Non-invasive ventilation in acute respiratory failure

I was asked an excellent question on the ward-round recently by one of our clever interns. Confronted by a patient with severe chronic lung disease who has become critically unwell, and having decided that intubation and mechanical ventilation via endo-tracheal tube would not be pursued, I was asked whether we would use non-invasive ventilation (NIV). Non-invasive ventilation involves the application of mechanical breathing support without the use of an endotracheal tube or tracheostomy, usually via an occlusive mask applied over the nose and mouth.

For the benefit of my interns, then, I thought it would be worth reviewing the recent literature on the use of non-invasive ventilation in the acute hospital setting. Unfortunately, there isn’t a hell of a lot of new information by the way of guidelines. However, there is some….

Firstly, in patients with COPD the following guidelines are based on recommendations from the global initiative in obstructive lung disease (GOLD):

• Selection criteria for NIV:
  o Moderate to severe dyspnoea with use of accessory muscles and paradoxical abdominal motion
  o Moderate to severe acidosis (pH <= 7.35) and/or hypercapnoea (PaCO2>45mmHg)
  o Respiratory frequency > 25bpm
  

Now it’s seldom quite so cut-and dried, but for those who like lists then you can learn that one.

There are contraindications to NIV which should be remembered:

Exclusion Criteria:

• respiratory arrest
• cardiovascular instability
• change in mental status / uncooperative patient
• high aspiration risk
• viscous or copious secretions
• recent facial or gastroesophageal surgery
• craniofacial surgery
• fixed nasopharyngeal abnormalities
• burns
• extreme obesity
  

A recent German review of over 2900 publications, weighted according to level of evidence, has come up with the following recommendations for use of NIV in acute respiratory failure – following the motherhood statement that ‘NIV should be preferred to invasive ventilation wherever possible to avoid the risk of ventilator-tube associated complications such as ventilator associated pneumonia’, (a level A recommendation);

• in hypercapnoeic acute respiratory failure (ARF) NIV reduces rate of hospital acquired pneumonia, length of hospital stay and mortality – both in hospital and in ICU (Level A)
• patients with cardiopulmonary oedema should be treated with CPAP or NIV (CPAP is fine. Level A recommendation. Very important – don’t just give them lasix. CPAP treats the heart failure by increasing intrathoracic pressure and reducing venous return – reducing preload on the failing ventricle and allowing it to contract more effectively.... all to do with the Starling curve. Complicated, but CPAP doesn’t just support their breathing, it treats the heart failure. Everyone with APO should get CPAP – says the respiratory physician - but remember that CPAP can drop blood pressure, so be wary in patients with hypotentsion)
• in immunocompromised patients with ARF, for reasons unclear, NIV reduces mortality (Level A)
• to prevent post-extubation failure and to facilitate weaning of intubated patients with hypercapnoeic respiratory failure (Level A)
• in patients who decline invasive intervention, NIV may be an acceptable alternative (Level B)
• to lessen dyspnoea in palliative care (level C)
  

In patients with simply acute hypoxic respiratory failure, the failure rate of NIV is 30 to 50 % and NIV is not generally recommended (except in those immunocompromised patients).

Hope that helps.

Andrew