Lopes Marcel Rezende, Auler José Otávio Costa, Michard Frédéric
Anesthesia and Surgical ICU Heart Institute, Hospital das Clínicas, University of São Paulo-SP, Brazil.
Clinics (Sao Paulo). 2006 Aug;61(4):345-50. doi: 10.1590/s1807-59322006000400012.
In order to turn a fluid challenge into a significant increase in stroke volume and cardiac output, 2 conditions must be met: 1) fluid infusion has to significantly increase cardiac preload and 2) the increase in cardiac preload has to induce a significant increase in stroke volume. In other words, a patient can be nonresponder to a fluid challenge because preload does not increase during fluid infusion or/and because the heart (more precisely, at least 1 of the ventricles) is operating on the flat portion of the Frank-Starling curve. Volumetric markers of cardiac preload are therefore useful for checking whether cardiac preload effectively increases during fluid infusion. If this is not the case, giving more fluid, using a venoconstricting agent (to avoid venous pooling), or reducing the intrathoracic pressure (to facilitate the increase in intrathoracic blood volume) may be useful for achieving increased cardiac preload. Arterial pulse pressure variation is useful for determining whether stroke volume can/will increase when preload does increase. If this is not the case, only an inotropic drug can improve cardiac output. Therefore, the best option for determining the usefulness of, and monitoring fluid therapy in critically ill patients is the combination of information provided by the static indicators of cardiac preload and arterial pulse pressure variation.
为了使液体负荷试验能显著增加每搏输出量和心输出量，必须满足两个条件：1）液体输注必须显著增加心脏前负荷；2）心脏前负荷的增加必须能显著增加每搏输出量。换句话说，患者对液体负荷试验无反应可能是因为在液体输注过程中前负荷未增加，和/或因为心脏（更确切地说，至少一个心室）处于Frank-Starling曲线的平台段。因此，心脏前负荷的容量指标对于检查液体输注期间心脏前负荷是否有效增加很有用。如果情况并非如此，给予更多液体、使用静脉收缩剂（以避免静脉淤血）或降低胸内压（以促进胸内血容量增加）可能有助于增加心脏前负荷。动脉脉压变异对于确定当前负荷增加时每搏输出量能否/是否会增加很有用。如果情况并非如此，只有使用正性肌力药物才能改善心输出量。因此，确定危重症患者液体治疗有效性并进行监测的最佳选择是结合心脏前负荷静态指标和动脉脉压变异所提供的信息。
