Biomedical Engineering Reference
In-Depth Information
apple sauce, bread and butter, yogurt, fruit
juice, and
reflex. Gentle, subtle adjustments in the position of the tube
within the pharynx facilitate proper advancement into the
esophagus. Inadvertent placement of the tube into
the trachea frequently elicits a cough response from the
subject. Once the nasogastric tube is in the esophagus, it is
advanced to the previously created mark.
To verify correct placement, a large syringe filled with
air is attached to the nasogastric tube; the air is then
expelled through the tube by firm depression of the plunger.
The resultant sound of air rushing into the stomach can be
auscultated with a stethoscope. Two easily accomplished
methods can be used to help rule out improper tube
placement. If a cough is elicited after injecting 5 ml of
sterile water through the tube, there is high probability that
the tube is in the trachea. Another means is to dip the
proximal end of the tube into water to form a meniscus.
Respiratory movement of the meniscus suggests that the
tube has been inserted into the trachea. Although not
always practical, the most reliable method to ensure proper
placement is via radiographic assessment.
marshmallows.
Oral gavage can be used when dosing with smaller
quantities of liquid drugs or drug preparations. Following
restraint of the conscious nonhuman primate, the loaded
syringe is directed into the mouth such that the syringe tip is
located slightly above and distal to the highest elevation of
the tongue. The compound can then be slowly administered
while allowing the subject to swallow. Nonhuman primates
may also be trained to accept oral delivery of a drug
(
Crouthamel and Sackett, 2004
). A tasty liquid is given via
a syringe. Upon finishing the complete dose, a positive
reward is given. The tasty liquid is then gradually replaced
with the drug carrier and then with drug compound. The
subject always receives positive reinforcement for finishing
the contents of the syringe.
Nasogastric Tube
Use of a nasogastric tube can be practical when the
nonhuman primate is small enough to be manually
restrained by an experienced primate technician
(
Figure 13.2
). Squirrel monkeys require a 5 French infant
feeding tube (
Abee, 1985
). Small macaque species
commonly require an 8 French pediatric nasogastric tube. It
is first necessary to determine the length of tube to be
passed. This is reliably accomplished by placing the distal
end of the tube at the xyphoid then running the tube to the
ear and then the mouth. The tubing is then marked with
permanent ink or tape at a point near the entrance of the
mouth. To pass the tube, use one hand to restrain the
nonhuman primate's head and the other to gently pass
the lubricated tube through the external nares medially,
then carefully on through the nasal turbinate (
Figure 13.4
).
As the tip of the nasogastric tube passes into the pharynx,
the operator should check for the animal's swallowing
Orogastric Tube
Orogastric intubation of a conscious animal involves the
use of a speculum in order to prevent the animal from
chewing the tube. The speculum is not required in an
anesthetized animal. The diameter of the orogastric tube
varies from 5 French in squirrel monkeys to 18 French for
larger monkeys and apes (
Abee, 1985
). The length of the
tube to be passed is measured and marked in the same
manner as described for nasogastric intubation (xyphoid,
ear, mouth). The jaws are allowed to close down over the
speculum after it has been positioned in the mouth. After
passing the lubricated tubing through the speculum, the
tube is advanced slowly through the pharynx, permitting
the animal to swallow. Once inside the esophagus, the tube
is progressed to the previously predetermined, marked
length. Correct placement of the orogastric tube in the
stomach is verified as for nasogastric tube placement.
Fecal Collection
Fresh fecal samples may be obtained from a clean cage
floor collection pan when nonhuman primates are housed in
individual cages. This method is usually adequate for
parasitic examination. Group housed primates necessarily
complicate the identification of the individual source of the
fecal sample.
Fecal loops may be used for in situ collection from
animals that are either anesthetized or physically
restrained. Fecal loops come in different sizes for large and
small animals. Lubricate the loop before gently inserting
into the rectum. Care must be taken in order to avoid
FIGURE 13.4
Positioning of a nonhuman primate for nasogastric
tube insertion.
