key: cord-0034790-iyuca9lv
authors: Keymel, Stefanie; Steiner, Stephan
title: Noninvasive Mechanical Ventilation Guidelines and Standard Protocols for Noninvasive Mechanical Ventilation in Patients with High-Risk Infections
date: 2013-05-29
journal: Noninvasive Ventilation in High-Risk Infections and Mass Casualty Events
DOI: 10.1007/978-3-7091-1496-4_40
sha: d97103ba7f54ec493e97b06a37785c7878d7b6e1
doc_id: 34790
cord_uid: iyuca9lv

Noninvasive ventilation (NIV) is associated with lower rates of endotracheal intubation and decreased mortality in patients with acute respiratory failure. Therefore, NIV should be preferred to invasive ventilation whenever possible [1]. In clinical settings, most of the patients were treated by NIV because of pulmonary edema or exacerbated chronic obstructive lung disease (COPD) [2]. With endemic and high-risk infection, most of the critically ill patients develop acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). Furthermore, NIV, an “aerosol-producing factor” might be regarded as a high-risk procedure for medical staff [3].

As a result of the growing importance of NIV in emergency and intensive care medicine, several guidelines on this topic were published during the last decade.

The following overview summarizes the recommendations on NIV in patients with ALI and ARDS, which are known to complicate high-risk infections.

In 2001, an international expert group concluded that NIV may substitute for invasive ventilatory support in patients with hypoxemic respiratory failure due to pneumonia. The authors noted that there were only three randomized studies comparing NIV with invasive ventilation and that they had different endpoints and results [ 2 ] . A year later, the British Thoracic Society (BTS) published guidelines on the use of NIV in patients with acute respiratory failure (ARF). They did not consider the treatment of ALI due to respiratory infection. Conversely, at this time severe hypoxemia was regarded as a contraindication for NIV [ 4 ] . Certainly, there was no link to high-risk infection at that time. The Canadian Critical Care Trials group made no recommendations about the use of NIV in ARDS patients or those with severe community-acquired pneumonia (CAP) in 2011 [ 5 ] . In summary, compared to NIV for exacerbated COPD (hypercapnic respiratory failure), cardiogenic lung edema, or postextubation failure, the data regarding the use of NIV in patients with hypoxemic ARF are less clear [ 1 ] .

Tables 40.1 and 40.2 summarize common accepted indications and contraindications for NIV. NIV might be considered in patients with tachypnea and a respiratory rate >24 breaths/min, a poor alveolar gas exchange level as indicated by PaO 2 / FiO 2 < 200 mmHg, and/or severe dyspnea accompanied by the use of accessory respiratory muscles [ 6 ] . Beyond this, NIV may be undertaken as a therapeutic trial with a view to tracheal intubation if it fails or as a ceiling of treatment in patients who are not candidates for intubation [ 4 ] . It should be emphasized that intubation 

There is a broad agreement that NIV should be conducted in the intensive care unit (ICU), where immediate expertise is available to enable a rapid transition to invasive ventilation if needed [ 1 , 8 , 9 ] .

Noninvasive ventilation is defi ned as ventilator assistance to the lungs without an artifi cial airway. There are various devices, including negative-pressure ventilators (e.g., the so-called tank ventilator, or "iron lung"), several masks, and helmets. Because of limited practicability, tank ventilators do not play a major role in modern intensive care medicine. Selection of the optimal interface-which connects the ventilator to the nose, mouth, or both-is an essential part of NIV. Air leakage, discomfort, or claustrophobia might result in patient intolerance. In the acute care setting, nasal, oronasal, or full-face masks are primarily used [ 1 , 4 , 5 ] . There are few randomized controlled trials comparing the use of an oronasal mask with a nasal mask. Nevertheless, the oronasal mask has been better tolerated than nasal mask or full-face mask [ 1 , 10 ] . Because there is a lack of evidence regarding which interface is best, some guidelines do not give recommendations about the use of interfaces [ 5 ] .

Others favor the use of a full-face mask for the fi rst 24 h, switching to a nose mask if preferred by the patient [ 4 , 11 ] . In general, masks and exhalation valves that are licensed as reusable by the manufacturer require high-level disinfection. They should be disassembled in their parts and then undergo an automatic process using washer, disinfector, and dryer.

Attaching a bacterial fi lter to the ventilator's output can minimize respirator contamination [ 4 ] . As an alternative, using single-use material could reduce the risk of infection.

Noninvasive ventilation can be performed using pressure support ventilation, proportional assist ventilation, or volume-controlled ventilation [ 1 , 2 ] . Schönhofer et al. [ 1 ] recommended the use of positive-pressure ventilation with inspiratory pressure support and positive end-expiratory pressure (PEEP). As patients with ARF are often agitated and have pronounced respiratory drive, ventilation triggered by the patient's own respiratory efforts is benefi cial compared to controlled, timebased ventilation. When there is not suffi cient spontaneous inspiratory effort or it is inadequate to trigger the ventilator, pressure-controlled ventilation could be used [ 1 , 2 ] . Other guidelines do not emphasize a mode of ventilation on the strength of insuffi cient evidence [ 5 ] . Similar to invasive ventilation, ventilator settings should be adjusted to provide the lowest inspiratory pressures or volumes needed to improve oxygenation and patient comfort, which can be estimated by the decrease in the respiratory rate and respiratory muscle unloading [ 2 ] . Because most of the critical ill patients with SARS or H1N1 virus infection develop ARDS and ALI, a lung-protective ventilatory strategy and fl uid restriction are essential.

The most important parameters during the clinical course are PaCO 2 (arterial partial pressure of carbon dioxide), pH, respiratory rate, dyspnea, and alertness. The aforementioned parameters have to show a trend toward improvement during the fi rst 2 h of NIV [ 1 ] . The NIV failure rate in patients with hypoxic respiratory failure is estimated to be 30 % (CAP) to 50 % (ARDS) [ 7 , 9 , 12 ] . Failure occurs early or after a few days [ 1 ] . It should be noted that NIV failure is associated with a worse outcome, which might be a consequence of a delayed response to the NIV failure because of inadequate monitoring or delayed defi nitive care [ 13 ] . Other predictors of failure are the duration of NIV, oxygenation index, and the Simplifi ed Acute Physiology Score II at admission, and, as expected, the length of ICU stay [ 7 ] . Other authors found a high APACHE score, copious respiratory secretions, poor nutritional status, and confusion or impaired consciousness to be associated with NIV failure [ 2 ] .

There are specifi c problems concerning the use of NIV in patients with endemic and high-risk infections. First, there are no controlled trials on this topic. Therefore, recommendations are largely based on supposition [ 3 ] . It is of concern that NIV, as an "aerosol-producing procedure," possibly increases the risk of caregiver exposure or of exposure to other patients, which would be disastrous in case of a pandemic. Therefore, organizations such as the World Health Organization [ 14 ] and the UK National Health Services Agency [ 15 ] published guidelines that treat NIV as a high-risk procedure. Nevertheless, there are no controlled data comparing particle dispersion between individuals undergoing NIV and those who are not. Furthermore, it should be kept in mind that endotracheal intubation also is at risk of transmitting disease. In an experimental model, Hui and coworkers [ 16 ] found that fl ow from a noninvasive ventilator may increase occupational risk. As this risk may be mediated by air leaks, fi tting the mask properly is essential. Full-face masks and helmets might be superior to nasal masks.

Also, NIV must be managed under strict isolation measures with adequate protection (e.g., N-95 mask) of the health care workers who attend to the patients. As far as possible, infected patients should be isolated in rooms with negative pressure.

Although most of the guidelines do not recommended use of NIV, it has become part of the standard treatment protocol for SARS [ 17 ] . Han et al. [ 18 ] demonstrated that NIV was not only effective in avoiding intubation and invasive ventilation, it effectively reduced the ICU length of stay. No infection was detected in 155 health care workers, and their serology tests for coronavirus were negative.

• Current guidelines do not recommend NIV for the treatment of hypoxemic respiratory failure in endemic and pandemic infections (e.g., SARS or H1N1). However, the level of evidence is low. • Noninvasive ventilation appears to be a reasonable option in carefully selected cases, which should be treated under optimal conditions with awareness of NIV failure and might be regarded as a high risk procedure for medical staff.

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