00:00
How about acid-base balance?
Does general
anesthesia have an impact upon
acid-bases balance? The body's functions
are only active through
a very narrow range of pH,
and it's the enzymes that only function
properly between a pH of about 7.35
and 7.45. The closer you are to 7.4,
the better. Neutral pH
is 7, so the body is always
slightly alkalotic to function
optimally. If you ever let it drop down to 7,
you're in real trouble. Anesthetic drugs
do not affect the body's acid-base balance directly,
but the actions of the anesthesiologist
can have a profound effect on pH.
In the section on Effects on Respiration,
we've already mentioned that monitoring and control
of ventilation can be an important part of the anesthesiologist's
work. Over breathing causes a drop
in blood carbon dioxide, which is known as
respiratory alkalosis, which can have a negative effect
upon many body functions. The opposite,
letting CO2 rise, underventilating the patient
can cause respiratory acidosis.
01:14
Mild respiratory acidosis, as I mentioned,
is well tolerated, but if bicarbonate
is reduced, in the presence of a metabolic
acidosis, metabolic acidosis
as opposed to respiratory acidosis,
it may not be possible to control pH
effectively by moderating the ventilatory
function of the patient. In the section
on Cardiovascular Function, where we've mentioned
the importance of maintaining blood flow to vital organs,
reduction of blood flow can cause reduction
in oxygen delivery to tissues or hypoxia,
which basically is suffocation of tissues.
Hypoxia, or low oxygen in tissues,
and hypoxemia, which is low oxygen
in blood, both cause tissue acidosis,
or metabolic acidosis, which has a major
adverse effect upon body functions.
02:08
Hypovolemia, low total body blood volume
as would happen with bleeding
or dehydration, can also lead
to decrease in oxygen
delivery and blood to vital organs, which increases
the probability of metabolic acidosis
forming. Some diseases, particularly
kidney disease, also have major
metabolic effects. Because, in the presence
of kidney disease, the ability to buffer
acidosis with bicarbonate, which the kidney
produces, is impaired.