Weaning from Mechanical Ventilation

Abstract

For most patients who require mechanical ventilation weaning and extubation is simple. In these patients a variety of strategies can be successful. In addition, sim ple criteria may predict when the patient is ready for extubation. For the small group of patients who require prolonged mechanical ventilation, however, contro versy exists about how best to remove ventilator sup port by weaning, and available data are sparse. Much of the controversy has centered on T-piece weaning ver sus intermittent mandatory ventilation. To date no con trolled study has demonstrated the superiority of either intermittent mandatory ventilation or T-piece weaning in difficult-to-wean patients. In the evolution of this con troversy, concern has developed over the potential for increased inspiratory work and expiratory resistance that may be associated with certain intermittent manda tory ventilation systems. The possibility that significant inspiratory work may occur during assist-control venti lation has also been demonstrated. Respiratory muscle weakness and fatigue is likely important in failure to wean. Other possible causes are failure of the cardiovas cular system and impaired ability of the lung to carry out gas exchange. In this article we first examine criteria and techniques for weaning short-term ventilator pa tients. We then examine criteria to begin the weaning process in prolonged ventilation patients, potential causes of failure to wean, and techniques that can be used to remove ventilator support from patients who are difficult to wean. Much literature has been devoted to techniques and criteria for weaning and extubation of patients from mechanical ventilation. For most patients who require ventilatory support, weaning and extuba tion can be easily accomplished by a variety of tech niques [1-4]. At one referral center 77.2% of all surviving patients were weaned from the ventilator within 72 hours of the onset of mechanical ventila tion, and 91% were weaned within 7 days [1]. Less than 10% of ventilated patients potentially posed problems in weaning from mechanical ventilation. Similarly, at a community hospital, few surviving patients required prolonged ventilatory support [2]. In easy-to-wean patients, Sahn and Lakshminarayan [5] described simple criteria that are predictive of successful discontinuation of ventilator support. For the small group of patients who require pro longed mechanical ventilation, however, minimal data are available. In these patients criteria to deter mine weaning ability or which measurements to follow are not clearly defined. Furthermore, no controlled trials are available to compare the differ ent weaning techniques proposed. In this article we first address routine weaning of the patient who has not required prolonged ventilator support. We then examine the difficult-to-wean patient and dis cuss criteria to begin the weaning process, poten tial causes of failure to wean, and available weaning techniques.