Fluid & electrolytes

Question 1

21713 – Total body water
1: is used to calculate intracellular fluid volume
2: is a greater percentage of body weight in men than women
3: is calculated using Deuterium oxide dilution
4: increases with age

Answer 1

TTTF
Ganong 13th Ed. Chapter: 1 Page: 2-3 Guyton 7th Ed. Chapter: 33 Page: 382-386

Question 2

23174 – The total body water expressed as a percentage of body weight is
1: unaffected by obesity
2: greater in women than in men
3: approximately 45% in a 70 kilogram man of normal build
4: decreased in Cushing’s disease

Answer 2

FFFT
Manual of Resource Material Ganong, 19th Ed, Ch 1, p1-3

Question 3

7367 – Which of the following is/are true with regard to body composition?
1: The total amount of the exchangeable sodium in the body is approximately 3000 mmol, this being 70% of the total body sodium.
2: The total body potassium is approximately 3000 mmol and of this, 90% is exchangeable.
3: Serum osmolality is approximately 300 milliosmoles / kg.
4: The pH of the extracellular fluid is approximately 7.36 to 7.44.

Answer 3

TTTT

Question 4

21433 – Which of the following is/are true with respect to percentage water composition of the body?
1: it is lower in females
2: it can be estimated from measurement of plasma volume
3: it decreases with age
4: it is independent of body fat composition

Answer 4

TFTF
Ganong 13th ed CHAPTER: 1 PAGE: 3

Question 5

12793, 21218 – Concerning body water compartments
1: the extracellular fluid is isosmotic with the intracellular fluid at equilibrium
2: the extracellular volume of a 70 kg man is 18-20 litres
3: transcellular water is that component of extracellular water that has been processed through cells into special compartments
4: an individual’s total water is directly proportional to his fat content

Answer 5

TFTF
Ganong 13th Ed. Chapter: 1 Page: 1-3 Guyton 7th Ed. Chapter: 33 Page: 382-386.
Transcellular water is, by definition, that component of extra-cellular fluid (ECF) that has been processed through cells into special compartments (C true); examples include aqueous humour, CSF and synovial fluid. ECF comprises 20% of total body water (TBW) and in a 70kg man is approximately 14 l (B false). Water content of fat is lower than that of muscle and other tissues so that TBW is inversely proportional to the amount of fat (D false). Women have relatively less TBW than men. ECF is isoosmotic with intracellular fluid (ICF) at osmotic equilibrium; any changes in osmolarity of either ECF or ICF are accompanied by movement of water across the cell membrane to restore osmotic equilibrium with resultant change in volume of either compartment (A true).

Question 6

21428 – Concerning plasma
1: it has a higher sodium concentration than interstitial fluid
2: it has a higher magnesium concentration than interstitial fluid
3: it has a higher protein concentration than interstitial fluid
4: it has a higher chloride content than interstitial fluid

Answer 6

TTTF
Ganong 13th Ed. Ch. 1 P. 5 Guyton 7th Ed. Ch. 33 P. 389 Ch. 30 P. 356
The electrolyte concentration of the plasma is greater than the electrolyte concentration of the interstitial fluid BECAUSE plasma proteins are negatively charged

Question 7

7291 – The following are true or false for plasma components
1: the half-life of factor VIII infusion is 12 - 16 hours
2: Prothrombin complex concentrates contain factors II, IX and X, and are useful in vitamin K deficiency, warfarin overdose and patients with haemophilia B
3: Cryoprecipitate contains factor VIII, IX and von Willebrand factor and fibrinogen
4: the main use of intravenous albumin is for nutritional purposes, rather than as a volume expander
5: fresh frozen plasma contains normal levels of all coagulation factors

Answer 7

TTFFT

Question 8

20133 – S. The electrolyte concentration of the plasma is greater than the electrolyte concentration of the interstitial fluid BECAUSE R. plasma proteins are negatively charged

Answer 8

S is true, R is true and a valid explanation of S
Guyton Ch. 30 P. 356-7 Ganong 13th Ed. Ch. 1 P. 5

Question 9

23194 – Regarding the buffer systems of the body
1: bicarbonate is the most important buffer in the body
2: bicarbonate is not a good buffer at body fluid pH
3: phosphate is a good physiological buffer because of its pKa
4: bicarbonate is the most plentiful buffer in body fluid

Answer 9

TTTF
Guyton 7th ed. Chapter: 37 Page: 441

Question 10

19653 – Derangements of body fluid and electrolytes characteristic of gastric outlet obstruction are
A. HCO3 18 mmol/l, K 4.5 mmol/l Cl 101 mmol/l Na 135 mmol/l
B. HCO3 10 mmol/l, K 2.5 mmol/l Cl 112 mmol/l Na 140 mmol/l
C. HCO3 35 mmol/l, K 3.0 mmol/l Cl 152 mmol/l Na 120 mmol/l
D. HCO3 37 mmol/l, K 2.8 mmol/l Cl 71 mmol/l Na 135 mmol/l
E. HCO3 27 mmol/l, K 3.0 mmol/l Cl 164 mmol/l Na 140 mmol/l

Answer 10

D
Guyton 7th Edition CHAPTER: 37 PAGE: 449

Question 11

22569 – In intracellular fluid
1: the potassium concentration is about 160 mmol/l
2: potassium, magnesium and sodium are the main cations present
3: organic phosphates are present in high concentration
4: the hydrogen ion concentration exceeds that in extracellular fluid

Answer 11

TTTT
Ganong 11th Edition CHAPTER: 1 PAGE: 17. Page 7 table 1-2 Ganong 20th edition states K+concentration inside the cell is 150mmol/L -
10mmol diff

Question 12

21293 – Interstitial fluid production is increased in patients who have
1: extensive thermal burns
2: irreversible shock
3: major deep vein thrombosis
4: acute hypoalbuminaemia

Answer 12

TTTT

Question 13

19300 – Under basal conditions, the route of greatest water loss is via the
A. skin
B. lung
C. kidney
D. gastrointestinal tract
E. salivary glands

Answer 13

C
Guyton 7th Ed. Ch. 33 P. 383

Question 14

18964 – To correct metabolic alkalosis due to vomiting, the best initial replacement solution is
A. sodium chloride
B. calcium chloride
C. potassium chloride
D. sodium lactate
E. ammonium lactate

Answer 14

A

Question 15

21693 – Potassium depletion may be associated with
1: flaccid paralysis
2: T wave inversion and U waves in the ECG
3: paralytic ileus
4: polyuria

Answer 15

TTTT
Ganong 13th Ed. Chapter: 20 Page: 316-317 Ch. 28 P. 465 Ch. 33 P. 533 Ch. 26 P. 423

Question 15

18280 – Concerning daily fluid and electrolyte balance in adults, which one of the following statements is most correct?
A. The minimal obligatory urinary loss is 1000 ml
B. Insensible losses normally total about 200 ml
C. About 500 ml is normally lost in the stool
D. Average fluid intake varies between 2000 and 3000 ml
E. Urinary losses of potassium exceed those of sodium

Answer 15

D
Total daily fluid intake (as ingested liquid and as water of food) averages between 2-3 litres in adults (D). The other responses are all incorrect.

Question 16

19006 – Serum hyperosmolality is LEAST likely to occur as a possible complication early in the course of
A. a severe body burn
B. acute oliguric renal failure
C. hyperpyrexia
D. total parenteral nutrition
E. hyperglycaemia

Answer 16

B
Burnett - C. S. S. CHAPTER: 13.5

Question 17

25704 – Hyponatraemia
A. may appear to be present if the blood sample is taken from a patient with frank lipaemia
B. is associated with sodium depletion rather than water overload
C. is best treated by sodium chloride infusion if the patient has normal renal function
D. in association with a high urine sodium is likely in nephrotic syndrome
E. when associated with systemic inflammatory response syndrome (SIRS) results in decreased ECF volume

Answer 17

A

Question 18

25840 – Regarding electrolyte balance
1: the principal intra-cellular cation is potassium
2: a patient with a serum sodium level of 125 mmol/L could be sodium replete
3: hypernatraemia is preferably corrected by oral administration of water
4: hypomagnesaemia can occur from long term loop diuretic therapy

Answer 18

TTTT

Question 19

21268 – Regarding potassium requirements in a post-operative patient, it is true that
1: during the first 24 hours normally no parenteral potassium is necessary
2: kidney function must be adequate before any parenteral potassium is administered
3: 60 to 80 mmol/day are adequate in a normal adult
4: daily estimations of urinary potassium are necessary before any potassium salts are administered

Answer 19

TTTF

Question 20

12828, 23899 – A plasma osmolality of 230 mOsm/Kg induced by rapid water infusion would be associated with
1: an increase in interstitial fluid volume
2: marked haemolysis in vivo of red blood cells
3: altered consciousness
4: a marked rise in the blood urea concentration

Answer 20

TFTF
Guyton 7th Ed. Ch. 33 P. 390 Ch. 36 P. 431 Ganong 13th Ed. Ch. 27 P. 438.
A rapid water infusion into the intravascular space with a reduced plasma osmolarity is an example of acute water intoxication. There is an immediate expansion of ECF including the interstitial fluid volume (B true). To maintain osmotic equilibrium water will pass into the cells. As the cerebral neurones are the most sensitive an altered state of consciousness will result (D true). Spontaneous haemolysis will only occur when the osmolarity is less than 200 mOsm/kg (A false). Urea is a freely diffusible compound and rapidly obtains equilibrium with ECF without any significant changes in its concentration in plasma (C false).

Question 21

19408 – The most important buffer base in the extracellular fluid is
A. plasma protein
B. phosphate
C. bicarbonate
D. haemoglobin
E. lactate

Answer 21

C
Guyton 7th Ed. Chapter: 37 Page: 441-442

Question 22

4009 – Hypokalaemia may be associated with
1: paralytic ileus
2: muscle weakness
3: increased sensitivity to digitalis
4: peaked T waves and ST elevations on an electrocardiogram

Answer 22

TTTF
Clinical Science for Surgeons CHAPTER: 13.6.5 PAGE: 203

Question 23

15047 – A 65-year-old man of 70 kg body weight is vomiting from a small bowel obstruction. He has lost approximately 5 litres of fluid. It is likely that
1: he will pass urine with a high osmolarity
2: his urine output will be decreased
3: his plasma protein concentration will be increased
4: his plasma Na+ concentration will be increased

Answer 23

TTTF
Refer to Ganong, 19th Ed, Ch 39, page 702; MCQ Book

Question 24

12596 – S: Cl- levels in the interstitial fluid are higher than in the blood plasma because R: capillary membranes are not freely permeable to protein anions

Answer 24

S is true, R is true and a valid explanation of S
The Donnan effect is that, in the presence of non-diffusible ions, the diffusible ions will distribute themselves in equilibrium across a semipermeable membrane. In plasma the protein anions are in a greater concentration than in the interstitial fluid but are non-diffusible (not freely permeable) and, therefore, exert a Donnan effect; thus chloride anion concentration is slightly greater in interstitial fluid than in the plasma. Therefore S and R are true and R is a valid explanation of S.

Question 25

9886, 20739 – S. Tetany results from plasma proteins binding more calcium during hyperventilation BECAUSE R. plasma proteins are less ionized at higher pH

Answer 25

S is true and R is false
Ganong, 19th ed, Ch 25, Ganong 19th ed. Chapter: 21 Page: 365

Question 26

22989 – Osmoreceptor cells
1: are located in the supraventricular and paraventricular nuclei
2: control the rate of discharge of oxytocin containing neurons in the posterior pituitary
3: respond to changes in extracellular fluid volume
4: are sensitive to small changes in plasma osmolarity

Answer 26

FFFT
Ganong 16th Ed. CHAPTER: 14 PAGE: 215-216
1 - at hypothalamus
2 - ADH

Question 27

952 – The most clinically useful form of nutritional assessment related to body weight is:
A. Absolute weight measured on an accurate set of scales.
B. A 72-hour dietary recall history.
C. Body mass index (BMI: weight divided by the square of height).
D. A history of unintentional weight loss greater than 10% over the preceeding 6 months.
E. Body composition measurement using neutron activation

Answer 27

D
Body weight can be compared with an “ideal” or “desirable” weight, or assessment of body mass index can be used to determine both undernutrition and overnutrition. However, measurement of body weight in sick patients is confounded by changes in body water because of dehydration, oedema, and ascites. Furthermore, a person who starts at the upper end of the normal range may be classified as
“normal” despite considerable changes in the measured value. Dietary recall histories lack reliability and are associated with poor compliance from those who are seriously ill. Unintentional weight loss greater than 10% over the previous six months is a good prognosticator of clinical outcome. However, it can be difficult to determine true weight loss because of errors in recall. It has been estimated that one-third of patients with weight loss would be missed and one-quarter of weight-stable patients would be diagnosed as having lost weight when weight loss is based on patient recall. So, although it is the most clinically useful of the measurements that have been listed, it is a far from perfect measure of nutritional status. Formal measures of body composition, such as neutron activation, provide accurate and precise information, but a detailed understanding of the body’s muscle, fat, and water content is more relevant to clinical research than it is to clinical practice.