BACKGROUND: The endotracheal cardiac output system (ECOM) is a new device that uses an endotracheal tube with multiple electrodes to measure cardiac output. It measures the changes in electrical impedance caused by pulsatile blood flow in the aorta. The system was designed and developed by the Cardiac Engineering group. It has been tested in 75 chronically instrumented pigs and 7 humans. Most recently the system was tested for safety and efficacy in 10 chronically instrumented swine.
METHODS: Swine (60-80 kg) were chronically instrumented with a Transonicsâ transit time flow probe (TTFP) on the ascending aorta and vascular occluders on the vena cava and pulmonary artery. After a minimum of four days recovery, the animals were anesthetized and intubated with an Imagyn ECOM endotracheal tube (model 3D-6). Cardiac output measurements from the ECOM system were compared to transit time flow probe measurements using linear regression and Bland-Altman analysis. Three different inotropic states were studied: a) baseline, b) increased (dobutamine), and c) decreased (esmolol). Cardiac output was changed at each inotropic state by impeding left ventricular filling with the vena cava and/or pulmonary artery occluders. Cardiac outputs between 0 and 15 liters/min were studied. Pigs were anesthetized and studied for 24 consecutive hours.
RESULTS: There was no deterioration of the impedance signal with time and no tracheal injury from the ECOM electrodes. There is a linear relationship between the ECOM and TTFP cardiac output between 0 and 15 l/min (Slope = 0.999, Intercept = 0.00, R2= 0.84). The mean difference between the two measures (bias) is 0.00 and the standard deviation 1.1 l/min. The limits of agreement are -2.3 to 2.3 l/min.
CONCLUSION: ECOM is able to measure cardiac output with safety and accuracy.
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