So what are analgesics?
In Wikipedia, analgesic
is defined as a painkiller
in any number of these groups of drugs
used to achieve analgesia, relief from pain.
It derives from Greek,
and the "analgesia"
was “without pain.” So an analgesic
is something that prevents pain, obviously.
"Gesia" was "pain." Analgesic drugs
act in a variety of ways
on the peripheral and central nervous system.
Some classes of drugs have no central effect at all.
Others have little or no peripheral
effect. They're distinct from
anesthetics, which reversibly eliminate
sensations, and they include
such drugs as paracetamol (known in North America
as acetaminophen or simply
as APAP), and the non-steroidal
such as salicylates, and opioid drugs
such as morphine and opium.
Additionally, other drugs such as antidepressant
drugs, anticonvulsant drugs
and some anesthetics at sub-anesthetic doses
can also cause, can relieve certain
kinds of pain. So we've talked about nitrous oxide
and Ketamine previously. So in general, in most parts
of the world, non-steroidals and salicylates
are non-controlled drugs. And opiates
are controlled drugs right across the world. There's actually
an international convention that controls these drugs.
Other analgesic drugs are usually provided
by prescription only. Again, depending on where
you live. Opioids work centrally in the brain
and spinal cord to reduce perception
of pain. So they work at every level of the central
nervous system and the peripheral nervous system.
They're either derived from naturally
occurring alkaloids, opium from opium
poppy, and these are opiates,
or they're chemically derived
and they're called opioids. I'm going to use these words
interchangeably, because they mean the same thing in essence,
it just is an indication of where they come
from. They're similar in structure,
although it's interesting, when you look at them
chemically, they don't really look very much
alike, but they all have one common feature.
They have the ability to bind
to opioid receptors in the brain and spinal
cord, as do enkephalins and endorphins,
which are naturally occurring opiates which we
produce within our bodies. These are the most
effective drugs for relief of acute pain,
surgical pain, trauma pain.
They all create tolerance, and they create
tolerance in 100% of us.
They all create physical dependency,
and they create physical dependency
in 100% of us. They all have
the potential to create addiction.
All are controlled drugs. But the incidence
of addiction is actually quite low
in people who use opioids, even though tolerance
and dependency are very common.
They all produce nausea and vomiting,
itching, constipation, and funny
feelings, emotional feelings, dysphoria we call it,
it's hard to describe, just an unpleasant general
feeling. They can all cause muscle rigidity,
which is something you probably will never see
unless you're giving high doses of these drugs during
anesthesia. I've certainly seen that and it's very profound.
They all have respiratory depressant effects,
and can cause death from hypoxemia.
The comous, when you hear about somebody
dying from an overdose of opioids,
it's nearly always a respiratory arrest,
that is the initiating factor,
and then the ongoing development of cardiac
arrest and death. So there are a huge
number of opioids out there. And they vary
by potency, duration of action, mode
of absorption. Some of them tend to be
very short acting and have less
profound effect on respiratory depression
than others. Others are very
slow in onset, have very long actions, methadone
being the classic, and don't produce
the dysphoria that addicts seek
when they seek narcotics.
So morphine, heroin, meperidine
or demerol, was the, or pethidine
in most parts of the world actually, codeine,
oxycodone, hydromorphone, fentanyl, sufentanil,
which is a 1000 times more potent than morphine and is only
used by anesthesiologists, alfentanil, remifentanil,
which is very short half-life, about a minute and a half,
and again, is only by anesthesiologists.
And they have a very wide range of delivery methods.
You can think of almost any entry to the body,
you can give an opioid by that entry.
So how do we deal with some of the pain
issues associated with surgery? One thing we can do is,
we can put in an epidural. And I'll speak
more about the difference between epidural and spinal
in a future lecture. But let's, at this moment,
just talk about putting in an epidural, which is placed
before surgery. We put a catheter in,
and we use a pump like this, not necessarily
exactly like this, to inject,
usually a combination of local anesthetics and opioids.
And this can produce profound
pain relief, particularly for patients who've had
thoracic surgery, which is very painful,
or abdominal surgery, which can also be very painful.
For less severe types of pain we often use
patient controlled analgesia. And this is
an example of a fairly old pump that we
used in our hospital. And you can see, the patient
is holding something that looks like a nurse call button.
It's virtually the same. And the patient can
deliver narcotics to himself or herself
when it's needed. So, they can push
the button, they get a dose of narcotic.
And you must think to yourself, “Well, isn't there a chance you're going
to overdose with that?” Well, it's based on a microprocessor,
it's based on metabolic and distribution
rates for the normally used narcotics.
And we always have a lockout period built into the system.
So, if you push the button multiple times,
you will only get one dose of the drug
until such time as a lockout period has
passed. At which point, another push of the pump
will give you another dose. It works
really well. It works extremely well and patients
like it, because they feel they have some control.
One of the things I always advise patients using patient
controlled analgesia is, don't wait until the pain's bad.
Don't be stoical. Get on top of it right away,
take the drug early, control the pain
and pump, push the button whenever
the pain is there.