Page 399 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Monitoring Fluid Therapy and Complications of Fluid Therapy 389

TABLE 16-4 Interpretation of CVP Values in Response to a Rapid Infusion of
20 mL/kg Crystalloid or 5 mL/kg Colloid 20[30]
Interpretation of Response Response to Infusion

Euvolemia and normal cardiac function 2-4 cm H 2 O increase from baseline returning to baseline in 15 min
Increased venous blood volume, reduced cardiac An increase in CVP maintained >4cm H 2 O above baseline
compliance, or both
Normal blood volume A slow (15 min) return to baseline
Increased blood volume relative to cardiac performance A prolonged (>30 min) return to baseline
Markedly reduced intravascular volume; requires further Minimal to no increase in CVP
resuscitation
Reduced intravascular volume and accommodation of fluid An increase in CVP with rapid (<5 min) return to baseline
within the intravascular space and subsequent reduction
in vascular tone; requires further resuscitation
Further resuscitation Raise CVP by 2-4 cm H 2 O within first few minutes of bolus therapy.
If falls rapidly to baseline, repeat bolus therapy until CVP 5-10 cm H 2 O
(3-7 mm Hg) requiring 10-15 min to fall; at this point, blood volume
and venous return are optimal relative to cardiac performance.
CVP 7-9 cm H 2 O (10-12 mm Hg) with normal Higher volume may predispose to pulmonary edema; continued fluid
intrapleural and intraabdominal pressures resuscitation probably will not improve cardiac output

However, when the limbs are poorly perfused or the
BOX 16-1 Signs Associated with patient is cold, the oscillometric and Doppler methods
Overhydration are insensitive, and it is difficult to obtain accurate
measurements, especially in small animals. In my experi-
• Shivering ence, the coccygeal artery, with the cuff positioned as far
• Nausea (swallowing and licking lips) proximal as possible, tends to be more reliable in this
• Vomiting (may be early or late) instance. The MAP is dependent on CO and systemic vas-
• Restlessness cular resistance (SVR), according to the equation MAP ¼
• Polyuria (patient dependent) CO SVR. Therefore adequate MAP does not necessar-
• Serous nasal discharge ily indicate adequate CO if SVR is increased as may occur
• Tachypnea (early or late) in a compensatory sympathetic response. During acute
• Cough (late)
• Chemosis (late) blood loss, especially in otherwise young healthy animals,
• Dyspnea (late) the compensatory response can be quite dramatic and
• Diarrhea (late) result in nearly normal or normal MAP. If resuscitation
• Ascites (late) is based on normal MAP or SBP alone, inadequate resus-
• Exophthalmos (late) citation with continued poor perfusion likely will occur
• Depressed mentation (late) until the patient decompensates. However, if normal
• Tachycardia (followed by bradycardia when severely MAP or SBP is accompanied by a physical examination
overloaded) (see Physical Findings section) that indicates the presence
• Subcutaneous edema (especially hock joint and
of a sympathetic response, the clinician will be aware of
intermandibular space) (late)
the requirement for additional resuscitation or analgesics
• Pulmonary crackles and edema (late)
(Table 16-3). In this setting, it is difficult to know how
much blood has been lost and the contribution of pain
and anxiety. Pain, anxiety, and hypothermia also contrib-
ute to the sympathetic response, and the findings
ARTERIAL BLOOD PRESSURE
observed may be more a result of these factors than of
Although systemic blood pressure is not an absolute mea- fluid and blood loss. In this setting, intravascular volume
sure of volume, it is frequently monitored during periods loss may be overestimated, resulting in excessive fluid
of bolus fluid administration when managing shock. administration. Therefore fluid requirements and moni-
When extensive monitoring is required, direct arterial toring progress should be assessed based on several
pressure measurements should be obtained. However, factors in addition to pressure measurements. These
on presentation, it may not be possible to successfully per- considerations include a relatively pain-free patient and
form arterial catheterization, and pressures may be an improvement in physical findings (see Physical
obtained with oscillometric or Doppler monitors. Findings section).