In recent years, the level of cardiovascular surgery technology has improved year by year, and cardiovascular surgery in infants has also increased year by year. Nowadays, cardiovascular surgery in our hospital is becoming more and more complex and the weight of the infants is becoming smaller, so the management of Cardiopulmonary bypass (CPB) needs to be updated to meet the clinical needs. The management experience of 168 cases of direct intracardiac surgery performed under CPB in infants weighing less than 5 kg from February 2009 to January 2011 in our hospital is described as follows.
1. Clinical data and methods
1.1 Clinical data There were 168 cases in the whole group, including 104 males and 64 females; age 3d~6 (3.00±2.21) months; weight 2.0~5.0 (3.85±0.85) Kg.
1.2 Disease classification: 70 cases of ventricular septal defect combined with atrial septal defect; 36 cases of ventricular septal defect combined with patent ductus arteriosus or patent foramen ovale; 5 cases of pulmonary valve stenosis combined with atrial septal defect or patent ductus arteriosus; 10 cases of tetralogy of Fallot; 8 cases of complete pulmonary venous malformation drainage; 10 cases of complete atrial septal defect; 4 cases of right ventricular double outlet; 5 cases of complete aortic dislocation; 10 cases of pulmonary artery atresia There were 4 cases of aortic arch dissection and 6 cases of aortic arch narrowing.
1.3 Methods: The whole group was anesthetized by static inhalation compound anesthesia, and intraoperative monitoring of electrocardiogram, mean arterial pressure, central venous pressure, left atrial pressure, transcutaneous oxygen saturation, nasopharyngeal temperature, anal temperature, and urine volume. StockertC CPB machine was used, Dideco 901 membrane lung was applied in 60 cases, Terumo membrane lung in 108 cases, and Terumo ultrafilter in 168 cases.
1.4 Pre-charge regimen: compound electrolyte injection, red blood cells, plasma, albumin, dexamethasone or methylprednisolone, antibiotics, 5% sodium bicarbonate, 10% potassium chloride, 10% magnesium sulfate, 10% calcium gluconate and heparin were used for the whole group. Maintain erythrocyte pressure product (hematocrit ,Hct) 25%-30%.
1.5 CPB management: 5 cases of normothermia, 88 cases of shallow hypothermia, 52 cases of medium hypothermia, 23 cases of deep hypothermia, and 10 cases of deep hypothermia to stop circulatory selective cerebral perfusion were used. The children were warmed with a variable temperature blanket (39°C) after admission to the room, and the room temperature was >25°C. The prefilled fluid was heated to 34~35°C. CPB was started by opening the upper and lower vena cava drains before starting to increase the flow, and attention was paid to avoid cardiac hyperinflation and empty turtle when increasing the flow. Use 4℃ high potassium crystalloid stopping solution (20ml/Kg for the first time) to re-infuse once and a half volume for 30min, if the perfusion cannot be done in time during surgery, pericardial placement of ice saline can be given and re-infuse for maximum 60min. CPB flow rate is 2.6~3.8L/min?m2 at room temperature, keeping Hct 25%~30%. Deep hypothermia flow rate is 0.8~1.2L/ min?m2, deep hypothermia stop circulating brain perfusion flow rate 15~20ml/Kg?min. pH steady state management is used for deep hypothermia, and steady state is used for temperature above 28℃. After rewarming, methylprednisolone 30mg/Kg and 20% mannitol 0.5g/Kg (given at temperature >28℃) were used. CPB mean arterial pressure was maintained at 30-60mmHg, >60mmHg to deepen anesthesia or apply vasodilator drug phentolamine 0.1~0.2mg/Kg, below 30mmHg phenylephrine 10~40μg/time was used to prevent insufficient tissue perfusion. Children with mild to moderate pulmonary hypertension were treated with methylprednisolone 30mg/Kg to reduce inflammatory response, and milrinone 0.5~1μg/Kg?min was routinely applied postoperatively, and iloprost was added in children with severe pulmonary hypertension. After rewarming, perform ultrafiltration and balanced ultrafiltration according to Hct and lactate levels, and perform modified ultrafiltration after shutdown. Maintain venous mixed oxygen saturation >65% during rewarming to prevent tissue hypoxia. Before the opening of ascending aorta, adjust blood gas, electrolytes, Hct, lactate, blood glucose, and blood pressure to maintain them in normal range, which can create conditions for cardiac resuscitation. Increase left heart drainage after aortic opening, 50~100ml/min to prevent cardiac overinflation. Auxiliary until rhythm recovery, temperature, blood gas, electrolytes, blood pressure normal, gradually reduce the flow of smooth termination of CPB.
2 .Results
The duration of extracorporeal circulation was 18~155 (45.26±23.36) min; the aortic block was 18~85 (33.22±20.25) min; the automatic resuscitation rate was 98.2%. All children were successfully discharged from the extracorporeal circulation. 15 cases had complications, including 3 cases of hypocapnia syndrome, 1 case of pulmonary insufficiency, 1 case of pneumothorax, 1 case of renal insufficiency, 1 case of mediastinal infection, 3 cases of hypoxemia, 1 case of gastrointestinal bleeding, 2 cases of delayed chest closure, 1 case of re-opening to stop bleeding, and 1 case of residual shunt. There were 4 cases of postoperative death, with a mortality rate of 2.34%. The main cause of death was cardiopulmonary failure.
3, Discussion
Low weight infants have their own peculiarities, some of them have preoperative malnutrition, hypoproteinemia, hypoxia, metabolic acidosis and need for ventilator assistance. CPB should take active and effective measures to reduce the complications and mortality of children.
3.1 Excellent equipment and appropriate pre-charge program
Infants are light weight, poorly developed, and the total CPB flow is still relatively small, requiring high accuracy of the artificial heart-lung machine, precise flow control, light damage to the blood, easy to manipulate, and good safety. The small blood volume of infants and children, and dilutive precharge of CPB will cause a significant decrease in Hct and plasma colloid osmotic pressure, which requires that the precharge volume should be minimized in low-birth-weight children [1]. Ping Chen et al [2] were able to reduce the amount of blood used and inflammatory response during cardiac surgery in neonates and small infants by miniaturizing CPB lines. Membrane lungs with good biocompatibility and low prefilling volume were selected for the whole group. The use of 1/4-inch arteriovenous tubing with a minimum prefilling volume of 350 ml reduces the adverse effects of large amounts of reservoir blood and reduces the potential risk of edema caused by large amounts of crystals in the body. The maintenance of high Hct in CPB is beneficial to the tissues, especially to ensure the oxygen supply to the brain. In the whole group of children, the Hct was controlled from 25% to 30% in CPB, and the Hct reached 40% after modified ultrafiltration.
3.2 Flow rate, organ protection
During CPB, high flow rate was the main focus of perfusion, and the flow rate was adjusted according to the need of surgery. Infants with high metabolism and high oxygen consumption need high flow perfusion, which is adjusted according to the child’s body temperature, mixed venous oxygen saturation >65% and lactate value below 2.5 mmol/L for reference. The flow rate of 150~200ml/Kg applied at room temperature for the whole group of children can meet the blood supply and oxygen demand of the body and important organs. Infant myocardium is immature myocardium, its morphological structure, physiological function and myocardial development are not yet perfect. Qi Bo et al. found that perfusion of blood-containing stopping fluid during cardiac surgery could significantly reduce the levels of interleukin-6 and 10 and mitigate the systemic inflammatory response and myocardial injury. Zhu et al. concluded that cold-blooded crystal stop solution can maintain the need for normal cellular metabolism during myocardial ischemia, ensure a stable internal environment, and reduce the damage to ischemic myocardium. The whole group in our hospital used infused crystalloid pacing solution, of which 165 cases resumed automatically, with a resumption rate of 98.2%. The whole group had 3 cases of low cardiac output syndrome after surgery, and the cardiac arrest was well observed intraoperatively. 2 cases failed to maintain satisfactory circulatory function after surgery and gradually developed multi-organ insufficiency leading to death. Hypothermia is a double-edged sword, as it can reduce the oxygen consumption of the organism, but some studies have shown that medium- and low-temperature CPB can significantly cause postoperative pulmonary injury in infants and children after cardiac surgery. Infants with less developed lung tissue, less elastic fibers, smaller tracheobronchial diameters, and more respiratory secretions are prone to complications after CPB, and pulmonary complications account for 30% of the whole group of children, which shows that lung protection is crucial after surgery. Good left heart drainage can reduce pulmonary circulatory resistance, reduce perfused lung, and avoid the occurrence of pulmonary stasis. The application of methylprednisolone reduces the inflammatory response of the organism, and the use of mannitol during the rewarming period can scavenge oxygen free radicals and reduce the effect of pulmonary stasis reperfusion injury. Milrinone and iloprost should be applied early in children with pulmonary hypertension. Normally cerebral blood flow has a self-regulatory function to temperature changes, which can ensure the blood and oxygen supply to brain tissue, and the self-regulatory function of brain tissue will be lost when the temperature is lower than 30℃, thus causing brain damage. Wang Shunmin et al. found that under deep hypothermia, the oxygen dissociation curve shifted left, and the additional carbon dioxide added by pH steady state management could compensate for the left shift of the oxygen dissociation curve and improve the local brain tissue hypoxia and asymmetric distribution of cerebral blood flow, which was conducive to uniform cooling of the brain. There were 33 children in the whole group who applied deep hypothermic pH steady-state management and were awake early after surgery, and none of them had neurological complications.
3.3 Oxygenation management
Mainly for children with cyanotic heart disease because of the low oxygen content of the blood in the body circulation, resulting in chronic hypoxia in the systemic tissues and organs. In hypoxic myocardial CPB, excessive partial pressure of oxygen can lead to a large production of oxygen radicals and cause hypoxia-reoxygenation injury. Low arterial partial pressure of oxygen (PaO2) to initiate CPB and PaO2 ≤130 mmHg before controlled flow rewarming during CPB are beneficial in reducing oxygen radical production [7]. high oxygen concentration during CPB can lead to myocardial mitochondrial damage in infants and children with cyanotic precordial disease, and the use of oxygen concentration 21% can reduce myocardial damage [8]. Conventional diversion methods use high partial pressure oxygen to reverse systemic hypoxia, but have the potential to cause oxygen radical-mediated reoxygenation damage. Children with cyanosis in our entire group were managed with a stepwise oxygenation technique, which starts with 21% to 30% oxygen concentration (FiO2) to provide gas exchange in the oxygenator. As the diversion time increases, the FiO2, is gradually raised to 60%, typically by 10% to 20% every 2 min. To a certain extent, it reduces the degree of myocardial, brain tissue and oxygen radical damage caused by high oxygen partial pressure CPB.
3.4 Importance of ultrafiltration
Infants and young children also have imperfect kidney development, short renal tubules, poor renal concentration function, immature enzyme system function, poor filtration function and easy dehydration or excess water. Ultrafiltration can remove excess water from the body, increase colloid osmotic pressure, enhance myocardial contractility, elevate blood pressure, improve pulmonary compliance, increase Hct, improve coagulation function and reduce renal burden. In our hospital, the whole group added balanced ultrafiltration in the whole process of diversion to regulate the internal environment and remove some inflammatory mediators, so that the efficacy of ultrafiltration can be further revealed. One case in the whole group developed renal insufficiency, and renal function recovered after 3 days of applying peritoneal dialysis. Because of the many disadvantages of stock blood, ultrafiltration of pre-charged fluid is also an attempt done in recent years. After ultrafiltration of precharged fluid by Li Penxi et al. found that ultrafiltration of precharged fluid could improve the blood gas index and electrolytes of precharged fluid to a certain extent, and improved the Hct of precharged fluid.
3.5 Other details treatment
Maintain proper blood calcium level during CPB parallel circulation, especially during the treatment of collateral vessels or arterial catheterization can maintain a good heartbeat; using compound electrolyte injection as the base fluid prefilling can significantly reduce the lactate concentration during CPB; venous reflux should be unobstructed, and timely communication with the surgeon should be made to adjust the cannulation position timely according to the state of reflux; maintaining blood glucose level in CPB in normal Some studies have shown that strict blood glucose control can significantly reduce the incidence of clinically relevant complications and morbidity and mortality in patients undergoing cardiac surgery and improve the prognosis; take reasonable treatment of reservoir blood to reduce adverse inflammatory reactions; Yang Xun et al. showed that fresh blood leukocyte filtration followed by transfusion can reduce serum tumor necrosis factor a levels in infants and children after CPB, reduce inflammatory reactions in patients in the early postoperative period, and improve patients’ early This can shorten the postoperative time with ventilator and thus shorten the patient’s hospital stay.
In conclusion, the application of individualized management and the use of comprehensive measures in CPB is a guarantee of successful direct infant surgery.