Anesthesia is an essential medical practice that enables pain-free surgical procedures. However, it has significant physiological effects, particularly on blood pressure. Depending on the type of anesthesia used and the patient's health status, blood pressure can fluctuate considerably. In this article, we will examine how anesthesia affects blood pressure, the underlying mechanisms, and strategies for managing these effects.

Introduction to Anesthesia and Blood Pressure

What is Anesthesia?

Anesthesia is a medical technique that blocks the sensation of pain during a surgical or medical procedure.

There are three main types of anesthesia: general anesthesia, which puts the patient into a state of controlled unconsciousness; regional anesthesia, which numbs a specific part of the body; and local anesthesia, which numbs a very limited area and is often used in dental or minor surgery. What is blood pressure? Blood pressure is the force exerted by the blood against the walls of the arteries. It is measured in millimeters of mercury (mmHg) and consists of:

• Systolic pressure (the highest pressure during heart contraction).
• Diastolic pressure (the lowest pressure when the heart relaxes between beats).

Good blood pressure control is essential for good health, and any significant fluctuation can have serious consequences.

Effects of Anesthesia on Blood Pressure

Anesthesia can have various effects on blood pressure depending on the type used and the patient's health.

General Anesthesia and the Drop in Blood Pressure

General anesthesia usually causes hypotension (a drop in blood pressure). Several mechanisms are involved:

• Vasodilation: Many anesthetics (e.g., propofol, isoflurane, sevoflurane) cause blood vessels to dilate, reducing vascular resistance and, consequently, blood pressure.
• Myocardial depression: Some anesthetic agents reduce the force of the heart's contraction, which decreases cardiac output.
• Inhibition of the sympathetic nervous system: The sympathetic nervous system regulates blood pressure. Anesthesia partially blocks this regulation, which can worsen hypotension.

Possible consequences:

• Reduced blood flow to vital organs (brain, kidneys, heart).
• Increased risk of hypoperfusion (reduced blood flow to an organ).

Regional anesthesia and its effects on blood pressure

Regional anesthesia (spinal, epidural) can also affect blood pressure, but in a different way.

• Spinal and epidural anesthesia: These techniques block the nerves of the autonomic nervous system, which can cause significant vasodilation and severe hypotension.
• Peripheral nerve block: Less likely to cause significant drops in blood pressure, unless large amounts of local anesthetics are used.

Factors influencing these effects:

• Level of anesthesia (the higher the block, the greater the risk of hypotension).
• Patient hydration prior to the procedure.

Special case: anesthesia-induced hypertension

Although hypotension is the most common, some patients may develop hypertension under anesthesia.

• Reaction to surgical stress: Some patients react to intubation or to pain by an excessive activation of the sympathetic nervous system, which raises blood pressure.
• Sudden discontinuation of antihypertensive treatment: A patient with high blood pressure who abruptly stops taking their medication may experience spikes in blood pressure during anesthesia.
• Side effects of certain anesthetics: Some agents (e.g., ketamine, ephedrine) can cause an increase in blood pressure.

Underlying physiological mechanisms

Anesthesia affects several physiological systems that influence blood pressure:

The autonomic nervous system

Anesthesia can suppress sympathetic activity, which reduces vasoconstriction and leads to a drop in blood pressure.

Some anesthetic agents can cause significant vasodilation, thereby decreasing venous return to the heart and reducing cardiac output.

Myocardial function

Some anesthetics directly suppress cardiac contractility, reducing the heart's pumping force.

Strategies for Managing Blood Pressure in Anesthesia

Monitoring and foresight

• Continuous monitoring using a sphygmomanometer or invasive monitoring.
• Fluid administration to prevent hypotension.
• Adjustment of anesthetic doses based on the patient's response.

Medications used to stabilize blood pressure

• To treat hypotension: Vasopressors (ephedrine, phenylephrine), administration of intravenous fluids.
• To treat hypertension: Beta-blockers, anesthetics with a vasodilatory effect (e.g., propofol).

Preoperative optimization

• Review of medical history.
• Correction of fluid imbalances prior to surgery.
• Continuation of antihypertensive treatment if necessary.

(Long, 1924).

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