Fluids, Electrolytes, and Acid-Base Disorders

Question 1

What % of body weight is water in men? In women? What two factors cause total body water % to decrease?

Answer 1

60% of men’s total body weight = water,
50% of women’s total body weight = water
Age and obesity cause total body water to decrease over time

Question 2

How much of total body water is intracellular fluid and how much is extracellular fluid?

Answer 2

2/3 is ICF and 1/3 is ECF

Question 3

How much of body’s weight is water in intracellular fluid? How much of body’s weight is water in extracellular fluid?

Answer 3

ICF = 40% of body weight (2/3 * 60)
ECF = 20% of body weight (1/3 * 60)

Question 4

What compartment is plasma and interstitial fluid apart of?

Answer 4

ECF

Question 5

What two forces determine fluid shift in the body?

Answer 5

Hydrostatic pressure and oncotic pressure

Question 6

True/False: Skin turgor and mucous membrane appearance are good indicators of volume status?

Answer 6

False

Question 7

What is normal urine output in infants and what is normal urine output in adults?

Answer 7

Infants = 1.0 mL/kg/hr
Adults = .5-1.0 mL/kg/hr

Question 8

What causes the body to be hypervolemic on an overall level but intravascularly depleted and why?

Answer 8

Anything that causes hypoalbuminemia (nephrotic syndrome or liver disease) will cause fluid to shift to third space and out of the vasculature.

Question 9

What fluids can be used to increase intravascular volume? (3)

Answer 9

1. Normal saline (unless the patient has CHF)
2. D51/2NS
3. Lacted Ringer

Question 10

D51/2NS has what that can help prevent muscle breakdown but should be used in caution in what patients?

Answer 10

It has glucose to help prevent muscle breakdown, however, it should be used in caution in diabetics

Question 11

What is the standard maintenance fluid?

Answer 11

D51/2NS

Question 12

What is D5W used for? (2) and how much of it remains intravascularly?

Answer 12

1. dilute powdered medications
2. Sometimes indicated in correcting hypernatremia

Only 1/12th remains intravascularly because a large amount of it distributes to total body water compartment

Question 13

What electrolyte does lacted ringer contain and what is its use?

Answer 13

Used as replacement for intravascular volume, not a maintenance fluid, contains potassium (don’t use if hyperkalemia is suspected)

Question 14

What are three broad causes of hypovolemia?

Answer 14

1. Third spacing due to ascites, effusions, bowel obstructions, crush injuries, burns
2. significant loss
3. Inadequate intake

Question 15

What are some clinical features of hypovolemia?

1. CNS findings?
2. Cardiovascular findings?
3. Skin?
4. Urine output?
5. Renal conditions?

Answer 15

1. CNS findings: mental status changes, sleepiness, apathy, coma
2. Cardiovascular: (due to decrease in plasma volume): orthostatic hypotension, tachycardia, decreased pulse pressure, decreased CVP, decreased PCWP
3. Skin: Poor turgor, hypothermia, dry tongue, pale extremities
4. Oliguria
5. Acute renal failure (prerenal azotemia lab findings)

Question 16

What % increase is seen in hematocrit for each liter of volume depletion in a patient?

Answer 16

3% increase for each liter of deficit in a patient

Question 17

How is hypovolemia treated?

Answer 17

1. Correct volume deficit
   
   • Use bolus to achieve euvolemia. Begin with isotonic solution (lactated ringer, or NS). Maintain urine output at 0.5 to 1.0 mL/kg/hr.
2. Maintenance fluid - D51/2NS with 20 mEq KCL/L is most common adult maintenance fluid

Question 18

How is maintenance fluid calculated?

Answer 18

4/2/1 rule:
4 mL/kg for first 10 kg, 2 mL/kg for next 10 kg, 1 mL/kg for every 1 kg over 20

Example) 70kg person = 410 = 40; 210 = 20, 1*50 = 50; total = 110 ml/hr

Question 19

What are two broad causes of hypervolemia?

Answer 19

1. Iatrogenic (parenteral overhydration)

2. Fluid-retaining states: CHF, nephrotic syndrome, cirrhosis, ESRD

Question 20

What are the clinical features of hypervolemia?

Answer 20

1. Weight gain
2. Peripheral edema
3. Ascites
4. Pulmonary edema
5. JVD
6. Pulmonary rales
7. Low hematocrit and albumin concentration

Question 21

How is hypervolemia treated?

Answer 21

1. Fluid restriction

2. Judicious use of diuretics

Question 22

Hyponatremia in the blood causes water to flow which way?

Answer 22

Water from the blood flows into cells, causing them to expand

Question 23

Hypernatremia in the blood causes water to flow which way?

Answer 23

Water from cells flows into cells, causing them to shrink

Question 24

How is serum osmolality calculated?

Answer 24

2*Sodium + Glucose/18 + BUN/2.8

Question 25

What is normal serum osmolality?

Answer 25

Approximately 280-295 mOsm/kg

Question 26

How do loop diuretics work?

Answer 26

They inhibit sodium reabsorption in the thick ascending loop of henle (Na+, K+, Cl- transporter inhibition)

Question 27

How do thiazide diuretics work?

Answer 27

They inhibit Na+ Cl- cotransporter in the distal tubule.

Question 28

Where does the majority of sodium reabsorption occur?

Answer 28

In the proximal tubule of the kidney

Question 29

What effect does aldosterone have on the kidney?

Answer 29

Aldosterone increases sodium reabsorption and potassium secretion from the late distal tubules

Question 30

Plasma hypertonicity (above >295 mOsm/kg) causes what? (2)

Answer 30

Activation of osmoreceptors in the hypothalamus which stimulates thirst; secretion of ADH

Question 31

How does ADH work?

Answer 31

Binds to V2 receptors in renal collecting ducts and water channels are synthesized and more water is reabsorbed

Question 32

What causes ADH secretion to be suppressed?

Answer 32

Increasing plasma tonicity

Question 33

Below which amount of sodium concentration, do symptoms of hyponatremia begin?

Answer 33

<120 mEq/L

Question 34

How many different broad categories of hyponatremia are there?

Answer 34

3, hypotonic hyponatremia, hypertonic hyponatremia, and isotonic hyponatremia

Question 35

How is hypotonic hyponatremia characterized?

Answer 35

It is characterized by hyponatremia along with decreased serum osmolality <280 mOsm/kg

Question 36

What are three broad categories of hypotonic hyponatremia?

Answer 36

1. Hypovolemic hypotonic hyponatremia 2. Euvolemic hypotonic hyponatremia 3. Hypervolemic hypotonic hyponatremia

Question 37

What are the symptoms and causes of hypervolemic hypotonic hyponatremia?

Answer 37

Symptoms are edema, JVD, crackles in the lungs, and causes are water-retaining states such as CHF, nephrotic syndrome, and liver disease

Question 38

What are the symptoms and broad causes (2) of hypovolemic hypotonic hyponatremia?

Answer 38

Symptoms are sunken eyes, dry mucous membranes, skin tenting, and causes are extrarenal salt loss or renal salt loss. Extrarenal salt loss shows up as low urine sodium (<10). Renal salt loss shows up as high urine sodium (>20)

Question 39

What are some causes of extrarenal salt loss?

Answer 39

Diarrhea, vomiting, diaphoresis, third spacing

Question 40

What are some causes of renal salt loss?

Answer 40

Excessive diuretic use, low aldosterone, and acute tubular necrosis

Question 41

What are the symptoms and causes of euvolemic hypotonic hyponatremia?

Answer 41

No symptoms of hypovolemia or hypervolemia. ``` Causes are RATS Renal Tubular acidosis Addison's Dz Thyroid Dz SIADH ```

Question 42

What is the serum osmolality for isotonic hyponatremia and what are the causes? Isotonic hyponatremia aka?

Answer 42

Aka psuedohyponatremia. Caused by anything that increases triglycerides or proteins in the blood. Hyponatremia + normal serum osmolality (280-295)

Question 43

What are the causes and serum osmolality for hypertonic hyponatremia?

Answer 43

Serum osmolality >295 Caused by hyperglycemia, mannitol and glycerol in the blood

Question 44

Draw out the evaluation of hyponatremia

Answer 44

See SUTM pg 308

Question 45

What are the clinical features of hyponatremia?

Answer 45

Neurological symptoms predominate: cerebral edema, headache, delirum, irritability, muscle twitching, weakness, hyperactive deep tendon reflexes Hypertension Oliguria progressing to anuria

Question 46

How does hyperglycemia affect serum sodium levels?

Answer 46

For every 100 mg/dL increase in blood glucose level above normal, the serum sodium decreases by 3 mEq/L.

Question 47

How is isotonic and hypertonic hyponatremia's managed?

Answer 47

Diagnose and treat the underlying disorder

Question 48

How is hypotonic hyponatremia managed?

Answer 48

1. Mild cases (Na+ 120-130): withhold free water, allow patient to re-equilibrate naturally. 2. Moderate cases (Na+ 110 to 120): loop diuretics given with saline 3. Severe cases (Na+ <110): give hypertonic saline to increase serum sodium concentration by 1-2 mEq/L/hr until symptoms improve. DO NOT INCREASE serum sodium by more than 8 mmol/L during the first 24 hours because it may lead to central pontine demyelination

Question 49

How is hypernatremia defined? (Plasma Na+ concentration)

Answer 49

Na+ > 145 mmol/L

Question 50

What are two broad causes for hypernatremia?

Answer 50

Water loss or sodium infusion

Question 51

What are three broad categorizations and causes of hypernatremia? (Describe each category)

Answer 51

1. Hypovolemic hypernatremia (sodium stores are depleted, but more water loss than sodium loss) Causes: Renal loss or Extrarenal loss 2. Isovolemic hypernatremia (sodium stores are normal, water loss) Cause: Diabetes Inspidus 3. Hypervolemic hypernatremia (excess sodium) Causes: cushing syndrome, exogenous corticosteroids, iatrogenic causes

Question 52

Rapid correction of hypernatremia leads to what? Rapid correction of hyponatremia leads to what?

Answer 52

Rapid correction of hypernatremia leads to cerebral edema Rapid correction of hyponatremia leads to central pontine demyelination

Question 53

What are some clinical features of hypernatremia?

Answer 53

Neurological symptoms predominate: altered mental status, restlessness, weakness, focal neurological deficits, confusion, seizures, coma Salivation increases, tissue and mucous membranes are dry

Question 54

What is a good lab test for hypernatremia?

Answer 54

Urine osmolality > 800 mOsm/kg

Question 55

What is formula for calculating free water deficit?

Answer 55

1. Water Deficit = TBW (1- actual Na+/desired Na+)

Question 56

How is hypovolemic hypernatremia treated?

Answer 56

Give isotonic saline to restore hemodynamics. Correction of hypernatremia can wait until patient is hemodynamically stable, then replace free water deficit

Question 57

How is isovolemic hypernatremia treated?

Answer 57

Since cause is usually diabetes inspidus, treatment may require vasopressin

Question 58

How is hypervolemic hypernatremia treated?

Answer 58

Give diuretics (furosemide) and D5W to remove excess sodium. Dialyze patients with renal failure