L.10 Hydration Status and Sodium Regulation Flashcards
1
Q
What is the total body water percentage?
A
60%
Total body water refers to the amount of water contained in the body.
2
Q
What percentage of total body water is extracellular?
A
33%
Extracellular water includes interstitial fluid and blood plasma.
3
Q
What is the percentage of interstitial fluid in total body water?
A
25%
Interstitial fluid is the fluid found between cells.
4
Q
What percentage of total body water is blood plasma?
A
8%
Blood plasma is the liquid component of blood.
5
Q
What percentage of total body water is intracellular?
A
66%
Intracellular fluid is the fluid within cells.
6
Q
What is the average total body fluid in a 70kg adult?
A
≈ 42L
This is the total volume of fluid in the body.
7
Q
What is the approximate volume of intracellular fluid (ICF) in a 70kg adult?
A
≈ 28L
ICF is crucial for cellular function.
8
Q
What is the approximate volume of extracellular fluid (ECF) in a 70kg adult?
A
≈ 14L
ECF includes interstitial fluid and plasma.
9
Q
What should total intake equal?
A
Total output
This principle is essential for maintaining homeostasis.
10
Q
What drives the movement of water between compartments?
A
Osmotic pressure
Osmotic pressure is created by dissolved solutes.
11
Q
What do osmoreceptors in the hypothalamus monitor?
A
ECF osmolality
These receptors help regulate hydration status.
12
Q
If ECF osmolality is greater than ICF osmolality, what happens to water?
A
Water moves out of cells
This can lead to cell shrinkage.
13
Q
If ECF osmolality is less than ICF osmolality, what happens to water?
A
Water moves into cells
This can lead to cell swelling.
14
Q
What are electrolytes?
A
Substances that dissociate into ions in solution
Electrolytes are crucial for various physiological functions.
15
Q
What are the two types of charged particles in electrolytes?
A
Cations and anions
Cations are positively charged and anions are negatively charged.
16
Q
What is the major cation in extracellular fluid (ECF)?
A
Sodium (Na+)
Sodium plays key roles in fluid balance and nerve function.
17
Q
What is the normal range of sodium in ECF?
A
135-145 mmol/L
Maintaining sodium levels is vital for health.
18
Q
What is the major cation in intracellular fluid (ICF)?
A
Potassium (K+)
Potassium is essential for cellular function.
19
Q
What is the normal range of potassium in ECF?
A
3.5-5.0 mmol/L
Potassium levels must be carefully regulated.
20
Q
What is the normal range of potassium in ICF?
A
140-150 mmol
High levels of potassium are found within cells.
21
Q
Fill in the blank: Cation levels must equal _______ levels in each compartment.
A
anion
This balance is crucial for maintaining electrical neutrality.
22
Q
What is the function of the Na+/K+ ATPase pump?
A
Active transport pump which requires ATP and maintains concentration gradients
The Na+/K+ ATPase pump is crucial for cellular function and maintaining electrochemical gradients.
23
Q
What is the total sodium distribution in the body?
A
≈ 3,700 mmol of sodium
Sodium is vital for various physiological processes.
24
Q
What percentage of body sodium is exchangeable?
A
75%
Exchangeable sodium can move between compartments in the body.
25
Where is the majority of sodium found in the body?
Extracellular space
## Footnote
Sodium is predominantly located outside cells.
26
What percentage of body sodium is located in bone?
25%
## Footnote
Bone serves as a storage site for sodium.
27
What does sodium intake equal in healthy conditions?
Sodium output (balance)
## Footnote
This balance is essential for homeostasis.
28
What major determinant does sodium represent for ECF volume?
Sodium is the major determinant of ECF volume
## Footnote
ECF stands for extracellular fluid.
29
How does water relate to sodium in the body?
Water follows sodium
## Footnote
This relationship is crucial for maintaining fluid balance.
30
What is sodium's role in ECF osmolality?
Sodium is the major determinant of ECF osmolality
## Footnote
Osmolality reflects the concentration of solutes in body fluids.
31
What can impaired blood volume lead to?
Impaired blood pressure ⇒ circulatory shock/collapse ⇒ impaired perfusion of tissues ⇒ impaired oxygen delivery (hypoxia) ⇒ impaired clearance of waste products
## Footnote
This cascade highlights the importance of sodium and fluid balance.
32
What are some mechanisms in place to maintain sodium and fluid balance?
1. Thirst
2. Hormone regulation
3. Kidney function
## Footnote
These mechanisms help the body adapt to different hydration needs.
33
What happens when large volumes of water are consumed?
Dilute urine and increased urine output
## Footnote
This occurs due to the kidneys' retention of water.
34
What happens when small volumes of water are consumed?
Concentrated urine and decreased urine output
## Footnote
The kidneys adjust to conserve water in this scenario.
35
How should urine output and color be monitored?
Monitor urine output and colour
## Footnote
Changes can indicate hydration status and renal function.
36
What is ADH also known as?
Vasopressin
## Footnote
ADH stands for antidiuretic hormone.
37
Where is ADH released from?
Posterior pituitary gland
38
What is the primary action of ADH?
Increase water reabsorption in the kidneys
39
ADH responds to changes in _______ osmolality.
ECF
40
What type of water reabsorption does ADH primarily facilitate?
Pure water reabsorption
41
Which part of the nephron does ADH act on?
Distal convoluted tubule and collecting ducts
42
What protein does ADH incorporate into the collecting ducts?
Aquaporin-4
43
What does the renin-angiotensin-aldosterone system (RAAS) respond to?
Changes in afferent arteriole pressure
44
What is released by the kidneys in the RAAS?
Renin
45
Sodium reabsorption in RAAS leads to _______.
Water following sodium
46
What does angiotensin II induce the release of?
Aldosterone from the adrenal cortex
47
Aldosterone acts on which parts of the nephron?
Distal tubule and collecting ducts
48
What are the preferred tubes for laboratory measurement of electrolytes?
Serum (Yellow or Red Cap) and Lithium Heparin (Green Cap)
49
What is the purpose of the Lithium Heparin tube?
Used for plasma electrolyte testing
50
Which tube should be avoided due to affecting sodium measurements?
Sodium Citrate (Blue Cap)
51
What effect does Potassium EDTA (Purple Cap) have on readings?
Adds potassium and chelates calcium
52
What pre-analytical consideration involves sample type?
Serum, plasma, whole blood
53
What should be avoided to prevent IV fluid contamination?
Drawing from the same arm receiving IV fluids
54
What effect does 0.9% Normal Saline (NaCl) have on sodium levels?
Falsely elevates sodium
55
What can 5% Dextrose (D5W) lead to?
Dilutional hyponatraemia
56
What should always be noted regarding IV fluid administration?
Time since last infusion and type of IV fluid
57
What is the principle behind ion-selective electrodes?
Electrolytes are measured using ion-selective membranes that allow only the target ion to pass
## Footnote
Target ions include Na⁺, K⁺, Cl⁻, among others.
58
What are the steps involved in the functioning of ion-selective electrodes?
1. Ion passes through a selective membrane.
2. It interacts with an internal reference solution.
3. A potential difference (voltage) is generated across the membrane.
4. This voltage is proportional to ion activity.
5. Measured by a voltmeter and interpreted using the Nernst equation.
59
What is the difference between direct and indirect ion-selective electrodes?
Direct ISE measures ion activity directly in undiluted samples, while Indirect ISE measures ion activity in a diluted sample.
60
In what applications are direct ion-selective electrodes commonly used?
1. Point-of-care testing (POCT)
2. Blood gas analysers
61
What are the advantages and disadvantages of direct ion-selective electrodes?
Advantages: Rapid results.
Disadvantages: More susceptible to interference from lipids or proteins.
62
What are the advantages and disadvantages of indirect ion-selective electrodes?
Advantages: More stable and less affected by sample composition.
Disadvantages: Slower due to dilution step and can underestimate ions in hyperlipidaemic or hyperproteinaemic samples.
63
What is osmolality?
Osmolality is a measure of the number of particles in a solution.
64
How does water movement relate to osmolality?
Water moves from a region of low osmolality to high osmolality.
65
Fill in the blank: The voltage generated across the membrane of an ion-selective electrode is proportional to _______.
ion activity
66
True or False: Indirect ion-selective electrodes are commonly used for point-of-care testing.
False
67
What is the primary use of plasma and urine osmolality?
Assessing sodium disorders and water balance
## Footnote
Plasma and urine osmolality are crucial for diagnosing and managing conditions related to fluid and electrolyte balance.
68
How does osmolality affect the freezing point of a solution?
Solutions with more particles freeze at lower temperatures
## Footnote
This phenomenon is utilized in the measurement of osmolality using an osmometer.
69
What does a higher osmolality indicate about the freezing point?
Lower freezing point
## Footnote
Higher osmolality corresponds to a greater depression of the freezing point.
70
What are the main contributors to osmolality?
* Sodium
* Potassium
* Glucose
* Urea
## Footnote
These substances play significant roles in determining the osmolality of body fluids.
71
How is osmolality calculated?
Osmolality = 2[NA+] + [K+] + [Glucose] + [Urea]
## Footnote
This formula helps in quantifying the osmolality based on the concentrations of key solutes.
72
What is hyponatraemia?
Serum/plasma sodium level below 135 mmol/L
## Footnote
It is the most common electrolyte disorder, leading to various clinical symptoms.
73
What are some potential causes of hyponatraemia?
* Reduced sodium intake (rare)
* Increased water intake
* Increased sodium loss
* Increased water retention
* Redistribution within body compartments
## Footnote
Understanding these causes is critical for diagnosing and treating hyponatraemia.
74
What happens to water movement in hyponatraemia?
Water moves into cells, causing cell swelling
## Footnote
This can lead to serious complications like cerebral oedema.
75
What are the predominant clinical symptoms of hyponatraemia?
* Muscle cramps
* Lethargy
* Nausea and vomiting
* Headache
* Seizures
* Confusion
## Footnote
Symptoms may vary based on the speed of onset of hyponatraemia.
76
What are the types of hyponatraemia?
* Hypovolaemic
* Euvolemic
* Hypervolemic
## Footnote
Each type of hyponatraemia has different underlying mechanisms and implications for treatment.
77
What is Hypervolaemic Hyponatraemia?
Increased total body sodium and water with water retention exceeding sodium retention
## Footnote
Also referred to as dilutional hyponatraemia or oedematous hyponatraemia.
78
What causes Hypervolaemic Hyponatraemia?
* Increased water intake (e.g. inappropriate IV fluids)
* Decreased water excretion (e.g. renal failure, heart failure, nephrotic syndrome, liver failure)
79
How can urinary sodium help differentiate the causes of Hypervolaemic Hyponatraemia?
Urinary sodium < 20 mmol/L indicates not renal failure; urinary sodium > 20 mmol/L indicates renal failure.
80
What is the treatment for Hypervolaemic Hyponatraemia?
Treat with diuretics to induce natriuresis and restrict water intake.
81
What is Euvolaemic Hyponatraemia?
Increase in total body water with normal total body sodium
## Footnote
Most common cause of hyponatraemia in hospitalised patients.
82
What are the causes of Euvolaemic Hyponatraemia?
* Increased water intake (e.g. psychogenic polydipsia, water overload)
* Decreased water excretion (e.g. SIADH)
83
What is SIADH?
Syndrome of inappropriate antidiuretic hormone secretion
## Footnote
Inappropriate secretion of ADH in relation to plasma osmolality.
84
What characterizes the diagnosis of SIADH?
Hyponatraemia with hypoosmolality and inappropriately concentrated urine.
85
What is the treatment for Euvolaemic Hyponatraemia?
Treat with fluid restriction.
86
What is Hypovolaemic Hyponatraemia?
Decrease in total body sodium and water with water loss exceeding sodium loss
## Footnote
ECF decrease.
87
What causes Hypovolaemic Hyponatraemia?
* Sodium loss (e.g. diuretics, vomiting, diarrhoea, burns)
* Decreased sodium intake (rare)
88
How can urinary sodium help differentiate the causes of Hypovolaemic Hyponatraemia?
Urinary sodium > 20 mmol/L indicates renal loss; urinary sodium < 20 mmol/L indicates extrarenal loss.
89
What is the initial response to sodium loss in Hypovolaemic Hyponatraemia?
Initially sodium loss is accompanied by water loss, leading to hypovolaemia.
90
What is the treatment for Hypovolaemic Hyponatraemia?
Treat with sodium replacement and fluid replacement.
91
What is pseudo-hyponatraemia?
Hyponatraemia due to artefact
## Footnote
Associated with hyperlipidaemia and hyperproteinaemia, which can cause a 5-10 mmol/L decrease in sodium levels falsely.
92
What conditions are associated with pseudo-hyponatraemia?
* Hyperlipidaemia
* Hyperproteinaemia
## Footnote
These conditions can lead to a false reading of sodium levels.
93
How can you rule out pseudo-hyponatraemia?
* Measure serum osmolality
* Measure serum sodium by direct ISE
## Footnote
These tests confirm whether the hyponatraemia is artefactual.
94
What is hypernatraemia?
Serum/plasma sodium level above the reference range (>145 mmol/L)
## Footnote
It is less common than hyponatraemia.
95
What are the possible causes of hypernatraemia?
* Increased sodium intake
* Decreased water intake
* Increased water loss
## Footnote
These factors contribute to elevated sodium levels.
96
What are common symptoms of hypernatraemia?
* Thirst
* Anorexia
* Restlessness
* Nausea and vomiting
* Coma
* Bleeding
## Footnote
Symptoms vary in severity based on sodium levels.
97
What causes pure water loss leading to hypernatraemia?
* Decreased intake (e.g. elderly, infants)
* Low volume of unconcentrated urine
* Increased loss (e.g. fever, sweating, burns, diabetes insipidus)
* High volume of unconcentrated urine
## Footnote
Pure water loss can significantly raise sodium levels.
98
What are the causes of water and sodium loss associated with hypernatraemia?
* Renal loss (e.g. diuretics, osmotic diuresis)
* Extrarenal loss (e.g. vomiting, diarrhoea)
* High volume of unconcentrated urine
* Low volume of concentrated urine
## Footnote
These conditions can lead to combined losses of water and sodium.
99
What can lead to sodium gain resulting in hypernatraemia?
* Sodium bicarbonate therapy
* Drownings in salt water
* Hormone disorders (e.g. hyperaldosteronism, hypercortisolism)
* Low volume of concentrated urine
## Footnote
Sodium gain can exacerbate hypernatraemia.
100
What is the treatment for hypernatraemia due to pure water loss?
Give IV fluids
## Footnote
This helps to correct the fluid deficit.
101
What should be done for sodium overload in hypernatraemia?
Diuretics should be used instead of IV fluids
## Footnote
Volume is already expanded in sodium overload.
102
What is diabetes insipidus?
Associated with hypernatraemia due to inappropriate excretion of water (polyuria)
## Footnote
It results in excessive urination and thirst.
103
What are the two types of diabetes insipidus?
* Central diabetes insipidus (lack of ADH)
* Nephrogenic diabetes insipidus (kidneys do not respond to ADH)
## Footnote
Both types lead to symptoms of polydipsia and polyuria.
104
What tests are used to diagnose diabetes insipidus?
Water deprivation test and measure urine osmolality
## Footnote
These tests help determine the cause of the condition.
