IntroductionMechanical ventilation (MV) can be monitored by analysing particles in exhaled air as measured by particle flow rate (PFR). This could be a potential method of detecting ventilator induced lung injury (VILI) before changes in conventional parameters can be detected. The aim of this study was to investigate PFR during different ventilation modes in patients without lung pathology.MethodA prospective study was conducted on patients on MV in the cardiothoracic intensive care unit (ICU). A PExA 2.0 device was connected to the expiratory limb on the ventilator for continuous measurement of PFR in 30 patients randomised to either volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV) for 30 min including a recruitment manoeuvre (RM). PFR measurements were continued as the patients were transitioned to pressure regulated volume control (PRVC) and then pressure support ventilation (PSV) until extubation.ResultsPRVC resulted in significantly lower PFR while those on PSV had the highest PFR. The distribution of particles differed significantly between the different ventilation modes.ConclusionsMeasuring PFR is safe after cardiac surgery in the ICU and may constitute a novel method of continuously monitoring the small airways in real time. A low PFR during mechanical ventilation may correlate to a gentle ventilation strategy. PFR increases as the patient transitions from controlled MV to autonomous breathing, which most likely occurs as recruitment by the diaphragm opens up more distal airways. Different ventilation modes resulted in unique particle patterns and could be used as a fingerprint for the different ventilation modes.