Classic cube box

Santé libre established the design of this classic cube box based on the original Hsien box design and its variations in the literature. The dimensions of width and height of the box, the location of the arm ports and vacuum port, the angle of the front panel, etc. have all been modified and improved following the feedback of the doctors who have tested numerous iterations of the prototype. It can be easily manufactured by folding and/or cutting flat transparent plastic sheets and assembling them into a cube. The flat panels make it easy to cut holes for port entries and arm entries guaranteeing access to the patient. The square base mimics the shape of the hospital beds.

We started from Santé Libre’s latest CAD model (background picture) and designed a slightly different version of their box. The major problem with the cube is the recirculation zones of airflow that form around the sharp corners. This creates local turbulences and impairs viral particle capture. To counter this, our design incorporates an octopus ventilation system. The main ventilation unit is extended with a manifold into 5 ventilation units; one for each top corner of the box and the last one via the patient’s mouth on the top of the box.

We designed a base that can be placed semi-permanently on a bed. All tubing connections needed during the intubation procedure (for the oxygen mask, the endotracheal tube, etc.) are made through the base. The box can be quickly attached to the base with a slide and lock system. The base is designed with hooks and straps so it can be secured to the bed from underneath it. In this manner, if necessary, the box alone can be quickly removed allowing the doctor to have the immediate access to the patient; the base and all the connections will remain on the bed with no obstructions for the medical workers around the box.

• Base prototype
• Box prototype_1
• Box prototype_2
• Octopus ventilation system_1
• Octopus ventilation system_2

We also improved the sealing at the torso of the patient by designing a flexible drape with elastic band. The elastic rubber band, sewn around the edges of the plastic film, allows the drape to be secured to the box and go around the patient’s torso with a minimum gap. The gap at the patient’s torso is the only unsealed region on the prototype. It is from this gap that the outside air enters the box and gets ventilated by the vacuum ports. We will also use this design on the tunnel shape box, dome shape box and tent box.

• Inspiration-elastic rubber band
• Our torso drape design

As for the access to the patient, different approaches are being studied. The preferred one up until now is that of an extruded circular hole in the plastic sheet. This outgrow has a diameter matching that of a glove’s long sleeve. The sleeve is sealed on the plastic cylinder with a hose clamp. The inside of the box is completely isolated from the doctors hands which enter the box via the glove. The sleeve of the gloves being very long, the mobility of the doctors in the box is not diminished. In the event that the access needs to be made through a plastic film (i.e. tent model) then the same kind of glove is fused on the film (plastic to plastic).

• Extruded glove ports

How to use this box

1. Use the quick connect belts to tie the base around the bed;
2. Connect the face mask to the ventilation circuit through the adapter on the base;
3. Put the wireless video laryngoscope, stylet, endotracheal tube inside the base;
4. Carry the box on the base and insert the edges into the rubber groove in the base;
5. Put the gloves around the glove adapters on the box;
6. Put the torso drape around the box.

How to make this box

The cube box includes two pieces of PVC sheet: one piece for the front panel, the other for ceiling and side walls. The two pieces were first cut with glove/ventilation holes by a CNC router, then hot-bended into designed shape, and finally glued together by epoxy glue.

The base was milled with HDPE plate and assembled with PVC sheets and 3D-printed adapters. Rubber grooves were added to the bottom edges of the cube box so that when the box is inserted in the base, the rubber ensures a perfect seal between the box and the base.

The octopus system was assembled by PVC tubes and adapters. The ventilation unit is placed on the top of the box. A two parts adpater with thread connections was 3D printed with PLA.

The flexible plastic drape was made by sewing a closed rubber band around the edge of the transprent plastic film. The length of the rubber band fits well around the box and the patient torso, ensuring a good seal.

• Base prototype_1
• Base prototype_2
• Base with belts
• Cube box prototype

Particle capture efficiency simulation

The classic box because of it’s shape with many corners is less efficient than the tunnel model and than the dome model. The particles tend to get stuck in the corners which we call recirculation zones. To improve the classic box prototype different strategies have been simulated. Corners have been rounded testing different ranges, dead zones were cut off to decrease the volume inside the box, the aspiration unit was placed at may locations, etc.

Here is the prototype simulated with various types of rounded corners:

Various types of rounded corners tested to better airflow in the classic box model

The efficiency of each of these tested classic box models are presented in the graphs below. The first graph shows the evolution of the percentage of particles captured in time. We aim to reach higher the percentage of particle capture and this as quickly as possible. The second graph tells us by how many percent the model is more efficient than the orginal classic box model with no rounded corners.

Particle capture efficiency results for the different types of rounded corners

The efficiency of the octopus ventilation system with the aspiration unit separated into 5 units has also been validated with simulations. The results shows that by separating the flowrate into smaller parts to cover many units we are diminishing the efficiency of the ventilation system. It is better to have one aspiration unit with maximum flowrate to capture rapidly the virus particles.

We are currently doing more simulations to investigate the idea of placing oneway valves in the corners of the classical box. We are hoping this way to break the recirculation zones that can form in the corners of the box. More information to come.