• 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.

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