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A3274 - Noninvasive Cardiac Output Monitoring in Critically Ill Adults: A Comparison of Bioreactance (NICOM™) with Transthoracic Echocardiography
Author Block: M. Abdulmahdi1, V. Amaral2, A. Skaanland3, P. Garcia4; 1Pulmonary and Critical Care Medicine, University of Maryland School of Medicine, Baltimore, MD, United States, 2Internal Medicine, Saint Agnes Hospital, Baltimore, MD, United States, 3Critical Care, Saint Agnes Hospital, Baltimore, MD, United States, 4Critical Care Medicine, Sinai Hospital, Baltimore, MD, United States.
Objective: To evaluate the correlation between cardiac output (CO) measured noninvasively using bioreactance (NICOM™) and transthoracic echocardiography (TTE) in critically ill adults. Methods: This was a prospective observational study conducted in a medical-surgical Intensive Care Unit (ICU) at a community teaching hospital. IRB approval was obtained; patient consent was waived. The selected patients were (1) admitted to the ICU service with systolic blood pressure less than 100 mmHg, (2) had both NICOM™ and TTE ordered by the ICU team for diagnosis and management of therapies, and (3) were age 18 and older. All patients had a CO measured with NICOM™ within a four-hour time frame of a TTE study. All the TTE studies were performed by experienced echocardiography technicians and interpreted by board-certified cardiologists. Those collecting data from the NICOM™ were blinded to the CO obtained by echo, and cardiologists interpreting TTE studies had no access to the NICOM™ data. NICOM™ Measurement: NICOM™ uses bioreactance to provide a continuous measurement of stroke volume (SV) and CO, and is used commonly in critical care settings. Four sensors are placed on the thorax in quadrants surrounding the heart. Sensors contain both an emitting and receiving electrode. A 75 kHz signal of alternating current (AC) is delivered through the thorax by the outer portion of the sensors and received by the inner sensor to determine the phase shift. The phase shift detected in the thorax is predominately altered by pulsatile flow in the aorta and measurement of the time delay allows determination of the volume passing from the left ventricle into the aorta (SV), and CO is then displayed on the NICOM™ screen. TTE Measurement: SV can be obtained by multiplying the area of the left ventricular outflow tract (LVOT) by the velocity time integral (VTI) of blood exiting the LVOT. CO may then be calculated by multiplying heart rate by SV (LVOT area x LVOT VTI x HR). Statistical Methods It was determined that a sample size of 21 patients would give 80% power to detect a Pearson correlation of at least 0.6 between the NICOM™ and TTE measures. Results: This study failed to find statistical correlation (r=0.009) between the CO measured by NICOM™ and TTE. Linear regression analysis showed a flat-line relationship. Conclusion: The measurement of CO with NICOM™ is convenient and noninvasive, but further validation of various methods for noninvasive CO measurement in critically ill adults is still needed.