Hindawi Publishing Corporation Cardiology Research and Practice Volume 2012, Article ID 894308, 7 pages doi:10.1155/2012/894308 Review Article Appreciating the Strengths and Weaknesses of Transthoracic Echocardiography in Hemodynamic Assessments Stephen J. Huang and Anthony S. McLean Department of Critical Care Medicine, Nepean Hospital, Sydney Medical School, Penrith, NSW 2750, Australia Correspondence should be addressed to Stephen J. Huang, stephen.huang@sydney.edu.au Received 7 June 2011; Accepted 14 November 2011 Academic Editor: Philippe Vignon Copyright © 2012 S. J. Huang and A. S. McLean. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Transthoracic echocardiography (TTE) is becoming the choice of hemodynamic assessment tool in many intensive care units. With an ever increasing number of training programs available worldwide, learning the skills to perform TTE is no longer a limiting fac- tor. Instead, the future emphasis will be shifted to teach the users how to recognize measurement errors and artefacts (internal validity), to realize the limitations of TTE in various applications, and ﬁnally how to apply the information to the patient in ques- tion (external validity). This paper aims to achieve these objectives in a common area of TTE application—hemodynamic assessments. We explore the strengths and weaknesses of TTE in such assessments in this paper. Various methods of hemodynamic assessments, such as cardiac output measurements, estimation of preload, and assessment of ﬂuid responsiveness, will be discussed. 1. Introduction Hemodynamic assessments form an indispensable part in optimizing ﬂuid status, with the objective of improving adequate tissue perfusion in critically ill patients. In the last decade or two, the practice of critical care medicine is slow- ly moving away from traditional high-risks invasive proce- dures wherever possible. Echocardiography, especially trans- thoracic echocardiography (TTE), has been gaining popular- ity due to its noninvasiveness where the beneﬁt far outweighs the risk [1]. Its ability to provide vital information about the cardiovascular and hemodynamic status of the patients with- in a short time frame (within 30 minutes) is another attrac- tion for its use in the critical care setting [2]. A proper focused bedside assessment of cardiac function by TTE can provide answers to important questions about the cardiac function within 10–15 minutes [3]. Assessment for ﬂuid status can also be done within 10–15 minutes. At present, there are no other bedside investigative tools that provide the same level and amount of information as echocardiography. That said, it is important to realize that echocardiography has its strengths and weaknesses. It can suﬀer from internal and external validity problems. Internal validity refers to the errors associated with the study procedure such as artefacts and measurement errors, and external validity refers to the applicability of the study ﬁndings to a particular patients. This article will discuss some of the strengths and validities of TTE in hemodynamic assessments. 2. Hemodynamics The term “hemodynamics” is not very well deﬁned but is generally used to refer to “the physics of blood circulation”. It involves the study of the control of circulation and the factors that alter it. Figure 1 shows the general scheme of hemo- dynamics in the body. The main function of blood circu- lation is to ensure adequate tissue perfusion, which is re- lated to two important factors: cardiac output and vascular resistance. Cardiac output is the product of stroke volume and heart rate, where the former can be aﬀected by pre- load, afterload and cardiac contractility. Afterload, or the tension on myocardial wall during systole, depends on the blood pressure downstream and is determined by the intra- vascular volume and the resistance of the vasculature where the vasomotor tone is under continuous control by various neurohumoral and local factors. On the other hand, preload,