The most frequent reasons for admission to a critical care unit are to receive support for a low blood pressure or breathing difficulties.

Patients may need help to correct a low blood pressure. Low blood pressure is called "hypotension" ("hypo" means decreased; "tension" refers to pressure). When the blood pressure is too low, the flow of blood to the organs and tissues decreases. Because oxygen is carried to the tissues in the bloodstream, a reduction in blood flow can cause injury to the body organs from low oxygen levels. Injury due to low oxygen is called ischemia. Shock is a term that is used to describe a patient whose tissues are being deprived of oxygen. The blood pressure is often low during shock.

The blood pressure can become too low for many reasons. Low blood volume (called hypovolemia), abnormal heart rhythms (called arrhythmias) and heart muscle damage are common reasons for low blood pressure. Systemic diseases such as infection, allergic reactions (anaphylaxis), certain type of lung disorders and brain injuries can also cause blood pressure problems. The treatment for a low blood pressure depends upon the underlying cause.

We often need to use medications to raise the blood pressure. These drugs work by making the muscle layer of the blood vessel contract, causing the blood vessel to tighten up and become narrow. This contraction of the blood vessel with subsequent reduction in the blood vessel diameter is called "Vasoconstriction". Vasoconstriction increases the blood pressure.

Drugs that cause the blood vessels to constrict are considered "life-support" drugs. These drugs are very potent. Very small changes in the drug dose can affect the blood pressure. These drugs are given intravenously as a slow, controlled infusion that is regulated by an infusion pump. The patient must be monitored very closely, and will usually have a central and arterial line in place to provide continuous pressure monitoring.

We frequently use one or more of the following 4 drugs when we want to produce vasoconstriction and correct a low blood pressure. These drugs are often referred to as "vasoconstrictors", "vasopressors", or "pressors".

Three of these drugs are actually produced by our body during a stress response, when our Sympathetic Nervous System (SNS) is activated. The SNS is our "Fight or Flight" response and is responsible for restoring our blood pressure during times of stress. Dopamine, epinephrine (often called Adrenalin) and norepinephrine are important hormones and neurotransmitters produced by our body. When a patient's blood pressure remains low, we may need to give additional amounts of one or more of these agents. Adrenalin is another name for epinephine and Levophed is the drug name for norepinephrine.

Neosynephrine is the fourth medication we can use when we want to raise the blood pressure. It is similar to norepinephrine. The other name for Neosynephrine is phenylephrine. Neosynephrine is found in many over-the-counter cold medications and is added to constrict the blood vessels in the nose. It is also one of the ingredients that can be used to illegally manufacture amphetamines. Amphetamines are drugs that have an "Adrenalin like" or stimulating effect.

Another group of drugs used in the treatment of low blood pressure is a group of drugs called inotropes. An inotrope is a drug that increases the force of the heart's contraction during pumping. An inotrope is used when the amount of blood being pumped by the heart is too low (which can be a cause for a low blood pressure). The amount of blood being pumped by the heart is measured as a volume of blood per minute and is called the "Cardiac Output".

Inotropes that are used during critical illness are also given intravenously. Intravenous administration allows us to stop the drugs quickly and maintain a very tight control over the dose. Dopamine and Epinephrine (Adrenalin) are both vasopressors AND inotropes. Two other drugs that may be used when we want the patient to receive an inotrope are dobutamine and milrinone.

Dobutamine and milrinone are different than the first group of drugs because they are actually inotropes AND vasodilators. A vasodilator is a drug that has the opposite effect of a vasoconstrictor. A vasodilator relaxes the blood vessels and makes their diameter wider. Vasodilators can lower the blood pressure. Drugs that have strong vasodilator effect are used to lower a blood pressure that is too high.

Drugs like dobutamine and milrinone have very mild vasodilating effects, therefore, they are not used to treat high blood pressure. Their combination effect make the heart pump harder (inotrope), while producing mild relaxation of the blood vessels.

Relaxation or vasodilation of the blood vessels reduces the resistance in the blood vessels, and makes it easier for blood to flow. The resistance in a blood vessel is called the Systemic Vascular Resistance. It is commonly called the "SVR" or "SVRI". Drugs that lower the SVR makes it easier for the heart to pump blood. These drugs can actually help to increase the amount of blood that the heart is able to pump out of the heart (or the cardiac output). They can also reduce the amount of effort that the heart has to make during pumping. Drugs like dobutamine and milrinone can be very helpful during critical illness when the heart is not able to pump enough blood.

Unfortunately, all of these potent medication can lead to other problems. Patients may not be able to tolerate the mild vasodilation that dobutamine or milrinone produces. Drugs like epinephrine and dopamine can cause the heart rate to become too rapid and some of these drugs may make the heart work too hard. We also worry that these drugs might reduce the blood flow to other organs of the body, such as the bowel, kidney or skin.

We monitor patients very carefully when they are on vasopressors or inotropes, and we use these drugs only when absolutely necessary. We often have to use a combination of more than one of these drugs to get the best results and reduce complications.

While most blood pressure problems that are treated in the critical care unit are the result of a pressure that is too low, patients may also have blood pressure that is dangerously high. High blood pressure is called hypertension ("hyper" is increased; "tension" refers to pressure).

Hypertension or high blood pressure is treated with medications that relax the blood vessel muscles and have a powerful vasodilating effect. During critical illness, these drugs are also given as continuous intravenous infusions and delivered by an infusion pump. Examples of potent vasodilators that are used to lower blood pressure are: nitropusside (also called Nipride), labetalol and hydralazine.

Nitroglycerine is another type of vasodilator that can be be given intravenously. It is used to produce mild vasodilation or to relax the arteries of the heart muscle. Mild vasodilation can lower the Systemic Vascular Resistance and help the heart to pump more effectively. Relaxation of the coronary arteries can help to get more blood to flow to the heart muscle.

When a patient begins to recover, some patients may need to be started on oral medications to relax blood vessels or control heart rate. This is common in patients who are admitted with heart disease. Other patients may recover without the need of long-term medications.








Last Reviewed: October 23, 2014

LHSCPatients, Families & Visitors

Last Updated October 23, 2014 | © 2007, LHSC, London Ontario Canada