A Novel Liquid Flow-Loop Testing Methodology for Comprehensive Evaluation of Medical Suction Devices

Introduction: Airway clearance is paramount in emergency and trauma scenarios, ranking as the second most common cause of preventable mortality on the battlefield. In these critical settings, portable and main-powered suction devices are essential for managing airway obstructions. Although ISO 10079-1 provides a manufacturing standard for these devices, it notably lacks specific protocols for evaluating critical performance metrics- liquid flow rates, and battery life. To address these gaps, we introduce a novel liquid flow-loop testing methodology specifically designed to assess the performance of suction devices under conditions that simulate a patient care scenario. This methodology focuses on assessing key metrics such as flow rates of liquids of different viscosities and the associated power consumption and battery longevity during sustained operations. This study details the application of this innovative testing framework to the Zoll 303 device and SCRAMM’s (Suction: Combat Ready Advanced Multifunctional Machine) three pumps simultaneous operations, highlighting its effectiveness in delivering quantitative data on device performance under simulated patient scenarios. The battery-powered “luggable” suction devices designed for field use are expected to handle substantial volumes of liquid for prolonged periods continuously. These situations include high-volume blood loss during surgical operations, extensive drainage of massive hemothorax, and even low-volume yet protracted drainage for the Wound VAC (vacuum-assisted closure) system. By replicating these realistic usage scenarios, our testing methodology will be effective in setting up a standard to test device performance and support the development of suction devices that are better suited for critical patient-care environments.

Materials and

Methods: The liquid flow-loop testing setup utilized a canister with multiple entry and exit conduits integrated with a suction unit connected to a vacuum channel. A positively displaced liquid inlet drew water from a reservoir, and a pump-driven outlet pipe facilitated controlled fluid flow. The setup included a hydrophobic filter and a pressure control valve to regulate vacuum pressure and maintain water levels. Fluid level stability in the canister was ensured where device flow rate was calculated by the flow rate balance equation Qin=Qout=AV, where Q represents flow rate, A represents cross-sectional area, and V represents velocity. The pressure was regulated by Pc= Patm-∆P, where internal pressure (Pc) was adjusted (∆P) relative to atmospheric conditions (Patm). One commercially available infield medical suction device, Zoll 330, and a newly developed SCRAMM’s three pumps simultaneous operation were tested. The setup included a 1200 ml collector, a 2000 ml reservoir, and a 3.5 liters/min liquid pump. The system circulated liquid through 6.15 mm ID suction tubing and 9.2 mm ID discharge tubing. The Zoll 330 device operating at peak power to record vacuum pressure and time for a 10% battery drop across multiple trials and compared to airflow testing at 550 mmHg. For the SCRAMM, the configuration included suction pumps (one high-pressure, two low-pressure), similar collector and reservoir dimensions, and a 14.4-volt battery to monitor current consumption using a multimeter and voltage converter. Five trials were conducted to estimate battery lifespan under liquid flow-loop testing conditions, providing valuable data on device durability and efficiency.

Results, Conclusions, and Discussions:

Results:
The application of our testing methodology to the Zoll 330 and SCRAMM devices highlighted significant improvements in device performance metrics. Here, only one unit of Zoll 330 was tested in five trials and it exhibited a 10% battery discharge every 15 minutes ± 1 minutes during liquid flow-loop testing, showing a linear trend. After 1 hour, the battery dropped to 65.33% ± 2.62%, and after 2 hours, it dropped to 23% ± 0.82%. In comparison, the Zoll 330's battery discharge duration during air flow testing was 4 hours and 48 minutes. In contrast, The SCRAMM's 14.4-volt battery also exhibited a linear discharge process during liquid flow-loop testing. It measured 16.8 V when fully charged and 10.00 V upon complete depletion. The battery lifespan of the SCRAMM during liquid flow-loop testing was 9 hours and 27 minutes ± 3 minutes.
Table 1: Battery Discharge Duration in Liquid Flow Loop Testing
Devices Discharge Duration Standard Deviation (SD)
Zoll 330 2 hours and 33 minutes ± 2 minutes
SCRAMM’s 3 pump 9 hours 27 minutes ± 3 minutes

Discussions and

Conclusions:
This study highlights an important potential supplement to the current ISO 10079-1 standards, by testing liquid flow performance and associated battery life. Our findings from a Zoll device's novel liquid flow-loop testing and the SCRAMM’s three pump system reveal critical insights into their operational efficiencies under realistic conditions. These results highlight the necessity of revising existing testing protocols to simulate better actual usage, particularly in emergency and combat scenarios. Limitations of the study include testing a single unit of each type; however, we were successful in demonstrating the potential utility of the test. Future work includes the use of different viscosities of fluids to simulate the types of liquid found in clinical situations such as blood, vomitus, and particulate matter contamination. Pending confirmation of the verification and validity of this test, we recommend its adoption as an iso-standard for suction devices.

Acknowledgements (Optional): We sincerely thank all those who supported the development and evaluation of the testing methodologies described in this study. We especially thank our colleagues at the University of Texas at San Antonio and the University of Texas Health Science Center at San Antonio for their invaluable contributions. We would also like to acknowledge that Dr. R. Lyle Hood and Dr. Robert A. De Lorenzo are equity holders in EmergenceMed, LLC, working to commercialize the technology discussed in this paper.