During your child's surgery, it is very likely that your child will be supported by a number of machines and techniques to keep them stable. These include but are not limited to mechanical ventilation, cardiopulmonary bypass, extracorporeal life support, hemoconcentration, circulatory arrest, and selective cerebral perfusion.
Mechanical ventilation
Mechanical ventilation involves putting a tube through the nose or mouth and down the windpipe (intubation) in order to pass oxygen and air into your child's body from the ventilator machine. The tube is inserted after your child is sedated, so there is no discomfort. When the tube is down the windpipe, patients are said to be intubated, and when they come off the ventilator, they are extubated.
The ventilator can help a child with breathing or take over completely if your child is not breathing at all. In the operating room, the anaesthesiologist adjusts the amount of oxygen, frequency of breaths, and airway pressure to meet your child's needs. Once the rate, volume, and oxygen concentration have been set, the machine helps the child take in breaths of pressurized oxygen.
A child may be on a ventilator during heart surgery or catheterization. The reason is because sedation or anaesthesia can suppress the natural urge to breathe. Sometimes children will be placed on a ventilator after surgery to regulate breathing and ease the heart's work.
Children on ventilators stay in the critical care unit, where they are closely and regularly observed by nurses, doctors, and respiratory therapists. How long a child needs ventilating depends on the condition, its severity, the type of surgery, and sometimes the age of the patient.
When your child is ready to be "weaned" off the machine, the controls are turned down until they are breathing fully on their own. The tube is then removed from the windpipe and the machine is turned off.
Cardiopulmonary bypass
To perform open heart surgery, the surgeon usually has to stop the lungs and the heart from working. This means the heart is motionless and not pumping blood. A process called cardiopulmonary bypass (CPB) allows the blood to move through the body artificially after the surgeon has stopped the heart.
Special tubes (cannulae) are inserted in the great vessels of the heart to divert the patient’s blood to a mechanical pump and an artificial lung. This machine takes over the function of the heart and lungs. It adds oxygen and removes carbon dioxide, then returns the blood to the patient’s aorta so the body and vital organs get the oxygen they need. The system also involves blood salvage pumps, control and monitoring devices, reservoirs, tubing, and filters.
This bypass machine is often referred to as the heart-lung machine because it basically takes over the work of both organs. When this happens, the patient is said to be "on bypass." The person who operates the machine is called a perfusionist.
Before and while your child is on bypass, a blood-thinning drug will be administered to prevent blood clots from forming.
The surgeon often decides to cool the child down a few degrees during bypass. This reduces the amount of support needed and increases safety.
Depending on the type of surgery, the heart may be stopped completely using a fluid called cardioplegia. Cardioplegia is a cold liquid that is injected into the heart to stop it. It is high in potassium, which helps protect the heart muscle when it is not beating and when its blood supply is interrupted.
The body temperature is then gradually raised just before the surgery is completed.
What risks are involved with cardiopulmonary bypass?
Risks of heart surgery vary according to the age of the child, the condition being treated, and the difficulty of the surgery.
Complications are rare. They can include death, stroke or seizures, bleeding, and infection, as well as organ or tissue damage. The surgical procedure sometimes also requires blood transfusions. Also, being on the bypass machine exposes the blood circulating in the circuit to foreign surfaces, which may cause inflammation.
Extracorporeal life support
Extracorporeal life support (ECLS) involves using an "artificial lung" to get oxygen into the blood and a pump or circulatory assist device. This technique is commonly known as ECMO (Extracorporeal Membrane Oxygenation). ECLS is similar to bypass, in that it involves a machine to support the function of the heart and lungs, but it is usually not used in situations where surgery is the primary objective. However, it is used to support the heart or to allow the heart and lungs to rest, and surgery may sometimes be required while a child is on the machine.
The machine is often used in the cardiac critical care unit (CCCU) after surgery to support recovery, particularly in cases where the child's condition is unstable, or before surgery if the heart and lungs are failing. ECLS may also be used to support patients who have respiratory distress. One example is for newborn babies who have had lung damage from breathing meconium into the lungs. Meconium is the thick, blackish, and sticky material that is the newborn baby’s first bowel movements. Perfusionists or ECMO specialists operate the machine.
The ECLS procedure is very similar to cardiopulmonary bypass in terms of the use of special tubes to redirect the blood. Once ECLS is in place, however, some children are allowed to be conscious.
The main complications with ECLS involve bleeding, infection, brain injury, and multi-organ system failure.
Hemoconcentration
Hemoconcentration is a process undertaken during or after bypass. It involves removing fluid from the blood to increase the concentration of hemoglobin and red blood cells. Solutions administered during surgery can increase in the patient’s blood volume and can dilute the concentration of red blood cells. This is referred to as hemodilution.
Deep hypothermia with circulatory arrest
Hypothermia refers to the cooling of the body below its regular temperature of 37°C (98.6°F).
People can get hypothermia when they are out in the cold for long periods of time and are not wearing enough warm clothing to protect themselves from the cold wind and air. It can be very damaging to the body. In contrast, deep hypothermia with circulatory arrest (DHCA) is done on purpose and in a controlled manner.
Circulatory arrest refers to a technique that is only used to facilitate complex heart surgery. It involves stopping the blood flow to the patient’s body.
With DHCA, the body temperature is cooled down to approximately 20°C and the heart/lung machine is turned off. This cooling is achieved through a number of approaches, including lowering the room temperature, putting ice around the patient's body, and using a special cooling blanket (surface cooling). The main way, however, is by cooling the blood when it goes through the heat exchanger on the heart-lung machine.
How does circulatory arrest help during surgery?
Children on CPB are cooled because this reduces their metabolism and may protect against brain injury. Occasionally, it is necessary to stop all circulation to the patient to perform specific operations. In these cases, the patient is cooled to 20°C and ice is placed on the patient's head to protect against brain injury. This is called deep hypothermic circulatory arrest. Cooling down the body protects it and reduces the need for oxygen, much in the same way that animals are protected when they hibernate during cold winters.
Selective cerebral perfusion
Selective cerebral perfusion is a technique that involves providing blood flow and metabolic support to the brain while the blood flow to the rest of the body is stopped during circulatory arrest.
This approach is commonly used during complex surgery that requires circulatory arrest, such as surgery to repair complex congenital heart defects. It offers more protection for the brain and minimizes the risk of stroke and other serious complications. Keeping the blood flowing and oxygen circulating in the brain means that circulatory arrest does not need to last as long.