Fluid and electrolyte management

Question 1

Insensible losses

Answer 1

Fever, RR, breathing of dry O2

Lose to sites of tissue damage, obstructed bowel, serous body cavities, and relaxation of capillary bed

Question 2

ADH

Answer 2

Volume receptors –> release ADH even in the face of hyponatraemia and a low plasma osmolality

Question 3

Sodium

Answer 3

Body responds to fall in central volume or renal perfusion by reducing renal sodium exertion to extremely low levels

Excretion is slower so retention and overload is the response in surgical stress

Question 4

Fluid assessment

Answer 4

Intracellular volume extremely difficult to assess
Extracellular is easier to assess clinically as increased salt and water manifests itself as oedema and salt and water depletion

Balance between blood volume and ECF is maintained by oncotic pressure and relative leakiness of the capillaries

In haemorrhage plasma volume is partly replenished from the ECF

Sepsis causes capillary leak and low oncotic pressure

Question 5

Biochemical

Answer 5

Need 30-40mL/kg of water per day

Need 50-100mmOl sodium per day

Frank lipaemia or infusion close by can cause erroneous value

Question 6

Hyponatreamia

Answer 6

If urine sodium is high and ECF volume is low
Diuretics, salt losing renal disease
Mineralocorticoid deficiency

If urine sodium high and ECF normal/slightly raised
Glucocorticoid deficiency
Hypothyroidism
SIDAH

If urine sodium is high and ECF volume high
Renal dysfunction

Urine sodium low and ECF low
Outwith body, sequestration

If Urine sodium low and ECF volume is high
Dilution / water ingestion
Cirrhosis
Cardiac failure
Nephrotic syndrome

Question 7

Hypernatraemia

Answer 7

Usually abnormal water loss (diabetes insidious, fever, DM, osmotic diuretics when intake of water impaired

Give water via gut or IV dextrose

Question 8

Potassium

Answer 8

3 ways to lose
Renal
Intestinal
Medical (high ng outputs)

Plasma level is poor reflection 1% of body total only

Usually from loss of body via kidney of bowel

Acidosis, catecholamines, administration of salbutamol, referring with start of anabolic activity

Question 9

Calcium

Answer 9

Absolute hypocalcaemia in pancreatitis, rhabdo, following thyroid or parathyroid surgery

Symptoms - treaty, numbness and parasthesia
Chovstek’s sign, Trosseau’s sign, seizures

High calcium usually due to paraneoplastic
Can also be parathyroid

Diminishes kidney ability to retain salt and hypovolaemia reduces ability to excrete calcium

Malaise, abdominal pain and possible ureteric colic
Dysrhythmias

Saline diuresis to treat

Bisphosphonate IV if that does not help

Effective treatment of primary cause is the mainstay

Question 10

Magnesium

Answer 10

Second most important intracellular cation after potassium

Depletion causes confusion, seizures and is associated with range of dysrhythmias

Excess causes muscle paralysis and CNS depression

Hypo common in early recovery period from things such as peritonitis

Chronic losses from bowel, kidney, alcohol abuse also contribute

Acute stage treatment avoids purgative effects of magnesium salts

Hypermagnesaemia almost always secondary to iatrogenic administration in presence of impaired renal function

Question 11

Phosphate

Answer 11

High levels in renal impairment
Or following massive muscle or bowel necrosis

Hypo usually seen in recovery

When below 0.6 –> skeletal muscle function and immune system impaired

Question 12

Trace metals

Answer 12

–> given in situations where there is prolonged dependence upon parental feeding or prolonged gut dysfunction

Question 13

Fluid losses

Answer 13

ECF
Blood loss
Vomiting
Diarrhoea
Gut fistulae
Unwell patients
DM

Water
Fever
RR
Prolonged water deprivation
DI