The heart-lung machine is a special medical equipment that is able to provide human vital processes if the heart or lungs cease to fully or partially fulfill their functions. The idea of the possibility of realizing “keeping any part of the body alive” appeared in 1812, but the first primitive device, which consisted of a mechanism for pumping blood and oxygenation, appeared only in 1885.
The first open-heart operation, where the heart-lung machine was involved, was performed in 1930. Since then, several basic techniques for the use of AIC have been used: cardiopulmonary bypass completely of the whole organism, regional, where a specific organ or site is supplied with biological fluid, and various variations of the auxiliary blood circulation.
Method Features
General artificial blood circulation is the complete replacement of the functions of the heart muscle and gas exchange in the lungs with special mechanical devices and devices. It is widely used in heart surgery.
Regional called blood circulation of a particular organ or part of the body. This method is used to introduce a significant amount of drugs into the area of purulent infection or a malignant tumor.
Regional cardiopulmonary bypass has an option used for short heart surgeries in combination with a deliberate reduction in human body temperature (hypothermia). This method is called coronary carotid perfusion.
Features of devices
A modern heart-lung machine, the principle 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 RT. st .;
- apparatus filling volume no more than 3 l;
- the presence of a device for returning the patient's blood to the circulatory circuit;
- should not injure blood as it passes through structural elements;
- the 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, circulatory circuit) and a mechanical unit. From the patient's body, venous blood enters the oxygenator, where it is enriched with oxygen and cleansed of 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 necessary temperature regime. If the blood in the body is in the cavities, it is sent to the heart-lung machine using a special pump.
Essential elements
AIK has the following structural elements:
- Oxygenators. There are mechanisms in which blood is enriched with oxygen through direct contact, and there are those where the interaction occurs through a special membrane.
- Pumps Valve and valveless are distinguished depending on how the movement of blood occurs.
- Heat exchanger. Maintains temperature in the blood and body of the patient. Correction of the temperature regime occurs with the help of water, which washes the device.
- Additional nodes. These include traps, containers for storing removed from cavities or reserve blood.
- Mechanical block. It consists of the body of the apparatus, moving parts of the oxygenator, equipment for determining various indicators, emergency manual drive.
The HL 20 heart-lung machine is one of the best examples. The perfusion system in this mechanism meets the highest standards and requirements. It combines safety and reliability, an advanced data collection system, flexibility and the ability to adapt to any manipulation.
Preparation and connection of the device
Before use, it is necessary to check the readiness of the mechanism for work. AIK (heart-lung machine) should 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 alkali solutions of high concentration with further washing with water. After sterilization is carried out. After complete assembly and filling of the apparatus 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 often used, sometimes through the ascending aorta. 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). So that the patient is safe, access to the arterial system is performed earlier than catheterization of the venous bed.
Anesthesia and anesthesia
The use of a cardiopulmonary bypass during operations has certain features, which is why anesthesia during this period is different.
- Multicomponent sedation.
- The period before perfusion requires artificial ventilation of the lungs with increased rates of pressure on the inhale and exhale.
- In the period of perfusion, anesthetics enter the body through AIC. Mechanical ventilation is characterized by increased expiratory pressure.
- In the post-perfusion period, hemodynamic parameters are restored, prolonged ventilation of the lungs is required.
Pathophysiology
When using a cardiopulmonary bypass, the human body is in unusual conditions. Pathological reactions to perfusion may develop, since a retrograde blood flow in the aorta, a decrease in pressure in the cavities of the heart, and the lack of a 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 use of AIC, this interferes with the normal restoration of blood circulation.
The consequence 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, particles of calcium;
- hypoxia - may develop due to insufficient work of the oxygenator or arterial pump through which blood must flow back into the body;
- hematological complications - the incompatibility of the blood of the patient and the donor by the group or Rh factor, the patient’s reaction to the infusion of citrate blood, trauma to blood cells in the heart-lung machine, and clotting disorder.
The devices are constantly being improved to reduce possible complications during the procedure. Modern innovations, technologies and high qualifications of the team of doctors are the key to a successful intervention.