WCS25 Fluid, Electrolytes And Blood Transfusion

Question 1

Total body water

Answer 1

***Extracellular (Intravascular : Interstitial = 1:3): Intracellular = 2:3

Body weight:

• Male: 60%
• Female: 50-55%

Extracellular fluid (40%):

• 25% Body weight
• 40% Total body water
• Intravascular : Interstitial = 1:3

Intracellular fluid (60%):

• 35% Body weight
• 60% Total body water

Question 2

Requirement and Loss

Answer 2

Water: 30-40 ml/kg/day
Na: 1-1.7 mmol/kg/day
K: 0.9-1.3 mmol/kg/day
Ca: 10-20 mmol/day
PO4: 18 mmol/day
Mg: 10 mmol/day

Question 3

***IV fluid regimen consideration

Answer 3

1. Basal requirement (maintenance)
2. Pre-existing dehydration + Electrolyte loss
3. Ongoing loss

Question 4

1. Basal requirement (maintenance)

Answer 4

1st 10kg: 4 ml/kg/hour
2nd 10kg: 2 ml/kg/hour
Each kg afterwards: 1 ml/kg/hour

Question 5

2. Pre-existing dehydration + Electrolyte loss

Answer 5

1. Source in surgical patients
   - Poor intake: pain, cachexia
   - Bleeding
   - GI loss
   —> Excessive output e.g. vomiting, diarrhoea
   —> Failure to reabsorb GI fluid (Mechanical large bowel obstruction, Paralytic ileus due to abdominal pathology)
   —> Different GI juices have different composition!!! —> Adjust fluid, electrolyte replacement accordingly
2. **Third space loss
   - important element of septic shock
   - **Inflammation: endotoxin, exotoxin, cytokine release, complement activation
   —> **Vasodilatation + ↑ capillary permeability
   —> **Sequestration: lots of fluid into interstitial space
   —> Hypovolaemia intravascularly but lots of fluid in interstitial space
   —> Replace fluid aggressively
3. Fasting before IV fluid replacement
   - AED, investigations, transferral

Question 6

3. Ongoing loss

Answer 6

Haemorrhagic / Hypovolaemic shock

6 parameters:

1. HR
2. SBP
3. Pulse pressure
4. Urine output
5. Mental state
6. Tachypnea

Class I - IV

Class I:
- 750mL blood loss
—> ***Crystalloid replacement (aqueous solution of mineral salts and other small, water-soluble molecules, isotonic to human plasma)

Class II:
- 750-1500 mL blood loss
- **Tachycardia
—> **Crystalloid replacement

Class III:
- 1500-2000 mL blood loss
- Tachycardia
- ***SBP ↓
- ***Urine output: 5-15 mL/hr
—> Crystalloid + ***Blood replacement

Class IV:
- >2000 mL blood loss
- Tachycardia
- SBP ↓
- ***Urine output: Negligible
—> Crystalloid + ***Blood replacement

Question 7

***Type of fluid

Answer 7

1. Crystalloid
   - Low MW
   - glucose, aqueous solution
   - shorter intravascular t1/2 (20-30 mins) —> ***rapid equilibrium with ECF
   - cheaper
   - 5% Dextrose, 0.9% NaCl, Ringer’s lactate
2. Colloid
   - High MW
   - protein, glucose polymer
   - longer intravascular t1/2 (3-6 hours) —> ***maintain oncotic pressure
   - expensive
   - Gelatin, Dextrans, Hetastarch —> Good for resuscitation

Choice:

1. Replace intravascular volume
   - ***3-4x crystalloid = 1 colloid
2. Rapid restoration of intra-vascular volume —> Colloid
3. Rapid restoration of extra-vascular volume —> Crystalloid

Most surgical patients:
**Extravascular deficit > Intravascular deficit
—> **Crystalloid administration
—> beware rapid administration of large amount of Crystalloid prone to significant tissue edema (e.g. Pulmonary edema —> Be careful!)

Question 8

Fluid replacement

Answer 8

1. Replace in small amount
2. Keep reassessing
   - Basal requirement
   - Pre-existing loss
   - Ongoing loss
3. Fluid overload
   - elderly, CHF, chronic renal failure
   - **post-operative patients
   —> **stress hormone: ADH / Aldosterone / Catecholamines
   —> Na, H2O retention, increase K retention

Question 9

Hypokalaemia in surgical patients

Answer 9

Cause:
1. **GI loss (e.g. vomiting, diarrhoea, bowel obstruction, high output fistula)
2. **Renal loss (e.g. diuresis, ketoacidosis, hypo-Mg)
3. **Alkalosis (e.g. aldosteronism)
4. Drugs (e.g. diuretics, laxatives, insulin, beta-agonists effect)
5. **Lack of replacement (commonest)
- 2D/1S Q8H (most commonly given) —> 2 dextrose 1 saline alternate
—> but D/S do not contain K!!!
—> 2D/1S + 10 mmol ***KCl per pint Q8H / Q6H

Effect:
**Hyperpolarisation of resting potential —> Greater than normal stimulus required to generate action potential —> **↓ excitability in muscle but ***↑ excitability in heart (enhance funny current in pacemaker cells, faster phase 4 depolarisation, ↑ HR, ↑ automaticity, delayed ventricular repolarisation —> EAD)

1. CVS
   - Arrhythmia (commonest cause of AF in post-op patients)
   - ECG changes (T inversion, ST depression, PR prolong)
   - Reduce cardiac contractility
2. Neuromuscular
   - Intestinal ileus
   - Muscle weakness

Treatment:

1. ***Slow K tablet (600mg tablet = 8 mmol K)
2. ***Syrup KCl (1g = 13.5 mmol K)
3. ***IV replacement (10-20 mmol KCl in 100ml NS, over 1 hour)
   - if K <3 mmol/L (to avoid arrhythmia)
   - should not excess 10 mmol/hr in non-ICU setting
   - recheck after 20-30 mmol of IV KCl

Question 10

***Blood transfusion

Answer 10

Risk of transfusion:

1. ***Haemolytic reaction
   - ABO incompatibility
   - Minor blood group incompatibility (DHTR)
2. ***Febrile reaction
   - FNHTR
3. ***Urticaria
4. Anaphylaxis
5. ARDS
   - TRALI
   - TACO
6. Infection complications
   - Hepatitis
   - AIDS
   - CMV, EBV
   - Bacterial
7. ***Immunosuppression

Indication:

1. ***Hb < 7g/dL
2. Danger of anaemia > Risk of transfusion
3. Symptoms of anaemia severe
4. Varies according to patients’ age, co-morbidities, clinical condition

Low threshold of initiation:

• Advanced age >80
• History of IHD, aim Hb > 8g/dL
• In shock with active bleeding

High threshold of initiation:
- Young patients
- After curative cancer surgery
—> do not want transfusion to cause immunosuppression
—> increase chance of recurrence

Question 11

Type of blood

Answer 11

1. Whole blood
   - **Plasma + All elements of blood
   - Effective in **volume resuscitation
   - Granulocytes, Platelet, Factor 5, 8 lose their function after storage
   - Storage: 35 days
2. Packed cell
   - **Whole blood without plasma / platelet
   - Less volume overload
   - Effective in **correction of anaemia
   - Storage: 42 days
3. Platelet concentrate
   - ***Platelet in plasma
   - ABO compatible
   - Storage: 7 days
4. Fresh frozen plasma
   - **Plasma containing **vWF, Factor 2, 7, 9, 10, 8
   - ABO compatible
   - Storage: 1 year

Question 12

Massive transfusion

Answer 12

Transfuse 1-2 times of patients’ blood volume (> 10 units of blood)

Complications after transfusion:

1. ***Hypothermia
2. ***Coagulopathy
3. ***Hyper K
4. ***Citrate toxicity (HypoCa, Cardiac dysfunction)
5. ***Metabolic alkalosis (Citrate + Lactate —> HCO3-: conversion of citrate, an anticoagulant in blood bags, to HCO3- predominantly in the liver)