fluid in human body physiology

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Fluid & Electrolytes
part one
Radhwan Hazem Alkhashab
Consultant anaesthesia & ICU
2022

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Introduction
 Body water is distributed between two major fluid
compartments separated by cell membranes:
intracellular fluid (ICF) and extracellualr fluid (ECF).
 ECF is subdivided into intravascular and interstitial
compartments. The interstitium includes all fluid that is
both outside cells and outside the vascular endothelium.

3. Body fluid compartments (based on average 70-kg male).
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4. The composition of fluid compartments
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Intracellular (ICF):
The outer membrane of cells plays an important role in
regulating intracellular volume and composition. A
membrane-bound adenosine triphosphate (ATP)–dependent
pump exchanges Na+ for K+ in a 3:2 ratio. Because cell
membranes are relatively impermeable to sodium and, to a
lesser extent potassium ions, potassium is concentrated
intracellularly, whereas sodium is concentrated extracellularly.

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Extracellular (ECF)
The principal function of ECF is to provide a medium for
delivery of cell nutrients and electrolytes and for removal of
cellular waste products. Maintenance of a normal
extracellular volume particularly the circulating component
(intravascular volume) is critical, Changes in ECF volume are
therefore related to changes in total body sodium content,
which are regulated by sodium intake, renal sodium
excretion, and extrarenal sodium losses .

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Intravascular Component
This compartment made by plasma which is fluid portion
of blood & this is made of:
 Water.
 Plasma proteins.
 Small amount of other substances.
Most electrolytes (small ions) freely pass between
plasma and the interstitium, resulting in nearly
identical electrolyte composition.

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Interstitial component
Which is a fluid (Exactly – lymph) between cells, and
responsible for transport medium for nutrients, gases,
waste products and other substances between blood and
body cells.
Interstitial fluid pressure is generally thought to be
negative (approximately –5 mm Hg). Increases in
extracellular volume are normally proportionately
reflected in intravascular and interstitial volume.
However, as interstitial fluid volume progressively
increases, interstitial pressure also rises and eventually
becomes positive.

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Transcellular component
Constitute about 1% of ECF which is located in joints,
connective tissue, bones, body cavities, CSF, pericardial,
synovial, intraocular, pleural fluids, sweat, digestive
secretions and other tissues

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Regulation of Fluids in Compartments
Fluid normally shifts between the ICF and ECF compartment
every day, to help keep our bodies in homeostasis. The principles
involved in this shifting are osmosis, diffusion, and filtration.
Osmosis:
Movement of water through a selectively permeable
membrane from an area of low solute concentration to a
higher concentration until equilibrium occurs,movement
occurs until near equal concentration found, it`s usually
passive process

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Diffusion:
Movement of solutes from an area of higher concentration
to an area of lower concentration in a solution and/or
across a permeable membrane (permeable for that solute),
movement occurs until near equal state, also it`s passive
process

12. Filtration :
Is the removal or filtering of the toxins and waste products from
the blood by the kidney. They are excreted from the body through
urine. In general, filtration refers to the passing of a liquid through
a filter. In the human body, the kidney functions as a filter
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13. Factors affectinf rate of diffusion
The rate of diffusion of a substance across a membrane depends
upon
(1) The permeability of that substance through that membrane.
(2) The concentration difference for that substance between the two
sides.
(3) The pressure difference between either side, because pressure
imparts greater kinetic energy.
(4) The electrical potential across the membrane for charged
substances.
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14. Osmosis versus Diffusion
Osmosis
Low to high
Water potential
Diffusion
High to low
Movement of particles
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Both can occur at the same time

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Active Transport
Allows molecules to move against concentration and osmotic
pressure to areas of higher concentration
Active process – energy is expended

16. Diffusion Through Capillary Endothelium
Capillary walls are typically 0.5 μm thick, consisting of a
single layer of endothelial cells with their basement membrane.
Intercellular clefts, 6 to 7 nm wide, sepa rate each cell from its
neighbors. Oxygen, CO2 , water, and lipid-soluble substances
can penetrate directly through both sides of the endothelial cell
membrane. Only low-molecular-weight, water-soluble
substances such as sodium, chloride, potassium, and glucose
readily cross intercellular clefts. High-molecular weight
substances such as plasma proteins penetrate the endothelial
clefts poorly.
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17. Fluid exchange across capillaries differs from that across cell
membranes in that it is governed by significant differences in
hydrostatic pressures in addition to osmotic forces. These
forces are operative on both arterial and venous ends of
capillaries, with a tendency for fluid to move out of
capillaries at the arterial end and back into capil laries at the
venous end
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18. Capillary fluid exchange
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Osmolality
The osmolality of ECF is equal to the sum of the concentrations
of all dissolved solutes. Na+ and its anions account for nearly
90% of these solutes
It can be measured by serum and urine. The main solutes
measured are urea, glucose, and sodium.

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Osmolality
So serum osmolality =
(serum Na x 2) + BUN/2.8 + Glucose/18 (Osm/kg)
Normal serum value - 280-300 mOsm/Kg
Serum <240 or >320 is critically abnormal
Normal urine Osm – 250 – 900 mOsm / kg.
Total body osmolality =
Na x 2 (extracellular comp.) + (Kx 2 intracellual comp.)
TBW

21. Factors that affect Osmolality
 Serum
– Increasing Osm
• Free water loss
• Diabetes Insipidus
• Na overload
• Hyperglycemia
• Uremia
– Decreasing Osm
• SIADH
• Renal failure
• Diuretic use
• Adrenal
insufficiency

22. Factors that affect Osmolality
 Urine
– Increasing Osm
• Fluid volume
deficit
• SIADH
• Heart Failure
• Acidosis
– Decreasing Osm
• Diabetes Insipidus
• Fluid volume
excess
– Urine specific gravity
• Factors affecting
urine Osm affect
urine specific
gravity identically
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Fluid Volume Shifts
Fluid normally shifts between intracellular and extracellular
compartments to maintain equilibrium between spaces
Fluid not lost from body but not available for use in either
compartment – considered third-space fluid shift (“third-
spacing”)
Enters serous cavities (transcellular)

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Causes of Third-Spacing
 Burns
 Peritonitis
 Bowel obstruction
 Massive bleeding into joint or cavity
 Liver or renal failure
 Lowered plasma proteins
 Increased capillary permeability
 Lymphatic blockage

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Assessment of Third-Spacing
 More difficult – fluid sequestered in deeper structures
 Signs/Symptoms
– Decreased urine output with adequate intake
– Increased HR
– Decreased BP, CVP
– Increased weight
– Pitting edema, ascites

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Treatment of 3rd space loss
 Treat underlying cause if possible
 Monitor I & O more frequently
 Daily weights
 Measure abdominal girth in ascites
 Measure extremities if necessary
 Monitor lab values
albumin level important

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Fluid volume deficit
Hypovolemia : Abnormally low volume of body fluid in
intravascular and/or interstitial compartments
 Causes:
Vomiting
Diarrhea
Fever
Excess sweating
Burns
Diabetes insipidus
Uncontrolled diabetes mellitus

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Fluid volume deficit
When Output > Input Water extracted from ECF
• When ECF osmolality increases, these cells shrink and
release ADH from the posterior pituitary. ADH
markedly increases water reabsorption in renal
collecting tubules, which tends to reduce plasma
osmolality back to normal. Decreased ECF volume
adrenal glands secrete Aldosterone which lead to Na &
water reabsorption.

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Signs and Symptoms of volume deficit
 Acute weight loss
 Decreased skin turgor
 Oliguria
 Concentrated urine
 Weak, rapid pulse
 Capillary filling time elongated
 Decreased BP
 Increased pulse
 Sensations of thirst, weakness, dizziness, muscle cramps

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Significant Points
 Dehydration – one of most common disturbances in infants
and children
 Additional sign & symptoms:
Sunken eyeballs
Depressed fontanels
Significant wt loss

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Labratory tests
 Increased HCT
 Increased BUN out of proportion to Cr
 High serum osmolality
 Increased urine osmolality
 Increased specific gravity
 Decreased urine volume, dark color

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Management
 Major goal is to correct abnormal fluid volume status
before ARF occurs, this done by :
 IV fluids: Isotonic solutions (0.9% NS or LR) until BP
back to normal.
 Monitor input & output , urine specific gravity, daily
weights.
 Monitor skin turgor
 Monitor mental status.

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Fluid Volume Excess (FVE)
 Hypervolemia
 Isotonic expansion of ECF caused by abnormal retention
of water and sodium
 Fluid moves out of ECF into cells and cells swell

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Causes
 Cardiovascular – Heart failure
 Urinary – Renal failure
 Hepatic – Liver failure, cirrhosis
 Other – Cancer, thrombus, PVD, drug therapy (i.e.,
corticosteriods), high sodium intake, protein malnutrition

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Signs/Symptoms
 Physical assessment
Weight gain
Distended neck veins
Periorbital edema, pitting edema
Adventitious lung sounds (mainly crackles)
Dyspnea
Mental status changes
Generalized or dependent edema

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Signs / Symptoms
CVS
High CVP/PAWP
↑ cardiac output
Lab data
↓ Hct (dilutional)
Low serum osmolality
Low specific gravity
↓ BUN (dilutional)

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Signs / Sympotms
Radiography
Pulmonary vascular congestion
Pleural effusion
Pericardial effusion
Ascites

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Interventions
 Sodium restriction (foods/water high in sodium)
 Fluid restriction, if necessary
 Closely monitor IVF
 If dyspnea or orthopnea > Semi-Fowler’s
 Strict I & O, lung sounds, daily weight, degree of edema,
reposition q 2 hr
 Promote rest and diuresis

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Normal Water balance
The normal adult daily water intake averages 2500.
Daily water loss averages 2500 mL and is typically accounted
for by 1500 mL in urine, 400 mL in respiratory tract
evaporation, 400 mL in skin evaporation, 100 mL in sweat, and
100 mL in feces.
Evaporative loss is very important in thermoregulation because
this mechanism normally accounts for 20% to 25% of heat loss

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Other Causes of Water Loss
 Fever
 Burns :The largest contributor to abnormal loss is burns because
of the loss of natural skin barrier.
 Diarrhea
 Vomiting
 N-G Suction
 Fistulas
 Wound drainage

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Other causes of water loss
 Mechanical ventilation
 Increased metabolism
 Diabetes Insipidus
 Uncontrolled DM:(water needed to dilute sugar for CHO
metabolism)
 Acute tubular necrosis: (increased urination secondary to
inability to concentrate urine)

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IV Fluid Replacement
Intravenous fluid therapy may consist of infusions of
crystalloids, colloids, or a combination of both.
Crystalloid solutions are aqueous solutions of ions
(salts) with or without glucose, whereas colloid
solu tions also contain high-molecular-weight
substances such as proteins or large glucose polymers.

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IV Fluid Replacement
Colloid solutions help maintain plasma colloid oncotic
pres sure and for the most part remain intravascular, whereas
crystalloid solutions rapidly equilibrate with and distribute
throughout the entire extracellular fluid space.

44. Crystalloids
Although the intravascular half-life of a crystalloid solution
is 20 to 30 min, Crystalloids are often considered as the initial
resuscitation fluid in patients with:
o hemorrhagic and septic shock.
o burn patients.
o head injury (to maintain cerebral perfusion pressure).
o intraoperative fluid losses are usually isotonic loss ,so
isotonic crystalloid solutions such as normal saline or
balanced electrolyte solutions such as lactated Ringer’s
solution or PlasmaLyte are most commonly used for
replacement
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45. Crystalloids have three types:
1. Isotonic Crystalloid Solution
 The isotonic crystalloid solution is a crystalloid solution with
a concentration that is very close to that of normal bodily
fluids. They are electrolyte and water-based solutions that
mimic the body's fluid composition. It can also be used to
replace fluids or maintain a stable bodily state. Isotonic
crystalloid solutions have the advantages of being readily
available, having no side effects, and being inexpensive.
Common isotonic crystalloids examples are 0.9% sodium
chloride and lactate Ringer's solution.
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46. 2. Hypotonic Crystalloid Solution
The hypotonic crystalloid solution is a crystalloid solution
with a concentration lower than that of normal bodily fluids.
Electrolyte concentrations in hypotonic solutions are lower
than 250 mEq/L. Hypotonic solutions cause water to flow
into cells, making them an effective treatment for some types
of dehydration. Examples of hypotonic solutions are 0.45%
sodium chloride and 0.25% sodium chloride.
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47. 3. Hypertonic Crystalloid Solution
The hypertonic crystalloid solution is a crystalloid solution with
a concentration higher than that of normal bodily fluids.
Hypertonic solutions are specialized solutions that aid in the
recovery of a patient following or during a severe illness.
Electrolyte concentrations in hypertonic solutions are greater than
350 mEq/L. For hypotonic solutions, the concentration of sodium
chloride will be less than 0.9%. Examples of hypertonic solutions
are 10% dextrose in water, 3% sodium chloride, and 5% sodium
chloride.
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48. 1. Plasma Lyte solution
It mimics human plasma in its content of electrolytes,
osmolality, and pH. These solutions also have additional
buffer capacity and contain anions such as acetate, gluconate,
and even lactate that are converted to bicarbonate, CO2, and
water. The advantages of PlasmaLyte include volume and
electrolyte deficit. It shares the same problems as most other
crystalloid fluids (fluid overload, edema with weight gain,
lung edema, and worsening of the intracranial pressure).
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49. Plasma Lyte solution
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50. 2. Normal saline
Normal saline, when given in large volumes, produces
hyperchloremic metabolic acidosis because of its high
chloride content and lack of bicarbonate . In addition,
chloride-rich crystalloids such as normal saline may
contribute to perioperative acute kidney injury. Therefore, we
prefer balanced salt solutions for most intraopera tive uses.
Normal saline is the preferred solution for hypochloremic
metabolic alkalosis and for diluting packed red blood cells
prior to transfusion.
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51. Colloids solution
The osmotic activity of high-molecular-weight sub stances in
colloids tends to maintain these solutions intravascularly. most
colloid solutions have intravascular half-lives between 3 and 6 h.
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52. Indication of colloids infusion
1. Fluid resuscitation in patients with severe intravascular
fluid defi cits (eg, hemorrhagic shock) prior to the arrival
of blood for transfusion.
2. Fluid resuscitation in the presence of severe
hypoalbuminemia or condi tions associated with large
protein losses such as burns.
3. Colloid solutions in conjunction with crystalloids when
fluid replace ment needs exceed 3 to 4 L prior to
transfusion.
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53. All are derived from either plasma proteins or syn thetic
glucose polymers and are supplied in isotonic electrolyte
solutions. Blood-derived colloids include albumin (5% and
25% solutions) and plasma protein fraction (5%). Both are
heated to 60°C for at least 10 h to minimize the risk of
transmitting hepatitis and other viral diseases
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54. Plasma protein fraction contains α- and β-globulins in addition to
albumin and has occasionally resulted in hypotensive allergic
reactions. Synthetic colloids include gelatins and dextrose
starches. Gelatins (eg, Gelofusine) are associated with histamine-
mediated allergic reactions. Dextran is a complex polysaccharide
available as dextran 70 & 40 , which have average molecular
weights of 70,000 and 40,000, respectively.
Dextran is used as a volume expander but also reduces blood
viscosity, von Willebrand factor antigen, platelet adhesion, and
red blood cell aggregation
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55. Infusions exceeding 20 mL/kg per day can interfere with blood
typing, may prolong bleeding time, and have been associated
with bleeding com plications. Dextran has been associated with
acute kidney injury and failure
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56. Hetastarch (hydroxyethyl starch) is available in multiple
formulations , Hetastarch is highly effective as a plasma expander
and is less expensive than albumin. Allergic reactions are rare, but
anaphylactoid and anaphylactic reac tions have been reported.
Hetastarch can decrease von Willebrand factor antigen levels, may
prolong the prothrombin time, and has been associated with
hemorrhagic complications. It is potentially neph rotoxic and
should not be administered to patients at risk for acute kidney
injury
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57. Perioperative fluid replacement
1. Replacement of fasting: replacement 4,2,1 regimen /kg body
weight. Type of fluid?why?
2. Abnormal fluid losses frequently contribute to preoperative
deficits. Preoperative bleeding, vomit ing, nasogastric suction,
diuresis, and diarrhea
3. Blood Loss: most important loss should be replace, this done
after assessment of amount of loss by many methods.what are
these methods ?
4. Internal redistribution of fluids often called third-spacing can
cause massive fluid shifts and severe intravascular depletion in
patients.
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58. Replacing Blood Loss Ideally, blood loss should be replaced with
sufficient crystalloid or colloid solutions to maintain
normo volemia until the danger of anemia outweighs the risks of
transfusion. At that point, further blood loss is replaced with
transfusion of red blood cells to maintain hemoglobin
concentration
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59. Below a hemoglobin concentration of 7 g/dL, the resting
cardiac output increases to maintain a nor mal oxygen delivery.
An increased hemoglobin con centration may be appropriate
for older and sicker patients with cardiac or pulmonary disease,
particu larly when there is clinical evidence (eg, a reduced
mixed venous oxygen saturation and a persisting tachycardia)
that transfusion would be beneficial
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Any Questions ?