Fluid prescription and nutrition Flashcards
Fluid compartments of body
Causes of low serum and low urine osmolarity
- Overhydration
- Hyponatraemia
- Adrenocortical insufficiency
- Sodium loss - diuretic or low salt diet
Causes of low serum osmolarity but high urine osmolarity
SIADH
Cause of normal/increased serum osmolarity and decreased urine osmolarity
Diabetes insipidus
Cause of normal/increased serum osmolarity and increased urine osmolarity
- Dehydration
- Renal disease + uraemia - but urine becomes more dilute as kidneys lose their ability to concentrate urine
- Hypercalcaemia
- Diabetes mellitus
- Hypernatraemia
- Alcohol - if accompanied with dehydration
What factors may increase water loss re surgery?
- Immediate post phase - trauma response
- Blood loss
- Infection - fever, increased sweating, hyperventilation
What is the body’s physiological response to trauma?
- Increased sympathetic activity
- Increased ACTH and cortisol - lack -ve feedback
- Increased renin
- Increased cytokines
- More gluconeogenesis
- Decreased insulin - this then increases 2nd->3rd day
- Increased ADH
Why is potassium not given post op immediately and why is there sometimes Na+ retention and oliguria immediate post op?
- Increase ACTH and cortisol
- Also reduced perfusion to kidney can increase renin
- = increased aldosterone
- = increased Na+ retention
- Increased ADH release = oliguria due to water retention
- Could also be due to reduced renal perfusion
- Do not replace K+ as damaged tissues release K+ in phase following surgery, so could cause hyperkalaemia esp with oliguria alongside
Why can inflamed peritoneal cavity cause large losses of fluid?
- Large SA - 2 square meteres
- Large SA = large losses = exudes litres of fluid if inflamed
How does fluid loss occur in bowel obstruction?
- Normally 7-9L fluids exreted into upper intestinal tract
- Accumulation of fluids, increased secretion, decreased reabsorption - secretion from inflam, accumulation within bowel etc
- When vomitting begins, this clears the system and results in more fluid losses into GI tract
- = hypovolaemic shock
Indicators for dehyration in small bowel obstruction
- Raised Ht >55%
- Raised serum urea
Acid base disturbance in small bowel obstruction
- Vomitting = loss of HCl
- = metabolic alkalosis
- = K+ into cells and H+ out to replace
- = hypokalaemia
- = hypochloraemic, hypokalaemic metabolic alkalosis
Why do we need to correct fluid balance prior to anaesthesia?
- Anaesthetic agents dramatically drop sympathetic tone
- can also have negative inotropic effects
- if dehydration not corrected = hypotensive and poor organ perfusion
- = death
- Also must correct K+ as these agents also effect cardiac muscle/conduction function
Why does serum urea to creatinine ratio rise in dehydration?
- Dehydration = decreased renal perfusion so reduced filtration rate
- also less dilution
- potentially AKI
- and dehydration = increased ADH release
- = increased urea transporters on collecting duct is it?
- = increased reabsorption of urea
Consequences of starvation prior to surgery
- Metabolic acidosis - ketoacidosis
- Reduced IV volume sometimes
- Insulin resistance
- Nutrient depletion
- Muscle wasting
- Impaired immune function
- Electrolyte imbalances
- Increased stress response
