A simple device to inject indicator gas for wash-out tests during mechanical ventilation

Area of Science:

• Pulmonary Physiology
• Critical Care Medicine
• Medical Device Engineering

Background:

• Multi-breath wash-out (MBW) tests are crucial for pulmonary monitoring in intensive care units (ICUs).
• Accurate measurement of end-expiratory lung volume (EEV) is essential for assessing lung function during mechanical ventilation.
• Existing methods for MBW testing may require complex setups or specialized equipment.

Purpose of the Study:

• To evaluate a simple, cost-effective device for performing MBW tests.
• To assess the accuracy of a novel indicator gas injector for controlled ventilation.
• To compare two techniques of indicator gas administration (post-mix vs. pre-mix) for MBW analysis.

Main Methods:

• A simple device was developed to inject a constant fraction of indicator gas into the inspiratory mixture.
• Two methods were compared: injecting gas at the patient's mouth (post-mix) versus into the ventilator bellows (pre-mix).
• MBW tests were conducted on 10 post-operative mechanically ventilated patients in a Surgical Intensive Care Unit.

Main Results:

• The mean end-expiratory lung volume (EEV) calculated using the post-mix technique was 1.91 ± 0.87 L.
• The mean EEV calculated using the pre-mix technique was 1.89 ± 0.88 L.
• Good agreement was observed between the two techniques, with a mean difference of -1.9 ± 6.5% in EEV values.

Conclusions:

• The described injector is an affordable and easily assembled device for MBW testing.
• It can be integrated with most electronically regulated ventilators for bedside pulmonary monitoring in ICUs.
• The device facilitates reliable MBW tests, aiding in the management of mechanically ventilated patients.