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Junior Surgery- GI > Metabolic response to surgery and Principles of fluid and electrolyte balance > Flashcards

Metabolic response to surgery and Principles of fluid and electrolyte balance Flashcards

1
Q

WHy can hypovolaemia occur in response to injury?

A
  • Blood loss
  • Sequestration of protein-rich fluid into interstitial space (third-space loss)
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2
Q

Why does oliguria with sodium and water retention occur commonly after major surgery?

A

Due to ADH and aldosterone release

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3
Q

What factors play a role in ADH secretion in surgery?

A
  • Nerve impulses from site of injury
  • Atrial stretch receptors responding to reduced circulating volume
  • Aortic/carotid baroreceptor responding to reduced pressure
  • Increased plasma osmolality
  • Higher centre input - pain, emotion, anxiety
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4
Q

Why is aldosterone released as a response to surgery?

A
  • Activation of RAAS
  • ACTH release in response to hypovolaemia and hypotension
  • Direct adrenal cortex stimulation
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5
Q

How long after surgery does ADH/aldosterone stay raised?

A

48-72 hours - causes oliguria and increased plasma osmolality

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6
Q

What are urinary changes which occur in metabolic response to injury?

A
  • Oliguria - due to ADH and aldosterone secretion
  • Decreased urinary sodium/increased potassium
  • Increased urinary osmolality
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7
Q

How much does total energy expenditure increase by following surgery?

A

10-30%

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8
Q

Why are patients frequently pyrexial following surgery for the first 24-48 hours?

A

Pro-inlammatory cytokine release, which reset temperature-regulating centres in the hypothalamus.

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9
Q

By roughly what percentage does BMR increase by per 1oC increase in temperature?

A

10%

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10
Q

Why does starvation occur following surgery?

A
  • Reduced nutritional intake due to illness
  • Fasting prior to surgery
  • Fasting after surgery
  • Loss of appetite
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11
Q

What are the metabolic effects of acute starvation?

A
  • Glycogenolysis and gluconeogenesis in the liver - glucose more readily available
  • Lipolysis

These processes can supply normal energy requirments of the body for up to 10 hours

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12
Q

What are metabolic effects of chronic starvation?

A
  • Muscle catabolism -> release of amino acids -> converted to glucose in liver
  • FFAs -> ketones -> used as energy

Ketone use compensates for chronic starvation until fat stores deplete, meaning that muscle catabolism begins again

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13
Q

Why is anaemia common after surgery?

A
  • Bleeding
  • Haemodilution
  • Impaired RBC production
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14
Q

Why does RBC production become inhibited following surgery?

A
  • Reduced EPO production by the kidneys
  • Reduced iron availibility due to increased ferritin and reduced transferrin binding capacity
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15
Q

What can increase insensible fluid loss in a surgical patient?

A
  • Hyperventilation
  • Intubation/non-humidified high-flow oxygen
  • Pyrexia - from the skin
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16
Q

What are third space losses?

A

Occurs when too much fluid moves from the intravascular space (blood vessels) into the interstitial or “third” space-the nonfunctional area between cells. This can cause potentially serious problems such as edema, reduced cardiac output, and hypotension.

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17
Q

Why do obstructions which occur high up in the upper GI tract result in greater fluid losses?

A

Fluids secreted by the upper GI tract fail to reach the absorptive areas of the distal jejunum and ileum

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18
Q

Why do you get fluid losses from paralytic ileus?

A

Fluid can’t be reabsorbed in distal jejunum and ileum

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19
Q

What types of fluids can be used for fluid optimisation in a pre-operative surgical context?

A
  • 0.9% saline
  • Dextrose 4% + Saline 0.18%
  • Hartmann’s solution
  • Ringer’s lactate
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20
Q

What are sources of fluid loss in surgery patients?

A
  • Insesible loss
  • Urine
  • Gut
  • Third space
21
Q

What increases the risk of third space losses in surgery?

A

Greater extent of surgery and tissue trauma

22
Q

What are the main causes of GI fluid loss in a surgical patient?

A
  • Obstruction
  • Ileus
  • Fistulae
  • Diarrhoea
23
Q

How many grams of sodium per 100ml does 0.9% NaCl contain?

A

9g

24
Q

If you were to give a rapid infusion of 1000ml 5% dextrose solution, how would it distribute in the body within 30-60 minutes of the infusion?

A
  • 670 ml into ICF
  • 260 ml into ECF
  • 70 ml into IVF
25
Q

If you were to give a rapid infusion of 1000 ml saline, how would it distribute in the body within 30-60 minutes of the infusion?

A
  • 786 into ECF
  • 214 into IVF
26
Q

How does Ringer’s lactate work?

A

Closely matches ECF compostition - physiological concentrations of sodium and lactate. After infusion, lactate is broken down leading to bicarb generation. This solution reduces the risk of hyperchloraemia

27
Q

What are examples of colloid solutions?

A
  • 4.5% albumin
  • Staches
  • Gelfusine
  • Haemaccel
28
Q

How do colloid solutions work?

A

They remain largely in the intravascular space until the colloid particles are removed by the reticuloendothelial system. Intravascular half-life is 6-24 hours

29
Q

What are risks with using colloid solutions?

A
  • Coagulopathy
  • Anaphylaxis
  • Pruritis
  • Reticuloendothelial dysfuntion
30
Q

How would you manage someone who is hypovolaemic following surgery?

A

250ml bolus saline, reassess -> if still hypovolaemic, give more

31
Q

What are the main causes of hypoovolaemic hypernatraemia in surgery?

A
  • Decreased oral intake
  • Nausea and vomiting
  • Diarrhoea
  • Increased insensible loss
  • Severe burns
  • Diuresis
32
Q

What are causes of hypervolaemic hypernatraemia in surgery?

A
  • Excessive sodium loading
  • Mineralocorticoid activity
33
Q

How would you manage someone with hypovolaemic hypernatraemia?

A

Replace intravascular volume, then slowly replace water deficit

34
Q

If, when trying to correct hypovolaemic hypernatraemia, you tried to replace water deficits to quickly, what could happen?

A

Cerebral oedema - cells in the brain adapt to hypernatraemic state, so when this is corrected rapidly, it results in a rise in intracellular volume, leading to cerebral oedema, seizures and coma

35
Q

What patients might need fluid optimisation in a pre-operative setting?

A
  • Illness that has affected absorption - D&V, intestinal obstruction, biliary colic, gastroenteritis
  • Those with poor renal function
  • Low body weight
  • Children
  • Illness that has caused reduced fluid intake - pancreatitis, chest infection etc.
36
Q

How would you monitor fluid optimisation in a pre-operative setting?

A
  • Skin turgor and mucosal hydration
  • 1 hrly urine output - 0.5ml/kg/hr
  • Monitor serum urea
37
Q

What are causes of hyperkalaemia in surgery?

A
  • Metabolic acidosis
  • Massive blood transfusion
  • Rhabdomyolysis
  • Massive tissue damage
  • Drugs
  • AKI/CKD
38
Q

What are causes of hypokalaemia in a surgical context?

A

Increased potassium excretion and losses

  • Vomiting
  • Fistulae
  • Diarrhoea
  • Ileus
  • Intestinal obstruction
  • Metabolic alakalosis
  • Diuretics
39
Q

How would you treat hyperkalaemia?

A
  • Treat cause
  • Calcium gluconate - protect the heart
  • Dextrose + insulin
  • Salbutamol nebs
  • Consider haemodialysis
40
Q

How would you manage someone with hypokalaemia?

A

Oral/IV replacement therapy

41
Q

What is the maximum rate of administration advised for potassium replacement?

A

20 mmol/h

42
Q

What factors contribute to a sugical patient developing hypomagnesemia?

A

Decreased oral intake + IV fluids for several days

43
Q

What are common causes of lactic acidosis in surgery?

A
  • Shock
  • Severe hypoxaemia
  • Severe haemorrhage/anaemia
  • Liver failure
44
Q

What are causes of metabolic acidosis in surgical cases?

A
  • Lactic acidosis
  • DKA
  • Starvation ketoacidosis
  • AKI/CKD
  • Poisonining
  • Diarrhoea
  • Intestinal fistulae
  • Hyperchloraemic acidosis
45
Q

What is the commonest cause of metabolic acidosis in surgical patients?

A

Lactic acidosis due to hypovolaemia and impaired tissue oxygen delivery

46
Q

What are causes of fluid loss following surgery?

A
  • Haemorrhage
  • Vomiting
  • NG drainage
  • Diarrhoea
  • Sweating
  • Evaporation
  • Third space loss
47
Q

What are common causes of metabolic alkalosis in surgical patients?

A
  • Vomiting
  • Loss of gastric secretions
  • Diuretics
48
Q

What are common causes of respiratory alkalosis in a surgical patient?

A
  • Pain
  • Apprehension/fear -> hyperventilation
  • Pneumonia
  • CNS disorders - meningitis, encephalitis
  • PE
  • Septicaemia
  • Liver failure
49
Q

What are causes of respiratory acidosis in surgical patients?

A
  • Opiod drugs
  • Head injury
  • Severe asthma
  • COPD
  • Severe chest infection

Junior Surgery- GI (43 decks)

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