容积保证压力支持通气时不同水平恒定供气流量对呼吸衰竭患者肺力学的影响

Effects of different levels of constant flow on respiratory mechanics in respiratory failure patients during volume-assured pressure support ventilation

目的 探讨在容积保证压力支持 (VAPS)通气时不同水平的恒定供气流量 (CF)对呼吸衰竭患者肺力学参数的影响。方法 呼吸衰竭患者 14例 ,其中男性 11例 ,女性 3例 ,年龄 (6 7± 2 )岁。基础疾病为慢性阻塞性肺疾病 (COPD) 8例 ,急性肺损伤 (ALI) 6例 ,所有患者均接受气管插管及机械通气支持 2 4h以上。保持患者处于镇静状态 ,首先应用定容型通气模式 (VCV) ,潮气量 (VT) 7～ 9ml/kg;随后转为VAPS通气 ,吸气压 (Pinspl)等于VCV时的Pplat,CF分别为 15L/min和 10L/min ,最后予以压力支持通气 (PSV)。COPD呼吸衰竭患者在沙丁胺醇 6 0 0 μg后重复上述各模式通气。 结果 与VCV相比 ,COPD患者在VAPS通气时的气道峰压 (PSV)以及峰压与气道平台压之差 (PIP Pplat)明显降低 ,在VT 相近的情况下 ,平均吸气流量 (VT/TI)呈显著下降 [(17 8± 3 6 )L/min (CF为 15L/min) ,(13 6± 2 7)L/min (CF为10L/min)与 (31 3± 2 9)L/min (VCV) ],而与PSV时相近 (均P <0 0 5 )。吸入沙丁胺醇后 ,VAPS时的吸气峰流量 (PIF)明显增高 [(2 7 1± 1 3)L/min与 (937 1± 1 9)L/min ,P <0 0 5 ) ],但PIP与PIP Pplat却进一步降低。ALI患者在VAPS时的PIF增高最为明显 ,CF为 10L/min时PIP Pplat降至 (1 2± 0 3)cmH2 O 。

Objective To investigate the effects of different levels of constant flow (CF)on respiratory mechanics in respiratory failure patients during volume-assured pressure support ventilation (VAPS), and the changes of ventilator parameters in patients with chronic obstructive pulmonary disease (COPD) after salbutamol inhalation. Methods Fourteen patients(aged 67±2 years old), intubated and mechanically ventilated for at least 24 hours because of acute respiratory failure with diverse causes (8with COPD,6 with acute lung injury). After 20 minutes with VCV (tidal volume 7～9ml/kg),respiratory mechanics was measured and the patients were ventilated in VAPS mode for 40 minutes (CF=15L/min and 10L/min), when the inspiratory pressure (Pinsp) was equal to the plateau pressure (Pplat) during VCV. At last these patients were supported with pressure support ventilation (PSV). VCV, VAPS and PSV were repeated in the 8 COPD patients after inhalation of 600μg salbutamol.Results With the same tidal volume,peak inspiratory pressure (PIP), the difference between PIP and Pplat (PlP-Pplat) were significantly lower in 8 COPD patients,and mean inspiratory flow rate (V T/T I) during VAPS was lower than that during VCV[(17.8 ± 3.6)L/min(CF=15L/min),(13.6 ± 2.7)L/min(CF=10)L/min versus(31.3 ±2.9)L/min(VCV), P<0.05]. After salbutamol inhalation, peak inspiratory flow (PIF) during VAPS mode was significantly increased from(27.1 ±1.3)L/min to(37.1 ±1.9)L/min (P<0.05),but PIP and PIP-Pplat were further decreased. PIF was increased more obviously in the 6 ALI patients with VAPS and PSV modes than in the 8 COPD patients. CF/PIF was(23.3 ± 1.1)% when CF was 10 L/min, more close to 25% (expiratory trigger sensitivity with PSV), meanwhile PIP-Pplat was(1.2±0.3)cmH 2O. Conclusion VAPS is a mechanical ventilation mode using the theory of dual control within a breath. Compared with VCV, VAPS is able to assure a minimum preset V T and reduce patient workload.PIP can be decreased by setting lower CF (≤ 15L/min).