1. Proper management of fluid and electrolytes facilitates
crucial homeostasis that allows cardiovascular perfusion, organ
system function, and cellular mechanisms to respond to surgical
2. Knowledge of the compartmentalization of body fluids forms the
basis for understanding pathologic shifts in these fluid spaces
in disease states. Although difficult to quantify, a deficiency
in the functional extracellular fluid compartment often requires
resuscitation with isotonic fluids in surgical and trauma patients.
3. Alterations in the concentration of serum sodium have profound
effects on cellular function due to water shifts between the intracellular
and extracellular spaces.
4. Different rates of compensation between respiratory and metabolic
components of acid-base homeostasis require frequent laboratory
reassessment during therapy.
5. Most acute surgical illnesses are accompanied by some degree
of volume loss or redistribution. Consequently, isotonic fluid administration
is the most common initial IV fluid strategy, while attention is being
given to alterations in concentration and composition.
6. Although active investigation continues, alternative resuscitation
fluids have limited clinical utility, other than the correction
of specific electrolyte abnormalities.
7. Some surgical patients with neurologic illness, malnutrition,
acute renal failure, or cancer require special attention to well-defined,
disease-specific abnormalities in fluid and electrolyte status.
Fluid and electrolyte management is paramount to the care of
the surgical patient. Changes in both fluid volume and electrolyte composition
occur preoperatively, intraoperatively, and postoperatively, as
well as in response to trauma and sepsis. The sections that follow
review the normal anatomy of body fluids, electrolyte composition
and concentration abnormalities and treatments, common metabolic
derangements, and alternative resuscitative fluids. These concepts
are then discussed in relationship to management of specific surgical
patients and their commonly encountered fluid and electrolyte abnormalities.
Water constitutes approximately 50 to 60% of total body
weight. The relationship between total body weight and total body
water (TBW) is relatively constant for an individual and is primarily
a reflection of body fat. Lean tissues such as muscle and solid
organs have higher water content than fat and bone. As a result,
young, lean males have a higher proportion of body weight as water
than elderly or obese individuals. Deuterium oxide and tritiated
water have been used in clinical research to measure TBW by indicator dilution
methods. In an average young adult male 60% of total body weight
is TBW, whereas in an average young adult female it is 50%.1 The
lower percentage of TBW in females correlates with a higher percentage
of adipose tissue and lower percentage of muscle mass in most. Estimates
of percentage of TBW should be adjusted downward approximately 10
to 20% for obese individuals and upward by 10% for
malnourished individuals. The highest percentage of TBW is found
in newborns, with approximately 80% of their total body weight
comprised of water. This decreases to approximately 65% by 1
year of age ...