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Archived Comments for: Routine use of weaning predictors: not so fast

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  1. Routine use of weaning preditors: better if we go faster

    Sergio Nemer, Hospital de Clínicas de Niterói

    6 November 2009

    Sérgio N. Nemer and Carmen S.V. Barbas

    We thank Dr. Epstein for his interest in our article. We also thank him for his interesting comments and considerations. We agree that the great majority of weaning predictors presented only moderate accuracy in predicting the weaning outcome. Although, some integrative indexes, like the frequency to tidal volume ratio (f / Vt ratio) [1] and the ratio of airway occlusion pressure to maximal inspiratory pressure (P 0.1 / MIP) [2], have already presented the accuracy higher than the other single parameters [1,2].
    In the Evidence-Based Guidelines for Weaning and Discontinuing Ventilatory Support [3], eight parameters presented statistically significant likelihood ratio to predict the outcome of a ventilator discontinuation in more than one study. As 15% of the patients who can complete a SBT require reintubation in the following 48 hours after extubation [4], clinical impression is so inaccurate [3] and at least eight parameters for weaning were considered accurate, we think that there are no reasons of not considering the weaning predictors.
    We also know and agree with Dr. Epstein that weaning predictors are really useful in a presence of favorable clinical condition, although, this one alone did not reflect the respiratory mechanics, the inspiratory endurance and other factors that are important too. Several patients with favorable clinical condition are reintubated as a consequence of these factors.
    In a Statement of the Sixth International Consensus Conference on Intensive Care Medicine [4], patients that presented favorable clinical condition and weaning predictors like f / Vt ratio in less than 105 breaths / minute / liter, respiratory frequency in less than or equal 35 breaths / minute, MIP in less than or equal to 20 – 25 cmH2O, vital capacity in more than 10 ml / kg, tidal volume in more than 5 ml/kg should be considered ready for weaning. So, our opinion is that the combination of a favorable clinical condition with favorable weaning predictors leads to more probability for a successful weaning. We think that there is no consensus about the recommendation of weaning predictors and that it is a very polemic topic, but the two weaning consensus [3,4] are not contrary to the weaning parameters, and there are other important revisions, wrote by Dr Tobin, the expert on this theme, that recommend the weaning predictors, mainly the f/Vt ratio [5,6]. Is so hard to find one research about weaning that do not consider the f/Vt ratio, once this one is incorporated in the daily practice in the great majority of the intensive care units.
    The f/Vt ratio is the more popular [5] and the most or one of the most accurate weaning predictor [7]. Another great advantage of the f/Vt ratio is its feasibility. In our study [8], the new index that we developed showed to be the most accurate weaning predictor among the parameters evaluated, even when compared to the f/Vt ratio. Regarding the consideration of extubation failure and spontaneous breathing trial (SBT) failure (or weaning failure) as the same outcome, it is important to emphasize that if one patient that tolerated SBT and was extubated but, after some hours needed reintubation, it does not necessarily mean that the reason of extubation failure had been related to the capacity of protecting the airway. As cited in our manuscript, the study of Frutos-Vivar et al [9] presented 13.4% (121 of the 900 patients) of extubation failure related to f/Vt ratio, positive fluid balance 24 hours prior extubation and presence of pneumonia at the beginning of mechanical ventilation. In our study, no patient was reintubated as a consequence of laryngeal edema, copious secretion, ineffective cough or other reason related to the capacity to protect the airway. Among the 10 reintubated patients in our study, all of them were like that as a consequence of reasons related to the respiratory system (as fatigue, hypoxemia and rapid shallow breathing), not to the capacity of protecting the airway. When a patient present a extubation failure as a consequence of inability to protect the airway, the signs are so clear, like a stridor, that developed sometimes immediately after the extubation. So, the definitions about weaning failure and extubation failure present factors that could be present in both of them and should not be separated until the inability to protect the airway had been clearly proved. SBT is not a perfect test and there are patients that tolerate short SBTs but not longer ones without reasons related to the capacity to protect the airway. So, we see no reasons why not classifying our 54 patients as weaning failure, even that 10 of them had been reintubated, once there were no reasons related to the capacity of protecting the airway. We agree with Dr. Epstein that the reasons related to the capacity to protect the airway cannot be detected by weaning predictors, because in this situation, the signs of respiratory distress are presented only after the extubation. So, we do not have the intention to prove that our IWI can detect extubation failure related to the capacity of protecting the airway, but we showed that our IWI was accurate in detect extubation failure without reasons related to the capacity to protect the airway in 9 of 10 patients. It is true that this is a small number of events that preclude meaningful analysis, but once more, we do not have the intention to prove that our IWI can detect extubation failure related to the airway protection. However, we also hope to detect patients that are extubated but cannot tolerate 48 hours after extubation without reasons related to the airway protection. Even though 10 of the 54 weaning failure patients had been reintubated in our study, the reason of failure was basically the same and in reality, all of them failed. We think that these definitions should be revised, because not all patients that are reintubated are related to the airway protection.
    We do not hope that our IWI can change the recommendations about weaning predictors, because in our opinion, these ones are not discouraged and they are only polemical. We hope that with the accuracy of our index, weaning predictors like our IWI and the f/Vt ratio could be more used and more credited. We still think that the f/Vt ratio remains as one of the best weaning predictors and should be considered for weaning. We think that our IWI can be used routinely in the great majority of the intensive care units. In order to prove the accuracy of our IWI, it will be a pleasure that prestigious authors like Dr. Epstein and Dr. Tobin could use our index one day and prove its accuracy.

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    9. Frutos-Vivar, Ferguson ND, Esteban A, Epstein SK, Arabi Y, Apezteguía C, González M, Hill NS, Nava S, D’Empaire G: Risk Factors for Extubation Failure in Patients Following a Successful Spontaneous Breathing Trial. Chest 2006, 130: 1664-1671.

    Competing interests

    The author declares that they have no competing interests.