Table 4 shows factors associated with failed weaning from MV. The variables included in the multiple are sex, Apache score, main compromised system, and time in assisted modes. Independent factors associated with failed weaning were compromise of the respiratory system as the main compromise on admission to the ICU (RR 3.89; 95% CI 1.33–11.33) and the Apache score (RR 0.95; 95% CI 0.91–0.98, P = 0.009).
The results obtained indicate that factors associated with failed weaning from MV in patients with MV support for 48 hours or longer were identified. Those factors were non-modifiable factors and the most frequent was admission to the ICU with the respiratory system being the most compromised (RR 3.89; 95% CI 1.33–11.37; P = 0.01), whereas the incidence of failed weaning dropped with the increase in the Apache level (RR 0.96; 95% CI 0.92–0.98; P = 0.02). The incidence of failed weaning from MV in the cohort was 24.09%, 95% CI 16.83–31.33.
Of the patients with failed weaning (n = 33), the largest proportion (n = 17–15, 82%) needed tracheostomy during the period of MV. Consequently, the main mechanism for failed weaning in the study cohort was apparently related to the lack of airway integrity, considering that patients with upper airway obstruction or disorder were not excluded. This may also explain why the incidence of failed weaning dropped as the Apache score increased (RR 0.96; 95% CI 0.92–0.98; P = 0.02), probably as these patients had respiratory compromise only with no other system compromise, hence the lower Apache score.
Factors such as the neuromuscular component, nutritional status, respiratory and cardiovascular integrity, and psychological conditions did not influence weaning from MV.6
In this study, compromise mainly of the respiratory system on admission to the ICU was the risk factor most frequently associated with a higher frequency of failed weaning. This category includes patients with respiratory disorders involving the lung parenchyma, the pleura cavity, airway integrity, or rib cage mechanics as main diagnoses on admission to the ICU.
Modifiable factors, such as receiving physical therapy or RMT, were not found to be associated with failed weaning from MV. Therefore, data related to the characteristics of physical therapy such as the number of sessions, goals, and activities were not recorded or evaluated as part of this study. On the other hand, patients who received RMT (n = 69) received between 1 and 14 sessions; 50% (n = 34) received up to two sessions and the remaining 50% (n = 35) received between 3 and 14 RMT sessions; this was due to the short period of MV received by the patients once they met the inclusion criteria. Authors have determined that close to 14 days of RMT are needed to produce significant changes in muscle strength that may be reflected on weaning from MV26,27; consequently, the patients did not receive the number of RMT sessions needed to create significant clinical changes.
Prior studies have evaluated factors associated with failed weaning from MV and failed extubation.
In 1998, Capdevila et al,28 in 17 patients with prolonged MV followed prospectively, determined that failed weaning is associated with prolonged MV, minute ventilation, respiratory rate, high arterial CO2 pressure, and presence of intrinsic PEEP. In 2009, Carlucci et al29 identified, in a population of 30 patients with difficult weaning from MV, that inspiratory burden is higher in relation to neuromuscular capacity, and this is a pathophysiological determining factor for failed weaning.
In 2000, Coplin et al determined, in 136 subjects with brain lesion, that the risk of failed extubation increases in the absence of reflex cough and the presence of secretions in the respiratory tract.18 In a prospective study with 91 patients conducted in 2001, Khamiees et al concluded that the coughing force and the volume of endotracheal secretions are determining factors for extubation results.19
In 2003, Smina et al determined, in a cohort of 95 patients, that coughing force is an important predictor of extubation outcomes.20 In a multicenter study conducted in 2006 by Frutos-Vivar et al in 900 patients who passed a spontaneous breathing test, the authors identified that a high positive fluid balance and the presence of pneumonia as the main reasons for requiring MV were the main factors associated with failed extubation.21
The results of this study and of prior studies are related to differences in the target population, the methodological design, sample size, exposure variables measured, and the definition of the outcome variable.
This study is an observational study of a cohort recorded during an experimental trial conducted with 139 patients exposed to ventilation support during 48 hours or more; it included patients with various diagnoses and excluded patients with tracheostomy. Studies that have evaluated associated factors are prospective analyses, and 2 of them have been conducted in patients with prolonged MV and included patients with tracheostomy.25,26 The remaining studies were conducted in patients that passed a trial of spontaneous breathing, without specifying MV time,18–20 and in the case of the study by Coplin et al, only patients with brain injury were included.18
On the other hand, only 1 study with a multicenter design has been conducted to date with a sample size larger than the one included in this research,21 and moreover, each author has focused on the measurement of specific exposure variables. Carlussi et al assessed respiratory pattern, respiratory mechanics, respiratory muscle function, and diaphragm tension-time index.30 Capdevila et al measured respiratory pattern, fast and shallow breathing rate, tracheal occlusion pressure, MIP, and inspiratory muscle tension-time index.25 Coplin et al assessed neurological status and airway function.18 Frutos-Vivar et al measured secretions, coughing pattern efficacy, presence of leukocytosis, temperature higher than 38 °C, and positive fluid balance.21 Smina et al measured length of intubation, the Apache score, fast and shallow breathing rate, hemoglobin levels, peak expiratory volume, and volume of secretions.20 This research assessed clinical factors considered critical for weaning from MV, as well as sociodemographic factors such as age, height, sex, dose of sedative and analgesic medications received, time on MV according to each ventilation modality, Apache level, respiratory muscle strength (MIP), and the main system compromised on admission to the ICU, among others, are already mentioned.
The outcome variable assessed in this study was failed weaning from MV, defined as the need for reintubation, tracheostomy, or death up to 48 hours following extubation, or the need for tracheostomy after 1 or more failed trials at spontaneous breathing.7 Frutos-Vivar and Ferguson20 evaluated risk factors associated with failed extubation without setting a time threshold, including only patients who required reintubation, and excluding patients who required tracheostomy or who died.
Previous studies have reported values for failed weaning from MV ranging between 26% and 42%,11,25,30,31 and, therefore, the results of this study are similar.
Given that specific conditions are required for measuring and recording exposure variables such as secretion volume and consistency and fluid balance, this study did not consider those variables, and that is a limitation. Other variables such as the level of consciousness and oxygen status were not considered as this study included patients with no oxygenation disorder and with the ability to respond to commands (PaO2 > 60 mm Hg, FiO2 ≤ 0.5, PEEP < 8 cmH2O, RASS between −1 and 0). Another limitation was the sample size which may have been insufficient to identify modifiable factors associated with weaning from MV.
Standardization of the process for measuring the study variables and recording the data, and the quality control over the collection, entry, and storage of the original data during the CCT, Efficacy of RMT in weaning from MV in patients on MV during 48 hours or more: a clinical controlled trial,1 minimize the possibility of information bias and are a methodological strength.
In conclusion, this research determines that non-modifiable conditions such as the compromised system that leads to ICU admission and the Apache level are mainly associated with failed weaning episodes; modifiable factors such as the level of muscle strength, lung rehabilitation, physical rehabilitation, RMT interventions, and specific ventilation strategies did not show association with this event in the study population.
Human and animal protection: The authors declare that no experiments were conducted in humans or animals for this research.
Data confidentiality: The authors declare having followed the protocols of their institution regarding disclosure of patient information.
Right to privacy and informed consent: The authors have obtained the informed consent of the patients and/or subjects referred to in the article. This document work in the power of the correspondence author. The authors declare that the names of the patients do not appear in this study.
The macro study was funded by the internal call of 2014 from the Research Vice President's Office of Universidad del Valle.
Conflicts of interest
The authors have no funding and conflicts of interest to disclose.
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Respiration, Artificial; Critical Care; Weaning; Intensive Care Units; Adult; Respiración artificial; Cuidados críticos; Destete; Unidades de cuidados intensivos; Adulto
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