Page 407 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Monitoring Fluid Therapy and Complications of Fluid Therapy 397

reason for the observed signs may be associated with a suffering from severe acute kidney injury. A recent review
vagally mediated baroreceptor reflex secondary to atrial on this topic focuses on the consequences associated with
stretch. Monitoring respiratory rate and effort is simple, fluid overload in critically ill patients, with or without
and a slight but consistent increase can be an early clue to associated acute kidney injury, and discusses the potential
fluid overload and development of pulmonary edema. mechanisms by which acute kidney injury can contribute
A slight but consistent reduction in oxygen saturation to fluid overload and whether fluid overload can also con-
(Spo 2 ) over a few minutes as detected by pulse oximetry tribute to kidney dysfunction. 17
may beanother indicationofpulmonary edema.Confirma-
tion by a reduction in Pao 2 on arterial blood gases may be Effusions
warranted to confirm the Spo 2 readings. As an aside, titra- When edema occurs in tissues, effusion may occur in
tion of oxygen via nasal cannula can be performed using potential spaces (e.g., pleural cavity, pericardial cavity,
pulse oximetry. As the Spo 2 reading consistently hovers peritoneal cavity, joint cavities). The extent to which effu-
around 92% to 95%, this would be the oxygen flow rate to sion occurs will depend on the severity of the fluid over-
administer to avoid potential oxygen toxicity while load and capillary leak. Fluid pressure in these potential
providing adequate oxygenation. Radiographic assessment spaces in the normal state is negative and similar to that
of the pulmonary vasculature can be used to monitor fluid of subcutaneous tissue. The interstitial hydrostatic pres-
administration.Inanimals,thewidthofthepulmonaryvein sure normally is 7to 8 mm Hg in the pleural cavity,
should be less than 1.5 times the width of the pulmonary 3to 5 mm Hg in the joint spaces, and 5to
artery, and fluid overload should be considered if the 6 mm Hg in the pericardial cavity. 22 The abdominal
measured difference exceeds this value. In human patients, cavity is prone to effusion (i.e., ascites). Pleural and peri-
changesinvascularpediclewidthhasproventobeavaluable toneal effusions may be present because of the disease
method for monitoring fluid balance in the intensive care process even before fluids are administered, and both
unit. 52 The radiographic appearance of pulmonary edema, often are present in patients with moderate to severe pan-
increasedlungsoundssuchascrackles,andcyanosisindicate creatitis. Small volumes of fluid in the peritoneal and
a late stage of edema with severe patient compromise. Cap- pleural cavity are difficult to detect on physical examina-
illary permeability is increased during systemic inflamma- tion. Baseline assessment of the chest should be made by
tory conditions, endothelial injury, pneumonia, and auscultation and thoracic radiography, and gentle
pancreatitis, and capillary leak would be expected to occur ballottement and radiography or ultrasonography can
with administration of smaller fluid volumes. Monitoring be used to assess the abdomen. Further monitoring
inaffectedanimalsmustbediligentwithevenslightchanges may be required during fluid therapy, and a change in
beingapotentialwarningsignofpulmonaryedema.Pancre- the type of fluid administered may be required. With
atitisisarelativelycommonproblemincatsanddogsrequir- increasing effusion and decreased COP, a colloid should
ing fluid therapy. In humans, approximately 33% of be considered and cautiously administered.
pancreatitispatientswilldevelopacutelunginjuryandacute As previously mentioned, fluid overload in critical ill-
36
respiratorydistresssyndrome. Thiscomplicationiscaused ness is an area of increasing attention, especially in the
by changes in the pulmonary endothelium associated with pathogenesis of abdominal compartment syndrome with
the systemic inflammatory process, liberation of pancreatic volume overload having an association with adverse clin-
digestive enzymes (especially elastase), and damage by ical outcomes in critically ill patients. 18,82
neutrophils that results in enhanced capillary leak. 13,37 Fluid accumulation can contribute to organ dysfunc-
These changes also occur in small animals. 33 tion by various different mechanisms. The resulting tissue
In a prospective observational study of human septic edema of abdominal organs may directly impair function
patients, a positive cumulative fluid balance had a signifi- such as gut absorption or kidney excretion as examples.
83
cant negative influence on survival. A retrospective The abdominal compartment syndrome has been increas-
study of human patients with septic shock and acute lung ingly recognized in medical and surgical patients follow-
injury confirmed the association between fluid accumula- ing intense volume resuscitation with consequent acute
tion and mortality after onset of septic shock. 63 While formation of ascites and edema. 49
there are no veterinary studies evaluating cumulative fluid
overload, clinical observation in septic or capillary leak Blood Loss
conditions in veterinary patients indicates similar findings Potentially deleterious effects of aggressive fluid therapy
to those in human patients . to treat patients after trauma before full assessment can
Fluid administration is a lifesaving procedure in many increase morbidity and mortality. After trauma, the term
situations. The rate and volume of administration must “shock” frequently is used to describe a patient that is
be carefully considered in the individual patient based tachycardic, tachypneic, and has weaker than normal
on their unique clinical and physical situation. Fluid accu- pulses, paler than normal MMs, and CRT of more than
mulation and fluid overload are frequent findings in 2 seconds. However, mentation also is an important part
human and veterinary critically ill patients and in those of the assessment. If the patient has depressed mentation