Surgery - Fluids & Electrolytes Flashcards
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
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
What proportion of an adult body is water?
60%
What proportion of body water is ICF/ECF?
ICF = 2/3 (40% mass) ECF = 1/3 (20% mass)
What proportion of ECF is IF/Plasma/TCF?
Interstitial Fluid = 3/4 (15% mass)
Plasma = 1/4 (5% mass)
Transcellular Fluid = <0.5L
What are sensible losses?
Urinary fluid losses
What are insensible losses?
Losses from sweat, lungs & faeces
What are additional losses?
Losses from NG tubes, drains, stomas, 3rd space losses
What is the MOVU and how is it calculated?
Minimum obligatory volume of urine
0.5ml/kg/hr (1L/day)
How much fluid is lost as insensible losses?
Lungs + Faeces = 500ml
Sweat = 500ml
What is the average fluid requirement for an adult patient?
3L/day
What is the average electrolyte loss per day?
Na = 2mmol/kg/day K = 1mmol/kg/day
What is the average electrolyte requirement per day?
Na = 100mmol/day K = 60mmol/day
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
How much fluid should be added to the standard regimen for pyrexic patients?
10% per degree of fever
What are the main endogenous factors controlling Na & water excretion?
RAAS
ADH secretion from post pituitary
Describe RAAS
Decreased EABV –> decreased renal blood flow at juxta-glomerular apparatus –> release of renin
Renin cleaves Angiotensinogen –> AT1 –> ATII via ACE
ATII
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?
- 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
