[Effects of aerosol inhalation on respiratory mechanical parameters under different ventilation patterns and ventilator parameters].

Objective: To investigate the effects of aerosol inhalation on respiratory mechanical parameters under different ventilation patterns and ventilator parameters in patients on mechanical ventilation and simulated model of aqualung in vitro.

Methods: (1) Clinical research: the patients needed sedative undergoing mechanical ventilation admitted to intensive care unit (ICU) of Qingdao Municipal Hospital from January 2016 to January 2018 were enrolled. They were randomly divided into volume controlled ventilation (VCV) group and pressure controlled ventilation (PCV) group according to random number table. Main parameters setting of respirator: the predetermined tidal volume (VT) was set at 500 mL in the VCV group; the preset pressure was regulated, so that when the atomizer was connected to the atomization device, the VT was nearly equal to or slightly larger than 500 mL in the PCV group. Respiratory mechanical indices [peak airway pressure (Ppeak), inspiratory tidal volume (VTi), exhaled tidal volume (VTe)] were recorded before atomization (atomized oxygen flow was 0) and 10 minutes after the beginning of atomization under the condition of 7 L/min and 9 L/min of atomized oxygen flow respectively. (2) Simulated scuba test in vitro: the ventilator was connected to the simulated scuba, and an external mechanical ventilation model was constructed. They were divided into VCV group and PCV group according to ventilation mode. Main parameters setting of respirator: VCV group was given 450, 550, 650 mL preset VT, and PCV group was given 12, 16, 20 cmHO (1 cmHO = 0.098 kPa) preset suction pressure. The changes in respiratory mechanical indexes were observed under different ventilation patterns and ventilator parameters of 0 (only connected with atomizing device), 5, 7, 9 L/min atomizing oxygen flow.

Results: (1) Clinical research results: all 77 patients were enrolled in the final analysis, including 20 patients with 7 L/min of atomized oxygen flow under VCV mode, 18 patients with 9 L/min of atomized oxygen flow, and 21 patients with 7 L/min of atomized oxygen flow under PCV mode and 18 patients with 9 L/min of atomized oxygen flow. Under VCV mode, the levels of Ppeak and VTe were increased with the increase in atomized oxygen flow, and there was significant difference at 9 L/min as compared with those before atomization [Ppeak (cmHO): 29.44±4.58 vs. 24.39±4.64, VTe (mL): 896.26±24.91 vs. 497.61±8.67, both P < 0.05]. There was no significant change in VTi, and no significant difference at 9 L/min of atomized oxygen flow as compared with that before atomization (mL: 494.67±3.07 vs. 492.61±6.05, P > 0.05). Under PCV mode, with the increase in oxygen atomization flow, VTi was decreased gradually, and VTe was increased gradually, with significant difference as compared with those before atomization when the atomized oxygen flow was 9 L/min [VTi (mL): 322.78±17.75 vs. 518.17±8.97, VTe (mL): 730.89±31.20 vs. 519.00±9.06, both P < 0.05]. There was no significant change in Ppeak, and no significant difference at 9 L/min of atomized oxygen flow as compared with that before atomization (cmHO: 21.44±2.23 vs. 21.39±2.55, P > 0.05). (2) Simulated scuba results in vitro: under VCV mode, VTe monitored by respirator and VT showed by simulated scuba in different preset VT groups were continuously increased with the increase in oxygen atomization flow, while VTi monitored by ventilator was not significantly changed. At 10 minutes after the beginning of atomization, the VTi monitored by ventilator in different preset VT groups was significantly lower than VT showed by simulated water lung (mL: 649.67±5.03 vs. 840.00±10.00 at 650 mL of preset VT and 9 L/min of atomized oxygen flow, P < 0.05), and VTe was significantly higher than VT showed by simulated water lung (mL: 1 270.33±11.06 vs. 840.00±10.00 at 650 mL of preset VT and 9 L/min of atomized oxygen flow, P < 0.05). Under PCV mode, with the increase in atomized oxygen flow, VTi monitored by ventilator in different preset suction pressure groups was decreased gradually, and VTe was increased gradually, but Ppeak monitored by ventilator did not changed significantly. At 10 minutes after the beginning of atomization, the VTi monitored by ventilator in different preset suction pressure groups was significantly lower than VT showed by simulated water lung (mL: 917.33±4.51 vs. 1 103.33±5.77 at 20 cmHO of preset suction pressure and 9 L/min of atomized oxygen flow, P < 0.05), and VTe was significantly higher than VT showed by simulated water lung (mL: 1 433.33±4.73 vs. 1 103.33±5.77 at 20 cmHO of preset suction pressure and 9 L/min of atomized oxygen flow, P < 0.05).

Conclusions: Under the VCV mode, the oxygen flow outside the atomization could lead to the increase in VT of the patient side, while under the PCV mode, the VT and Ppeak in the patient side had no significant change. Both VTi and VTe monitored by ventilator could not reflect the patient's VT under either VCV or PCV mode.