I compiled a competitive analysis table using information from IV fluid warmer manufacturer's websites to better understand the strengths and weaknesses of the OpenFluidWarmer design. All of the competitor IV fluid warmers I selected for this analysis are commercially available, portable, battery powered, and designed for use in disaster and combat zones.
In this log I will only comment what I consider to be the most important takeaways from this exercise. For those who want all the details, see the "IV_fluid_warmer_competitive_analysis" spreadsheet included in the files of this project.
Device weight and volume are two parameters that I excluded from this analysis. It's my full intention to minimize weight and volume of the OpenFluidWarmer design when convenient, but I don't consider those parameters to make-or-break an open source IV fluid warmer design.
The most telling performance parameter of an IV fluid warmer is the maximum allowable flow rate when warming fluid from 4 to 38 degC. This is especially true for IV fluid warmers that are designed for use in disaster and combat zones. In these applications, where blood loss from traumatic injuries is the most common reason for a blood transfusion, achieving high flow rate transfusions can be an important factor in patient outcomes. That being the case, most of the IV fluid warmer systems I selected for this analysis have maximum flow rates equal to or greater than 100 mL/min.
I arrived at a lower flow target of 80mL/min for the OpenFluidWarmer design because I am unsure if a higher flow rate is possible with easily sourced components. More specifically, I am unsure if I can achieve a high enough rate of heat transfer to the fluid while also minimizing the length of IV tubing used. Given a sufficiently long length of IV tubing, it would be relatively easy to design a device capable of higher flow rates. But longer IV tubing means a larger fluid pressure drop through the device (too high of a pressure drop and high flow rates are not even achievable), a larger IV prime volume, simply more IV tubing per procedure, and likely a larger volume of product that is left in the lines at the end of the procedure and never makes it to the patient.
The competitor designs all use their own custom, proprietary consumable inline IV tube "chamber" to maximize heat transfer to the IV fluid. This chamber increases the thermal contact surface area between the fluid and the heating element. Thus allowing a higher rate of heat transfer to the fluid. For the OpenFluidWarmer design to be easily sourced, it cannot use a custom heat transfer "chamber". At the moment, the only viable option I have been able to identify is to heat the fluid by contact through standard IV tubing.
The relaxed weight and volume requirements for the OpenFluidWarmer may allow a low-cost, easily sourced design that can achieve flow rates greater than 100mL/min. It's just going to take some ingenuity and design iteration to get there.