High-flow generators
Ventilators
Pros
Pros
Simpler, less parameters needed to set
No limits in high flow versus high FiO2
Cheaper
Leak compensation, more stable pressure
No triggering system
Waveforms, alarms, monitoring
Easier and lighter for transport or OOH use
Known FiO2
Cons
Cons
Compromise between high flow and/or high FiO2
More complex, more parameters to set
Less stable positive pressure
Expensive
No alarms, no monitoring
Need for synchronization and triggering
Inaccurate FiO2
Need for batteries or electricity
Lower performances
Need for specific NIV module
Today there is no reason to strongly recommend a specific device over another. A pivotal factor in the approach and the choice is the need to provide a high flow, high enough to meet the needs of a patient with ARF, mainly in the very early phase of inhalation. Some other simpler devices, with or without oxygen supply, are particularly tailored for home treatment of chronic conditions. On the other hand, patient comfort and tolerance of the interface are probably the crucial factors for successful NIMV [6]. Oro-nasal masks, full or total face masks, and helmets can be used to provide NCPAP in treating ARF. The pros and cons are listed in Table 14.2. Nasal masks, nasal prongs, and mouthpieces are used outside of the acute care setting; interfaces covering both the mouth and the nose are the first choice for acute NIMV. The ideal mask does not exist and cannot be expected a priori for an individual patient.
Table 14.2
NCPAP interface characteristics
Oro-nasal Mask | Full/total face mask | Helmet |
|---|---|---|
Pros | Pros | Pros |
Few air leaks | Scarce air leaks | Minimum air leaks |
Stable airway pressure | Easy fitting | Neither nasal nor facial skin damage |
Easy application | Stable airway pressure | No problem in facial trauma, burns, edentulism |
Less cooperation required | No nasal bridge skin lesions | Less flow resistance |
Cheaper | Less noisy | Easier speaking |
Panoramic view | ||
Possible drinking | ||
Enteral nutrition allowed | ||
Easier coughing and expectoration | ||
More suitable for long-lasting treatments | ||
Cons | Cons | Cons |
Nasal skin decubitus | Facial skin lesions | Very high gas flow required |
Vomiting | Vomiting | Noisy |
Claustrophobia | Claustrophobia | High dead space |
Eyes irritation | Eyes irritation | Risk for CO2 rebreathing |
Difficult seeing | Difficult speaking | Less stable airway pressure |
Difficult speaking | Ophthalmopathies | Axillae or neck skin lesions |
Neither eating nor drinking | Expensive | Longer time for application |
Difficult humidification | ||
Expensive |
In an ideal situation, even in the emergency setting, it is useful to be able to change the size or rotate different interfaces to reduce the rate of complications (Table 14.3) and increase patient comfort during NCPAP. The most common complications associated with interfaces for NCPAP can be, at least in part, prevented, treated, and resolved [3, 7]. The contribution provided by the nursing staff in the management of the interface can make the difference in the success of the treatment. Training, experience, skills, and motivation are vital factors, primarily in the early phases of treating ARF by NIMV, for a successful outcome [4].
Table 14.3
Most common complications due to NCPAP interfaces
Leaks |
Pressure sores and ulcers |
Discomfort |
Soft skin tissue damage |
Claustrophobia |
Aspiration |
Mucous plugging |
Conjunctivitis |
Keratitis |
Eye irritation |
Oral and nasal dryness |
Nasal congestion |
Vomiting |
Gastric distention |
Aerophagia |
Difficult speaking |
Difficult eating |
Difficult hearing |
Noise |
Allergy |
14.4 Main Clinical Indications
The efficacy of NIMV on patient outcome predominantly depends on the underlying pathology. ACPE provides the best evidence for efficacy of NCPAP in ARF [8]. By reducing WB and improving gas exchanges, lung and thorax mechanics (compliance, functional residual capacity (FRC)), right ventricular preload, and left ventricular afterload, it demonstrates the power to reduce mortality and rate of TI versus SO2T.
In 2008, a famous randomized controlled clinical trial (RCCT), which confirmed how NIMV can induce a quicker improvement in respiratory distress and metabolic disturbances versus SO2T, raised uncertainty about the ability of NIMV to reduce the rate of TI and mortality [9]. The paper was widely and harshly criticized for its methods and the structure of the study protocol [10, 11], but, even today, its consequences, when defining the grade of recommendation for NIMV in ACPE, endure [2].
In the field of NIMV, there is no recommendation to date that favors NCPAP over noninvasive double-level positive pressure ventilation (NPPV) for treating ACPE, even though the published data are slightly stronger for NCPAP [8]. Because it is easier and cheaper, NCPAP is considered by many authors as the first-line treatment in ACPE. Moreover, the presence of hypercapnia during an episode of ARF due to ACPE does not represent an indication to prefer NPPV over NCPAP; they are comparable in efficacy, even in this subgroup of cases. This confirms (and is a consequence of the fact) that hypercarbia, in the context of ACPE, is not mainly due to pump failure but has a multidimensional pathophysiological explanation [12].
NCPAP has demonstrated different, lower levels of evidence versus SO2T in the early treatment of other different causes of AHRF in the acute care setting. The pathophysiological background for NCPAP in these conditions is, most likely, one of the following reasons:
To reduce atelectasis
To regain and recover (“recruit”) flooded alveoli to ventilation (to open and keep open)
To increase compliance and FRC
To decrease WB
To unload respiratory muscles
To increase tidal volume
To decrease VPM
To improve oxygenation and correct gas exchange abnormalities
Many promising experiences have been reported in the literature regarding NCPAP for the treatment of AHRF resulting from blunt chest trauma, pneumonia (with or without chronic obstructive pulmonary disease (COPD)), peri- and postoperatively (for both prevention and treatment), mild acute respiratory distress syndrome (ARDS), pandemics, aspiration, pleural effusion, restrictive conditions, facilitation of weaning/extubation, and prevention of extubation failure [1, 3, 13, 14].
Acute asthma (AA) is worthy of special mention. Currently, in the field of chronic obstructive pulmonary diseases, AA is a peculiar entity and one of the most common reasons for NIMV application in EDs in the United States [15]. For AA, NCPAP showed positive results in early prevention of AHRF, and less strong data in the treatment of AHRF itself, even with a convincing pathophysiological background (Table 14.4).
Table 14.4
Pathophysiological rationale for NCPAP in AA
Increased bronchodilation (mechanically, equal pressure point, alveolar patency at end expiration), decreased airway resistance, re-expanded atelectasis (collateral reinflation), promoted removal of secretions, enhanced bronchial clearance, influencing medical treatment |
Increased functional residual capacity, raised minimal pleural pressure, decreased swing in transdiaphragmatic pressure, decreased adverse hemodynamic effects |
Reduction of respiratory muscles load, accessory recruitment and work: reduced transdiaphragmatic pressure, pressure time product for the inspiratory muscles and diaphragm, and fractional inspiratory time (endurance); reduction of elastic work (due to intrinsic PEEP); offset intrinsic PEEP and rest respiratory muscles; |
Reduction of dyspnea, respiratory rate, pulse rate |
Improvement in arterial blood gas exchanges, reduced inspiratory work (improved efficiency and decreased energy cost), increased FEV1 |
Need of lower inspiratory pressures versus IMV |
Reduced side effects and avoided complications versus TI, reduced need for sedation versus TI; decreased adverse hemodynamic effects of large negative peak and mean inspiratory pleural pressures; reduced need/frequency/duration of hospital admission |
NCPAP also has pathophysiological significance for ARF resulting from acute exacerbations of COPD, overcoming intrinsic PEEP and acting as a kind of mechanical bronchodilator, and reducing both dyspnea and WB. In this area, the efficacy of NPPV versus SO2T, and also versus CPAP, is evident [16].
NCPAP is used to treat AHRF in chronic conditions such as OSAS [17] and CHF, and also in some carefully selected patients, often overlapping, with neuromuscular diseases, obesity hypoventilation syndrome, restrictive pulmonary diseases, thoracic cage deformities, partial upper airway obstruction, sleep disorders, idiopathic pulmonary fibrosis, and so on. In these chronic conditions, the purpose for NCPAP is to achieve physiologic benefits, palliate symptoms, improve quality of life, decrease pulmonary morbidity, reverse reversible superimposed conditions responsible for acute deterioration, prevent hospitalizations, and, in some cases, extend survival.
Regardless of the specific causes of AHRF, there is a high grade of recommendation for NIMV and NCPAP in immunocompromised patients [3]. This is mainly due to the high rate of infectious complications during IMV and its consequences in terms of hospital mortality. The subgroup of immunosuppressed patients features one of the most striking and strong indications for NIMV and NCPAP, in terms of efficacy and outcome, for the treatment of various forms of ARF [18, 19].
In summary, each unusual or off-label application of NCPAP for AHRF has lights and shadows, and, even in cases of promising preliminary results, remains controversial. Large, prospective, multicenter RCCTs are needed. Out of shared indications, NCPAP should be provided early, cautiously, safely and carefully, during the proper “window of opportunity,” by an experienced team, in an appropriate setting (ICU or HMDU), with a quick access to facilities for TI and IMV [1, 3, 4].
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