VOL: 101, ISSUE: 14, PAGE NO: 57
Trevor Phillips, BSc, Dip Grad Phys, SRP, is clinical specialist physiotherapist, Physiotherapy Department, Derriford Hospital, Plymouth
What is NIV?
NIV is a simple method of assisting a patient’s breathing without using an invasive airway (endotracheal or tracheostomy tube). During NIV the patient usually wears a tightly fitting nasal or facial mask that is attached via wide-bore tubing to a portable ventilator. An interface (tight seal) is created between the patient’s face and the mask. The ventilator produces a rapid flow of gas (air or oxygen) that passes down the tubing to the patient-mask interface and exits via a small expiratory valve. The effect of the fast flowing gas passing through a small valve creates a back pressure that is transmitted to the patient’s lungs, so opening the airways and allowing air or oxygen to enter. This positive pressure can be continuous or intermittent.
Indications and benefits of domiciliary NIV
It has been reported that NIV is beneficial for managing a whole spectrum of acute and chronic respiratory conditions. The best evidence relates to its use in acute and acute-on-chronic respiratory failure. The use of NIV in acute care is not discussed in this article (a full review has been published by Brochard et al (2002).
There are three main conditions that benefit from domiciliary NIV:
- Obstructive sleep apnoea;
- Respiratory problems associated with neuromuscular disease and chest wall deformities;
- Chronic obstructive pulmonary disease (COPD).
Obstructive sleep apnoea - Patients with obstructive sleep apnoea are probably the largest group of patients who use domiciliary NIV. OSA is an obstruction to, and cessation of, the respiratory airflow for periods of 10 seconds or longer during sleep. Parts of the upper respiratory tract (usually the soft palate) collapse against the airways and cause a temporary occlusion and resistance to airflow in and out of the lungs. The condition ranges from simple snoring to multiple lengthy periods of apnoea, which can create significant alterations to the patient’s arterial blood gases and severely affect the quality of sleep.
Patients with significant OSA may complain of poor sleep, daytime tiredness and lack of concentration (including a tendency to fall asleep when performing certain tasks; for example, driving). Their partner or carer may be alarmed at periods of apparent choking and apnoea when the patient is asleep.
OSA is more common in patients with a high body mass index and it may be a risk factor for conditions such as hypertension, coronary heart disease and stroke (Young and Peppard, 2000; Partinen and Palomaki, 1985). NIV can prevent occlusion and apnoeic periods because it can be set to a constant pressure to keep the airways open when the patient is asleep.
Extended sleep studies at a specialist centre involving the monitoring of such parameters as arterial oxygen saturation, respiratory airflow, respiratory effort and electroencephalogram (to measure quality of sleep) are required to determine the level of treatment required.
The overall benefit to the patient with OSA of using overnight NIV is improved quality of sleep, with reduced daytime lethargy and improved concentration. This can facilitate increased levels of physical activity, ease weight reduction if appropriate and reduce the risk of arterial disease (Jenkinson et al, 1999).
Neuromuscular disease/chest wall deformities - Neuromuscular conditions that damage the respiratory muscles or their supplying nerves result in reduced lung volumes and may cause chronic respiratory failure that is characterised by respiratory distress and altered arterial blood gas levels (in particular raised levels of arterial carbon dioxide).
The underlying condition may itself be stable; for example, long-term complications associated with polio or spinal cord injury, or it may be progressive, as in the case of muscular dystrophies, for example.
Chest wall deformities such as scoliosis or kyphoscoliosis may lead to chronic respiratory failure owing to altered lung mechanics, reduced tidal volumes and reduced matching of ventilation and perfusion in the lungs. Thus, inspired air reaches areas of the lung where there is a poor arterial blood supply, or areas of the lung with a good blood supply do not receive inspired air. Overall, the ability to maintain good arterial oxygenation and excrete arterial carbon dioxide is reduced.
The application of NIV will potentially improve tidal volumes, reduce the effort of breathing and thus provide symptomatic support and possibly delay the onset of end-stage respiratory failure (Shneerson and Simonds, 2002).
For some patients, for example, those with high spinal cord lesions, the use of NIV may be essential life support.
Full assessment at a specialist centre is necessary to determine the exact form of respiratory support required.
Chronic obstructive pulmonary disease - NIV may be used by patients in the community who have chronic obstructive pulmonary disease (COPD) (Cuvelier and Muir, 2001).
Patients who have progressive chronic respiratory failure have a high incidence of sleep disturbance; however, the benefit of using NIV with this group of patients is less well established.
Following comprehensive assessment, NIV might be indicated to relieve symptoms of respiratory distress and sleep disturbance and improve quality of life. In particular, patients with high levels of arterial carbon dioxide might benefit from this treatment (Clini et al, 2002).
Providing domiciliary non-invasive ventilation
The standard equipment supplied to the patient having home NIV includes a portable ventilator with mains lead, wide-bore ventilator tubing, a face or nose mask, and an adjustable headset for attaching the mask.
Additionally, there may be a battery pack for travel or, for mains failure, a heated humidification unit, or a connector to allow the entrainment of oxygen into the ventilator circuit.
Organisation of home NIV in the UK - The assessment for home NIV is performed at tertiary referral centres, and patients will be established on NIV before their discharge into the community. Those working in these centres have a duty of care for the patient and should be the primary contact for any queries or advice.
From the perspective of the health-care professional involved in the care of patients using home NIV the practicalities and potential problems revolve around two areas:
- The care of the equipment;
- The compliance of the patient with the therapy.
Patients and/or their carers will have taken part in an education programme that should cover the following (Simonds, 2001):
- The nature and consequences of the patient’s respiratory condition;
- The basic principles of how the ventilator works, including how to connect it to the power supply; an understanding of the ventilator settings, and the functions of any alarms;
- How to connect the circuit, exhalation valve and mask to the ventilator and, if necessary, how to entrain oxygen from the concentrator or bottle;
- How to put the mask on and achieve a seal (interface);
- How to carry out simple cleaning operations, including changing the ventilator air filters, cleaning the circuit and mask and, if appropriate, cleaning the humidification equipment;
- What to do if the ventilator malfunctions.
Patient compliance - Compliance will depend on how effective patients feel the therapy is and how comfortable they feel when using it. If patients state that they are not benefiting from using NIV, a referral for a review should be made to the supplying centre.
Comfort partially depends on the fit of the face or nose mask and again the supplying centre can reassess the patient if this is a problem. Pressure-relieving dressings, particularly on the bridge of the nose, are useful if patients complain that the mask is making their skin sore.
Effective mouth care and adequate hydration is important, as NIV has a drying effect on the oral mucosa. Nasal decongestants can sometimes be effective for relieving the feeling of nasal drying.
Non-invasive ventilation is increasingly being used by patients at home. They will receive support from supplying centres to maintain this treatment, although they may also seek help from nurses working in the community. Nurses need to understand how this treatment works, and for whom it is applicable in order to offer appropriate support and to help maintain compliance. They also need to be aware of how to contact help and seek advice for patients who may be experiencing difficulties.