3D printed circuit splitter and flow restriction devices for multiple patient lung ventilation using one anaesthesia workstation or ventilator
A. Clarke
Abstract
The ongoing pandemic of SARS-CoV-2 virus and its associated disease COVID-19 has resulted in widespread ventilator shortages and rationing of care. Massive global supply chain disruption and quarantine measures prevent equipment movement and medical device production. In 2006, the concept of using an intensive care ventilator for multiple subjects was described using six Briggs T-tubes and a Puritan-Bennett 840 Series ventilator to ventilate four human lung simulators 1 and subsequently tested in four adult human-sized sheep 2. However, the Briggs T-tube is not readily available in many institutions. This problem can be overcome using the modern production method of three-dimensional (3D) printing. With digital designs distributed via the internet, 3D printing enables mass production at the point of need. In the Royal Women's Hospital in Victoria, Australia, we have designed and produced two parts using 3D printing: a splitter apparatus (Fig. 1) and a flow restrictor apparatus. The design concepts and computer-aided designs were created using Fusion 360 (Autodesk Inc, San Rafael, CA, USA). The splitter apparatus was designed to be connected directly to a ventilator with one device on each of the inspiratory and expiratory breathing circuit ports (Fig. 2). The flow restriction device was designed to selectively reduce flow to one limb of the parallel patient breathing circuit with the intention of allowing the operator to adjust the tidal volume delivered to one of the patients. This is similar in principle to a previously described technique for single-ventilator, two-lung differential ventilation 3. All parts were designed to be compatible with standard 22-mm 4 ISO 5356–1 (conical connectors for anaesthetic and respiratory equipment) breathing circuit connectors. The parts were printed using several inexpensive desktop fused deposition modelling 3D printers. Total production time on a desktop 3D printer (Original Prusa i3 MK3S, Prusa Research a.s., Prague, Czech Republic) was 6 h for one set of two splitters (inspiratory and expiratory limbs) and one inspiratory flow restrictor. Estimated total cost of raw material was $1.00 Australian (50p sterling, 57 cents Euro, 62 cents US). The equipment was tested using a Dräger® Primus anaesthesia workstation (Dräger, Lübeck, Germany) to ventilate two simulated lungs (reservoir bags) in a standard operating theatre. Two 22-mm anaesthesia circle breathing systems were connected in parallel to the anaesthesia workstation via the circuit splitter, with a flow restrictor placed on the inspiratory limb of the circuit. The total circuit leak (as measured by the automatic leak test) was < 120 ml, within the normal limits of operation. Using a 2-mm diameter flow restrictor, inspiratory pressure of 30 cmH2O, positive end expiratory pressure of 5 cmH2O, respiratory rate of 10 breaths per minute and an inspiratory time of 1.8 s, tidal volumes (measured by the ventilator) with pressure control ventilation decreased from a mean (95%CI) 354 ml (351–357 ml) without the flow restrictor to 167.5 ml (167–168 ml) with the flow restrictor. This is the first description of the use of 3D printed flow splitting and flow restrictor devices for the emergency ventilation of two patients. Bench testing demonstrated acceptable performance for use in the short-term emergency ventilation setting. The large drop in tidal volume with the restrictor demonstrates the potential for pairing two sets of lungs with markedly different compliance or target tidal volume. The publication of these device designs is intended to spur discussion and enable other researchers to evaluate the designs. Three-dimensional printing technology is now ubiquitous and affordable and parts can be replicated in the field by staff with minimal training. Of note, the circuit design is not capable of independent measurement of tidal volume or airway pressures, as has been previously reported in the literature 4. The use of a modified circuit to selectively control expiratory pressure 5 was considered; however, it was not possible to assess the effect of the flow restrictor on positive end expiratory pressure with the current study methodology. Experimental evaluation and laboratory testing of other variable flow restrictors is in progress. The 3D printing models have been published on the author's website (https://alexanderclarke.id.au) and Prusa Printers (https://prusaprinters.org) and are freely available for modification and 3D printing. We thank A/Prof A. Dennis for her comments on the manuscript.