Effects of Hemodynamic Monitoring Using the ImaCor Single Use Transesophageal Echocardiography Probe in Critically Ill Patients

Hemodynamic management of critically ill patients is a constant challenge in the intensive care unit (ICU). Commonly used monitoring parameters to guide hemodynamic management generally consist of measurements of pressures (systemic and pulmonary artery pressures, cardiac filling pressures) and flow (cardiac output measurements using a thermodilution method). However, cardiac filling pressures and flow data have known limitations and might not accurately represent cardiac preload and contractility. Hemodynamic management of critically ill patients based on these parameters might therefore not be optimal and delay stabilisation of the patient, leading to negative outcomes and increased use of resources.

Visualization of the heart using echocardiography offers the advantage of direct measurement of cardiac volumes and systolic function. Echocardiography has been established as a tool to evaluate the causes of hemodynamic instability in ICU patients by the visualization of cardiac chambers, valves and pericardium and cardiac functional abnormalities. A repeated echocardiographic assessment could potentially provide useful additional information resulting in more rapid resolution of hemodynamic instability. Using conventional TTE and TEE, however, limits the feasibility of such an approach due to a lack of time and availability of appropriately trained staff.

In recently published studies the feasibility of hemodynamic monitoring and safety of hTEE was demonstrated. In the context of a prospective quality review assessment, the investigators showed that the echocardiographic examinations using hTEE were of sufficient quality in a majority of examined ICU patients and that the inter-rater reliability between the intensivists and a trained cardiologist was substantial. However, as of yet studies assessing the impact of hemodynamic monitoring by hTEE on relevant patient outcomes are not available. Given the associated costs for the hTEE device and the ultrasound probes and the additional resource requirements for training and application, the efficacy and efficiency of hTEE monitoring in comparison to standard monitoring should be established.

Background

Hemodynamic management of critically ill patients is a constant challenge in the intensive care unit (ICU). Commonly used monitoring parameters to guide hemodynamic management generally consist of measurements of pressures (systemic and pulmonary artery pressures, cardiac filling pressures) and flow (cardiac output measurements using a thermodilution method). However, cardiac filling pressures and flow data have known limitations and might not accurately represent cardiac preload and contractility. To date, continuous or sequential recording of hemodynamic parameters is limited to pulse pressure variation measurement and indicator dilution techniques. The overall accuracy of these methods is not well established and comparisons of measurements of cardiac function parameters have been reported to trend differently in response to therapy and show limited interdevice agreement. Hemodynamic management of critically ill patients based on these parameters might therefore not be optimal and delay stabilisation of the patient, leading to negative outcomes and increased use of resources.

Visualization of the heart using echocardiography offers the advantage of direct measurement of cardiac volumes and systolic function. Echocardiography has been established as a tool to evaluate the causes of hemodynamic instability in ICU patients by the visualization of cardiac chambers, valves and pericardium and cardiac functional abnormalities. Transthoracic echocardiography (TTE) can be used as a first-line approach for a quick and focused examination to diagnose acute cor pulmonale, cardiac tamponade or major left ventricular systolic dysfunction. The training necessary to reliably perform such an abbreviated TTE use is substantial and the method is not readily available for every intensivist. Transesophageal echocardiography (TEE) can have a better diagnostic capability and is more reproducible than TTE. A minimum number of 31 TEE examinations has been reported to be required for intensivists to achieve competence in TEE driven hemodynamic evaluation of ventilated ICU patients. Additionally, repeatedly inserting the TEE probe as required for serial evaluation of a patients hemodynamic status is associated with a small but significant risk of injury to oral and esophageal structures. A repeated echocardiographic assessment could potentially provide useful additional information resulting in more rapid resolution of hemodynamic instability. Using conventional TTE and TEE, however, limits the feasibility of such an approach due to a lack of time and availability of appropriately trained staff.

In a recently published study the feasibility of hemodynamic monitoring and safety of hTEE was demonstrated in a group of ninety-four ventilated critically ill patients. In this study hTEE examinations were performed by four highly trained intensivist with extensive expertise in critically care echocardiography. The Department of Intensive Care Medicine Inselspital (KIM) has introduced hTEE in January 2012. The feasibility and quality of hemodynamic monitoring using hTEE by the department's intensivists was assessed in the context of a prospective quality review assessment. The study showed that the echocardiographic examinations using hTEE were of sufficient quality in a majority of examined ICU patients and that the inter-rater reliability between the intensivists and a trained cardiologist was substantial. However, as of yet studies assessing the impact of hemodynamic monitoring by hTEE on relevant patient outcomes are not available. Given the associated costs for the hTEE device and the ultrasound probes and the additional resource requirements for training and application, the efficacy and efficiency of hTEE monitoring in comparison to standard monitoring should be established.

The investigated device consists of a newly developed, commercially available transesophageal echocardiography system. The ImaCor ClariTEE technology (hTEE) device produces a single-plane two-dimensional image and has color Doppler capability (IMACOR, New-York NY, USA). The ImaCor probe is a 5.5 mm detachable probe; due to its small size it can remain in situ for up to 72h and therefore allows for reassessment of the patient's hemodynamic progress and the effect of selected interventions at any time. The probe has to be disposed after 72h for hygienic reasons. The probe is connected to a dedicated echocardiographic system which allows the recording of digital loops and performance of basic two-dimensional measurements of areas and distances. It provides a robust, but more rapid and user-friendly approach to monitoring hemodynamic status and cardiac function than conventional TTE/TEE.

Objective

The study hypothesis is that hemodynamic monitoring using hTEE of critically ill patients with hemodynamic compromise allows for an expedited reversal of circulatory impairment compared to standard ICU monitoring.

Primary Objective: To assess the impact of hemodynamic monitoring using the ImaCor ClariTEE technology on duration and amount of vasopressor use and time to reversal of shock in hemodynamically compromised patients in comparison to standard monitoring.

Secondary Objective: To assess the safety and tolerability of the ImaCor ClariTEE probe.

Methods

Subjects will be assigned to one of four groups stratified by method of hemodynamic monitoring (ImaCor vs control hemodynamic monitoring) and frequency of hemodynamic assessments (protocolized intervals PM vs standard monitoring intervals SM). In patients randomized to echocardiography-guided hemodynamic management (ImaCorPM and ImaCorSM) the ImaCor ClariTEE system will be installed at the time of study inclusion. An ICU consultant will assess the patients' hemodynamic condition based on the hTEE information (ImaCorPM and SM) and other available hemodynamic parameters (ControlPM and SM). Any changes in hemodynamic management are recorded.

Eligibility Criteria:
Inclusion Criteria:

* 18 years of age or older AND
* Mechanical ventilation AND
* Systemic mean blood pressure \< 60 mmHg (or \< 80 mmHg if the patient has baseline hypertension) for more than 30 minutes despite adequate fluid resuscitation (minimum of 20 ml/kg crystalloids) OR
* Maintaining the systemic mean blood pressure \> 60 mmHg requires any dose of vasopressors or inotropes AND at least one of the following:
* Capillary refilling time three seconds or longer
* Lactate \>2 mmol/L
* Urine output \<0.5 mL/kg for at least one hour
* Written informed consent

Exclusion Criteria

* Unrepaired tracheoesophageal fistula
* History of prior esophageal or gastric surgery precluding the use of TEE
* Esophageal obstruction or stricture
* Esophageal varices or diverticulum
* Esophageal or gastric perforation
* Gastric or esophageal bleeding
* Vascular ring, aortic arch anomaly with or without airway compromise
* Recent oropharyngeal surgery
* Severe coagulopathy (defined as thrombocyte count less than 30x10e9/l or INR \> 3)
* Cervical spine injury or anomaly
* Elective ICU admission after elective surgery
* Use of cardiac assist devices
* Use of extra-corporeal membrane oxygenation