ABSTRACT
Objective To explore the effect of airway humidification on lung injury as a result of mechanical ventilation with different tidal volume(VT). Methods Twenty-four male Japanese white rabbits were randomly divided into four groups:low VT with airway humidification group,high VT with airway humidification group,low VT and high VT group without humidification,with 6 rabbits in each group. Mechanical ventilation was started after intubation and lasted for 6 hours. Low VT denoted 8 mL/kg,while high VT was 16 mL/kg,fraction of inspired oxygen (FiO2)denoted 0.40,positive end-expiratory pressure(PEEP)was 0. Temperature at Y piece of circuit in airway humidification groups was monitored and controlled at 40℃. Arterial blood gas analysis,including pH value,arterial partial pressure of oxygen(PaO2),arterial partial pressure of carbon dioxide(PaCO2),lung mechanics indexes, including peak airway pressure(Ppeak)and airway resistance(Raw),and lung compliance was measured at 0,2,4, 6 hours of mechanical ventilation. The levels of tumor necrosis factor-α(TNF-α)and interleukin-8(IL-8)in plasma and bronchoalveolar lavage fluid(BALF)were determined by enzyme linked immunosorbent assay(ELISA). The animals were sacrificed at the end of mechanical ventilation. The wet to dry(W/D)ratio of lung tissues was calculated. Histopathologic changes in the lung tissueies were observed with microscope,and lung injury score was calculated. Scanning and transmission electron microscopies were used to examine the integrity of the airway cilia and the tracheal epithelium. Results Compared with low VT group,pH value in high VT group was significantly increased,PaCO2 was significantly lowered,and no difference in PaO2 was found. Ppeak,Raw,and lung compliance were significantly increased during mechanical ventilation. There were no significant differences in blood gas analysis and lung mechanics indexes between low VT with airway humidification group and low VT group. Compared with high VT group,PaCO2 in high VT with airway humidification group was significantly decreased,Ppeak raised obviously,and no difference in pH value,PaO2,Raw and pulmonary compliance was found. Compared with low VT with airway humidification group,no difference in blood gas analysis(PaCO2,mmHg,1 mmHg=0.133 kPa)was found,but Ppeak(cmH2O,1 cmH2O=0.098 kPa),Raw(cmH2O),and lung compliance(mL/cmH2O)were increased significantly in high VT with airway humidification group(PaCO2 at 2 hours:27.96±4.64 vs. 36.08±2.11,4 hours:28.62±2.93 vs. 34.55±5.50, 6 hours:29.33±2.14 vs. 35.01±5.53;Ppeak at 0 hour:14.34±1.97 vs. 8.84±1.32,2 hours:17.33±0.52 vs. 11.17±2.14,4 hours:17.83±0.98 vs. 12.67±2.06,6 hours:18.67±1.22 vs. 13.50±2.16;Raw at 0 hour:37.36±5.14 vs. 27.05±2.93,2 hours:43.94±6.58 vs. 31.95±3.56,4 hours:48.04±6.07 vs. 35.24±3.50, 6 hours:50.33±6.34 vs. 36.66±3.64;pulmonary compliance at 6 hours:2.28±0.18 vs. 1.86±0.37,all P0.05). Microscopic observation showed that cilia were partially detached,adhered and sparse in low VT group,while cilia in high VT group showed serious detachment and lodging. Remaining cilia were sparse,with lodging,and cellular structure was damaged. Lung tissue pathological injury score in the high VT group was significantly higher than that of low VT group(6.17±2.14 vs. 3.50±1.52,P0.05). Cilia were severely detached,adhered and lodging,and cellularity were not obvious in high VT with airway humidification group,and lung tissue pathological injury score was elevated significantly than that of the low VT with airway humidification group but without statistically significant difference(5.17±2.14 vs. 3.00±1.10,P>0.05). TNF-α and IL-8 concentrations showed no change in plasma and BALF in all groups during ventilation,and no significant difference was found among the groups. Conclusions Airway humidification can alleviate pathological lung injury,damage of cilia and cellular structure in trachea caused by mechanical ventilation with low and high VT. High VT with humidification can result in serious pulmonary edema.