This document discusses fluid and electrolyte management in surgical patients. It covers the normal anatomy of body fluids, including total body water, fluid compartments, and composition. It describes how fluid volume and electrolyte levels can change preoperatively, intraoperatively, and postoperatively. Common fluid and electrolyte disturbances like volume deficits, volume excess, hyponatremia, and hypernatremia are explained in terms of their causes, signs, and impacts.

1. dr. Andri Feisal Nasution
dr. Adang Sunandar

2. INTRODUCTION
 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

3. BODY FLUIDS
 Total Body Water
 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
 Young, lean males have a higher proportion of body
weight as water than elderly or obese individuals
 In an average young adult male 60% of total body weight
is TBW, whereas in an average young adult female it is
50%

4.  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 and
thereafter remains fairly constant

5. Fluid Compartments
 TBW is divided into three functional fluid
compartments: plasma, extravascular interstitial fluid,
and intracew fluid
 The extracellular fluids (ECF), plasma and interstitial
fluid, together comprise about one third of the TBW
and the intracellular compartment the remaining two
thirds

6. 20% of the total body weight
5% of body weight
15% of body weight
40% of an individual's total body weight

7. Composition of Fluid Compartments
 The ECF compartment is balanced between sodium, the
principal cation, and chloride and bicarbonate, the
principal anions
 The intracellular fluid compartment is comprised
primarily of the cations potassium and magnesium, and
the anions phosphate and proteins
 The concentration gradient between compartments is
maintained by adenosine triphosphate–driven sodium-
potassium pumps located with the cell membranes.
 The composition of the plasma and interstitial fluid differs
only slightly in ionic composition

8.  Proteins add to the osmolality of the plasma and
contribute to the balance of forces that determine
fluid balance across the capillary endothelium
 Water is distributed evenly throughout all fluid
compartments of the body
 Sodium-containing fluids are distributed throughout
the ECF and add to the volume of both the
intravascular and interstitial spaces

10. Osmotic Pressure
 The concentration of electrolytes usually is expressed
in terms of the chemical combining activity, or
equivalents. An equivalent of an ion is its atomic
weight expressed in grams divided by the valence:
For univalent ions such as sodium, 1 mEq is the same as 1 mmol
For divalent ions such as magnesium, 1 mmol equals 2 mEq

11.  The principal determinants of osmolality are the
concentrations of sodium, glucose, and urea (blood
urea nitrogen, or BUN):
 The osmolality of the intracellular and extracellular
fluids is maintained between 290 and 310 mOsm in
each compartment
 Because cell membranes are permeable to water, any
change in osmotic pressure in one compartment is
accompanied by a redistribution of water until the
effective osmotic pressure between compartments is
equal

12.  If the ECF concentration of sodium increases, there
will be a net movement of water from the intracellular
to the extracellular compartment
 Conversely, if the ECF concentration of sodium
decreases, water will move into the cells

13. BODY FLUID CHANGES
 Normal Exchange of Fluid and Electrolytes
 The healthy person consumes an average of 2000 mL of water
per day, approximately 75% from oral intake and the rest
extracted from solid foods
 Daily water losses include 800 to 1200 mL in urine, 250 mL in
stool, and 600 mL in insensible losses
 Insensible losses of water occur through both the skin (75%)
and lungs (25%), and can be increased by such factors as
fever, hypermetabolism, and hyperventilation
 Sensible water losses such as sweating or pathologic loss of GI
fluids vary widely, but these include the loss of electrolytes as
well as water
 To clear the products of metabolism, the kidneys must
excrete a minimum of 500 to 800 mL of urine per day,
regardless of the amount of oral intake

14. Routes Average Daily
Volume (mL)
Minimal (mL) Maximal (mL)
H2O gain:
Sensible:
Oral fluids 800–1500 0 1500/h
Solid foods 500–700 0 1500
Insensible:
Water of oxidation 250 125 800
Water of solution 0 0 500
H2O loss:
Sensible:
Urine 800–1500 300 1400
Intestinal 0–250 0 2500
Sweat 0 0 4000
Insensible:
Lungs and skin 600 600 1500
Water Exchange (60- to 80-kg Man)

15.  The typical individual consumes 3 to 5 g of dietary salt
per day, with the balance maintained by the kidneys
 With hyponatremia or hypovolemia, sodium excretion
can be reduced to as little as 1 mEq/d or maximized to
as much as 5000 mEq/d to achieve balance except in
people with salt-wasting kidneys
 GI losses are isotonic to slightly hypotonic and
contribute little to net gain or loss of free water when
measured and appropriately replaced by isotonic salt
solutions

16. Classification of Body Fluid Changes
 Disorders in fluid balance may be classified into three
general categories:
disturbances in
(a) volume
(b) concentration
(c) composition
 Isotonic gain or loss of salt solution results in
extracellular volume changes, with little impact on
intracellular fluid volume

17.  If free water is added or lost from the ECF, water will
pass between the ECF and intracellular fluid until
solute concentration or osmolarity is equalized
between the compartments
 Unlike with sodium, the concentration of most other
ions in the ECF can be altered without significant
change in the total number of osmotically active
particles, producing only a compositional change
 For instance, doubling the serum potassium
concentration will profoundly alter myocardial
function without significantly altering volume or
concentration of the fluid spaces

18. Disturbances in Fluid Balance
 Extracellular volume deficit is the most common fluid
disorder in surgical patients and can be either acute or
chronic
 Acute volume deficit is associated with cardiovascular
and central nervous system signs, whereas chronic
deficits display tissue signs, such as a decrease in skin
turgor and sunken eyes, in addition to cardiovascular
and central nervous system signs
 Laboratory examination may reveal an elevated blood
urea nitrogen level if the deficit is severe enough to
reduce glomerular filtration and hemoconcentration

19.  Urine osmolality usually will be higher than serum
osmolality, and urine sodium will be low, typically <20
mEq/L
 Serum sodium concentration does not necessarily
reflect volume status and therefore may be high,
normal, or low when a volume deficit is present
 The most common cause of volume deficit in surgical
patients is a loss of GI fluids from nasogastric suction,
vomiting, diarrhea, or enterocutaneous fistula
 In addition, sequestration secondary to soft tissue
injuries, burns, and intra-abdominal processes such as
peritonitis, obstruction, or prolonged surgery can also
lead to massive volume deficits

20. System VolumeDeficit Volume Excess
Generalized Weight loss Weight gain
Decreased skin turgor Peripheral edema
Cardiac Tachycardia Increased
cardiac output
Orthostasis/hypotension Increased central venous pressure
Collapsed neck veins Distended neck veins
Murmur
Renal Oliguria —
Azotemia
GI Ileus Bowel edema
Pulmonary —
Pulmonary edema
Signs and Symptoms of Volume Disturbances

21. Type of
Secretion
Volume
(mL/24 h)
Na (mEq/L) K (mEq/L) Cl (mEq/L) HCO3– (mEq/L)
Stomach 1000–2000 60–90 10–30 100–130 0
Small
intestine
2000–3000 120–140 5–10 90–120 30–40
Colon — 60 30 40 0
Pancreas 600–800 135–145 5–10 70–90 95–115
Bile 300–800 135–145 5–10 90–110 30–40
Composition of GI Secretions

22.  Extracellular volume excess may be iatrogenic or
secondary to renal dysfunction, congestive heart
failure, or cirrhosis
 Both plasma and interstitial volumes usually are
increased. Symptoms are primarily pulmonary and
cardiovascular
 In fit patients, edema and hyperdynamic circulation
are common and well tolerated. However, the elderly
and patients with cardiac disease may quickly develop
congestive heart failure and pulmonary edema in
response to only a moderate volume excess

23. Volume Control
 Volume changes are sensed by both osmoreceptors
and baroreceptors
 Osmoreceptors are specialized sensors that detect
even small changes in fluid osmolality and drive
changes in thirst and diuresis through the kidneys
 Baroreceptors also modulate volume in response to
changes in pressure and circulating volume through
specialized pressure sensors located in the aortic arch
and carotid sinuses.

24. Concentration Changes
HYPONATREMIA
 A low serum sodium level occurs when there is an
excess of extracellular water relative to sodium.
 In most cases of hyponatremia, sodium concentration
is decreased as a consequence of either sodium
depletion or dilution.
 Dilutional hyponatremia frequently results from
excess extracellular water and therefore is associated
with a high extracellular volume status

25.  Excessive oral water intake or iatrogenic IV excess free
water administration can cause hyponatremia
 Postoperative patients are particularly prone to
increased secretion of antidiuretic hormone (ADH),
which increases reabsorption of free water from the
kidneys with subsequent volume expansion and
hyponatremia
 Causes include decreased sodium intake, such as
consumption of a lowsodium diet or use of enteral
feeds, which are typically low in sodium ; GI losses
from vomiting, prolonged nasogastric suctioning, or
diarrhea; and renal losses due to diuretic use or
primary renal disease

27. HYPERNATREMIA
 Hypernatremia results from either a loss of free water
or a gain of sodium in excess of water
 Hypervolemic hypernatremia usually is caused either
by iatrogenic administration of sodium-containing
fluids, including sodium bicarbonate, or mineralo
corticoid excess as seen in hyperaldosteronism,
Cushing's syndrome, and congenital adrenal
hyperplasia
 Normovolemic hypernatremia can result from renal
causes, including diabetes insipidus, diuretic use, and
renal disease, or from nonrenal water loss from the GI
tract or skin, although the same conditions can result
in hypovolemic hypernatremia