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
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.
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.
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.
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
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