Weaning in ARDS
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Weaning in ARDS Ross Freebairn
9.1
Introduction
Depending upon case mix, about one in four ventilated in an ICU has ARDS- induced respiratory failure [1]. Mechanical ventilation (MV), the mainstay of support for ARDS and also a driver of intensive care costs, is associated with complications that pose risks to patients [2, 3]. Increasing the duration of MV increases that risk [4]. As respiratory function improves, MV needs to be withdrawn at the earliest possible juncture. Very few randomized trials of MV weaning have had a primary focus on patients suffering from ARDS. For reasons outlined below, substituting results acquired from general populations or applying techniques developed in non-ARDS patient groups may have limitations. In patients with ARDS, reversal or control of the precipitant of the respiratory failure is essential before the “weaning” can begin. This entails correction or attenuation of the precipitating cause of the ARDS as well as restoring the respiratory systems to a stable, functional state. ARDS impact is not confined to the respiratory system, and thus weaning is not solely ventilator focused. Restoration of cardiovascular, neuromuscular, neurological, and psychiatric homeostasis is required for successful weaning [5, 6].
9.1.1 Definitions Weaning is the successful separation (or liberation) of the patient from the ventilator. Weaning definitions range from being totally free of MV support to just being free of invasive ventilation [7]. The lack of standard definitions and the varied end
R. Freebairn, FANZCA, FRCPE, FCICM Intensive Care Services, Hawke’s Bay Hospital, Hastings, New Zealand Chinese University of Hong Kong, Hong Kong, China e-mail: [email protected] © Springer International Publishing Switzerland 2017 D. Chiumello (ed.), Acute Respiratory Distress Syndrome (ARDS), DOI 10.1007/978-3-319-41852-0_9
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points for weaning complicate analysis [7, 8]. Prolonged MV also has a myriad of definitions including MV periods for as brief as 2 days to as long as 29 days [9–11]. A 2004 consensus defined prolonged MV as greater than or equal to 21 consecutive days of MV, for greater than or equal to 6 h/d [10]. The end of the weaning process also lacks agreed definitions and is variously defined as first extubation, successful extubation, unassisted breathing for 24 or 72 h, the first spontaneous breathing trial (SBT) or successful SBT, or an ill-defined “successful weaning” [7, 12–17]. The spectrum of transitioning supportive therapy such as high-flow nasal cannula (HFNC) as adjuncts to weaning adds further complexity [18–21].
9.1.2 Routine Weaning Standard weaning should be employed early in the ICU stay. Once the need for muscle paralysis, deep sedation, prone positioning, and other complex respiratory interventions is no longer needed, active weaning should commence. Generally, once the underlying condition is reversed, the majority of patients can be weaned by simple sequential cessation of neuromuscular blocking agents, sedation, and respiratory
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