Fluid Therapy Flashcards
How do different fluids get distributed in different body compartments?
o Water –> total body water (TBW)
o Isotonic solution –> extracellular fluid (ECF)
o Iso-oncotic solution –> plasma
Low sodium fluids (e.g. 5% dextrose) –> ICF & ECF
Na containing fluids (e.g. normal saline) –> ECF ONLY –> smaller Vd (greater proportion remains intravascular when compared to low sodium fluids, sodium is pumped out by intracellular pumps..).
Note: use of hypertonic crystalloids (e.g. 7.5% saline) +/- colloids for initial resus (to draw fluid from ICF –> ECF) does not improve outcome in general trauma patients but may reduce cerebral oedema and benefit head trauma patients.
What are crystalloids?
Inexpensive: water where solutes (e.g. NaCl, glucose) have been added.
Usually isotonic: redistribute rapidly following IV infusion (~1-4 hours) from the intravascular compartment to other compartments (ICF, ECF). Therefore, large volumes required to maintain intravascular volume, and this could cause interstitial oedema!
- 0.9% NaCl (normal saline i.e. 9g of NaCl in 1000ml / 1L)
- Hartmann’s
- 5% dextrose
- Dextrose saline (0.45% or 0.18% NaCl with 4% dextrose)
- 0.9% Dextrose saline (5%, 0.9%)
What are colloids?
Expensive: albumin or synthetic colloids e.g. gelatin, dextran, hydroxyethyl starch
Large molecules cannot easily diffuse out of blood vessels; remain intravascular for longer – oncotic pressure pulls water into / expands intravascular compartment
Often employed for initial resuscitation, however, study showed that volume ratio of 4% albumin to saline for equivalent resuscitation was 1:1.4 and meta-analysis showed no advantage of colloids over crystalloids.
- Albumin may be beneficial in hypoalbuminaemic (<15g/dl) patients with severe sepsis or in ARDS patients to aid lung water clearance
- Disadvantages: allergic reactions, clotting abnormalities and renal impairment
What are the general uses of IV fluid therapy?
Maintenance therapy (hydration / insensible loss balance)
Electrolyte balance (Na⁺, K⁺, Mg, Pi, Ca etc.),
Fluid replacement losses (vomiting, diarrhoea, sweating, bowel fistulae, high stoma losses, burns),
Hypovolaemic resuscitation
Drug administration
NOT nutrition
What should be considered when calculating maintenance fluids?
Age, weight (question accuracy), comorbidity (HF oedematous states, renal failure), clinical situation: well or unwell, medications, anticipated time for ‘nil by mouth’ period
How does fluid balance affect Na and K?
Hyponatraemia nearly always due to water overload. Hypernatraemia nearly always due to water depletion.
Hyponatraemia can be consistent with being hypo or hypervolaemic (does not always mean hypovolaemic – just signifies a net whole body depletion of water!)
Being oedematous does not mean you are normovolaemic
Genuine Na⁺ excess or depletion requires specialist advice
Potassium: Hypokalaemia nearly always due to depletion.
Hyperkalaemia nearly always due to overload.
What are the 5 stages of giving fluids?
Resuscitation (urgent restoration of circulation to vital organs, bolus <20mins)
Routine maintenance (for those who cannot meet own needs)
Replacement (correction for subacute or chronic existing fluid or electrolyte deficits or excesses)
Redistribution (seek help for those with abnormal fluid handling)
Reassessment.
Before giving fluids, what do you assess in the patient?
Assess for hypovolaemia
Clinical examination & look at trends / context
Signs may need resuscitation: systolic <100, HR >90, capillary refill >2, peripheries cold to touch, RR >20, NEWS ≥5
45° passive leg raising (PLR) can mimic fluid challenge (suggests fluids responsiveness)
IF HYPOVOLAEMIC –> Resuscitation (step 2)
How do you give fluid RESUSCITATION?
Isotonic crystalloids e.g. 0.9% saline, Hartmanns (should contain sodium in range of 130-154mmol/L) over 15 minutes.
500ml bolus stat, over range of 15 mins.
On reassessment (ABCDE), if fluid resuscitation is still indicated, repeat with bolus of 250-500ml crystalloid until a maximum of 2000ml is given.
(Seek expert help if 2000ml given!)
If fluid resuscitation no longer indicated but pt has signs of shock, also seek expert help.
If no longer indicated and no signs of shock, assess electrolyte needs + maintenance needs
How to give fluid maintenance?
Consider a 70kg pt?
ROUTINE MAINTENANCE (if not hypovolaemic)
Water: 25-30/ml/kg/day
Na/K/Cl: 1mmol/kg/day
Glucose: 50-100g/day (e.g. glucose 5% contains 5g/100ml)
Reassess + monitor: IV fluids must be stopped when no longer needed, NG fluids or enteral feeding are preferable when maintenance needs >3 days.
e.g. 70kg patient: 80ml/hr of 1000ml Dex-saline with 27-35mmol KCl
If patient has complex fluid or electrolytes issues / abnormal distributions: REPLACEMENT + REDISTRIBUTION
What are complex situations for providing fluid maintenance where extra support is required?
Oedematous states: chronic liver disease, CCF, nephrosis
Malnutrition complicating complex abdominal surgery / serious medical illness
Multiple fluid requirements
Hypovolaemia in the presence of hyponatraemia
Acute renal failure and the combined use of loop diuretics + IV fluids
Drugs: ACEIs, diuretics, NSAIDs, metformin, aminoglycosides, beta blockers
What is the physiological response to haemorrhage?
think renal
Seconds: Baroreceptors & chemoreceptors > adrenoceptor mediated response, increase HR, increase RR, vasoconstriction in splanchnic & renal vascular bed
Minutes: RAAS > direct vasoconstriction, thirst, salt & water retention. Anti-diuretic hormone (ADH)
Days (weeks): erythropoietin – increased red cell production
What to consider when deciding whether to transfuse?
Context of blood loss: (rapid, large volume, ongoing, site of bleeding)
Clinical adverse signs: (peripheral perfusion, urine output, conscious level)
Haemoglobin level (g/L): beware acute haemorrhage
Decision based on individual patient > limit harm & preserve scarce resource, transfuse to clinical endpoints.
In trauma: ‘turn off the tap’, splinting long bones & tourniquet.
How are blood donations tested?
Hep B (antigen), Hep C (antibody), HIV 1 & 2 (antibody): risk if donation occurs between infection & antibody production – nucleic acid antigen testing. HTLV, Syphilis
Special circumstances – CMV.
Transfusion transmitted infection (risk very low):
• Hep B <1 in 1.2 million donations
• HIV <1 in 7 million
• Hep C <1 in 28 million
Constant vigilance to counter risk from other pathogens – mass international travel.
What is vCLD?
Prion-associated disease: vCJD
Excluded from donation if transfusion 1980 onwards
Other possible exposure e.g. infected surgical instruments
Leucocyte depletion
Limit use of pooled products
