does not stimulate more breathing.
So how do we take care of these changes?
We can assist the patient's breathing by simply supplying
more ventilation through a bag and mask, or through
intubating the patient and using a ventilator. And we can
increase the minute ventilation very easily through that
process. We can allow the patient
to breathe spontaneously, with a reduced
minute ventilation and allow the CO2
to rise somewhat. This is generally not
a problem, at least in relatively healthy people,
and for short, relatively short periods of time.
We try to avoid this in older people or people
who have cardiovascular problems, which
may be unstable. Because
a rising CO2 in that situation
may cause instability. Under very unusual
circumstances, the anesthesiologist
may give a respiratory stimulant. But I can say that,
in the nearly 40 years I've been in practice,
I've never done this. And in fact I fear it,
because when you do use respiratory
stimulants, there's a high probability of increasing
cardiac oxygen demand and also it can lead
to seizures, and other unexplained
and unexpected events. You must carefully
monitor the patient's expired carbon dioxide levels
and adjust ventilation to maintain a tolerated
level of carbon dioxide. And this
is basically what we all do.
So this slide is to try to indicate to you
the different effects the drugs have upon
the carbon dioxide stimulation of breathing at
the respiratory center. The first line shows
what happens if there is slight increase
in arterial CO2, in a normal person
who's awake. You can see that, even
a very minor change in PaCO2,
will result in a marked increase in minute
ventilation as we try to blow off
the CO2 and improve breathing levels.
With opiates, we tend to push this curve to the right,
so there continues to be a response
to increasing CO2, but the response
is late and slow. When we add
inhalational agents, we further depress
the response, not only shifting it further
to the right, but decreasing the slope as well,
so that there is delay in response
to rising CO2, and an inadequate
response to a rising CO2.
So, should we ventilate or should we let
the patient breath spontaneously?