What is Aortocaval Compression Syndrome?
Aortocaval compression syndrome, also known as supine hypotensive syndrome, is a condition that can occur in pregnant women, typically after 20 weeks of pregnancy. It happens when the woman lies flat on her back. This position can cause the uterus to press on the large blood vessels, the inferior vena cava and the aorta, which can interfere with blood flow from the lower part of the body back to the heart, and out to the placenta.
This can cause serious health risks for both the mother and the baby, including low blood pressure in the mother, and might even be life-threatening. As a result, it’s extremely important for the health care team to be aware of this condition, recognize its symptoms in pregnant patients, and immediately take steps to correct it if suspected.
What Causes Aortocaval Compression Syndrome?
The lower area of the spine usually has a natural outward curve, which is referred to as lordotic curvature. This part of the spine, known as the lumbar region, points towards the abdomen and pelvic area. The uterus is situated in the same area, inside the abdomen, at the same level as this part of the spine.
Between the lower spine and the uterus, there’s a major vein called the inferior vena cava. When a woman is standing or sitting, gravity naturally keeps the uterus, and the fetus it contains, away from the vein and the lower spine. However, when a woman lies flat on her back, or in the “supine” position, gravity causes the uterus to rest on the spine. This can potentially squeeze the inferior vena cava and drastically impede the flow of blood returning from the legs and lower body. This loss of blood flow can lead to maternal low blood pressure.
The term ‘supine hypotensive syndrome’ was first introduced in 1953 to describe this situation. This was after a study found that lying down caused blood pressure to drop in 18 out of 160 pregnant women. This drop in blood pressure was attributed to the weight of the pregnant uterus pressing on the inferior vena cava, although this was not confirmed by scans or blood flow tests. In 1966, another study further suggested that the aorta, the main artery in the body, could also be compressed by the uterus when a woman is laying flat on her back. This contributed to the understanding and terminology of ‘supine hypotensive syndrome’ or ‘aortocaval compression syndrome’.
Risk Factors and Frequency for Aortocaval Compression Syndrome
Sadly, physical accidents and injuries can happen quite often during pregnancy, affecting about six to seven percent of all pregnancies. A condition known as Aortocaval Compression Syndrome can happen during these injuries, especially when the patient is being transferred safely, their spine is immobilized, or while they are being resuscitated. Interestingly, this condition can also happen during routine procedures and deliveries if the pregnant person is put in the same position. This usually takes place in patients who are more than 20 weeks pregnant, but in certain conditions, it can occur earlier.
Signs and Symptoms of Aortocaval Compression Syndrome
Aortocaval compression syndrome doesn’t have any specific signs that doctors can look for during a physical examination. Therefore, doctors rely on clinical evaluations and possibly ultrasound imaging for diagnosis. It’s a tricky diagnosis because without knowledge of this syndrome, it can easily go unnoticed. What’s really essential is paying attention to the patient’s vital signs, especially keeping in mind the normal alterations during pregnancy.
For example, blood pressure tends to decrease throughout pregnancy, but returns to normal by the end of the term. In the first and second trimesters, both the diastolic (bottom number) and systolic (top number) blood pressure decrease by around 15 to 20 mmHg. So, any unusually low blood pressure in a patient in their third trimester can indicate a problem.
Like with any person with low blood pressure, doctors should look out for and quickly address potential causes. Some possible problems could be:
- Bleeding from the liver, spleen, or kidneys due to injury
- Pelvic fractures
- Ruptured uterus
- Placental abruption (the placenta detaching from the uterus)
- Amniotic fluid embolus (blockage in the blood stream)
- Pulmonary embolus (blockage in the lungs)
- Sepsis (a serious infection that can cause organ failure)
- Other potential causes
Testing for Aortocaval Compression Syndrome
The process of examining aortocaval compression syndrome is usually done solely through a medical check-up. We’re not entirely sure if using ultrasound can help in evaluating this condition, as there hasn’t been sufficient research on this yet.
Treatment Options for Aortocaval Compression Syndrome
When someone has low blood pressure that isn’t caused by other issues, they may need to move their uterus away from their spine and a large vein called the inferior vena cava. There are a couple of ways to do this. If there’s no physical injury involved, the person can be placed on their left side. However, if the person has had a trauma or injury, they’ll need to make sure their spine doesn’t move while they’re changing position.
In situations like this, the person will probably be lying on a flat board while their neck is kept still in a specific way. This can present some difficulties. There are three ways outlined to move onto their side without causing their spine to move or change position.
Firstly, lifting the right hip alone could ease the pressure. Another option, as per the Advanced Trauma Life Support Guidelines, is to tilt the board to the left by somewhere between 15 to 30 degrees. People may do this manually or by using tools, like pre-made elevators or rolled up towels under the board. However, this can be tricky because the weight of the abdomen pulls the person towards the left which may cause the spine to move. Even though it’s challenging, keeping the spine in line is a crucial aspect of these methods.
Lastly, if the first two methods aren’t an option, perhaps due to a severe condition requiring CPR, the person can manually move their uterus away from the middle line of their body. A healthcare provider can do this by putting their hand on the right side of the stomach, to the side of the uterus and then shifting it over to the left, away from the vena cava. This method is straightforward, does not require specific skills, and will not harm the uterus or the baby.
What else can Aortocaval Compression Syndrome be?
- Bleeding in the aortic wall
- Aortic valve problem causing blood to flow backward into the heart
- Inflammation in the small airways of the lungs
- Serious condition where fluid builds up around the heart, restricting its function
- A state where the heart can’t pump enough blood to the body
- Shock caused by severe blood loss
- Condition in infants causing floppy tissue above the vocal cords
- Common type of back pain not caused by a serious condition
- Inflammation of the heart muscle
- Inflammation of the pancreas
- Surgery to treat narrowing of the airway in children
- Injuries to the blood vessels outside of the heart and brain
- Noisy breathing usually caused by blockage or narrowing of the throat or airways
- Condition causing pain or weakness in the neck and shoulder due to compressed nerves or vessels
- Condition causing the windpipe to collapse easily as the cartilage is soft or weak
