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Anesthesia

Anesthesia/Surgery/Low Blood Pressure

08/04/2008

Question:

I recently had surgery and when reviewing some forms before I sent them to the insurance company, I noticed that during surgery my blood pressure fell to 70/45 (my blood pressure before surgery was normal 110/70). Why would that have happened? I know they gave me some drug to increase the blood pressure, but I don`t know what it was. I am very perplexed about this. Is this common during surgical procedures? Should this be followed up on? Thank you.

Answer:

Thanks for your interesting question.

110/70 is a normal blood pressure (BP) and 70/45 is a low blood pressure for a normal person. BP is normally recorded at least every 5 minutes during anesthesia. A single reading of 70/45 would not be considered unusual. Decreases in blood pressure are common during anesthesia and surgery and there are a few reasons why this might happen.

The most common reason for the decrease is a side-effect of the anesthesia drugs, which generally cause dilatation (enlargement of the diameter) of blood vessels. This dilatation may actually increase the flow of blood to the organs of the body but does decrease the blood pressure. A decreased blood pressure is often seen a few minutes after anesthesia is induced (go to sleep) when the effects of the drugs are still present while there is nothing "stimulating" the body to produce the substances, like epinephrine, which restore the BP. The anesthesiologist, if the BP drops too low, may step in and administer a drug which corrects the drop in BP. Later on, during surgical cutting and other stimulating parts of the procedure, the body does in fact produce those substances, and the BP tends to rise of its own accord. Anesthesia is a bit of a balancing act (amount of surgical stimulation vs level of anesthesia).

How low is too low? This depends on the individual patient. Young healthy people may tolerate a low BP for quite some time without ill effects. Older sicker people may need a higher BP to provide adequate blood flow to vital organs. Your anesthesiologist makes the judgment about the right level to intervene and treat. Sometimes not only drugs but fluids, or even a blood transfusion, may be needed to restore BP, especially if there has been a lot of bleeding during the operation.

An additional possibility is that the single abnormal blood pressure was not a correct reading. An error in the machine or committed by the person operating the machine could have been responsible. An anesthesiologist will very seldom act on a single abnormal value - it will always be checked.

For more information:

Go to the Anesthesia health topic, where you can:

Response by:

Gareth S Kantor, MD Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University