Perioperative fluid management Flashcards
Define insensible losses of fluid
Water loss due to:
Transepidermal diffusion and evaporation
Evaporative water loss from respiratory tract
‘insensible’ as we are not aware of it.
Loss of pure water with no associated solute loss (which occurs in sweating)
Insensible losses cannot be eliminated
What is the minimal insensible fluid loss in the average adult?
400ml/d from skin
400ml/d from respiratory tract
What can cause insensible fluid loss to vary?
Changes in minute ventilation - e.g. disease and controlled ventilation
Changes with humidity
Define sensible losses of fluid
Water loss due to: Urine Sweat Defection Wounds etc.
‘sensible’ as it can be seen/felt/measured
Loss of water +/- solutes
Can be eliminated
What is the primary cation in ICF?
Potassium
What is the primary cation in ECF?
Sodium
How much sodium is required daily?
1-1.5mmol/kg/day
How much potassium is required daily?
0.7-1mmol/kg/day
Which patients are more likely to need preoperative fluid resuscitation?
Acute presentations with vomiting or diarrhoea
Acute presentations where patient has been immobile or debilitated prior, causing reduced fluid intake
Elderly patients with impaired renal function
Drugs that impair renal function
Patients with low body weight and total body fluid
Children - may not show obvious physical signs of dehydration
What fluids are used for correcting the majority of fluid imbalances?
Isotonic crystalloids:
- Isotonic 0.9% saline*
- Dextrose (4%) saline (0.18%)
- Hartmann’s solution
When may non-isotonic fluid optimisation be necessary?
Significant disorders of sodium balance. Likely to require optimisation in high-dependence unit (HDU)
How is volume of fluid depletion assessed?
Body weight on admission vs recent when healthy
Haematocrit on admission vs recent when healthy
Serum urea is raised disproportionately more than serum creatinine
What are signs of intravascular volume depletion? When are these seen?
Hypotension
Tachycardia
Seen with loss of 10-15% of body water
Name 3 symptoms and signs of extracellular fluid depletion
Increased thirst Drowsiness Reduced urine output Headache Dizziness Lax skin tone Reduced sweating Dry mucosa
How is fluid need initially assessed?
ABCDE assessment
Name 3 indications for potential fluid resuscitation
SBP <100mmHg HR >90bpm Capillary refill >2s Peripheries cold to touch RR >20 NEWS 5+ Passive leg raise test
What is the initial treatment for fluid resuscitation?
Identify cause of deficit and respond
Give a fluid bolus of 500ml crystalloid over 15min
*Keep Na within 130-154mmol/L
What can be given following initial treatment for fluid resuscitation if required?
Further fluid bolus of 250-500ml of crystalloid up to 2000ml before seeking expert help
Outline how fluid resuscitation is monitored
Skin turgor and mucosal hydration change slowly - unreliable
1-hourly urine output - target 0.5ml/kg/h
Serum urea provided adequate renal function and no acute GI bleed
What are the indications for fluid routine maintenance?
Patient cannot meet fluid and/or electrolyte needs
No complex fluid or electrolyte replacement
No abnormal distribution issues
Outline the normal daily fluid and electrolyte requirements for routine fluid maintenance
Water: 25-30 ml/kg/d
Na/K/Cl: 1 mmol/kg/d
Glucose: 50-100 g/d
What are the indications for fluid replacement and redistribution?
Patient cannot meet their fluid and/or electrolyte needs
Patient has complex fluid or electrolyte replacement, or
Patient has abnormal distribution issues
List 3 causes of abnormal fluid or electrolyte loss
Vomiting and NG tube loss Biliary drainage loss High/low volume ileal stoma loss Diarrhoea/excess colostomy loss Ongoing blood loss Sweating/fever/dehydration Pancreatic/jejunal distula/stoma loss Urinary loss
List 3 types of redistribution or complex fluid issues
Gross oedema Severe sepsis Hyper/hyponatraemia Renal, liver and/or cardiac impairment Post-op fluid retention and redistribution Malnourished and refeeding issues
