NIV
9/10/10
OH pages 429-434
= non-invasive ventilation
- the application of respiratory support without requiring intubation
- includes the application of positive airway pressure or the application of a negative-pressure
generator to the chest (‘iron lung’)
PHYSIOLOGY
NIV can reverse many of the physiological and mechanical derangements associated with
respiratory failure:
-
augmentation of alveolar ventilation -> reverse acidosis and hypercapnoea
alveolar recruitment and increased of FiO2 -> reverse hypoxia
reduction in WOB
stabilisation of chest wall in the presence of chest trauma/surgery
reduction in LV afterload -> improved cardiac function
-> counterbalances the respiratory workload and/or reduces respiratory muscle effort ->
maintains alveolar ventilation
CONTRAINDICATIONS
-
respiratory arrest
unprotected airway (coma, sedation)
upper airway obstruction
untreated pneumothorax
inability to clear secretions
marked haemodynamic instability
oesophageal or maxillofacial surgery
patient refusal
staff inexperience
Jeremy Fernando (2011)
TYPES:
-
CPAP
Inspiratory positive airway pressure (IPAP) and PSV
Bilevel positive airway pressure (PSV + CPAP)
Controlled ventilation
COMPLICATIONS
-
pressure ulcers/necrosis (nasal bridge)
facial or ocular abrasions
claustrophobia/anxiety
agitation
air swallowing with abdominal distension -> vomiting and aspiration
hypotension if hypovolaemic
aspiration
oronasal dryness
raised ICP
increased intraocular pressure
INDICATIONS BY TYPE OF RESPIRATORY FAILURE
Hypercapnic
-
acute asthma
acute exacerbation of COPD
post extubation acute respiratory failure
cystic fibrosis
patients awaiting lung transplantation
patients not candidates for intubation (DNR or terminal illness)
Hypoxaemic
-
cardiogenic pulmonary oedema
post operative respiratory failure
post-traumatic respiratory failure
respiratory failure in AIDS
patient not candidates for intubation
sleep apnoea syndromes
chronic hypoventilation syndromes
Jeremy Fernando (2011)
DISEASE PROCESSES AND 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
- just need CPAP @ 10cmH2O
- BIPAP may increase risk of MI
- over 20 RCT’s that show:
-> improvements in respiratory failure
-> reduction in need to intubate
-> reduced hospital stay
-> improved survival
-> shorter periods of respiratory support (MV vs NIV)
Chronic Obstructive Pulmonary Disease
- often respond to both CPAP but also need BIPAP
- over 14 RCT’s show:
-> decreased hypercapnic respiratory failure
-> decreased intubation rates
-> decreased in hospital mortality
-> reduced nosocomial pneumoniae
Asthma
- CPAP 5cmH2O and BiLevel
-> significant increase in FEV1
-> significant decrease in hospital admission rates
ALI and ARDS
- little supportive evidence for NIV
-> high failure rates
Pneumonia and the Immunocompromised
- MV is associated with high morbidity and mortality in these patients.
- thus may benefit from a reduction in intubation and MV
Post-operative and Post-traumatic Acute Respiratory Failure
- CPAP improves oxygenation and respiratory rate in general surgical and cardiothoracic
patients with mild hypoxaemia.
- outcome data is less clear
NIV-assisted Weaning
Jeremy Fernando (2011)
- COPD patients respond well
- not so clear cut for other patients
Sleep Apnoea Syndromes
- CPAP can reverse the chronic changes associated with chronic hypoxia
- if there is a central component, BiLevel or controlled ventilation can be used until can be
weaned to CPAP
Chronic Hypoventilation Syndromes
- neuromuscular disease
- no real benefit in stable COPD
Jeremy Fernando (2011)