Noninvasive Ventilation in the Hospital Setting Applications and Interfaces

NonInvasive Ventilation (NIV) provides ventilatory support without the use of an invasive artificial airway device. Compared to invasive ventilation, NIV reduces the risk of infections, prevents tracheal injury and diminishes the use of sedatives and analgesia. The physiological benefits from NIV are similar to invasive ventilation, providing reduced work of breathing and improving gas exchange. In selected patients, NIV has been increasingly used to serve as an alternative to intubation. Compared to invasive ventilation, NIV improves survival and reduces complications in selected patients with acute respiratory failure. Main indications for NIV therapy are exacerbation of chronic obstructive pulmonary disease, cardiogenic pulmonary edema, acute respiratory failure in immune-compromised patients and prevention of respiratory failure after extubation. NIV may also have other, less well-described clinical applications, such as in the postoperative setting. NIV shall not be used when patients cannot protect their airway or posses other contraindications for noninvasive ventilation. The success of NIV critically depends on the correct patient selection, the expertise of the team applying it and the type of interface used. In general, NIV is considered safe with most complications being related to interface intolerance. The design of the interface is therefore critical to the success of the noninvasive ventilation. Ambu provides various types of NIV interfaces, all designed to optimize patient comfort and minimize air leaks to ensure success of the NIV therapy. Noninvasive Ventilation in the Hospital Setting Applications and Interfaces Malene Barré Pedersen, PhD, Clinical Research Specialist, Ambu 1 THe ReSpIRAToRy SySTem ANd NoNINVASIVe VeNTIlATIoN The process of Ventilation The primary function of the respiratory system is to exchange oxygen and carbon dioxide. Ventilation is the process by which air moves in and out of the lungs thereby allowing air to be exchanged between the atmosphere and the blood. Inhaled oxygen enters the lungs and reaches the alveoli, the tiny hollow sacs constituting the final branching of the respiratory tree. The surfaces of the alveoli are covered with small blood vessel, the capillaries. During ventilation, oxygen is inhaled into the lungs and passes from the alveoli into the bloodstream through which it is distributed to all the organs and cells of the body. Carbon dioxide, a waste product from the cells, passes from the capillaries through the alveoli wall into the lungs where it is breathed out during ventilation (1). Normal inspiration is initiated when the diaphragm muscle and the intercostal muscles contract, resulting in the thorax to enlarge which in turn forces the lungs to expand. The enlargement of the lungs causes the pressure inside the lungs to drop to less than the pressure of the surroundings thereby causing a bulk flow of air from the atmosphere through the airways into the alveoli. At the end of inspiration, the diaphragm muscle and the intercostal muscles relax which in turn causes the thorax and the lung to passively return to their normal dimension forcing the air out of the alveoli and into the atmosphere (1, 2). Acute respiratory failure is a condition in which pulmonary function is markedly impaired, usually characterized by elevated carbon dioxide or decreased oxygen (or both) in the arterial blood. Acute respiratory failure may e.g. result from acute diseases of the lung such as cardiogenic pulmonary edema characterized by fluid filling, or collapse of the alveoli leading to impairment in the gas exchange during ventilation. Through the promotion of pulmonary gas exchange, noninvasive ventilation can be used in a wide range of disorders that lead to acute respiratory failure (2, 3). Noninvasive Ventilation modes Noninvasive ventilation (NIV), often also referred to as NonInvasive Positive-Pressure Ventilation (NIPPV), is the administration of ventilatory support without using an invasive artificial airway (an endotracheal tube or a tracheostomy tube). NIV is delivered through an interface, typically a facial or a nasal mask, which connects the patient’s airway to the ventilator tubing (4). Bilevel Positive Airway Pressure (BiPAP) is the most commonly used modality of NIV. BiPAP supports breathing and provides two levels of positive pressure: A high inspiratory positive airway pressure and a lower expiratory positive airway pressure (5). Continuous Positive Airway Pressure (CPAP) is a ventilation mode which provides a constant pressure in the airway, both during inspiration and expiration. Although CPAP does not actively assist inspiration as do other forms of NIV, CPAP is often classified as a NIV mode in the literature (4, 6). Like BiPAP, the positive pressure during expiration ensures the opening of collapsed alveoli, which in turn enhances gas exchange and oxygenation. However, CPAP does not actively aid the inspiration phase as BiPAP. CPAP is a relatively simple technique compared to BiPAP which is a more complex mode demanding much more expertise from the health personal applying it (5). In the present review, the specific type and mode of NIV is not always specified in the described applications. NIV may represent BiPAP, CPAP or other noninvasive modalities unless otherwise specified. ApplIcATIoNS of NoNINVASIVe VeNTIlATIoN In Europe, the rate of use of NIV in Intensive Care Units (ICU’s) is about 35% of ventilated patients and higher in respiratory intensive care units or emergency departments. In North America, NIV is begun most often in emergency departments with most patients subsequently transferred to ICU’s (6). The current review presents the clinical applications of NIV having broad acceptance and a solid documentation for the clinical performance. However, the list of applications of NIV in the hospital setting presented here is not exhaustive. Additionally, applications of NIV in the domestic setting, e.g. in the treatment of sleep apnea, are not included in the present review. Noninvasive Ventilation of patients with exacerbation of copd Chronic Obstructive Pulmonary Disease (COPD) is an umbrella term for patients with chronic bronchitis, emphysema, or both. In patients suffering from COPD, the airflow to the lungs is restricted. Smoking is the major cause of COPD. Exacerbations, the acute worsening of COPD symptoms, include increased breathlessness often accompanied by increased cough and sputum production, wheezing, chest tightness and fever. The dominant clinical feature in COPD is impairment of expiratory airflow (3). NIV is currently the first-line treatment in the initial management of patients with acute respiratory failure due to COPD exacerbations (7). Several randomized controlled trials have shown that the addition of NIV to the medical treatment of COPD exacerbations relieves dyspnea, improves vital signs and gas exchange, prevents endotracheal intubation, lowers mortality and shorten the time spent in the hospital. The literature indicates that NIV should primarily be used for the early treatment of COPD patients with mild-moderate respiratory distress to avoid further deterioration and thus avoid endotracheal intubation (6, 7). Noninvasive Ventilation of patients with cardiogenic pulmonary edema During pulmonary edema, excess fluid accumulates in the alveoli in the lungs. The presence of excess fluid in the alveoli reduces gas exchange and results in difficulty of breathing and poor oxygenation of the blood. In cardiogenic pulmonary edema, the edema is due to failure of the heart to remove blood from the lung circulation (2) . The use of NIV in patients with cardiogenic pulmonary edema is supported by multiple randomized trials (7, 8). The main physiological benefits from NIV in these patients are likely due to an increase in functional residual capacity that reopens collapsed alveoli and improves oxygenation. This also increases lung compliance and reduces work of breathing. Several meta-analysis have shown equivalent reductions in intubations and mortality rate with CPAP and BiPAP for cardiogenic pulmonary edema. Thus both CPAP and BiPAP can be used to treat cardiogenic pulmonary edema with equal expectations of success. Some recommend starting with CPAP because it is simpler. If patients remain dyspneic or hypercapnic on CPAP alone, BiPAP may be initiated (7, 8). Together with exacerbations of COPD, acute pulmonary edema is the most common indication for NIV therapy (6). Noninvasive Ventilation of Immuno-compromised patients with Respiratory failure Immuno-compromised patients have a suppressed immune response due to e.g. the administration of immunosuppressive drugs after transplantation or due to certain disease processes such as Acquired Immune Deficiency Syndrome (AIDS). Because the immune system has a reduced ability to fight infections, infectious complications are a common problem in these patients. Prevention of health-care associated infections, e.g. pneumonia resulting from the use of invasive intubation, is therefore an important factor in the treatment strategy of immune-compromised patients. Randomised controlled trials demonstrate that NIV treatment of respiratory failure in patients having received solid-organ or bone-marrow transplants, results in decreased intubation rates, decreased mortality rates and shorter ICU lengths of stay when compared to conventional therapy. Similar findings have been reported for AIDS patients. The reduced mortality was considered to be related to a reduced number of infectious complications associated with NIV compared to invasive ventilation, including ventilator-associated pneumonia and other nosocomial infections (4, 6, 7). Noninvasive Ventilation during Weaning In the majority of cases, ventilation through an endotracheal tube can be withdrawn immediately after significant improvement of the underlying indication for the invasive ventilation. However, in approximately 25% of patients, gradual withdrawal of ventilatory support, called weaning, is required (9). Extubation, the process of removing the endotracheal tube from the patient’s airway, may be a major challenge especially in patients with chronic respiratory disorders such as COPD. Persistent weaning failure is associated with prolonged invasive mechanical ventilation and increased morbidity and mortality. NIV has been used to treat respiratory failure after extubation and to prevent acute respiratory failure during weaning. However, the clinical evidence for the use of NIV in the treatment of respiratory failure after extubation is not substantial and in some circumstances it appears to be unfavorable. One study suggests that NIV delayed necessary reintubation in patients developing respiratory failure after extubation, with the consequent risk of fatal complications (4, 10). The scientific evidence is more favorable for the use of NIV in the prevention rather than in the treatment of respiratory failure after extubation. In certain subsets of patients whose clinical characteristics at the time of extubation may predict re-intubation, NIV may prevent post-extubation respiratory failure. Two randomized trials were performed to assess whether NIV was effective in preventing the occurrence of post-extubation failure in patients at risk (11). Both studies, which adopted similar criteria to define patients at risk and had comparable study designs, showed that the groups treated with NIV had a lower rate of re-intubation than did the groups in which standard therapy was used. Furthermore, in one of the two studies, mortality was also reduced in the subgroup of patients treated with NIV (11). This suggests that, when promptly started, the use of NIV in selected patients “at risk” may prevent post-extubation respiratory failure. Noninvasive Ventilation for postoperative Ventilatory Support Major abdominal and thoracic surgeries are often complicated postoperatively by respiratory failure. Pulmonary atelectasis, the collapse of lung tissue reducing gas exchange in the alveoli, is a frequent complication after major surgery and may predispose patients to pneumonia. In randomized clinical trials, NIV reduced atelectases and prevented pneumonia more effectively than standard therapy after upper abdominal surgery. Moreover, NIV substantially improved gas exchange after gastroplasty in obese patients (6). Preventive use of NIV for a week before or immediately after thoracic, cardiac or vascular surgeries may reduce loss of lung volume. Thus data exists that may support the use of NIV in the postoperative setting. However, more data from randomized controlled clinical trials are needed before specific recommendations can be made (6). 2 NONINVASIVE VENTILATION IN THE HOSPITAL SETTINg APPLICATIONS AND INTERFACES