Surgery Basics

Question 1

Nutritive Requirements

fluid

food

vitamins, minerals, electrolytes, trace metals

Answer 1

• 2–3 litres water (lying in bed)
• 1800 calories
  
  • 2/3 carbs
  • 1/3 fats
  • 14g protein (nitrogen) (varies 8 - 20)
• Fat soluble vitamins - these are stored by body, beware overdose
• Water soluble vitamins - these are excreted, give generously
• Minerals and trace elements
• Sodium, potassium, calcium, magnesium, phosphate
• Zinc, copper, iron, selenium, iodide

Question 2

Osmolality

Answer 2

total particle concentration by weight

mOsm/kg

measured in lab

normal = 280 - 295

accumulation of organic solutes can increase osmolality pathologically

• urea in renal failure
• glucose in uncontrolled diabetes

Question 3

Osmolarity

Answer 3

concentration of particles by volume

mmol/l

from calculations = 2 x Na + 2 x K + Ur + glucose

Question 4

Daily Fluid Intake

(normal)

Answer 4

drinking - 1500ml
eating - 1000ml
produced by oxidation - 300ml

approx 3 litres

Question 5

Normal Fluid Output

Answer 5

• urine - 1500ml
• stool - 300ml
• lungs - 500ml
• skin - 500ml

Question 6

Daily Sodium Requirement

Answer 6

1.5 mml/kg

approx 100 mM

Question 7

Daily Potassium Requirement

Answer 7

1 mmol/kg

approx 60mM

1 mmol/kg potassium = ~ 60mM

Question 8

Indications for IV fluids

Answer 8

• extra losses
  
  • vomiting, diarrhoea
  • ileostomy
  • drains
• pre-op, especially if jaundiced
• post-op
• decreased intake
  
  • nausea
  • swallow problems
  • nil by mouth
• electrolyte disorders

Question 9

Increased Fluid Requirements

Answer 9

1. Diarrhoea, vomiting, stomas, drains, polyuria = electrolyte-rich losses, replace with 0.9% saline with 20 mmol/L K+ or Hartmann’s
2. Fever = mainly water, replace extra 500ml per day

NB. may omit potassium after surgery as cell injury, stress, reduced renal clearance and stress hormones opposing insulin all put the K+ up

Question 10

What is in Normal Saline?

Answer 10

• 154 mmol Na
• 154 mmol Cl

pH 5

Question 11

What is in 5% Dextrose?

Answer 11

• 50g glucose

pH 4

Question 12

What is in Hartmann’s?

Answer 12

• 131 mmol Na
• 5 mmol K
• 2 mmol Ca
• 111 mmol Cl
• 29g lactate

pH 6.5

NB. Even this small amount of potassium may be too much if the patient has very poor renal function

Question 13

What is in Dextrose-Saline?

Answer 13

• 30 mmol Na
• 30 mmol Cl
• 40g glucose

pH 4

0.18% saline

Question 14

Fluid Challenge

Answer 14

• 500ml crystalloid (NOT dextrose) or 250ml colloid
• Give as fast as possible
  
  • Heart failure – reduce volume not rate
• Assess response
  
  • should respond within minutes
  • size and duration of response is more important than actual CVP numbers
• Repeat as needed

Question 15

Crystalloids

Answer 15

= electrolyte in water

• saline
• dextrose
• Hartmann’s

can diffuse through semipermeable membranes

Question 16

Colloids

Answer 16

= fluid + high molecular weight molecules

• albumin (natural)
• synthetic
  
  • Haemaccel
  • Gelofusin

can’t pass through semi-permeable membrane so remain longer in vascular compartment longer

Question 17

What is in a colloid?

Answer 17

for example:

• 35g gelatine
• 6.25mmol calcium
• 145 mmol sodium
• 145 mmol chloride

Question 18

Minimal Obligatory Output of Urine

Answer 18

0.5 ml/kg/hr

= 35ml per hour

= 850ml per day

lower than this suggests inadequate perfusion of the kidneys

Question 19

Patient Not Responding to Fluid Challenge