Published in:
01-01-2011 | Experimental
Effects of different mechanical ventilation strategies on the mucociliary system
Published in: Intensive Care Medicine | Issue 1/2011
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Objective
To evaluate the effects of different mechanical ventilation (MV) strategies on the mucociliary system.
Design and setting
Experimental study.
Subjects
Twenty-seven male New Zealand rabbits.
Interventions
After anesthesia, animals were tracheotomized and ventilated with standard ventilation [tidal volume (Vt) 8 ml/kg, positive end expiratory pressure (PEEP) 5 cmH2O, flow 3 L/min, FiO2 0.4] for 30 min. Next, animals were randomized into three groups and ventilated for 3 h with low volume (LV): Vt 8 ml/kg, PEEP 5 cmH2O, flow 3 L/min (n = 6); high volume (HV): Vt 16 ml/kg, PEEP 5 cmH2O, flow 5 L/min (n = 7); or high pressure (HP): Ppeak 30 cmH2O, PEEP 12 cmH2O (n = 8). Six animals (controls) were ventilated for 10 min with standard ventilation. Vital signals, blood lactate, and respiratory system mechanics were verified. Tracheal tissue was collected before and after MV.
Measurements
Lung and tracheal tissue sections were stained to analyze inflammation and mucosubstances by the point-counting method. Electron microscopy verified tracheal cell ultrastructure. In situ tracheal ciliary beating frequency (CBF), determined using a videoscopic technique, and tracheal mucociliary transport (TMCT), assessed by stereoscopic microscope, were evaluated before and after MV.
Results
Respiratory compliance decreased in the HP group. The HV and HP groups showed higher lactate levels after MV. Macroscopy showed areas of atelectasis and congestion on HV and HP lungs. Lung inflammatory infiltrate increased in all ventilated groups. Compared to the control, ventilated animals also showed a reduction of total and acid mucus on tracheal epithelium. Under electron microscopy, injury was observed in the ciliated cells of the HP group. CBF decreased significantly after MV only in the HP group. TMCT did not change significantly in the ventilated groups.
Conclusions
Different MV strategies induce not only distal lung alterations but also morphological and physiological tracheal alterations leading to mucociliary system dysfunction.