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Medicine Finals - Imperial & Quick Medical Revision > Fluid Homeostasis - Surgery > Flashcards

Fluid Homeostasis - Surgery Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the water composition in the body?

A

Total water: 60% of 70kg = 42L

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2
Q

What fraction of body water is intracellular?

A

2/3 so 28L

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3
Q

What fraction of body water is extracellular?

A

1/3 so 14L

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4
Q

What are Starling’s Forces?

A

Osmotic and Hydrostatic Pressure

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5
Q

What is osmotic pressure?

A
  • Pressure which needs to be applied to prevent the inflow of water across a semipermeable membrane.

This is the ability of a solute to attract water

Oncotic pressure: form of osmotic pressure exerted by proteins

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6
Q

What is hydrostatic pressure?

A

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

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7
Q

How is fluid distributed in the body?

A

Distribution between ECF and ICF is driven by differences in osmotic pressure only.

Distributions within the ECF is determined by Starling’s forces.

  • Capillary and interstitial oncotic pressures
  • Capillary and interstitial hydrostatic pressure
  • Filtration coefficient.
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8
Q

3rd space losses –> Decreased ECF

A

Fluid moving from plasma/blood cells (ECF) into the spaces between cells.

Bowel obstruction –> decreased fluid reabsorption –> 3rd space loss.

Sudden diuresis on day 2-3 post op = recovery of ileus

Peritonitis –> ascites –> 3rd space loss.

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9
Q

Fluid balance - total water input and food input?

A

1500ml + 1000ml

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10
Q

Total water output in urine and stool?

A

1500ml + 300ml

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11
Q

Total input from metabolism?

A

300ml

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12
Q

Total output from insensible losses?

A

1000ml

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13
Q

Total input

A

2000ml = 25-30ml/kg/d

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14
Q

Total output

A

2800ml= 40ml/kg/d

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15
Q

Minimum urine output?

A

0.5ml/kg/h = ~30ml/h

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16
Q

Glucose requirment

A

50-100g/day of glucose

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17
Q

K requirement + Na Requiremnt

A

1mmol/kg/d

= 80 mmol

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18
Q

Need to replace other losses too?

A 
VOmiting and Diarrhoea
NGT
Drains
Fever (+500ml for each degree) 
Tachypnoea
High-output stomas.
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19
Q

CVP monitoring?

A

Indicate RV preload and depends on

  • Venous return
  • Cardiac output

Increased CVP

  • Increased circulating volume
  • Decreased CO: pump failure

Decreased CVP
- Decreased circulating volume

Normal value: -5-10cmH20

SIngle reading is not as useful as serial measurements before and after fluid challenge

  • Unchanged: Hypovolaemic
  • Increased that reverses after 30mins : euvolaemia
  • Sustains increased >5cmH20: overload/failure
  • Passive leg raising may be more useful than fluid challenge in determining response to fluid
  • Sustained increased in CVP suggest heart failure.
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20
Q

24 hr NICE recommendation for fluid?

A

When prescribing for routine maintenance alone, consider using 25-30ml/kg/day sodium chloride 0.18% in 4% glucose with 27 mmol/l potassium on day 1.

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21
Q

What does NS Contain?

A

0.9% NaCl = 9g/L
154 mM NaCl.

Use for normal daily fluid requirements + replace losses.

If large volumes are used there is an increased risk of hyperchloraemic metabolic acidosis.

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22
Q

5% dextrose?

A

50g dextrose/L

Normal daily fluid requirement

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23
Q

Dextrose saline?

A

4% dextrose = 40g/L
0.18% NaCL = 31 mM NaCL

Normal daily fluid requirements

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24
Q

What does Hartmann’s contain?

A 
Na: 131 mM 
Cl: 111mM 
K: 5mM 
Ca: 2.2 mM 
Lactate/HCO3: 29mM
25
Q

Use of Hartmann’s

A

Resuscitations in trauma patients

pH: 6.5 but Hartmann’s is an alkalising solution
Lactate is not an acid itself: conjugate base.

26
Q

Daily requirements?

A

3L dex-saline with 20mM K+ in each bag

1L NS + 2L dex with 20mM K+ in each bag.

27
Q

Types of colloid?

A

Contains large molecular weight molecules - gelatin/dextrans. Preserved oncotic pressure therefore remains intravascular –> to increased intravascular volume.

Natural = Albumin, blood.

Synthetic = Gelofusin, voluven.

USe: fluid challenge: 250-500ml over 15-30mins.
Hypovolaemic shock.

Problems

  • Anaphylaxis
  • Volume overload.
28
Q

How to assess fluid status?

A

Hx: balance chart, surgery, other loss, thirsty

Impression: drowsy, alert

INspection: drips, drains, stomas, catheters, CVP.

29
Q

Examination of IV volume?

A

CRT
HR
BP lying and standing
JVP

30
Q

Examination of Tissue perfusion

A

Skin turgor
Oedema: ankle, pulmonary ascitis
Mucus membranes

31
Q

Examination of end-organ perfusion?

A

UO, Increased U+Cr
Consciousness
Lactate

32
Q

Other assessments of perfusions?

A

PCWP: indirect measure of left atrial pressure
- pulmonary wedge pressure (measure the pulmonary artery)

  • CVP
33
Q

Post-op Fluids?

A

Problems
- Increased ADH, increased aldosterone, increased cortisol –> Na + H20 conservation.

Increased K+: tissue damage, transfusion, stress hormone.

34
Q

Solutions to post-op fluid issues?

A

Use UO to guide fluid replacement but may need to decreased maintenance fluid to 2L first 24hr post op
Avoid K+ supplementation for first 24hr post-op.

35
Q

Cardiac or renal failure problem + solution?

A

RAS activation –> NA and H20 retention

Therefore solution = avoid fluid with Na –> give 5% dextrose.

36
Q

Bowel obstruction and fluid?

A

Pts have significant third space losses with loss of both water and electrolytes

Likely to need significantly more than standard daily requirements.

Regiments

  • 0.9% NS with 20-40mml KCL to each bag
  • Titrate rate of fluid to clinical findings on serial examination
  • Serial U+E to guide electrolyte replacement.
37
Q

Pancreatitis fluid management?

A

Inflammation –> significant fluid shift tinto the abdomen

Pts require aggressive fluid resus and maintenance

  • Insert urinary catheter and consider CVP monitoring
  • 0.9% NS with 20-40mmol KCL added to each bag.
  • Keep UO >30ml/h
  • serial U+E guide electrolyte replacement.
38
Q

Ileostomy fluid management?

A

Normal output: 10-15ml/Kg/d = 700ml/day

High output = >1000ml/d

Ileum will adapt to limit fluid + electrolyte losses.

  • Fluid - 0.9% NS + KCL
  • Daily requirements + replaces losses, titrated to UO.
  • Serial U+E guide electrolyte replacement

High output

  • Loperamide
  • Codeine
39
Q

Reduced Urine Output Post-op

A

Causes

  • Pre-renal: Hypovolaemia
  • Renal: NSAIDs, Gentamicin
  • Post-renal: Commonest cause - blocked catheter, acute urinary retention.

Anuria usually = blocked or malsited catheter
Oliguria usually = inadequate fluid replacement

40
Q

Management of reduced urine output post-op?

A

Information

  • Op Hx
  • Obs Chart UO
  • Drug chart: nephrotoxin

Examination

  • examine fluid status
  • Examinate for palpable bladder
  • Inspect drips, drains, stomas, CVP

Action

  • Flush with 50ml NS and aspirate back
  • fluid challenge

Suspecte catheter problem
- Flush with 50ml NS and aspirate back

Suspect pre-renal problem
- Fluid challenge
250-500ml colloid bolus over 15-30 mins.
Look for CVP or UO response within minutes.

41
Q

Clinical assessment of nutrition?

A

Hx

  • weight loss
  • Diet

Examination

  • Skin fat
  • Dry hair
  • Pressure sore
  • Cheilitis
  • Weight + BMI (<20kg/m2)
42
Q

Anthropometric assessment of nutrition?

A

Skin-fold thickness

Arm circumference

43
Q

Investigations of nutrition?

A

Albumin
Transthyretin
Phosphate

44
Q

What is enteral nutrition?

A

Requirements for body /kg/24hr.

20-40 kcal
Carbs: 2g
Fat: 3g
Protein: 0.5-1
Nitrogen: 0.2-0.4

Enteral nutrition
- Delivery
PO is best . Consider semi-solid if risk of aspiration
- Fine bore NGT
- Percutaneous endoscopic gastrostomy
- Jejunostomy
- Build up feeds gradually to prevent diarrhoea.

45
Q

What feeds are possible through enteral feeding?

A

Oral supplements
- Polymeric: E.g osmolite, jevity: Intact proteins, starches and long-chain FAs.

  • Disease Specific. e.g decreased branched chains AA in hepatic encephalopathy
  • Elemental
    Simple AA and oligo/monosaccharides
    Require minimal digestion and used if abnormal GIT: E.g in Crohns.
46
Q

Indications for enteral feeding?

A

Catabolic: sepsis, burns, major surgery
Coma/ITU
Malnutrition
Dysphagia: Stricture, stroke.

47
Q

Complications of enteral feeding?

A

NGT

  • Nasal trauma
  • Malposition or tube blockage

Feeding

  • Feed intolerance –> Diarrhoea
  • Electrolyte imbalance
  • Aspiration
  • Refeeding syndrome
48
Q

What is parental nutrition?

A

May be total or used to supplement enteral feeding

- Combined with H20 to deliver total daily requirements.

49
Q

Indications for parenteral nutrition?

A
  • Prolonged obstruction or ileus (<7days)
  • High output fistula
  • Short bowel syndrome
  • Severe Crohn’s
  • Severe malnutrition
  • Severe pancreatitis
  • Unable to swallow: e.g oesophageal Ca.
50
Q

Delivery of parenteral nutrition?

A
  • Delivered centrally as high osmolality is toxic to veins
    Short-term: CV cather
    LOng-term: Hickman or PICC line

Sterility is essential: use line only for PN.

51
Q

Monitoring of parenteral nutrition?

A

Standard

  • Weight, fluid balance and urine glucose daily.
  • Zn, Mg weekly.

Initially

  • Blood glucose, FBC, U+E, PO4 3x a week.
  • LFTs 3x /week

Once stable

  • Blood glucose, FBC, U+E + PO4 daily
  • LFTs weekly.
52
Q

Content of parenteral nutrition

A

2000Kcal: 50% fat, 50% carbs
10-14g nitrogen
Vitamins, minerals and trace elements.

53
Q

Complications of Parenteral nutrtion?

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 deficiency
54
Q

What is refeeding syndrome?

A
  • Life-threatening metabolic complications of refeeding via any route after a prolonged period of starvation.
55
Q

Pathophysiology of refeeding?

A

Decreased carbs - catabolic state with low insulin, fat and protein catabolism and depletion of intracellular phosphate.

  • Refeeding –> increased insulin response to carbs and increased cellular phosphate uptake
- Hypophosphatemia 
Rhabdomyolysis 
Respiratory insufficiency 
Arrhythmias 
Shock 
Seizures
56
Q

What is the chemistry of refeeding syndrome?

A

Decreased K, Decreased Mg, Decreased Po4

57
Q

Patients at risk of refeeding syndrome?

A 
Malignancy
Anorexia nervosa
Alcoholism 
GI surgery
Starvation
58
Q

Prevention of refeeding syndrome?

A

Identify and monitor at-risk patients

Liaise with dietician

59
Q

Management of refeeding syndrome?

A
  • Identify at-risk pts in advance and liaise with dietician
  • Parenteral and oral PO4 supplementation
  • Manage complications

Medicine Finals - Imperial & Quick Medical Revision (29 decks)

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