Well-designed ventilator weaning protocols are only as effective as the respiratory staff implementing them.
Weaning patients from mechanical ventilation is one of the most challenging and rewarding aspects of respiratory care. Since the development of the first therapist-driven protocols, a myriad of weaning protocols have been developed and implemented to improve the weaning process. When developing a protocol, it is highly desirable to ensure that it is both expeditious and safe, because both premature weaning and delayed weaning can cause harm. Protocols should also be designed to standardize the method for liberating patients from mechanical ventilation to improve the continuity of care, which can reduce the morbidity, mortality, and costs associated with mechanical ventilation.1,2
Without protocols, there are no clear written goals; therefore, it is left to the experiences of the individuals on each shift or to the attending physicians to direct the weaning process. In hospitals without protocols, the latter is most likely the norm. This inefficiency can lead to longer intensive care unit (ICU) stays, which will increase mortality, morbidity, and cost. Although this fact is supported by current research, many clinicians still disagree on the best methodology for weaning. Until recently, this disagreement was due in part to the lack of generally accepted clinical practice guidelines, which could serve as a framework for developing protocols.
In the January 2002 edition of Respiratory Care Journal, evidence-based guidelines for weaning were published in a special article reprinted from Chest based on a meta-analysis of the current literature. It was written by a collective 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). The panel of experts developed recommendations based on the current information available on weaning.1 These recommendations were intended to provide clinical practice guidelines that could serve as the framework for developing weaning protocols. The recommendations were graded based on the following:
A) Scientific evidence provided by well-designed, well-conducted, controlled trials (randomized and nonrandomized) with statistically significant results that consistently support the guideline recommendation;
B) Scientific evidence provided by observational studies or by controlled trials with less consistent results to support the guideline recommendation; and
C) Expert opinion supported the guideline recommendation, but scientific evidence either provided inconsistent results or was lacking.1
Evidence-based guidelines for weaning and discontinuing ventilatory support.
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.
Additional information that was considered useful but was not in their final recommendation included:
6) Adequate hemoglobin ( >8-10 g/dl).
7) No significant acidosis (pH >7.25).
8) Stable metabolic status (acceptable electrolytes).
9) Adequate mentation.
10) Subjective decision by the physician.
Numbers 1-4 adapted from a 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. Numbers 5-10 adapted from Epstein SK. Weaning from mechanical ventilation. Respir Care. 2002;47:454-468.
The most useful recommendations for weaning were reviewed in the editorial section of that same journal. In his editorial, Neil MacIntyre, MD, from Duke University Medical Center, Durham, NC, who is the chairman of the ACCP/AARC/SCCM Task Force on Ventilator Weaning and Discontinuation, cited four particular issues that are worth emphasizing from the panels 12 recommendations. First, the current data collected by the panel indicated that clinicians are poorly assessing ventilator discontinuation potential. He emphasized that patients deemed ventilator dependent for more than several days is the category that is most poorly assessed; therefore, there is a need for a more focused assessment strategy for such patients.
Second, he stressed that the information that is most useful as the indicator of ventilator discontinuation potential is the clinical assessment, which includes respiratory pattern, cardiovascular response, comfort/anxiety, and oxygenation of patients during 30-120 minute spontaneous breathing trials (SBTs). Contrary to popular belief, weaning parameters that focus 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.2
Third, for patients failing an SBT, there are virtually no data showing that progressive ventilator reduction strategies offer any benefit in shortening the duration of ventilator support. MacIntyre stated that it would be more cost-effective to use health care professionals to search for the reversible causes of respiratory failure rather than ritualistic attempts at gradual reductions in ventilator settings. As long as SBTs are performed every 24 hours, stable, comfortable, assisted forms of ventilatory support aimed at providing a non-fatiguing breathing load seem all that is necessary.
Last, he stressed the point that nonphysician health care professionals (HCPs), especially respiratory therapists, can effectively achieve all of these goals when operating under well-designed ventilator management protocols; therefore, weaning/discontinuation protocols designed for nonphysician HCPs (including RRTs, RNs) should be developed and implemented by ICUs.2
According to the panel recommendations, protocols should be developed that are expeditious and safe in order to reduce morbidity, mortality, and costs; therefore, respiratory therapists must be up-to-date on the best methods to use during the weaning process.1,3 Before adopting any protocol, HCPs should be aware that protocols are meant only to be guidelines. Based on the recommendations of the panel, a good protocol would include a formal clinical assessment by a staff that is competent in recognizing weaning and extubation readiness as well as understanding the pathophysiology of weaning failure; however, even the best protocols cannot and should not replace common sense.3 The experiences of seasoned clinicians are extremely important to make decisions when there is a need to step outside the protocol.
This formal assessment should be conducted on any patient receiving mechanical ventilation for >24 hours secondary to respiratory failure to determine discontinuation potential. Reversing all possible ventilatory and nonventilatory issues should be an integral part before the ventilator discontinuation process proceeds. A thorough search for all the causes that may be contributing to ventilator dependence should be undertaken, especially in patients who have failed attempts at withdrawing the mechanical ventilator.1
Predictors of Weaning
Respiratory therapists have traditionally used many predictors of weaning readiness such as maximal inspiratory pressure, vital capacity (VC), minute ventilation, respiratory rate (RR), tidal volume, and maximum voluntary ventilation. Most recently, more complex measurements have been used such as CROP (compliance, rate, oxygen, and pressure) index and rapid shallow breathing index (RSBI).1-3 Despite the value that we place on our tools of the trade, the evidence does not support their use as adequate predictors of weaning readiness.1-4
In regard to readiness, the recommendations provided a much simpler approach to the initial clinical evaluation that included the following objective criteria in order to determine readiness for weaning:
If they meet the first four criteria, the weaning process can begin; however, the decision to use these criteria must be individualized. Despite not satisfying all of the above criteria (patients with chronic hypoxemia below the thresholds cited), some patients may be ready for attempts at discontinuation of mechanical ventilation. If you carefully read the panels recommendations, you can see that they are recommending a method to determine readiness to wean with the initial criteria.
One thing is clearclinical assessment alone was not sufficient to determine readiness since clinicians may not be able to recognize the readiness to wean based on that assessment. One study cited by the panel indicated that two thirds of the patients who were ready to wean were not properly identified by clinical assessment alone.1 One of the reasons is the reliance on the traditional weaning parameters such as negative inspiratory force maneuver (NIFM), VC, and RSBI. These parameters alone can not determine readiness but could be used to support the decision to discontinue ventilation or to determine the cause of weaning failure (muscular failure vs muscle weakness).3,4
Studies show that the predictive value for the traditional parameters is quite low.3,4 Consider the possible scenarios: it is possible to get a false-positive result with patients who perform well on NIFM and VC, but fail to wean; a false-negative result may occur if patients do not meet the criteria for the NIFM and VC (due to the inability to follow instructions or airway problems) but are ready to wean. Determining readiness to wean does not mean to discontinue continuous mandatory ventilation (CMV) completely. Discontinuance from CMV will require further evaluation.
Current data indicate that 75%-77% of patients are successfully weaned when they recover from acute respiratory failure, assuming they meet the above-mentioned criteria. Most do not require any gradual weaning process; however, patients who have required prolonged mechanical ventilation (PMV) will require a more gradual approach. The gradual approach to weaning can comprise as much as 40%-60% of the total ventilator time.3 Regardless of approach, patients must meet the criteria recommended on the initial clinical assessment in order to move to discontinuance.
Additional assessments need to be conducted during and after a SBT to determine the ability to discontinue or to continue with weaning. 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 onto a formal SBT. For example, the initial trial would last 1-5 minutes while on continuous positive airway pressure (CPAP) or a T-piece. If this is tolerated, then the formal SBT protocol can be conducted. Clinicians can utilize T-piece or low-level pressure support (5-7 cm H2O) and/or low-level CPAP (5 cm H2O) during this trial. Although low synchronized intermittent mandatory ventilation (SIMV) rates were mentioned as a method to perform these trials, they did not indicate the number of breaths per minute, but most research has been done with SIMV rate <4 breaths per minute.3,4
During the SBT, it is important to monitor patients tolerance. This assessment should include the respiratory pattern, adequacy of gas exchange, hemodynamic stability, and subjective comfort. The trial can be stopped when patients have either satisfied the criteria for a successful SBT or failed to tolerate the SBT. Intolerance to weaning could be defined as:
- RR >35 (may exceed 35 for more than 5 minutes);
- Spo2 <88% (<5 minutes at <88% may be tolerated); and
- Respiratory distress (any two of the following):
- Pulse >120% of rate at 6 am >5 minutes.
- Marked use of accessory muscles.
- Abdominal paradox.
- Marked complaint of dyspnea.
If tolerated for 30 minutes, clinicians should consider permanent ventilator discontinuation and extubation; however, if there is any uncertainty, clinicians may choose to extend it up to but no more than 120 minutes.1
Seasoned therapists will recognize this as nothing more than the T-piece trials that were used before intermittent mandatory ventilation (IMV)/SIMV modes became popular. Prior to the more modern ventilator systems, therapists would conduct T-piece trials in incremental steps of 30-45-60-90-120 minutes or longer, but after each successful trial patients were returned to assist-control ventilation (A/C) for the rest periods. Research has now proven that this is an effective technique, but it also shows there are other ways to accomplish the same goal with the newer modes of ventilation to make the process safer.
Research also indicates that a 30-minute trial may be all that is needed to determine the need for ventilator discontinuance.3 One caveat concerning T-piece trials is the lack of monitoring ability. Maintaining patients on a ventilator during the SBT will allow clinicians to monitor patients more closely. An argument could be made that using a ventilator during the SBT would be expensive, but remember that they are already using the ventilator. There would be no additional equipment cost other than the electricity used.
If weaning failure does occur during the SBT, patients should be returned to a stable, nonfatiguing, and comfortable form of ventilatory support and reevaluated in 24 hours.1 In the past, clinicians often took the approach of returning patients to their previous settings prior to the trial. It would be somewhat arbitrary to return patients to the previous settings since these settings may be too low and inadequate to rest the muscles of ventilation. In fact, this practice may account for many weaning failures; therefore, upon returning patients to their original settings, evaluation of them is necessary to minimize this problem.
Minimizing any further weaning failure may also require that clinicians consider that SIMV may not be the best mode for progressive weaning. Actually, there is evidence that SIMV without PSV may slow weaning since it will not adequately unload the muscles during rest periods.3,4 It would be unreasonable not to consider the use of other modes. Choosing 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 endotracheal tube during the rest periods. The rest period should allow patients to recover fully before beginning the next SBT. Additionally, any weaning failure should have the cause determined during this time period.
Identifying the weaning failure may delay the next SBT attempt; however, once the cause of failure has been reversed, the SBT may be continued. Subsequent SBTs should be performed every 24 hours according to the panels recommendation. This method of weaning should also apply to postoperative patients; however, additional protocols optimizing sedation and analgesia targeted at early extubation would be required.1
Once a patient has been successfully weaned and before extubation, an airway assessment also should be included since there may still be a need for the artificial airway. 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, in most cases, can be avoided and reversed. Despite our best efforts, some patients will not be weaned and should be considered for a tracheostomy and permanent mechanical ventilation; however, the panel recommended that a patient requiring prolonged mechanical ventilatory support for respiratory failure should not be considered permanently ventilator dependent until 3 months of weaning attempts have failed unless there was evidence for clearly irreversible disease.1
In the absence of irreversible disease, studies have shown therapist-driven weaning protocols are effective in reducing weaning times when compared with physician-directed weaning. In order for any protocol to be effective, several concepts must be fully realized, the respiratory therapy staff must be extremely competent at physical assessment in order to determine readiness for weaning and extubation, they must possess a thorough knowledge of the pathophysiology involved in weaning failures, they should use a simpler approach to clinical assessment by using only the information that is most useful, they should ensure adequate ventilatory support for patients aimed at providing a nonfatiguing breathing load when not engaged in an SBT, and they should ensure that the weaning process is safe and expeditious. When operating under well-designed ventilator management protocols, a well-trained staff can effectively liberate the majority of patients from the ventilator while improving the continuity of care, which can reduce morbidity, mortality, and costs associated with mechanical ventilation.
Bill Croft, MS, RRT, RCP, CN, is program director and associate professor of respiratory therapy at Sandhills Community College, Pinehurst, NC.
1. MacIntyre NR, Cook DJ, Epstein SK, et al. Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians, the American Association for Respiratory Care, and the American College of Critical Care Medicine. Respir Care. 2002;47:69-90.
2. MacIntyre NR. Bringing scientific evidence to the ventilator weaning and discontinuation process: evidence-based practice guidelines. Respir Care. 2001;47:29.
3. Epstein SK. Weaning from mechanical ventilation. Respir Care. 2002;47:454-468.
4. Meade MO, Guyatt GH, Cook DJ. Weaning from mechanical ventilation: the evidence from clinical research. Respir Care. 2001;46:1408-1415.