Surgery - Fluids & Electrolytes Flashcards by Jack Gorard

What are the physiological limits of normal blood gases?

pH = 7.35-7.45
PaO2 = >10.6kPa
PaCO2 = 4.7-6.0kPa
HCO3- = 22-26mmol/L
BE = +/-2mmol/L

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What are the electrolyte values in serum?

Na = 135-145
K = 3.5-5
Ca = 2.2-2.6
Cl = 94-111
Latate = 1-2

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What proportion of an adult body is water?

60%

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What proportion of body water is ICF/ECF?

ICF = 2/3 (40% mass)
ECF = 1/3 (20% mass)

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What proportion of ECF is IF/Plasma/TCF?

Interstitial Fluid = 3/4 (15% mass)
Plasma = 1/4 (5% mass)
Transcellular Fluid = <0.5L

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What are sensible losses?

Urinary fluid losses

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What are insensible losses?

Losses from sweat, lungs & faeces

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What are additional losses?

Losses from NG tubes, drains, stomas, 3rd space losses

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What is the MOVU and how is it calculated?

Minimum obligatory volume of urine

0.5ml/kg/hr (1L/day)

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How much fluid is lost as insensible losses?

Lungs + Faeces = 500ml

Sweat = 500ml

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What is the average fluid requirement for an adult patient?

3L/day

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What is the average electrolyte loss per day?

Na = 2mmol/kg/day
K = 1mmol/kg/day

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What is the average electrolyte requirement per day?

Na = 100mmol/day
K = 60mmol/day

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What is the standard fluid maintenance regime?

1 SALTY 2 SWEET
1L normal saline w/ 20mmol KCL over 8h
1L 5% dextrose w/ 20mmol KCL over 8h
1L 5% dextrose w/ 20mmol KCL over 8h

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How much fluid should be added to the standard regimen for pyrexic patients?

10% per degree of fever

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What are the main endogenous factors controlling Na & water excretion?

RAAS

ADH secretion from post pituitary

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Describe RAAS

Decreased EABV –> decreased renal blood flow at juxta-glomerular apparatus –> release of renin
Renin cleaves Angiotensinogen –> AT1 –> ATII via ACE
ATII

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What are the effects of Angiotensinogen II?

Efferent renal artery constriction
Peripheral vasoconstriction
Proximal Na reabsorption
SNS activation
Aldosterone release
Thirst + ADH release --> CD water reabsorption

What are the Sx of dehydration?

Mild - headache, lack of energy, tiredness
Mod - dry mouth, decreased alertness, sunken eyes, muscle cramps
Sev - confusion, disorientation, tachycardia, tachypnoea, low BP

What is the electrolyte composition of 0.9% saline?

Osmolarity = 208
Na = 154mmol/L
Cl- = 154mmol/L

What is the electrolyte composition of Ringers lactate/Hartmann’s?

Osmolarity = 278
Na = 131mmol/L
K = 5mmol/L
Ca = 2mmol/L
Cl = 111mmol/L
Lactate = 29mmol/L

What is the electrolyte composition of 5% dextrose in water?

50g dextrose in 1L pure water

What is the electrolyte composition of dextrose saline?

4% dextrose/0.18% saline
Osmolarity = 283
Na = 30mmol/L
Cl=30mmol/L

What is the electrolyte composition of 5% albumin?

Osmolarity = 300
Na = 150mmol/L
Cl = 150mmol/L

What is the difference between cristalloids &; colloids?

``` Cristalloids = balanced electrolyte comp, expand ECV Colloids = exert high oncotic pressure, can keep more fluid in intravascular space, can cause anaphylaxis ```

What are the fluid, electrolyte & acid-base abnormalities in excessive vomiting?

Hypochloraemic, hypokalaemic metabolic alkalosis | -Na often low

How are the fluid, electrolyte & acid-base abnormalities in excessive vomiting managed?

0. 9% saline & 20mmol KCl | - check U&Es frequently

What are the fluid, electrolyte & acid-base abnormalities in a high volume Pancreatic/Ileal/Jejunal/Bile Fistula?

Bicarb deficiency Acidosis Hypokalaemia

How are the fluid, electrolyte & acid-base abnormalities in a high volume Pancreatic/Ileal/Jejunal/Bile Fistula managed?

Fluid & Bicarbonate replacement

What are the fluid, electrolyte & acid-base abnormalities in diarrhoea?

Hyperchloraemic metabolic acidosis - hypokalaemia if profuse - metabolic alkalosis if chronic

How are the fluid, electrolyte & acid-base abnormalities in diarrhoea managed?

Oral rehydration OR | 0.9% saline & 20mmol K+

How should a closed head injury be managed w/ regards to fluids & electrolytes?

Maintain euvolaemia (reduces risk of 2o brain injury) - if pt haemodynamically stable 2/3 maintenance w/ isotonic - avoid hypotonic fluids

What are the fluid, electrolyte & acid-base abnormalities in acute tubular necrosis?

``` Hyperkalaemia Hyperphosphataemia Hypermagnesia Hyponatremia Hypocalcaemia Metabolic acidosis -if vomiting no acidosis ```

What are the fluid, electrolyte & acid-base abnormalities in dehydration?

Isonatremic - can be hyponatremic if hypertonic fluid lost - can be hypernatraemic if hypotonic fluid lost

How are the fluid, electrolyte & acid-base abnormalities in dehydration investigated?

``` FBC U&Es Lactate Glucose Urinalysis ```

How are the fluid, electrolyte & acid-base abnormalities in dehydration managed?

Specific treatment regimens

What is SIADH?

Syndrome of inappropriate ADH secretion - decreased water excretion - normal sodium excretion

What are the fluid, electrolyte & acid-base abnormalities in SIADH?

Dilutional hyponatremia

What are the causes of SIADH?

``` Malignancy (SCC, pancreas, prostate) CNS (meningoencephalitis, haemorrhage, head injury) Chest (TB, pneumonia, abscess) Endocrine (hypothyroidism) Drugs (opiates, psychotropics) Major surgery Trauma Symptomatic HIV ```

How are the fluid, electrolyte & acid-base abnormalities in SIADH investigated?

``` Na -hyponatremia -increased urinary Na -increased specific gravity Urea -normal/creatinine ```

What is diabetes insipidus?

Passage of large volumes of dilute urine (3L/day) | -impaired water resorption by kidney collecting ducts

What are the causes of diabetes insipidus?

Reduced ADH secretion from post pituitary (cranial) | Impaired response of the kidney (nephrogenic)

What are the fluid, electrolyte & acid-base abnormalities in diabetes insipidus?

Hypernatraemia | Reduced plasma osmolality

What are the fluid, electrolyte & acid-base abnormalities in diabetes insipidus?

Dilutional hyponatremia | Hypokalaemia