OBJECTIVETo study the effects of high frequency oscillatory ventilation (HFOV) combined with incremental positive end-expiratory pressure (IP) on respiratory and circulatory functions, and lung histopathology of dogs with smoke inhalation injury.

METHODSAfter being treated with conventional mechanical ventilation, 12 dogs were inflicted with severe smoke inhalation injury and divided into group HFOV and group HFOV+IP according to the random number table, with 6 dogs in each group. Then they received corresponding ventilation for 8 hours respectively. Blood gas analysis results (pH value, PaO2 and PaCO2 levels) and hemodynamic parameters [heart rate, mean arterial pressure (MAP), pulmonary arterial pressure (PAP), central venous pressure (CVP), cardiac output (CO)] were recorded before injury, immediately after injury, and at post ventilation hour (PVH) 2, 4, 6, and 8. The dogs of two groups were sacrificed at PVH 8. A healthy dog without any treatment and a dog with smoke inhalation injury but no subsequent treatment were sacrificed in addition. Lung tissues of all dogs were obtained for histopathological observation. Lung injury score examination was conducted in both groups. Data were processed with rank sum test, analysis of variance of repeated measurement, and LSD- t test.

RESULTS(1) The PaO2 levels in both groups were significantly decreased immediately after injury, compared with those before injury (with t values respectively 4.960, 5.310, P values all below 0.01). The PaO2 levels in both groups from PVH 2 to PVH 8 were significantly increased, compared with those observed immediately after injury (with t values from 4.930 to 6.050, P values all below 0.01). At PVH 2, 4, and 8, PaO2 levels in group HFOV+IP were significantly higher than those in group HFOV (with t values from 3.775 to 5.774, P values all below 0.01); no statistically significant differences were observed in pH value and PaCO2 level at each time point between two groups (with t values from 0.002 to 0.997, P values all above 0.05). (2) There were no statistically significant differences in MAP, PAP, and CVP within two groups at each time point (with F values from 1.316 to 4.959, P values all above 0.05). In group HFOV, heart rate from PVH 2 to PVH 8 was significantly lower than that observed immediately after injury (with t values from 3.780 to 8.970, P values all below 0.01). In group HFOV+IP, CO at PVH 4, 6, and 8 was significantly lower than that observed immediately after injury (with t values from 3.990 to 11.200, P values all below 0.01). There were no statistically significant differences in MAP, PAP, and CVP between two groups at the same time point (with t values from 0.089 to 2.123, P values all above 0.05). At PVH 4, 6, and 8, heart rate in group HFOV+IP was higher than that in group HFOV (with t values from 2.931 to 7.229, P < 0.05 or P < 0.01), while CO was lower (with t values from 4.297 to 11.206, P values all below 0.01). (3) Compared with those of the healthy dog, inflammatory cell infiltration and bleeding in the lung were observed in alveolar space in both group HFOV and group HFOV+IP, while the degree was less serious than that of the dog with smoke inhalation injury only. Compared with those of group HFOV, inflammatory cell infiltration in group HFOV+IP was less significant, the alveolar structure was relatively intact, and no thickening of alveolar walls was observed. The lung injury score in group HFOV [(3.27 ± 0.24) points] was higher than that of group HFOV+IP [(2.79 ± 0.31) points, t = 27, P < 0.05].

CONCLUSIONSHFOV combined with IP can improve gas exchange and alleviate pulmonary injury without any adverse effect on blood gas analysis or hemodynamic parameters. Therefore, it may be considered as an appropriate mode of ventilation for the treatment of smoke inhalation injury.