Despite the many technological advances in our profession during the last two decades, mechanical ventilation still remains one of the most challenging aspects of our field. Weaning or liberating patients from mechanical ventilation offers additional challenges that require excellent assessment skills as well as demonstrated competence using these new technologies. While often making our practice more efficient by facilitating safer ventilation and/or weaning, these same advances also make it more challenging, since the additional improvements also provide more choices for respiratory therapists. In many cases, the “new” modes or advanced technologies have never been proven to be more effective than traditional methods. Instead, they add to the current perplexing volume of names in our ventilator management lexicon serving to confuse and confound practitioners and students alike; therefore, demystifying and simplifying the weaning processes by designing a “patient centered,” therapist-driven protocol (TDP) would prove beneficial to patients and practitioners.1,2

Jogging the Memory

Many processes in health care are simplified by using acronyms to remind practitioners of the correct order of steps for a procedure, such as airway, breathing, circulation, and defibrillation during basic cardiac life support (BCLS) that is denoted by the acronym ABCD. This acronym could also be used throughout a ventilator weaning protocol by simply substituting and/or adding a few words. For example, “A” would represent assessment and airway; “B,” breathing and blood gases; “C,” circulation, comorbidities, and comfort level; and “D,” diffusion. These letters can be practical reminders for the important factors that must be considered before, during, and after weaning as well as prior to extubation.

The ABCD model may be useful in simplifying the weaning process in conjunction with the evidence-based weaning guidelines published in Chest,3 wherein a task force facilitated by the American College of Chest Physicians (ACCP), the American Association for Respiratory Care (AARC), and the Society of Critical Care Medicine (SCCM) presented a meta-analysis of the current evidence-based literature on weaning. The panel’s recommendations were intended to provide evidence-based practice guidelines that could serve as the framework for developing weaning protocols. Neil MacIntyre, MD, from Duke University Medical Center, Durham, NC, who was the chairman of the ACCP/AARC/SCCM Task Force on Ventilator Weaning and Discontinuation, cited four themes from the panel’s 12 recommendations.

The main themes revolve around conducting frequent patient assessment, which should include an ongoing reevaluation of patients’ overall medical management, since comorbidities can influence ventilator dependency. According to MacIntyre, ventilatory support should be aimed at “maximizing patient comfort and unloading the respiratory muscles. If patients require prolonged ventilatory support, these patients should be sent to specialized facilities that can provide a gradual reduction of support. In addition, evidence also supported the concept of therapist-driven protocols as an effective alternative to physician-managed protocols.3,4

Incorporating the main themes from the report with the ABCD model, the assessment process for weaning would include assessing for adequate exchange gas (D-diffusion), hemodynamic stability (C-circulation), and capability to initiate an inspiratory effort (B-breathing). In addition, assessing for an intact airway (A-airway and/or assessment) must be included prior to extubation. While the literature is very clear that weaning does not guarantee or predict extubation success, most would agree the intent is to proceed with extubation after successfully weaning a patient. Since a compromised airway could result in a failed weaning attempt, it seems reasonable to include airway assessment (A) in the weaning protocol to avoid reintubation and/or prolonging ventilation. According to recent studies, it is reasonable and beneficial to consider a tracheostomy earlier in the process, as it expedites weaning when compared to endotracheal or nasotracheal intubation, thus reducing morbidity, mortality, and costs associated with mechanical ventilation.5-7/p>

According to Protocol

Is The Patient Ready?

  1. Evidence for some reversal of the underlying cause of respiratory failure.
  2. Adequate oxygenation (Pao2/Fio2 ≥150-200; requiring positive end-expiratory pressure ≤5-8 cm H2O; Fio2 ≤0.4-0.5) and pH (≥7.25).
  3. Hemodynamic stability as defined by the absence of active myocardial ischemia and the absence of clinically important hypotension (a condition requiring no vasopressor therapy or therapy with only low-dose vasopressors such as dopamine or dobutamine >5 mg/kg/min).
  4. The capability to initiate an inspiratory effort.

Table 1. Excerpt from the collective task force facilitated by the American College of Chest Physicians, the American Association for Respiratory Care, and the Society of Critical Care Medicine. Respir Care. 2002;47:69-90. With permission

A protocol must be expeditious and safe, because premature weaning and delayed weaning can cause harm. In addition, a protocol should reflect a standardized method for liberating patients from mechanical ventilation to improve the continuity of care and reduce the morbidity, mortality, and associated costs.5,8 While a standardized protocol may not work in every case, a well-designed, patient-centered, therapist-driven protocol can successfully liberate a patient in 60% to 70% of the cases, according to the most recent studies.9 To ensure successful liberation for mechanical ventilation, an initial assessment of the four criteria outlined by the task force in Table 1 should be required in the protocol, since it provides the best evidence for weaning readiness.3

Adapting the suggested ABCD model to the criteria in Table 1, a series of logical queries can be reflected in each letter. A) airway or assessment: Is the airway intact? Does the initial assessment suggest weaning? B) breathing: Is the patient able to initiate breathing? C) hemodynamic stability: Is the cardiovascular system stable? D) diffusion: Has the underlying respiratory failure issue been resolved? Is gas exchange or diffusion adequate? If all of these can be answered in the affirmative, proceeding with the next step in the weaning process is desirable; however, many practitioners may want to assess additional parameters that have traditionally been used.

In this simplified weaning process, traditional weaning parameters focusing on complex physiologic measurements, such as muscle strength, respiratory system mechanics, metabolic parameters, and work of breathing, add very little to the assessment of individual patients for discontinuation potential. This also applies to the more recent complex measurements used today, such as the CROP (compliance, rate, oxygen, and pressure) index and rapid shallow breathing index (RSBI). In fact, the task force further recommended that no single parameter be used to judge the success or failure of a weaning trial. For example, the frequency/tidal volume ratio (f/Vt) is commonly used to predict weaning success; however, recent literature suggests that it actually slows the weaning process. This delay may occur when the practitioner is focusing on the numbers rather than the patient.3,5 These parameters alone cannot determine readiness but can be used to support the decision to discontinue ventilation or to determine the cause of weaning failure (muscular failure versus muscle weakness); however, studies show that the predictive value for the traditional parameters is quite low.4,10

It’s About the Patient

When Should The Trial Be Stopped?

*A and C: Assessment and Comfort noted by the degree of respiratory distress (any two of the following):

Diaphoresis and signs of anxiety.

Pulse >120% of rate at 6 am >5 minutes.

Marked use of accessory muscles.

Abdominal paradox.

Marked complaint of dyspnea.

B: RR >35 (may exceed 35 for more than 5 minutes)

D: Spo2 <88% (<5 minutes at <88% may be tolerated)

Table 2. ABCD model adapted using the information from the collective task force facilitated by the American College of Chest Physicians, the American Association for Respiratory Care, and the Society of Critical Care Medicine. Respir Care. 2002;47:69-90.

*Note: A for airway is not considered at this point.

In a more recent review of the literature, MacIntyre et al stressed the most useful indicator of ventilator discontinuation potential is the clinical assessment, which includes respiratory pattern, cardiovascular response, gas exchange, and comfort of a patient during a 30- to 120-minute spontaneous breathing trial (SBT). Focusing on such things as development of anxiety or diaphoresis is vitally important, since these outward signs are reflections of the “numbers on the inside.”4,5 While the value of a laboratory number should not be minimized, the numbers only confirm the bedside assessment of the patient. The essence of the recommendation is to become patient centered, which requires focusing on the general appearance of the patient while using very basic values during the trial to simplify the process. If the 120-minute trial is questionable, it should be considered a failure according to MacIntyre.5,9

The SBT should be done without substantial ventilatory support, using only a mode of partial support. The initial SBT should be brief and used to assess the capability of continuing with a formal SBT. The initial trial could last 1 to 5 minutes while on continuous positive airway pressure (CPAP) or a T-piece. If this is tolerated, then the formal SBT protocol can be conducted. In today’s environment, clinicians would likely choose the safety of maintaining a patient on the ventilator rather than utilizing a T-piece, since advanced technology offers close monitoring with alarms such as apnea, high and low volumes, high or low minute ventilation, and high respiratory rate. Utilizing the ventilator over a T-piece also offers the ability to use the low-level pressure support (5 to 7 cm H2O) and/or low-level CPAP (5 cm H2O) during the SBT as recommended by the task force.9,10

During the SBT, it is important to monitor patients’ tolerance and comfort level by once again using the ABCD model. This assessment should include the respiratory pattern (B), adequacy of gas exchange (D), hemodynamic stability (C), and patient comfort (C). If SBT is tolerated for 30 minutes, clinicians should consider permanent ventilator discontinuation and extubation. If there is any uncertainty, however, clinicians may choose to extend it up to, but no more than, 120 minutes. The trial can be stopped when patients have either satisfied the criteria for a successful SBT or failed to tolerate the SBT.3,9 Weaning intolerance can be adapted to the ABCD model as illustrated in Table 2.

As noted in Table 2, these are not overly complex measurements and can quickly be observed to make a decision. If weaning failure does occur during the SBT, patients should be returned to a stable, nonfatiguing, comfortable form of ventilatory support and reevaluated in 24 hours.3,9,12 Although SIMV is traditionally used for this purpose, it may not be the best mode for progressive weaning unless combined with pressure support ventilation (PSV). Evidence suggests that SIMV without PSV may slow weaning, since it will not adequately unload the muscles during rest periods.5 When considering other modes, it is important to make the selection based on adequate muscle unloading. For example, modes such as CPAP+PSV, SIMV+PSV, or A/C with volume or pressure targeting would be advantageous to reduce the ventilatory load imposed by the ventilator and by the endotracheal tube during the rest periods. The rest period should allow the patient to recover fully before beginning the next SBT. Additionally, any weaning failure should have the cause determined during this time period.3,13

Using the simplified approach, respiratory therapists could explore the potential reasons for failure, which may involve respiratory muscle failure (B), excessive secretions in the conducting airways (A), unresolved lung condition (D), cardiovascular instability (C), or other comorbidities (C). Identifying the weaning failure may delay the next SBT attempt; but once the cause of failure has been reversed, the SBT may be continued. Subsequent SBTs should be performed every 24 hours according to the panel’s recommendation. This method of weaning should also apply to postoperative patients, although additional protocols optimizing sedation and analgesia targeted at early extubation would be required.3

While most patients do not require a gradual weaning process, repeated weaning failures may necessitate a more conservative approach, thus extending the time on the ventilator. The gradual approach to weaning can comprise as much as 40% to 60% of the total ventilator time.14 Developing an approach beyond the SBTs should be included as part of the protocol or as a separate prolonged mechanical ventilation (PMV) weaning protocol. Once a patient has been weaned, an airway assessment should be included, since there may still be a need for the artificial airway.9,15

Weaning failures are often the result of problems associated with the upper airway. Reintubation occurs, not because patients fail to wean but rather fail to maintain a patent airway, which can be avoided and reversed in most cases. Early tracheostomy should be considered to expedite weaning and to avoid the consequences of prolonged ventilation. In the absence of irreversible lung disease and airway issues, studies indicate therapist-driven weaning protocols are effective in reducing weaning times when compared with physician-directed weaning.2,4 Unfortunately, only one therapist-driven protocol study has been published on PubMED in the last 5 years, while 787 were published on ventilator weaning in general. This one study is among 76 articles published specifically on ventilator weaning protocols, thus it represents only 1.3% of the articles devoted to TDPs. Despite this weakness in the literature, research is quite clear that a well-constructed weaning protocol is effective when implemented by nonphysicians, so more specific research may not be needed.2,5


Regardless of the paucity of TDPs and ventilator weaning articles in the literature, it is important to have a working model constructed from the best evidence available. The ABCD model may offer a unique way to demystify the process and structure a “patient centered,” therapist-driven protocol to help your staff remain focused on the fundamentals of weaning, if you do not currently use one or if you need to revise the one you are currently using. For any protocol to be effective, five basic criteria must be achieved: 1) the respiratory therapy staff must be extremely competent at physical assessment in order to determine readiness for weaning and extubation; 2) they must possess a thorough knowledge of the pathophysiology involved in weaning failures; 3) they should utilize a simpler is better approach when performing clinical assessment by using the most pertinent information; 4) they should ensure adequate ventilatory support for patients aimed at providing a nonfatiguing breathing load when not engaged in a SBT; 5) they should ensure that the weaning process is safe and expeditious.2,5,9,16 If these criteria are met, a well-designed protocol can liberate the majority of patients from the ventilator while improving continuity of care and reducing morbidity, mortality, and costs associated with mechanical ventilation. In fact, it may be as simple as A,B,C—and D.

Bill Croft, PhD, RRT, RCP, is the Health Sciences Department chair, program director, and professor of respiratory therapy at Sandhills Community College, Pinehurst, NC. He is also a Diplomate in the College of Education: American Association of Integrative Medicine and Certified Whole Health Educator. For further information, contact [email protected]


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