الفهرس 
ANATOMY OF THE RESPIRATORY SYSTEMOnly 14 pages are availabe for public view
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Abstract
Non invasive ventilation (NIV) is defined as any form of ventilatory support applied without ETI, and is considered to include: CPAP, with or without inspiratory pressure support; volume- and pressure-cycled systems; proportional assist ventilation (PAV). NIV is one of the most important developments in pulmonology over the past two decades . When the cause of acute respiratory failure (ARF) is reversible, medical treatment works to maximise lung function and reverse the precipitating cause, whereas the aim of ventilatory support is to ‘‘gain time’’ by unloading respiratory muscles, increasing ventilation and thus reducing dyspnoea and respiratory rate, and improving arterial oxygenation and, eventually, hypercapnia and related respiratory acidosis. Most of the complications of invasive mechanical ventilation are related to endotracheal intubation (ETI) or to the placement of a tracheostomy tube, to barotraumas or volutrauma and to the loss of airway defence mechanisms; some others may follow extubation or complicate long-term tracheostomy. Noninvasive mechanical ventilation may avoid most of these complications, ensuring at the same time a similar degree of efficacy . Ventilation acquired pneumonia (VAP) and other nosocomial infections are reduced by noninvasive ventilation by preserving airway defence mechanisms, owing to the lower requirement for invasive monitoring. This modality enhances patient’s comfort, allowing for eating, drinking, cough and communication, avoiding or reducing the need for sedation without an increase in cost and nurse workload compared with invasive mechanical ventilation. In addition, chest physiotherapy can be sufficiently applied.
Different conditions leading to acute or acute-on-chronic respiratory failure have been treated with NPPV, but only a few are supported by strong evidence, as follows: prevention of ETI in patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) or acute cardiogenic pulmonary oedema (CPO); in immuno-compromised patients; as a means of weaning from invasive mechanical ventilation in patients with AECOPD who undergo ETI. Weaker evidence supports the use of NPPV: for patients with hypoxemic failure like post-operative or post-extubation ARF; for patients with ARF due to asthma exacerbations, pneumonia, acute lung injury (ALI) or acute respiratory distress syndrome (ARDS); during bronchoscopy; or as a means of pre-oxygenation before ETI in critically ill patients with severe hypoxaemia . The goals of NPPV may be different according to the underlying pathologies. During AECOPD or acute asthma, the goal is to reduce hypercapnia by unloading the respiratory muscles and increasing alveolar ventilation, thereby improving respiratory acidosis until the underlying problem can be reversed. In acute CPO, the goal of NPPV is to improve oxygenation, reduce the work of breathing and increase cardiac output. During hypoxaemic ARF, the goal is to ensure adequate arterial oxygen tension (PaO2).
Patients for NPPV could be on controlled mandatory ventilation, assist/controlled ventilation, synchronized intermittent mechanical ventilation, or spontaneous modes of ventilation. Pressure support ventilation (PSV) and continuous positive airway pressure (CPAP) provide ventilatory support while the patient spontaneously breathing. A constant positive pressure is applied both during inspiration and expiration with CPAP but with PSV it is applied only during inspiration. Bi-level positive airway pressure (Bi-PAP) is a modification in ventilatory modes in which different inspiratory and expiratory pressures are set.
Ventilators employed in NPPV range from ICU ventilators with full monitoring and alarm systems normally employed in the intubated patient, to light weight, portable, free standing devices with limited alarm systems specifically designed for non-invasive respiratory support.
Initiation of NIV requires proper selection of the patients, mode of ventilation, and interface. Uncooperative patients and patients with impaired mental status, excessive secretions, hemodynamic instability, or high risk of aspiration are not good candidates for NIV. NIV is safe and well tolerated in most properly selected patients, however, it has some adverse effects. Most of these adverse effects are related to mask and air flow pressure and are usually minor and avoidable. NPPV is rarely associated with major complications such as hypotension, aspiration, and barotraumas .