12. Non-invasive respiratory support
In the UK, non-invasive ventilation ( NIV) is currently provided predominately in acute respiratory units/respiratory high dependency units, and much of the expertise in NIV resides in respiratory team members. This is likely to be the situation in an influenza pandemic where critical care beds are likely to be filled with patients receiving mechanical ventilation. The following guidance on NIV has been developed in conjunction with the British Thoracic Society and the Intensive Care Society.
The role of NIV in the treatment of pandemic flu remains controversial. 55 It has been demonstrated previously that NIV does not have an extensive role in the management of acute respiratory failure due to pneumonia, 56 although it may improve outcome in those with underlying lung disease e.g. chronic obstructive pulmonary disease ( COPD). It is also clear that NIV is not likely to be successful in individuals with severe/rapidly progressive acute lung injury, extensive bilateral pulmonary shadowing on chest X-ray, or >1 system failure.
There is therefore the potential for NIV to:
- reduce the need for intubation in influenza-related pneumonia when used as an early intervention, particularly in those with co-morbidities such as COPD
- widen the provision of ventilatory support outside the critical care unit, thereby reducing pressure on intensive care unit beds
- provide step-down respiratory support to recovering patients to speed discharge from critical care
- act as a ceiling to ventilatory care in patients with severe COPD/congestive cardiac failure in whom existing co-morbidities would diminish the prospect of survival if invasive ventilation was initiated. 57
This should be set against the likelihood of droplet dissemination during the delivery of NIV, increasing the risk of infection to healthcare workers, other patients and family members. 58 In a pandemic in which the infection is relatively mild in normal individuals, but produces ventilatory decompensation in those with chronic conditions, the balance is tipped towards providing NIV; if the pandemic is associated with high mortality in previously healthy individuals, the balance moves away from providing NIV unless strict safety measures for healthcare workers are effective. NIV is classed as a potential aerosol generating procedure and appropriate infection control procedures should be followed (gown, gloves and eye protection should be worn and use of an FFP3 respirator instead of surgical mask may be prudent; see Pandemic influenza: Guidance for infection control in critical care for further information). 59 Pragmatically the risks of NIV should also be set against providing high flow oxygen to patients, which at very high FiO2 begins to approximate flows generated by NIV and continuous positive airway pressure ( CPAP).
Local healthcare providers should be aware of the type and quantity of NIV used locally and the potential to increase capacity, should this be required.
NIV should be applied by teams experienced in the use of NIV in acute respiratory failure, as expertise in ventilator settings and rapidly applying interfaces is essential. A range of interfaces including non-vented full facemasks and helmets should be available. There is no evidence that any particular ventilator is superior to another in acute respiratory failure, although bilevel ventilation is likely to offer advantages over single level ventilation. Local training needs should be addressed in the pre-surge period.
Monitoring is vital and teams should be able to identify patients in whom NIV is failing in order to escalate to Invasive Positive Pressure Ventilation ( IPPV) or withdraw therapy/provide palliative care as appropriate. Decisions as to whether patients should proceed to IPPV if NIV fails or NIV is to be the ceiling of care should be made pre-treatment, or early in the course of treatment (e.g. after 2 hour trial) if sufficient evidence is not available at start of therapy.
There should be close liaison between respiratory NIV units and critical care units so that patients can receive step up or step down care expeditiously, and surge triage guidelines are followed. Ideally, units should be contiguous or close to minimise transfers.
Teams providing NIV should be familiar with palliative care guidelines and withdrawal of therapy in patients in whom NIV fails and where it represents the ceiling of therapy. 60