Poelaert J I, Visser C A, Everaert J A, De Deyne C S, Decruyenaere J, Colardyn F A
Department of Intensive Care, University Hospital, Ghent, Belgium.
J Cardiothorac Vasc Anesth. 1994 Aug;8(4):392-7. doi: 10.1016/1053-0770(94)90276-3.
Positive-pressure ventilation has often been advocated to increase oxygen delivery. This ventilation mode itself, however, can impair right ventricular ejection and, thus, diminish cardiac output. In this study, alterations of right ventricular outflow impedance were evaluated after stepwise increases of positive end-expiratory pressure (PEEP). Different pulmonary artery flow characteristics were evaluated with transesophageal echocardiography in mechanically ventilated postoperative coronary artery bypass surgery patients without pulmonary hypertension. A progressive decrease of pulmonary artery flow velocity and time velocity integrals was found with increasing PEEP levels. No changes in acceleration time or pre-ejection period were observed. In order to decrease the influence of heart rate, the ratios of the different pulmonary artery flow characteristics were calculated. At end-inspiration, both the ratio of acceleration time to right ventricular ejection period and the ratio of pre-ejection period to right ventricular ejection period showed progressive increases above 10 cmH2O positive end-expiratory pressure (13.3% at the level of 15 cmH2O and 8.5% at the level of 20 cmH2O). In this study, acceleration time appears not to be of importance in ventilated patients. These data strongly support the hypothesis that intermittent squeezing of the pulmonary arterial tree during inspiration, rather than positive end-expiratory pressure, creates an increase of right ventricular outflow impedance.
人们常常主张采用正压通气来增加氧输送。然而，这种通气模式本身会损害右心室射血，进而降低心输出量。在本研究中，我们评估了呼气末正压（PEEP）逐步增加后右心室流出阻抗的变化。在无肺动脉高压的机械通气冠状动脉搭桥术后患者中，通过经食管超声心动图评估不同的肺动脉血流特征。结果发现，随着PEEP水平的升高，肺动脉血流速度和时间速度积分逐渐降低。未观察到加速时间或射血前期的变化。为了减少心率的影响，我们计算了不同肺动脉血流特征的比值。在吸气末，加速时间与右心室射血期的比值以及射血前期与右心室射血期的比值在呼气末正压高于10 cmH2O时均呈现逐渐增加的趋势（在15 cmH2O水平时增加13.3%，在20 cmH2O水平时增加8.5%）。在本研究中，加速时间在通气患者中似乎并不重要。这些数据有力地支持了这样一种假说，即吸气过程中肺动脉树的间歇性挤压而非呼气末正压导致了右心室流出阻抗的增加。
