4.7 NIV Machines and Interfaces
Non invasive ventilation can be provided through a number of different devices. There are specifically designed NIV machines that can only provide NIV and not invasive ventilation in the hospital environment. An example of these machine is the Philips Respironics V60 and V680. In the past, these machines provided superior NIV due to complex leak detection and synchronization algorithms. Nowadays most ICU ventilators and transport ventilators can provide NIV with enhancing software and algorithms as well as invasive ventilation.
Additionally there are home CPAP units that are primarily used to provide CPAP to OSA patients. There are also home devices that can be used to provide NIV (BIPAP) to patients at home.
There are a number of different NIV mask interfaces. There are those that cover just the nose such as the nasal mask or nasal pillows/prongs. These masks are primarily used for patients on home CPAP with OSA.
NIV Mask Interfaces
- Nasal Mask
- Nasal Pillows/Prongs
- Oral Mask
- Oral – Nasal
- Full Face Masks
- Total Face Masks
- Helmets
Ventilator NIV with Dual Limb Circuit
When providing NIV through a ventilator with a dual limb circuit (inspiratory and expiratory) limb. A non vented full face mask that covers both the mouth and nose is recommended. In this setup, expiration occurs through the expiratory valve in the ventilator and the mask must not have a vent or anti-asphyxia valve built in. A vent or leak in the mask or circuit is not needed as the patients exhaled volume will travel to the expiratory limb and out the ventilators expiratory valve. An anti-asphyxia valve is not required as the gas flows in a series from inspiratory to expiratory limb and therefore does not require the anti-asphyxia safety system built in. Additionally these patients are more likely to be in a closely monitored ICU bed.
NIV Machine with Single Limb Circuit
When providing NIV with a full face mask and a specially NIV machine such as the Philips Respironics V60 and a single limb circuit is used, it is important to select a mask that has an anti-asphyxia valve built in. An anti-asphyxia valve is a safety feature on a single limb circuit that opens if the pressure in the ventilator circuit falls below a predetermined level (usually [latex]3\text{ cmH}_2\text{O}[/latex]). This may occur if the machine malfunctions or the circuit becomes detached. The purpose of this anti-asphyxia valve is to allow the patient to exhale and breathe without having to breathe through the entire length of the single limb circuit that could cause CO2 re-breathing. The anti-asphyxia valve opens to ambient and would allow the patient to exhale and also breath in room air gas. During regular NIV, the anti-asphyxia valve flap is pushed closed due to the pressure inside the circuit and it would only open to ambient if you pressure in the circuit decreased.
Anti-asphyxia Valve / Safety Valve
- Loss in pressure causes valve to fall during exhalation to facilitate CO2 removal and prevent rebreathing
- Required for vented and non vented masks used with single limb circuits
- Also called an anti-asphyxiation valve
- Basic design features
- Vented
- Holes in the mask
- Non-vented
- Leak is in the circuit
- Whisper swivel
- Exhalation port
- Safety/anti-asphyxiation valve
- Not used with dual limb circuits (ventilators)
The next important feature when using a NIV machine with single limb circuit is the location of the exhalation valve or sometimes called a leak valve. When a Vented Mask is used, the exhalation port is built into the mask. A vented mask will have holes that allow for fixed resistance to flow during exhalation. Because the resistance is fixed, CPAP is increased by increasing flow from the ventilator through the circuit.
When a Non-vented mask is used, a fixed/intentional leak valve must be added to the circuit, which contains holes that allow fixed resistance to flow during expiration.
