1、Section I: GuidelinesEvidence-Based Guidelines for Weaning and DiscontinuingVentilatory Support*A Collective Task Force Facilitated by the American College of ChestPhysicians; the American Association for Respiratory Care; and theAmerican College of Critical Care MedicineChairmanNeil R. MacIntyre, M
2、D, FCCPWriting Committee on Behalf of the PanelDeborah J. Cook, MD, FCCPE. Wesley Ely, Jr., MD, MPH, FCCPScott K. Epstein, MD, FCCPJames B. Fink, MS, RRTJohn E. Heffner, MD, FCCPDean Hess, PhD, RRTRolf D. Hubmayer, MD, FCCPDavid J. Scheinhorn, MD, FCCPMembersSuzanne Burns, RN, MSN, CCRN, RRNDavid Ch
3、ao, MD, FCCPAndres Esteban, MDDouglas R. Gracey, MD, FCCPJesse Hall, MD, FCCPEdward F. Haponik, MD, FCCPMarin H. Kollef, MD, FCCPJordi Mancebo, MDConstantine Manthous, MD, FCCPArthur S. Slutsky, MD, FCCPMeg Stearn-Hassenpflug, MS, RDJames K. Stoller, MD, FCCP(CHEST 2001; 120:375S395S)Abbreviations:
4、AHCPR H11005 Agency for Healthcare Policy andResearch; ASV H11005 adaptive support ventilation; CPAP H11005 contin-uous positive airway pressure; Fio2H11005fraction of inspired oxygen;HCP H11005 health-care professional; IMV H11005 intermittent mandatoryventilation; LOS H11005 length of stay; LR H11
5、005 likelihood ratio; MMV H11005minimum minute ventilation; NPPV H11005 noninvasive positive-pres-sure ventilation; NRCU H11005 noninvasive respiratory-care unit; Pdi H11005transdiaphragmatic pressure; PEEP H11005 positive end-expiratory pres-sure; PMV H11005 prolonged mechanical ventilation; RWC H1
6、1005 regionalweaning center; SBT H11005 spontaneous breathing trial;The discontinuation or withdrawal process from me-chanical ventilation is an important clinical issue.1,2Patients are generally intubated and placed on mechanicalventilators when their own ventilatory and/or gas exchangecapabilities
7、 are outstripped by the demands placed onthem from a variety of diseases. Mechanical ventilationalso is required when the respiratory drive is incapable ofinitiating ventilatory activity either because of diseaseprocesses or drugs. As the conditions that warrantedplacing the patient on the ventilato
8、r stabilize and begin toresolve, attention should be placed on removing theventilator as quickly as possible. Although this processoften is termed “ventilator weaning” (implying a gradualprocess), we prefer the more encompassing term “discon-tinuation.”Unnecessary delays in this discontinuation proc
9、ess in-crease the complication rate for mechanical ventilation(eg, pneumonia or airway trauma) as well as the cost.Aggressiveness in removing the ventilator, however, mustbe balanced against the possibility that premature discon-tinuation may occur. Premature discontinuation carries itsown set of pr
10、oblems, including difficulty in reestablishingartificial airways and compromised gas exchange. It hasbeen estimated that as much as 42% of the time that amedical patient spends on a mechanical ventilator isduring the discontinuation process.3This percentage islikely to be much higher in patients wit
11、h more slowlyresolving lung disease processes.There are a number of important issues involved in themanagement of a mechanically ventilated patient whosedisease process has begun to stabilize and/or reverse suchthat the discontinuation of mechanical ventilation be-*Correspondence to: Neil R. MacInty
12、re, MD, FCCP, Duke Uni-versity Medical Center, Box 3911, Durham, NC 27710; e-mail:neil.macintyreduke.eduCHESTVOLUME 120 / NUMBER 6 / DECEMBER, 2001 SupplementCHEST / 120/6/DECEMBER, 2001 SUPPLEMENT 375Scomes a consideration. First, an understanding of all thereasons that a given patient required a m
13、echanical venti-lator is needed. Only with this understanding can medicalmanagement be optimized. Second, assessment tech-niques to identify patients who are capable of ventilatordiscontinuation need to be utilized. Ideal assessmenttechniques should be able to easily and safely distinguishwhich pati
14、ents need prompt discontinuation and whichneed continued ventilatory support. Third, ventilator man-agement strategies for stable/recovering patients who stillrequire some level of ventilatory support need to beemployed. These strategies need to minimize both com-plications and resource consumption.
15、 Fourth, extendedmanagement plans (including tracheotomy and long-termventilator facilities) need to be considered for the long-term ventilator-dependent patient.To address many of these issues, the Agency for Health-care Policy and Research (AHCPR) charged the McMas-ter University Evidence Based Pr
16、actice Center to performa comprehensive evidence-based review of many of theissues involved in ventilator weaning/discontinuation. Ledby Deborah Cook, MD, an exhaustive review of severalthousand articles in the world literature resulted in acomprehensive assessment of the state of the literature in1
17、999.4At the same time, the American College of ChestPhysicians, the Society for Critical Care Medicine, and theAmerican Association for Respiratory Care formed a taskforce to produce evidence-based clinical practice guide-lines for managing the ventilator-dependent patient dur-ing the discontinuatio
18、n process. The charge of this taskforce was to utilize the McMaster AHCPR report as wellas their own literature review to address the following fiveissues: (1) the pathophysiology of ventilator dependence;(2) the criteria for identifying patients who are capable ofventilator discontinuation; (3) ven
19、tilator managementstrategies to maximize the discontinuation potential; (4)the role of tracheotomy; and (5) the role of long-termfacilities. Review/writing teams were formed for each ofthese issues.From these evidence-based reviews, a series of recom-mendations were developed by the task force, whic
20、h arethe basis of this report. Each recommendation is followedby a review of the supporting evidence, including anassessment of the strength of the evidence (Table 1). Asthere were many areas in which evidence was weak orabsent, the expert opinion of the task force was relied onto “fill in the gaps.
21、” Consensus was reached, first, by teamdiscussions and, later, through the repeated cycling of thedraft through all members of the task force.Both the McMaster AHCPR group and the task forcerecognized the needs for the future. These include morerandomized controlled trials to look at a number of iss
22、ues.Among the more important questions that need answeringare the following: (1) Which criteria are the best indicatorsof the reversal of respiratory failure in the screeningprocess? (2) What factors are involved in ventilator depen-dence, and which measurement techniques are mostuseful in determini
23、ng ultimate success in the discontinu-ation process? (3) In balancing discontinuation aggressive-ness against the risks of premature discontinuation, what isa reasonable reintubation rate in patients who recentlyhave been removed from ventilatory support? (4) What isthe value of trying to reduce the
24、 levels of partial ventilatorsupport in stable/recovering patients who have failed adiscontinuation assessment? (5) What role do tracheoto-mies have in facilitating the discontinuation process? (6)What is the role of the long-term facility, and when shouldpatients be transferred to such facilities?P
25、athophysiology of VentilatorDependenceIntroductionPatients require mechanical ventilatory support whenthe ventilatory and/or gas exchange capabilities of theirrespiratory system fail. This failure can be the result ofprocesses both within the lung as well as in other organsystems, most notably the C
26、NS and the cardiovascularsystem. Although patients may be dependent on ventila-tory support for brief periods of anesthesia or neuromus-cular blockade, the term “ventilator dependent” is usuallyreserved for patients with a need for mechanical ventila-tion beyond 24 h or by the fact that they have fa
27、iled torespond during discontinuation attempts. Under thesecircumstances, the clinical focus should be not only onventilator management but also should include a searchfor all of the possible reasons (especially potentially re-versible ones) that may explain the ventilator dependency.Recommendation
28、1: In patients requiring mechanicalventilation for H11022 24 h, a search for all the causes that maybe contributing to ventilator dependence should be under-taken. This is particularly true in the patient who hasfailed attempts at withdrawing the mechanical ventilator.Reversing all possible ventilat
29、ory and nonventilatory is-sues should be an integral part of the ventilator discontin-uation process.Evidence (Grade B)There are a number of specific reasons why patientsmay be ventilator-dependent (Table 2). Determiningwhich factor or factors may be involved in a given patientrequires both clinical
30、 awareness of these factors as well asfocused clinical assessments. The search for the underly-ing causes for ventilator dependence may be especiallyimportant if previously unrecognized, but reversible, con-ditions are discovered.Table 1Grades of EvidenceGrades DescriptionA Scientific evidence provi
31、ded by well-designed, well-conducted, controlled trials (randomized andnonrandomized) with statistically significant results thatconsistently support the guideline recommendationB Scientific evidence provided by observational studies or bycontrolled trials with less consistent results to supportthe
32、guideline recommendationC Expert opinion supported the guideline recommendation,but scientific evidence either provided inconsistentresults or was lacking376S Evidence-Based Guidelines for Weaning and Discontinuing Ventilatory SupportNeurologic Issues: The ventilatory pump controller inthe brainstem
33、 is a rhythm and pattern generator, whichreceives feedback from cortical, chemoreceptive, andmechanoreceptive sensors. The failure of this controllercan come from several factors.512These factors can beeither structural (eg, brainstem strokes or central apneas)or metabolic (eg, electrolyte disturban
34、ces or sedation/narcotic usage13,14). The failure of the peripheral nervesalso can be the result of either structural factors15ormetabolic/drug factors.16,17A unique neurologic dysfunc-tion that also could cause ventilator dependence is ob-structive sleep apnea, in which an artificial airway may ben
35、ecessary to maintain airway patency.10,11Respiratory System Muscle/Load Interactions: Often,patients who exhibit ventilator dependence do so becausethere appears to be a mismatch between the performancecapacity of the ventilatory pump and the load placed on it(ie, the capacity/load imbalance hypothe
36、sis).1823There isample evidence that ventilatory pump performance maybe impaired in ventilator-dependent patients becauseventilatory muscles are weak. This may be a consequenceof atrophy and remodeling from inactivity.2,24It also maybe a consequence of injury from overuse and of insultsassociated wi
37、th critical illness neuropathy and myop-athy.2529A number of drugs (eg, neuromuscular blockers,aminoglycosides, and corticosteroids) also can contributeto myopathy,17,3032as can various metabolic derange-ments (see below). Finally, dynamic hyperinflation can putventilatory muscles in a mechanically
38、disadvantageousposition.33In a number of studies, patients who failed torespond to a withdrawal from mechanical ventilationtended to be weaker (ie, they had a lower performancecapacity) than those who succeeded,3449but, in general,the within-group variability in respiratory muscle strengthwas too la
39、rge to justify general conclusions.Ventilatory muscle fatigue also could contribute to poormuscle performance. However, the role of fatigue inventilator dependence is not well-understood, and thestudies performed to date21,26,5054have failed to delineatethe sensitivity and specificity of specific fa
40、tigue tests inventilator-dependent patients. Ventilatory support reduc-tion-related changes in transdiaphragmatic pressure (Pdi),respiratory rate, and thoracoabdominal dyssynchrony areclearly not specific manifestations of respiratory musclefatigue.5560The most promising diagnostic test of dia-phrag
41、m contractility to date is the Pdi measurementduring twitch stimulation of the phrenic nerves.21,61How-ever, too few patients have been studied with this tech-nique to draw any meaningful conclusions about theprevalence of diaphragm fatigue that is attributable toventilator dependence.The load on th
42、e ventilatory muscles is a function ofventilation demands and respiratory system mechanics (ie,primarily compliance and resistance). Normal minuteventilation during spontaneous breathing is generallyH11021 10L/min, normal respiratory system compliance (ie, tidalvolume/static inflation pressure) is g
43、enerally H11022 50 to 100mL/cm H2O, and normal airway resistance (ie, peak staticinflation pressure/constant inspiratory flow) is generallyH11021 5to15cmH2O/L/s. Ventilation demands can increaseas a consequence of increased oxygen demands in patientswith sepsis or increased dead space in patients wi
44、thobstructive diseases. Compliance worsening can be aconsequence of lung edema, infection, inflammation, orfibrosis and of chest wall abnormalities such as edema orsurgical dressings. Resistance worsening can be a conse-quence of bronchoconstriction and airway inflammation.Additional load also can b
45、e imposed by narrow endotra-cheal tubes and by insensitive or poorly responsive venti-lator demand valves.The load imposed by ventilation demands interactingwith respiratory system mechanics can be expressed asrespiratory work, the pressure-time integral, or the changein metabolism (eg, the oxygen c
46、ost attributable to breath-ing). Many studies19,35,6266show that patients who areventilator-dependent tend to have larger respiratory mus-cle loads than do patients who can be withdrawn frommechanical ventilation. In patients with airways obstruc-tion, the load imposed by dynamic hyperinflation hasr
47、eceived particular attention as an important contributorto ventilator dependence.23,33,65,6771As is true for mea-sures of ventilatory pump capacity, however, most inves-tigators report a considerable overlap in load parametersbetween patients with different discontinuation outcomes.Patients who go o
48、n to fail to respond to ventilatorwithdrawal attempts because of a capacity/load imbalancetend to display rapid, shallow breathing patterns.2,72,73Thispattern is advantageous from an energetics perspective,but it is also associated with increased dead space andwasted ventilation, and hence with impa
49、ired CO2elimina-tion. Chemoreceptive and mechanoreceptive feedbackinto the neural control of breathing is not well-understood,and thus it is difficult to distinguish whether this breathingpattern is a consequence of a reduced respiratory drive perbreath or an inability of ventilatory muscles to respond toan appropriately increased neural stimulus.19,62,65,71,72Metabolic Factors and Ventilatory Muscle Function:Nutrition, electrolytes, hormones, and oxygen transportare all metabolic factors that can affect ventilatory musclefunction. Inadequate nutrition leads to protein catabolisman
