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Anesthesia: Numbed by choices?

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.

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.

Procaine, better known by its brand name, Novocain, was developed as an alternative to cocaine, the first local anesthetic. 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.

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 drugs are similar, too, with lidocaine the mainstay. Typically, doses are larger; sometimes they’re combined with other agents.

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. 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.

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.

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 to monitor brain activity so the patient doesn’t go too “deep.” They watch breathing, too. A breathing tube of some kind is usually inserted, though not every patient will need it.

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. Diazepam (Valium) is the best known of these drugs, but Versed is favored because it’s three times stronger.

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.

Muscle relaxants. 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.

Regionalists versus generalists

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. And doctors must be careful not to overdo calming drugs like Versed because they can suppress blood pressure and breathing.

January 2007 update
Help prevent coronary artery disease with this heart health report
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