There are a number of invasive
monitors that are used
in specific procedures and for high risk patients.
So, invasive monitors are any monitor in which
we have to put a line into the patient in some fashion,
and then connect to one of these
colored transducers outside the patient.
And each of these transducers has to be calibrated
at the time we connect it to the patient.
And this allows us to measure the actual pressure
the patient is generating. This can be blood pressure,
this is a very common use of this.
We just place some freezing in the wrist and we pass
a catheter into the radial artery, and we connect the radial
artery to a transducer, and we can measure the actual
blood pressure every time the patient's heart beats. Plus,
we can take blood samples without sticking more needles
in the patient. But there are a lot of other pressures we also
measure, including cerebral, excuse me,
central venous pressure, which is the pressure
of the venous blood within the body. We put
a catheter through the external, internal jugular
vein, usually into the superior vena cava or even
into the right atrium, and we can measure
pressures there. We can pass a catheter down through
the heart and through the tricuspid valve, out
into the pulmonary circulation and measure
pressures in the lung. This kind
of device can also measure cardiac output,
can measure mixed venous saturation,
which is an indication of oxygen used
by the patient. Very sophisticated,
very, very impressive, very helpful monitors.
And patients who have intracranial hemorrhages
or trauma to their head, and have bleeding into their,
into their skull, can have monitors placed that measure
their intracranial pressure. So, that kind of monitor
is placed by a neurosurgeon, but we're the ones
who hook it up, and we often monitor it.
In certain cardiac cases, or in other cases where
we're concerned about the patient's
overall hemodynamic stability, we can pass
a trans-esophageal echocardiogram
through the esophagus of the patient. And we can
do ultrasounds from the esophagus, through the heart
anteriorly. And we can measure cardiac output.
We can look at the actual contraction
of the ventricle. And we can look
at the function of the various cardiac
valves. This is extremely valuable in cardiac surgery,
but can also be used in other high risk forms
of surgery where the patient may be hemodynamically
unstable. Sensory and motor
evoked potentials are used in spinal cord surgery
to make sure that nervous connections
between the spine and the lower limbs don't get damaged
during the surgery. Electroencephalogram
is sometimes used in surgery.
In one of the hospitals I work in, we use it
all the time when we're doing carotid endarterectomy. In other words,
cleaning out the carotid artery. We use an EEG to make sure
that the patient's not having a decrease
in the cerebral circulation, which
might be a precursor to a stroke.
In addition, there are new cerebral
monitors. A very well known one in the United States
is the BIS monitor. It's not widely
used elsewhere, because it's actually never been shown to be
very useful. But the BIS monitor is widely used in the United
States and is supposed to be an indicator
of depth of anesthesia, and is supposed
to help the anesthesiologist prevent
recall during anesthesia. Cerebral
oximetry monitoring actually allows us to look
at the blood going into the brain, and determine
its oxygen saturation. We can do fetal heart monitoring
through the abdominal wall of the mother
towards birth. And we do uterine
contraction monitoring, particularly
when we're doing emergency Cesarean sections
on patients who are in labour.