Selection guide for Sensirion gas flow sensors

Overview of Sensirion Gas Flow Sensors

Sensirion's flow sensor portfolio offers a comprehensive range of gas flow sensors optimized for medical applications. The SFM product range is specifically engineered for medical ventilation, addresses all relevant flow monitoring requirements, and is organized in three families, depending on the position of the sensor in the ventilation system:

1. Inspiratory
2. Expiratory
3. Proximal

The figure below provides a first guideline to select a suitable sensor depending on the application position.

Inspiratory Flow Sensors

Inspiratory flow sensors are typically used inside the ventilator to measure the individual air/O2/heliox gas lines as well as the total flow of the mixed gas before delivery to the patient.

Selection can be based on operating gage pressure:

• Up to 6 bar: SFM4300
• Up to 1 bar: SFM3013
• Up to 650 mbar: SFM3505
• Lower operating overpressure: SFM3505, SFM3003 family, SFM3119.

Consider the following criteria for sensor selection:

• Form factor and size
• Mechanical connection
• Measured gases
• Flow range and range of best performance
• Pressure drop across the sensor
• Analog or digital output
• Special features like gas NTC temperature sensor etc.

A table detailing inspiratory flow sensors:

Proximal Flow Sensors

Gas flow sensors specifically designed to monitor flow in close proximity to the patient, where the following main challenges have been resolved:

• High humidity and condensation: All proximal sensors measure saturated gas/air and feature a heater to prevent condensation at the sensor's chip, ensuring continued accuracy.
• Contamination: Both single-use and washable sensors are offered.
• Sensor handling by medical personnel: All proximal sensors feature a mechanical interface allowing a clip-on connection, easy to disconnect and reconnect.
• Inspiration and expiration flow: All proximal sensors allow bi-directional flow sensing.
• Individual sensor packaging for single-use sensors: Individual sensors are protected against contamination from production until use. Quality control is improved, supply chain management is simplified, and a customized label provides all needed information to the users.

Sensor selection is based on two main criteria:

• Patient group: neonates or adults/pediatric
• Use in clinical setting: single use/disposable or washable

A table detailing proximal flow sensors:

Expiratory Flow Sensors

The SFM3200-AW is specifically designed for the expiratory position with a minimized pressure drop, washability, a heater, and the capability to measure vapor-saturated gas/air.

Alternative options:

• Proximal sensors can be used further from the patient in the expiratory position if a disposable option is preferred.
• Inspiratory sensors can be placed in the expiratory position if measures are taken against contamination (e.g., HMF filters) and condensation (water traps). Inspiratory sensors are not designed to be cleaned or disinfected and require non-condensing operating conditions.

A table detailing expiratory flow sensors: