By: Nellie Nguyen
Hypothermia is a state where a significant, dangerous drop in body temperature is caused by exposure to extreme cold. Oftentimes, hypothermia can be fatal when left untreated, because it leads to a complete failure of the heart and respiratory system, resulting in death. However, purposefully induced and carefully monitored hypothermia has led to astounding advancements in medical techniques, especially for cardiac surgery purposes.
Deep hypothermic circulatory arrest (DHCA) is a technique involving clinical death, and it is when a patient’s body temperature is greatly lowered and blood flow is reduced through the blood vessels, which can last up to 40 minutes. Clinical death is a term referring to the cessation of blood circulation and breathing, but this does not necessarily mean a person is truly dead; clinical death is reversible, and if handled carefully, it is extremely useful in surgical operations. The safest temperature range for DHCA is between 20º C, or 68º F, and 25º C, or 77º F; this is a major drop, considering that the average human body temperature is approximately 36.1º C to 37.2º C or 97º F to 99º F. The earliest documentation of using this technique dates back to 1959 when it was done on children undergoing repair of a condition caused by four heart defects, called Tetralogy of Fallot.
Normally, patients undergoing surgery to repair damaged or abnormal blood vessels leading to or from the brain were recommended DHCA during their surgery. This gives surgeons a bloodless operating site and a better visual field during the surgery. An example of a surgery in which DHCA is recommended is the repairing of a weakened area in the aorta, a large blood vessel leading into the heart that supplies the body with blood. The purpose of using this technique is to stop blood circulation in order to protect the brain and other organs.
The actual process of using DHCA begins with a patient being put to sleep using general anesthesia and being put on cardiopulmonary bypass, also called the CPB machine, which is a device that replaces the function of the heart and lungs. Afterward, the patient’s blood is cooled by the machine to the optimal range for the technique, causing the heart to stop beating and eventually terminating brain function as well. The machine is turned off and the surgery is conducted, and once it is complete, the machine is turned on again to circulate warmed blood. The patient’s body is no longer in a hypothermic state, and the heart and brain start functioning again.
While there are many advantages of using DHCA as a surgical technique, it definitely comes with some risks, such as temporary memory loss, kidney damage, strokes or seizures, blood clots, and even possible heart failure. Additionally, the CPB machine can also cause inflammation from contact with the machine parts, which is called postpericardiotomy syndrome. These risks can be even greater if patients have additional medical conditions prior to the surgery or if the surgery itself is complicated. Even if a patient does not suffer from any of the associated risks, he or she will still have to spend several days in the hospital after the surgery to recover.
Deep hypothermic circulatory arrest is a key medical technique that greatly improved surgical operations, such as safer and more efficient cardiac surgeries. Without DHCA, there is a much higher risk of damaging the organs in the cardiovascular system, other bodily organs, and even death. The usage of hypothermia may appear alarming at first, but knowing the specifics of the technique and how it contributes to a surgery helps lessen the ominosity of DHCA.
Q: How is deep hypothermic circulatory arrest performed?
A: A machine called the cardiopulmonary bypass is the main machine used for DHCA since it replaces the heart and lungs for a patient during the surgery. After using anesthesia to put the patient to sleep, the machine circulates cool blood throughout the body to lower the core body temperature, putting the body into a hypothermic state and ceasing heart and brain function. After the surgery is completed, the same machine starts circulating warm blood to bring the body back to a normal temperature; the heart begins beating again, and the brain starts functioning.
Q: Why do some patients need to undergo deep hypothermic circulatory arrest?
A: Patients that need to undergo cardiac related surgeries are normally recommended DHCA. These surgeries include fixing damaged blood vessels that lead to or are from the brain, such as an aortic arch surgery, a complex operation that replaces damaged portions of the aortic arch. The aortic arch is a part of the main artery that helps distribute blood to the head. DHCA allows surgeons to have a bloodless operation site due to the ceased blood flow, which helps them have a better visual field. It also helps protect other parts of the body.
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