Delivers higher oxygen flow rates via large bore nasal cannula compared with conventional nasal cannula devices.
In patients with a high respiratory workload, inspiratory flow rates are high and room air is entrained. The high flow rates provided with HFNC lead to less room air dilution of the administered oxygen, therefore higher FiO2 is delivered.
Provides a minimal amount of positive pressure secondary to its high flow rates. It has been shown that with the mouth closed, pharyngeal pressure (end‐expiratory pressure) increases as flow increases. End‐expiratory lung volume is higher.
Provides good humidification which can reduce airway irritation and improve mucous clearance.
Decreased anatomic dead space compared with use of NPPV due to increased carbon dioxide washout.
Table 22.1Indications and contraindications for NPPV.
Ventilatory failure (acute exacerbations of COPD, OHS) Cardiogenic pulmonary edema Acute exacerbation of asthma Post extubation ARF Postoperative ARF Patients at high risk for complications of intubation (older age, obesity) Do not intubate status
Need for emergent intubation Cardiac arrest Respiratory arrest Inability to protect airway due to altered mental status Presence of secretions Sinusitis/otitis media Epistaxis/hemoptysis/hematemesis Ileus/gastric distention Pneumothorax/pneumomediastinum Recent facial trauma or surgery Hemodynamic instability
Table 22.2Indications and contraindications for HFNC.
Acute hypoxemic respiratory failure with mild to moderate work of breathing Presence of secretions preventing NPPV use Post extubation
Primary ventilatory failure (hypercapnic failure) Markedly increased work of breathing Respiratory arrest Hemodynamic instability
Basic terminology and settings
Bilevel spontaneous: the set inspiratory/expiratory pressures are delivered with each patient‐generated breath. This is the most common mode of NPPV in ARF.
Bilevel spontaneous timed (ST): in addition to spontaneous mode, the machine mandates the time for delivery of inspiratory positive pressure, and also a minimum number of mandatory breaths per minute.
CPAP: the machine delivers a continuous level of pressure throughout the respiratory cycle (inspiration and expiration).
IPAP is the inspiratory positive airway pressure, defined as the positive airway pressure delivered during the inspiratory phase (as determined by cessation of airflow or maximal inspiratory time). It is usually titrated to achieve a desired tidal volume VT and ensure adequate ventilation.
EPAP is the end‐expiratory positive airway pressure. This is analogous to PEEP during mechanical ventilation, and is defined as the pressure delivered during each expiratory phase and during the pause until the next inspiration.
Rate on bilevel mode serves as the backup rate (minimum breaths per minute).
Flow rate (HFNC):
The flow rate can be set in liters per minute, and higher flow rates enable the delivery of greater concentrations of O2, as well as slightly higher positive pressures.
Both NPPV and HFNC use high flow, closed O2 delivery systems with an oxygen blender that enable precise titrations of FiO2, similar to a mechanical ventilator.
Patient interfaces (NPPV, HFNC):
While several interfaces are available for NPPV machines, the most commonly used interface in ARF settings is the nasal–oral mask which covers the apertures of both nares and mouth with a tight seal to ensure adequate delivery of FiO2 and pressures (Figure 22.1).
High flow oxygen is most commonly delivered by nasal prongs similar in appearance to low flow nasal cannulas, but with a larger bore to accommodate the higher flow rates (Figure 22.2).
Use of NPPV in disease states
NPPV in acute exacerbation of COPD (AECOPD)
This is the most common indication for NPPV use with the largest body of evidence.
Considered first line ventilatory support in patients with AECOPD.
Strong evidence for:
Reduced rates of endotracheal intubation.
Less treatment failure and faster resolution of clinical symptoms compared with oxygen therapy alone.
Reduction in ICU and hospital length of stay and treatment complications compared with invasive mechanical ventilation.
More cost effective than invasive mechanical ventilation.
Can be utilized in the ICU or in closely monitored non‐ICU settings.
Can be used in patients with AECOPD and encephalopathy due to CO2 narcosis.
NPPV in acute cardiogenic pulmonary edema (CPE)
There is a robust and growing body of data supporting the use of NPPV in CPE.
CPAP mode generally first line; patients with concurrent ventilatory failure may benefit from bilevel NPPV.
Data show improved SpO2, decreased work of breathing, reduced rates of intubation, and faster clinical improvement.
Trend towards decreased mortality.
Contraindicated in patients with cardiogenic shock or altered consciousness.
NPPV in acute exacerbation of asthma
There is a mixed body of evidence for this indication.
In early phase of exacerbation can temporize impending respiratory failure by allowing time for medical intervention to work.
Trend towards quicker reduction in dyspnea, and reduced length of stay.
No evidence to support reduced rates of intubation or long‐term morbidity/mortality benefits.
NPPV in neuromuscular disorders with ARF
Patients with neuromuscular disease states, whether acute (Guillain–Barré syndrome) or chronic (myasthenia gravis, amyotrophic lateral sclerosis) often present with ARF.
The use of NPPV in these patients has been shown to reduce the rates of intubation and therefore reduce complications of mechanical ventilation and length of stay.
Patients with neuromuscular disease in ARF must be watched in a monitored setting with frequent reassessment of respiratory status, since they can worsen and require mechanical ventilation.
Parameters for monitoring include negative inspiratory force (NIF) and vital capacity. Forced vital capacity (FVC) <20 mL/kg and/or a NIF <30 cmH2O are considered indications for intubation and mechanical ventilation.
Patients meeting these criteria may be monitored closely on NPPV while treatment for the underlying conditions commences; however, they should be promptly intubated if any further deterioration occurs.
NPPV and HFNC in acute hypoxemic respiratory failure
NPPV had not been recommended for patients with pure hypoxemic respiratory failure, especially those meeting ARDS criteria, for fear of delaying intubation and increasing morbidity and mortality.
However, there is evidence to support the use of NPPV in immunocompromised patients with hypoxemic respiratory failure.
NPPV and HFNC are also used for respiratory support in patients with interstitial lung disease in acute respiratory distress with beneficial outcomes including decreased length of stay.
New studies suggest that HFNC in acute hypoxemic respiratory failure can reduce intubation rates and mortality.
There are ongoing trials to evaluate whether extubation to HFNC improves outcomes.
Special considerations for NPPV
Data suggest that NPPV can forestall reintubation in patients at risk of ARF post extubation; particularly patients with pre‐existing cardiac or pulmonary dysfunction.
NPPV should be applied pre‐emptively to patients with a high likelihood of post‐extubation ARF; application of NPPV after onset of ARF shows no benefit and may inappropriately delay reintubation.
Appropriate selection of patients is essential: not all patients would benefit with application of NPPV post extubation.
Cardiothoracic surgery: in thoracic resections, extubation to NPPV has led to a decrease in reintubation rates, shorter length of stay, and improved oxygenation and ventilation. In cardiac surgery, the rate of postoperative pulmonary complications is decreased but there is no significant reduction in reintubation rates. To prevent surgical complications, lower pressure settings are advisable.
Abdominal surgery: data show that the postoperative use of NPPV can prevent atelectasis and associated complications (hypoxia, postoperative pneumonia). Decreased reintubation rates are also evident.
Patients with a DNR order:
NPPV can be used to relieve dyspnea.
Use depends on the goals of care: either for palliation or as the maximal level of respiratory support.
HFNC may also be used in palliation and may be better tolerated.
NPPV as a bridge to extubation:
In patients with COPD, extubation directly to NPPV may be an option. These patients are often borderline during their spontaneous breathing trials and thus their extubation can often be delayed.
Extubating these patients directly to NPPV has been successful, without increased rates of reintubation and with decreased length of mechanical ventilation.
NPPV as a preoxygenation modality prior to Intubation:
Patients with ARF are often initially placed on NPPV and subsequently progress to intubation.
In these patients, the NPPV device may be used as a preoxygenation tool.
The FiO2 should always be set to 100% when NPPV is used for this indication.
NPPV during procedures in patients at risk for respiratory failure:
Patients undergoing bronchoscopy can be at risk for respiratory failure and have increased respiratory demands; the use of NPPV in these patients peri‐procedure has been successfully described throughout the literature.
Patients undergoing GI endoscopy with a tenuous respiratory status may also benefit from peri‐procedure NPPV; however, the data are more scant and the risk of complications, including aspiration, are higher when invasive GI procedures are undertaken on NPPV. Nevertheless, several cases have been described and this may be an option for a patient with contraindications to intubation (such as DNI status).
Predictors of success and failure of NPPV
Predictors of success
Higher level of consciousness.
Lower severity of illness.
Less severe gas exchange abnormalities.
Lack of severe acidosis pH 7.10–7.35.
Minimal air leak around the interface.
Predictors of failure
Encephalopathy (except AECOPD patients).
Low pH (especially <7.1).
Patient dyssynchrony with NPPV.
On reassessment (0.5–2 hours):
No improvement in mental state.
No improvement in pH/PaCO2.
No improvement in respiratory rate or work of breathing.
Guidelines for use
Protocol for initiation of NPPV
Monitor in ICU or other closely monitored settings, such as step down or respiratory care units.
Oximetry and vital signs monitoring as clinically indicated, preferably continuous.
Position patient at >30° angle.
Select the appropriate interface based on face size and patient comfort.
Select ventilator and mode of ventilation.
Avoid excessive strap tension from headgear to prevent discomfort and potential skin ulceration.
Claustrophobia: use of a nasal mask may be beneficial in claustrophobic patients.
Adverse hemodynamic effects are unusual but have been reported.
Very low risk of barotrauma.
Mild gastric distention, incidence 10–50%.
Aspiration of gastric contents, rarely significant at routinely applied levels of inspiratory pressure support.
Addition of agents that accelerate intestinal transit (domperidone or simethicone).
Decrease in IPAP may be beneficial.
Airway dryness sinus or ear pain, decreased sputum clearance, or nasal congestion.
Skin breakdown due to pressure: most common location of skin breakdown is the bridge of the nose:
Alternating between different masks helps to prevent skin breakdown.
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Type of evidence
Title and comment
Date and reference/weblink
Consensus guideline statement
International Consensus Conferences in Intensive Care Medicine: Non‐invasive Positive Pressure Ventilation in Acute Respiratory Failure. Organized jointly by the American Thoracic Society, the European Respiratory Society, the European Society of Intensive Care Medicine, and the Societe de Reanimation de Langue Francaise, 2000 The guidelines establishing general principles of use as adopted by several leading respiratory societies throughout the world. Guidelines are based on analysis of various metadata and review articles
Noninvasive ventilation and survival in acute care settings: a comprehensive systematic review and metaanalysis of randomized controlled trials Use of NPPV in acute care settings and patient outcomes. The meta analysis data show increased survival rates for patients in whom NPPV was used as primary support therapy and used post extubation
2015 Crit Care Med 2015;43(4):880–8
Clinical practice guidelines for the use of noninvasive positive‐pressure ventilation and noninvasive continuous positive airway pressure in the acute care setting An analysis of multiple studies and guidelines. Conclusions supported the early use of NPPV in AECOPD, CPE, and to prevent reintubation in these patients
2011 CMAJ 2011;183(3):195–214
Reversal of acute exacerbations of chronic obstructive lung disease by inspiratory assistance with a face mask The landmark trial of NPPV use and outcomes in patients with AECOPD
1990 N Engl J Med 1990;323:1523–30
Treatment of severe cardiogenic pulmonary edema with continuous positive airway pressure delivered by face mask The landmark trial of NPPV use and outcomes in patients with cardiogenic pulmonary edema
1991 N Engl J Med 1991;325:1825–30
High flow oxygen through nasal cannula in acute hypoxemic respiratory failure Discusses the benefits of HFNC in patients with acute hypoxemic respiratory failure