(Source: Heart & Soul: Your Guide to Living with Congenital Heart Disease, Heart & Stroke Foundation)
What is Cardiopulmonary Bypass
To repair most cardiac defects, the cardiothoracic surgeon requires a bloodless, motionless field in which to work. To achieve this, the motion of the heart and lungs must be stopped. For this to occur, there needs to be a means for blood to circulate throughout the body, delivering the nutrients and oxygen necessary for life, while the heart and lungs are not functioning. This is made possible through a process known as cardiopulmonary bypass (CPB). Tubing made of clear polyvinyl chloride (PVC) contains the patients' blood as it is diverted from the body. Large bore catheters (called cannula) are placed in the right side of the heart, allowing the desaturated blood from the body to enter the cardiopulmonary bypass circuit.
The PVC tubing runs through a mechanical pump that can be regulated to the proper cardiac output for a given patient. PVC tubing delivers blood from the mechanical pump to a gas exchange device called an oxygenator, or artificial lung. The oxygenator performs the same job as the lungs: oxygenations of the blood as well as removal of carbon dioxide.
This re-oxygenated blood is then returned to the body via another cannula placed in the aorta. In this way, cardiopulmonary bypass permits the patients' blood to bypass the heart and lungs, achieving the desired bloodless, motionless operative field and still supplying all the other organs of the body with a constant supply of oxygen and nutrient-rich blood. The sum total of the mechanical pump, oxygenator, cannula and PVC tubing is often referred to as the heart-lung machine, or simply 'the pump". When a patient is being supported by a heart-lung machine, the patient is said to be "on bypass" or "on the pump". Conversely, when a patient is taken off this support, it is termed "off bypass" or "off the pump".
Cardiopulmonary Bypass Risks
It is necessary to recognize some adverse effects that may be seen when the circulation of the body is taken over artificially. Cardiopulmonary bypass has a very wide range of effects on the body. All organ systems are arrected by cardiopulmonary bypass, mainly the heart, lungs, brain, and kidneys. These effects can range from mild to severe based on how sick the patient is before surgery, the length of time that a patient is supported by cardiopulmonary bypass and the complexity of the operation being performed. The function of the heart may be compromised to a degree after bypass surgery. Some patients have subtle neurologic changes after bypass surgery. The occurrence of stroke or seizures during or after bypass remains low, but is a possibility. The kidney may experience damage ranging from decreased urine output to complete renal failure. Areas of the lung may fail to fully expand after bypass. This condition is known as atelectasis. During cardiopulmonary bypass, the patients' blood is making contact with the foreign surfaces that make up the heart-lung machine, causing the patients' inflammatory system to be activated. Research has shown that this response can be danaging to certain tissues in the body. Due to the extra fluid volume needed to fill the cardiopulmonary bypass circuit, the patients' blood volume is diluted. This may require transfusion of blood products to the patient while on cardiopulmonary bypass and blood clotting abnormalities during the postoperative period.
The risk of serious complications related to being placed on cardiopulmonary support depends on the age of the patient, how ill they are at the time of the operation, and the complexity of the surgery to be performed. In most cases the risk is below one percent, but in higher complexity situations, it may be as high as 10 percent to 20 percent. Who operates the heart-lung machine during surgery? The cardiovascular perfusionist is the member of the open-heart surgical team responsible for setting up and running the heart-lung machine.
Echocardiography
Echocardiography can provide the following information:
- Cardiac structures: The various components of the heart (muscle, valves, etc.) could be seen. Therefore a hole in a heart septal wall or deformity of a cardiac valve, etc could be identified.
- The motion of the ventricular muscular walls can be seen (as ventricles pump blood out of them). Reduction in the capability of the ventricles to pump can therefore be evaluated.
- The flow of blood within the heart and blood vessels could also be seen in a feature termed color Doppler. This will represent the blood in usually two different colors: blue and red. The blue represents the blood which is heading away from the transducer and the red represents the blood which is flowing towards the transducer. This enables the visualization of abnormalities of blood flow such as leakage of blood through valves (regurgitation or insufficiency) since blood would be seen to leak back after the valve closes.
- In addition the pressure difference between one part of the heart and the other could be determined since the ultrasound waves bouncing off blood would change its sound wave length depending upon the speed with which the blood flows (blood velocity). This is known as the Doppler phenomenon. Blood travels at higher velocities when there is a greater pressure difference between two parts of the heart. For example, if there is a narrowing of the pulmonary valve (pulmonary stenosis) the right ventricle will squeeze harder to push the blood through the smaller than normal pulmonary valve opening resulting in propelling the blood at a higher speed. This higher speed (velocity) of blood can then be measured by the Doppler equipment of the echocardiogram and an estimation of pressure gradient across the pulmonary valve can be calculated.
ECMO (Extracorpeal Membrane Oxygenation)
(Taken from www.choa.org)
ECMO uses a heart-lung machine similar to the one in open-heart surgery. There are two types of ECMO your child may use. Venoarterial (VA) ECMO uses an artery and a vein, venovenous (VV) ECMO uses one or two veins. The doctor decides which type your child needs. When a child goes on ECMO, the following things happen: The child is given medications to prevent pain and movement during the surgery. The surgery will happen in the Intensive Care Unit (ICU), not the Operating Room.
A pediatric surgeon places tubes, or cannulas, into large veins and/or arteries located on the right side of the neck or in the groin. The number of tubes used depends on the type of ECMO your child needs. These vessels are called the internal jugular vein, the carotid artery, the femoral vein, and the cephalad vein. Your child may have one special cannula placed into the internal jugular vein, depending on how big your child is. This cannula will do the job of the two cannulas. The ECMO machine is made up of several parts: a pump, an artificial lung, a blood warmer, and an arterial filter. The ECMO machine takes the blue blood (without oxygen) out of the right side of the heart and pumps it through the artificial lung (oxygenator). The blood is now red blood (with oxygen). This blood is warmed and filtered before returning to the child.
The ECMO machine does the work for your child's lungs and/or heart and allows them time to heal. During the time your child is on ECMO, he is still connected to the ventilator. The ventilator is used to keep the lungs from collapsing while they get better.
Holter Monitoring
The Holter monitoring is a 24-hour continuous recording of the child's electrocardiogram or ECG. It permits recognition of any rhythm problem of the heart which may occur during daily activities. Cardiogram leads are placed on the child's chest and attached to a small tape recorder which can be hooked to a belt or carried on a strap. While wearing the Holter monitor, a diary of the child's activities should be kept, and especially report any complaints which may be related to the heart. If cardiogram leads become loosened or detached from the chest with activity, they can be reinforced with tape. A shirt or blouse which buttons in front is suggeseted when the Holter is put on the child.
After the monitor has been work for 24 hours, it is taken off and brought or sent to the clinic to be read. The taped ECG is scanned electronically to see if there are any abnormal heartbeats. If any significant problem is found, the family is notified immediately. A written report is sent to the referring physician.
MRI Replacing Some Tests in Heart Babies
Improving technology in magnetic resonance imaging (MRI) may replace the need for more invasive procedures in children born with congenital heart disease.
The special diagnostic tool of cardiac MRI is becoming more available for pediatric use because technology is improving, creating better imaging resolution.
MRI offers a non-surgical option for obtaining important heart information.
