ANESTHETIC
INDUCTION
1)
GENERAL
a)
Induction and maintenance anesthetic plans should be reviewed by a
staff veterinarian
b)
Regardless of the apparent similarity between anesthetic
candidates, anesthetic agents should not be selected automatically.
i)
Each patient should be considered a unique individual and the
anesthetist must have considered the species, breed, size, age, attitude,
health status, and planned procedure when selecting pre-anesthetic
medications and anesthetic agents
c)
Insure that adequate monitors are present at the site of the
procedure
d)
An anesthetic machine should be carefully examined and moved to the
site of induction
i)
insure adequate anesthetic is present in the vaporizer
ii)
check for any system leaks
iii)
confirm adequate oxygen source
iv)
select circuit hoses
(1)
the circuit hoses should always be significantly larger than
endotracheal tube diameter to minimize system resistance
(2)
pediatric tubes for patients under 20 lbs.
(a)
Some prefer a nonrebreathing system for patients under 15 lbs.
(3)
Standard hoses for patients over 20 lbs.
v)
Select a reservoir bag for circle systems
(1)
Bag size should be 3 to 5 times tidal volume
(a)
Tidal volume is 10 to 15 ml/kg
e)
A reasonable selection of endotracheal tubes should be available at
induction. Make sure all disinfectant residue has been rinsed from the
tubes prior to use. Chlorhexidine will cause significant mucosal
irritation if allowed to contact the airways.
i)
3 tube sizes usually will suffice – the size you expect to use,
one size smaller, and one size larger
(1)
inflate the cuff prior to induction to insure no leaks are present
ii)
Keep in mind that brachycephalic breeds have disproportionately
smaller tracheal diameters than their body size would indicate
(1)
Select the size you expect to use and the next 2 smaller sizes
(2)
this is particularly true for large brachycephalic dogs such as
English Bulldogs
f)
Confirm proper intubation by:
i)
direct visual confirmation if possible
ii)
palpation of one clearly
defined, firm tube in the cervical region
iii)
auscultation of lung sounds bilaterally when bagging patient
iv)
if the animal is draped, manually follow the tube to the laryngeal
opening to confirm proper intubation
g)
1 - 2 drops of lidocaine (0.2 ml max.) can be placed on the
arytenoids to facilitate cat intubation
h)
Because benzocaine(Cetacaineâ)
is capable of producing deleterious methemoglobinemia, its use cannot be
recommended. Lidocaine is the preferred topical laryngeal anesthetic as it
is readily available and very inexpensive.
i)
Only inflate the endotracheal cuff to the point that a seal will
allow bagging at 20 cm of water
i)
excessive cuff pressure can cause serious tracheal damage including
tracheal rupture
(1)
Simply feeling the small reservoir bubble at the cuff valve can be
misleading
ii)
to minimize risk of tracheal trauma, use a
3 cc syringe for cat and small dog cuff inflation and a 6 cc syringe for
medium and larger dog cuff inflation
(1)
Inflate the cuff to low pressure, close the pop-off valve, and
pressurize the system by squeezing the reservoir bag. Add or remove air
from the cuff until you just hear gases leak around the cuff at 15 to 20
cm H2O circuit pressure
j)
An anticholinergic drug dose appropriate for the patient must be on
hand at all times even if already
given as a pre-anesthetic component
k)
A syringe containing saline should be available at all times during
the procedure to flush the catheter after administering medications,
facilitating the medication’s introduction into systemic circulation. It
is common to use heparinized saline for this task but heparin may not be
necessary if the catheter is connected to an active fluid line.
i)
heparinized saline is produced by mixing 1 ml of heparin
(1000 units/ml) with 1 liter 0.9% Saline (or 0.5 ml of heparin in a
500 ml 0.9% saline bag)
(1)
A dated high visibility fluorescent orange label must be used to
identify any medications added to a fluid bag
(2)
Discard heparinized saline bags over 1 week old
(a)
Immediately discard any fluid bags that contain cloudy fluid or
those suspected to be contaminated
ii)
Another option is to coat the inside of the syringe with heparin,
empty the syringe of all excess heparin, then fill the syringe with 0.9%
sterile saline.
(1)
This method reduces the wastage of the method above but may lead to
some variability in heparin content and increase the potential for
contamination of the heparin vial.
l)
The maintenance of a patient’s body temperature is an important
consideration paramount to a successful outcome
i)
The use of an insulating material during patient
clipping/preparation should be considered to minimize body temperature
loss that may occur from contact with a stainless steel surface.
(1)
This is especially critical for small, short haired animals
ii)
During the anesthetic event, the patient should be maintained on a
warm water blanket and covered with a towel when possible
(1)
Warm water blankets are relatively inefficient heat sources
(a)
Placing the patient directly on the pad is recommended
iii)
Warm air patient warmers like the Bair Hugger are a particularly
effective way to support patient body temperature
(1)
The surgical site should be fully draped before the Bair Hugger is
turned on to minimize the contamination risks of the increased regional
airflow
iv)
IV fluids can be warmed at the time of administration by:
(1)
curling up the terminal portion of the IV line and placing it under
the warm water blanket
(2)
utilizing a commercial IV fluid warmer
v)
Bubble wrap is an efficient insulating material
m)
Additional induction agent should be on hand at all times to
accommodate:
i)
Sudden patient arousal due to:
(1)
Surgical stimulation
(2)
Improper endotracheal tube placement or tube slippage during
procedure
ii)
Respiratory distress at extubation requiring patient re-intubation |
