5. Non Invasive ventilation Flashcards
From LIFTL
OVERVIEW
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
CLASSIFICATION
- 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
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
INDICATIONS
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
PREDICTORS OF SUCCESSFUL USE
Younger age
Unimpaired conscious state
Moderate rather than severe hypercarbia
Rapid improvement in physiological parameters
CONTRAINDICATIONS
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)
USE OF NIV
Starting NIV
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
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
COMPLICATIONS
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
EVIDENCE
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
AN APPROACH
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
How dose NIV work?
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.
Q3. Whats the difference between CPAP & BiPAP?
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.
