Fluid types and therapy Flashcards
What types of isotonic crystalloid fluids?
Hartmann’s - most common
Sodium Chloride (Saline) - only useful in some situations
Dextrose solutions - do not use
What is the purpose of isotonic fluids
Used for fluid resuscitation (hypovolaemia and dehydration)
They equilibrate across membranes rapidly to restore both intravascular and extravascular spaces - this does mean the effect of intravascular volume expansion can be short lived
What does Hartmann’s solution contain and what is it used for?
Na, Cl, K, Ca, lactate +/- Mg
Lactate is pre-cursor for bicarbonate - alkalinising fluid
Alkalinising - many sick patients have metabolic acidosis due to poor perfusion => lactic acid
What is sodium chloride (saline) fluid used for?
Acidifying - useful for metabolic alkalosis e.g., severe vomiting
Not advised for long term use due to acidifying effect
What is the drawback of dextrose solutions?
Glucose is rapidly metabolised - hypotonic fluid in reality - causes electrolyte disturbances due to dilutional effect
DO NOT USE - dangerous
Describe the use of hypertonic saline crystalloids fluids
Markedly hypertonic – Pulls fluid from interstitial space into the vascular space.
Rapid volume expansion using minimal total volume (large animals) - great in hypovolaemic patient
If blood loss is from trauma - hypertonic saline causes spike in BP - increases bleeding
Osmotically pulls fluid from the brain across BBB - reduces intracranial pressure (great in head trauma)
BUT – hypernatremia (high sodium) can be dangerous – 1-2 uses per 24h.
Describe the use of hypotonic saline crystalloid solution
Rarely used in first opinion practice
Dilutional so resolves hypernatremia
Danger – Rapidly resolution of hypernatremia creates an osmotic gradient into the brain – cerebral oedema – seizure, coma, death.
What blood products can be infused into patients?
Whole blood - RBCs, WBCs, platelets, plasma - blood loss
Packed RBCs - anaemia
Fresh frozen plasma - coagulation factors, albumin, globulin - coagulopathy, hypoalbuminaemia/oncotic pressure support
Frozen plasma - Clotting factors, albumin - coagulopathy (2nd choice), hypoalbuminaemia/oncotic pressure support
Platelet concentrate - life threatening thrombocytopaenia
Albumin - only human available - life threatening hypoalbuminaemia
What is the risk of infusing albumin into a patient?
only human albumin available - associated with anaphylaxis and delayed acute kidney injury
What is the purpose of colloid fluids?
Synthetic macromolecules mimic albumin - increase oncotic pressure - hold onto water in blood
What is the endothelial glycocalyx?
the vascular sieve that protects hydrated structures and vital to normal endothelial function. In critical illness it becomes degraded, leading to vascular leakage
vascular leakage => colloids also leak => interstitial oedema and minimal volume expansion
Give examples of colloid fluids
Hetastarch - no longer available
Geloplasma
Dextrans
Use fresh frozen plasma or frozen plasma instead
How is hypovolaemia treated?
Give a bolus of isotonic fluid
Dogs/cows/horses/sheep – 10-15ml/kg
Cats – 5-10mls/kg
Given over 10-15 mins, up to 3 times
Consider hypertonic saline in larger animals - 3ml/kg over 10 mins (follow with isotonic if dehydrated)
What are the end points for fluid resuscitation?
Improved oxygen supply to tissues:
- Mentation improving
- Clinical exam (TPMR) normalising
- Blood pressure >60 MAP minimum
- lactate improving <2mmol/L within 6hrs
- POCUS - improving volume status of heart and caudal vena cava size
How is dehydration treated?
Aim is the slow the dehydration down - normovolaemic patient so do not need bolus
Work out deficit - replace deficit over 24hrs
End target - weight gain equivalent to deficit over 24hrs
Assume a 20kg dehydrated dog, 7% deficit equating to 1.4kg
What should the dog weigh tomorrow after treatment?
21.4kg
How do you calculate the rate for dehydration therapy?
Rate = Deficit + maintenance + ongoing losses
How can ongoing fluid losses be calculated in a dehydrated patient?
either monitor precisely in mls (e.g. urinary catheter, faecal catheter, weighing bedding) or use a surrogate measure e.g. bodyweight change.
What is the biggest risk when treating dehydrated patients?
Fluid overload:
- vascular leakage (unable to retain fluid)
- generation of interstitial oedema (increasing the distance between blood vessels and tissues -> reduced oxygen and nutrient supply, and evacuation of waste products)
- pulmonary oedema
- acute kidney injury
How can fluid therapy be monitored to prevent complications
Basic monitoring – weight, respiratory rate and effort, chest auscultation, POCUS, checking for peripheral oedema, hypertension (BP).
Advanced monitoring – blood gas analysis (A-a gradient) on an arterial sample
How can fluid overload be avoided?
Calculate ins and outs
easier in small animals:
Ins - Food and water measured, IVFT measured via drip pump
Outs - urinary catheter, faecal catheter, weight bedding before and after (vomit, diarrhoea, urine), insensible losses (breathing)
Track weight change to assess if treatment is working
Harder in larger animals - relying on clinical signs of hydration/overload
