Good day, so I was curious about this after watching a heart transplant surgery. Normally speaking, the cardiovascular system can be considered as a closed loop system where fluids that leak out don’t introduce air bubbles into the blood stream. However, when transplanting an organ, say a heart, from a donor to a recipient, there are multiple instances where there might be a risk of introducing air bubbles to the blood stream either when being connected to an artificial blood pump or sewing the new organ in.
My question is, how is it that they manage to remove air bubbles from a patients blood stream after completing a heart transplant?
When putting a patient on cardiac bypass, the bypass machine hoses initially are filled with saline. Major vessels are clamped. The heart is submerged with saline. Vessels are separated one at a time, then canulas are inserted, all while submerged in saline.
To be honest unless it’s a continuous air bubble greater than 30 mls, your lungs will absorb it after the bypass is off. So unless it’s more than a continuous ounce of air, not cumulative: you should be fine.
I’m not a doctor, but I recently learned that a little air is okay. I actually had a “bubble test” done recently where they inject air into my veins with a needle, and use Ultrasound to watch the tiny bubbles go through my heart to check for any holes between the chambers allowing blood to flow the wrong way (I did indeed have a tiny defect, but small enough to be benign). So a few little bubbles are fine.
During the procedure, the surgeon places a cannula in the aorta, and two in the vena cava (SVC & IVC) and snares them so all the blood flow is diverted to the pump, and the patient is placed on cardiopulmonary bypass. The aorta is clamped below the aortic cannula, and then the old heart can be removed. The patients full blood flow is going through the bypass machine, so the heart and lungs are no longer contributing to the body. When a new heart is connected, an aortic root vent is placed, which helps to pull air out. Then the snares on the vena cava cannulas are released so some blood can fill the heart and allow the air to release through the aortic root vent. The patient is placed in trendellenburg so that any remaining bubbles will hopefully go down instead of up to the brain, and the cross clamp is released. Basically it’s a complicated answer but there are ways to vent the heart so the bubbles come out before the cross clamp is removed.
The patients are placed on cardiopulmonary bypass, which is essentially disconnecting the vasculature from the heart and lungs and connecting it up to a machine that oxygenates blood and returns it to the body while we work on the heart. The introduction of air bubbles can happen either during connection to or disconnection from the CPB system, but we minimize that essentially by filling the tubing with saline so there’s as little air as possible in the circuit and the bypass machine itself has several filters that are supposed to minimize air bubbles. There is also constant communication between the surgeons and the perfusionist, which ensures that the blood flow is occurring correctly and in the right direction, the heart is not beating when it’s not supposed to be, etc. But there is always a small amount of air that enters the system and it can cause inflammation and intravascular thrombosis. < 20 mL of air is usually considered to be minimally harmful, and the risks of these air emboli are considered to be less than the benefit of the transplant/CABG/etc., which is why we proceed with these cases.