Technical Information

Requirements / Specifications

The requirements/specifications of the ventilator can be divided into different categories. A full list with all requirements can be found in the full documentation (coming soon).

Medical requirements/specifications:

• Ventilation mode: mandatory ventilation with volume control (VC-CMV)
• optional: assisted ventilation mode, e.g. volume controlled synchronized intermittent mandatory ventilation (VC-SIMV)
• Respiratory rate / frequency: 5 to 30 breaths/minute
• Inspiratory:Expiratory ratio (I:E): from 1:1 to 1:3)
• Tidal Volume (Vt): 350 ml, 400 ml, 450 ml
• Max. inspiratory pressure: emergency valve set to 40 cmH2O
• Expiratory pressure: adjustable from 5 to 25 cmH2O (via mechanical PEEP valve)

Monitoring and alarms:

• The settings of all adjustable parameters mentioned above must be visualized, and the pressure in the patient’s airway should be constantly displayed
• Alarms are categorized in fatal alarms (red) and critical alarms (yellow). Alarms are indicated by flashing lights and an alarm sound.

Connections:

• Use standard connections (electricity, tubing, oxygen etc.)
• Meet safety standards (fire, biological, oxygen safety)

Infection control:

• All parts in contact with patients’ breath have to be disposable/decontaminatable
• HEPA filter to prevent virus to become airborne

General design requirements:

• Compact
• Robust
• Modular with as many standard parts as possible
• Portable
• Simple
• Easy to use with only basic training (30 minutes)
  

Design Rationale

Among all different types of emergency ventilator systems proposed during this crisis (e.g. fan, pneumatic valve system, bellow etc.), the concept of automating the compression of a manual resuscitator (MR) seems to be the most promising option to fulfill all our key requirements. MRs are certified medical equipment and widely available for emergency ventilation in medical facilities all over the world. The use of MRs provides standard connectors for all necessary tubes and allows us to rely on standard medical parts for the full patient breathing system. This makes the breathing system a separate system with only medically certified components and decouples it from the mechanical actuation. As a safety feature, the MR can be removed any time in case of an emergency and can be operated by hand to maintain the patient’s ventilation. Our design is compatible with any type of MR.

System Overview

The complete system can be broken down into four types of components: standard parts, custom mechanical parts, electronics and controllers, and user interface.

The flow diagram shown in fig. 1 shows how the different components of the system interact. Signals are depicted with dashed lines, while air is depicted with a solid blue line.

The standards parts, shown in grey, can all be sourced directly and plugged into the system. There is a push to use as many standard parts as possible to reduce cost and accelerate the medical approval process.

The custom mechanical parts are all within the compression mechanism. There as well, the whole design is designed to avoid custom parts as much as possible. Only the bag holders, the motor holder and the paddles-finger assembly are custom parts. 

The electronics and controls are designed for rapid prototyping rather than cost and robustness. The sensors are chosen and calibrated carefully to monitor flow and pressure. Their output determines the pressure displayed and can trigger any necessary alarm.

The user interface is designed to help the doctors quickly assimilate the information and set the three main parameters: breathing frequency, tidal volume, and expiration ratio. It also flashes different color alarms for power failure, low tidal volume, exceeded maximum pressure, or disconnection, which the doctor can all silence for 30s using a mute button.