What is Anesthesia?

During surgery, you will be given some form of anesthesia –medications administered for the relief of pain and sensation during the procedure. The type of anesthetic that will be used is determined by an anesthesiologist after consideration of a number of factors; these include the surgical procedure to be performed, other coexisting medical conditions, surgeon preferences and, of most importance, your personal preferences.

Anesthesia is not a single entity, drug, or technique. There are many different approaches ranging from Sedation (with or without simple local anesthetic injection), to Regional Anesthesia (such as spinal, epidural, upper extremity and lower extremity nerve blocks), and General Anesthesia. In addition, there are many different medications and methods of administration utilized in providing a safe anesthetic.

Historically, the term anesthesia derives from Greek for “loss of sensation”. But it is not quite that simple. An anesthetic may be used to reduce anxiety, relieve pain, cause amnesia, and when needed, relax muscles – all to facilitate both patient comfort and optimize surgical requirements. As you might imagine, understanding the way anesthetics work can be complicated and is best understood by looking at the more common types of anesthetics.

Types of Anesthesia

There are three broad categories of anesthesia that are commonly used by the Anesthesia Care Team: Sedation with or without the injection of a local anesthetic (numbing medicine) by the surgeon, Regional Anesthesia such as upper and lower extremity blocks, spinal and epidural blocks (typically in combination with some degree of sedation) and General Anesthesia.

General Anesthesia

When you think of anesthesia, it is likely that you are thinking about general anesthesia. General anesthesia results in loss of consciousness, amnesia, analgesia, and muscle relaxation. Although this is by far the most common form of anesthesia administered, the way general anesthesia works is probably least understood. That is not to say that general anesthesia is less safe, only there are still many “theories” that are used to explain how some of the medications used for general anesthesia work. Parts of the body targeted by medications used for general anesthesia include the brain, spinal cord (central nervous system), peripheral nerves (to a lesser extent than other types of anesthesia – see below), the upper airway/lungs, muscles, and the heart/blood vessels.

Medications used for this type of anesthesia are either inhaled, or administered intravenously.

The administration of general anesthesia may appear complex. However, the safety of this form of anesthesia has significantly increased by way of modern technology, better medications (short acting, predictable with less side effects) and ongoing research within the specialty of anesthesiology.

General anesthesia is sometimes the only option available for many surgical procedures because it provides the best operating conditions for the surgeon.

Regional Anesthesia

Regional anesthesia refers to the use of a local anesthetic drug to block sensation, pain, and to some degree, muscle function in a portion of your body. The anesthesiologist will assess the area of your body requiring anesthesia and select the appropriate nerves to block so that there is no pain throughout your surgery. Regional anesthesia via specific nerve block is often used in surgeries of the shoulder, arm, and leg.

The most common regional anesthetics for the shoulder and arm are the interscalene block and the axillary block. A small needle is used for the placement of local anesthetic medication close to the bundle of nerves going from the neck into the arm – just under the skin of the neck in the case of an interscalene block for shoulder surgery and just under the skin in the arm pit in the case of an axillary block for arm, wrist and hand procedures. These injections are made through skin that is numbed with local anesthetic using a very small needle. They are usually accompanied by light sedation.

Another form of regional anesthesia involves numbing nerves centrally from their origin at the spinal cord.

Spinal Anesthesia is frequently used for lower abdominal, pelvic, rectal and lower extremity surgery as well as for obstetrical surgery such as cervical cerclage and caesarian section. A small area of skin over the lower back is numbed with local anesthetic using a very small needle. A single dose of local anesthetic is then injected through an equally small needle into a space within the spinal canal, well below the spinal cord. Again this form of anesthesia is facilitated by varying degrees of sedation through an intravenous catheter.

Figure 1: For Spinal Anesthesia, a needle is placed in the lower back into the space containing spinal fluid. Note the needle’s location well below the spinal cord.

Epidural Anesthesia is one of the most versatile forms of anesthesia, providing a wide range of pain relief for procedures described above for spinal anesthesia as well as to reduce the discomfort associated with the labor of childbirth. Similar to spinal anesthesia, a needle is placed in the lower back through an area of skin that has been numbed with local anesthetic, usually below the level of the spinal cord. A thin catheter (tube) that resembles fishing line is placed through the needle which is then removed, leaving the catheter comfortably and securely taped in place. The catheter which rests in a specific space within the vertebral column is then dosed continuously or intermittently with local anesthetic medication.

Figure 2: Placement of a catheter for Epidural Anesthesia or Labor Analgesia. Note the catheter location outside of the space containing the spinal fluid.

Epidural Anesthesia can also be used for chest surgical procedures. In this case the catheter and local anesthetic medication is placed higher in the back to numb the chest and upper abdominal areas.

All regional anesthetics are associated with a preserved sense of movement and pressure, but not pain. These non-painful sensations may be uncomfortable for some patients, but are typically responsive to light sedation.



Sedative medications are frequently used to help patients who undergo diagnostic and therapeutic procedures such as colonoscopy, endoscopy of the esophagus/stomach, and bronchoscopy of the lungs. Propofol, a sedative drug administered intravenously, is often used to keep patients asleep and comfortable. The correct dosage is given so that the patient is asleep yet still breathing spontaneously. Usually, patients sleep throughout the entire procedure. However, there are times when a patient will need to be awakened during the procedure to ensure that their breathing is not compromised.

The addition of local anesthetic injection by the surgeon is common in surgical procedures that involve a small region of the body such and the hand, foot and many forms of hernia repairs. The involvement of the anesthesia care team in this form of anesthesia is often called MAC or Monitored Anesthesia Care.

Again, sedation is achieved with drugs such as propofol, midazolam (Versed) and fentanyl. Your level of awareness during these anesthetics can range from an awake but relaxed state to near unconsciousness, all requiring close oversight and diligent monitoring. The “depth” of sedation used is something that can be discussed in advance of surgery with your preferences noted and incorporated into your care.