© Springer International Publishing Switzerland 2016
Antonio M. Esquinas (ed.)Noninvasive Mechanical Ventilation and Difficult Weaning in Critical Care10.1007/978-3-319-04259-6_22. Prolonged Weaning from Mechanical Ventilation: Pathophysiology and Weaning Strategies, Key Major Recommendations
(1)
Intensive Care Unit, Democritus University of Thrace, Alexandroupolis Hospital, Dragana, Alexandroupolis, 68100, Greece
Keywords
Chronic critical illnessLong-term-care hospitalProlonged mechanical ventilationTracheostomyWeaningAbbreviations
APACHE
acute physiology and health evaluation
ARDS
acute respiratory distress syndrome
BNP
B-type natriuretic peptide
CCI
chronically critically ill
CCIS
chronic critical illness syndrome
CINM
critical illness neuromyopathy
COPD
chronic obstructive pulmonary disease
ICU
intensive care unit
GCS
Glasgow coma scale
LTAC
long-term acute care
MV
mechanical ventilation
NAMDRC
National Association for Medical Direction of Respiratory Care
NIV
noninvasive ventilation
PMV
prolonged mechanical ventilation
PSV
pressure support ventilation
RCT
randomized controlled trial
RSBI
rapid shallow breathing index
SBT
spontaneous breathing trial
SWU
specialized weaning units
2.1 Introduction
Advances in the management of critically ill patients in intensive care unit (ICU) have improved mortality and morbidity as well as reduced length of stay and, subsequently, cost of treatment. However, despite improvements in short-term mortality and stabilization of acute organ dysfunction, a small but substantial population of critically ill patients who survive the initial critical illness continue to suffer from prolonged dependence on life support or to need long-term therapeutic interventions. These patients have been grouped under the classification of chronically critically ill (CCI) patients. Such a group is characterized by heterogeneity, prolonged need for high-cost interventions, and high long-term (around 1 year) mortality rate [1]. The best characterized component of the CCI population is patients on prolonged mechanical ventilation (PMV). In 2005, the National Association for Medical Direction of Respiratory Care (NAMDRC) defined PMV as the need for ≥21 consecutive days of mechanical ventilation (MV) for ≥6 h/day [2]. According to the European Respiratory Society Task Force, these patients constitute a particular group needing prolonged weaning from the ventilator, defined as more than three spontaneous breathing trials (SBTs), or more than 7 days from the first unsuccessful SBT [3]. Nevertheless, other investigators have favored Medicare’s definition of MV >96 h, with tracheostomy as the marker of PMV [2].
Patients requiring PMV have clearly different needs and resource consumption patterns in relation with patients during the acute phase of critical illness. Moreover, these patients may represent as many as 14 % of patients admitted to the ICU for intubation and MV, whereas it is estimated that they account for 37 % of all ICU costs and are associated with in-hospital mortality up to 32 % [4, 5]. Finally, available data suggest that the global prevalence of PMV in Europe ranges from 2 to 30 per 100,000 population according to different countries [6], whereas different studies have demonstrated that as many as 20 % of medical ICU patients remained dependent on ventilator support after 21 days [3].
2.2 Discontinuation of PMV
2.2.1 Pathophysiology of Weaning Failure
The successful weaning process from PMV is based on the understanding of the complexity of different causes associated with the need for prolonged ventilatory support. In this respect, it has been suggested that the major mechanisms of weaning failure in this group of patients include either an isolated failure of the respiratory system or respiratory failure occurring within the context of chronic critical illness syndrome (CCIS) [2, 3, 7].
It is estimated that pulmonary disease accounts for approximately 50 % of causes for PMV, associated with inspiratory muscle weakness, increased work of breathing, and reduced respiratory drive [2, 7]. Pulmonary disease results in reduced lung compliance and increased load upon respiratory muscles. In this respect, ventilator-associated pneumonia and acute respiratory distress syndrome (ARDS) are considered the main pulmonary pathologies leading to prolonged weaning from the ventilator. Airway disease in patients with chronic obstructive pulmonary disease (COPD) may also increase work of breathing through air-flow limitation, dynamic hyperinflation, and auto-positive end-expiratory pressure (PEEP). Furthermore, congestive heart disease has been reported in up to 26 % of patients hospitalized in long-term acute care (LTAC) hospitals in the United States [8]. Such cardiac dysfunction can be uncovered during SBTs due to increased venous return, end-diastolic volume augmentation, and increased metabolic demands. In these cases, performance of cardiac echocardiography and determination of B-type natriuretic peptide (BNP) serum levels during SBTs can be of significant value for early diagnosis and prompt treatment of possible myocardial dysfunction and/or hypervolemia [7–9].
Critical illness neuromyopathy (CINM) can manifest itself as ICU-acquired weakness and subsequent PMV, usually associated with multiple organ failure, muscle inactivity, hyperglycemia, or use of corticosteroids and neuromuscular blockers. As a result, early mobilization, minimizing the use of deep sedation and steroids, and avoidance of hyperglycemia have been advocated as effective preventive strategies during the acute phase of critical illness [7, 10]. Ventilator-induced diaphragm dysfunction constitutes a rapid form of skeletal muscle injury that may occur within only 18 h of MV [7, 11]. Age, malnutrition, and continuous mandatory ventilation have been found to promote such muscle weakness, whereas pressure support ventilation (PSV) seems to minimize diaphragmatic ventilator-induced injury [11]. In addition, optimal patient-ventilator synchrony through properly adjusted ventilator settings, psychotropic medications, and delirium management seems to reduce work of breathing and further promote earlier weaning from ventilatory support [7].
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