2. ANATOMY OF BODY FLUIDS
• Total Body Water
• Intracellular Fluid
• Extracellular Fluid
• Osmotic Pressure
3. Total Body Water
• constitutes 50-70 % of total body weight
• fat contains little water, the lean individual
has a greater proportion of water to total
body weight than the obese person
• total body water as a percentage of total
body weight decreases steadily and
significantly with increasing age
4. Total Body Water
% of Body Weight % of Total Body Water
Body Water 60 100
ICF 40 67
ECF 20 33
Intravascular 4 8
Interstitial 16 25
5. Intracellular Fluid
• largest proportion in the skeletal muscle
• potassium and magnesium are the
principal cations
• phosphates and proteins the principal
anions
6. Extracellular Fluid
• interstitial fluid: two types
– functional component (90%) - rapidly
equilibrating
– nonfunctioning components (10%) - slowly
equilibrating
• connective tissue water and transcellular water
• called a “third space” or distributional change
• sodium is the principal cation
• chloride and bicarb the principal anions
7. Osmotic Pressure
• physiologic and chemical activity of electrolytes depend
on three factors:
– the number of particles present per unit volume
(moles or millimoles [mmol] per liter)
– the number of electric charges per unit volume
(equivalents or milliequivalents per liter)
– the number of osmotically active particles or ions per
unit volume (osmoles or milliosmoles [mOsm] per liter)
8. Terminology
• mole: molecular weight of that substance in grams mole
eg: sodium chloride is 58 g (Na–23, Cl–35)
• equivalent: chemical combining activity; atomic weight
expressed in grams divided by the valence
– divalent ions (calcium or magnesium) 1 mmol equals 2
mEq
• osmole: used when the actual number of osmotically
active particles present in solution is considered
• millimole of sodium chloride, which dissociates
nearly completely into sodium and chloride,
contributes 2 mOsm
9. NORMAL EXCHANGE OF FLUID AND
ELECTROLYTES
• Water Exchange
• Salt Gain & Losses
10. Water Exchange
• daily water gains
–normal individual consumes 2000 to
2500 mL water per day
–approximately 1500 mL taken by mouth
–rest is extracted from solid food, either
from the contents of the food or as the
product of oxidation
11. Water Exchange
• daily water losses
– 250 mL in stools, 800 - 1500 mL in urine, and 600 mL
as insensible loss
– total losses ~ 2.2 liters
– Insensible loss: skin (75%) and lungs (25%)
• increased by hypermetabolism, hyperventilation,
and fever
• 250 mL/day per degree of fever
• unhumidified tracheostomy with hyperventilation =
insensible loss up to 1.5 L/day
12. Water Exchange
Minimum of 500 to 800 mL urine
per day required to excrete the
products of catabolism
13. Salt Gain and Losses
• daily salt intake varies 3-5 gm as NaCl
• kidneys excretes excess salt: can vary
from < 1 to > 200 mEq/day
• Volume and composition of various types
of gastrointestinal secretions
• Gastrointestinal losses usually are isotonic
or slightly hypotonic
• should replace by isotonic salt solution
15. Volume Changes
• If isotonic salt solution is added to or lost from
the body fluids, only the volume of the ECF is
changed, ICF is relatively unaffected
• If water is added to or lost from the ECF, the
conc. of osmotically active particles changes
– Water will pass into the intracellular space until
osmolarity is again equal in the two
compartments
16. Volume Changes
• BUN level rises with an ECF deficit of sufficient
magnitude to reduce GFR
• creatinine level may not incr. proportionally in young
people with healthy kidneys
• hematocrit increases with an ECF deficit and
decreases with ECF excess
• sodium is not reliably related to the volume status of
ECF
– a severe volume deficit may exist with a normal,
low, or high serum level
17. Volume Deficit
• ECF volume deficit is most common fluid
loss in surgical patients
• most common causes of ECF volume
deficit are: GI losses from vomiting,
nasogastric suction,diarrhea, and fistular
drainage
• other common causes: soft-tissue injuries
and infections, peritonitis, obstruction,
and burns
18. Volume Deficit
• signs and symptoms of volume deficit:
• CNS: sleepy, apathy – stupor, coma
• GI: dec food consumption – N/V
• CVS: orthostatic, tachy, collapsed
veins - hypotension
• Tissue: dec skin turgor, small tongue
– sunken eyes, atonia
19. Volume Excess
• Iatrogenic or Secondary to renal
insufficiency, cirrhosis, or CHF
• signs & symptoms of volume excess:
–CNS: none
–GI: edema of bowel
–CVS: elevated CVP, venous distension
– pulmonary edema
–Tissue: pitting edema – anasarca
20. Concentration Changes
• Na+ primarily responsible for ECF osmolarity
• Hyponatremia and hypernatremia s&s often occur if
changes are severe or occur rapidly
• The concentration of most ions within the ECF can be
altered without significant osmolality change, thus
producing only a compositional change
– Example: rise of potassium from 4 to 8 mEq/L would
significantly effect the myocardium, but not the effective
osmotic pressure of the ECF
21. Hyponatremia
(water intoxication)
• acute symptomatic hyponatremia (< 130)
• hypertension can occur & is probably induced by the rise
in intracranial pressure
• signs & symptoms:
– CNS: twitching, hyperactive reflexes – inc ICP,
convulsions, areflexia
– CVS: HTN/brady due to inc ICP
– Tissue: salivation, watery diarrhea
– Renal: oliguria - anuria
22. Hyponatremia
(water intoxication)
• Hyponatremia occurs when water is given to
replace losses of sodium-containing fluids or
when water administration consistently
exceeds water losses
• Hyperglycemia: glucose exerts an osmotic
force in the ECF and causes the transfer of
cellular water into the ECF, resulting in a
dilutional hyponatremia
23. Hypernatremia
(water deficit)
• The only state in which dry, sticky mucous membranes are
characteristic
• sign does not occur with pure ECF deficit alone
• signs & symptoms:
– CNS: restless, weak - delirium
– CVS: tachycardia - hypotension
– Tissue: dry/sticky muc membranes – swollen tongue
– Renal: oliguria
– Metabolic: fever – heat stroke
25. Acid-Base Balance
• large load of acid produced endogenously as a by-product
of body metabolism
• acids are neutralized efficiently by several buffer systems
and subsequently excreted by the lungs and kidneys
• Buffers:
– proteins and phosphates: primary role in maintaining
intracellular pH
– bicarbonate–carbonic acid system: operates principally
in ECF
26. Acid-Base Balance
• buffer systems consists of a weak acid or base
and the salt of that acid or base
• Henderson-Hasselbalch equation, which defines
the pH in terms of the ratio of the salt and acid:
– pH = pK + log BHCO3 / H2CO3 = 27 mEq/L /
1.33 mEq/L = 20 / 1 = 7.4
– As long as the 20:1 ratio is maintained,
regardless of the absolute values, the pH will
remain at 7.4
27. Acid-Base Balance
• Four types of acid-base disturbances
• combinations of respiratory and metabolic
changes may represent:
• compensation for the initial acid-base
disturbance or,
• two or more coexisting primary disorders
• 10-mmHg PaCO2 change yields a 0.08 pH
change
28. Respiratory Acidosis
• retention of CO2 secondary to decreased alveolar
ventilation
• management involves prompt correction of the
pulmonary defect, when feasible, and measures to
ensure adequate ventilation
• prevention: tracheobronchial hygiene during the
postoperative , humidified air, and avoiding oversedation
29. Respiratory Alkalosis
• PaCO2 should not be below 30 mmHg
• dangers of a severe respiratory alkalosis
are those related to potassium depletion
– hypokalemia is related to entry of potassium ions into
the cells in exchange for hydrogen and an excessive
urinary potassium loss in exchange for sodium
• shift of the oxyhemoglobin dissociation
curve to the left, which limits the ability of
hemoglobin to unload oxygen at tissues
30. Metabolic Acidosis
• Anion gap is a useful aid:
• normal value is 10 to 15 mEq/L
• unmeasured anions that account for the
“gap” are sulfate and phosphate plus
lactate and other organic anions
• measured ions are sodium, bicarb, and
chloride
31. Metabolic Acidosis
• treatment of metabolic acidosis should be
directed toward correction of the underlying
disorder
• sodium bicarbonate is discouraged, attempt to
treat underlying cause
• shifts the oxyhemoglobin dissociation curve left
• interference with O2 unloading at the tissue level
32. Metabolic Alkalosis
• common surgical patient has hypochloremic,
hypokalemic metabolic alkalosis resulting from
persistent vomiting or gastric suction in the
patient with pyloric obstruction
• unlike vomiting with an open pylorus, which
involves a combined loss of gastric, pancreatic,
biliary, and intestinal secretions
33. Pathophysiology of Paradoxic
Aciduria occurring with GOO
• GOO -> hypochloremic, hypokalemic, metabolic alkalosis
• urinary bicarb excretion to compensate for alkalosis
• volume deficit progresses aldosterone-mediated
sodium resorption is accompanied by potassium excretion
• kidneys primary goal becomes volume preservation
sodium resorption
• either K+ or H+ must be excreted to keep a
balanced
• due to already excessive hypokalemia, the kidney
excretes H+ in place of K+, producing paradoxic aciduria
34. Potassium Abnormalities
• normal daily dietary intake of K+ is approx. 50 to
100 mEq
• majority of K+ is excreted in the urine
• 98% of the potassium in the body is located in ICF
@ 150 mEq/L and it is the major cation of
intracellular water
• intracellular K+ is released into the extracellular
space in response to severe injury or surgical
stress, acidosis, and the catabolic state
35. Hyperkalemia
• signs & symptoms:
–CVS: peaked T waves, widened QRS
complex, and depressed ST segments
Disappearance of T waves, heart
block, and diastolic cardiac arrest
–GI: nausea, vomiting, diarrhea
(hyperfunctional bowel)
36. Hypokalemia
• K+ has an important role in the regulation
of acid-base balance
• alkalosis causes increased renal K+/H+ excretion
• signs & symptoms:
– CVS: flatten T waves, depressed ST segments
– GI: paralytic ileus
– Muscular: weakness - flaccid paralysis,
diminished to absent tendon reflexes
37. Calcium Abnormalities
• majority of the 1000 to 1200g of calcium in the
average-sized adult is found in the bone
• Normal daily intake of calcium is 1 to 3 gm
• Most is excreted via the GI tract
• half is non-ionized and bound to proteins
• ionized portion is responsible for neuromuscular
stability
38. Hypocalcemia
• signs & symptoms (serum level < 8):
– numbness and tingling of the circumoral
region and the tips of the fingers and toes
– hyperactive tendon reflexes, positive
Chvostek's sign, muscle and abdominal
cramps, tetany with carpopedal spasm,
convulsions (with severe deficit), and
prolongation of the Q-T interval on the ECG
39. Hypocalcemia
• causes:
• acute pancreatitis, massive soft-tissue
infections (necrotizing fasciitis), acute
and chronic renal failure, pancreatic
and small-bowel fistulas, and
hypoparathyroidism
40. Hypercalcemia
• signs & symptoms:
–CNS: easy fatigue, weakness, stupor,
and coma
–GI: anorexia, nausea, vomiting, and
weight loss, thirst, polydipsia, and
polyuria
41. Hypercalcemia
• two major causes:
• hyperparathyroidism and cancer
– bone mets
– PTH-like peptide in malignancies
42. Magnesium Abnormalities
• total body content of magnesium 2000 mEq
• about half of which is incorporated in bone
• distribution of Mg similar to K+, the major portion
being intracellular
• normal daily dietary intake of magnesium is
approximately 240 mg
• most is excreted in the feces and the remainder
in the urine
43. Magnesium Deficiency
• causes:
–starvation, malabsorption syndromes, GI
losses, prolonged IV or TPN with
magnesium-free solutions
• signs & symptoms:
–similar to those of calcium deficiency
44. Magnesium Excess
• Symptomatic hypermagnesemia, although
rare, is most commonly seen with severe
renal insufficiency
• signs & symptoms:
– CNS: lethargy and weakness with progressive
loss of DTR’s – somnolence, coma, death
– CVS: increased P-R interval, widened QRS
complex, and elevated T waves (resemble
hyperkalemia) – cardiac arrest
47. Preoperative Fluid Therapy
• Correction of Volume Changes: Volume deficits result
from external loss of fluids or from an internal
redistribution of ECF into a nonfunctional compartment
– nonfunctional because it is no longer able to participate in the
normal function of the ECF and may just as well have been lost
externally
• Correction of Concentration Changes: If severe
symptomatic hypo or hypernatremia complicates the
volume loss, prompt correction of the concentration
abnormality to the extent that symptoms are relieved is
necessary
48. Postoperative Fluid Management
• replace losses & supply a maintenance:
– open abdomen losses: 8 cc/kg/hr
– NGT & urine output
– Blood loss x 3
– Replace with isotonic salt solution (LR or NS)
– unwise to administer potassium during the
first 24 h, until adequate urine output has
been established even a small quantity of
potassium may be detrimental because of
fluid shifts
52. Laboratory Studies
• Urinalysis: blood or myoglobin is a positive
diagnostic test - can test via Hemoccult
card
• Urinary lytes: urine sodium, creatinine,
urea, osmolality, and specific gravity help
classify type of renal failure using Renal
failure indices
53. Renal Indices
Indices Prerenal Renal Postrenal
U Osm > 500 < 350 Varies
U/P osm >1.25 <1.1 Varies
U/P urea > 8 < 3 Varies
U/P cr > 40 < 20 < 20
Urine Na < 20 > 40 > 40
FENa < 1% > 3% > 3%
54. Indications for use of Dialysis in
Acute Renal Failure
• Severe acidosis
• Electrolyte abnormalities
• Inability to clear toxins
• Volume overload
• Uremic signs and symptoms
(encephalopathy, BUN > 100)
