the Application of Respiratory Support Without Requiring Intubation

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

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

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

- 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)