Page 396 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 16

Monitoring Fluid Therapy and

Complications of Fluid Therapy

Karol A. Mathews

Intravenous administration of fluids to veterinary patients administration to young otherwise healthy individuals.
is very common, and placement of an intravenous cathe- Physical examination should identify the compartment
ter is one of the most common invasive procedures most affected by the fluid deficit: intravascular volume
performed in veterinary practice. Monitoring the depletion with perfusion deficit such as occurs in acute
patient’s response to fluid therapy and considering the hemorrhage, tissue water loss (dehydration) with normal
potential for complications arising from these products perfusion, or depletion of both compartments (perfusion
and the presence of a vascular access catheter are funda- deficits and dehydration) indicating a large deficit of total
mental features of treatment. body water.
Intravenous fluids are “drugs,” and fluid therapy is a Intravascular volume (perfusion) deficits are managed
“prescription,” and should be considered as such to avoid and monitored differently than are tissue water deficits.
potential complications resulting from inappropriate Unless severe total body water loss is present, the
selection, underdosing, and overdosing. 59 Selection of dehydrated animal may still have adequate tissue perfu-
fluid type and volume is a major component of the thera- sion as indicated by a heart rate within normal range, a
peutic plan and should include careful assessment of tis- normal digital pulse and capillary refill time, normal
sue and intravascular losses, acid-base and electrolyte acid-base status, normal blood lactate concentration, ade-
status, age and species of the animal, nature of illness or quate urine production and appropriate concentrating
injury, acute or chronic history, hematocrit and serum ability, and normal renal and hepatic function (unless pri-
albumin concentration, coagulation status, cardiorespira- mary problems are known to exist with these organs).
tory function, and cost. The animal’s illness or injury is a However, hypoxia resulting from anemia may contribute
dynamic event, and selection of fluid type and volume to end-organ dysfunction or injury despite adequate
may change according to the patient’s response to fluid perfusion.
therapy and with improvement or deterioration of the A thorough physical examination must accompany
underlying problem. Therefore constant monitoring to monitoring using the various technical devices available.
achieve desired endpoints is required. This chapter will Although monitoring central venous pressure (CVP),
introduce the various monitoring techniques frequently systemic arterial blood pressure (SABP), pulmonary cap-
used in veterinary practice, the potential for misinterpre- illary wedge pressure (PCWP), and cardiac output (CO)
tation, and complications associated with fluid therapy provides very useful (and sometimes essential) informa-
and catheters. tion, monitoring the patient by physical examination
The patient’s history must be considered when and biochemical evaluation of organ function also are
formulating a fluid therapy plan. Rapid loss of intravascu- very important, with improvement of these being the
lar fluid such as occurs in sepsis associated with third- ultimate endpoints for achieving success with fluid ther-
space sequestration requires judicious fluid selection apy. As with the various monitoring devices, standard
and rapid replacement, whereas chronic loss in a patient guidelines for assessing fluid deficits and overload by
with adequate perfusion can be afforded a less aggressive physical examination exist. However, there are many
approach to prevent excessive diuresis and iatrogenic elec- caveats, and interpretation is not necessarily clear-cut
trolyte disturbances. The history must include the nor can it be assumed that absolute numbers or specific
patient’s age and previously diagnosed organ dysfunc- findings are related to fluid volume alone (Tables 16-1
tion. Fluid administration to geriatric patients or those through 16-3). Each patient must be assessed individually
with heart disease must be more cautious than based on history, physical findings, and laboratory data.

386