cung lượng tim sau đó tính toán bằng cách phân tích của đường cong thermodilution bằng cách sử dụng thuật toán Stewart-Hamilton. Sản lượng lithium pha loãng tim (ví dụ, LiDCOplus, LiDCO, Cambridge, Anh) sử dụng đo lường nồng độ lithium động mạch | 138 R. Holsten cardiac output is then calculated by analysis of the thermodilution curve using the Stewart-Hamilton algorithm. The lithium dilution cardiac output . LiDCOplus LiDCO Cambridge UK uses the measurement of the arterial lithium concentration after a small intravenous bolus injection of lithium and development of a concentration-time curve to calculate the cardiac output 14 . This technique cannot be used in patients being treated with lithium and nondepolarizing muscle relaxants interfere with calibration. Using either technique other parameters can also be estimated including pulse pressure variation and stroke volume variation which can indicate fluid responsiveness 15 . Measurement of cardiac output with these techniques has been validated against standard PAC thermodilution cardiac output 16-19 and they may be of use in patients who do not require a PAC. Pulmonary Artery Catheter The PAC possesses at its tip an inflatable balloon that allows it to move with the blood by flotation. Introduced intravenously usually via the subclavian or internal jugular veins the PAC progresses through the right atrium and ventricle to the pulmonary artery. The PAC was initially developed to measure the pulmonary artery occlusion pressure PAOP measured from the distal end of the catheter but with the balloon briefly inflated. The inflated balloon is carried by the flow of blood and wedges in a branch of the PA occluding blood flow distal to this point. The pressure measured at this time thus represents the pressure that exists beyond the pulmonary capillaries . the pressure present in the left atrium which in the absence of any abnormality of the mitral valve is itself equal to the filling pressure in the left ventricle thus providing an indication of left ventricular preload. However the PAC also provides measurement of right atrial pressure equivalent to the CVP right ventricular pressure and pulmonary artery pressures. The PAC can be equipped with
