VII. Induction
A. The trick is to balance the needs for
intubation with the later consideration of lack
of need for anesthesia. To balance the drop in
blood pressure/need for volume and the desire to
not give a lot of fluids to minimize brain volume.
1. The frontline drugs for the control of
blood presure are phenylepherine for
hypotension and trimethopan, which may in
some cases be preferable to nitroprusside, for
hypertension.
a. The dose of trimethaphan for acutely
lowering the bp is 1cc of a 1mg/ml
mixture.
b. Phenylephrine is often delivered as an
infusion using only a minidripper
B. There are three basic induction techniques. The
first one is the standard induction for tumors
where ICP is the driving concern. The second
is the standard sequence for aneurysms where
hypertensive response is the main concern. The
third is for full stomach patients.
1. Technique 1: Vecuronium 1mg - a little pentothal -
hyperventilate - a lot of vecuronium - a lot of
fentanyl (divided doses) - maybe isoflurane (forane)
- maybe more pentothal - consider adjuncts (see # 6
below) - intubate.
2. Technique 2: Vecuronium 1mg - a lot of fentanyl
(divided doses) - encourge the patient to
breath - a little pentothal - normoventilate -
a lot of vecuronium - maybe Forane - maybe more
pentothal - make very sure there is no hypertensive
response - consider adjuncts (see #6) - intubate.
a. A steadily rising BP with this
technique prior to the pentothal may
mean that CO2 is rising. Even nipride
may not work well under these
conditions. The ICP may be rising to
dangerous levels. Its time for
pentothal to be given.
3. Technique 3: A rapid sequence intubation holding
cricoid pressure from the time the pt. starts
to get sleepy until the ETT position is confirmed
and the cuff is inflated. For rapid onset neuro-
muscular paralysis, use vecuronium 2 mg/kg. For
adequate anesthetic depth use a hefty dose of
pentothal. Carefully ventillate through cricoid
pressure (less than 15 cm H2O to prevent gastric
inflation). You should have good intubating
conditions within 2-3 minutes. Some people try
to sneak in some fentanyl to time its peak effects
(at about 5 minutes) to coincide with the intubation,
although not used in a pure technique due to concern
of depression of airway reflexs before the airway
can be properly controlled. Consideration of the
patient's fluid and hemodynamic status is important
lest a sudden bolus of too much anesthesia plummet
the patient into a hypotensive death.
4. These are, of course, oversimplifications. Some
patients undergoing surgery for aneurysm can have
intracranial hypertension as well.
5. The fentanyl dose for induction is usually
on the order of 7mcg/kg. By the time
surgery starts, the total dose should be
about 10mcg/kg. The vecuronium dose is
about 14mg. It is better to give a lot of
vecuronium rather than just 10mg.
a. These doses are modified by the
response of the blood pressure.
b. If the blood pressure holds constant
despite the pentothal and some of the
fentanyl, then the Forane can be
started.
6. Adjuncts to intubation include IV lidocaine
(1.5mg/kg 3 minutes prior to intubation),
esmolol (0.5-1.0 mg/kg 1-2 min prior to
intubation), and lidocaine laryngotracheal
anesthesia (LTA). The LTA is valuable for
seeing just how deep the patient is prior to
actual intubation. The patients may
sometimes respond to medications with an
apparent low blood pressure without
actually being in a deep plane of
anesthesia. Intubation then results in a
hypertensive response.
7. Etomidate is often substituted for the
initial dose of pentothal, especially in
hypovolemic patients. The idea is to
get the patient asleep without causing
hypotension. You don't want to have the
patient become hypotensive prior to the
full onset of the neuromuscular blockade,
because this will cause the patient to
buck.
C. Draw up 20cc of fentanyl into a 20cc syringe
for induction. The average patient will need
1 to 2 micrograms per kilogram for induction.
This syringe can then be attached to an infusion
pump. The usual dose for a fentanyl is 1 to 2
micrograms per kilogram per hour.
D. When inducing with a small amount of pentothal,
if you find that you can't ventilate the
patient, your options are:
1. give more pentothal.
2. to place an oral airway. If the patient
pushes the airway out with his tongue,
then you probably need more pentothal.
3. If the oral airway and more pentothal
doesn't work, then consider a small amount
of sux (40mg). This will wear off about
the same time as the pentothal. A
milligram of vecuronium should have been
given earlier to prevent fasciculations.
4. Treating head pin hypertension with
pentothal can wipe out evoked potentials.
In brain cases, this is not a problem. For
spine cases, it is a problem. Wake up
tests have been necessitated by pentothal
in this setting. Suspicion is cast on the
intubation as having caused C-spine
injury. Using monitoring to guide position
changes of the patient is impossible. Use
lidocaine in the scalp.
E. Blood pressure goals
1. After intubation, 50% N2O is usually all
that is required if the fentanyl dose has
been adequate. Young patients on phenytoin
(dilantin) or carbamazepine (tegretol) may
be an exception to this.
2. A labile blood pressure in a known
hypertensive patient can be a sign of
relative hypovolemia. This is best treated
with 5% Albumin.
3. A Neo infusion may be necessary for blood
pressure support. Before using this
modality, make sure that the volume status
is adequate.
4. Severe drops in the blood presure can also
cause Brain Protection
Positioning