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4th year everything > Fluid Homeostasis - Surgery > Flashcards

Fluid Homeostasis - Surgery 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
Use of Hartmann's
Resuscitations in trauma patients pH: 6.5 but Hartmann's is an alkalising solution Lactate is not an acid itself: conjugate base.
26
Daily requirements?
3L dex-saline with 20mM K+ in each bag 1L NS + 2L dex with 20mM K+ in each bag.
27
Types of colloid?
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
How to assess fluid status?
Hx: balance chart, surgery, other loss, thirsty Impression: drowsy, alert INspection: drips, drains, stomas, catheters, CVP.
29
Examination of IV volume?
CRT HR BP lying and standing JVP
30
Examination of Tissue perfusion
Skin turgor Oedema: ankle, pulmonary ascitis Mucus membranes
31
Examination of end-organ perfusion?
UO, Increased U+Cr Consciousness Lactate
32
Other assessments of perfusions?
PCWP: indirect measure of left atrial pressure - pulmonary wedge pressure (measure the pulmonary artery) - CVP
33
Post-op Fluids?
Problems - Increased ADH, increased aldosterone, increased cortisol --> Na + H20 conservation. Increased K+: tissue damage, transfusion, stress hormone.
34
Solutions to post-op fluid issues?
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
Cardiac or renal failure problem + solution?
RAS activation --> NA and H20 retention Therefore solution = avoid fluid with Na --> give 5% dextrose.
36
Bowel obstruction and fluid?
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
Pancreatitis fluid management?
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
Ileostomy fluid management?
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
Reduced Urine Output Post-op
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
Management of reduced urine output post-op?
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
Clinical assessment of nutrition?
Hx - weight loss - Diet Examination - Skin fat - Dry hair - Pressure sore - Cheilitis - Weight + BMI (<20kg/m2)
42
Anthropometric assessment of nutrition?
Skin-fold thickness | Arm circumference
43
Investigations of nutrition?
Albumin Transthyretin Phosphate
44
What is enteral nutrition?
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
What feeds are possible through enteral feeding?
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
Indications for enteral feeding?
Catabolic: sepsis, burns, major surgery Coma/ITU Malnutrition Dysphagia: Stricture, stroke.
47
Complications of enteral feeding?
NGT - Nasal trauma - Malposition or tube blockage Feeding - Feed intolerance --> Diarrhoea - Electrolyte imbalance - Aspiration - Refeeding syndrome
48
What is parental nutrition?
May be total or used to supplement enteral feeding | - Combined with H20 to deliver total daily requirements.
49
Indications for parenteral nutrition?
- 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
Delivery of parenteral nutrition?
- 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
Monitoring of parenteral nutrition?
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
Content of parenteral nutrition
2000Kcal: 50% fat, 50% carbs 10-14g nitrogen Vitamins, minerals and trace elements.
53
Complications of Parenteral nutrtion?
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
What is refeeding syndrome?
- Life-threatening metabolic complications of refeeding via any route after a prolonged period of starvation.
55
Pathophysiology of refeeding?
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
What is the chemistry of refeeding syndrome?
Decreased K, Decreased Mg, Decreased Po4
57
Patients at risk of refeeding syndrome?
``` Malignancy Anorexia nervosa Alcoholism GI surgery Starvation ```
58
Prevention of refeeding syndrome?
Identify and monitor at-risk patients | Liaise with dietician
59
Management of refeeding syndrome?
- Identify at-risk pts in advance and liaise with dietician - Parenteral and oral PO4 supplementation - Manage complications

4th year everything (43 decks)

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