氮气洗入/洗出法测定急性肺损伤患者肺复张容积的研究

  目的 探讨氮气洗入/洗出法测急性肺损伤(ALI)患者肺复张容积的准确性及可行性。方法 将15例有创机械通气的ALI患者纳入本研究，根据ARDSnet法和跨肺压法滴定2种呼气末正压(PEEP) 水平，分别通气30 min，记录各PEEP水平下潮气量(Vt)、气道平台压等呼吸力学及血流动力学指标，并利用氮气洗入/洗出法测2种PEEP水平的呼气末肺容积(EELV)，根据公式推算氮气洗入/洗出法测的肺复张容积，同时根据低流速压力-容积(P-V)曲线法获得肺复张容积，比较2种方法获得的肺复张容积的相关性及一致性。结果 (1)ARDSnet法滴定的PEEP为（7±2） cm H₂O（1 cm H₂O=0.098 kPa），气道峰压为（23±5） cm H₂O，气道平台压为(17±4） cm H₂O；跨肺压法滴定的PEEP为（14±5 )cm H₂O，气道峰压为（28±6） cm H₂O，气道平台压为（22±6） cm H₂O，2种方法比较差异有统计学意义(P<0.05)。(2) 低流速P-V曲线法测的肺复张容积为100（-25~185）ml，氮气洗入/洗出法测的肺复张容积为180（-19~255）ml，两者具有较好的相关性，R²=0.755，P<0.0001，且测量误差为46（8~80）ml。结论 氮气洗入/洗出法可测定ALI患者的肺复张容积。   

The value of nitrogen washout/washin method in assessing alveolar recruitment volume in acute lung injury patients

Objective To evaluate the precision and feasibility of nitrogen washout/washin method in assessing lung recruitment of acute lung injury(ALI) patients.Methods Fifteen ALI patients underwent mechanical ventilation were involved. Two positive end-expiratory pressure （PEEP） levels (high and low) were adjusted according to ARDSnet recommendations or measurement of transpulmonary pressure, each for 30 minutes. Tidal volume(Vt), plateau of airway pressure(Pplat), other respiratory mechanics, gas-exchange and hemodynamics were measured. End expiration lung volume(EELV) was measured at different PEEP levels through nitrogen washout/washin method, and formula（EELV_highPEEP-EELV_lowPEEP）-Vt_lowPEEP/(Pplat_lowPEEP-PEEP_lowPEEP)×(PEEP_high-PEEP_low） was used as recruitment (Rec-N₂). Alveolar recruitment was measured using pressure-volume(P-V) curves (Rec-mes). Correlation and consistency of Rec-N₂ and Rec-mes were compared by correlation analysis and Bland-Altman technique. Results PEEP titrated by ARDSnet recommendations or transpulmonary pressure were (7±2) cm H₂O(1 cm H₂O=0.098 kPa) vs (14±5) cm H₂O(P=0.008); and there were significant differences in peak pressure(23±5) cm H₂O vs （28±6) cm H₂O, plateau of airway pressure(17±4)cm H₂O vs (22±6) cm H₂O, esophageal pressure, transpulmonary pressure and other respiratory mechanics between the two PEEP levels(P<0.05). The P-V curve technique gave Rec-mes a value of 100(-25~185)ml. The nitrogen washout/washin technique gave Rec-N₂ a value of 180(-19~255) ml, which showed a good correlation with a bias of 46(8~80)ml (R²=0.755, P<0.0001).Conclusion Nitrogen washout/washin technique can be used to determine lung recruitment volume of ALI patients.