Non-invasive ventilation is used as an alternative to full intubation and ventilation to support the lungs in respiratory failure due to obstructive lung disease. Intubation and ventilation involves giving the patient a general anaesthetic, putting a plastic tube into the trachea and ventilating the lungs artificially. Non-invasive ventilation involves using a full face mask or a tight fitting nasal mask to blow air forcefully into the lungs and ventilate them without having to intubate them. It is not pleasant however it is much less invasive than intubation and ventilation and acts as a useful middle point between basic oxygen and intubation.
Non invasive ventilation can either be BiPAP or CPAP.
BiPAP stands for bilevel positive airway pressure. This involves a cycle of high and low pressure to correspond to the patients inspiration and expiration. BiPAP is used where there is type 2 respiratory failure, typically due to COPD. The criteria for initiating BiPAP are:
- Respiratory acidosis (pH < 7.35, PaCO2 >6) despite adequate medical treatment.
The decision to initiate it would be made by a registrar or above. The main contraindications are an untreated pneumothorax or any structural abnormality or pathology affecting the face, airway or GI tract. Patients should have a chest xray prior to NIV to exclude pneumothorax where this does not cause a delay. A plan should be in place in case the NIV fails so that everyone agrees whether the patient should proceed to intubuation and ventilation and ICU or whether palliative care is more appropriate.
IPAP (inspiratory positive airway pressure) is the pressure during inspiration. This is where air is forced into the lungs.
EPAP (expiratory positive airway pressure) is the pressure during expiration. This provides some pressure during expiration so that the airways don’t collapse and it helps air to escape the lungs in patients with obstructive lung disease.
The initial pressures are estimated based on the patients body mass and measured in cm of water. Potential starting points for an average male patient might be:
- IPAP 16-20cm H2O
- EPAP 4-6cm H2O
Repeat an ABG 1 hour after every change and 4 hours after that until stable. The IPAP is increased by 2-5 cm increments until the acidosis resolves.
CPAP stands for continuous positive airway pressure. It provides continuous air being blown into the lungs that keeps the airways expanded so that air can more easily travel in and out. It is used to maintain the patient’s airway in conditions where it is prone to collapse.
Indications for CPAP:
- Obstructive sleep apnoea
- Congestive cardiac failure
- Acute pulmonary oedema
Last updated March 2019