So, should we ventilate or should we let
the patient breath spontaneously?
The advantages of mechanical ventilation is,
it's very easy to control the minute ventilation. With mechanical
ventilation you just adjust the tidal volume
or adjust the rate. Very easy to do.
But then, on the other hand, spontaneous ventilation requires
no instrumentation of the patient's airway, you don't have
to intubate them. Spontaneous ventilation
allows the patient to set their own ventilatory
pattern, which is often perfectly Ok.
But, in the presence of many drugs
or other disease processes that may be going on,
it's not always the best, the best model to follow.
In either case, constant monitoring
of breathing and expired CO2,
plus the patient's oxygen saturation
is necessary with all general anesthesia.
So that, mechanical versus spontaneous ventilation
is usually determined by the expected
length of the surgery, the patient's position
during the surgery, and the need
or lack of need for muscle relaxation
during the surgery. Some of the cons
of managing ventilation with a ventilator,
it's very easy to over ventilate the patient
and this can cause a decrease in CO2 in the blood,
which causes a condition known as
respiratory alkalosis. This again
is generally not terribly important,
but it's not something you want to allow
to exist for any extended period of time.
In addition, if you're going to mechanically ventilate
a patient, you must instrument their airway.
And there are always risks that you won't be able to do the instrumentation,
won't be able to get the endotracheal tube in,
or that in your struggle to get it in, you may damage
the airway and cause the patient not only difficulties
during the surgery, but difficulty subsequent to surgery. Spontaneous
ventilation on the other hand is often associated with a rise
in the carbon dioxide and the development of respiratory
acidosis. This is well tolerated at moderate levels
and is well tolerated for short periods
of time, particularly in healthy and younger patients,
but may be a critical mistake in elderly
patients with unstable cardiac disease.
So how about the cardiovascular