Page 408 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

398 FLUID THERAPY

of varying degree but without known brain injury, this a MAP of 40 mm Hg and allowing hemostasis and clot
finding suggests clinically important blood loss and shock. formation with a gradual increase in MAP over several
However, if the patient still is alert, the physical findings hours, survival was significantly increased when compared
may be the result of a sympathetic response caused by pain with immediate resuscitation to a MAP of 80 mm Hg. 7
and fright and not necessarily associated with blood loss. (The consequences of a MAP of <60 mm Hg for a few
If the initial clinical response, in the latter case, is to imme- hours have not been reported in cats and dogs in the clin-
diately institute aggressive fluid therapy to treat presumed ical setting). Although a clot is formed immediately, it
shock, one must consider the potential role ofthe neuroen- tends to be soft and “jelly-like” and inadequate to main-
docrine response in producing these clinical signs with or tain vascular integrity at high pressures. Allowing a little
withoutbloodloss.Asanexamplerelatingbloodlosstoclin- time for the clot to become a more rigid hemostatic plug
icalsigns,a30-kgblooddonornormallycandonate450 mL facilitates hemostasis. 75 Clinical trials in human patients
blood (i.e., 20% of blood volume) without obvious clinical are underway to further investigate this strategy. A recent
signs. However, it is prudent to consider that a traumatized review found no evidence to suggest that prehospital
patient or one with a coagulopathy is bleedingand consider intravenous fluid resuscitation was beneficial and found
all potential sites of ongoing hemorrhage. If hemorrhage is some evidence that it may be harmful. 14 However, this
present, one must determine its severity based on clinical evidence was not conclusive. A UK Consensus Statement
signs, physical examination findings, and serial monitoring suggests a more cautious approach to fluid management
of physiologic and laboratory test results. Crystalloids, than previously advocated and concludes that further
colloids,orbloodproductsshouldbeadministeredatcalcu- research is required on hypotensive (i.e., cautious) resus-
lated rates based on clinical signs, physical examination citation versus delayed or no fluid replacement, especially
14
findings, and laboratory data. Immediate compression of in those with blunt trauma. In my experience, a more
an area of hemorrhage should be performed. When com- cautious approach to resuscitation in blunt abdominal
pressionisnot feasible (i.e., withinthe abdomenor thorax), trauma patients with blood pressure correction to a
a careful and skilled approach to volume resuscitation must MAP of 65 mm Hg, systolic pressure of approximately
be conducted. Trauma patients also may have pulmonary 95-100 mm Hg, with resulting physiologic parameters
contusions. Aggressive fluid therapy in these patients may of decreased HR, decreased RR, and improvement in
cause pulmonary edema, and pulmonary status must be MM color and CRT, and urine produced at 0.5 mL/
evaluated and monitored. If pulmonary contusions are kg/hour has proved successful. However, when physio-
noted,judiciousfluidadministrationtoadequateendpoints logic parameters do not improve, surgical exploration is
should be carried out. It should not be assumed that these warranted. Unnecessary aggressive fluid therapy in a
patients are necessarily hypovolemic. On many occasions, slightly hypotensive or normotensive animal before ade-
intravenous fluid therapy is not required, and the need for quate clot formation could increase blood pressure and
fluid therapy must be assessed on an individual basis. disrupt a clot on a lacerated vein or on a splenic or hepatic
fracture. Minimum resuscitation to that required to
Noncompressible Hemorrhage afford adequate perfusion until such time as the hemor-
Laboratory studies performed in the 1950s and 1960s set rhage is controlled makes more sense clinically. Volume
guidelines for the standard approach to resuscitation of resuscitation should be aggressive when the patient’s con-
patients with hypotensive hemorrhagic shock 84 and dition is life threatening. These patients are easily
focused on early, aggressive administration of crystalloid identified, and rapid resuscitation to an adequate hemo-
solutions and blood products. The goal was to restore dynamic state (MAP, approximately 65 mm Hg; systolic,
intravascular volume and vital signs toward normal as approximately 90 to 95 mm Hg) is warranted until hem-
quickly as possible regardless of the site of hemorrhage. orrhage is controlled surgically or spontaneously stops.
However, these guidelines have come into question. Early With blood volume loss of 30% or more, transfusion of
laboratory studies used controlled hemorrhage models, whole blood, packed cells, and plasma or colloids is
whereas hemorrhage occurring in the clinical setting as required in addition to crystalloids. Many abdominal
a result of blunt or penetrating trauma is uncontrolled trauma patients can be managed this way if blood
until definitive therapy controls bleeding. More recent products are readily available. However, surgical interven-
hemorrhage models have demonstrated that aggressive tion may be necessary when resuscitative efforts are not
fluid resuscitation may be harmful and may result in successful. The clinician must remember that abdomino-
increased hemorrhage and mortality. Using splenic injury centesis will be negative if hemorrhage into the retroperi-
models, aggressive fluid therapy significantly increased toneal space has occurred. Conversely, blood loss into the
hemorrhage and mortality. 42,78 Availability of blood pericardial space resulting in tamponade requires aggres-
products in veterinary practice is limited, and ongoing sive fluid therapy while preparing the patient for
hemorrhage will be fatal. Other studies demonstrated pericardiocentesis. In the acute setting, only very small
that achieving a MAP of 40 to 60 mm Hg improved sur- volumes of blood within the pericardial space are required
vival compared with a MAP of 80 mm Hg. 79 By achieving to cause tamponade.