A Simple Procedure to Measure the Tidal Volume Delivered by Mechanical Ventilators: A Tool for Bedside Verification and Quality Control.

Farré R, Artigas A, Torres A, Albaiceta GM, Dinh-Xuan AT, Gozal D.

Arch Bronconeumol. 2023 Jan;59(1):61-62. doi: 10.1016/j.arbres.2022.07.008

 

ABSTRACT

Background: Measurement of tidal volume (VT), a crucial variable in mechanical ventilation, is complex since several corrections (for the oxygen fraction, for circuit compressibility and for air temperature and humidity) are required. As each of these factors can account for more than 10% variance in computed VT, accurate quality control of the ventilator with expensive devices is required. As this is difficult in low- and middle-income countries (LMICs) hospitals, we aimed to describe an inexpensive and straightforward procedure that can be readily followed by clinical staff who are not experts in instrumentation techniques. Methods: The method is based on a resistance and bag simulating a patient (test lung) enclosed in a water-filled rigid-wall chamber. The VT applied by the ventilator under test is measured from the difference in water levels (Δh) along the ventilator cycle, for instance during end-inspiration and end-expiration pauses: VT= S·Δh, where S is the internal section of the vertical tube to measure h. The VT measured by water displacement is the VT is the reference value to be compared with the VT measured by the ventilator. Results: Assuming the 1-mm resolution in the common ruler for assessing h in the setting, resolution in VT measurement is 4.3 mL, which corresponds to 0.43% and 0.86% for maximum and typical VT values of 1000 and 500 mL, respectively. Such precision is by far sufficient to detect any potential real-life errors when VT is measured by mechanical ventilators. Conclusion: The method can help verify the accuracy of VT and thus can be a realistic and easily implementable quality control procedure in LMICs where routine maintenance of medical devices is not necessarily widely available.