Flashcards in Sodium, Potassium, Calcium, and Fluids Deck (50):
What is the normal concentration of sodium in extra- and intracellular space?
Extracellular Na: 144 mmol/L
Intracellular Na: 10 mmol/L
What is the normal concentration of potassium in the extra- and intracellular space?
Extracellular K: 4 mmol/L
Intracellular K: 160 mmol/L
What is the normal concentration of calcium in the extra- and intracellular space?
Extracellular Ca: 1.5 mmol/L
Intracellular Ca: 100 nmol/L
What is the total water volume of the average 70kg male?
What proportion of fluid is extracellular and intracellular?
Extracellular: 1/3 (14L)
Intracellular 2/3 (28L)
How can extracellular fluid be further divided?
Interstitial fluid (11L)
What is the primary ion present in intercellular fluid?
What is the primary ion present in extracellular fluid?
What anion is mainly present in the plasma?
What are the 3 reasons for prescribing IV fluids?
What are the indications for fluid resuscitation?
Provides urgent intravascular correction to restore organ perfusion.
What changes should be made to fluid prescribing if the patient is septic?
Significantly higher amount of fluid due to increased vascular permeability.
What are the indications for fluid maintenance?
To meet fluid and/or electrolyte requirements that are not being met orally or enterally.
What are the indications for fluid replacement?
To replace any losses due to imbalances, ongoing losses, or redistribution problems.
What constitutes insensible fluid losses?
Other pathological processes
What considerations should be made when prescribing fluids?
Aim of the fluid
Weight and size of patient
Patient co-morbidities: especially CKD and HF
Reason for admission
State the contents of 0.9% saline
Sodium (154 mmol)
Chloride (154 mmol)
State the contents of 5% dextrose
Glucose (50 mmol)
State the contents of Hartmann's
Sodium (131 mmol)
Chloride (111 mmol)
Potassium (5 mmol)
Why is 0.9% saline ideal for fluid resus and maintenence?
It quickly equilibriates across the ECF. Distributes across ICF slower than dextrose.
Why is 5% dextrose appropriate for fluid maintenence?
It quickly distributes across all fluid compartments.
What is the benefit of using Hartmann's solution?
It provides some potassium in addition to fluid.
What IV infusion can be given in hypoglycaemic emergencies? Why is monitoring required afterwards?
Hypertonic 10-20% glucose
It can irritate veins
What are the daily requirements of water, Na, and K for the average patient?
Na: 50-100 mmol
K: 40-80 mmol
List 4 signs of mild-moderate dehydration
Dry mucous membranes
Reduced skin turgor
Slow capillary refill
List 3 signs of severe dehydration
List 4 signs of fluid overload
List 2 signs of severe fluid overload
What should be done after fluid replacement?
Reassessment to determine if additional maintence is required.
Define hyponatraemia and state how its causes can be grouped
Na <135 mmol/L
Hyponatraemia with hypovolaemia
Hyponatraemia with euvolaemia
Hyponatraemia with hypervolaemia
Outline the causes of hyponatraemia with hypovolaemia
Extrarenal: (Urinary sodium <20 mmol/L)
Kidney: (Urinary sodium >20 mmol/L)
Tubulo-interstitial renal disease
Unilateral renal artery stenosis
Recovery phase of ATN
How does hyponatraemia with hypovolaemia present?
Dominated by features of volume depletion.
Outline the causes of hyponatraemia with euvolaemia
Abnormal ADH release, SIADH
Major psychiatric illness
Increased ADH sensitivity
ADH-like subtances, oxytocin
Chronic alcohol abuse
What is a serious complication of hyponatraemia with euvolaemia? Which patients are most at risk?
At risk: Post-op premenopausal females, children, hypoxic
Outline the causes of hyponatraemia with hypervolaemia
Oliguric kidney injury
What is SIADH
Syndrom of inappropriate ADH secretion.
Causes water retention and hyponatraemia
Outline causes of hypernatraemia
ADH deficiency: pituitary diabetes insipidus
Insensitivity to ADH: nephrogenic diabetes insipidus
When are clinical features present in hyponatraemia?
Often asymptomatic if mild to moderate or chronic (due to cerebral adaption).
Symptoms are dependent on severity of hyponatraemia and rate of fall.
Sudden fall to 125 mmol/L can result in convulsions
What symptoms can occur in mild hyponatraemia?
What symptoms can occur in moderate hyponatraemia?
Muscle cramps and weakness
What symptom can occur in severe hyponatramia?
What causes convulsions in hyponatraemia?
Sudden fall to 125 mmol/L
What signs can present in hyponatraemia?
Signs of hypovolaemia
Signs of hypervolaemia
State the neurological signs present in hyponatraemia
Decreased level of consciousness
Focal or generalised seizures
Brainstem herniation (severe acute)
Which investigations should be done in suspected hyponatraemia?
Potassium - Addison's disease
Serum hypo-osmolality to confirm SIADH
Urine sodium - renal cause
TSH and thyroxine
Outline management principles for hyponatraemia
Correct underlying cause
Acute symptomatic: Hypertonic saline 3%
Chronic/asymptomatic: Saline (not hypertonic)
IV saline if hypovolaemic
Fluid restrict if SIADH
What is the commonest cause of acute hyponatraemia in adults?
Post-operative iatrogenic hyponatraemia
What complication can occur with hyponatraemia?
Sudden fall: Severe cerebral oedema and herniation.
Chronic: Cerebral oedema without herniation, Rhabdomyolysis, seizures, respiratory arrest.
What complication can occur if hyponatraemia is corrected too rapidly? How does this present?
Central pontine myelinolysis (Osmotic demyelination syndrome).
Typically presents with quadriplegia and pseudobulbar palsy. Locked-in syndrome can also occur.