Historically, the assessment of volume status and cardiac function with the goal of achieving appropriate resuscitation targets has been an area of ongoing interest to intensivists worldwide. The pulmonary artery catheter has long been used in the intensive care unit (ICU) to evaluate volume status, cardiac function, and to guide resuscitation. Recently, multiple studies have questioned the benefits of pulmonary artery catheter use and increased the awareness of associated complications, resulting in a decline in its use [1, 2].
Recently, the debate between static and dynamic indices of volume responsiveness was resolved in favor of the latter with multiple studies demonstrating that central venous pressure lacks predictability as a measure of volume responsiveness  compared with stroke volume and pulse pressure variation . It is important to mention, however, that the validity of dynamic indices is limited by the presence of spontaneous respiration, dysrhythmia, or vasopressor use .
Over the last few years, the use of bedside ultrasonography and echocardiography has expanded both in trauma and ICU settings; surgeons, intensivists, and emergency care physicians have developed training protocols to facilitate the ability to detect free fluid in the abdomen with high sensitivity and specificity . The BEAT exam (Bedside Echocardiographic Assessment in Trauma/Critical Care) is an example of a bedside hemodynamic evaluation protocol that has been developed to assess stroke volume, the presence of pericardial or pleural effusion, ventricular function, size, and volume status .
Monoplane hemodynamic transesophageal echocardiography (hTEE; ImaCor, Inc., Garden City, NY) is a relatively new diagnostic tool, allowing the intensivist to directly assess both the contractility and filling status of both the right and left ventricles at the bedside in real-time. Unlike conventional transesophageal echocardiography (TEE) probes, the hTEE probe is smaller (5.5 mm in diameter), disposable, and can remain in place for up to 72 h, permitting continuous visual quantitative estimation of cardiac contractility and cardiac filling. The probe can be placed safely  in intubated patients by intensivists with a basic level of hTEE training without the need for formal training in conventional TEE . Additionally, hTEE is only capable of displaying three echocardiographic windows compared with 28 views in the case of conventional TEE. The diagnostic yield of hTEE was shown to be non-inferior to thermodilution in the postoperative care of cardiac surgical patients . In fact, information recovered from hTEE led to changes in the plan of care for those patients compared to those evaluated solely with thermodilution [8, 10]. In addition, hTEE was proven useful in weaning from ventriculoarterial extracorporeal membrane oxygenation (VA ECMO) , and has led to changes in intensive care management in patients with left ventricular assist devices . To date, however, no validation studies have been performed to compare hTEE with conventional multiplane TEE.
Echocardiographically estimated fractional area of change (FAC) calculated as the percentage change between left ventricular end-systolic and end-diastolic areas (LVESA and LVEDA, respectively) has been used as a surrogate marker for left ventricular ejection fraction (and thus, systolic function). Similarly, LV preload can also be assessed using LVEDA with consistent accuracy . Despite their obvious appeal, LV area-based measurements are time-consuming and challenging to obtain due to technical issues associated with chamber border detection. These measurements become even more challenging during periods of hemodynamic instability. Additionally, hTEE is incapable of measuring ejection fraction (EF) because it lacks the echocardiographic windows necessary to measure EF such as the midesophageal 2-chamber view. This limitation becomes more evident in current-generation hTEE systems that lack software capable of calculating end-systolic and end-diastolic volumes and hence performing automatic ejection fraction calculation. The current hTEE systems are only capable of calculating end-diastolic and end-systolic areas, requiring multiple manual steps for LV FAC calculation compared with conventional TEE systems that are capable of volumetric EF calculation.
In this study, the authors used hTEE to obtain LV diameter measurements to estimate left ventricular systolic function (using left ventricular fractional shortening), and filling status (using left ventricular end-diastolic diameter) as a technically feasible, less time-consuming alternative to area-based measurements.