fluid types & therapy Flashcards
What is the difference between dehydration & hypovolaemia?
Hypovolemia: Reduced circulating blood volume; can be life-threatening
Dehydration: Loss of total body water affecting interstitial & intracellular compartments
Key Difference: Hypovolemia affects perfusion & requires immediate correction before addressing dehydration
What are isotonic crystalloids and what are they used for?
E.g.: Hartmann’s (Lactated Ringers), 0.9% Sodium Chloride
Indications: Fluid resuscitation in hypovolemia & dehydration
Key Feature: Rapidly equilibrate across membranes but have a short-lived effect on intravascular volume
Why is Hartmann’s the most popular
Lactate as Buffer: Metabolized in liver to bicarbonate, helping to correct metabolic acidosis (common in critically ill patients)
Electrolyte Balance: Contains Na, Cl, K, Ca & lactate, more physiologically balanced than normal saline
Less Acidifying: maintains stable acid-base balance
Versatile Use: Suitable for treating hypovolemia & dehydration
Describe the limited use of 0.9% Sodium Chloride (saline)
While saline is useful for metabolic alkalosis (e.g., in vomiting patients), it’s not ideal for long-term fluid therapy due to its acidifying effects
Why should Dextrose solution (D5W) be avoided?
D5W is not truly isotonic—glucose is rapidly metabolised, leaving behind 0.18% saline, which is hypotonic & can cause dangerous electrolyte imbalances due to dilution
When is hypertonic saline (7.2%) useful and what are the risks?
Uses:
- Rapid volume expansion with minimal total fluid (esp. in large animals)
- Pulls fluid from interstitial space into vascular system
- Reduces raised intracranial pressure (e.g. head trauma) by osmotic fluid shift from the brain
Risks:
- Hypernatremia (excess Na) – limit to 1-2 doses per 24h
- If hypovolemia is due to trauma & active bleeding, sudden blood pressure spike may disrupt clots & worsen hemorrhage
What are the uses and risks of hypotonic saline (0.45% NaCl)?
Uses: Resolves hypernatremia (high sodium levels)
Dangers:
- Cerebral oedema risk – Rapid Na correction creates osmotic gradient into brain, leading to fluid shift, swelling, seizures, coma, or death
- Idiogenic osmoles: brain retains osmoles to prevent dehydration in chronic hypernatremia; if Na is lowered too quickly, these osmoles pull excess fluid into brain, worsening swelling
What are the different blood products and their uses?
Whole Blood: For anemia due to blood loss
Packed Red Blood Cells (pRBCs): For anemia when whole blood is unavailable
Fresh Frozen Plasma (FFP): Contains coagulation factors; used in coagulopathy
Frozen Plasma: Contains factors II, VII, IX, X; used when FFP is unavailable
Platelet Concentrate: For life-threatening thrombocytopenia
Albumin: Used for hypoalbuminemia but can cause anaphylaxis (controversial)
What can you give if you dont have access to whole blood
RBC and Plasma
What is the primary function of synthetic colloids?
To mimic albumin & provide oncotic pressure support in cases of hypoalbuminemia
What is the endothelial glycocalyx?
acts as vascular sieve, maintaining normal endothelial function & preventing excessive vascular leakage
How does the endothelial glycocalyx affect colloid use?
In critical illness or hypoalbuminemia, glycocalyx is degraded, leading to vascular leakage
This means colloids may also leak into interstitial space, causing oedema & reduced volume expansion
What are the common types of colloids?
Hetastarch, Geloplasma & Dextrans
Can cause adverse effects so avoid use - risk of acute kidney injury & coagulopathy
What is the general recommendation regarding synthetic colloids?
Avoid using synthetic colloids unless no other alternatives exist
Fresh Frozen Plasma (FFP) or Frozen Plasma (FP) are preferred choices for oncotic support
Is this patient dehydrated or hypovolaemic?
Dehydration – reduced access to water, dry mucous membranes but quality of pulse alright, normal blood pressure, quiet because of headache
Is this patient dehydrated or hypovolaemic?
Hypovolaemia – low temp, no time to develop dehydration (acute), poor pulse quality, tachycardic, tachypnoeic due to pain, low BP
What is the first step in treating hypovolemia?
Administering a micro bolus to test response
What are the fluid bolus recommendations for different species?
Dogs/cows/horses/sheep: 10-15 ml/kg
Cats: 5-10 ml/kg
Large animals: Consider hypertonic saline (3 ml/kg)
Over 10-15min for up to 3x
Apart from fluid therapy, what else can you do to manage hypovolaemic patients?
If bolus therapy fails – reconsider cause; non fluid responsive indicates poor vascular tone e.g. sepsis
Vasopressors – e.g. noradrenaline/dopamine
Oncotic support – e.g. plasma & feed patient (protein)
What are the end points for fluid resuscitation?
Improved mentation
Normalizing clinical exam (TPMR)
Blood pressure >60 MAP
Lactate <2.0 mmol/L within 6 hours (shows that what you’re doing is working)
Improved oxygen supply to tissues
POCUS
- improving volume status when looking at heart
- improving caudal vena cava size
If patient is both hypovolaemic and dehydrated what do you treat first?
Hypovolaemia (restore perfusion)
How is dehydration deficit calculated?
Deficit = % dehydration x body weight (kg)
E.g: 7% deficit in 20kg dog = 1.4L
(aim to replace deficit over 24h)
What is the formula for fluid therapy rate?
Rate = Deficit + Maintenance + Ongoing losses
What is the fluid maintenance rate?
40-70ml/day
How can ongoing losses be measured?
either monitor precisely in mls (e.g. urinary catheter, faecal catheter, weighing bedding) or use surrogate measure e.g. bodyweight change
What are the signs of fluid overload?
Pulmonary oedema
Acute kidney injury
Increased respiratory rate/effort
Peripheral edema
Hypertension
How can fluid overload be prevented?
By monitoring ins & outs, tracking weight changes & adjusting fluid therapy accordingly
