• Short- versus long-term weaning is not clearly defined in the literature. Further, definitions vary in studies, which makes comparisons difficult. Regardless, patients who need mechanical ventilation for longer than 3 consecutive days clearly are at risk of needing mechanical ventilation for 12 to 14 days or longer.¹³ As duration of ventilation increases, the risk of iatrogenic (i.e., hospital-acquired) complications increases, all of which lengthen time on the ventilator. To that end, appropriate prophylaxis regimens, interventions designed to improve clinical factors that impede weaning, early assessment of weaning readiness, and protocol-directed weaning trials are essential to good outcomes.

• In some patients, especially those with anticipated long stays on the ventilator (spinal cord injury, progressive neurologic disorders, etc), a tracheostomy tube is placed early in the hospitalization. Other patients may also receive a tracheostomy, especially if they have had multiple unsuccessful attempts at weaning. These patients often have long stays on the ventilator, and weaning trials tend to be accomplished with progressively longer tracheostomy collar trials in comparison with other methods, as described subsequently.

• A recent randomized controlled trial (RCT) suggests that patients with early tracheostomy placement who are considered at risk of 2 weeks of mechanical ventilation have better outcomes if provided with a tracheostomy on day 2 of mechanical ventilation.⁴⁰ Although the results are intriguing, they may be attributable to the fact that less sedation is necessary in patients with tracheostomies than in those with endotracheal tubes.³⁷ As described subsequently, the use of sedation infusions is linked to prolonged ventilator times.

• In the past, the assessment of weaning readiness was accomplished by determining whether or not the patient’s condition was stable, the reason for mechanical ventilation was resolved or improving, and the results of selected weaning criteria (or weaning indices) met threshold levels (Tables 37-1 and 37-2; see Procedure 36).^10,41,50 Experts also noted that before weaning trials were initiated, attention to other clinical factors was essential.^12,32 Clinical tools and checklists that ensure systematic attention to these factors help ensure good outcomes, an example of which is found in Table 37-3. In addition, prophylaxis regimes are necessary to prevent complications in patients on ventilation. These complications include ventilator-associated pneumonia (VAP), deep vein thrombosis, gastrointestinal bleeding, and sinusitis. Refer to Procedure 35 for a discussion of VAP prophylaxis and system-specific chapters for the others.

• Unfortunately, weaning indices have proven to be disappointing predictors of a patient’s ability to wean.12,32,35,45 Most predictors focus on pulmonary-specific factors. Some investigators have combined indices and pulmonary factors to enhance the comprehensive nature of the indices and their predictive potential. In general, the indices are poor positive predictors (they do not tell us the patient will wean), but they are good negative predictors (they tell us the patient will not wean).13,32,35,45 Thus, use of the indices is not widespread. In fact, the various weaning indices are best used to evaluate the components from which they are designed (breathing pattern, respiratory muscle strength, etc.).

• The weaning process has changed dramatically as a result of a number of RCTs published in the late 1990s and early 2000s.7,14,19,26,34,48 The studies showed that protocol-directed spontaneous breathing trials greatly reduced ventilator duration. Additional studies with protocols linked tight glucose control and aggressive sedation management to ventilator duration, intensive care unit (ICU) length of stay (LOS), hospital LOS, and mortality.^4,27,28,47 These protocols are briefly described.

• Protocol-directed multidisciplinary weaning with “weaning screens” and short duration spontaneous breathing trials (SBTs) have been shown to be superior to “individualized” weaning processes.7,14,19,34,48 The use of the protocols decreases practice variation, perhaps the major reason for their effectiveness. Key to the success of the protocols is the use of the weaning screen, which requires that a minimum of clinical factor thresholds (e.g., hemodynamic stability, fraction of inspired oxygen [FiO₂], positive end-expiratory pressure [PEEP] level) is met.¹⁴ This requirement ensures early and aggressive testing of patient readiness. Once the screen is passed, the patient is placed on a SBT for a short duration. One hour is generally adequate. If signs of intolerance emerge, the patient is returned to ventilatory support and a trial is reattempted at a later time as predetermined by the protocol. See Table 37-4 for an example of a protocol.

• The association between sedation infusion use and negative clinical outcomes of patients on ventilation resulted in studies that tested the efficacy of methods to reduce the use of sedatives in these patients. Two RCTs used nurse-managed methods.4,27 In a study by Brook and colleagues,⁴ a sedation algorithm was used to direct sedation use. Kress and colleagues²⁷ performed a daily sedation interruption. Both methods resulted in improved outcomes. Concerns about the potential negative impact of abrupt withdrawal of sedation in the critically ill were addressed. One study showed that those who had a daily interruption of sedation sustained significantly less psychologic harm and fewer complications than those who were not provided a daily sedation interruption.^28,43 Additional studies linked sedation use (specifically benzodiazepines) to delirium and subsequent cognitive dysfunction in ICU patients on ventilation.^16–18,39 Current guidelines on sedation use in critical care incorporate these elements in recommendations for management of both sedation and delirium.²⁵

• Another RCT focused on the management of blood glucose in a surgical (mostly cardiac) patient population. In this study, a glucose level maintained at or below 110 g/dL (or 6.1 μmol/L) resulted in decreased sternal wound infections, shortened weaning times, and decreased ICU and hospital LOS. It also significantly reduced in-hospital mortality rates.⁴⁷

• Recently, a multicenter RCT was accomplished that combined sedation interruption with a “wake-up and breathe” trial (i.e., SBT). In this study, patients assigned to the intervention (sedation interruption and wake up) had significantly more days of spontaneous breathing, earlier discharge from the ICU and hospital, and better 1-year survival rates than those in the control group.²² See Table 37-5 for summary of protocols for weaning and sedation use.

• Although the RCTs described show the importance of wean screens, SBTs, sedation management, and tight glucose control to weaning outcomes, studies on the adherence with the same are not encouraging. Adherence studies show that acceptance is low and that the protocols may not be realistic for use in everyday practice33,36,38,49, Given the increasing complexity of the clinical setting and the increasing shortage of ICU nurses and other healthcare professionals, rigorous protocols designed and implemented by study investigators are unlikely to be easily duplicated. We have much to learn in this area.

• We have learned much about methods for weaning, but no specific weaning modes have emerged as superior.10,12,19,32,48 As previously noted, SBTs appear to be the best method; most of these use breathing through a T-piece or on the ventilator (with or without the addition of continuous positive airway pressure [CPAP] or other flow mechanisms, such as automatic tube compensation).¹⁴ Regardless, advocates of other modes such as pressure support ventilation (PSV) suggest they may be equally as effective. Although RCTs do not exist to support these hypotheses, evidence-based data exist that may provide rationale for the application of these modes.

• The concept of respiratory muscle fatigue must be understood if it is to be prevented in the patient weaning from ventilation. All muscles may fatigue if work exceeds energy stores. Signs and symptoms of impending fatigue include dyspnea, tachypnea, chest-abdominal asynchrony, and increasing arterial partial pressure of carbon dioxide (PaCO₂, a late sign).2,11,46 Generally, fatigue may be prevented by avoiding premature or excessively long or difficult weaning trials.

• The concepts of work, rest, and conditioning are useful to consider when selecting weaning modes and methods. Two classifications—high-pressure low-volume work and low-pressure high-volume work—are essential to the understanding of these three categories.

• With both types of conditioning, the goal is to progress the trials without inducing fatigue. To that end, rest is that level of ventilatory support that “unloads” the respiratory muscles. The level of support needed may differ with each patient; however, two basic concepts may be useful: 1, when signs of intolerance emerge, the trial is stopped and the patient is rested; and 2, application of rest varies with the weaning mode. For example, if the mode is PSV, then the PSV is increased to that level necessary to decrease the spontaneous rate (e.g., <20/min) and result in a synchronous comfortable breathing pattern. With high-pressure low-volume modes such as CPAP, the patient is returned to full ventilatory support.

• Weaning is the process of gradual reduction of ventilatory support. To that end, a plan for weaning is determined by the multidisciplinary team and is applied and monitored carefully.8,9,14,15,23,24,34,44 The plan, whether it uses a protocol or consists of a more individualized written plan, should be available to all healthcare workers involved in the weaning process. Assessment of weaning potential may include checklists of factors important to weaning, such as the Burns Weaning Assessment Program (BWAP8–10; Table 37-3). In addition, prophylaxis for VAP and other potential complications associated with mechanical ventilation must be ensured.

• Outcomes of system initiatives designed to ensure the comprehensive implementation of evidence-based interventions are promising. Advanced practice nurses were used to manage and monitor the conditions of patients in their care.8,9,24,44 The results suggest that use of such models of care are to be encouraged, but few have been developed, tested, and published (Table 37-6). Further, they tend to compare retrospective with prospective data elements, thus limiting the strength of the evidence. Unfortunately, RCTs of such system initiatives are unlikely to be accomplished in the future.

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• Regular evaluation of factors that impede weaning in conjunction with factors that measure respiratory muscle strength, endurance, and gas exchange is necessary to ensure that all factors are being addressed appropriately (see Tables 37-1, 37-2, and 37-3). Rationale: Improvement of factors that impede weaning is essential to the attainment of positive outcomes.

• Assess progress toward achievement of individual short-term goals frequently. Rationale: Successful weaning may be achieved within a short time (1/2 to 2 hours) if patient response is monitored closely and interventions are applied in tandem with patient response.

• In patients who need mechanical ventilation for very long times (and often need a tracheostomy), assessment of daily progress toward achievement of individual long-term goals is important, in collaboration with the physician, respiratory therapist, patient, and family, as appropriate. Rationale: Successful weaning may be achieved within days to weeks in these patients if patient response is methodically evaluated and interventions are applied in tandem with patient response.

• Observe breathing pattern and note symptoms of dyspnea in response to decrements in PPV support. Other signs of fatigue include the following:

Rationale: These are signs and symptoms of potential or actual respiratory muscle fatigue. Interventions to offset the work of breathing are necessary.

• Note whether the patient experiences changes in level of consciousness or nonverbal behavior and has symptoms of dyspnea or fatigue. Rationale: Work of breathing may be such that the patient is maintaining an adequate breathing pattern and gas exchange at the moment but does not have sufficient reserves to continue expending energy to breathe. Patient exhaustion during weaning results in psychologic and physiologic delays in the weaning progress.

• Assess arterial blood gases as needed. Rationale: Although frequent arterial blood gas assessments are rarely necessary during weaning if active attention is paid to signs and symptoms of intolerance, arterial blood gases are the only definitive method of evaluating efficiency of gas exchange. Evaluate of PaCO₂ is especially important with spontaneous breathing if rapid return to increased ventilatory settings is not part of the plan or if dramatic changes in the patient’s condition are seen. PaCO₂ is the definitive indicator of the adequacy of ventilation. PaCO₂ (and pH) within the patient’s normal physiologic range indicates that the patient’s spontaneous ventilation is adequate. Weaning protocols are extremely helpful in that they identify intolerance criteria so that if they should emerge, return to ventilatory support may be prompt.

• Assess end-tidal carbon dioxide (PetCO₂) levels. Rationale: PetCO₂ levels are best used to trend CO₂ levels. It is important to know the PaCO₂ level that corresponds to the PetCO₂ level to use the PetCO₂ values most efficiently. Remember that the PetCO₂ values vary depending on the size of the breath. Larger tidal volume breaths provide more accurate values; the PaCO₂ PetCO₂– difference is less than when the tidal volumes are small. With small tidal volumes, there is more dead space ventilation and the PaCO₂ PetCO₂– difference is larger, which makes accurate trending difficult. This is especially the case during a spontaneous breathing trial when breath size varies. See Procedure 15 on PetCO₂ for more in-depth information.

• Assess oxygenation indices (see Procedure 33) during trials: arterial oxygen saturation (SaO₂) or arterial partial pressure of oxygen (PaO₂). Rationale: SaO₂ is a real-time continuous indicator of oxygenation during weaning trials and should be monitored continually. A saturation of greater than or equal to 90% generally indicates oxygenation adequacy. PaO₂ is the definitive indicator of the adequacy of oxygenation and, in some cases, is required. A PaO₂ within the patient’s normal physiologic range indicates that the patient’s oxygenation is adequate with spontaneous breathing. Generally, PaO₂ greater than 60 mm Hg and SaO₂ greater than or equal to 90% on a fraction of inspired oxygen (FiO₂) of less than or equal to 0.4 is acceptable during trials.

• Assess patient anxiety level. Rationale: Resumption of spontaneous breathing may cause anxiety, particularly in patients who have been on prolonged PPV support. Encouragement is necessary, in addition to assurance that prompt return to ventilatory support will be accomplished, if the patient becomes excessively tired, anxious, or otherwise distressed. Patients must trust that the healthcare workers will address their concerns competently and rapidly during weaning trials.

• Verify correct patient with two identifiers. Rationale: Prior to performing a procedure, the nurse should ensure the correct identification of the patient for the intended intervention.

• Ensure that the patient understands preprocedural teachings. Answer questions as they arise, and reinforce information as needed. Rationale: This communication evaluates and reinforces understanding of previously taught information.

• Address factors that are impeding wean potential. These factors may include pH level, hemodynamic stability, electrolytes, strength, endurance, mobility, nutrition, and fluid status, to name a few. A systematic approach with use of a checklist helps avoid variation in practice. Rationale: Weaning has been associated with the correction of a myriad of physiologic factors. Weaning is not solely dependent on respiratory muscle strength and endurance.

• Establish weaning screen criteria. Rationale: Weaning screen criteria are essential for the rapid and safe assessment of weaning trial readiness.

• Wean trial duration should be set before beginning the trial. Rationale: Prolonged SBTs may fatigue the patient and result in poor outcomes. All key bedside caregivers must be aware of the limits of the trial and when to stop should signs of intolerance emerge.