Low Blood Pressure After Surgery

Most of us throughout our lives will either have or know someone who has had surgery. As with everything in life, there are always risks involved. One of those risks is low blood pressure after surgery. This is known as postoperative hypotension.

The main causes of postoperative hypotension are:

• Anesthesia 
• Hypovolemic shock
• Septic shock

By the end of this article, you will have a comprehensive understanding of blood pressure and the main causes and treatment of postoperative hypotension.

Understanding blood pressure

How is blood pressure measured

Blood pressure is the measure of how much or how little pressure is being put on the walls of blood vessels as the heart pumps blood around the body. The reading is comprised of two numbers:

• Systolic blood pressure is the pressure when your heart contracts (squeezes). Top number
• Diastolic blood pressure is the pressure when your heart relaxes. Bottom number

Blood pressure is measured in units of millimeters of mercury (mmHg). For example, someone with a reading of 120/70 mmHg: 120 would be the systolic and 70 the diastolic.

Two devices are generally used to measure blood pressure. The first is a digital blood pressure monitor. These detect changes in blood volume in the arteries and are easy to use on your own. However, they can be inaccurate in people with specific heart rhythm problems or hardened arteries. 

The second is a sphygmomanometer. This takes more skill to use and is used more by doctors. There are 3 parts in a sphygmomanometer:

• An inflatable cuff,
• A manometer (a pressure meter)
• A stethoscope.

There is also ambulatory blood pressure monitoring. This involves wearing a cuff which is attached to a portable measuring device. This device is used to see whether blood pressure varies greatly over a 24-hour period in order to better evaluate blood pressure readings. This is because blood pressure changes based on the activities you are doing. For example, if you do a lot of exercise at certain times of the day you will have higher blood pressure for a short time afterward, which is perfectly healthy. Your blood pressure then comes back down over time. 

Blood pressure should be measured at different times throughout the day and night over a number of days in order to give an accurate picture of someone's blood pressure. Reading can then determine which category you fall into.¹

• High blood pressure: 140/90 mmHg or over
• Pre-high blood pressure: 121/81 - 139/89 mmHg
• Normal blood pressure: 90/60 - 120/80 mmHg 
• Low blood pressure: Below 90/60 mmHg

Low blood pressure after surgery

Common causes 

Surgery is an exceptional medical intervention for many conditions. However, a risk associated with surgery is postoperative hypotension. There are 3 main causes of this condition.

1. Anesthesia - Anesthetics are drugs that are used to put you to and keep you asleep during surgery. These drugs can affect your blood pressure. Changes can happen while they are putting you to sleep and when the drug is wearing off. In some people, anesthesia can cause a significant drop in blood pressure. Luckily you will be in the hospital so doctors can monitor this closely and provide treatment to correct this problem²
2. Hypovolemic shock - Hypovolemic shock happens when your body loses a severe amount of blood or fluid. Losing a large amount of blood can happen in surgery. This causes a drop in blood pressure as there is less blood being pumped around your body, so there is less pressure on the blood vessels. This means the body cannot get the blood to the organs it needs to reach as easily. This is an emergency situation and you will be treated in the hospital to restore the blood and fluids lost³ 
3. Septic shock - Sepsis happens when an infection causes the walls of your blood vessels to leak fluids into other tissue. The infection can be bacterial, fungal, or viral. This sends your body into shock and one of the signs is dangerously low blood pressure. During infection, your temperature rises dramatically, in turn, your body will dilate blood vessels in order to cool you down. However in this case your blood pressure plummets. Although many steps are taken to prevent infection in patients in hospitals, it can still happen. This is another emergency situation which will require hospital treatment to fight the infection⁴

Symptoms

• Light-headedness or dizziness
• Feeling sick
• Blurred vision
• General weakness
• Confusion 
• Fainting

Risk factors

1. Intraoperative hypotension - This means having low blood pressure during surgery, typically caused by anesthesia. Studies have shown that intraoperative hypotension increases your risk of having major postoperative complications
2. High-risk blood clot - If you are at a high risk of having blood clots, this can cause you to have a heart attack which, as stated before, is one cause of postoperative hypotension⁴

Managing low blood pressure after surgery

Medications

Treatment of postoperative hypotension will involve medication and monitoring. Vasopressors and I.V fluids are used alongside other medications; but the other medication will depend on the cause of the postoperative hypotension. 

Vasopressors are a type of drug that are given to constrict blood vessels, making your heart's contractions more forceful. This is often given when a patient is in shock. This leads to an increase in blood pressure. This combats the effect of dangerously low blood pressure and allows blood to reach vital organs, preventing possible fatality. They are usually delivered through an I.V tube inserted into a large vein usually in the neck, which decreases the likelihood of complications. One of the main advantages of vasopressors is how quickly they work. There are some side effects of vasopressors. However, you will most likely be in the hospital, so your healthcare provider will be able to monitor you.⁵

Intravenous (I.V) fluids are specially formulated liquids that are injected through a tube into a vein to prevent or treat dehydration. This is given commonly to people in hospital as sickness and surgery typically leave people dehydrated. This rebalances electrolytes (sodium, potassium, and calcium), provides your body with sugar, and rehydrates your body with water. 60% of our body is made of water and is crucial for your cells to function. One common sign of dehydration is low blood pressure. So, treating this dehydration can put your blood pressure back into a healthy range. There are different types of fluids given and this will be decided by your healthcare provider. Crystalloid solutions are dissolved molecules that pass easily into tissue from the bloodstream. Normal saline (sodium chloride) salt and D5W (dextrose), a type of sugar, are examples of this type of solution and are widely used in hospitals after surgery. Calcium and lactate can also be added, which are used when fluid replacement needs to be more vigorous.

Colloids are another type of fluid which contain bigger molecules, such as albumin.⁶

Antibiotics will also be used, but only if the cause is sepsis. It is important to also treat this along with low blood pressure. Killing the culprit is vital for treating sepsis and not doing so is most likely fatal. The type of antibiotic given will then depend on the type of bacteria that is causing it and the local microbial guidelines provided. These are guidelines that different hospitals have due to differences in types of bacteria in that area.⁷

Home remedies

• Stand up slowly after long periods of lying or sitting
• Raise the head of your bed by 15cm
• Eat small, frequent meals
• Increase fluid and electrolyte intake

Lifestyle changes

• Limit standing or sitting for long periods
• Limit sudden changes in posture
• Avoid caffeinated drinks at night
• Limit alcohol consumption 

Complications

Studies have shown that having postoperative hypotension in critical care can increase your risk of damaging your kidney and heart. This can lead to what is known as an acute kidney injury. This is when the kidney does not function properly, resulting in waste products not being excreted as well as electrolyte imbalances. Multiple heart problems can occur such as blood clots, which can lead to heart attack or stroke.⁸

When to seek medical attention

You should seek medical attention if you are experiencing severe symptoms:

• Loss of consciousness
• Confusion
• Pale/blue skin
• Difficulty breathing
• Fever
• Chest pain

This is because there are several medical emergencies that cause dangerously low blood pressure and are accompanied by one or more of these symptoms.

Summary

In conclusion, postoperative blood pressure can occur after surgery for a number of reasons. Thankfully, you are most likely going to already be in the hospital if this happens, so doctors and nurses can respond quickly with effective treatment. If your blood pressure continues to be on the lower side once you return home, there are home remedies you can use. If things don't return to normal, you should contact your healthcare provider for a check-up.