extracorporeal circulation

It is a life support technique that uses a special artificial device to introduce the returning venous blood out of the body, perform gas exchange, adjust temperature and filter, and return to the internal arteries. Mainly used in heart and large blood vessel surgery. Congenital or acquired cardiovascular disease must be operated under direct vision. For open heart surgery, it is necessary to block the circulation, provide a bloodless surgical field for the operation, and perform intracardiac operation. During the block cycle, the venous blood in the human body needs to be drained from the outside of the body to the artificial heart-lung machine for oxygenation and carbon dioxide emission. Then it is pumped back into the body to maintain the blood circulation. Treatment of diseases: cardiovascular disease cardiovascular and thromboembolic syndrome Indication Mainly used in heart and large blood vessel surgery. Congenital or acquired cardiovascular disease must be operated under direct vision. For open heart surgery, it is necessary to block the circulation, provide a bloodless surgical field for the operation, and perform intracardiac operation. During the block cycle, the venous blood in the human body needs to be drained from the outside of the body to the artificial heart-lung machine for oxygenation and carbon dioxide emission. Then it is pumped back into the body to maintain the blood circulation. Preoperative preparation 1. Eliminate all infected lesions. 2. Correct malnutrition, anemia, and liver, kidney, and other organ dysfunction. 3. Correct heart failure or put the patient in the best possible condition. 4. Stop the digitalis and diuretics 48 hours before surgery. 5. Use an ordinary diet 1 week before surgery to adjust the electrolyte balance. If the patient takes long-term diuretics, the oral potassium chloride should be increased in the first week before surgery to overcome the deficiency of potassium in the body. 6. Start antibiotics with antibiotics on the 3rd day before surgery. Give a dose of antibiotics when you use the medicine before surgery. 7. In severe cases, glucose, insulin and potassium chloride solution (GIK) are intravenously administered 1 week before surgery to protect the myocardium. 8. Psychotherapy should be performed on patients before surgery to eliminate concerns and enhance cooperation between doctors and patients. Let the patient understand the various situations that may occur during the operation to facilitate the patient's active cooperation. Surgical procedure 1. Incision: The sternal median incision is a standard extracorporeal circulation open heart surgery incision, which is well exposed and suitable for cardiac surgery in any part. The incision was slightly from the sternal notch and reached about 5 cm below the xiphoid. 2. Saw the sternum: Cut the sternal periosteum with an electric knife along the center, and separate the sternal incision to the sternum; then dissect the xiphoid and separate the posterior sternal space. After the xiphoid is removed, the sternum is sawn along the midline with a wind (electric) saw. The periosteum is electrocoagulated to stop bleeding, and the sternum is stopped by bone wax. 3. Cut the happy bag: cut the happy bag in the middle of the line, get the ascending aorta reflexed part, release the diaphragm, and cut the lower part of the incision to the side to facilitate the exposure. After that, the pericardial margin is sutured to the soft tissue outside the sternum, and the sternum is opened with a spreader to reveal the heart. 4. Extracardiac exploration: Exploring the size, tension, and tremor of the aorta, pulmonary artery, left and right atrium, left and right ventricles, superior and inferior vena cava, and pulmonary veins. Also check for the presence of left superior vena cava and other abnormalities that can be found outside the heart. 5. Establish extracorporeal circulation (1) Vena cava strap: first separate the gap between the aorta and the pulmonary artery, lift the aortic band, pull the band on the ascending aorta to the left, reveal the inside of the superior vena cava, and use the right angle pliers to wrap around the inside of the superior vena cava. After the strap. In the same way, the lower vena cava was placed around the inferior vena cava with a lower lumen. (2) Arterial intubation: At the distal end of the ascending aorta, the concentric purse is sutured with the 7th line, and the blood vessels are not penetrated, and are sutured in the adventitia of the aorta, and the opening of the purse line is one by one. Put the purse string into the hemostatic device to stop bleeding and fix when intubating. The outer membrane of the central portion of the purse is removed. After injecting heparin into the right atrial appendage (3mg/kg), use a small round (tip) blade to cut a small incision in the center of the purse, which is slightly smaller than the diameter of the arterial cannula. When the blade is withdrawn, the artery cannula is sent into the ascending aortic incision. Tighten the hemostats of the two purse lines and secure the arterial cannula to the hemostat with a thick wire. Finally, the arterial cannula is fixed on the edge of the incision or the petiole of the distractor, and the cannula is connected to the artificial heart-lung machine. (3) Cavernous vein cannulation: a purse string is sutured in the right atrial appendage and the right atrium, and a hemostatic device is placed, and then the incision is inserted into the superior and inferior vena cava cannula (generally inserted through the atrial appendage) to tighten the hemostat. A 2 to 3 mm atrial appendage and atrial wall below the incision were ligated around the cannula with a thick wire, and the upper and lower lumen cannula was fixed by the ligature to prevent slipping. Connect the upper and lower lumen cannula to the artificial heart-lung machine. (4) Cold heart cardioplegic perfusion cannula: a suture was placed on the anterior lateral membrane of the ascending aorta and placed in a hemostat. The cold heart cardioplegia is filled with the needle and the gas is inserted into the central part of the sacral suture into the ascending aorta. The hemostasis is tightened, and the cannula and the hemostat are fixed together by thick lines. Connect the cannula to the infusion device. (5) Left heart drainage cannula: You can choose one of the following: Left atrial drainage: a large suture suture at the junction of the right upper pulmonary vein root and the left atrium, with a hemostat. After cutting a small opening in the fistula suture, insert the left atrial drainage tube into the left atrium and tighten. The hemostat is ligated with a thick wire and the drainage tube is fixed to the hemostat. Connect the drainage tube to the artificial heart-lung machine. Left ventricular drainage: some patients have better left ventricular drainage, a suture in the left ventricle near apical avascular region, a hemostat, a small incision in the center of the sacral suture, and a small incision The left ventricular drainage tube tightens the hemostat and fixes the drainage tube together with the hemostat. Connect the drainage tube to the artificial heart-lung machine system. Check all the pipes and their connections without error. It is sure that there is no obstacle in each channel, and the extracorporeal circulation can be started. After several minutes of parallel circulation, the upper and lower vena cava are blocked and enter the complete extracorporeal circulation. At this time, the upper and lower vena cava blood It is completely intubated into the artificial heart-lung machine and does not flow into the right atrium. At the same time, the blood is cooled. (6) Blocking the ascending aorta: When the whole body temperature drops to about 30 °C, lift the ascending aorta and use the aortic occlusion forceps to block the ascending aorta. Immediately, 4°C cold heart cardioplegia (1015ml/kg) was injected from the perfusion tube of the aortic root, and the surface of the heart was cooled with 4°C iced saline or ice particles to make the heart stop quickly. The operational indicators of cardiopulmonary bypass are as follows: Mean arterial pressure: 5.33 ~ 9.33 kPa (60 ~ 90 mmhg). Central venous pressure: 0.59~1.18kpa (6~12cmh2o) Body temperature: general surgery about 28 ° C; complex heart surgery can be used in deep low temperature 20 ° C ~ 25 ° C. Myocardial temperature: maintained at 15 ° C ~ 20 ° C. Flow rate: 50 ~ 60ml / kg for medium flow; 70 ~ 80ml / kg for high flow, clinically used high flow. Children and infants should have a higher flow rate than adults. Dilution: The cell volume is generally between 25% and 30%. Blood gas analysis: pao2: 13.3 ~ 26.6kpa (100 ~ 200mmhg). Pvo2: 3.3 to 5.3 kPa (25 to 40 mmhg). Ph: 7.35 to 7.45. Paco2: 4.6 ~ 6.0kpa (35 ~ 45mmhg). Urine volume: 2 ~ 10ml / kg / hour. Blood potassium: During the extracorporeal circulation, k+ is maintained at 4-6 mmol/l, and potassium chloride should be given 1 to 2 mmol/kg per hour. Heparinization: human body according to 3mg/kg; pre-filled liquid 1mg/100ml; after 1 hour of operation, heparin was supplemented by artificial heart-lung machine. The act should be kept at around 600 seconds during operation. 6. Terminate extracorporeal circulation (1) Rewarming: After the main operation in the heart is completed, rewarming can be started, but the heart still needs low temperature protection. (2) Exhaust: After the heart incision is sutured, the apical pin can be vented, the aortic root can be vented, or the perfusion needle can be removed and vented through the pinhole on the aortic wall. Remove the ice or ice brine from the pericardium before venting. (3) Open aorta: Open the ascending aorta blocking forceps. At this time, the left heart should be circulated smoothly to prevent the left heart from expanding. (4) Defibrillation: After opening the ascending aorta blocking forceps, if the conditions are right, the heart can automatically re-jump. If there is no re-jump, the electric shock can be used to debounce. Generally, the direct current is 5 to 50 watts. Blood gas and ions should be checked before defibrillation. If it is not normal, it should be corrected immediately to ensure successful recovery under physiological conditions. After the double jump, the heart should be kept at no load for a period of time to facilitate the recovery of myocardial function. (5) Auxiliary circulation: open the upper and lower cavity blocking bands after resuscitation, so that the complete extracorporeal circulation becomes a parallel cycle to assist the heart beat and reduce the burden on the heart. The longer the intracardiac operation time, the longer the time required for the assisted circulation to facilitate the recovery of cardiac metabolism and function. (6) Stop cardiopulmonary bypass: The conditions for cardiopulmonary bypass are: 1 body temperature up to 36 ° C; 2 mean arterial pressure 8 ~ 10.66 kPa (60 ~ 80 mmhg); 3 no significant bleeding in the surgical field; 4 blood gas analysis report normal; 5 blood ion normal; 6 no serious heart rhythm disorder. Before the shutdown, vasodilators and diuretics, such as sodium nitroprusside, furosemide, etc., can be used to gradually reduce the blood in the artificial heart-lung machine and achieve a positive balance to the human body. By the time of the shutdown, only the minimum amount of blood necessary to maintain operation is left in the machine. After the shutdown, continue to use the arterial pump to slowly transfuse blood to prevent blood shortage, and also prevent the input speed from being too fast, causing the heart to swell and damage the myocardial function. (7) Neutralization of heparin: The amount of protamine is calculated based on the measured value of act; or heparin is neutralized by protamine in an amount of 1:1. Prevent excessive or insufficient use of protamine. (8) Supplemental potassium: Before terminating extracorporeal circulation, the general patient has natural diuretic. If the urinary flow rate is not ideal enough, furosemide can be used. At this time, the rhythm disorder caused by hypokalemia is most likely to occur. The amount of potassium should be monitored according to the amount of urine and serum potassium: generally 0.7 to 1.0 g of potassium chloride should be input for every 500 ml of urine. To prevent excessive liquid load, intravenous infusion of 6:1000 to 15:1000 potassium chloride solution is required. Note that high-concentration potassium should be intubated from the large vein, and high-concentration potassium in the peripheral vein is difficult to ensure smoothness. (9) Supplementary blood volume: After the machine is stopped, the wound is still losing blood, and diuresis (urinary flow is often faster), so fresh blood and plasma should be input immediately to supplement the lack of blood volume. The ratio of blood to plasma can be determined based on cell pressure and hemoglobin measurements. (10) Extubation: After the shutdown, under the condition of stable condition, the upper lumen cannula can be removed and the inferior cannula can be retracted into the right atrium. If the condition continues to be stable, the inferior cannula can be removed. If you do not need to enter the blood inside the machine, the arterial cannula should be removed as early as possible. At the same time, protamine was injected into the ligature line at the aortic cannula, and the injection of protamine into the aorta rarely caused a decrease in blood pressure. complication 1. Treatment of low cardiac output: The normal cardiac output index is 2.5 to 4.4 l/m 2 of body surface area. Low-level diagnosis cannot be based on a single sign or symptom, but should be based on the patient's overall condition. The diagnosis is based on the following: 1 irritability, anxiety or apathy; 2 peripheral pulse is fine and fast; 3 skin cold and wet, nail bed purpura; 4 oliguria, adult urine volume less than 30ml; 5 hypoxemia; 6 blood pressure More low, but low blood pressure can also be normal or high; 7 cardiac output index <2.5l / m2. Dealing with low platoons is for reasons, especially prevention. (1) Low blood volume: 1 Before stopping the extracorporeal circulation, the blood of the machine should be input into the body as much as possible, that is, the proper positive balance should be required before stopping the machine; the residual blood in the machine should be input slowly after the stop. The average arterial pressure is generally required to be 8 to 8.66 kPa (60 to 80 mmhg), and the central venous pressure is 2 to 2.67 kPa (15 to 20 mmhg). 2 After stopping the machine's residual blood input, immediately start to input the stock blood. The input speed and quantity should be adjusted according to hemodynamic changes, urination speed, mean arterial pressure and central venous pressure. However, avoid entering too much blood or fluid, too fast, so as to avoid excessive heart load or pulmonary edema. Some patients should be guided by left atrial pressure measurement for blood transfusion. 3 When the extracorporeal circulation is just terminated, the urine flow is often very fast. At this time, the blood volume changes rapidly. The changes of arterial, venous pressure and left atrial pressure should be closely monitored, and cell volume and hemoglobin should be checked regularly to guide the blood transfusion speed and quantity. (2) Treatment of cardiac insufficiency: Patients with low cardiac output after cardiopulmonary bypass often have increased peripheral vascular resistance. The use of vasodilators often improves heart function and reduces the load on the heart before and after. Patients with severe low-grade can use positive drugs while using vasodilators, which can both strengthen the heart and reduce the heart load. For example, the application of sodium nitroprusside 0.55g/kg·min has a good effect on reducing the load before and after. . It should be emphasized that low blood pressure is not a contraindication to the application of sodium nitroprusside. The use of sodium nitroprusside plus dopamine 2~10g/kg·min can reduce the front and back load of the heart, increase the cardiac output, and improve the heart. The blood supply to the kidney, raising blood pressure, reducing the surrounding resistance, improving the microcirculation, and often making the circulation gradually stable. But adjusting the two drugs to achieve the right input speed requires a balancing process. Do not rush to terminate extracorporeal circulation after cardiac resuscitation, should be given a certain time limit of assisted circulation, help the recovery of cardiac function, will play a role in preventing low-level discharge; even after stopping extracorporeal circulation, such as patients with cardiac insufficiency, can be repeated Cardiopulmonary bypass assisted cardiac excretion, recovery of beneficial function, often plays a role in the treatment of low row. Severe patients with intra-aortic balloon counterpulsation can often be significantly improved. (3) Treatment of pericardial occlusion: The key to the treatment of pericardial occlusion is timely diagnosis and rapid treatment. Hesitating often leads to catastrophic results. There are several reasons to consider the possibility of pericardial occlusion: 1 clinically no other factors of cardiac insufficiency (such as poor myocardial protection, malformation or incomplete correction of lesions, insufficient blood flow, etc.), but low performance, alignment Poor drug response; 2 chest tube drainage volume is more, or drainage is particularly small; 3 chest tube drainage decreased suddenly or clots; 4 jugular vein engorgement, venous pressure increased; 5 arterial pressure drop The pulse pressure difference is narrowed, and the positive drug is not improved. Once diagnosed, it should be urgently sent to the operating room, surgical removal of blood clots, blood accumulation and complete hemostasis. If the situation is tight, the lower part of the incision can be opened in the ward, and the finger wearing the sterile gloves is inserted into the pericardium, that is, there is blood rush. Out of or out of the blood clots, the condition suddenly improved, and then rushed to the operating room for thorough treatment. It should be noted that pericardial occlusion can occur within 3 days after surgery, and delayed pericardial occlusion can still occur thereafter. 2. Treatment of heart rhythm disorder: The main cause of heart rhythm disorder after cardiopulmonary bypass is hypokalemia. Therefore, prevention of hypokalemia is an important part of preventing heart rhythm disorders. Potassium deficiency should be fully corrected before surgery. Potassium should be given routinely during surgery. Potassium should be added according to the urine output and blood potassium measurement results. (1) treatment of supraventricular tachycardia: 1 verapamil 5 ~ 10mg intravenous injection, is currently the drug of choice. 2 Xindean 10mg oral or aminoacylcholine 25mg orally. 3 methoxyamine 5 ~ 10mg intravenous or 10 ~ 20mg intramuscular injection. 4 excited vagus nerve drugs, such as Xinsi Ming 0.5 ~ 1.0mg intramuscular injection. 5 phenytoin 100mg intravenously. 6 potassium chloride can be used from 0.4% to 0.6% static point. 7 Foxglove: Silandia 0.4 ~ 0.8mg intravenous (unused), every 2 hours after intravenous injection 0.1 ~ 0.2mg, not more than 1.2mg within 24 hours. 8 synchronous DC cardioversion: This method can be used for all kinds of different drugs, but it is not suitable for those who are poisoned by digitalis. 9 atrial pacing overspeed suppression, pacing at a rate higher than its frequency, sudden stop pacing after 20 seconds can often be converted to sinus rhythm. (2) atrial fibrillation: cedilan or digoxin intravenously, can also use electrical cardioversion or overspeed pacing methods. (3) atrial flutter: available verapamil, beta blocker or digitalis preparation and pacing overspeed method. (4) ventricular premature beats: occasional ventricular premature beats do not have to be treated. When recurring, you can use lidocaine 50 ~ 100mg intravenous or 1-3mg / kg · min intravenous drip, such as foxglove poisoning can be used phenytoin 50 ~ 100mg intravenous or static. (5) ventricular tachycardia: 1 lidocaine intravenous injection, such as repeated occurrence of 1 ~ 3mg / kg · min, intravenous drip. 2 electrical cardioversion. 3. Treatment of acid-base and electrolyte imbalance: common acid-base balance disorders are metabolic acidosis. Alkali loss > 3mmol / l, ph < 7.35, paco2 < 4.0kpa (30mmhg) should be corrected. Calculated as follows: Total extracellular base loss = base deletion mmol number × 0.3 × body weight The amount of 1/2 total base loss was supplemented with 5% nahco3. After half an hour, review the blood gas and decide the amount to be further corrected. The most serious electrolyte disorder after cardiopulmonary bypass is hypokalemia, especially in patients with long-term diuretics before surgery. The overall potassium is often low. Although serum potassium can be measured normally, potassium in cardiomyocytes may be low. Therefore, to maintain the balance of potassium to start before the strong potassium supplementation, extracorporeal circulation should be supplemented with 1 ~ 2mmol / kg / hour, after the termination of extracorporeal circulation, potassium should be added according to urine volume, chlorine should be added every 500ml of urine Potassium is 0.7g to 1.0g, and the serum potassium is kept at 4-5mmol/l. Low calcium can often lead to myocardial insufficiency. If the blood volume is large, appropriate calcium supplementation should be used. 4. Prevent excessive fluid overload: Due to the application of the blood dilution method, or there is a certain cardiac dysfunction before surgery, after the end of the extracorporeal circulation, there is a certain amount of water retention in the body. Therefore, the negative balance of the fluid should be maintained within 72 hours after surgery, especially when the heart is insufficiency, and the water and sodium input should be strictly controlled. Natural diuresis after the end of cardiopulmonary bypass, such as diuretic is not ideal, should consider whether there is cardiac function or poor kidney function, or the colloid osmotic pressure is not enough. In addition to treatment for the cause, diuretics such as furosemide can also be applied. However, attention should be paid to the relationship between diuresis and blood volume, and the relationship between diuresis and hypokalemia. Ion monitoring should be repeated to maintain dynamic balance. 5. Treatment of bleeding: There is a certain incidence of bleeding after cardiopulmonary bypass. The key is prevention. That is, after surgery, especially after termination of cardiopulmonary bypass, patiently and thoroughly stop bleeding. The treatment of postoperative oozing is: 1 equal volume of fresh blood; 2 input dry frozen plasma; 3 input platelets; 4 appropriate use of hemostatic agents. However, if the bleeding is fierce, especially in the dynamic observation, there is no reduction trend. It should be cut off and sent to the operating room for hemostasis before the patient has had a shock. 6. Assisted breathing: After cardiopulmonary bypass, if the circulation is stable, there is no possibility of bleeding, no serious ion disorder causes heart rhythm disorder, no pulmonary complications, sufficient spontaneous exchange, and appropriate respiratory rate (30 beats / min or less). The blood gas analysis results are normal, and the patient is awake and can be removed from the operating room. However, if the patient is suffering from severe heart disease, or if there is a certain abnormality in the above situation, artificial respiration is required to ensure adequate gas exchange to reduce the heart load and facilitate postoperative recovery. It is helpful to have 6 to 12 hours of artificial respiration after surgery. When applying a respirator, it is necessary to perform several blood gas analyses in a short period of time to adjust the parameters of the ventilator. After determining the parameters appropriate for the patient, the blood gas analysis can be changed to 4 to 6 hours, or twice daily. Pay attention to the management of the respiratory tract, ensure smoothness, ensure adequate gas exchange; regularly attract secretions to prevent infection; if the synchronization is not ideal, you can eliminate spontaneous breathing, ensure adequate exchange, and reduce patient load. To correctly grasp the conditions required for shutdown: 1 conscious, directed; 2 stable circulation, no serious heart rhythm disorder; 3 spontaneous respiratory frequency does not exceed 30 beats / min, sufficient exchange; 4 blood gas analysis is normal; 5 no bleeding possibility . It is also necessary to follow the routine procedure of the ventilator application. Before the shutdown, use the intermittent forced ventilation (imv) to make the transition, gradually reduce the number of imv, and finally stop, and the blood gas should be in the normal range 1 hour after the shutdown, it is proved that the shutdown is appropriate. . 7. Prevention of infection: Prevention of infection should begin before surgery, strictly in the operation, followed by postoperative. Preoperative antibiotics are required before surgery. It can be started 2 to 3 days before surgery, but it is important to give large doses of antibiotics before the operation on the day of surgery to ensure a certain blood concentration during surgery. Operation, including the establishment of various channels, is strictly in accordance with the aseptic protocol; a certain amount of antibiotics can be added to the machine during surgery, and a dose of antibiotics is given immediately after the cardiopulmonary bypass is terminated, followed by regular application. All infusion transfusion channels should be kept sterile to prevent contamination. 8. Prevent high temperature: It is easy to rebound after low temperature on the day of surgery. Therefore, when the body temperature reaches 36.5 °C, physical cooling should be started, generally it can prevent the occurrence of postoperative high fever; if the body temperature is as high as 38 °C, in addition to physical cooling, hibernation drugs or antipyretic drugs can be added to make the body temperature drop to normal. range. 9. Anticoagulant therapy: Oral warfarin (warfarin) is usually 2 to 10 mg/d 24 hours after surgery, and then adjusted according to the measured prothrombin time until the anticoagulant is fixed at a certain level. Within the daily usage range. However, the prothrombin measurement time should be gradually opened, and finally measured once every 1-2 months. It should be noted that many drugs, such as anti-rheumatic drugs, anti-arrhythmia drugs and long-term use of barbiturates, have interference with anticoagulant therapy and should be told to the patient. 10. Strict monitoring: Postoperative patients should be monitored in the intensive care unit (icu). Need to monitor ECG, heart rate, arterial pressure, central venous pressure; critically ill patients should be left atrial pressure, and even for cardiac output monitoring. Patients with stable circulation should be recorded once every 15 minutes, and critically ill patients should be recorded once every 5 minutes. The volume of urine and the drainage of the chest drainage tube were recorded every hour. Blood gas analysis, serum potassium, hemoglobin and cell volume should be measured as needed. The guardianship staff should be good at observing the development of the disease, and should analyze the development trend at any time, and do not wait for obvious abnormalities to pay attention.