Acid-Base, Fluids, and Electrolytes

Question 1

Total body water (TBW) makes up about _____ percent of body weight in men and ____ percent in women.

Answer 1

60% in men 50% in women

Question 2

Why does total body water percentage decrease with age?

Answer 2

Percentage of body fat increases

Question 3

Approximately _____ percent of total body water is located in the intracellular compartment and constitutes the _______ _____ volume.

Answer 3

67% (2/3), intracellular fluid (ICFV)

Question 4

About _____ percent of total body water is located in the extracellular compartment and comprises the _________ ______ volume.

Answer 4

33% (1/3), extracellular fluid (ECFV)

Question 5

What is the major extracellular cation that is responsible for most of the osmotic driving force that maintains the size of the ECFV.

Answer 5

Sodium The total amount of sodium in extracellular fluid (ECF) is the major determinant of the size of the ECFV.

Question 6

If the total amount of sodium in the ECF increases, what will happen to the size of the ECFV?

Answer 6

The size will increase

Question 7

Congestive heart failure, cirrhosis, nephrotic syndrome all have edematous states–what is happening to the level of sodium in their extracellular fluid comparment?

Answer 7

SODIUM IN INCREASING

This increse in sodium in the extracellular fluid compartment causes ECFV overload (volume overload). The increased amount of ECF sodium leads to expansion of the ECFV and the expanded ECFV presents clinically as edema.

Question 8

Breaking it down:

ECFV overload results from too much _______ in the ECF compartment, and ECFV depletion results from too little ______ in the ECF compartment.

Answer 8

Sodium.

Question 9

The amount of sodium in the ECF compartment is sometimes referred to as?

Answer 9

total body sodium

Question 10

When the ECFV increases, the kidney ______ sodium excretion to prevent ECFV overload. When ECFV decreases, the kidney _______ sodium excretion to prevent ECFV depletion.

Answer 10

increases, decreases

Question 11

_______ is determined by the total solute concentration in a fluid comparment.

Answer 11

Osmolality

Question 12

_____ refers to the ability of the combined effect of all of the solutes to generate an osmotic driving force that causes water movement from one compartment to another.

Answer 12

Tonicity

Question 13

How do we increase ECF tonicity?

Answer 13

A solute must be confined to the extracellular fluid compartment.

Question 14

When tonicity increases, what is generally happening to extracellular sodium concentration?

Answer 14

It is increasing.

Question 15

What is the main stimulus for thirst and for antidiuretic hormone (ADH) release?

Answer 15

Hypertonicity

Question 16

In uncontrolled diabetes mellitus, serverly elevated plasma glucose concentration can lead to substantial hyper/hyptonicity and water movment into/out of the ECF?

Answer 16

Hypertonicity, into

Question 17

What happens when a large portion of glomerular filtrate is reabsorbed proximally?

Answer 17

Sufficient water cannot reach the distal nephron to be excreted.

Question 18

What can increased proximal reabsorption lead to?

Answer 18

Water retention and consequent hyponatremia

Question 19

What two situations may cause increased proximal reabsoprtion of water and are important causes of hyponatremia?

Answer 19

1. Volume depletion (often form vomiting with continued ingestion of water)
2. Edematous states: CHF, cirrhosis, and nephrotic syndrome

Question 20

Under the influence of ADH, the collecting tubule is rendered permeable to?

Answer 20

Water.

Question 21

As tubular fluid passes through the collecing tubule, water leaves the tubule and enters the hypertonic interstitium down its concentration gradient and is reabsorbed. What does this process lead to?

Answer 21

Concentrated urine

Question 22

What effect do loop diuretics have on sodium?

Answer 22

They block the reabsorption of sodium in the loop of Henle and impair the formation of the medullary concentration gradient. Therefore, loop diuretics reduce the ability of the kidney to concentrate the urine.

Question 23

In the loop of Henle, what is transported out and what is left behind?

Answer 23

Sodium, chloride, and potassium are transported OUT of the lumen

Water is left behind.

Loop diuretics stop this from happening.

Question 24

In the distal tubule, what is transported out?

Answer 24

Sodium and chloride are transported out of the lumen (by a sodium-chloride transporter which is very important in producing a dilute urine).

This transporter is blocked by thiazide diuretics.

Question 25

What is the most important factor in determing whether the final urine is concentrated or dilute?

Answer 25

The presence or absence of ADH

Question 26

What is the main determinant of ADH secretion?

Answer 26

Changes in sodium concentration

Question 27

What effect does ADH have on the permeability of the renal collecting tubule to water?

Answer 27

ADH increases the permeability.

It allows water to flow down its concentration gradient to be reasorbed into the hypertonic medullary interstitium.

Question 28

What effect does AH have on tonicity of the ECFV?

Answer 28

It decreases tonicity.

Release of ADH will lead to renal water retention and a decrease in the tonicity of the ECFV.

Question 29

What is the clinical syndrome of nonosmotic release or enhancement of ADH action leading to pathologic water retention and hyponatremia?

Answer 29

Syndrome of inappropriate ADH (SIADH)

Question 30

ADH deficiency leading to excessive renal water loss is called__________

ADH unresponsiveness leading to excessive renal water loss is called______

Answer 30

1. Central diabetes insipidus
2. Nephrogenic diabetes insipidus

Question 31

In nephrogenic diabetes insipidus, there are adequate levels of circulating ADH, but the collecting tubule does not appropriately increase its permeability to allow water reabsorption, adn this leads to excessive reanl water loss and the potential for__________.

Answer 31

Hypernatremia

Question 32

Why do loop diuretics cause greater loss of both sodium and water than thiazides?

Answer 32

The sodium loss from loop diuretics is greater because they block sodium reabsorption in the ascending loop of Henle, where 20-30% of filtered sodium is normally reabsorbed, whereas thiazides block sodium reabsorption in the distal tubule, where only 5-10% of filtered sodium is reabsorbed.

Question 33

Are loops or thiazides more likely to cause hyponatremia?

Answer 33

Thiazides! They cause proportional losses of sodium and water such that a relatively less amount of water is excreted than sodium.

Thiazides cause hyponatremia to a degree that they are contraindicated in patients with hyponatremia.

Question 34

What is the major intracellular cation?

Answer 34

potassium

Question 35

Insulin causes potassium to move in or out of cells?

Answer 35

Into

Patients with a deficiency of insulin have impaired assimilation of potassium into cells and are at risk for developing hyperkalemia.

Question 36

What affect will acidosis have on potassium?

Answer 36

Acidosis tends to cause potassium ions to leave cells in exchnage for hydrogen ions and thereofre raises the plasma potassium concentration.

Alkalosis, exact opposite happens.

Question 37

If your patient has hyponatremia nad hypertonicity, what is most likely going on?

Answer 37

Uncontrolled diabetes mellitus.

The sodium is low becasue of transcellular shifting of water, but both tonicity and measured serum osmolality are very high.

Glucose is an effective osmole, the high glucose concentration causes water movement from the intracellular compartment, thereby reducing the extracellular sodium concentration.

Question 38

What is the most common form of hyponatremia?

Answer 38

Hyponatremia with hypotonicity is by far the most common form of hyponatremia and results from impaired renal water excretion in the presence of continued water intake.

Question 39

Hyponatremia with hypotonicity requires two things. What are they?

Answer 39

1. Impaired renal water excretion
2. Continued water intake

Question 40

What is the key to diagnosisng the cause of hyponatremia?

Answer 40

Finding the reason why the kidney cannot appropriately excrete excess water is the key to diagnosing the cause of hyponatremia.

Question 41

What are some possible causes of hyponatremia with hypotonicity?

Answer 41

Impaired GFR

ECFV depletion (often from vomiting with continued ingestion of water)

Edematous states: CHF, cirrhosis, and nephrotic syndrome

Thiazide diuretics

Syndrome of inappropriate ADH (SIADH)

Hypothyroidism or Adrenal Insufficiency

Markedly decreased solute intake combined with high water intake (“tea and toast” diet and excessive beer drinking)

Question 42

Hypernatremia generally results from a deficit of _______.

Answer 42

Water

Question 43

Most cases of hypernatremia require two things:

Answer 43

1. Loss of water
2. Failure to adequately replace the water loss

Question 44

What are the main causes of Hypernatremia?

Answer 44

1. Extrarenal water loss
2. Renal water loss
3. Iatrogenic

The first two are due to water loss with inadequate replacement. Patients are generally dehydrated, and water replacement is indicated. On the other hand, iatrogenic hypernatremia is due to administration of hypertonic saline or NaHCO₃

Iatrogenic hypernatremia results from the addition of hypertonic sodium, rather than water loss

Question 45

What are the most common causes of hypernatremia due to extrarenal water loss?

Answer 45

Fever, profuse sweating, hyperventilation, and severe diarrhea

Question 46

What is the hallmark of marked renal water loss?

Answer 46

Polyuria

The common defect in all cases of renal water loss is an inability of the kidney to conserve water appropriatelyf

Question 47

What is the key to the evaluation of hte patient with renal water loss?

Answer 47

Measurement of the urine osmolality