fluid and electrolyte balance

Question 1

what electrolytes and anions in ECF

Answer 1

Na+, Cl- and HC03

Question 2

what electrolytes and anions in ICF

Answer 2

K+, proteins and phosphate

Question 3

how is water excreted and what controls it? what secretes what controls it

Answer 3

Water excretion by the kidney is very tightly controlled by arginine vasopressin (AVP) also called ADH secreted from the posterior pituitary gland according to the osmolality.
A rising osmolality promotes the secretion of AVP, causing water to be retained by the kidney.
A declining osmolality switches the secretion off.

Question 4

concentration of sodium in circulation

Answer 4

135-145mmol/L maintains serum osmolality

100-300mmol per day intake in the west

Question 5

how is na+ lost

Answer 5

kidneys, sweat, poo, vommit( OTC diaralyte has electrolytes.

Na needs to be regulated otherwise hypotension

Question 6

what controls na urinary output homeostasis

Answer 6

Aldosterone: na and water retention and k+ excretion

Atrial natriuteric peptide: secreted from cardiocytes of the right atrium of the heart. It increases urinary sodium excretion

Question 7

explain RAAS system

Answer 7

at the end : increase reabsorption of na and h20 and decrease cardiac output

Question 8

what is the science name for low sodium and what are the causes, clinical symptoms and clinical signs?

Answer 8

hyponatraemia
Loss of Sodium; e.g. vomiting diarrhoea, loss from burns, fistulae, Addison’s disease.
Water retention; inappropriate secretion of ADH (SIAD), e.g. post trauma or inappropriate treatment with iv dextrose

Clinical symptoms: nausea, malaise, headache, lethargy and a reduced level of consciousness. Seizures and coma are not seen usually until Na+ Conc. < 110-115 mmol/l.
Clinical signs: signs of volume depletion e.g. hypotension, decreased urine output, decreased consciousness, decreased skin turgor, soft/ sunken eyeballs, dry mucous membrane, increased pulse
-demeclocycline- for hyponatraemia

Question 9

toxicity of which drug is made worse by hyponatraemia

Answer 9

Lithium- causes lithium retention and causes toxicity bc narrow therapeutic index.

Question 10

what is hypernatraemia and what causes it

Answer 10

Water depletion:
water intake e.g. post-op ( due to unconciousness or nil by mouth) or dysphagia.
Excessive water loss, diabetes insipidus (failure of ADH), sweating, hyperventilation
Sodium retention
Excessive intake e.g. over infusion of saline, salts etc.
Excessive adrenocortical hormones e.g. Conn’s syndrome and Cushing’s syndrome

Question 11

potassium serum levels

Answer 11

K+ is the major ICF cation, 2% of body content being in the ECF (serum level is 3.5-5mmol/l)
Potassium intake is variable, 30-100mmol/day in the UK.
The kidney excretes the bulk of ingested potassium (20-100mmol/day), with some lost in the faeces (~5mmol/day).
Serum potassium conc. does not vary appreciably in response to water loss or retention. However, factors that cause even a small or sudden shift of intracellular potassium will cause a big change in the ECF K+ conc.

Question 12

how does k+ move, cellular paths and in acids and alkaline situations?

Answer 12

Cellular uptake of potassium is stimulated by insulin.
A reciprocal relationship exists between K+ and H+ ions. In acidosis, H+ ions conc. , K+ ions are displaced from the cells into ECF to maintain electroneutrality. The opposite occurs in alkalosis. Hence, H+ ions changes cause marked alteration in serum K+ conc.
One of the main functions of potassium is to maintain excitability of neuromuscular tissue.

Question 13

what’s name for high k+ and what’s the causes

Answer 13

Is caused by:
Renal failure
Mineralocorticoid deficiency (hypoaldosteronism (Addison’s disease))
Acidosis
Hormonal effects-low plasma insulin
Severe tissue damage
Excessive doses of K+ sparing diuretics, what others?
Excessive doses of K+ supplements

Question 14

how k+ clinical symptoms

Answer 14

Clinical symptoms;
Hyperkalaemia results in an enhanced state of excitability of cells. The main effects are on cardiac and skeletal muscle. In many cases, cardiac signs appear and lead to death before skeletal muscle symptoms appear.
Cardiac toxicity manifests as the sudden development of cardiac irregularity, tachycardia, ventricular fibrillation and asystole. Sudden death from cardiac arrest is common.

Question 15

name for low k+? and what are causes?

Answer 15

hypokalaemia may be caused by:

• gastrointestinal losses eg. vomiting, diarrhoea or surgical fistula
• renal losses in renal tubular failure
• drug induced: diuretics, corticosteroids

patients with hypokalaemia may have sever muscle weakness, neurological and cardiac arrhythmia

Question 16

what is the calcium serum level

Answer 16

2.2-2.6mmol/l

Question 17

factors that control calcium homeostasis

Answer 17

vitamin d and parathyroid hormone PTH

PTH is secreted from the parathyroid glands in response to low unbound plasma calcium. It causes an;
Increase in osteoclastic resorption of bone
Increase in renal tubular reabsorption of calcium
Increase synthesis of 1,25-(OH)2D3
Increase intestinal absorption of calcium

Question 18

Calcium calculation

Answer 18

About half of serum calcium is bound to proteins, mostly to albumin.
Unbound calcium is the biologically active fraction of the total calcium in plasma and maintenance of its concentration within tight limits is required. It is this fraction that is recognised by the parathyroid gland.
Laboratories routinely measure total calcium concentration (both bound and unbound).
This may give to problems in interpreting results, as changes in serum albumin concentration cause changes in total calcium concentration.
E.g. if albumin concentration falls, total serum calcium is low because the bound fraction is decreased.

Corrected calcium (mmol/L)= Total measured calcium + 0.02 (40-albumin)

Question 19

hypocalcaemia causes

Answer 19

• vit d deficiency: malabsorption, inadequate diet, lack of sun
• renal disease: unable to synthesise 1,25-DHCC

Question 20

Hypocalcaemia symptoms and management

Answer 20

• numbness and tingling and burning in extremities
• tetany occurs when levels are 1.5-1.6mmol/l
• prolonged hpocalcaemia can interfere with metabolism of the lens and cause cataracts

management:

• calcium supplemets
• calcitriol or alfacacidol can be given

Question 21

hypercalcaemia causes and clinical signs

Answer 21

causes of high calcium:

• vitamin d oversode
• hyperparathyroidism
• neoplasms
• Bone disease: pagets

clinical signs of hypercalcaemia:

• heart: cardiac arrhythmias
• neurological and physc: legsrthy, confusion, dementia, depression
  renal: thirst, polyuria
• gi: anorexia, constipation, n and v

Question 22

what are the functions of the kidney

Answer 22

• regulation of water, electrolytes and acid base balance
• excretion of urea, creatinine and uric acid
• produced hormones eg renin and erythop

Question 23

Cockcroft and Gault equation for egfr

Answer 23

GFR= A X (140 – age(years)) X weight (kg)
		      Serum Creatinine (µmol/L)

Where A=1.23 for males, A = 1.04 for females

Question 24

considerations for obese patients for egfr calculations?

Answer 24

To normalise the calculation, use ideal body weight where fat is likely
to be the major contributor to body mass

	IBW male = 50 + (2.3 x height in inches over 5 feet)
	IBW female= 45.5 + (2.3 x height in inches over 5 feet)

Many other formulas used:

Ideal body weight (kilograms) = Constant + 0.91 (Height - 152.4)
Where:
Constant = 50 for men; 45.5 for women
Height in centimetres

Question 25

limitations in GFR calculations

Answer 25

• not valid in pregnancy
• not valid in elderly
• amputees
• vegans
• bodybuilders