Non-invasive respiratory support

Devices of varying sophistication are available to augment spontaneous breathing in the compliant patient by either assisting inspiration (inspiratory support) and/or providing CPAP. Non-invasive support is usually delivered by tight-fitting face or nasal mask, or via a helmet. Inspiratory support can also be delivered via a mouthpiece. Some devices allow connection to an endotracheal tube for the intubated but spontaneously breathing patient.

Indications

• Hypoxaemia requiring high respiratory rate, effort, and FIO2.

• Hypercapnia in a fatiguing patient.

• Weaning modality.

• To avoid endotracheal intubation where desirable (e.g. severe chronic airflow limitation, immunosuppressed patients).

• Reduces work of breathing in patients with high PEEPi (e.g. asthma, chronic airflow limitation). Use with caution and monitor closely.

• Physiotherapy technique for improving FRC.

• Sleep apnoea.

Inspiratory support (IS)

A preset inspiratory pressure is given when triggered by the patient’s breath. The trigger can be adjusted according to the degree of patient effort. Some devices deliver breaths automatically at adjustable rates. The I:E ratio may also be adjustable. The VT delivered for a given level of inspiratory support varies according to the patient’s respiratory compliance. An example of an IS device is the Bird ventilator, commonly used by physiotherapists to improve FRC and expand lung bases.

BiPAP (Bilevel positive airways pressure)

This device delivers adjustable levels of pressure support and PEEP. Delivered breaths can be either patient-triggered and/or mandatory. Some BiPAP devices are driven by air; to increase the FIO2, supplemental O2 can be given via a circuit connection or through a portal in the mask.

Management

1 Select type and delivery mode of ventilatory support.

2 Connect patient as per device instructions.

3 Use an appropriate-sized mask that is comfortable and leak-free.

4 A delivered pressure (IPAP) of 10–15cmH2O is a usual starting point which can be adjusted according to patient response (respiratory rate, degree of fatigue, comfort, blood gases, etc.).

5 Expiratory pressure support (EPAP) is usually in the 5–12cmH2O range.

6 Patients in respiratory distress may have initial difficulty in coping. Constant attention and encouragement will help to accustom them to the device and/or mask while different levels of support, I:E ratios, etc. are tested to fi nd optimal settings. Cautious administration of low dose opiate injections (e.g. diamorphine 2.5mg SC) may help to calm the patient without depressing respiratory drive. The tight-fitting mask may become increasingly claustrophobic after a few days’ use. Pre-empt if possible by allowing the patient regular breaks. Protect pressure areas such as the bridge of the nose.