Decreased cardiac output

Introduction The cardiac output (CO) refers to the total amount of blood emitted per minute from one side of the ventricle, also known as the output per cent, or the output of the heart. In a quiet state, the normal adult left ventricular end-diastolic volume is about 125 ml, and the end-systolic volume is about 55 ml. The difference between the two is the stroke volume, which is 70 ml. It can be seen that the ventricle does not emit all the blood filled in the heart chamber every time the blood is shot. The percentage of stroke volume to the end-diastolic volume of the ventricle is called the ejection fraction. A decrease in cardiac output can lead to shock.

Cause

Incomplete treatment of the right ventricular outflow tract obstruction or incomplete correction of pulmonary malformation is an important cause of postoperative low cardiac output. In addition to the imbalance of blood volume, the lack of diastolic capacity can affect the cardiac output. The main reason is that during cardiac surgery, the heart circulation needs to be blocked. Ischemia and hypoxia can cause damage to the myocardium, resulting in incomplete myocardial contraction. In addition, if there is insufficient oxygen exchange after surgery, hypoxia or acidemia can aggravate myocardial insufficiency. Tachycardia or bradycardia affects atrioventricular diastole. Arrhythmias, such as hypoxia or surgical trauma caused by sputum conduction block, are often the cause of low postoperative discharge. In addition, the pressure of the heart affects the filling of the ventricle, such as pericardial tamponade or tight-fitting after pericardial suture, which is also one of the reasons for postoperative low discharge. Coronary artery insufficiency and coronary artery thrombosis caused by myocardial infarction are occasional causes. Children with poor preoperative heart function have poor general condition, and their heart, lung, liver and kidney functions have different degrees of obstacles, which is prone to low cardiac output syndrome. Patients with large left-to-right heart flow are prone to pulmonary hypertension. Patients with severe pulmonary hypertension have pulmonary wall arteriosclerosis and thickening of the wall and stenosis, often accompanied by thickening of inter-alveolar and capillary cells, and interstitial edema. Increased pulmonary vascular resistance, right ventricular hypertrophy, preoperative myocardial oxygen supply and demand balance is in a state of compensation, improper treatment can also become a trigger for low cardiac output syndrome.

an examination

Related inspection

Ultrasound diagnosis of cardiovascular disease, electrocardiogram, dynamic electrocardiogram (Holter monitoring)

When the cardiac output drops, it is necessary to have a low heart index of 2.5L/(min·m2). Some clinical symptoms such as increased heart rate, small pulse pressure, and decreased blood pressure (systolic blood pressure below 12 kPa), radial artery and foot The dorsal artery pulse is weak, the central venous pressure rises, the peripheral blood vessels contract, the limbs are cold, pale or cyanotic. The amount of urine can be reduced to 0.5 to 1 ml/kg or less. At this time, the results of monitoring the cardiac output and the like: the heart index can be 20 mg%.

Differential diagnosis

Diagnosis is based on various tests and clinical manifestations.

1, monitoring of cardiac output, etc.;

2, some clinical symptoms of decreased cardiac output, such as increased heart rate, decreased pulse pressure, decreased blood pressure (systolic blood pressure below 12kPa), radial artery, small arterial pulse, weak central venous pressure, peripheral vasoconstriction, limbs Cold, pale or bun. The amount of urine can be reduced to 0.5 to 1 ml/kg or less.

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