Page 400 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

390 FLUID THERAPY

CARDIAC OUTPUT MEASUREMENTS the blood loss. Administration of these opioids com-
mencing with a low-dose and careful titration to effect
Several techniques are available to measure CO, but most 47
are technically challenging. The lithium dilution cardiac does not compromise the cardiovascular system and
will allow better assessment of the patient because the
output (LiDCO) and PulseCO (both from LiDCO,
London) have been investigated for use in humans, 39 effect of the sympathetic response to pain will be
and in large 45 and small animals. 55 Briefly, isotonic lith- eliminated from consideration. It is advised, however,
that depressed animals receive fluid therapy for a few
ium chloride is injected as a bolus via a central or periph-
minutes before opioid administration until mentation is
eral vein, and a concentration-time curve is generated by
improved. Depression (not associated with head trauma)
an arterial ion-selective electrode attached to an arterial
manometer system. The CO is calculated from the lith- indicates poor cerebral perfusion due to fluid or blood
ium dose and the area under the concentration time curve loss usually greater than 30% of the intravascular volume,
before recirculation. The PulseCO hemodynamic moni- and a potential slight reduction in SABP due to the opioid
tor was developed for use in conjunction with the LiDCO may compromise cerebral perfusion pressure further.
Hypothermia may be a result of poor perfusion caused
to give a beat-by-beat estimate of CO that is derived from
by low circulating volume or by a primary cause that
analysis of the arterial trace. Although these systems have
may interfere with achieving resuscitation goals; clinical
limitations, their use in veterinary research indicates
impression suggests this may be especially so in cats.
potential value in clinical practice in anesthetized animals
Marked hypothermia results in bradycardia and decreased
or nonmoving critically ill animals. Movement, flexion, 62
CO ; therefore, warming during resuscitation is neces-
and extension of the catheterized limb contribute to
sary. Again, opioid analgesic administration should be
erroneous results (personal observations). A great advan-
administered once the patient’s mentation improves.
tage of this system is that a central catheter is not
required, and continuous CO can be measured. Measur- Increased RR also may be associated with pulmonary
ing CO during fluid resuscitation has definite advantages injury, disease, or fluid overload. An improvement in atti-
over determination of SABP because the former is a tude (i.e., improved cerebral perfusion) should be noted
with adequate fluid resuscitation. The CRT and MM
more accurate measure of volume. Predetermined goals
color, pulse pressure, and urine production also should
for CO, stroke volume, and oxygen delivery can be set
improve. Palpation of the bladder and monitoring urine
and monitored with this system. For critically ill patients
produced by assessing bladder size can be useful when
being mechanically ventilated, intermittent cardiac
urinary bladder catheterization cannot be performed.
output measurements can be obtained by the use of a par-
tial CO 2 rebreathing noninvasive system (NICO, PACKED CELL VOLUME AND TOTAL
15
Novametrix Medical Systems Inc, Wallingford, Conn.). SOLIDS (OR PROTEIN)
This system requires body weight, Spo 2 , Fio 2 , Pao 2 , and
Paco 2 , all of which are available in ventilated patients, It is essential to obtain baseline packed cell volume (PCV)
and the CO 2 sensor measurement obtained from and total solids (TS) or total protein concentration on
expired CO 2 at the endotracheal tube and ventilation admission. During a traumatic event, sympathetic stimu-
circuit. 21 lation results in splenic contraction, especially in the dog,
increasing the PCV and potentially giving the impression
that hemorrhage has not occurred. A normal PCV may be
PHYSICAL FINDINGS
observed after trauma even with clinically relevant blood
As previously mentioned, SABP may be normal in loss. The TS in this setting will be lower than normal (6.0
patients with hypovolemia caused by blood loss, and to 8.0 g/dL), confirming blood loss. Monitoring these
therefore the physical examination must be considered tests as frequently as every 15 minutes during resuscita-
in conjunction with SABP when assessing adequate resus- tion may be necessary to evaluate ongoing blood loss
citation. Cool limbs, rectal temperature below normal, and the requirement for administration of red blood cells
increased HR and RR, paler than normal MM color, (PRBCs), whole blood, or hemoglobin-based oxygen-
prolonged CRT, and depressed mentation all indicate carrying solutions (HBOCs). A definitive recommenda-
poor perfusion, regardless of blood pressure readings. tion regarding transfusion of blood products has not been
If SABP is normal and the patient is free of pain but established in veterinary patients, but the use of PRBCs,
HR and RR are high and MMs still pale, a compensated whole blood, or HBOCs is suggested when the PCV
stage of shock may exist, and further resuscitation is decreases to less than 25% in the dog or less than 20%
required. When assessing response to fluid therapy in in the cat, especially when ongoing resuscitation is
animals with pain, an opioid analgesic (preferably required. The use of HBOCs may be an effective adjunct
hydromorphone or fentanyl) should be administered to to limited resuscitation from hemorrhagic shock 51 while
control pain. The sympathetic response associated with reducing complications of aggressive fluid therapy, How-
pain and anxiety will be reduced, allowing the clinician ever, complications associated with these solutions have
to assess cardiovascular dynamics solely associated with been reported in cats. 20