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These six stages are as follows:1) treatment of acute respiratory failure (ARF);2) suspicion that weaning may be possible; 3) assessment of readiness to wean; 4) spontaneous breathing trial (SBT); 5) extubation; and possibly 6) reintubation. It is important to recognise that delay in reaching stage 2, the suspicion that weaning may be possible, and beginning stage 3, assessing readiness to wean, is a common cause of delayed weaning. Stage 2 begins when the clinician first thinks there is a reasonable probability of weaning success. Stage 3 begins when the clinician actually initiates a process of daily tests of readiness to wean in order to confirm this suspicion. Stage 3 ends when the results of the daily test cause a reassessment of the probability to a high enough level to justify an SBT. The weaning process begins with the first SBT, defined as a T-tube trial or a low-level pressure support (f8 cmH2O; see Question 2). There is much evidence that weaning tends to be delayed, exposing the patient to unnecessary discomfort and increased risk of complications, and increasing the cost of care. Time spent in the weaning process represents 40–50% of the total duration of mechanical ventilation. ESTEBAN et al. demonstrated that mortality increases with increasing duration of mechanical ventilation, in part because of complications of prolonged mechanical ventilation, especially ventilator-associated pneumonia and airway trauma . Moreover, mechanical ventilation costs ,US$2,000 per day [9]. Subjects receiving prolonged mechanical ventilation account for 6% of all ventilated patients but consume 37% of intensive care unit (ICU) resources [10]. The incidence of unplanned extubation ranges 0.3–16%. In most cases (83%), the unplanned extubation is initiated by the patient, while 17% are accidental. Almost half of patients with self-extubation during the weaning period do not require reintubation, suggesting that many patients are maintained on mechanical ventilation longer than is necessary. Increase in the extubation delay between readiness day and effective extubation significantly increases mortality. In the study by COPLIN et al., mortality was 12% if there was no delay in extubation and 27% when extubation was delayed. Thus, criteria for readiness to begin weaning (see Question 3) should be systematically evaluated each day to allow prompt initiation of weaning as soon as the patient is ready. This will shorten the weaning process and minimise time on mechanical ventilation. This is also an independent predictor of successful extubation and survival. Definitions of weaning success and failure In most studies, weaning failure is defined as either the failure of SBT or the need for reintubation within 48 h following extubation. Failure of SBT is defined by: 1) objective indices of failure, such as tachypnoea, tachycardia, hypertension, hypotension, hypoxaemia or acidosis, arrhythmia; and 2) subjective indices, such as agitation or distress, depressed mental status, diaphoresis and evidence of increasing effort (see Question 3). Failure of a SBT is often related to cardiovascular dysfunction or inability of the respiratory pump to support the load of breathing. Extubation failure may be related to the same causes, in addition to upper airway obstruction or excessive secretions.
Failure of extubation is associated with high mortality rate, either by selecting for high-risk patients or by inducing deleterious effects such as aspiration, atelectasis and pneumonia. Interestingly, mortality is not especially increased when failure of extubation is related to upper airway obstruction (one out of nine patients; 11%) but is markedly increased in the other cases (19 out of 52 patients; 36%). Predictors of extubation failure have been reported, such as excess secretions, arterial carbon dioxide tension (Pa,CO2) .5.99 kPa (45 mmHg), duration of mechanical ventilation .72 h, upper airway disorders and a prior failed weaning attempt. Rate of weaning failure after a single SBT is reported to be 26– 42% . This variation in the rate of weaning failure among the studies may be due to differences in the definition of weaning failure, especially differences in the subjective indexes used to define failed SBT, or variation in the patients studied. For instance, chronic obstructive pulmonary disease (COPD) appears as an independent risk factor for increased duration of weaning and weaning failure. VALLVERDU et al. reported that weaning failure occurred in as many as 61% of COPD patients, in 41% of neurological patients and in 38% of hypoxaemic patients. Contradictory results exist regarding the rate of weaning success among neurological patients. The study by COPLIN et al. of brain-injured patients demonstrated that 80% of patients with a Glasgow coma score ,8 and 91% of patients with a Glasgow coma score ,4 were successfully extubated. Finally, as shown in 2,486 patients from six randomised studies, 524 patients failed SBT and 252 failed extubation after passing SBT, leading to a total weaning failure rate of 31.2%. Several studies have recently proposed the use of noninvasive ventilation (NIV) for extubated patients in different clinical situations, including prophylactic intervention in COPD patients who failed SBT [26], patients with repeated SBT failure and post-surgical patients. However, the effectiveness of NIV remains to be determined. The increased use of NIV raises the question of how to define weaning success or failure. The current authors propose the following definitions. Weaning success is defined as extubation and the absence of ventilatory support 48 h following the extubation. Weaning failure is defined as one of the following: 1) failed SBT; 2) reintubation and/or resumption of ventilatory support following successful extubation; or 3) death within 48 h following extubation. Since NIV may allow extubation while mechanical ventilation is continued in the form of NIV, an intermediate category called ‘‘weaning in progress’’ is recommended for patients who are extubated but remain supported by NIV. Classification of patients A new classification of patients into three groups is proposed, as suggested by BROCHARD during the International Concensus Conference, according to the difficulty and length of the weaning process .
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