Different particle flow patterns from the airways after recruitment manoeuvres using volume-controlled or pressure-controlled ventilation

Abstract

ObjectivesNoninvasive online monitoring of different particle flows from the airways may serve as an additional tool to assess mechanical ventilation. In the present study, we used a customised PExA, an optical particle counter for monitoring particle flow and size distribution in exhaled air, to analyse airway particle flow for three subsequent days. We compared volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) and performed recruitment manoeuvres (RM).MethodsSix animals were randomised into two groups: half received VCV before PCV and the other half received PCV before VCV. Measurements were taken daily for 1 h in each mode during three subsequent days in six fully anaesthetised domestic pigs. A RM was performed twice daily for 60 s at positive end-expiratory pressure (PEEP) of 10, 4 breaths/min and inspiratory-expiratory ratio (I:E) of 2:1. Measurements were taken for 3 min before the RM, 1 min during the RM and for 3 min after the RM. The particle sizes measured were between 0.48 and 3.37 μm.ResultsA significant stepwise decrease was observed in total particle count from day 1 to day 3, and at the same time, an increase in fluid levels was seen. Comparing VCV to PCV, a significant increase in total particle count was observed on day 2, with the highest particle count occurring during VCV. A significant increase was observed comparing before and after RM on day 1 and 2 but not on day 3. One animal developed ARDS and showed a different particle pattern compared to the other animals.ConclusionsThis study shows the safety and useability of the PExA technique used in conjunction with mechanical ventilation. We detected differences between the ventilation modes VCV and PCV in total particle count without any significant changes in ventilator pressure levels, FiO2 levels or the animals’ vital parameters. The findings during RM indicate an opening of the small airways, but the effect is short lived. We have also showed that VCV and PCV may affect the lung physiology differently during recruitment manoeuvres. These findings might indicate that this technique may provide more refined information on the impact of mechanical ventilation.

Mechanically ventilated patients exhibit decreased particle flow in exhaled breath as compared to normal breathing patients

“…opening up a previously closed lung, a significant increase in PFR was detected but there was no change in average particle mass per particle. We believe that these results are in line with the results of this and other studies that support the notion that opening and closing of the distal airways results in increased PFR in exhaled air and that the effect can be detected with this technique [14,15]. The fact that there is no significant difference in average particle mass between OLV and DLV is supportive of the concept that mechanical ventilation induces particles with similar mass profiles but that PFR is increased due to the fact that there are more accessible airways in the DLV scenario.…”

“…In conclusion, we did not detect any harmful effects on all the intubated patients using PExA, and we believe this technique can safely be used for intubated patients on mechanical ventilation during surgery. The findings from this study and from previous animal studies are encouraging and indicate that the PExA method might be a novel tool to give new insight to lung physiology during mechanical ventilation [14,15].…”

“…We have shown previously in animal models that blood flow and different ventilation modes, i.e. volume-controlled and pressure-controlled ventilation, alter PFR from the airways [14,15]. We believe that in this study, the magnitude of the difference we observed was primarily due to the degree of opening and closing of the distal airways and that this is the major factor influencing the particle flow and its composition.…”

“…PEx in the diameter range of 0.41-4.55 µm can be measured continuously using the OPC and the impactor samples particles in the size range 0.4-7.2 µm. In the present study, the PExA 2.0 instrument was customised to be able to be used in conjunction with mechanical ventilation as we have described previously in preclinical in vivo settings [14,15]. The device was connected to the outflow air of the mechanical respiratory circuit, as seen in figure 3.…”

“…Mass spectrometry was used to quantify the phospholipids di-palmitoyl-phosphatidyl-choline (DPPC) and palmitoyl-oleoyl-phosphocholine (POPC). The method is described in previous articles [2,15]. Albumin and SP-A were analysed by ELISA, described in previous articles [12,13,16,17].…”