We're going to move now
to Cardiac Anesthesia,
which is a very common type of anesthesia nowadays,
but is a very unique form of anesthesia.
In cardiac surgery, in open-heart surgery,
the cardio-pulmonary bypass machine, which is shown
in this picture, and which is operated
by a highly skilled member of the team called
a perfusionist, basically
bypasses the patient's own
heart and lungs. And it takes blood from
the central circulation, through the machine,
warms it, filters it, oxygenates it, sends it away
to the brain, the kidney, the rest of the body,
and completely bypasses the lung and the heart.
And this leaves the surgeon with a heart that's
immobile. And it makes it much easier to do the surgery
if the heart is on standby. Some surgeons
however prefer to have a beating heart and it is possible,
under certain circumstances, to keep the heart beating and still
do surgery on it. That's not the commonest
way of doing it. The anesthesiologist
is responsible for managing the patient while
they're on cardio-pulmonary bypass.
The surgeon is responsible for preserving
the myocardium while the patient's heart
is at rest. And the way this is done is one
of two ways. Either very cold solutions
with high potassium are forced through the coronary
arteries. This causes cardioplegia, it causes
the heart to stop working because of the high
potassium. And the cold just cools the heart and reduces
its oxygen demand. The other way
of dealing with this is, again using high
potassium solution, but this time blood, forcing it
through the coronary arteries, and that'll
stop the heart. And because you're putting blood
through the heart, you're actually supplying oxygen
to a heart that, because it's immobile, really
doesn't have very high oxygen demands.
The critical phase in cardiac
surgery is Coming Off Bypass.
And this is usually managed by the anesthesiologist,
although there tends to be a fair amount of back and forth
discussion going on between the surgeon,
the anesthesiologist, and the perfusionist at this time.
So these are just some valves that are replaced
during open heart surgery. The top valve
is a metal valve. And the advantage of a metal
valve is that they're tough and they will last for 20,
even 30 years. So, if you're a young person requiring
valve surgery, you want a metal valve, because you don't
want to come back again for as long as you possibly
can. The negative with metal valves is that clots
tend to form on the valves, so patients have to be
anticoagulated for the rest of their lives. They have to take
anticoagulation every day for the rest of their lives.
And some people find that a totally intolerable situation.
The lower two valves in this picture
are tissue valves. They could be
bovine, or they can be pig
valves. And they're much
safer in terms of embolic phenomena, they simply
don't cause embolic phenomena, so you don't need
to take anticoagulation. The negative with these valves
unfortunately is they don't last as long as the metal valves.
And they often need to be replaced every
10 years or so. And repeat cardiac surgery
is infinitely riskier and more complex
than first time cardiac surgery.
The scarring that goes on in the chest after cardiac
surgery is unbelievable. So getting back in
and finding the portion of the heart you need
to operate on can be extraordinarily challenging.
So the anesthesiologist is responsible
for protecting the heart
prior to cardio-pulmonary bypass, which is particularly
critical if the patient has ischemic heart disease,
or is unstable. We have to be very careful
to control tachycardia, and more
importantly, not to cause tachycardia. Because
tachycardia increases cardiac work and requires
increased oxygen supply to the heart. If you've got
ischemic heart disease, it means the vessels
into the myocardium are blocked, so you can't increase
oxygen supply to the heart. So you must keep
the heart rate slow. Frequently, very potent inotropic
drugs such as norepinephrine, epinephrine,
dobutamine, dopamine and milrinone
are given in bypass and coming off
bypass. Anticoagulation is required
during bypass, because the actual
bypass tubing in the cardio-pulmonary bypass
machine tends to induce clotting. And the last
thing you ever want to see,
and I'm thankful I have never seen it,
is a generalized clotting forming in your cardio-pulmonary
bypass. That's a fatal event. So we give very
high doses of anticoagulant. And the drug we use
is heparin. So these patients are very prone
to bleeding. Once the patient's off cardio-pulmonary
bypass, we reverse the heparin. But
by then, there's been some damage to platelet, there's been
some dilution of clotting factor, so bleeding is
not uncommon. When we wean patients
from bypass, they are sometimes extremely
unstable. And it's our job as anesthesiologists
to monitor and manage that
during the transfer to the Cardiac Surgical Intensive
Care Unit, and usually for the first few hours in that unit.
Once the patients are stable,
we can consider discontinuing
ventilation, which has been continued
following the surgery. And usually
they stabilize over about 4 hours and we can usually
extubate them later in the day of their surgery,
and have them transferred to the Cardiac
Ward the following day. I spent 20 years as
a Cardiac Anesthesiologist, and the changes
that occurred during that 20 years were phenomenal.
The rate of damage to patients
and the preservation of the myocardium improved
dramatically. So death on the table and death
immediately following, or nearly following
surgery has become really quite uncommon.
Most neurosurgical procedures require general anesthesia,
but a few can be done with deep sedation. And we'll talk
about those in a moment. One of the critical things
about neurosurgery is the duration of the surgery.
And surgeries of 10 to 12 hours are common. And the longest
I've ever personally done was 27 hours.
During that 27 hours, there were two surgeons
and they took time off. One would come in
and do some work and the other would go out and sleep.
I unfortunately, had nobody to relieve me, so I spent the whole
27 hours awake trying to concentrate
on taking care of this poor patient.
The most critical aspect of neuro-anesthesia
is the control of intra-cranial pressure.
We've talked a little bit about that in earlier
discussions. If intra-cranial pressure is lowered
too aggressively, cerebral blood flow can be
reduced and stroke could occur, ischemic
brain damage can occur. Vapours increase cerebral
blood flow, which is a good thing, but they can increase
intra-cranial pressure as well, and that's
not good. Propofol will decrease
intra-cranial pressure, but the decrease
in cerebral blood flow that can occur at the same
time is not a good thing. Ketamine will increase
cerebral blood flow, which is good,
but it can increase intra-cranial pressure as well,
which is not good. So Etomidate, which
is the drug that's most often used in patients
with brain trauma, is used largely because it has
very little effect on either cerebral blood flow, and it does
decrease intra-cranial pressure. So the combination
is a good combination. Narcotics
have little effect on cerebral blood
flow or intra-cranial pressure in patients
who are ventilated. And so, we can give narcotics
to prevent severe pain. Intra-cranial pressure
can be reduced by having the patient
hyperventilate before induction.
This tends to lower arterial carbon
dioxide which lowers intra-cranial pressure. And then,
once the patient is asleep and intubated, we provide
them with mild hyperventilation and try to control
that pressure from that perspective. We can
also give Osmotic diuretics such as Mannitol or Loop
diuretics such as Furosemide to reduce the water
in the brain. And that can reduce the pressure
in the brain as well. So certain surgical procedures
in the brain can be performed without general anesthesia.
Burr holes, which are just holes in the cranium,
can be given in the presence just of local
infiltration of the skin. And it's possible in those
patients to drill a hole and relief blood
in the brain and let the blood flow out.
And this is a procedure that's actually been done for hundreds
of years, actually thousands of years. There are pictures
from the Egyptian era of holes being
made in the brain or in the skull
to reduce blood in the intracranial
space. But some
modern procedures, such as Deep brain stimulation
for patients with Parkinson's disease, can be
done with virtually nothing, except local anesthesia
and a little sedation. This is a very interesting
procedure. We give the patient a little bit of sedation,
the surgeon puts local wherever they want to put it, drills
a hole through the cranium and then passes probes
deeply into the brain and stimulates them.
And by so doing, they can find the nerve
centers that cause, are causing
Parkinsonism rigidity or tremor.
And they can ablate those areas by sending
an electrical shock down the, down the probe.
And I've had patients who have come into the operating
room so rigid they could barely move, and leave
the operating room after 8 or 10 hours,
it's not a short procedure, mobile, talking,
immediately feeling better. So it's quite a remarkable
treatment and one that is really quite
new and is not done everywhere in the world. So, Complications
of neuro-anesthesia. The most important one,
and one that is unfortunately not uncommon,
is Massive Hemorrhage. It's extremely difficult to treat
and I'm not going to spend a lot of time on this,
because the actual amount of bleeding relative to what
happens when an aorta ruptures is actually quite
small. The problem is, there's no way to relieve
the pressure in the brain when hemorrhage occurs.
So, it means making bigger and bigger
craniotomies and let, trying to let out more and more
blood. It's very difficult. Cerebrovascular accidents
or strokes occur. These can be due to embolic
phenomena or when the brain is being manipulated
by the surgery, surgeon, it's always possible
that certain areas of the brain will have their blood
supply occluded. And that area of the brain
will then develop an ischemic injury or a stroke.
There could be permanent damage to the brain from increased
intra-cranial pressure. And this is a situation which we
see relatively rarely, thank goodness, but when it
does occur, it's usually an extraordinarily bad sign.
The patient fails to awaken for anesthesia and this isn't because
there's something the matter with the anesthetic, it's because
there's something seriously the matter with the brain.
What you try to do in that situation is, you try
to find a cause for the failure to awaken. And if
it's a surgical cause, you go back in and try
to correct it, if it's an anesthesia cause you try
to correct it. But in most cases, it's caused
by the brain itself being so damaged by the previous increased
intra-cranial pressure or the injury that occurred prior
to the patient coming to the operating room, that they just
simply don't wake up. And these are patients who end up
in a chronic vegetative state and may last for many
months, or even years in some cases,
before they finally die. So in summary,
in this lecture we've discussed
a number of specialized areas of anesthesia.
We've discussed Pediatric Anesthesia and some
of the differences that the anesthetist has to be aware
of when dealing with children. They are not small adults.
We've also talked about Thoracic Anesthesia
and the highly risky process of putting
an endobronchial tube in place and isolating one lung,
and doing one-lung ventilation. Special training
is often required for people who are going to do this
on a regular basis, but every anesthesiologist
has to be aware of the principles, and has to be able
to deal with potential emergency patients
who require one-lung anesthesia. We talked
about Cardiac Anesthesia and some
of the complications associated with that. And we
talked a little bit about Cardio-pulmonary bypass.
We ended by talking about Neuro-anesthesia,
about some of the Risks and Dangers associated
with neuro-anesthesia. But also, very briefly, about
some of the Opportunities in neuro-anesthesia,
and some of the good things that are happening in our
Development of New Surgical Procedures for patients
of all kinds.