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processing.... Drugs & Diseases > Clinical Procedures Noninvasive Ventilation Updated: Jun 18, 2020 Author: Guy W Soo Hoo, MD, MPH; Chief Editor: Zab Mosenifar, MD, FACP, FCCP more...
Share Email Print Feedback Close Facebook Twitter LinkedIn WhatsApp webmd.ads2.defineAd(id: 'ads-pos-421-sfp',pos: 421); Sections Noninvasive Ventilation Sections Noninvasive Ventilation Overview Methods of Delivery General Considerations Application of Noninvasive Ventilation Noninvasive Ventilation in COPD Noninvasive Ventilation in Cardiogenic Pulmonary Edema Noninvasive Ventilation and High-Flow Nasal Cannula Oxygen After Extubation Noninvasive Ventilation in COVID-19 Noninvasive Ventilation in Other Conditions Complications of Noninvasive Ventilation Other Issues Questions & Answers Show All Media Gallery References Overview Overview Noninvasive ventilation (NIV) refers to the administration of ventilatory support without using an invasive artificial airway (endotracheal tube or tracheostomy tube). The use of noninvasive ventilation (see the video below) has markedly increased over the past two decades, and noninvasive ventilation has now become an integral tool in the management of both acute and chronic respiratory failure, in both the home setting and in the critical care unit. Noninvasive ventilation has been used as a replacement for invasive ventilation, and its flexibility also allows it to be a valuable complement in patient management. Its use in acute respiratory failure is well accepted and widespread. It is the focus of this review. The role of noninvasive ventilation in those with chronic respiratory failure is not as clear and remains to be defined.
An interest in the methods of artificial respiration has long persisted, stimulated by attempts at resuscitation of drowning victims. Reports dating from the mid 1700s document a bellows-type device being the most commonly used form of respiratory assistance. Negative-pressure tank-type ventilators came into use in the next century, with a prototype developed by Dalziel in 1832. This spawned a variety of cuirass and tank negative-pressure ventilators, with the general principle of enclosing the thorax, creating negative pressure to passively expand the chest wall and lungs. This led to the Drinker-Shaw iron lung in 1928, which was the first widely used negative-pressure ventilator. In 1931, Emerson modified these large devices, and the Emerson tank ventilator became the standard for ventilatory support. The Emerson tank ventilator was especially crucial in the treatment of poliomyelitis victims.
Rudimentary devices that provided continuous positive airway pressure were described in the 1930s, but the negative-pressure ventilators were the predominant method of ventilatory support until the polio epidemics overwhelmed their capacity in the 1950s. Development of positive-pressure valves delivered through tracheostomy tubes permitted the delivery of intermittent positive pressure during inspiration. This quickly replaced the negative-pressure ventilators, further supported by the development of the cuffed endotracheal tube and bedside ventilators. However, positive-pressure ventilation delivered through either a translaryngeal endotracheal tube or a tracheostomy tube was also associated with a host of complications, specifically injury to the larynx and trachea, as well as other issues involving the timing of extubation, preservation of speech, and the ability to continue swallowing.
In the 1980s, increasing experience with positive-pressure ventilation delivered through a mask in patients with obstructive sleep apnea led to this type of ventilatory support, initially in patients with neuromuscular respiratory failure. Success led to its adoption in other conditions, and noninvasive ventilation became especially promising in the treatment of patients with decompensated chronic obstructive pulmonary disease. In the ensuing 20 years, noninvasive positive-pressure ventilation delivered via a mask has been widely adopted, to the point where it is a first-line therapy in some medical centers. The conditions and patients best suited for noninvasive ventilation are discussed.
Positive-pressure ventilation delivered through a mask has become the predominant method of providing noninvasive ventilatory support and is the focus of this and subsequent sections. Early bedside physiologic studies in healthy patients and in patients with respiratory conditions document successful ventilatory support (ie, reduction in respiratory rate, increase in tidal volume, decrease in dyspnea) with reduction in diaphragmatic electromyography (EMG), transdiaphragmatic pressures, work of breathing and improvement in oxygenation with a reduction in hypercapnia.
Ventilatory support can be achieved through a variety of interfaces (mouth piece or nasal, face, or helmet mask), using a variety of ventilatory modes (eg, volume ventilation, pressure support, bilevel positive airway pressure [BiPAP; see the image below], proportional-assist ventilation [PAV], continuous positive airway pressure [CPAP]) with either ventilators dedicated to noninvasive ventilation (NIV) or those capable of providing support through an endotracheal tube or mask. Older models of noninvasive ventilators required oxygen to be bled into the system, but current models incorporate oxygen blenders for precise delivery of the fraction of inspired oxygen (FIO2).
Negative-pressure ventilators provide ventilatory support using a device that encases the thoracic cage starting from the neck, and devices range from a whole-body tank to a cuirass shell. The general principal is the same with a vacuum device, which lowers the pressure surrounding the thorax, creating subatmospheric pressure and thereby passively expanding the chest wall with diaphragmatic descent, all leading to lung inflation. Exhalation occurs with passive recoil of the chest wall.
This was the predominant technology during the polio epidemics, but these devices were bulky and cumbersome to use. Upper airway obstruction was also a problem. These ventilators have been largely supplanted by the more widespread positive-pressure noninvasive ventilators; however, some patients continue to be treated with this modality. While the bulk of the experience lies in patients with chronic respiratory failure, specifically neuromuscular respiratory failure, reports described successful application in patients with acute respiratory failure.
With respect to the two modes, positive-pressure ventilation has supplanted negative-pressure ventilation as the dominant mode of delivery of noninvasive ventilation. Positive-pressure ventilation is more effective than negative-pressure ventilation in unloading the respiratory muscles, at least under investigational conditions. The primary focus of this article is positive-pressure noninvasive ventilation, and the mention of "noninvasive ventilation" will refer to positive-pressure delivery. That being stated, the reader should be aware that in certain patients and under certain circumstances, negative-pressure ventilatory support may also be acceptable. [1]
As a result of prospective, randomized clinical trials, another option has emerged for the patient with hypoxemic respiratory failure. Heated, humidified, high-flow nasal cannula oxygen (HFNC) has been available for over a decade, but refinements and increasing clinical experience have made it a solid alternative for management that exists in the spectrum of options before noninvasive and invasive mechanical ventilation. This modality was initially developed for neonatal patients, and refinements have permitted its use in adults. Conventional oxygen therapy is not well tolerated at high flow rates because of problems with unheated and nonhumidified oxygen. The high-flow nasal cannula oxygen systems are able to heat and humidify, improving patient tolerance and comfort. The high flow rates have other advantages in that high flow rates minimize room air entrainment, thereby increasing the FIO2 that can be provided to patients; are able to wash out dead space carbon dioxide, improving the efficiency of oxygen delivery; and the increased flow rate translates into positive end-expiratory pressure (PEEP). The amount of PEEP provided is a function of the flow rate but falls somewhere in the range of 0.35-0.69 cm water for each 10 L/min of increased flow rate. [2] Therefore, while high-flow nasal cannula devices technically do not provide assisted support or augment inspired tidal volume as provided by the other forms of mechanical ventilation, the small amount of positive pressure provided does help reduce the work of breathing and improve breathing patterns similarly to that achieved with CPAP. An intact respiratory drive is required with this modality, which means that it is not suited for patients with hypoventilation or a blunted respiratory drive. It is reasonable to consider this modality as a method of providing low-level positive pressure. While this is not assisted ventilation, it is at its most rudimentary level, is a form of noninvasive ventilation. 2ff7e9595c
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