Clinical meaning
Hemodynamic monitoring provides objective, continuous measurement of cardiovascular function to guide critical care management. The fundamental concepts are: Preload (the volume of blood stretching the ventricle at end-diastole, measured by CVP for the right heart and PAWP/PCWP for the left heart), Afterload (the resistance the ventricle must overcome to eject blood, measured by SVR for the left ventricle and PVR for the right ventricle), and Contractility (the intrinsic force of myocardial contraction, inferred from cardiac output/cardiac index in relation to preload). Cardiac Output (CO = Heart Rate x Stroke Volume) is the total volume of blood pumped per minute (normal 4-8 L/min); Cardiac Index (CI = CO/BSA) adjusts for body size (normal 2.5-4.0 L/min/m2). Mean Arterial Pressure (MAP = [(2 x Diastolic) + Systolic] / 3) represents the average pressure driving organ perfusion (target >65 mmHg). An arterial line provides continuous, beat-to-beat blood pressure monitoring and allows arterial blood sampling. Central venous pressure (CVP) is measured via a central venous catheter (internal jugular, subclavian, or femoral vein) and reflects right heart preload (normal 2-8 mmHg). A pulmonary artery (Swan-Ganz) catheter is threaded through the right heart into the pulmonary artery, providing: RA pressure (preload), RV pressure, PA pressure, and PAWP/wedge pressure (left heart preload proxy, normal 8-12 mmHg). When the balloon is inflated, it occludes forward flow and the transducer reads the downstream pressure, which approximates left atrial pressure and LVEDP. SVR (normal 800-1200 dyn-s-cm-5) is calculated from MAP, CVP, and CO: SVR = [(MAP - CVP) / CO] x 80. The phlebostatic axis (4th intercostal space at mid-axillary line) is the reference point for transducer leveling; all readings should be taken at end-expiration to eliminate respiratory artifact.