Cardiac output (CO)

It refers to the amount of blood injected into the aorta or pulmonary artery every minute from the left or right ventricle. The output of the left and right ventricles is substantially equal. The amount of blood output per beat of the ventricle is called the stroke volume. When the body is at rest, it is about 70 ml (60-80 ml). If the heart rate is 75 times per minute, the blood output per minute is about 5000 ml. (4500 ~ 6000 ml), that is, the output per cent. Usually the output of the heart is generally referred to as the output per cent. Basic Information Specialist classification: cardiovascular examination classification: ultrasound Applicable gender: whether men and women apply fasting: fasting Tips: No special preparation is required, follow the doctor's instructions. Normal value In the same period, the blood volume of the left heart and the right heart received by the normal person is roughly equal, and the blood volume output is also roughly equal. In the resting state, the ventricular volume is 60-80 ml, and the heart volume is equal to the stroke. Multiply the heart rate by about 5 to 6 liters of cupping net per minute. Clinical significance The main hemodynamic change in heart failure is the reduction of cardiac output, which does not meet the needs of tissue metabolism, and the degree of reduction is consistent with the degree of heart failure. Patients with acute myocardial infarction have a progressive decline in cardiac output, which often indicates that cardiogenic shock will occur. Precautions Cardiac output is an important indicator for evaluating the efficiency of the circulatory system. In order to facilitate comparison between different individuals, the heart output index per centimeter of surface area per square meter of fasting and resting is generally used as an indicator: The body surface area of ​​a typical adult is about 1.6 to 1.7 square meters. At rest, the output per cent is 5-6 liters, so the heart index is about 3.0-3.5 liters/min/m2. Under different physiological conditions, the metabolic rate of the surface area of ​​the unit body is different, so the heart index is also different. Newborn babies have a lower resting heart index of about 2.5 liters per minute per square meter. At the age of 10, the resting heart index is the highest, reaching 4 liters/min. Inspection process First, non-invasive cardiac output measurement (1) Thoracicelectrical bioimpedance (TEB) 1. Principle and method: TEB uses the change of chest electrical impedance in the cardiac cycle to measure left ventricular systolic time and calculate stroke volume. The basic principle is Ohm's law (resistance = voltage / current). In 1966, Kubicek used a direct impedance meter to measure changes in cardiac impedance and derived the famous Kubicek formula. However, the application of the Kubicek formula to measure the stroke volume (SV) was significantly increased, which is obviously inconsistent with the clinical manifestations. Therefore, in 1981, Sramek proposed to modify the Kubicek formula. The corrected formula is: SV=(Vept.T.ΔZ/sec)/Zo where Vept is the volume of high-frequency low amperage through the chest tissue, and T is the ventricular ejection time. Sramek stored the mathematical model in a computer and developed it into NCCOM Type 1~3 (BOMed). NCCOM is easy to operate: 8 electrodes are placed on both sides of the neck and chest to continuously display changes in parameters such as HR and CO. It can not only reflect the changes of the above parameters in each heartbeat, but also calculate the mean of 4 and 10 seconds. However, it is susceptible to interference from patient breathing, surgical procedures, and arrhythmia. In recent years, a more advanced impedance monitor has been born, using the modified Kubicek formula and the Rheo CardioMonitor connected to the computer. The main improvement is that the left side of the physiological impedance and ECG signals are analyzed. The accuracy of the ventricular effective ejection time (ELVET) measurement is improved. It is equipped with 6 electrodes, two of which are glued to the sides of the neck, two electrodes stick to the midline of the xiphoid level on both sides of the chest, and the other two electrodes are glued to the forehead and the left lower limb knee. The measurement period is 10s, and measurement accuracy and repeatability are better. The Department of Anesthesiology of Renji Hospital affiliated to Shanghai Second Medical University underwent CO monitoring in 16 coronary artery bypass grafts, and compared with invasive CO and exhaled, partially reabsorbed gas CO2 measurement CO (RBCO), the correlation coefficient was 0.85. (n=180) and 0.87 (n=118). 2, clinical application and evaluation: TEB operation is simple, low cost and can dynamically observe the trend of CO. However, due to its poor anti-interference ability, especially the inability to identify abnormal results is caused by changes in the patient's condition, or due to the factors of the machine itself, the absolute value sometimes varies greatly, so it is limited to a certain extent in clinical practice. Widely used. However, the CO measured by the TEB method is non-invasive and continuous, and is convenient for comparison before and after. It has unique advantages in studying the effects of anesthesia and drugs on the circulatory function. (2) Ultrasound Doppler method There are two main ways to measure CO by ultrasound Doppler: transesophageal ultrasound Doppler (EDM) and transtracheal ultrasound Doppler (TTD). Currently mainly using EDM. The HemoSonicTM 100EDM monitor produced by Arrow by transesophageal ultrasound Doppler has been widely used abroad. The results show that the operation is simple and accurate. Principles and Methods: The HemoSonicTM100 ultrasound Doppler probe estimates the blood flow of the descending aorta by measuring the rate of red blood cell movement. It is equipped with an M-mode ultrasound probe that directly measures the diameter of the descending aorta without the need to The aortic diameter is indirectly estimated by parameters such as age and height, which improves the accuracy of the measurement results. Since the blood flow of the descending aorta is 70% of CO (the correlation coefficient between descending aortic blood flow and CO is 0.92), the calculation formula is: CO = descending aortic blood flow × cross-sectional area of ​​descending aorta ÷ 70 %. The specific method is to insert a transesophageal catheter with a Doppler probe and an M-mode ultrasound probe into the esophagus (equivalent to the third intercostal level, the esophagus and the descending aorta are balanced), according to the display Aortic wall, blood flow waveform and Doppler sound up and down to adjust the probe position until a satisfactory signal quality is obtained, and then the monitor can enter the measurement state to display descending aortic blood flow, aortic diameter, CO, left ventricular contraction Hemodynamic parameters such as sex, MAP, and peripheral vascular resistance. Combined with CO2 map analysis, it can also prompt the perfusion status of the tissue. Not suitable for the crowd No taboos. Adverse reactions and risks Discomfort: There may be pain, swelling, tenderness, and visible subcutaneous ecchymosis at the puncture site.