Fluid and Volume States
Structure and Function
Phospholipid by-layer
- Phospholipids – hydrophobic end/hydrophilic end (surfactant – e.g. soap)
- Semipermeable membrane
Creates two main compartments
- Intracellular
- Extracellular
- Vascular compartment
- Interstitial compartment
Components of this semipermeable membrane that allow movement across the membrane
- membrane itself can allow for diffusion
- Protein Channels
- Ion Channels
- Receptors
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Solutes and Solvents
Solvents – water – moves my osmosis
Solutes – Na. K, etc. move by force (charge, pump etc)
Ions
Cations (positive charge)
- Sodium – notice Plasma and Interstitial concentration – MUCH higher than Intracellular –
concentration gradient
- Potassium – notice Intracellular concentration – MUCH higher that extra cellular –
concentration gradient
- Magnesium
- Calcium
Anions (Negative charge)
- Bicarbonate – notice Plasma and Interstitial concentration – higher than Intracellular –
concentration gradient
- Chloride – notice Plasma and Interstitial concentration – MUCH higher than Intracellular –
concentration gradient
- Phosphorus – notice Intracellular concentration – MUCH higher that extra cellular –
concentration gradient
These Ions
- make up the Osmolarity of these compartments
- directly impact fluid balance (i.e. movement across the membrane)
- nerve and muscle action potential/depolarization/repolarization
- acid/base balance
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Anion Gap
The difference between the major plasma positive ions and negative ions.
• Positive – (Negative + Negative)
• Sodium – (Chloride + Bicarbonate)
Positive (Cation)
• Sodium (Na+)
Negative (Anions)
• Chloride (Cl-)
103
• Bicarbonate (HCO3-)
27
142
-130
12
Osmosis – osmos = a push
• Osmosis: movement of water across a semi-permeable membrane
• Concentration gradient
• Osmotic pressure
• Diffusion (passive transport)
• Tonicity – ability of a solution to move water
* relative to normal plasma/cellular osmolarity
This is where the cell membrane, tissue compartments and their composition come together
Osmosis = movement of water across a semi-permeable membrane
• Membrane is permeable to water but not solutes
• Movement by osmosis is caused by osmolarity
• Water passes from an area of lesser solute concentration and more water to an area of
greater solute concentration and less water until equilibrium is achieved
• Water → lesser to GREATER CONCENTRATION
Concentration gradient: Difference in osmolarity across a semipermeable membrane
• H20 moves across the concentration gradient from LOW to HIGH Osmolarity by osmosis
• NO energy required
• Volume change will occur
• More concentrated solutes = greater Osmolarity = greater “pull” for H2O (water is
pulled in that direction)
• Movement stops when osmolarity on both sides of membrane is equal (i.e. there is NO
concentration gradient)
Osmotic pressure
• The amount of pressure required to stop the osmotic flow of water
• Determined by the concentration of solutes in a solution
Tonicity
o Measurement of osmotic pressure between two solutions. The name is relative to
normal plasma/cellular osmolarity
– Iso-osmolar = isotonic = Equal osmolality
– Hypo-osmolar = hypotonic = less osmolality
– Hyper-osmolar = hypertonic = greater osmolality
Osmosis
Fluid movement between ECS & ICS affected by:
o Osmolarity of fluid in adjacent area
Direction fluid moves between ECS & ICS affected by:
Osmolarity of fluid in adjacent area
• Higher the Osmolarity = greater amount of “pull” it has
• Water will then move in that direction
– To the cells, or to the capillaries?
Osmolarity - measurements
Lab tests to determine fluid status, kidney perfusion, and osmolarity
• Urine Specific Gravity (SG)
• Blood urea nitrogen (BUN)
• Creatinine
• Hematocrit
• Urine sodium
• Urine Specific Gravity (SG)
• The weight of solutes in fluid
• Distilled water = 1
• Normal 1.010 to 1.025
• Dilute (<1.010) = lower SG
• Overhydrated?
• Concentrated (>1.025) = higher SG
Dehydrated?
Blood urea nitrogen (BUN)
• Urea (waste product) remaining in the blood
• Protein is broken into amino acids, which are broken into ammonia which is converted
into urea which is excreted in urine
• Normal BUN 10-20
• Increased BUN (retained) = poor kidney function, GI bleeding, dehydration, increased
protein intake, fever, sepsis
• Decreased BUN (not retained) = end stage liver disease, low-protein diet, starvation, and
conditions that cause increased fluid volume, such as pregnancy
Creatinine
• Creatinine remaining in the blood
• An end product of muscle metabolism
• The better test for assessing kidney function
• Normal is 0.7 to 1.4 mg/dL
• Serum creatinine increases when renal function decreases
Hematocrit
• Hematocrit = a percentage of how much volume the red blood cells (erythrocytes) are
taking up in the blood
• Men 42-52%; women 35-47%
• About 3 x Hemoglobin, e.g. if Hgb = 8 then Hct = 24
• Increase; dehydration and polycythemia
• Decrease; overhydrated or anemic (low RBC)
Iso-Osmolar/Isotonic
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Osmolarity is the same in both compartments
The solution’s ability to push water is the SAME on both sides
Example:
– Normal Saline
– Osmolarity ~300 mOsm
– No movement across the membrane or no NET movement
HyPO-osmolar/HyPOtonic
Osmolarity of the solution is LESS than the adjacent compartment
Fluid is pushed/pulled into the cell
Example:
– 0.45 Normal Saline
– Osmolarity ~ 154 mOsm
HypER-osmolar/HypERtonic
Osmolarity of the solution is HIGHER than the adjacent compartment
Fluid is pulled tout of the cell
Example:
– 3% Normal Saline
– Osmolarity ~ 900 mOsm
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Other Forces
Oncotic Pressure – Osmotic pressure created by proteins. Proteins do not readily move
across the cell membrane. (think Albumin)
Filtration – Hydrostatic pressure drives solutes through based on size and force
Active Transport – energy moves ions across the membrane
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Active Transport: Solute movement
Active transport = energy used to move molecules against concentration
gradient
Sodium (Na) moved out, potassium (K) moved in = sodium-potassium pump
Energy source = adenosine triphosphate (ATP) - 33% powers pump
For each ATP, pump moves 3 Na out and 2 K in
As cell loses Na, electrical gradient, and concentration gradient form
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Fluid Movement in Capillaries
• Shift of Plasma → Interstitial Fluid
– Elevation of Venous Hydrostatic Pressure
• Eg. Fluid overload, HF, obstruction of venous return, venous insufficiency
– Decrease in Plasma Oncotic Pressure
• Eg. Renal disorders, liver disease, malnutrition
– Elevation of Interstitial Oncotic Pressure
• Eg. Trauma, burns, inflammation
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Shift of Interstitial Fluid → Plasma
– Elevation of plasma osmotic or oncotic pressure
• Eg. Administration of colloids, dextran, mannitol, or hypertonic solutions
– Elevation of Tissue Hydrostatic Pressure
• Eg. Compression stockings
Intravenous Fluids
• Osmolarity of IV fluid is based on plasma osmolarity
– Plasma osmolality is 275 – 290 mOsm/kg
• Osmolarity of any solution will change with amount of solute dissolved in it
– Sodium
– Glucose
Isotonic Fluid
0.9% NaCl = Normal Saline or NS
• A vascular fluid replacement
• Frequently used to dilute medications (piggybacks, IV)
• NS is the ONLY fluid that can be given with blood products!
• Excessive administration can cause↑ sodium & chloride levels in plasma
Lactated Ringers = LR
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Similar to NS; replace intravascular volume
Used for burns & lower GI issues
Contains Na+, K+, Cl-, Ca+, and lactate
Do NOT give to patient with alkalosis
Do not give if in lactic acidosis – can’t convert lactate to bicarb
May treat mild metabolic acidosis (why?)
Hypotonic Fluid
Dextrose 5% in water = D5W
• Used to treat water losses / dehydration & hypernatremia
• Isotonic in IV bag; Hypotonic in the body
• Provides free water for renal function and 170 calories/L
• Dextrose quickly metabolized  free water moves from the vessels into the cells (For
every liter, 2/3 ICF, 1/3 ECF)
Hypertonic Fluids
• Dextrose 5% in Lactated Ringers (D5LR)
• Dextrose 5% in half normal saline (D5 ½ NS)
• 3% NS, 5% NS
Considered plasma expanders
Increase circulatory volume via movement of intracellular and interstitial water into the
intravascular space
Used to treat hypovolemia & hyponatremia
Stabilizes blood pressure, increases urine output, decreases edema
Can use to provide calories & treat hypoglycemia
≤ 10% Dextrose can go in peripheral IV
Must give > 10% Dextrose in central IV
Must monitor: vital signs, neuro status, lung sounds, urine output, serum sodium levels
Use caution to avoid hypernatremia & vascular volume overload
Crystalloids
• Balanced salt / electrolyte solution
– Clear water & electrolyte solutions
• Known as IV fluids
– May be isotonic, hypertonic, or hypotonic
• Capable of passing through semipermeable membranes
– Volume expansion; water & electrolytes cross semi-permeable membrane into
interstitial space → equilibrium in 2-3 hours
– It takes 3 mL crystalloid to replace 1mL of blood
– Hemorrhage treatment: no more than 3L crystalloid before must use
whole blood; risk of edema, especially pulmonary edema
Colloids
High-molecular-weight solutions: macromolecules
• Plasma expanders / volume expanders
• Plasma proteins in capillary too big to pass through capillary wall membranes, create
oncotic pressure
• Oncotic pressure pulls fluids from interstitium into capillary = reduce edema, increase
intravascular volume
• Types
– Albumin (human source)
– Hetastarch
– Pentastarch (Pentaspan®)
– Plasma (human source)
– Dextran
Three MAJOR regulatory mechanisms
1. Vasopressin(AVP)/Antidiuretic Hormone (ADH) – Hypothalamus - osmoreceptors
2. Water Ingestion – thirst –Hypotalmus
3. Water Transport – removal/shifting - kidney
– Glomerulus – Na+ retention/excretion
– Renin/Aldosterone/Angiotensin – Arterio-Venous constriction
4. Lungs – Angiotensin II – Arterio-Venous constriction
5. Stretch Receptors – Arterio-Venous constriction
– Atria of the Heart - Atrial Natriuretic Peptide (ANP)
– Ventricles – B type Natriuretic Peptide (BNP)
6. Baroreceptors – Carotid Sinuses
7. Adrenal Glands – Aldosterone – Water retention
8. Thirst – drink more water
Fluid Management/Loses
• Kideys/Urination
• Lungs/Insensible loses
• Skin
• Feces
• Total
1500mL/day
300mL/day
500mL/day
200mL/day
2500mL/day
Assessment: Notice what you are noticing
• Skin (Color, temperature, turgor, moisture)
• Mucous Membranes
• Mentation
• Lungs
• Veins
– Hands
– Neck
• Edema
• Blood Pressure
• Labs
Labs: Fluids and Electrolytes
• Serum Osmolarity
275 – 290 mOsm/L
• Urine Specific Gravity
1.010 – 1.025
• Blood Urea Nitrogen (BUN) 0-20
• Creatinine
0.4 – 1.2 mg/dL
• Potassium
3.5 – 5 mEq/L
• Sodium
135 – 145 mEq/L
• Hemaglobin Men:13.5 –17.5
Women: 12 –15.5
• Hematocrit Men:42-52% Women: 35-47%
Hypovolemia
• Dehydration – Fluid loss creates a HyPERtonic state
– Volume/Preload is Decreased
– Hypothalamus  Increased ADH (hold onto water)
– Thirst  Drink some water!!
– Adrenal Glands  Increase Aldosterone (hold onto water)
– Stretch Receptors  not getting stretched $’d ANP  “tighten up”
– Kidney  Renin  Liver  Angiotensin I Lung Angiotensin II ” tighten
up”
Hypovolemia: Assessment
• Skin – dry, clammy, poor skin turgor,
• Mucous Membranes – dry
• Decreased Mentation/Confusion
• Lungs – clear
• Veins
– Hands – flat
– Neck – flat
• Blood Pressure – low or high – orthostatic pressures
• Heart rate – tachycardic (maintaining cardiac output)
Labs: Fluids and Electrolytes
• Serum Osmolarity
• Urine Specific Gravity
• Blood Urea Nitrogen (BUN)
• Creatinine
• Potassium
• Sodium
• Hemaglobin
• Hematocrit
Increased
Increased
Increased
depends
depends
Increased
Increased
Increased
Case Study #1
• August: 35 yr. old female presents to you after waiting 3 hrs in the triage area. She is
here after a mountain bike accident. C/C: headache, shoulder pain, muscle cramps and
multiple abrasions. She is irritible, skin is dry, her lungs are clear. She is on Room Air. She
has not voided.
• VS: HR:110 RR: 22 BP: 100/70 SpO2: 98%
• Ordered test: Head CT, Basic Chemistry, H&H, urine Hcg
What’s your differential diagnosis?
• What would you expect results to be based on your diagnosis?
• Sodium:
154 mEq/L
• BUN:
30 mg/dL
• Creatinine:
1.0 mg/dL
• Hgb:
16 g/dL
• Hct
50 %
• HcG
Negative
Case Study #2
• 28 yr. old Male was admitted 4 days ago for flu-like symptoms. He reported that he had
a cold and allergies for a week prior to that. He came to the hospital because he was
short of breath with normal activity. He gets dizzy when he tries to stand.
• VS: HR: 140 BP: 85/60 RR: 30 SpO2: 93%
What would you assess next?
What did you notice?
• Flush and diaphoretic
• Dry
• Confused at time/ Oriented x2
• Crackles – bilateral bases
• Hand veins distended
• +1 edema in lower extremities
• Hypotensive
• Tachycardic
Labs
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Na+
K+
Bun
Creatinine
Hgb
HCT
Lactic Acid
Blood Cultures
137 mEq/L
3.8 mEq/L
25 mg/dL
0.8 mg/dL
11 g/dL
38%
5 mg/dL
Positive
(Gram-negative coccobacillus)
What’s going on?
• Influenza Sepsis
• Treatment
– Antivirals/Antibiotics/Antifungals
– Increase PRELOAD – VOLUME!!! – 30 mL/kg
– What kind of fluids?
ISOTONIC
– Vasopressors
– Oxygen Support
1. Hypervolemia - Pregnancy
• Circulating Blood Volume –#’d ~ 1000 – 1500 mL
• Heart Rate –#’d~25 %
• Cardiac Output –#’d 30 – 50%
C0 = HR x SV
• Plasma Volume#’d > Red Blood Cells (physiologic anemia)
• Progesterone – Peripheral Vasodilation – $’d Afterload
• #’d Kidney Size and GFR
Physiology
Volume Management
• #’d CBV  #’d CO  #’d GFR  #’d UOP  Maintained Fluid Volume
Afterload Management
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#’d CBV  #’d Arterial/Aortic Stretch  #’d ANP  #’d Vasodilation BP regulated
Assessment
• Skin
• Mucous Membranes
• Mentation
• Lungs
• Veins
• Edema
• Blood Pressure – low or high – orthostatic pressures
• Heart rate
Labs
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Na+
K+
Bun
Creatinine
Hgb
HCT
140 mEq/L
3.8 mEq/L
12 mg/dL
0.8 mg/dL
11 g/dL
38 %
Management/Treatment
Give Birth
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2. Hypervolemia – Heart Failure
– Excess Fluid creates a HyPOtonic state
– #’d Na+consumption  Hypothalmus  #’d ADH
– #’d Volume/Preload
– Na+ is diluted  Kidney  Renin  Liver  Angiotensin I Lung Angiotensin
II ”tighten up” and Na retention
– “Tightening up”  #’d Resistance (afterload)  $’d CO  #’d Fluid Retention
– Adrenal Glands  Increase Aldosterone (hold onto water)
– Stretch Receptors  getting stretched #’d ANP  vasodilation
Assessment
• Distended hand veins / neck veins
• + Hepatojugular reflex
• Skin – taught/shinny
• Edematous
• HR – Maybe tachycardia/maybe S3
• Lung sounds – Crackles/Rales/Rhonchi
• UOP – varies
• Appetite – may be poor (poor perfusion)
• G.I. motility may be slowed (poor perfusion)
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Labs
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Na+
K+
Bun
Creatinine
Hgb
HCT
Serum Osmolarity
BNP
132 mEq/L
3.5 mEq/L
30 mg/dL
1.4 mg/dL
10 g/dL
30 %
240 mOsm/L
1800 pg/mL
Treatment
• Diuretics - $ Volume/Preload
• Inotropic Agents – Dobutamine/Milranone
Amrinone/Digoxin - #Contractility
• Ace Inhibitors – Depends on Kidney function –
$ Resistance/Afterload
• Angiotensin Reuptake Inhibitors (Block reuptake of Angiostensin) – $Afterload
• Nitrates – (afterload & preload reduction)
• b - Blockers – $Afterload(SBP)/ #Contractility/ $Cardiac Workload (Beta)
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3. Hypervolemia – Renal Failure
• Excess Fluid creates a HyPOtonic state
• #’d Volume/Preload
• Na+ is diluted  Kidney  Renin  Liver  Angiotensin I Lung Angiotensin
II ”tighten up” and Na retention
• “Tightening up”  #’d Resistance (afterload)  $’d CO  #’d Fluid Retention
• Adrenal Glands  Increase Aldosterone (hold onto water)
• Stretch Receptors  getting stretched #’d ANP  vasodilation
Assessment
• Distended hand veins / neck veins
• + Hepatojugular reflex
• Skin – taught/shinny
• Edematous
• HR – Maybe tachycardia/maybe S3
• Lung sounds – Crackles/Rales/Rhonchi
• UOP – varies/likely anuric
• Kidneys are not filtering or excreting
Labs
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Na+
K+
Bun
Creatinine
Hgb
132 mEq/L
6 mEq/L
60 mg/dL
8 mg/dL
10 g/dL
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HCT
Serum Osmolarity
30 %
240