Harvard Health Letter

Anesthesia: Numbed by choices

Anesthesia: Numbed by choices?

No more "knock me out, doc." Increasingly, you're given choices about anesthesia.

Before anesthesia, doctors dulled pain with alcohol, opium, or even bloodletting. But none was really satisfactory, and surgical wards remained nightmarish places where shrieking patients were held down by brute force during surgery. In the 1840s, all that began to change. Surgeons and dentists experimented with various agents, including nitrous oxide and chloroform. At Boston's Massachusetts General Hospital on Oct. 16, 1846, Dr. John C. Warren successfully operated on a patient anesthetized with ether. To the dumbfounded audience, Dr. Warren declared, "Gentlemen, this is no humbug!"

Today our problem isn't belief in anesthesia; it's sorting out the choices of agents and strategies. Here's a quick primer.

A little numbness

Local anesthetics are injected just under the skin to block pain at its source. But the drugs aren't discriminating; they affect the transmission of other sensory information. That's why local anesthetics produce numbness — that odd lack of feeling — not just an absence of pain.

Cocaine, the first local anesthetic, was introduced in ophthalmologic procedures in 1880s. Procaine, better known by its brand name, Novocain, was developed as an alternative. Now lidocaine has largely replaced procaine because it works faster and lasts longer. Unlike procaine, it's absorbed through the skin and is the active ingredient in topical agents.

Local anesthesia

Lidocaine and other agents cause numbness by blocking ion channels in the membranes of nerve endings.

Blocking pain

If local anesthesia targets pain "on site," regional anesthesia does so "in transit," further along the line of nerves leading to the brain. Otherwise, it's mostly a scaled-up local anesthesia. You still remain conscious. The goal is pain blockade but as with local anesthesia, you experience loss of other sensations. The drugs are similar, too, with lidocaine the mainstay. Typically, doses are larger; sometimes they're combined with other agents, for example, some epinephrine — better known as adrenaline — to constrict blood vessels so the lidocaine doesn't spread to other parts of the body.

Nerve blocks are a form of regional anesthesia. Lidocaine or something similar is injected near (but not directly into) a nerve or nerve cluster. The numbed spot blocks pain signals. For example, regional anesthesia for carotid endarterectomy (surgical removal of plaque from the carotid arteries) involves numbing the cervical plexus, an intersection of several nerves in the side of the neck.

Epidurals and spinals (sometimes called spinal blocks) also count as regional anesthesia. Drugs are delivered to the spinal cord, with a spinal block going a bit deeper than an epidural. Both numb the lower part of the body for lower abdominal procedures, childbirth, and hip and knee surgery.

Spinals usually involve a single injection. In epidurals, the drug is delivered a bit at a time through a tiny catheter inserted into the epidural space in the spinal cord. The catheter can remain in place for extended periods, making epidurals the choice for childbirth, long procedures, or situations when postsurgical pain might be an issue.

Regional anesthesia

The lower part of the body is numbed by introducing anesthetic agents into the epidural space of the spinal cord.

Sedation lite

Many people have experienced light sedation (conscious sedation or sedation analgesia) because it's used for colonoscopies. It produces a relaxed grogginess. The drugs, administered intravenously, generally include the benzodiazepine midazolam (Versed) and the pain drug fentanyl. Some people are sensitive to Versed and will lose consciousness for a time.

Going under

Instead of blocking pain en route, general anesthesia shuts down pain at its final destination, those parts of the brain responsible for pain reception. Anesthesiologists use electroencephalography (EEG) and tests called "evoke potentials" to monitor brain activity so the patient doesn't go too "deep." They watch breathing, too. (Drugs that render patients unconscious also suppress respiratory reflexes.) A breathing tube of some kind is usually inserted, though not every patient will need it. General anesthesia is significantly safer than it used to be. The improvement is often cited as a model of how to reduce medical mistakes through technology and training.

Today most drugs for general anesthesia are delivered intravenously through a line inserted in a vein in the back of the hand. The exact drug combination depends on the patient and procedure, the hospital, and the anesthesiologist. Here are five typical "ingredients":

Benzodiazepines. Benzodiazepines are often given first to "take the edge off." They relieve anxiety and cause drowsiness. Some people feel a little tipsy, which makes sense because "benzos" act on GABA receptors in the brain much like alcohol does. Diazepam (Valium) is the best known of these drugs, but Versed is favored because it's three times stronger. Patients undergoing surgery with regional anesthesia are often given Versed intravenously so they stay calm and relaxed.

Induction agents. These drugs make you lose consciousness. Barbiturates such as methohexital (Brevital) or thiopental (Pentothal) — better known as sodium pentothal, or "truth serum" — are often used. Each drug has its pros and cons. The barbiturates, for example, depress breathing and increase heart rate, a tricky combination, but they also constrict blood vessels, which is sometimes important.

Muscle relaxants. Most muscle relaxants are related to curare, the plant extract South American hunters used on their darts and arrows to paralyze prey. In anesthesia, these drugs help keep patients still and make it easier to insert a breathing tube.

Opioids. Unconscious patients would still react to painful stimuli if opioids weren't used. Morphine is the classic opioid, but it releases histamine, which lowers blood pressure. Fentanyl is 100 times more potent and doesn't affect blood pressure, so it's used more often.

Inhaled agents. These drugs keep patients unconscious. Nitrous oxide (laughing gas), one of the earliest anesthetics, is still used. Ether is not because it's very flammable. It does have many widely used descendants, including enflurane (Ethrane) and sevoflurane (Ultane).

General anesthesia

Most of the drugs used in general anesthesia are administered intravenously.

Regionalists versus generalists

The main character in Philip Roth's latest novel, Everyman, is about to have a carotid endarterectomy when doctors ask what type of anesthesia he wants. He picks regional anesthesia (Roth calls it local) because he thinks they believe it's safer.

"It was a mistake, a barely endurable mistake," Roth writes, going on to describe how "the cutting and scraping took place so close to his ear, he could hear every move their instruments made as though he were inside an echo chamber." This is from a work of fiction but it has the ring of truth, says Dr. Linda Aglio, director of neuroanesthesia at Harvard-affiliated Brigham and Women's Hospital.

Several procedures can be done with either regional or general anesthesia, including hip and knee operations. Dr. Aglio says one advantage to the regional approach is that placement of the epidural reduces the risk for blood clots. But for carotid endarterectomies, it's more of a toss-up.

Anesthesiologists who favor regional anesthesia believe they're better able to monitor brain function in conscious patients. They can ask questions to see if patients are okay and test motor function by having them squeeze a rubber ball. They also don't have to use an endotracheal tube, which can cause a downswing in blood pressure — especially dangerous for patients with cardiovascular disease.

"Generalists" counter that they can monitor brain function as well or better using EEG and other tests that don't require a conscious patient. Limiting anesthesia is a valid goal, they say, but it's outweighed by the stress on patients who, like the character in Roth's book, can hear what is going on. "What good is it having the patient awake, if he or she is at high risk for a cardiovascular problem and you're subjecting them to all that anxiety?" Dr. Aglio asks. "Aren't you just stressing them more?" And doctors must be careful not to overdo calming drugs like Versed because they can suppress blood pressure and breathing.

Dr. Aglio says a patient's temperament should also be factored in. She may steer a tense person toward general anesthesia. Likewise, she considers how fast the surgeon works, ruling out regional anesthesia for carotid endarterectomy if a surgeon is a slow worker. "Fortunately," she says, "the carotid is a critical enough surgery that surgeons really know where their skills are — and they don't fool around. The ones that are quick know they can use a regional and the ones that aren't know that they can't."

Some patients may choose general anesthesia over an epidural to avoid being awake during the insertion of a catheter into the bladder so urine can be voided. But general anesthesia doesn't mean that catheterization won't be needed. Both general and epidural anesthesia numb the nerves necessary for urination.