Exam_2_ROK Hemodynamics & Hemodynamic Monitoring Hemodynamics & Hemodynamic Monitoring

1. Determinants of cardiac output The cardiac output (CO) is the volume of blood ejected by the left ventricle every minute. CO is determined by heart rate (HR) × stroke volume (SV). HR affects the CO when it is either too slow or too fast. Stroke volume is the volume of blood ejected from each ventricle w/each heartbeat.  Cardiac output (CO)- Amt. Of blood ejected by heart each minute. The normal value is 4 to 6 L/min o HR × SV  Heart rate o Too fast or slow affects CO o Tachycardia shortens filling time, leading to decreased volume = decreased CO o Bradycardia decreases ejection = decreased CO  Stroke volume- Amt. of blood ejected w/each heartbeat. Approximately same amt. ejected by right & left ventricle o 60–100 mL/heartbeat 2. Determinants of stroke volume The primary factors that determine stroke volume are preload, afterload, & contractility. Preload is the stretch on the ventricular myocardium at end diastole. Afterload is the pressure (resistance) against which the right or left ventricle has to pump to eject the blood. Contractility is the ability of the myocardium to shorten the muscle fibers.  Preload- Stretch on the ventricular myocardium at end diastole o Determined by volume left in the ventricles o Pressures are used to evaluate volume at the end of diastole o Also known as “filling pressures”  Afterload- The pressure (resistance) against which the R or L ventricle has to pump to eject the blood o Right ventricular resistance is pulmonary vascular resistance (PVR) o Elevations in PVR occur in pulmonary HTN, hypoxia, PE, & pulmonary stenosis o Left ventricular resistance is systemic vascular resistance (SVR) o Elevations in SVR occur in HTN, vasopressor use, aortic stenosis, & hypothermia  Contractility o Ability of the myocardium to shorten the muscle fibers o Influenced by electrolyte abnormalities (potassium & calcium), acid-base abnormalities, or myocardial O2 supply/demand abnormalities o Decreased contractility may be found in pt.’s w/hyperkalemia, hypocalcaemia, myocardial ischemia, administration of negative inotropic medications, hypercapnea, hypoxia, & acidosis. o Increased contractility may be found in pt.s w/hypercalcemia, administration of positive inotropic medications, or sympathetic stimulation. 3. Determinants of O2 supply to tissues The primary goal of the cardiopulmonary system is to maintain a balance between O2 supply to the tissues & O2 demand of the tissues at any given time. An imbalance of O2 supply & demand can lead to tissue hypoxia & eventual organ failure & cellular death. O2 supply to the tissues is dependent on how much O2 is in the arterial bloodstream (PaO2-O2 content) & how effectively that O2 content is being delivered to the tissues.  O2 content o Arterial blood saturation (SaO2) & O2 dissolved in plasma (pO2) o Majority of O2 in the blood is in the form of O2 bound to hemoglobin (Hgb) o If a pt. has a low Hgb level, the SaO2 may appear adequate but the overall O2-carrying capacity will be reduced due to the low hemoglobin level o O2 content may be calculated on an ABG  CO Exam 2 Comprehensive Review of Knowledge March 2014 Page 2 of 21 o O