Water and electrolyte Metabolism Flashcards
Total Body Water
42L
Water distribution percentages
ICF - 66% (28L)
ECF - 33% (14L)
Plasma - 8% (3.5L)
Interstitial (11L)
Osmotic concentrations of the ICF and ECF are always equal T/F
F. except in the kidney
ECF osmolality
282-295 osmol/kg of water
A rising ECF osmolality promotes/switches off secretion of AVP
Promotes
AVP causes
Water to be retained by the kidneys with reduction of urine production
ECF osmolality comprises
Na, Cl, HCO3, glucose and urea
ICF osmolality comprises
K
Phosphates
Interstitial fluid comprises two pressures
Colloid osmotic pressure
Oncotic pressure
Evidences of cerebral dysfunction
Drowsiness
Coma
Total body sodium in a 70kg man
3700 mmol
What percentage of total body sodium is exchangeable
75%
Sodium concentration interval
135-145 mmol/L
Urinary Sodium output is regulated by
Aldosterone
Atrial Natriuretic Peptide
Aldosterone stimulation is stimulated by
Decreased ECF volume
Cells of the JG apparatus sense decrease in BP and secrete ……….., ………… then …………….
Renin
Angiotensin
Aldosterone
Atrial Natriuretic peptide is a polypeptide hormone secreted by
Cardiocytes of the right atrium of the heart
ANP increases/decreases sodium excretion
Increases
……………. and ………….. interact to maintain normal volume and concentration of ECF
Aldosterone
AVP
ECF contraction can lead to
- Development of pre-renal uraemia
- Stimulation of AVP secretion
- Stimulation of aldosterone secretion
Causes of Oedematous Hyponatremia
CCF
Nephrotic Syndrome
Inappropriate IV saline
Treatment of hyponatremia (oedematous)
Diuretics
Fluid restriction
Causes of Non-oedematous hyponatremia
SIAD
Renal failure
Increased intake eg compulsive water drinking
Causes of Hyponatremia due to sodium loss from GIT or Urine
Vomiting - Pulmonary Stenosis
Diarrhoea
Fistula
Urinary loss
Aldosterone Deficiency
Aldosterone Antagonists
What disease is due to aldosterone deficiency
Addisons disease
Examples of aldosterone antagonists
Spironolactone or Triamterine
Diagnosis of hyponatremia due to Na loss
Hypotension
Tachycardia
Regarding SIAD, What type of hyponatremia?
Non oedematous hyponatremia
Regarding SIAD, level of sodium in ICF
Normal total body sodium
Regarding SIAD, level of sodium in ECF
Hyponatraemic
Regarding SIAD, what level of blood pressure
Normal, normotensive
Concerning SIAD, glomerular filtration rate is
is normal
Concerning SIAD, Serum urea and creatinine are
Normal
Hyponatremia caused by SIAD can be induced by
Thiazide Diuretics
In SIAD there is osmotic AVP stimulation and if they are exposed to excess water load they become hyponatraemic T/F
F. There is non osmotic AVP stimulation
Non-osmotic stimuli in SIAD include
Reduction in circulating blood volume
Nausea and vomiting
Pain
There is a continued natriuresis in SIADH T/F
T
Hyponatremia with natriuresis only occurs in SIADH T/F
F. Also occurs in adrenal failure and renal disorders
Features of Hyponatremia patients that have water overload
No oedema
Normal serum
Normal creatinine
Normal blood pressure
Water overload is treated by
Fluid restriction
Causes of hypernatremia
- Excess sweating
- Diarrhoea in children
- Excess sodium intake or retention
- Na bicarbonate in the correction of acidosis
- Conn’s syndrome
- Cushing’s syndrome
Clinical Presentation of Hypernatremia
Dehydration in water loss and indication of fluid overload (hypervolemia) in Na retention -
INCREASED JVP
PULMONARY OEDEMA
Management of Hypernatremia
Give oral fluids slowly or
5% dextrose slowly
Total body potassium
3600 mmol
% of potassium intracellular and extra cellular
98% intracellular, 5% extra cellular
Intake interval of potassium per day
30-100 mmol
Excretion dependent on glomerular filtration T/F
T
What % of K is lost in faeces
5%
Interval of Potassium concentration in the body
3.3-5 mmol/L
Cellular uptake of potassium is stimulated by
Insulin
Clinical effects of hypokalemia
Severe weakness
Hyporeflexia
Cardiac Arrhythmias
Cardiac arrest
ECG changes concerned with Hypokalemia
Flattened T waves
Prominent U wave
Increased sensitivity to digoxin
Causes of hypokalemia
- GIT losses – vomiting, diarrhoea, fistula
- Renal losses – from renal disease, diuretic therapy or increased aldosterone production (Conns Syndrome)
- Drug induced – thiazide diuretics and corticosteroids. Cabenoxolone has mineralocorticoid activity
- Alkalosis causes a shift of potassium from the ECF to the ICF
What drug(s) induce hypokalemia
Thiazide diuretics
Corticosteroids
Cabenoxolone
Treatment of hypokalemia
Oral potassium supplements
Intravenous potassium
Intravenous potassium should not be given faster than ………… mmol/h and should be monitored by
20mmol/hour
ECG
Commonest and most serious electrolyte emergency encountered in clinical practice
Hyperkalemia
Clinical feature of hyperkalemia includes muscle weakness T/F
T
ECG changes of hyperkalemia
Widened QRS complex
Peaked T waves
At what level of serum potassium is there a risk of cardiac arrest
7mmol/L
Causes of hyperkalemia
- Renal disease
- Mineralocorticoid deficiency (Addison’s disease, patients on aldosterone antagonists eg SPIRONOLACTONE or TRIAMTERENE
- Acidosis
- K released from damaged cells
- Artefactual increase in haemolysis serum
Treatment of hyperkalemia
- Infusion of insulin and glucose
- Infusion of calcium gluconate
- Dialysis
- Cation exchange resin e.g Resonium A
What does high anion gap indicate?
Lactic acidosis
Fluids
- Water
- Isotonic NaCl
- Plasma
- 1.26% Na2CO3
- K supplements
Water -
5% dextrose
Isotonic NaCl
0.9% NaCl
Sodium bicarbonate-
1.26%
Reference range of Hydrogen ions in the body
35-45 nmol/L
Oxidation of the nitrogen containing amino acids of proteins is a source of hydrogen ions in the body T/F
F. Sulphur containing amino acids
Arterial blood gas values, H+, Bicarbonate, PCO2, PO2
H+ - 35-46 nmol/L
Bicarbonate - 18-31mmol/L
PCO2 - 4-6kP (36-46mmHg)
PO2 - 11-15kP (85-105mmHg)
What happens to H and bicarbonate in metabolic acidosis
H is high or normal
Bicarbonate is always low
Diseases associated with metabolic acidosis
Renal disease
Diabetic ketoacidosis
Lactic acidosis
In respiratory acidosis, what happens to H and PCO2
Both raised
There’s hypoxia and overbreathing in respiratory alkalosis T/F
T
Commonest cause of metabolic alkalosis
Prolonged vomiting
Diseases associated with metabolic alkalosis
Nasogastric suction
Conns syndrome
Respiratory compensation of metabolic alkalosis leads to
Elevated PCO2