Abstract
Invasive ventilation is a critical respiratory support technology in the intensive care unit (ICU). Increasing evidence suggests that early liberation from invasive ventilation can benefit patients. However, further research is needed to establish optimal criteria for invasive ventilator liberation programs, including the ideal screening frequency, appropriate techniques and duration of spontaneous breathing trials (SBT), evaluation of airway extubation readiness, and decision-making regarding extubation. The management of the invasive ventilator liberation process should encompass feasibility screening for SBTs, conducting SBTs, evaluating SBT outcomes, assessing airway extubation readiness, performing extubation itself, identifying high-risk factors associated with weaning failure, and developing clinical strategies. Additionally, a patient-centered assessment of the risks and consequences of extubation failure may serve as crucial measures to enhance the success rate of invasive ventilator liberation. Therefore, we conduct a detailed review of the related studies on invasive mechanical ventilation weaning to determine the best invasive ventilator liberation strategy.
1
Introduction
Mechanical ventilation is a critical intervention for the management of acute respiratory failure [ , ], encompassing both invasive and noninvasive ventilation (NIV). Invasive ventilation plays a pivotal role in treating acute respiratory failure within the intensive care unit (ICU) [ ], and early extubation has been shown to enhance patient prognosis [ ]. However, patients undergoing invasive ventilation are at risk of various ventilator-related complications. These include inappropriate use of sedative medications that may lead to delayed extubation, resulting in muscle weakness and ventilator-associated pneumonia (VAP), among other issues. Such complications can prolong the duration of invasive ventilation, adversely affecting treatment outcomes [ ] and potentially increasing mortality rates [ ].
The traditional approach to liberating patients from invasive ventilation involves weaning and extubation following the successful completion of a spontaneous breathing test (SBT). Nonetheless, there are numerous indicators used to assess SBT success; many exhibit poor sensitivity and specificity, with results often influenced by subjective operator judgment. Consequently, some patients continue to experience delays in weaning or failed attempts at extubation altogether, which negatively impacts their prognosis. Therefore, identifying strategies for timely removal from mechanical ventilation while preventing extubation failure is essential for improving treatment efficacy in cases of respiratory failure [ , ].
In light of these challenges, it is imperative to conduct a comprehensive review of existing research on strategies for liberating patients from invasive mechanical ventilation to determine the most effective approaches available ( Fig. 1 . Mind map.).
2
Definitions, classifications, and methods
2.1
Definitions
Invasive ventilator liberation refers to the process of freeing patients from invasive mechanical ventilation, encompassing both weaning and extubation [ ]. This involves the concerted efforts of medical personnel to reduce and ultimately eliminate the need for invasive ventilation. The weaning process entails addressing or ameliorating the underlying factors contributing to respiratory failure, thereby determining the earliest possible moment at which a patient can regain spontaneous breathing ability (liberated from the ventilator) while maintaining airway patency (liberated from artificial airways). Extubation specifically denotes the removal of an endotracheal tube. During the phase of respiratory liberation, patients experiencing acute respiratory failure typically spend approximately 40 % of their time on invasive mechanical ventilation [ ]. The timely and successful liberation of critically ill patients from invasive ventilation has been recognized as a paramount priority within intensive care units (ICUs) [ ].
2.2
Classifications
The classification of weaning from invasive ventilation has been changed several times. The International Consensus Conference (ICC) in 2007 divided weaning into simple weaning, difficult weaning, and delayed weaning [ ]. Its evaluation involved the number of SBTs, results, and duration of mechanical ventilation, and did not cover patients with tracheotomy, no SBT, and failure to wean. In 2017, WIND research [ ] proposed weaning attempts and introduced them. Patients with endotracheal intubation included SBT and direct extubation. Patients with tracheotomy had spontaneous breathing for more than 24 h in the weaning state, and the judgment time window of weaning results was extended to 7 d (whether non-invasive ventilation or not). In 2023, the WIND SAFE study [ ] improved and revised the WIND classification, defining five weaning outcomes: no weaning attempt, short-range weaning (successful weaning within 1 d of the first weaning attempt), medium-range weaning (successful weaning within 1–7 d of the first weaning attempt), delayed weaning (successful weaning after 7 d of the first weaning attempt), and weaning failure (artificial airway retention or death at 90 d of the first weaning attempt or transfer out of ICU).
2.3
Methods
A comprehensive literature search was conducted using computerized databases including PubMed, MEDLINE, EMbase, CNKI, WanFang Data, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) to identify research reports on the weaning process from invasive mechanical ventilation published over the past 15 years. The search strategy combined subject headings with free-text terms, including “invasive mechanical ventilation,” “weaning,” “extubation,” and related keywords. Additionally, reference lists of included studies were manually reviewed to identify supplementary relevant literature. Two researchers independently performed the initial screening of titles and abstracts to identify potentially eligible articles, followed by full-text assessment based on predefined inclusion criteria. Two independent reviewers (TI and FO) evaluated each article for quality assurance, compared their assessments, and resolved any discrepancies through a third reviewer to ensure the exclusion of low-quality studies that could compromise accuracy and credibility. However, certain limitations may arise due to the unavailability of some literature because of copyright restrictions.
3
Current situation of invasive ventilator liberation
Ideally, when the root cause of invasive ventilation due to acute respiratory failure is improved or resolved, and patients begin to be able to breathe autonomously, they can be liberated from invasive ventilation [ , ]. In the recovery process of critical illness, as long as patients do not show insufficient or excessive spontaneous breathing during weaning, spontaneous ventilation mode should be used as soon as possible [ ]. These weaning procedures usually include determining the timing of SBT, performing SBT, and extubating after successful SBT [ ].
However, the results of the 2023 WIND SAFE study [ ] revealed that the current situation of weaning patients from invasive ventilation in the world is not optimistic. A total of 5869 patients (481 ICUs in 50 countries) were included in the study. 35 % of patients failed to wean within 90 days, and the in-hospital mortality rate was as high as 38.3 %. Most of the dead patients did not attempt to wean and failed to wean, while the in-hospital mortality rate of patients with successful weaning was as high as 11.4 %. In the WIND SAFE study, short-term weaning accounted for 64.7 %, tracheotomy accounted for 21.4 %, reintubation accounted for 13.7 %, and the mortality of reintubation patients was as high as 29.5 %. At the same time, the WIND SAFE study also reflected that patients with invasive ventilation were generally delayed in weaning, especially the delay of weaning attempts. 91.5 % of patients reached the weaning screening standard at 3 days of invasive ventilation, but only 77.1 % of patients had weaning attempts. The interval between reaching the weaning screening standard and weaning attempts was more than 5 days in 22.4 % of patients. The median time from the first weaning attempt to the successful weaning of patients with delayed weaning was as long as 12 days, reflecting that the delay of weaning attempts and the delay of weaning after successful weaning attempts may be important reasons for the delay of weaning.
4
Invasive ventilator liberation decision
The results of the WIND SAFE study have important implications for the management of invasive mechanical ventilation. We should understand SBT, weaning methods, and weaning processes, including SBT, sedation management, extubation decision-making and extubation, and sequential high respiratory support. It is extremely necessary to formulate a new consensus on the liberation of invasive ventilators.
4.1
SBT
Invasive ventilated patients should be screened for weaning feasibility once a day to determine whether they meet the criteria for possible weaning, receive SBT [ , ], or test their spontaneous breathing ability for 30–120 min [ ]. Compared with subjective judgment, weaning programs have been shown to reduce invasive ventilation time by 25 h (95 % CI, 12.5–35.5 h) and ICU stay by about 1 d (95 % CI, 0.24–1.7 d) [ , ]. Similarly, the Cochrane study [ ] found that the weaning scheme can reduce the average mechanical ventilation time, especially in the medical, surgical, and comprehensive ICU, except the neurosurgical ICU. Therefore, the American Thoracic Society (ATS)/American College of Chest Physicians (ACCP) has developed invasive mechanical ventilation weaning guidelines for patients with acute respiratory failure who have been ventilated for more than 24 h [ , ].
In the weaning feasibility screening program, the parameters used to identify patients ready for SBT vary from study to study. Including objective parameters, such as rapid shallow breathing index (RSBI) [ , ], tidal volume (VT), respiratory rate (RR) [ ], esophageal pressure monitoring [ ], inspiratory effort and maximum inspiratory pressure [ ], as well as arterial blood gas and hemodynamic parameters; The subjective parameters of possible weaning and extubation preparation were evaluated, namely, the control or reversal of the root cause of respiratory failure, the reduction of cough intensity and airway secretion volume; Other parameters, i.e. stable hemodynamic state, no or only minor vasoactive drugs, etc. [ ] Taking RSBI as an example, it is defined as the ratio of RR of spontaneous breathing divided by VT (unit: L) within 1 min [ , ]. With the reduction of ventilator support, it can evaluate whether patients have shallow and fast breathing. Some studies [ ] showed that RSBI was less than 105 times/min/L, with a sensitivity of 97 % and a specificity of 64 % for predicting extubation success. Later, some studies [ ] questioned the utility of RSBI in predicting extubation success, believing that this result confused weaning and extubation, and its value in predicting extubation success was limited. Studies [ , ] have shown that RSBI exhibits moderate accuracy and poor sensitivity and specificity in predicting successful extubation.
SBT represents the reduction of the use or non-use of ventilator support. It is a formal evaluation of the preparation for extubation, including T-tube, low-level Pressure support (PS) (with or without PEEP), continuous positive airway pressure (CPAP), automatic catheter compensation, and other uncommon technologies [ , ]. Clinical research conclusions on the optimal SBT technique are conflicting. A meta-analysis by Sklar et al. [ ] found that SBT using PS reduced respiratory work more than using other techniques, including T-tubes or CPAP. In contrast, a meta-analysis by Burns et al. [ ] found that compared with T-tube SBT, the pass rate of SBT using PS was not significantly different, but it may be 6 % higher for successful extubation. ATS/ACCP guidelines have made conditional recommendations for performing SBT with PS [ , ]. At the same time, some studies [ ] found that there was no significant difference in SBT results, extubation results, and reintubation rate between shorter (20 or 30 min) and longer (120 min) SBT.
The criteria for evaluating SBT results (failure/pass) mainly come from clinical studies and guidelines [ ]. Further research is needed to determine the best combination of criteria for weaning screening, screening frequency, SBT technology, and SBT duration. In addition, the effects of specific interventions on respiratory release (time to first successful SBT) and extubation (time to successful extubation) need to be clarified and standardized. The optimal duration for evaluating and reporting extubation success (48 h vs 72 h vs 7 d) needs to be further clarified.
4.2
Extubation decision and extubation
Burns et al. [ ] found that medical staff of different occupations participated in all links of offline and extubation, while ICU doctors were largely responsible for extubation decisions. In the extubation decision-making process, clinicians’ goal is to avoid extubation failure (i.e., reintubation within 48 h), because this is associated with an increased risk of death, longer ICU stay, and hospitalization costs [ ]. Although few studies have reported how extubation decisions are made, clinicians should take patients as the center to make extubation decisions, including dynamically evaluating patients’ extubation readiness and the risks and consequences of extubation failure, formulating extubation failure treatment plans, and reducing the risk of extubation failure through predictive intervention.
Determining the risk of extubation failure involves the scientificity of predicting extubation outcomes, and extubation preparation typically (but not always) involves SBT. Surgical postoperative patients undergoing short-term invasive ventilation may not require formal SBT, as it may prolong unnecessary ventilation time [ ]. For acute hospitalized patients with invasive ventilation time less of than 24 h, guidelines [ , ] recommend adding PS as part of extubation assessment during SBT, which can not only help evaluate patients’ spontaneous breathing ability but also help predict extubation outcomes. Clinical doctors may believe that some patients have a greater risk of extubation failure, such as those with severe coronary artery disease, myocardial ischemia, and weakness, who may suffer greater potential harm after extubation failure. The measurement of the risk and consequences of extubation failure can help clinicians determine when extubation trials should not be attempted and consider tracheotomy, which may be an important research area that benefits patients.
Reducing the risk of extubation failure includes identifying specific risk factors and developing treatment protocols to address potential risk factors. Risk-coping strategies should be developed before extubation, and extubation should be delayed if the risk of extubation failure is high [ , ].
4.3
NIV
Some studies have proposed NIV as a method of weaning, which can reduce the use of invasive mechanical ventilation during weaning by extubating patients who still need mechanical ventilation to NIV in advance. NIV can establish a human-machine connection through a mask/nasal mask, provide partial ventilator support, and retain the patient’s ability to cough, swallow, and communicate verbally [ ]. It can increase VT, reduce RR, and improve gas exchange by applying the PEEP function [ ]. Some studies [ ] have suggested that patients with acute respiratory failure may be more tolerant of NIV with dexmedetomidine without increasing the risk of intubation. NIV can be used to facilitate weaning (by extubating directly to NIV for weaning) and prophylactically in patients who are at risk for extubation failure or who develop respiratory failure after extubation [ ].
NIV weaning may be very suitable for patients with chronic obstructive pulmonary disease (COPD) because weaning failure in this population is characterized by respiratory muscle weakness, carbon dioxide retention, and increased endogenous PEEP. NIV has been shown to increase VT, reduce RR, improve gas exchange, and rest respiratory muscles, which can completely solve the above risk factors [ ]. A meta-analysis [ ] reported that compared with continuous invasive mechanical ventilation in 2066 critically ill patients, extubation sequential NIV weaning reduced mortality, VAP, and weaning failure rates, and shortened the incidence of tracheotomy, ICU length of stay and length of hospital stay. The weaning time of invasive ventilation and the total time of invasive ventilation were significantly shortened. A sequential approach to weaning from NIV had a greater benefit for COPD than did a mixed patient population, with significant between-group differences in mortality, length of ICU stay, and reintubation. In this meta-analysis, patients with COPD accounted for 44.6 % of those enrolled in the trial.
For patients receiving mechanical ventilation for more than 24 h who pass SBT but are considered to be at high risk for extubation failure, the ATS/ACCP guidelines [ ] strongly recommend prophylactic sequential NIV with extubation. However, the guideline does not address the question of early NIV in patients who fail initial SBT or undergo SBT too early. Overall, the above findings support that weaning from NIV has a beneficial effect on important clinical outcomes, particularly in patients with COPD, whereas the benefit of NIV in patients without COPD is unclear and is an area for future research.
4.4
High flow nasal Cannula(HFNC)
HFNC delivers heated and humidified oxygen at high gas flow rates (60–70 L/min) to achieve reliable high FiO 2 delivery. Some studies [ ] have demonstrated the benefits of HFNC in patients with acute hypoxic respiratory failure, and the results of new studies [ ] have also shown similar benefits in hypercapnic respiratory failure. Compared with NIV, HFNC is better tolerated and more comfortable for patients and can eat and communicate verbally during treatment.
Because HFNC is a relatively new oxygen strategy in adults, the evidence base is less well-developed than NIV. Studies [ ] support testing HFNC in patients with a tracheotomy to increase airway pressure and reduce the work of breathing, but these data are limited to small crossover physiological trials. Thus, variation in HFNC use remains, given the paucity of evidence supporting its use .
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