A heart-lung machine is a special medical equipment that is capable of providing human life processes if the heart or lungs cease to fully or partially perform their functions. The idea of being able to "keep alive any part of the body" appeared in 1812, but the first primitive device, which consisted of a mechanism for pumping blood and oxygenation, did not appear until 1885.
The first open-heart surgery using a heart-lung machine was performed in 1930. Since then, several main methods of using AIC have been used: artificial circulation of the entire body, regional, where a certain organ or area is supplied with biological fluid, and various variations of circulatory support.
Features of methods
General artificial circulation is called the complete replacement of the functions of the heart muscle and gas exchange in the lungs with specialmechanical tools and devices. It is widely used in cardiac surgery.
Regional is the circulation of a certain organ or part of the body. This method is used to introduce a significant amount of drugs into the area of a purulent infection or malignant tumor.
Regional cardiopulmonary bypass has a variant used for short heart surgeries combined with intentional lowering of the person's body temperature (hypothermia). This method is called coronary-carotid perfusion.
Features of the devices
A modern heart-lung machine, the principle of operation of which will be discussed below, must meet the following requirements:
- support at the required level of minute volume of blood circulation in the patient's body;
- high-quality oxygenation, in which oxygen saturation should be at least 95%, and the amount of carbon dioxide - 35-45 mm Hg. Art.;
- filling volume of the device is not more than 3 l;
- presence of a device for returning the patient's blood to the circulatory circuit;
- should not injure blood as it passes through structural elements;
- material for the manufacture of mechanisms must be non-toxic in order to be able to carry out disinfection and sterilization.
Device
Any heart-lung machine consists of a physiological (arterial pump, oxygenator, circulatorycircuit) and the mechanical block. From the patient's body, venous blood enters the oxygenator, where it is enriched with oxygen and purified from carbon dioxide, and then, with the help of an arterial pump, it returns to the bloodstream.
Before the blood comes back, it passes through special filters that trap blood clots, air bubbles, pieces of calcium from the valve system, as well as through a heat exchanger that maintains the required temperature. If the blood in the body is in the cavities, it is sent to the heart-lung machine using a special pump.
Basic elements
AIC has the following structural elements:
- Oxygenators. There are mechanisms in which the blood is enriched with oxygen by direct contact, and there are those where the interaction occurs through a special membrane.
- Pumps. There are valvular and valveless depending on how the blood moves.
- Heat exchanger. Maintains the temperature in the blood and body of the patient. The temperature regime is corrected with the help of water that washes the device.
- Additional nodes. This includes traps, containers for storing blood removed from cavities or reserve blood.
- Mechanical block. It consists of the body of the device, moving parts of the oxygenator, equipment for determining various indicators, emergency manual drive.
Heart-lung machine HL 20 -one of the best examples. The perfusion system in this machine meets the highest standards and requirements. It combines safety and reliability, perfect data collection system, flexibility and adaptability to any manipulation.
Preparing and connecting the machine
Before use, it is imperative to check the readiness of the mechanism for operation. AEC (cardiopulmonary bypass apparatus) must have absolute cleanliness and sterility of those surfaces that are in direct contact with blood.
All structural elements included in the physiological block are treated with detergents or high concentration alkali solutions, followed by washing with water. After sterilization is carried out. After complete assembly and filling of the device with blood, it is connected to the patient at a certain stage of the operation.
To return blood to the body, access from the femoral or iliac artery is more often used, sometimes through the ascending aorta. The biological fluid enters the apparatus through drained vena cava. Before the blood enters the oxygenator, the patient is injected with heparin (2-3 mg per kilogram of body weight). To keep the patient safe, access to the arterial system is carried out before catheterization of the venous bed.
Anesthesia and anesthesia
The use of a heart-lung machine during operations has certain features, therefore, anesthesia during this period is different.
- Multicomponentpremedication.
- The pre-perfusion period requires mechanical ventilation with elevated inspiratory and expiratory pressures.
- During the perfusion period, anesthetics enter the body through the AIC. Ventilation is characterized by increased expiratory pressure.
- In the post-perfusion period, hemodynamic parameters are restored, long-term ventilation is required.
Pathophysiology
When using a heart-lung machine, the human body is in unusual conditions. Pathological reactions to perfusion may develop, since retrograde blood flow in the aorta, a decrease in pressure in the cavities of the heart, and the lack of work of the pulmonary circulation are conditions that are not characteristic of the normal state of the body.
During the intervention, the person is in a state close to hemorrhagic shock. There is a decrease in blood pressure and total peripheral resistance. Under normal conditions, such a reaction is considered protective, but under the conditions of using AIC, it interferes with the normal restoration of blood circulation.
The result is the development of hypoxia and metabolic acidosis in the blood. Prevention of complications is based on improving microcirculation, eliminating the phenomenon of protective redistribution of blood.
Possible Complications
The main complications are:
- vascular embolism, which can be caused by blockage by blood clots, gas, lipids, particlescalcium;
- hypoxia - may develop due to insufficient work of the oxygenator or arterial pump, through which blood must flow back into the body;
- hematological complications - incompatibility of the patient's blood and the donor's blood group or Rh factor, the reaction of the patient's body to the infusion of citrated blood, traumatization of blood cells in the heart-lung machine, clotting disorders.
The devices are constantly being improved to reduce possible complications during the procedure. Modern innovations, technologies and high qualification of the team of doctors are the key to a successful intervention.
