00:00
acidosis with bicarbonate, which the kidney
produces, is impaired. This is
a slide of the Oxyhemoglobin dissociation curve.
And the way this is represented,
is that on the vertical axis shows
the oxyhemoglobin saturation,
and on the horizontal axis we have
the oxygen level in the blood. Under normal
circumstances, the oxygen level in the blood
is around 90 to 100. So,
you can see that there's
a period during which oxygen is very rapidly taken up
by the hemoglobin, that's the steep
part of the curve, and then there's a relative flattening
of the curve, and there's little change in the oxygen level
at that point. Conditions in the body
can either interfere,
or actually improve the delivery of Oxygen,
by shifting the Oxyhemoglobin curve either
to the left, or to the right. If it's shifted
to the left, the hemoglobin
becomes much more avid for oxygen, it doesn't
release oxygen well. So this occurs when there's
alkalosis, when there is hypothermia,
and when DPG is decreased.
01:12
The shift is to the left, oxygen is not delivered
to tissues well. On the other hand,
a shift to the right will allow more easy
delivery of oxygen to tissues.
01:24
It's easier for oxygen to be released
by hemoglobin, when the Oxyhemoglobin
dissociation curve moves to the right. And this
can occur with acidosis, with hyperthermia,
and with increases in DPG.
What most of us try to do
is try to keep the Oxyhemoglobin dissociation curve
from moving at all. So we maintain normal
blood pressure, normal temperature, and we try
to maintain normal pH. But if you have
a choice between alkalosis in this situation,
or a little bit of acidosis,
acidosis at least improves offloading
of oxygen to tissues. So,
the anesthesiologist role in maintaining acid-base balance
is to provide a well controlled anesthesia,
with minimal negative effects upon respiratory
and cardiac function. Major
hemodynamic changes are always a negative
in this situation, because they'll nearly
always cause acidosis. In addition,
the anesthesiologist must aggressively resuscitate
patients who have become volume depleted
through trauma, or other bleeding
disorders, or who are dehydrated through diarrhea,
or too much heat prior to coming
to the operating room. Kidney disease is a common
problem in society, and it's becoming more common
all the time. These patients require monitoring
of their acid-base status during surgery,
and correction of the dangerous changes such as
metabolic acidosis and metabolic alkalosis
that can occur. Unfortunately, it's not easy
to change these things, it's not always easy
to fix them, but at least you should know
what's happening and be prepared to attempt to fix them.
03:12
Fortunately, anesthesia itself, except for its expected
effects upon respiratory and cardiac function,
does not adversely affect acid-base status.
However, it is the duty of the anesthesiologist
to monitor acid-base status, and to correct
adverse changes wherever possible.
03:30
So in summary, in this lecture we've talked
about some of the physiologic effects
of anesthetic vapours, opiates
and induction agents. We've talked
specifically and primarily about respiratory function and cardiac
function, because that's where the major effects are.
03:48
We've alluded to some of the effects that occur
on hemostasis and on acid-base balance.
03:54
The bottom line for every anesthesiologist
is that, it's his or her duty
to constantly monitor the patient for all of these conditions,
and to adjust the patient's condition in the appropriate
direction when any of these areas
go out of line. The constant
monitoring is absolutely critical and is really
the duty of every anesthesiologist.