Continuous Cardiac Output and Left Atrial Pressure Monitoring by Pulmonary Artery Pressure Waveform Analysis

We introduce a novel technique for continuous (i.e., automatic) monitoring of cardiac output (CO) and left atrial pressure (LAP) by mathematical analysis of a pulmonary artery pressure (PAP) waveform. To obtain an initial evaluation of the technique, we applied it to PAP waveforms obtained from nine critically ill patients and compared the resulting CO and LAP estimates with standard operator- dependent thermodilution and pulmonary capillary wedge pressure measurements, respectively. We report that the technique achieved an overall CO error of 17.2% and an overall LAP error of 15.8%. With further testing, the technique may ultimately be employed so as to permit, for the first time, continuous CO and LAP monitoring in critically ill patients. I. INTRODUCTION ARDIAC output (CO) represents the total blood flow rate in the circulation, while left atrial pressure (LAP) generally indicates the blood pressure attained in the left ventricle during the cardiac filling phase. CO and LAP are two of the most important quantities to be able to monitor in critically ill patients, as they facilitate the diagnosis, monitoring, and treatment of various disease processes such as left ventricular failure, mitral valve disease, and shock of any cause. For example, a decrease in CO while LAP is rising would indicate that the patient is in left ventricular failure, whereas a decrease in CO while LAP is falling may indicate that the patient is going into hypovolemic shock. The standard methods for monitoring CO and LAP in critically ill patients both involve the use of the balloon- tipped, flow-directed pulmonary artery catheter (1)(2). CO is specifically estimated according to the thermodilution method. This method involves injecting a bolus of cold saline in the right atrium, measuring temperature downstream in the pulmonary artery, and computing the average CO based on conservation laws. LAP is estimated through the pulmonary capillary wedge pressure (PCWP) method. This method involves advancing the catheter into a branch of the pulmonary artery, inflating the balloon, and measuring the resulting steady-state PCWP. In theory, PCWP should nearly equal LAP, since flow has ceased