With the outbreak of the novel coronavirus, Covid-19, in 2020 the demand for medical ventilators has skyrocketed. Production of these medical devices have ramped up so high that some companies are retooling their production lines to help meet this increased demand. With the increase in production, quality control of these life sustaining devices and assemblies cannot be overlooked. In this article we will go over leak testing the consumable parts of a ventilator, primarily the ventilator tubing set assembly.
What is a Ventilator
A medical ventilator is a life support system sometimes referred to as a breathing machine. The ventilator is designed to blow gas into a patient’s lungs via an endotracheal or ET tube. 1 The gas is a mixture of air and measured amounts of oxygen. The amount of oxygen is dependent upon the patient’s oxygen saturation and can be adjusted at any time. The pressure of this gas is also closely monitored. The pressure that is applied by the ventilator at the end of each breath is known as PEEP or Positive End Expiratory Pressure. PEEP is the pressure in the lungs above atmospheric pressure that exists at the end of expiration. 2 Medical ventilators, as well as CPAP machines, use PEEP to help hold the lung open so the alveoli (air sacs) don’t collapse.1
The ET tube is part or a tubing assembly that connects the patient to the ventilator. This tubing assembly is made up of many components. Corrugated hoses for maximum controlled air flow. Pitot tubes to measure air pressure coming out of the patient to ensure enough PEEP pressure is being applied by the machine to keep the lungs from collapsing. Soft valves on the exhalation tube to ensure the patient is taking in the controlled gas. Air filters protect the machine from contamination. All these components are assembled using a myriad of fittings, adhesives, and ultrasonic welds.
A Clinical Background
How Do You Leak Test Ventilator Tubes and Assemblies?
When leak testing a ventilator tubing assembly there are two primary defects to look for:
- Proper (non-leaking) Seals Between Assembled Parts
- No Obstructions in the Airway
The fastest and most inexpensive way to test tubing walls and assembly connections is a Pressure Decay test. In a PD test, one side of the tube or tubing set is attached to a leak tester while the other side is sealed. The assembly is pressurized to set value. With the incoming supply shut off, the part settles to reduce the thermodynamic and elastomeric effects on the part. During the test step, any decrease in air pressure over time signifies a leak. If the assembly does not leak/decay past its predetermined reject value, it is a good part.
To check for obstructions in a ventilator tubing set, it is best to use a Back-Pressure Flow test. The BP Flow test measures the back pressure created by the part at a specific flow rate. Obstructions will cause the pressure to increase or decrease from the nominal value. This pressure change is compared to the programmed tolerance for pass/fail status. These flow values are very specific to each tubing set design. Variables like filters, tube diameter, and tube length can affect what an acceptable value is for one tube design but not for another.
How to Save Time
Unlike the ventilator device itself that can be used multiple times with many patients, the tubing assembly is a consumable product that can only be used by one patient. This makes high throughput essential to production.
The two best ways to reduce leak test cycle time for ventilator tube sets are:
- Minimizing the test circuit volume
- Use a multi-function leak tester that has both pressure decay and back-pressure flow as well as multiple test ports.
- Ensure that the part is the choke of the system, not the test pneumatics.
- Establish accurate but efficient test times.
The nearer the leak tester is to the part under test, the faster the test can run. By eliminating excess volume contained in connection hoses and fittings, the sensitivity to pressure change increases. Geometric differences in the test lines and fittings (diameter changes) can cause pressure drops in the system.
A multi-tester is a leak tester that can perform multiple test types in a single machine. Zaxis pioneered this technology with the first ever multi-function tester. The Isaac HD by Zaxis can attach to a ventilator tube assembly, pressurize the part, run a PD test and immediately run a back-pressure flow test. The tubing set doesn’t have to go to a second testing cell for the second test, it is all done by one machine in a matter of seconds.
A global pandemic involving the spread of a novel virus that can severely affect the respiratory system has woefully increased the demand for medical ventilators and consumable tubing sets. Quality leak testing these life sustaining parts is critical. A Pressure Decay test coupled with a back-pressure Flow test can validate a parts functionality. Using a multi-tester such as the Isaac HD by Zaxis can save time and improve production throughput. Lastly minimizing the test circuit volume and optimizing test configuration parameters can decrease test times yielding a more efficient production process.
- Am J Respir Crit Care Med Vol. 196, P3-4, 2017 ATS Patient Education Series © 2017 American Thoracic Society – https://www.thoracic.org/patients/patient-resources/resources/mechanical-ventilation.pdf
- Positive end-expiratory pressure (PEEP)”. com. Citing: Saunders Comprehensive Veterinary Dictionary. 2007.
- Andres L. Mora Carpio; Jorge I. Mora, Ventilator Management, National Center for Biotechnology Information, June 2, 2019, https://www.ncbi.nlm.nih.gov/books/NBK448186/