Fluid & Electrolyte Balance Flashcards
What factors can be observed via measurements of Na+/K+/Cl-/HCO3-?
Fluid, electrolyte status and urine function
How is water secretion by the kidneys controlled?
It is controlled by ADH (anti-diuretic hormone), which is secreted from the posterior pituitary glands depending on the osmolarity of the body.
- Increased salt conc. in blood (high osmolality) = ADH secreted (increasing water reabsorption)
- Low osmolality (blood being more diluted) = ADH switched off
What are normal Na+ levels in the blood?
135-145 mmol/L
How can Na+ be excreted?
Via kidneys, sweat, gut and vomiting
Which 2 substances regulate urinary Na+ output?
- Aldosterone - causing Na+/H2O retention
- Atrial natriuretic peptide (ANP) - secreted by the heart to increase Na+ urinary excretion
Describe the RAAS process and the end result of this system.
- Liver produces angiotensin & kidneys produce the enzyme renin
- This produces angiotensin I
- Lungs produce angiotensin converting enzyme (ACE), which converts angiotensin I into angiotensin II
- Angiotensin II binds to the adrenal glands of the kidneys to stimulate aldosterone production
- Aldosterone works on:
- The heart
- The kidneys (increase Na+/H2O retention and K+ excretion)
- Blood vessels (vasoconstriction)
What is hyponatremia, and what causes it?
It is low Na+ levels in the body caused by vomiting, burns, diarrhoea, Addison’s disease (low aldosterone levels so Na+ not retained), or inappropriate ADH secretions
What happens to cells during hyponatremia?
Water moves from extracellular fluid (ECF) to intracellular fluid (ICF) to restore osmotic pressure of the cells
What are the symptoms of hyponatremia?
- Nausea
- Lethargy
- Reduced consciousness
- Headaches
What are the clinical signs of hyponatremia?
- Decreased urinary output
- Hypotension
- Increased pulse
- Decreased skin turgor
Which 2 drugs are associated with hyponatremia?
Lithium and SSRIs
What is hypernatremia, and what causes it?
It is high Na+ levels in the body caused by low water intake, excess water loss, diabetes insipidus (no ADH), sweating, over-infusion of saline/salts
How does hypernatremia form concentrated urine?
High Na+ levels induces a higher osmotic pressure.
This increases urea in the ECF of cells, which forms concentrated urine. ADH is then released.
What are the symptoms of hypernatremia?
- Thirst
- Dry mouth
- Weakness
- Loss of skin turgor
What are normal K+ levels in the blood?
3.5-5mmol/L
What type of electrolyte is K+?
It is an excitation electrolyte so used for e.g. muscle health
Which protein stimulates the uptake of K+ in cells?
Insulin
What occurs in acidosis in relation to K+ & H+?
During acidosis, K+ is displaced by H+ and increases, causing hyperkalaemia
What can cause hyperkalaemia?
- Renal failure
- Addisons disease
- Hormonal effects - e.g. low insulin
- Excess K+ supplements
- Excess of K+ sparing diuretics
How can hyperkalaemia be treated?
- Bicarbonate infusion
- Insulin - to increase K+ cellular uptake
- Salbutamol
Why is hyperkalaemia known as an medical emergency?
Because it can effect cardiac/skeletal muscles
What causes hypokalaemia?
- GI losses
- Renal failure
- Alkalosis
- High aldosterone levels - Conn’s syndrome
- Drug induced - e.g. diuretics, corticosteroids
Which specific drug increases in toxicity during hypokalaemia?
Digoxin.
Which protein can affect Ca2+ levels in the body?
Albumin, because it carries Ca2+
What 2 substances control Ca2+ homeostasis in the body?
- Vitamin D
2. Parathyroid hormone (PTH) - secreted from parathyroid glands in response to low unbound Ca2+ levels
What is the difference between osteoclasts and osteoblasts?
- Osteoclasts - shed Ca2+ from the bone to provide for the body
- Osteoblasts - puts Ca2+ into the bone
What is the effect of PTH in terms of Ca2+ in the body?
It increases osteoclastic reabsorption and increases renal reabsorption of Ca2+ - this all increases Ca2+ levels in the body
This equation is used for which types of patients specifically?
Corrected calcium (mmol/L) = total measured calcium + 0.02 (40-albumin)
Patients with low albumin levels
What can cause hypocalcaemia?
- Renal disease
- Vitamin D deficiency
- Hypoparathyroidism
What are the early symptoms of hypocalcaemia?
Numbing/tingling sensation of fingers, due to muscular disturbances.
How is hypocalcaemia managed?
Ca2+ supplements.
What can cause hypercalcaemia?
- Vitamin D overdose
- Bone diseases
- Hyperparathyroidism
Which drug class is used to treat hypercalcaemia?
Bisphosphonates - they bind to Ca2+ in the bone to retain it
