Monitoring: Equipment and Computers
Background: When a patient breathes through an anaesthetic breathing system an extra resistance is imposed on their respiratory muscles. This extra resistance may be overcome or may lead to hypoventilation and reduced gas exchange. A simple means of assessing breathing system resistance is to measure the pressure drop (PD) at a specified flow. The International Standard for breathing systems defines this flow and states that the PD at the patient connection port should not exceed 0.6 kPa (1). This study aims to determine the PD, and hence resistance, of various breathing systems and to compare it with the requirement of the standard.
Methods: We tested 5 samples each of 10 1.6 m breathing systems (4 Bain's coaxial, 3 Mapleson A [Map A] and 3 parallel systems) using a fresh gas flow of 10Lmin−1 and a sine-wave pump, to simulate spontaneous breathing, set to 1 L tidal volume at 20 min−1. Pressures and flows were measured using a Datex AS/3 monitor. All data were recorded onto a laptop using LabVIEW software.
Conclusion(s): Similar breathing systems from different manufacturers showed very different pressure drops and therefore resistance. Only 10 of the 50 systems tested complied with the requirements of the standard.
Acknowledgements: Flexicare, Intersurgical, Armstrong and Mallinckrodt for the samples.