Retamal Jaime, Libuy Javiera, Jiménez Magdalena, Delgado Matías, Besa Cecilia, Bugedo Guillermo, Bruhn Alejandro
Crit Care. 2013 Jan 28;17(1):R16. doi: 10.1186/cc12487.
Cyclic recruitment-derecruitment and overdistension contribute to ventilator-induced lung injury. Tidal volume (Vt) may influence both, cyclic recruitment-derecruitment and overdistension. The goal of this study was to determine if decreasing Vt from 6 to 4 ml/kg reduces cyclic recruitment-derecruitment and hyperinflation, and if it is possible to avoid severe hypercapnia.
Patients with pulmonary acute respiratory distress syndrome (ARDS) were included in a crossover study with two Vt levels: 6 and 4 ml/kg. The protocol had two parts: one bedside and other at the CT room. To avoid severe hypercapnia in the 4 ml/kg arm, we replaced the heat and moisture exchange filter by a heated humidifier, and respiratory rate was increased to keep minute ventilation constant. Data on lung mechanics and gas exchange were taken at baseline and after 30 minutes at each Vt (bedside). Thereafter, a dynamic CT (4 images/sec for 8 sec) was taken at each Vt at a fixed transverse region between the middle and lower third of the lungs. Afterward, CT images were analyzed and cyclic recruitment-derecruitment was determined as non-aerated tissue variation between inspiration and expiration, and hyperinflation as maximal hyperinflated tissue at end-inspiration, expressed as % of lung tissue weight.
We analyzed 10 patients. Decreasing Vt from 6 to 4 ml/kg consistently decreased cyclic recruitment-derecruitment from 3.6 (2.5 to 5.7) % to 2.9 (0.9 to 4.7) % (P <0.01) and end-inspiratory hyperinflation from 0.7 (0.3 to 2.2) to 0.6 (0.2 to 1.7) % (P = 0.01). No patient developed severe respiratory acidosis or severe hypercapnia when decreasing Vt to 4 ml/kg (pH 7.29 (7.21 to 7.46); PaCO2 48 (26 to 51) mmHg).
Decreasing Vt from 6 to 4 ml/kg reduces cyclic recruitment-derecruitment and hyperinflation. Severe respiratory acidosis may be effectively prevented by decreasing instrumental dead space and by increasing respiratory rate.
周期性的肺复张-萎陷和肺过度扩张会导致呼吸机诱导的肺损伤。潮气量（Vt）可能会影响周期性的肺复张-萎陷和肺过度扩张。本研究的目的是确定将Vt从6 ml/kg降至4 ml/kg是否能减少周期性的肺复张-萎陷和肺过度充气，以及是否有可能避免严重的高碳酸血症。
患有肺部急性呼吸窘迫综合征（ARDS）的患者被纳入一项交叉研究，该研究有两个Vt水平：6 ml/kg和4 ml/kg。该方案有两个部分：一部分在床边进行，另一部分在CT室进行。为了避免4 ml/kg组出现严重的高碳酸血症，我们将热湿交换过滤器换成了加热加湿器，并提高呼吸频率以保持分钟通气量恒定。在每个Vt水平的基线期和30分钟后（床边）采集肺力学和气体交换数据。此后，在肺部中下三分之一之间的固定横向区域，对每个Vt水平进行动态CT扫描（每秒4幅图像，共8秒）。然后，对CT图像进行分析，将周期性的肺复张-萎陷确定为吸气和呼气之间无气组织的变化，将肺过度充气确定为吸气末最大的过度充气组织，以肺组织重量的百分比表示。
我们分析了10名患者。将Vt从6 ml/kg降至4 ml/kg持续降低了周期性的肺复张-萎陷，从3.6（2.5至5.7）%降至2.9（0.9至4.7）%（P<0.01），吸气末肺过度充气从0.7（0.3至2.2）%降至0.6（0.2至1.7）%（P = 0.01）。当将Vt降至4 ml/kg时，没有患者出现严重的呼吸性酸中毒或严重的高碳酸血症（pH 7.29（7.21至7.46）；PaCO2 48（26至51）mmHg）。
将Vt从6 ml/kg降至4 ml/kg可减少周期性的肺复张-萎陷和肺过度充气。通过减少器械死腔和增加呼吸频率可有效预防严重的呼吸性酸中毒。
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