Surprises are not always welcome. We have studied total body water, quantified the volume and determined the extracellular space, interstitial, and plasma volumes. Nonetheless, estimating these parameters clinically (at the bedside) is frustratingly imprecise. The author ruminates over 50 years’ clinical experience in intensive care units and grapples with the literature.

Our understanding of the vasculature, the idea that the arteries are merely a grandiose extension of the heart (and vice‐versa), the heart's vasomotor control, and the regulation of blood pressure play pivotal roles in volume assessment. For instance, 300 years ago de Sénac wrote; “The arteries (and the heart) have the same movements; they alternate with dilations and contractions without pause.”³ The force inherent in the arteries depends on their muscular fibres and their length. Regulation of the cardiovascular tree concerns us to this date and 300 years of research, until the studies of McGee et al,⁴ prior to the “molecular” era, brought us to where we are. We are endowed with a reasonable knowledge of the circulatory intrinsic, local, neuronal, and central regulation. These advancements must not be forgotten.³ The >300 years of cardiovascular research include the contributions of Bernard, Brown‐Sequard, Magendie, Bayliss, Gaskell, Langley, Cannon, Dale, Frank, Starling, Hering and others. These brilliant investigators carried physiology on their (not‐yet molecular biology) shoulders, not to mention the clinical relevance of hypotension, hypertension, and central nervous system, cardiovascular, osmolar and renal‐volume, and regulation.

惊喜并不总是受欢迎的。我们研究了全身水分，量化了体积并确定了细胞外空间、间质和血浆体积。尽管如此，临床上（在床边）估计这些参数是非常不精确的。作者回顾了 50 多年在重症监护病房的临床经验，并与文献作斗争。

我们对脉管系统的理解、动脉只是心脏的宏伟延伸（反之亦然）、心脏的血管舒缩控制和血压调节在容量评估中起着关键作用。例如，300 年前 de Sénac 写道；“动脉（和心脏）有相同的运动；它们不停地交替扩张和收缩。” ³动脉内在的力量取决于它们的肌肉纤维和它们的长度。迄今为止，我们对心血管树的调节关注了 300 年，直到 McGee 等人的研究，⁴在“分子”时代之前，把我们带到了现在的位置。我们被赋予了循环内在、局部、神经元和中枢调节的合理知识。这些进步不能被遗忘。³超过 300 年的心血管研究包括 Bernard、Brown-Sequard、Magendie、Bayliss、Gaskell、Langley、Cannon、Dale、Frank、Starling、Hering 和其他人的贡献。这些杰出的研究人员将生理学放在了他们的（还不是分子生物学）肩膀上，更不用说低血压、高血压、中枢神经系统、心血管、渗透压和肾脏容量以及调节的临床相关性。