So how about the cardiovascular
system? Does general anesthesia have an impact
upon cardiac function? How about the anesthetic vapours?
Some anesthetic vapours can reduce
the contractility of the heart and reduce cardiac
output. These tended to be the older vapours
such as Halothane, but modern vapours such as
Isoflurane, Desflurane, and Sevoflurane have little
or no effect upon cardiac contractility.
They do unfortunately, or fortunately
depending on the situation, have an impact
upon peripheral resistance, which is
the resistance against which
the heart has to work when it contracts.
And low peripheral resistance may result
in low blood pressure, but it may also allow the heart
to contract more fully. So there's a balance all the time,
trying to maintain it just right. If you reduce blood flow
too much, you can reduce it to the brain,
the kidney, and the heart itself. Obviously,
not a good thing. Opiates and opioids
have little of direct effect upon the heart, other than
they slow heart rate, which in most cases is
a very positive situation. They also
have a moderate effect on lowering blood
pressure. The changes are moderate,
and they have very few side effects.
Induction drugs, unfortunately,
are much more problematic. The most popular
induction drugs are Thiopentone and Propofol.
Both of these have profound effects on reducing
cardiac contractility. In addition, Propofol
causes marked reduction in peripheral
resistance, thus potentiating hypotension,
and sometimes leading to reduced
blood flow to vital organs,
including the heart.