Smart Drain for Post–Cardiac Surgery Left Ventricular Volumes Evaluated in Large Animal Models

Background: Open heart surgeries for coronary arterial bypass graft and valve replacements are performed on 400,000 Americans each year. Unexplained hypotension during recovery causes morbidity and mortality through cerebral, kidney, and coronary hypoperfusion. An early detection method that distinguishes between hypovolemia and decreased myocardial function before onset of hypotension is desirable. We hypothesized that admittance measured from a modified pericardial drain can detect changes in left ventricular end-systolic, end-diastolic, and stroke volumes. Methods: Admittance was measured from 2 modified pericardial drains placed in 7 adult female dogs using an open chest preparation, each with 8 electrodes. The resistive and capacitive components of the measured admittance signal were used to distinguish blood and muscle components. Admittance measurements were taken from 12 electrode configurations in each experiment. Left ventricular preload was reduced by inferior vena cava occlusion. Physiologic response to vena cava occlusion was measured by aortic pressure, aortic flow, left ventricle diameter, left ventricular wall thickness, and electrocardiogram. Results: Admittance successfully detected a drop in left ventricular end-diastolic volume (P < .001), end-systolic volume (P < .001), and stroke volume (P < .001). Measured left ventricular muscle resistance correlated with crystal-derived left ventricular wall thickness (R² = 0.96), validating the method's ability to distinguish blood from muscle components. Conclusions: Admittance measured from chest tubes can detect changes in left ventricular end-systolic, end-diastolic, and stroke volumes and may therefore have diagnostic value for unexplained hypotension.