formulas to guide
tions. Analytical tools are also neces- their practice. They are now using
sary when the expert gets a wrong
take or a wrong grasp of the situation and finds that events and be-
past concrete experiences much like
the researcher uses paradigms.
haviors are not occurringaccording
the expert intended to accomplish
and what the outcomes were. Also,
it is possible to get a description
to expectations. When alternative
What can be described is what
perspectives are not available to the
experienced clinician, the only way
out of the wrong grasp of the problem is analytical problem solving.
from the patient and it is possible to
systematically observe and describe
expert practice. But it is not possible
Describing Expert Practice
to recapture from the expert in
explicit, formal steps the mental
We have much to learn from
processes or all the elements that go
into his or her expert recognitional
the expert nurse clinicians, but tocapacity in making rapid patient
describe or document expert nurseassessments. So, although you canpatient was psychotic and said,
performance, a new strategy fornot recapture elemental steps in the
“We’ll do an MMPI to see who’s
identifying and describing nursing process, you can observe and deright.” This nurse responded, “I am
competencies is needed. If, as thescribe in narrative interpretive form
sure that I am right regardless of
Dreyfus Model of Skill Acquisitionthe accomplishments and characterwhat the MMPI says.” The results
posits, the expert nurse’s perfor-istics of expert nurse performance.
mance is holistic rather than fracbacked up the nurse’s assessment,
Such a narrative, interpretive
and, based on her assessment, this
tionated, procedural, and based approach to describe expert nurse
nurse began what was a very sucupon incremental steps, then the performance is illustrated in the folcessful intervention for the patient.
strategy for describing expert nurs- lowing example which describes the
By studying proficient and exing performance must be holistic as coaching function of nursing.
pert performance, it is possible well.
to
Illness, pain, disfigurement,
obtain a rich description of the Currently, the language used
death, and even birth are, by and
kinds of goals and patient outcomes
to talk about nursing practice is too
large, segregated, isolated experiences. It makes little sense for the
that are possible in excellent nursing
simple, formal, and context-free to
practice. This knowledge of goals
capture the essence and complexity
lay person to personally prepare in
and possible outcomes can be useful
of expert nursing. At best, formal
advance for the many possible illness experiences.
Nurses, in contrast, through
their education and experience, develop and observe many ways to
“A competent nurse and a proficient
understand and cope with illness, as
nurse will not approach or solve a
well as many ways of experiencing
illness, suffering pain, death, and
clinical situation in the same way.”
birth. Nurses offer avenues of un-
derstanding, increased control, acceptance, and even triumph in the
in expanding the scope of practicemodels recognize and capture areas midst of what, for the patient, is a
of nurses who are less proficient. In
of performance typical of the nov- foreign, uncharted experience.
fact, a vision of what is possible is
ice, advanced-beginner, or compe-
Experience, in addition to
formal education preparation, is reone of the characteristics that sepa-tent nurse. But since most formal
rates competent performance frommodels focus on structure or pro-quired to develop this competency
proficient and expert performance.cess, the content and relational as-since it is impossible to learn ways of
Exemplars and descriptions of ex-pects of nursing practice in even thebeing and coping with an illness
solely by concept or theorem. A
cellence from expert nurse clini-beginning levels go undescribed.
It is important to underline the deep understanding of the situation
cians can raise the sights of the
competent nurse, and perhaps facil-claim of the Dreyfus model that is required before one acquires a
itate his or her movement to the
there is a transformation, a qualita-repertoire of ways of being and copproficient stage. By assisting the ex- tive leap, from the competent toing with a particular illness experipert to describe clinical situations proficient levels of performance. A ence. Often, these ways of being
where his or her interventions made competent nurse and a proficientand ways of coping are transmitted
a difference, some of the knowledge nurse will not approach or solve anonverbally by demonstration, by
406 American Journal of Nursing/March 1982
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attitudes, and by reactions as in the
a little smoother for those who had realities than can be captured by
to travel it. With that, he hugged theory alone. Theory, however,
me, said thank you, and turned guides clinicians and enables them
young man close to her own age away nodding his head, with tears to ask the right questions.
following example. A nurse clini-
cian described an encounter with a
Theory and research are generwho was visiting his father who was in his eyes. There were tears in my
ated from the practical world, from
dying. There was a rather sudden eyes too.
deterioration in the father, and the
In translating for the son how the practices of the experts in a
family was extremely distraught. the culturally avoided had become field. Only from the assumptions
and expectations of the clinical
practice of experts are questions
. *. . experience is not the mere
passage of time or longevity . . ”
The son stopped the nurse in the
understandable and approachable
to her, the nurse widened this young
hall and asked how long his father
would live. The nurse answered that
man’s perspective and acceptance.
she really didn’t know, that it could
be minutes, hours, days, or weeks.
There was no way to tell. He then
asked if there were other patients
dying on the floor. The nurse re-
This is what is meant by the coaching function of nursing, nurses who
have come to grips with the cultur-
ally avoided or uncharted and can
open ways of being and ways of
sponded, “Yes.” Then, as she re- coping for the patient and the
counts the incident, there was a long
pause, followed by a barrage of
questions:
How could I work here? How
family.
I have collected many examples of this particular skilled prac-
generated for scientific testing and
theory building.
Recognition, reward, and retention of the experienced nurse in
positions of direct clinical practice-along with the documention
and adequate description of their
practice-are the first steps in improving the quality of patient care.
The Dreyfus Model of Skill Acquisi-
tion, applied to nursing and combined with an interpretive approach
to describing nursing practices, of-
fers guidelines for career and for
knowledge development in clinical
nursing practice.
It also indicates the importance
of career ladders within clinical
nursing practice and adds to our
can I go home and sleep at night? case the nurse did not offer the
understanding of the need for and
How could I do what I do?
patient precepts or platitudes that
acceptance of the emergence of
No one had ever been so direct might sound like, “Even in the
clinicians and clinical specialists in
tice and am impressed that in each
with such questions as these before, midst of great handicap and impos-the patient-care setting.
and their bluntness threw me off sibility, I think it is possible to make
balance. But he was sincere and
the most of it.” This would be an
was waiting for my answer, and soexample of inflexible teaching by
I told him how I had resolved theseprecept.
same questions within myself. It
Nurses, in their practice, by the
was not quite a monologue, but forway they approach a wound or the
10 plus minutes he listened intent-way they talk about recovery from a
ly as I described to him my feelsurgery, offer ways of understand-
ings. I told him my philosophy
ing and avenues of acceptance.
about life and about dying and
Through the nurse’s own ability to
about nursing.
face and cope with the problem,
I told him how gradually I hadsuch as a difficult, draining wound,
settled into the medical floor inthe patient can come to sense that
stead of using it as a stepping stone
the problem is approachable and
to a surgical floor-which was my
manageable.
first intention. I told him how it Experience, as it is understood
was difficult, and how it was emo-and used in the acquisition of expertionally draining, and how it some-tise, has a particular definition that
should be clarified. As it is described
times was difficult to sleep at
night.
I told him how there was great
satisfaction in helping a patient
through the particular passage
known as death and how I felt I
was able to help the family also
through the pain of that passage. I
told him the gratification, the
thing that kept me here, was in
knowing that maybe somehow, I
had made this particular rocky road
in this model, experience is not the
mere passage of time or longevity; it
is the refinement of preconceived
notions and theory by encountering
many actual practical situations that
add nuances or shades of differences to theory(6,7).
Theory offers what can be
References
1. Dreyfus, H. L. What Computers Can’t Do: A
Critique of Artificial Reason. New York, Harp-
er & Row. 1972. (Paperback edition, 1979)
2. Dreyfus, Stuart, and Dreyfus, Hubert. A FiveStage Model of the Mental Activities Involved
in Directed Skill Acquisition. (Supported by
the U.S. Air Force, Office of Scientific Research (AFSC) under contract F49620-C-0063
with the University of California) Berkeley,
February, 1980. (Unpublished study)
3. Benner, Patricia, and Benner, R. V. The New
Nurse’s Work Entry: A Troubled Sponsorship.
New York, Tiresias Press, 1979.
4. Benner, P., and others. From Novice to Expert:
A Community View of Preparing for and
Rewarding Excellence in Clinical Nursing
Practice. (AMICAE Project Grant # 7 D20NU
29104) San Francisco, University of San Francisco, 1981. (Unpublished study)
5. Dreyfus, Stuart. Formal Models vs. Human
Situational Understanding: Inherent Limitations on the Modeling of Business Expertise.
(Supported by the U.S. Air Force, Office of
Scientific Research (AFSC), under contract
F49620-79-C-006x with the University of Cali-
fornia) Berkeley, Feb. 1981, p. 19. (Unpub-
lished report. Copies, for $5 each to cover the
cost of duplicating and mailing, are available
from Stuart Dreyfus, Director of Operations
Research Center, Univ. of Calif., Berkeley, Calif. 94720).
6. Cadamer, H.G. Truth and Method. London,
Sheet and Ward, 1970.
made explicit and formalized, but 7. Benner, Patricia, and Wrubel, Judith. Clinical
knowledge development: a neglected staff de-
clinical practice is always more
complex and presents many more
velopment and clinical function. (Submitted for
publication to Nurse Educ 1981)
American Journal of Nursing/March 1982 407
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All use subject to http://about.jstor.org/terms
 Copyright, 1995, by the Massachusetts Medical Society
Volume 332
FEBRUARY 9, 1995
Number 6
A COMPARISON OF FOUR METHODS OF WEANING PATIENTS FROM MECHANICAL
VENTILATION
ANDRÉS ESTEBAN, M.D., PH.D., FERNANDO FRUTOS, M.D., MARTIN J. TOBIN, M.D., INMACULADA ALÍA, M.D.,
JOSÉ F. SOLSONA, M.D., INMACULADA VALVERDÚ, M.D., RAFAEL FERNÁNDEZ, M.D.,
MIGUEL A. DE LA CAL, M.D., SALVADOR BENITO, M.D., PH.D., ROSER TOMÁS, M.D.,
DEMETRIO CARRIEDO, M.D., SANTIAGO MACÍAS, M.D., AND JESÚS BLANCO, M.D.,
FOR THE S PANISH L UNG F AILURE C OLLABORATIVE G ROUP *
Abstract Background. Weaning patients from mechanical ventilation is an important problem in intensive care
units. Weaning is usually conducted in an empirical manner, and a standardized approach has not been developed.
Methods. We carried out a prospective, randomized,
multicenter study involving 546 patients who had received
mechanical ventilation for a mean (SD) of 7.56.1 days
and who were considered by their physicians to be ready
for weaning. One hundred thirty patients had respiratory
distress during a two-hour trial of spontaneous breathing.
These patients were randomly assigned to undergo one
of four weaning techniques: intermittent mandatory ventilation, in which the ventilator rate was initially set at a
mean (SD) of 10.02.2 breaths per minute and then
decreased, if possible, at least twice a day, usually by 2 to
4 breaths per minute (29 patients); pressure-support ventilation, in which pressure support was initially set at
18.06.1 cm of water and then reduced, if possible, by
2 to 4 cm of water at least twice a day (37 patients);
intermittent trials of spontaneous breathing, conducted
two or more times a day if possible (33 patients); or a
once-daily trial of spontaneous breathing (31 patients).
Standardized protocols were followed for each technique.
Results. The median duration of weaning was 5 days
for intermittent mandatory ventilation (first quartile, 3 days;
third quartile, 11 days), 4 days for pressure-support ventilation (2 and 12 days, respectively), 3 days for intermittent (multiple) trials of spontaneous breathing (2 and
6 days, respectively), and 3 days for a once-daily trial of
spontaneous breathing (1 and 6 days, respectively). After
adjustment for other covariates, the rate of successful
weaning was higher with a once-daily trial of spontaneous
breathing than with intermittent mandatory ventilation
(rate ratio, 2.83; 95 percent confidence interval, 1.36 to
5.89; P0.006) or pressure-support ventilation (rate ratio,
2.05; 95 percent confidence interval, 1.04 to 4.04;
P0.04). There was no significant difference in the rate
of success between once-daily trials and multiple trials of
spontaneous breathing.
Conclusions. A once-daily trial of spontaneous breathing led to extubation about three times more quickly than
intermittent mandatory ventilation and about twice as
quickly as pressure-support ventilation. Multiple daily trials of spontaneous breathing were equally successful.
(N Engl J Med 1995;332:345-50.)
A
weaning, it is surprising that the process continues to
be managed empirically and that a standardized approach has not been developed.
Weaning techniques differ considerably from one another.3 Traditionally, intermittent trials of spontaneous
breathing, conducted one or more times a day, have
been used. Intermittent mandatory ventilation was
introduced amid claims that it was superior to the traditional weaning approach. It allows the patient to
breathe spontaneously between ventilator-delivered
breaths4; thus, weaning can be considered to begin with
the institution of mechanical ventilation. In the 1980s,
pressure-support ventilation became available5; it provides a titratable pressure boost to every inspiratory effort, and weaning is accomplished by gradually decreasing the level of the pressure boost.
Efficacy studies of weaning techniques can be faulted
for having a retrospective design, inappropriate study
LTHOUGH often lifesaving, mechanical ventilation
causes numerous life-threatening complications,1
making it important to discontinue ventilator support
at the earliest possible time. More than 40 percent of
the time that a patient receives mechanical ventilation
is spent trying to wean the patient from the ventilator.2
Considering the proportion of staff time devoted to
From the Hospital Universitario de Getafe, Madrid (A.E., F.F., I.A., M.A.C.);
Loyola University, Chicago, and Hines Veterans Affairs Hospital, Hines, Ill.
(M.J.T.); Hospital del Mar (J.F.S.) and Hospital Santa Creu i Sant Pau (I.V., S.B.),
Barcelona, Spain; Hospital Parc Tauli, Sabadell, Spain (R.F.); Hospital Germans
Trias i Pujol, Badalona, Spain (R.T.); Complejo Hospitalario de León, León,
Spain (D.C.); Hospital General de Segovia, Segovia, Spain (S.M.); and Hospital
del Río Ortega, Valladolid, Spain (J.B.). Address reprint requests to Dr. Esteban
at the Servicio de Cuidados Intensivos, Hospital Universitario de Getafe, Ctra. de
Toledo km 12’500, 28905 Getafe, Madrid, Spain.
Supported in part by a grant from the Veterans Affairs Research Service.
*The other members of the Spanish Lung Failure Collaborative Group are listed in the Appendix.
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346
THE NEW ENGLAND JOURNAL OF MEDICINE
populations, and poorly standardized protocols; in addition, most were conducted before the use of pressuresupport ventilation became widespread.6-8 Accordingly,
we performed a prospective, randomized study involving patients who were deemed ready to discontinue mechanical ventilation. In a subgroup of patients who
were difficult to wean we compared the length of time
required for weaning with the use of four techniques:
intermittent mandatory ventilation, pressure-support
ventilation, intermittent trials of spontaneous breathing
conducted several times a day, and a once-daily trial of
spontaneous breathing.
METHODS
Patients
The study was conducted between October 1992 and October
1993 in the medical–surgical intensive care units of 14 teaching hospitals in Spain. The study population consisted of 546 patients (378
men and 168 women), with a mean (SD) age of 58.218.4 years.
All received mechanical ventilation for more than 24 hours because
of acute respiratory failure. The following underlying conditions were
present: chronic obstructive pulmonary disease with acute respiratory failure in 128 patients, acute lung injury in 319, neurologic or neuromuscular disorders in 85, and miscellaneous causes in 14. The
acute lung injury was a result of surgery in 74 patients, infection in
73, heart failure in 69, multiple trauma in 51, adult respiratory distress syndrome in 23, and other pulmonary causes in 29. On admission to the intensive care unit, the patients had a mean score of
18.77.0 on the Acute Physiology and Chronic Health Evaluation
(APACHE II) scale.9 Until the first attempt was made to discontinue
ventilator support, all patients received assist–control ventilation.
The patients received mechanical ventilation for a mean of 7.56.1
days before weaning was started. No hospital contributed more than
10 percent of the study population.
To be enrolled in the study the patients had to have an improvement in or resolution of the underlying cause of acute respiratory failure; adequate gas exchange, as indicated by a ratio of the partial
pressure of arterial oxygen (PaO2) to the fraction of inspired oxygen
(FiO2) above 200 with a positive end-expiratory pressure of 5 cm
of water; a core temperature below 38ºC; a hemoglobin level above
10 g per deciliter; and no further need for vasoactive and sedative
agents. In addition, the attending physician had to agree that the patient was in stable condition and ready to be weaned from the ventilator. Patients with a tracheostomy were excluded. The study was approved by the ethics committees of the hospitals, and the patients
provided informed consent.
Protocol
Feb. 9, 1995
extubation, the patients received supplemental oxygen by face mask.
If a patient had signs of poor tolerance at any time during the trial,
assist–control ventilation was reinstituted. For the purpose of the
study, these patients were designated as being difficult to wean from
mechanical ventilation.
Even if there were no signs of distress by the end of this trial, extubation could be postponed for a maximum of 24 hours if the primary physician thought that a patient might not be able to clear secretions or protect the airway against aspiration. Patients continued
to breathe spontaneously through the T-tube circuit. If they met criteria for poor tolerance, mechanical ventilation was reinstituted.
These patients were not included in the weaning-protocol group.
Patients who were designated as being difficult to wean from mechanical ventilation were stratified according to center and randomly
assigned with the use of a random-number table10 to be weaned in
one of four ways: intermittent mandatory ventilation, pressure-support ventilation, intermittent trials of spontaneous breathing, and a
once-daily trial of spontaneous breathing. The patients were assigned
to the groups in a blinded fashion with the use of opaque, sealed,
numbered envelopes, which were opened only when a patient did not
successfully complete the two-hour trial of spontaneous breathing.
All adjustments for each weaning technique were made by the primary physician.
Intermittent Mandatory Ventilation
In the group that received intermittent mandatory ventilation, the
ventilator rate was initially set at half the frequency used during assist–control ventilation; this initial rate was 10.02.2 breaths per
minute, and mechanical breaths were synchronized with inspiratory
effort. We attempted to decrease the ventilator rate, usually by two
to four breaths per minute, at least twice a day. The ventilator rate
was decreased more rapidly if tolerated by the patient, as reflected by
clinical assessment and blood gas monitoring. Patients who tolerated
a ventilator rate of five breaths per minute for two hours without
signs of distress were extubated. A continuous positive airway pressure of 5 cm of water was permitted.
Pressure-Support Ventilation
In the group that received pressure-support ventilation, pressure
was titrated to achieve a frequency of 25 breaths per minute. Pressure support was initially set at 18.06.1 cm of water, and we attempted to reduce this level of support by 2 to 4 cm of water at least
twice a day. The pace was increased if the patient did not have signs
of distress (the same criteria were applied as in the initial trial of
spontaneous breathing, except that a respiratory frequency of 25
breaths per minute was required). Patients who tolerated pressure
support at a setting of 5 cm of water for two hours with no apparent
ill effects were extubated. A continuous positive airway pressure of
5 cm of water was permitted.
Intermittent Trials of Spontaneous Breathing
After patients were enrolled in the study, assist–control ventilation
was stopped and the patients breathed spontaneously for three minutes through a T-tube circuit, with the FiO2 set at the same level
(0.380.05) as that used during mechanical ventilation. Tidal volume and respiratory frequency were measured with a spirometer during this period. Maximal inspiratory pressure was measured three
times in succession, and the most negative value was selected. Patients who met at least two of the following criteria underwent a trial
of spontaneous breathing lasting up to two hours: maximal inspiratory pressure below 20 cm of water, tidal volume above 5 ml per
kilogram of body weight, and a respiratory frequency of less than 35
breaths per minute. Weaning was considered to have begun with the
onset of this trial. During this trial, patients received humidified oxygen-enriched gas through a T-tube circuit. The primary physician
terminated the trial if a patient had any of the following signs of distress: a respiratory frequency of more than 35 breaths per minute, arterial oxygen saturation below 90 percent, heart rate above 140 beats
per minute or a sustained increase or decrease in the heart rate of
more than 20 percent, systolic blood pressure above 180 mm Hg or
below 90 mm Hg, agitation, diaphoresis, or anxiety. Patients who had
none of these features at the end of the trial were extubated. After
Patients assigned to intermittent trials of spontaneous breathing
were disconnected from the ventilator and allowed to breathe spontaneously through either a T-tube circuit or a continuous-flow circuit
designed to provide a continuous positive airway pressure of 5 cm
of water. The duration of the trials was gradually increased, and they
were attempted at least twice a day. Between the trials, assist–control ventilation was provided for at least one hour. Patients able to
breathe on their own for at least two hours without signs of distress
were extubated.
Once-Daily Trial of Spontaneous Breathing
Patients assigned to a once-daily trial of spontaneous breathing
were disconnected from the ventilator and allowed to breathe spontaneously through a T-tube circuit for up to two hours each day. If
signs of intolerance developed, assist–control ventilation was reinstituted for 24 hours, at which time another trial was attempted. Patients who tolerated a two-hour trial without signs of distress were
extubated.
For all four methods, weaning was considered to have failed if
reintubation was necessary within 48 hours after extubation or if
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Vol. 332
No. 6
COMPARISON OF METHODS OF WEANING PATIENTS FROM MECHANICAL VENTILATION
extubation was not possible after 14 days of
weaning. Weaning was considered successful
if extubation was achieved within the 14-day
period and reintubation was not required
within 48 hours of extubation.
Statistical Analysis
347
Table 1. Characteristics of the Study Population at Base Line.*
CHARACTERISTIC
INTERMITTENT
MANDATORY
VENTILATION
(N  29)
PRESSURESUPPORT
VENTILATION
(N  37)
INTERMITTENT
SPONTANEOUSBREATHING TRIALS
(N  33)
ONCE-DAILY
SPONTANEOUSBREATHING TRIAL
(N  31)
Age — yr
64.213.3
59.916.4
59.116.4
65.014.3
APACHE II score
20.87.0
18.97.6
20.16.8
18.36.6
The chi-square test was used to compare
Chronic obstructive pulmonary
8 (27.6)
18 (48.6)
12 (36.4)
14 (45.2)
categorical data, and the Kruskal–Wallis test
disease —no. (%)
was used to compare continuous variables
Acute lung injury — no. (%)
19 (65.5)
17 (45.9)
18 (54.5)
14 (45.2)
among the groups. The Kaplan–Meier methNeurologic disorder — no. (%)
2 (6.9)
2 (5.4)
3 (9.1)
3 (9.7)
od was used to determine the probability of
the success of a particular method of weaning
243.557.9
242.360.3
223.661.8
229.265.6
Ratio of PaO2 to FiO2
over time.11 The relative probability of sucMaximal inspiratory pressure
25.911.9
30.716.7
31.418.7
30.813.4
cess over time was examined by a Cox pro— cm of water
12
portional-hazards model. Base-line covariTidal volume — ml/kg
5.30.9
6.61.7
5.21.8
7.42.1
ates included in the model were the weaning
Respiratory frequency — breaths/
28.45.4
26.86.4
28.95.4
29.98.4
technique, age, APACHE II score, ratio of
min
PaO2 to FiO2, maximal inspiratory pressure,
Duration of ventilator support be6.54.5†
10.88.6
11.57.4
8.45.3
spontaneous respiratory frequency, spontanefore weaning begun — days
ous tidal volume per kilogram, duration of
Time to failure of 1st spontaneous- 48.533.2
52.334.6
46.523.6
52.532.7
previous ventilator support, and the length of
breathing trial — min
time to the failure of the initial trial of spon*Plus–minus values are means SD.
taneous breathing. Backward elimination was
used to reduce the model to the subgroup of
†P  0.037 for the comparison with the other three groups.
factors that made statistically significant contributions to variation in the time required
for successful weaning. Data were censored on 2 patients who died
ration of ventilatory support before weaning was beduring the study, 2 patients in whom weaning was interrupted begun, which was shorter in the patients who received incause of intercurrent illness, 23 patients who required reintubation
termittent mandatory ventilation than in the other
within 48 hours of extubation, and 11 patients who were still receivgroups (Table 1).
ing ventilator support on day 14. We calculated that 31 patients were
Kaplan–Meier plots of the probability of successful
needed in each group to detect at a power of 80 percent a difference
in weaning time between groups of two days, with a two-tailed alpha
weaning with the use of each technique are shown
error of 0.05. Data are presented as means SD, medians, or proporin Figure 1, and the associated median times to suctions, as appropriate.
Of the 546 study patients, 416 (76.2 percent) successfully underwent a two-hour trial of spontaneous
breathing, and 372 (89.4 percent) of them were immediately extubated. Of these 372 patients, 58 (15.6 percent) required reintubation within 48 hours. Extubation was postponed for 24 hours in 44 patients,
primarily because of concern about their ability to
maintain clear airways. These patients breathed
through a T-tube circuit for up to 24 hours, but 16 (36.4
percent) required reinstitution of mechanical ventilation during this period. The remaining 28 (63.6 percent) were extubated within this 24-hour period, and
only 2 required reintubation within the subsequent 48
hours.
One hundred thirty patients (23.8 percent) had signs
of poor tolerance during the initial trial of spontaneous
breathing, which lasted a mean (SD) of 50.131.2
minutes (range, 5 to 110). These patients were randomly assigned to intermittent mandatory ventilation (29
patients), pressure-support ventilation (37), intermittent trials of spontaneous breathing (33) involving the
use of a T-tube (27) or continuous positive airway pressure (6) interspersed with assist–control ventilation, or
a once-daily trial of spontaneous breathing alternating
with assist–control ventilation (31). The groups were
similar with respect to the patients’ characteristics, the
indications for mechanical ventilation, and respiratory
function; the only significant difference was in the du-
cessful extubation are listed (with first and third quartiles) in Table 2. Cox proportional-hazards regression
analysis revealed four factors that predicted the time
1.0
Probability of Successful Weaning
RESULTS
0.9
0.8
0.7
0.6
0.5
Intermittent trials
0.4
0.3
Once – daily trial
0.2
Pressure – support ventilation
0.1
Intermittent mandatory
ventilation
0.0
2
4
6
8
10
12
14
Duration of Weaning (days)
Figure 1. Kaplan–Meier Curves of the Probability of Successful
Weaning with Intermittent Mandatory Ventilation, Pressure-Support Ventilation, Intermittent Trials of Spontaneous Breathing,
and a Once-Daily Trial of Spontaneous Breathing.
After adjustment for base-line characteristics in a Cox proportional-hazards model, the rate of successful weaning with a
once-daily trial of spontaneous breathing was 2.83 times higher
than that with intermittent mandatory ventilation (P0.006) and
2.05 times higher than that with pressure-support ventilation
(P0.04).
The New England Journal of Medicine
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Copyright © 1995 Massachusetts Medical Society. All rights reserved.
348
THE NEW ENGLAND JOURNAL OF MEDICINE
Table 2. The Length of Time from the Initiation of
Weaning to Successful Extubation in the Four
Groups.
WEANING TECHNIQUE
MEDIAN
FIRST
THIRD
QUARTILE QUARTILE
days
Intermittent mandatory ventilation
Pressure-support ventilation
Intermittent trials of spontaneous
breathing
Once-daily trial of spontaneous
breathing
5
3
11
4
3
2
2
12
6
3
1
6
Feb. 9, 1995
support ventilation was not significantly different from
that with intermittent mandatory ventilation (rate ratio,
1.38; 95 percent confidence interval, 0.68 to 2.79;
P= 0.32).
Table 4 lists outcomes for the various techniques.
More patients in the group that received intermittent
mandatory ventilation required continued ventilatory
support on the 14th day than in the groups that received once-daily trials (P=0.07) or intermittent trials
(P=0.06) of spontaneous breathing. The rates of extubation and reintubation did not significantly differ between the four groups.
DISCUSSION
required for successful weaning: age (P0.02), the duration of ventilatory support before weaning was begun
(P0.005), the time to the failure of the first trial of
spontaneous breathing (P0.001), and weaning technique (Table 3). The adjusted rate of successful weaning was higher with a once-daily trial of spontaneous
breathing than with intermittent mandatory ventilation
(rate ratio, 2.83; 95 percent confidence interval, 1.36 to
5.89; P0.006) or pressure-support ventilation (rate ratio, 2.05; 95 percent confidence interval, 1.04 to 4.04;
P0.04) but not significantly different from that with
intermittent trials of spontaneous breathing (rate ratio,
1.24; 95 percent confidence interval, 0.64 to 2.41;
P0.54). The adjusted rate of successful weaning with
intermittent trials of spontaneous breathing was higher
than that with intermittent mandatory ventilation (rate
ratio, 2.28; 95 percent confidence interval, 1.11 to 4.68;
P0.024), but it was not significantly different from
that with pressure-support ventilation (rate ratio, 1.66;
95 percent confidence interval, 0.87 to 3.16; P=0.126).
The adjusted rate of successful weaning with pressureTable 3. Rate of Successful Weaning with the Various Techniques and According to Base-Line Characteristics.*
VARIABLE
Weaning technique
Once-daily trial of spontaneous breathing vs. intermittent mandatory ventilation
Once-daily trial of spontaneous breathing vs. pressuresupport ventilation
Once-daily trial of spontaneous breathing vs. intermittent trials of spontaneous
breathing
Duration of ventilator support
before weaning begun
(1-day increments)
Time to failure of first trial of
spontaneous breathing
(10-min increments)
Age (10-yr increments)
RELATIVE RATE OF
SUCCESSFUL WEANING
(95% CONFIDENCE
INTERVAL)
P VALUE
2.83 (1.36–5.89)
0.006
2.05 (1.04–4.04)
0.04
1.24 (0.64–2.41)
0.54
0.94 (0.90–0.98)
0.005
1.15 (1.07–1.24)
0.001
0.83 (0.71–0.96)
0.02
*Proportional-hazards regression analysis was used to estimate the 95
percent confidence interval of the relative rate of successful weaning.
This study has two major findings. First, in a selected group of patients who were difficult to wean from
mechanical ventilation, the rate of successful weaning
depended on the technique employed: a once-daily trial
of spontaneous breathing led to extubation about three
times more quickly than intermittent mandatory ventilation and about twice as quickly as pressure-support
ventilation. There was no significant difference in the
rate of success between a once-daily trial and multiple
daily trials of spontaneous breathing or between intermittent mandatory ventilation and pressure-support
ventilation. Second, ventilator support was discontinued without any special weaning technique in two
thirds of an unselected group of patients, and only a
small proportion required reintubation within 48 hours.
Intermittent Mandatory Ventilation
Several advantages have been claimed for intermittent mandatory ventilation as a weaning technique: it
is supposed to prevent a patient from “fighting” the
ventilator, reduce respiratory-muscle fatigue, and expedite weaning.4,13 However, there are few data to support
these claims.14 Intermittent mandatory ventilation is
usually delivered in a synchronized manner with demand-valve circuitry, which increases the work of
breathing.14,15 The intermittent nature of assistance
also poses a problem. It was previously assumed that
the degree of respiratory-muscle rest was proportional
to the level of machine assistance. However, recent evidence indicates that respiratory-sensor output does
not adjust to breath-to-breath changes in respiratory
load,16,17 and intermittent mandatory ventilation may
therefore contribute to the development of respiratorymuscle fatigue or prevent recovery from it.
Studies of the efficacy of intermittent mandatory
ventilation in weaning have serious limitations. Schachter et al.6 compared it with conventional ventilation and
noted no difference between the two techniques in the
duration of ventilator support. Their study suffers from
a retrospective design, nonuniform study groups, and
inadequate description of the protocol. Hastings et al.7
compared trials of spontaneous breathing with intermittent mandatory ventilation at a fixed rate (4 breaths
per minute) in patients in stable condition after cardiac
surgery. The length of time to extubation was similar in
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Vol. 332
No. 6
COMPARISON OF METHODS OF WEANING PATIENTS FROM MECHANICAL VENTILATION
Table 4. Outcomes in Patients Who Were Difficult to Wean from
Mechanical Ventilation.*
WEANING TECHNIQUE
SUCCESSFUL
WEANING AND
EXTUBATION
REINTUBATION
CONTINUED MECHANICAL
VENTILATION AFTER
14 DAYS
no. of patients (%)
Intermittent mandatory
ventilation
Pressure-support ventilation
Intermittent trials of spontaneous breathing
Once-daily trial of spontaneous breathing
20 (69.0)
4 (13.8)
5 (17.2)
23 (62.2)
27 (81.8)
7 (18.9)
5 (15.2)
4 (10.8)
1 (3.0)
22 (71.0)
7 (22.6)
1 (3.2)
*The percentages do not total 100 percent in the groups that received pressure-support ventilation and a once-daily trial of spontaneous breathing because one patient died in each group
and weaning was interrupted because of an intercurrent illness in two patients in the pressuresupport group.
the two groups — approximately 2.6 hours. Their study
provides little insight, however, because 24 hours had
already elapsed since the operation and the patients
had good pulmonary function; thus, little difficulty in
weaning was anticipated. In patients in stable condition
who received ventilator support for 3.6 days, Tomlinson
et al.8 found that the duration of weaning was similar
with spontaneous-breathing trials and intermittent
mandatory ventilation — approximately 5.6 hours.
This study was weighted toward patients who received
short-term ventilatory support, and two thirds of those
weaned within 2 hours were patients who received ventilatory support for less than 72 hours postoperatively.
In contrast, we studied difficult-to-wean patients who
had received mechanical ventilation for 6.54.5 days.
Although most patients could theoretically have met
the extubation criteria within 24 hours of study entry,
17 percent were receiving ventilatory support after 14
days. Weaning took longer than in either of the trials
of spontaneous breathing.7,8 Despite the use of randomization, the patients in the group assigned to intermittent mandatory ventilation had received ventilation for
a shorter time than the patients in the other groups.
This actually resulted in a bias in their favor, since
weaning was accomplished more rapidly in patients receiving short-term support.
Pressure-Support Ventilation
Pressure-support ventilation is commonly used to
counteract the work of breathing imposed by endotracheal tubes and ventilator circuits. Theoretically, this
should help with weaning, because a patient who is
comfortable at the compensatory level of pressure support should be able to sustain ventilation after extubation. However, the level of pressure support necessary
to eliminate the work imposed by endotracheal tubes
and ventilator circuits varies considerably (from 3 to 14
cm of water)18,19; thus, any prediction of a patient’s ability to sustain ventilation after extubation is likely to be
misleading.
Brochard et al.20 recently reported that the duration
of weaning was significantly shorter with pressure sup-
349
port (5.73.7 days) than with intermittent mandatory
ventilation (9.98.2 days) or trials of spontaneous
breathing (8.58.3 days). In contrast, we found that
weaning with pressure-support ventilation took longer
than weaning with a once-daily trial of spontaneous
breathing and was not superior to weaning with intermittent mandatory ventilation. We suspect that the apparent superiority of pressure support in the study by
Brochard et al. was due to the constrained manner in
which they used other techniques. Patients had to tolerate an intermittent mandatory ventilation rate of
4 breaths per minute for at least 24 hours before being extubated. This poses a considerable ventilatory
challenge and is not the usual approach to this technique.3,4,14,21 In contrast, we extubated patients when
they tolerated a ventilator rate of five breaths per
minute for two hours. In the study by Brochard et al.,
physicians could request up to three trials of spontaneous breathing over a 24-hour period, each lasting
2 hours, before deciding to extubate a patient. Again,
this is a considerable ventilatory challenge — especially
in patients who have already had difficulty in weaning.
We consider the findings of their study and ours to be
complementary. Both show that the pace of weaning
depends on the manner in which a technique is employed. When intermittent mandatory ventilation and
spontaneous-breathing trials are used in a constrained
manner, weaning is slower than with pressure-support
ventilation.20 Weaning is expedited when a trial of
spontaneous breathing is attempted once a day. In both
studies, the results pertain to specific regimens for each
weaning technique and cannot be extrapolated to other
regimens using these techniques.
Trials of Spontaneous Breathing
Some physicians gradually increase the duration of
spontaneous-breathing trials while reinstituting mechanical ventilation between trials. Other physicians go
directly from offering a high level of ventilatory assistance to a trial of spontaneous breathing, and if the trial
is successful, extubate the patient without any further
weaning. In the present study, two thirds of the patients
initially enrolled were extubated after their first trial of
spontaneous breathing. A once-daily trial of spontaneous breathing also allowed speedier weaning than approaches offering partial ventilatory support. This approach simplifies management, since a patient’s ability
to breathe spontaneously without ventilatory support
needs to be assessed only once a day. In contrast, with
intermittent mandatory ventilation and pressure-support ventilation, ventilator settings must be adjusted repeatedly and each adjustment is usually followed by an
arterial-blood gas measurement.
An implied goal of the various weaning techniques is
to recondition respiratory muscles that may have been
weakened during the period of mechanical ventilation.
Theoretically, a once-daily trial of spontaneous breathing and a prolonged period of rest may be the most effective method of eliciting adaptive changes.22,23 This
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350
THE NEW ENGLAND JOURNAL OF MEDICINE
approach meets the three principal requirements of a
conditioning program: overload, specificity, and reversibility.22 During the trial, patients breathe against an elevated intrinsic load, thus satisfying the overload requirement. Specificity is also satisfied, in that the trial
is an endurance stimulus and the desired objective is
enhanced endurance. Finally, the use of a daily trial
prevents regression of the adaptive changes. It must be
emphasized that this reasoning is based on indirect evidence and that the effect of different weaning techniques on respiratory-muscle reconditioning has not
been investigated.
We are indebted to Amal Jubran, M.D., and Franco Laghi, M.D.,
for their careful review of the manuscript; to Victor Abraira and William Henderson, Ph.D., for review of the statistical analysis; and to
Alejandro Fernandez for artwork.
APPENDIX
The other members of the Spanish Lung Failure Collaborative
Group are as follows: F. del Nogal and A. Algora (Hospital Severo
Ochoa, Leganés); E. Palazón and M. Cerón (Hospital Universitario
de Murcia, Murcia); J. Ibañez and J.M. Raurich (Hospital Son Dureta, Palma de Mallorca); J. Gudín and J. Cebrián (Hospital La Fé, Valencia); G. González and J.A. Gómez Rubi (Hospital Virgen de la Arrixaca, Murcia); F. Iturbe (Hospital Arnau de Vilanova, Lleida);
A. Vazquez (Hospital del Mar, Barcelona); P. Saura (Hospital Parc
Tauli, Sabadell); J. Gener (Hospital Germans Trias i Pujol, Badalona); D. Fontaneda (Complejo Hospitalario de León, León); V. Sagredo (Hospital General de Segovia, Segovia); and M.J. Prieto (Hospital
del Río Ortega, Valladolid) — all in Spain.
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