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Evidence‐based approaches

NIV as a method of respiratory support is the maintenance of positive pressure throughout the respiratory cycle when the patient is breathing spontaneously. It provides an additional option of therapy between conventional oxygen therapy and controlled, invasive ventilation. Advances in NIV devices, the development of more comfortable interfaces, and improvements in patient monitoring and care during NIV delivery have contributed to the increased use of NIV within a variety of clinical settings (Corrêa et al. [50]).

The aims of NIV therapy are to improve gas exchange, reduce the work of breathing, relieve dyspnoea and prevent atelectasis (incomplete lung inflation). These outcomes are achieved by:

Increasing functional residual capacity (FRC), which is the amount of gas left in the lungs at the end of normal expiration available for pulmonary gas exchange. In acute lung injury where gaseous exchange is severely inhibited, NIV increases the FRC by reopening collapsed alveoli and improving ventilation and oxygenation (Chowdhury et al. [46]).
Improving the ventilation/perfusion ratio: under‐ventilation of the lungs can lead to intrapulmonary shunting (blood passing through the lungs without being oxygenated). NIV helps to decrease this by improving the ventilation/perfusion mismatch (Davison et al. [57]).
Improved lung compliance (elasticity) of the lungs: in respiratory failure, the lungs become much stiffer and less compliant and breathing can become more difficult. Reduction in lung volume below a certain level results in airway collapse, hypoventilation and reduced gaseous exchange. The increase in transpulmonary pressure required to overcome this can be achieved by NIV (Demoule et al. [60]).
Increasing lung volume (alveolar volume): NIV maximizes alveolar recruitment, leading to an increase in the surface area of the alveoli available for gaseous exchange (Demoule et al. [60]). Therefore, oxygen requirements can be reduced and the work of breathing relieved.

Other benefits include the preservation of the ability to speak, cough, clear secretions and swallow while warming and humidifying inspired air via natural upper airway mechanics (Davison et al. [57]).

Rationale

Indications

NIV methods are usually commenced to improve lung expansion and are indicated in the presence of clinically significant pulmonary atelectasis when other forms of therapy, such as high‐flow oxygen therapy, incentive spirometry, chest physiotherapy and deep breathing exercises, have been unsuccessful. Success of NIV will be influenced by patient selection, underlying pathology, severity of respiratory compromise, interface tolerance and presence of other organ dysfunction (Brill [30]).

The clinical presentations that may benefit from NIV therapy are outlined in Box 12.1.

Box 12.1

Clinical presentations that may require non‐invasive ventilation (NIV)

Acute respiratory failure (Beitler et al. [20], Ozsancak Ugurlu et al. [211], Vadde and Pastores [277])
Acute exacerbation of COPD (Schnell et al. [245])
Post‐surgical respiratory failure (Cammarota et al. [35], Ferrer and Torres [81]), except in cases of laryngeal trauma or recent tracheal anastomosis
Immunocompromised patients (Cortegiani et al. [51], Ferreira et al. [80], Huang et al. [112], Schnell et al. [245])
Obstructive sleep apnoea (Gulati et al. [97])
Obesity hypoventilation syndrome (Bry et al. [33])
Acute cardiogenic oedema (Masa et al. [148])
Neuromuscular disease (NICE [192])
Cystic fibrosis (Rodriguez‐Hortal et al. [237])
Chest wall deformities (Davies et al. [56])
Post‐extubation difficulties (Lin et al. [135])
Weaning difficulties (Yeung et al. [291])
Patients ‘not for intubation’ but who still have a need for aggressive or supportive interventions for reversible respiratory clinical presentations (Vadde and Pastores [277])

Contraindications

Contraindications to the use or application of NIV include:

recurrent pneumothoraces or untreated pneumothorax
inability to maintain own airway (Corrêa et al. [50])
upper airway obstruction secondary to tumour involvement (Vadde and Pastores [277])
recent facial or head and neck surgery (not necessarily a contraindication if using helmet NIV or CPAP)
facial burns
epitaxis
excessive secretions or ineffective cough (Olivieri et al. [210])
vomiting or high risk of aspiration (Vadde and Pastores [277])
haemodynamic instability or shock
cardiac arrhythmias
any condition where an elevated intracranial pressure is undesirable or where reduction in cerebral blood flow is inappropriate (Backhaus et al. [12]).

Assessment

Patient assessment and early escalation to NIV are paramount in ensuring the success of the therapy and avoiding further deterioration in respiratory function (which may result in the patient requiring intubation). A trial period of NIV is often useful to predict its effectiveness (Demoule et al. [60]).

Patients who meet the criteria for NIV should have therapy initiated within 60–120 minutes of an acute presentation or deterioration (Davison et al. [57]). A comprehensive initial assessment and timely review following NIV initiation can help to identify predictors for patients who may fail a NIV trial and allow for prompt intubation. NIV failure can be identified by (Corrêa et al. [50]):

lack of improvement in gas exchange within 2 hours (Olivieri et al. [210])
inability to correct dyspnoea
increased fatigue
incapacity to manage copious secretions
interface discomfort and/or intolerance
agitiation
anxiety
haemodynamic instability
progression of respiratory failure.

Anticipated patient outcomes

The anticipated patient outcomes of NIV include:

increased capillary oxygen saturations (SpO₂): oxygen should be prescribed to achieve a target saturation of 94–98% for most acutely ill patients or 88–92% for those at risk of hypercapnic respiratory failure (e.g. patients with COPD) (Davison et al. [57])
decreased administration of supplementary oxygen to achieve targeted oxygen saturation range (Davison et al. [57])
reduced dysopnea, aiming for a respiratory rate of under 30 breaths per minute (Brill and Wedzicha [31])
achievement of exhaled tidal volumes (Vt) of 6 mL/kg of ideal bodyweight (Corrêa et al. [50])
effective secretion clearance as a consequence of humidification, deep breathing and coughing
improvement of breath sounds on auscultation
increased peak flow
improvement in chest radiography
ability to wean the patient off the NIV mask or helmet and maintain an improvement of respiratory status with lower oxygen requirements.