5. Non Invasive ventilation

Non-invasive ventilation (NIV) is the application of respiratory support via a sealed face-mask, nasal mask, mouthpiece, full face visor or helmet without the need for intubation In the modern era it implies the application of positive airway pressure, however some classifications include the application of a negative-pressure generator to the chest (‘iron lung’) as NIV Positive pressure ventilatory support may be with CPAP or bi-level modes and delivered by a range of ventilators from specifically designed devices to full-service ICU ventilators NIV decreases resource utilisation compared with invasive ventilation and avoids the associated complications. Patient selection and a well-designed clinical protocol are important to avoid delaying intubation in patients who are not suitable for and/or failing NIV

• Negative pressure (cyclical) iron lung chest box used for COPD, neuromuscular disease • Positive pressure (non-cyclical) continusous positive airway pressure (CPAP) used for acute pulmonary edema, asthma, obstructive sleep apnoea (OSA) • Positive pressure (cyclical) Bilevel positive airway pressure (BIPAP), inspiratory positive airway pressure (IPAP), pressure support ventilation (PSV) and positive pressure ventilation (PPV) used for COPD, weaning, asthma, neuromuscular disease • Positive and negative pressure (cyclical) cough assist used for neuromuscular disease

PHYSIOLOGY NIV can reverse many of the physiological and mechanical derangements associated with respiratory failure: augmentation of alveolar ventilation, helps reverse acidosis and hypercapnoea alveolar recruitment and increased FiO2, helps reverse hypoxia reduction in work of breathing and respiratory effort/ fatigue stabilisation of chest wall in the presence of chest trauma/surgery reduction in left ventricular afterload, improves LV function counterbalances the respiratory workload and/or reduces respiratory muscle effort, helps maintain alveolar ventilation and prevents exhaustion

Primarily for hypercapnea acute exacerbation of COPD – decrease work of breathing and unload respiratory muscles post extubation acute respiratory failure — planned strategy in selected patients Obstructive sleep apnoea / Obesity hypoventilation syndrome Primarily for hypoxaemia cardiogenic pulmonary oedema – alveolar recruitment, decreased afterload, decreased work of breathing post operative respiratory failure – in selected patients post-traumatic respiratory failure — rib fractures respiratory failure in AIDS and other immunosuppressed states

Younger age Unimpaired conscious state Moderate rather than severe hypercarbia Rapid improvement in physiological parameters

Cardiac / respiratory arrest Inability to protect airway – poor cough, excessive/ inability to clear secretions, decreased conscious state/ coma upper airway obstruction untreated pneumothorax marked haemodynamic instability (e.g. shock, ventricular dysrhythmias, severe acute myocardial ischaemia GI bleeding)

patient reassurance well fitted mask with straps (nasal, full face or helmet) set appropriate FiO2 time or flow cycled start at low pressures e.g. 10/5 cmH2O or CPAP 5 cmH20 increase pressures by 2-3 cmH20 every 5 minutes until satisfactory response (up to 15-17 max) reassess after 60 minutes plus ABG

Weaning NIV typical approach is trial periods off NIV during the day (e.g. 1 hour off and 2 hours) with overnight rest on NIV if patient condition markedly improves NIV can be stopped abruptly monitor closely for respiratory fatigue or deterioration

pressure ulcers/necrosis (nasal bridge) facial or ocular abrasions claustrophobia/anxiety agitation air swallowing with gastric/ abdominal distension, potentially leading to vomiting and aspiration hypotension if hypovolaemic aspiration oronasal mucosal dryness

Summary of evidence for the use of NIV: Cardiogenic Pulmonary Oedema improves respiratory function using above mechanisms also allows for redistribution of extravascular lung water back into interstitial space through recruitment and surfactant production e.g. CPAP at ~ 10cmH2O Chronic Obstructive Pulmonary Disease often respond to both CPAP but also need BIPAP over 14 RCTs show improvements in: -> hypercapnic respiratory failure -> intubation rates -> hospital mortality -> nosocomial pneumonia

Role of NIV in the critically ill includes APO and respiratory failure in COPD and immunosuppressed patients Use NIV as a planned strategy post-extubation in selected patients and as ventilatory support for patients with respiratory failure and treatment directives limiting care Avoid the use of NIV to delay or withhold intubation in those who need it

Noninvasive ventilation improves lung mechanics by improving laminar airway flow by stenting closed airways or semi-obstructed airways this decreasing atelectatic alveoli, improving pulmonary compliance, and reducing work of breathing.

Answer and interpretation Continuous positive airway pressure (CPAP): CPAP is a fixed positive pressure throughout the respiratory cycle. CPAP appears to be more effective in reducing the need for tracheal intubation and possibly mortality in patients presenting with with acute cardiogenic pulmonary oedema (ACPE). Bi-level positive airway pressure (BiPAP): BiPAP is when the ventilator delivers different levels of pressure during inspiration (IPAP) and expiration (EPAP). BiPAP ventilation appears to be more effective in reducing mortality and the need for tracheal intubation in patients with an acute decompensation of COPD.