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Surgery Finals > Fluids and nutrition > Flashcards

Fluids and nutrition Flashcards

1
Q

What % of the body is water?

A

60%

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2
Q

Where is water stored in the body?

A

2/3 intracellular = 28L

1/3 extracellular = 14L: 3L plasma, 10L interstitial, 1L transcellular

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3
Q

Define osmotic pressure

A

The pressure which needs to be applied to prevent the inflow of water across a semipermeable membrane i.e. ability of a solute to attract water

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4
Q

Define oncotic pressure

A

Form of osmotic pressure exerted by proteins

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5
Q

Define hydrostatic pressure

A

Pressure exerted by a fluid at equilibrium due to the force of gravity

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6
Q

What are hydrostatic and osmotic pressures collectively known as (whose forces)?

A

Starling’s forces

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7
Q

What determines the distribution of fluid in the body?

A
  • ECF/ICF balance determined by osmotic pressure
  • Distribution within ECF is deterined by Starling’s forces:
    • Capillary and insterstitial oncotic pressure
    • Capillary and interstitial hydrostatic pressure
    • Filtration coefficient (capillary permeability)
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8
Q

What are some examples of 3rd space losses?

A
  • Bowel obstruction -> decreased fluid reabsorption
  • Sudden diuresis on day 2-3 post op = recovery of ileus
  • Peritonitis -> ascites
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9
Q

What is a typical minimum urine output?

A

0.5ml/kg/h = about 30ml/h

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10
Q

What is the usual sodium requirement?

A

1.5-2mmol/kg/day - about 100mmol/day

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11
Q

What is the normal potassium requirement?

A

1mmol/kg/day = 60mM/day

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12
Q

What would be a typical fluid regimen for adults with no specific comorbidity?

A
  • 1L normal saline + 40mmol KCl over 8h
  • 1L normal saline + 40mmol KCl over 8h
  • 1L dextrose (5%) over 8 hours
  • =3L fluid, 200mmol Na, 80mmol KCl/24h
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13
Q

What is the purpose of CVP monitoring?

A

Indicates RV preload; it depends on venous return and cardiac output such that a raised CVP indicates either increased circulating volume or decreased cardiac output (pump failure) whereas a low CVP indicates a low circulating volume.

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14
Q

What is a normal CVP?

A

~5-10cmH2O but remember a single reading isn’t as useful as serial

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15
Q

How do you interpret the CVP change after a fluid challenge?

A
  • Unchanged: hypovolaemic
  • Increase that reverses after 30 minutes: euvolaemic
  • Sustained increase >5cmH2O: overload/failure
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16
Q

What might be more useful than a fluid challenge in determining the CVP response to fluids?

A

Passive leg raising - a sustained increase in CVP indicates heart failure

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17
Q

What are some examples of crystalloid fluids?

A
  • Normal saline
  • 5% dextrose
  • Dextrose-saline
  • Hartmann’s/Ringer’s lactate
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18
Q

What are the contents of normal saline and what is its pH?

A
  • 0.9% NaCL - 9g/L or 154mM NaCl
  • pH 5-6
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19
Q

What can you use to give normal daily fluid requirements?

A

Normal saline, 5% dextrose or dextrose-saline

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20
Q

How many g of dextrose are in a bag of 5% dextrose?

A

50g

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21
Q

What are the contents of dextrose-saline?

A
  • 4% dextrose = 40g/L
  • 0.18% NaCl = 31mM NaCl
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22
Q

What are the contents of Hartmann’s/Ringer’s lactate?

A
  • Na: 131mM
  • Cl: 11mM
  • K: 5mM
  • Ca: 2.2mM
  • Lactate/HCO3: 29mM
23
Q

What do you use Hartmann’s/Ringer’s lactate for?

A
  • Resuscitation in trauma patients
  • Burns: use Parklands formula - 4 x weight x % burn = mL in 1st 24 hours
24
Q

What is the pH of Hartmann’s?

A

6.5, but it is an alkalinising solution - lactate isn’t an acid itself but a conjugate base. It’s given exogenously as sodium lactate, and lactate is metabolised in the liver producing HCO3 (Cori cycle)

25
Q

What is the physiological reason to use colloids?

A
  • Larger molecular weight molecules e.g. gelatin, dextrans
  • These preserve oncotic pressure
  • Therefore remain in the intravascular space, meaning they cause a preferential increase in intravascular volume
26
Q

What are some examples of colloids?

A
  • Synthetic
    • Gelofusin
    • Volplex
    • Haemaccel
    • Voluven
  • Natural
    • Albumin
    • Blood
27
Q

What do you use colloids for?

A
  • Fluid challenge:
    • 250-500ml over 15-30 mins
  • Hypovolaemic shock
  • Mount Vernon formula for burns:
    • (weight x % burn)/2 = ml colloid per unit time
28
Q

What are some of the problems with colloids?

A
  • Anaphylaxis
  • Volume overload
  • Can interfere with cross matching (so take a cross match befroe you give it)
29
Q

What are some of the problems with post op fluids and how can you solve them?

A
  • Issues:
    • High ADH, aldosterone and cortisol cause Na and water conservation
    • Hyperkalaemia: tissue damage, transfusion, stress hormones
  • Solutions
    • Use urine output (aiming for >30ml/hour) to guide fluid replacement but may need to decrease maintenance fluids to 2L first 24 hours post op
    • Avoid K+ supplementation for first 24 hours post op
30
Q

What are the issues with using fluids in cardiac or renal failure and how do you deal with them?

A
  • RAS activation causes sodium and water retention
  • Avoid fluids with sodium - give 5% dextrose
31
Q

How do you manage fluids in patients with bowel obstruction?

A
  • Significant third space losses of fluid and electrolytes, so probably need more than usual
  • Regimen: 0.9% normal saline with 20-40 mM KCl added to each bag
  • Titrate fluids to clinical findings on serial examination
  • Serial U+Es to guide electrolyte replacement
32
Q

What are the issues with fluids in pancreatitis and how do you manage them?

A
  • Inflammation causes a significant fluid shift into the abdomen
  • Patients need aggressive fluid resus and maintenance
  • Insert urinary catheter and consider CVP monitoring
  • 0.9% normal saline with 20-40mM KCl added to each bag
  • Keep urine output >30ml/hour
  • Serial U+Es for electrolyte replacement
33
Q

What is the composition of ileal fluid?

A
  • Na: 130mM
  • Cl: 110mM
  • K: 10mM
  • HCO3: 30mM
34
Q

What counts as normal or high output for an ileostomy?

A

Normal: 10-15mL/kg/day = ~700ml/day

High output = >1000ml/day

35
Q

How should you manage fluid status in ileostomy patients?

A
  • The ileum will adapt to limit fluid and electrolyte losses
  • Fluids:
    • 0.9% normal saline and KCl
    • Daily requirements and replace losses, titrated to urine output and U+Es
  • If high output give loperamide and codeine
36
Q

What are the causes of post op reduced urine output?

A
  • Post renal
    • Commonest cause
    • Blocked/malsited catheter
    • Acute urinary retention
  • Pre renal: hypovolaemia
  • Renal: NSAIDs, gentamicin
  • Anuria usually = blocked or malsited catheter
  • Oliguria usually = inadequate fluid replacement
37
Q

How do you manage reduced urine output post op?

A
  • Information: op history, obs chart (UO), drug chart (nephrotoxins)
  • Examinatino: assess fluid status, examine for palpable bladder, inspect drips, drains, stomas, CVP
  • Action:
    • Suspect catheter problem: flush with 50ml NS and aspirate back
    • Suspect pre renal problem: fluid challenge with 250-500ml colloid bolus over 15-30 mins and look for CVP or UO response within minutes
38
Q

How would you assess fluid status clinically?

A
  • History: balance chart, surgery, other losses, thirsty
  • Impression: drowsy, alert
  • Inspection: drips, drains, stomas, catheters, CVP
  • Examination
    • IV volume
      • CRT, HR, BP lying and standing, JVP
    • Tissue perfusion
      • Skin turgor, oedema (ankle, pulmonary, ascites), mucus membranes
    • End organ
      • UO, urea and creatinine, consciousness, lactate
  • Other tests
    • Pulmonary capillary wedge pressure: indirect measure of left atrial pressure
    • CVP
39
Q

How would you assess nutritional status of a patient?

A
  • Clinical
    • History: weight loss, diet
    • Examination: skin fat, dry hair, pressure sores, cheilitis, weight and BMI (<20kg/m2)
  • Anthropometric: skin fold thickness, arm circumference
  • Investigations: albumin, transthyretin (prealbumin), phosphate
40
Q

What are the daily nutritional requirements for an adult per kg?

A
  • 20-40 calories
  • 2g carb
  • 3g fat
  • 0.5-1g protein
  • 0.2-0.4g nitrogen
41
Q

What are the options for routes of delivery for enteral nutrition?

A
  • PO is best - consider a semi solid diet if risk of aspiration
  • Fine bore NGT (9Fr)
  • Percutaneous endoscopic gastrostomy
  • Jejunostomy
  • Build up feeds gradually to prevent diarrhoea
42
Q

What different kinds of enteral feeds are there?

A
  • Oral supplements
  • Polymeric e.g. osmolite, jevity
    • Intact proteins, starches and long chain FAs
  • Disease specific
    • E.g. low branched chain AAs in hepatic encephalopathy
  • Elemental
    • Simple AAs and oligo/monosaccharides
    • Require minimal digestion and used if abnormal GIT e.g. in Crohn’s
43
Q

What are the indications for enteral feeding?

A
  • Catabolic: sepsis, burns, major surgery
  • Coma/ITU
  • Malnutrition
  • Dysphagia: stroke, stricture
44
Q

What are some complications of enteral feeding?

A
  • NGT
    • Nasal trauma
    • Malposition or tube blockage
  • Feeding
    • Feed intolerance causing diarrhoea
    • Electrolyte imbalance
    • Aspiration
    • Refeeding syndrome
45
Q

What are the indications for parenteral feeding?

A
  • Prolonged obstruction or ileus (>7d)
  • High output fistula
  • Short bowel syndrome
  • Severe Crohn’s
  • Severe malnutrition
  • Severe pancreatitis
  • Unable to swallow e.g. oesophageal Ca
46
Q

How is parenteral nutrition given?

A
  • Centrally, because the high osmolality is toxic to veins
  • Short term: CV catheter
  • Long term: Hickmann or PICC line
  • Sterility is essential, so only use the line for PN
47
Q

How should parenteral nutrition be monitored?

A
  • Standard
    • Weight, fluid balance, urine glucose daily
    • Zinc, magnesium weekly
  • Initially
    • Blood glucose, FBC, U+E, LFTs, phosphate - 3 times a week
  • Once stable
    • Blood glucose, FBC, U+E, phosphate daily
    • LFTs weekly
48
Q

What are the contents of a typical parenteral feed?

A
  • 2000 Kcal: 50% fat, 50% carb
  • 10-14g nitrogen
  • Vitamins, minerals, trace elements
  • Combined with H2O
49
Q

What are the complications of parenteral feeding?

A
  • Line related
    • Pneumothorax/haemothorax
    • Cardiac arrhythmia
    • Line sepsis
    • Central venous thrombosis -> PE or SVCO
  • Feed related
    • Villous atrophy of GIT
    • Electrolyte disturbances
      • Refeeding syndrome
      • Hypercapnoea from excessive CO2 production
    • Hyperglycaemia and reactive hypoglycaemia
    • Line sepsis: increased risk with TPN
    • Vitamin and mineral deficiencies
50
Q

What is the definition of refeeding syndrome?

A

Life threatening metabolic complication of refeeding via any route after a prolonged period of starvation

51
Q

What is the pathophysiology of refeeding syndrome?

A
  • Low carbs induces a catabolic state with low insulin, fat and protein catabolism and depletion of intracellular phosphate
  • Refeeding causes increased insulin in response to carbs and a high cellular phosphate uptake
  • This leads to hypophsophataemia and:
    • Rhabdomyolysis
    • Respiratory insufficiency
    • Arrhythmias
    • Shock
    • Seizures
52
Q

What chemical abnormalities are seen in refeeding syndrome?

A

Low potassium, low magnesium, low phosphate

53
Q

Which patients are at risk of refeeding syndrome?

A
  • Malignancy
  • Anorexia nervosa
  • Alcoholism
  • GI surgery
  • Starvation
54
Q

How do you prevent and treat refeeding syndrome?

A
  • Prevent:
    • Identify and monitor at risk patients
    • Liaise with dietician
  • Treat
    • Parenteral and oral phosphate supplementation
    • Treat complications

Surgery Finals (12 decks)

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