Page 393 - Clinical Small Animal Internal Medicine

36 Fluid Therapy 361

it also provides oxygen‐carrying capacity that may be ratory parameters to quantify dehydration. It is impor-
VetBooks.ir crucial in the anemic, hypoperfused patient. tant to grasp just how limited these parameters really
are. It has been shown that an animal can range from 5%
One concern that has been visited many times over the
years is the risk of aggressive volume resuscitation in
patients that are actively bleeding. Concern centers on to 16% dehydrated based on body weight and yet have a
normal skin turgor. This flies in the face of commonly
the disruption of immature clots and the worsening of accepted guidelines where the percentage of dehydration
bleeding. The classic example of this in veterinary medi- is estimated based on the presence or absence of certain
cine is the patient that presents with a hemoabdomen physical parameters. In reality, all of these parameters
due to splenic trauma. The animal is aggressively resus- are flawed to a greater or lesser degree.
citated which results in a short‐term improvement in As skin turgor essentially assesses the interstitium, it
hemodynamic stability (i.e., blood pressure) followed by can be altered not only by the water balance within the
a decline as the clots forming on the traumatized spleen interstitium but also by alterations in the other compo-
are disrupted and active bleeding worsens. nents of the interstitium. For example, in the geriatric or
“Delayed resuscitation” refers to the practice of not cachectic patient, changes in collagen content may alter
administering fluid support to correct hemodynamic the skin turgor so that the animal appears more pro-
instability until definitive control of hemorrhage has foundly dehydrated than it truly is. By contrast, the obese
been achieved. “Hypotensive resuscitation” is the prac- patient may have dehydration but a normal skin turgor.
tice of administering rapid volume expansion to the Skin turgor is also affected by the location at which it is
hemodynamically unstable patient but only resuscitat- assessed, the posture of the animal (standing versus
ing to a mean arterial pressure of around 60 mmHg. supine), age, and body condition.
Here, the goal is to strike a compromise between the Although the use of percentage dehydration based on
need to perfuse vital organs and the desire to avoid sup- physical parameters is crude, it does still provide a
raphysiologic resuscitation that may worsen injuries starting point for selecting an initial fluid rate. Usually
such as pulmonary contusions and abdominal bleeding. changes in skin turgor with normal hemodynamic
Any of the fluids appropriate for rapid volume expan- parameters are consistent with mild dehydration of
sion can be used for hypotensive resuscitation. When about 5–7% body weight. As dehydration becomes
considering the use of either hypotensive or delayed more severe and approaches 10–12% dehydration,
resuscitation, it is important to keep in mind that these hypovolemia may also be evident when perfusion
techniques were designed for human trauma patients parameters are evaluated. This is evidenced by tachy-
with penetrating injuries, where the time from presenta- cardia, poor pulse quality, prolonged capillary refill
tion to definitive treatment rarely exceeds one hour. time, and cool extremities. Another indicator of pro-
There has been limited research in veterinary medicine found dehydration is the presence of sunken eyeballs
to examine their efficacy in small animal patients. If (enophthalmos).
definitive treatment is not possible or will not be pur- If hypoperfusion is present, rapid volume expansion to
sued then delayed or hypotensive resuscitation should stabilize the patient is indicated prior to attempting cor-
not be attempted. rection of interstitial or intracellular fluid deficits. When
“Small‐volume resuscitation,” which is also known as the tissue safety factors of the interstitium are under-
limited‐volume resuscitation, uses resuscitative fluids in stood, it is clear that rapid volume expansion is not effec-
small volumes to achieve moderate increases in hemody- tive for correcting interstitial deficits. This type of deficit
namic stability. In this type of resuscitation, synthetic must be corrected slowly over at least 12–24 hours.
colloids and hypertonic saline take center stage as they When fluids are administered at an aggressive rate in the
allow for expansion of the effective circulating volume in hope of shortening the time needed for correction, the
excess of the administered fluid volume. Again, the goal results are unrewarding. This is due to the characteris-
here is to minimize the deleterious effects seen with tics of the interstitium which oppose rapid expansion.
overaggressive crystalloid resuscitations. Endpoints with Aggressive fluid administration will result in rapid
this style of resuscitation include a mean arterial pres- increases in interstitial hydrostatic pressure as well as
sure of 70 mmHg, a systolic pressure of 90 mmHg, and decreases in interstitial oncotic pressure. This in turn
clinical improvement of perfusion parameters. will increase lymphatic driving pressure and promote
lymphatic flow. The end‐result is the clearance of vol-
ume via the kidneys instead of a more rapid rehydration
Dehydration
of the interstitial space.
The assessment and correction of dehydration remains Commonly assessed laboratory parameters should
one of the more challenging parts of fluid therapy. The provide more insight into fluid balance, but they, too, are
challenge lies in the poor sensitivity of physical and labo- limited. Alterations in hematocrit and total solids have