So, hello ladies and gentlemen.
This is a continuation
of our ongoing series of lectures on Anesthesiology.
And this particular lecture is a continuation
of the Management of Pain, which we started
in the last lecture. We're going to spend some time
in this lecture talking about the many other forms
of medication that are used in management of pain. We're
going to talk about three patients and how
one would go about managing their pain.
And then we're going to end with a discussion
of Obstetrical Analgesia and how we manage pain
during obstetrical care. So, these are some
of the drugs we use. And these are Classes of Drugs.
There's Opioids, which we've already talked about. Non-steroidal
anti-inflammatory drugs, we've talked about. We're going to talk a little bit
about Tricyclic antidepressants,
Serotonin-norepinephrine reuptake inhibitors,
Alpha2 - agonists, 5HT1 - agonists for migraine,
and then we're going, we've already talked
about Nitrous oxide as an analgesic. We won't
come back to that. So opioids, as I've mentioned,
act on the mu-receptor in the brain and spinal
cord to produce both effects, and unfortunately
side-effects. And the side-effects are common.
Respiratory depression in higher doses. Nausea
and vomiting in very low doses. Constipation,
extremely common. Sedation, very common.
Dizziness. Sometimes euphoria, but
the majority of people have Dysphoria,
which is the opposite of euphoria. Instead of feeling
happy, they just feel generally lousy. Confusion,
muscle rigidity, pruritus are also
potential complications. These drugs
are ideal for managing acute pain, but are often
ineffective in chronic pain and lead to dependence,
as we've talked about. We've already talked about tolerance
and physical dependence. They can lead, of course,
to addiction in those people who are susceptible. Remember
what I said earlier, physical dependence occurs
in anyone. So none of us are able to prevent
ourselves becoming physically
addicted to these drugs. It happens to
us all. But the majority of us hate them
and don't find any need to continue them
once the pain is well controlled. So, once
the pain is gone, we're able to stop the drugs. We
go through a short phase of physical withdrawal,
which may include some sweatingness, nausea
and vomiting, general unpleasant feeling.
But most of us don't want to use them anymore, we
don't like these drugs. Addiction occurs in those people,
relatively few, who get this high or this
euphoric phase from opiates.
And they become drug seekers. And they
become incredibly difficult to deal with, and
manage, and help. Here are a few of the drugs
that are commonly seen under the Opiate
banner. And I'm only going to go through this briefly
just because some of them are going to surprise you,
that they, actually a lot of them just turn into
morphine when they're given. So Codein,
which is used as, usually in very low doses as a non-prescription
drug, and in higher doses as a prescription
drug, is rapidly converted to morphine in the liver.
So, you take it orally, it goes to the lever,
it's turned into morphine. The dose of morphine
is very small, but that is what causes the analgesia.
It's commonly used also as an anti cough
medication, because all opiates suppress cough.
And it's a mild analgesic. I hate this drug,
the side-effects are very common.
And some medical groups, including the Canadian Medical
Association, have urged that it be removed from the market.
But the Canadian government hasn't caught on
yet and it's still out there. Heroin, the drug
which most addicts will tell you is the drug that
gives them the best feeling, is also converted
to morphine when it's given. There is no evidence
in the therapeutic literature that heroin
is a better analgesic than morphine. But
addicted people will tell you that it produces
more euphoria than morphine, but those
studies are inconclusive. So, why do people
crave heroin? We really don't know.
It doesn't appear to have any particular
properties that make it either superior or very
different from morphine. And the active agent from
heroin is morphine. Fentanyl
is a drug that's now
widely used for the treatment of chronic pain that was
initially only used by anesthesiologists. It's a very potent
drug, 100 times more potent than morphine.
It has an intermediate duration. It's used
by anesthesiologists, emergency physicians,
intensivists intravenously, but it's used
in chronic pain manager primarily in patches:
percutaneous or transcutaneous
fentanyl patches, can be effective in reducing
chronic pain. Sufentanil, another drug in
the same family, it's 1000 times more potent than morphine,
it's also of intermediate duration, and it's used almost
only by anesthesiologist during surgery.
Remifentanil is an oddball
opiate, it's 70 times as potent as morphine, but
it has a half life of only one and a half minutes.
So, it's given by infusion rather
than by intermittent injections.
It's also not metabolized in the liver
as all other opiates are,
it's metabolized by ester hydrolysis in plasma.
And it's given, as I mentioned, only
by continuous intravenous infusion. And I'm unaware
of anybody other than anesthesiologists using this drug.
So, the good news when it comes to opioids
is that, although the agonists
are very complex and difficult to manage
in some people, it's actually
incredibly easy to reverse these
drugs, using either Naloxone,
which is given intravenously, has a very rapid
effect, seconds before it reverses the effect
of the opioid. It's given primarily by emergency
physicians and anesthesiologists.
Emergency physicians tend to use
fairly high doses and this can cause
accelerated opium withdrawal in patients
who have been addicted to the drugs.
Anesthesiologists, being a more conservative
group, we tend to give very dilute Naloxone
and give it in small aliquots. And this technique
actually allows patients to resume respiratory
activity with relatively little effect upon return
of pain. So in patients, pain control
remains reasonably good and they breathe,
which is the goal of all of this. Naltrexone
is exactly the same as Naloxone
in its action, but it's longer acting
and it's used in the treatment of both opioid addiction
and alcoholism. And I honestly have no idea
how it works in alcoholism, because
there is no similarity between alcohol
and opiates, either chemically or in
terms of their actions on the brain.
The interesting things about Naloxone
and Naltrexone is that, if they're given
in the absence of opioids, they have virtually
no physiological effect. So they're quite
safe drugs to use and they can be used to help
people who are addicted to these drugs.