Page 388 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

378 FLUID THERAPY

patient’s end of the administration tubing to the catheter continuously drive fluid at a constant rate. Cassette-style
bandage helps prevent disconnection at the catheter. Use pumps require an in-line fluid path pump mechanism
of locking Luer connections (as opposed to slip-Luer (cassette) as an integral component of an intravenous
connections) is the best way to reduce the likelihood of fluid administration set that works only with a specific
an accidental disconnection. Those junctions may also model(s) of pump. When fluids need to be given at a very
be bridged with waterproof white tape to further reduce constant rate from moment to moment, peristaltic pumps
that risk. are generally better than cassette designs, which alternate
between pulling fluid from the bag and pushing it to the
FLUID ADMINISTRATION patient. Peristaltic pumps are less accurate over time, and
AND MONITORING their accuracy also depends on using an approved intrave-
nous tubing set and changing the tubing position within
The many different types of available fluid administration the pump at regular intervals. Metered cassette pumps are
sets and connection devices offer considerable flexibility volumetric and are used to deliver prescribed volumes of
in intravenous fluid administration. Multiple port flow fluid accurately over longer units of time (many minutes
connectors allow simultaneous infusion of compatible to hours). The rate-constant peristaltic type of fluid pump
solutions through a single catheter. In-line volume con- (or a screw mechanism syringe pump for small volumes) is
trol sets (Buretrol, Baxter Healthcare) permit accurate useful for infusions of fluid with drug additives that
delivery of small volumes of fluids. A variety of different require a constant flow rate (e.g., a consistent minute-
tubing lengths, diameters, and connections allow many to-minute dose of norepinephrine), whereas the volu-
different configurations and combinations of fluids to metric pumps are preferred for accurate administration
be delivered to a single catheter. Fluid administration sets of prescribed volumes of fluid over longer units of time
are available from several manufacturers. The two basic (e.g., hour-to-hour). Pumps marketed specifically for
types are vented and nonvented; these are available in sev- use in animals are available (e.g., Vet/IV, Heska, Fort
eral lengths. All administration sets use an in-line drip Collins, Colo.).
chamber to estimate the rate of flow. Depending on All pumps deliver fluid under pressure. This pressure
can overcome resistance to flow from viscous solutions,
the brand, the drip sizes are calibrated so that 1 mL ¼
10, 15, 20, or 60 drops. Drops per minute are calculated filters, and partially occluded veins. It also increases the
from the formula: risk to the patient in the case of extravasation because
fluid is pumped into the perivascular tissues under pres-
sure. To prevent this, most modern pumps are equipped
Drops per minute ¼ total infusion volume
with pressure monitoring circuitry and some can be
drops=mL=Total infusion time ð minÞ
adjusted to produce an occlusion alarm at preset values.
Intravenous solution containers should be numbered
For example, to administer 2000 mL over 24 hours using consecutively and clearly labeled with the date, time,
a basic solution set (10 drops ¼ 1mL): and patient’s name. Any additives should be clearly
identified as to type, quantity added, date and time
ð2000 mL 10 drops=mLÞ=1440 minutes added, and by whom. Do not use an indelible marker
¼ 14 drops= min to write directly on the bag because the solvents in the
ink may leach through the plastic into the solution inside.
The rate of flow is regulated by tightening or releasing the When not using a volumetric pump that tracks cumula-
intravenous tubing clamp while watching and counting tive fluid administered, a calibrated timing label should
the drip rate. Fluid administration rate may also be con- be applied to the container and is used to monitor and
trolled by in-line flow regulators (Stat 2 Pumpette, verify the rate of flow over time.
ConMed Corp., Utica, N.Y.) or more accurately by elec- All patients receiving intravenous fluid therapy should
tronic fluid pumps or rate controllers. In-line flow be weighed at least daily. Abnormal fluid losses through
regulators are calibrated tubing clamps. Accurate use of the urinary tract, nasogastric suction, or cavity drainage
these devices depends on unimpeded flow through short should be measured and replaced with equal volumes
catheters 20 gauge or larger and on maintaining a mini- of appropriate intravenous replacement fluids at frequent
mum height of about 75 cm (30 inches) between the drip intervals. Fluid losses in animals with vomiting or diar-
chamber and the level of the heart. rhea may be monitored by knowing the average dry
Fluid pumps are available from many manufacturers. weight of cage paper used in the clinic and subtracting
All are either peristaltic or metered cassette in design this from the weight of soiled cage papers. The difference
(Figure 15-10). Peristaltic pumps typically use standard (in grams) is converted to milliliters of water and replaced
intravenous administration sets, although some devices with appropriate intravenous replacement fluid. Monitor-
are restricted to certain brands of tubing. This pump ing of the PCV and total plasma solids is an inaccurate
design uses a continuous peristalsis mechanism to (PCV) and insensitive (total plasma solids) indicator of