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Anaesthesia - Fluids
Terms in this set (67)
deficit in blood volume
hypovolaemia can lead to hypoperfusion
inadequate tissue blood flow.
result of hypoperfusion
oxygen delivery to tissues will be reduced and there is a failure to remove metabolic waste products.
Hypoperfusion can also be caused by reduced cardiac output or maldistribution of blood flow as well as reduced volume.
reduction in water content of the body, but is often used to refer to combined water and solute losses in excess of intake.
can lead to hypovolaemia, hypoperfusion and increased PCV.
causes of hypovolaemia
- fluid loss in excess of intake (vomiting, diarrhoea, polyuria)
-loss of plasma volume may be internal (e.g. exudation or transudation into a third space)
assessing hydration state
moist mucous membranes?
skin tenting? (indicates severe dehydration)
retraction of the globe (sunken eyes)
history suggests low intake or excess losses but cannot be detected on physical examination
dry mucous membranes, subtle loss of skin elasticity
mild to moderate reduction in skin elasticity, slightly increased capillary refill time (CRT), dry mucous membranes, eyes may be sunken.
marked reduction in skin elasticity, capillary refill time >2 seconds, dry mucous membranes, sunken eyes.
May show signs of shock(tachycardia, cool extremities, weak pulses)
severe signs of shock, CRT > 3 seconds, severely debilitated
> 15% dehydration
incompatible with life
-HR & BP will change with severe hypoperfusion
-normal HR 60 to 120 depending on size of dog, 160-200 in cats
aims of fluid administration
- replace circulating blood volume
-replace pre-existing losses
-supply normal maintenance requirements
-allow for any ongoing abnormal losses
-need to aim to replace LIKE for LIKE fluid
clinical assessment and monitoring
-Pulse quality improving
-mucous membrane colour, moistness, CRT
-skin tenting reduced
<1 ml/kg/hr indicates renal perfusion may be inadequate assuming normal kidney function
1 to 2 ml/kg/hr = normal
>2 ml/kg/hr = overinfusion
-central venous pressure 1 to 5cm H2O but trends most important.
- PCV/total protein - useful in serial measurements
-urea, creatinine and electrolytes
-arterial blood pressure: systolic 100 - 120 mmHg, mean 80 mmHg (less than 60mmHg poor renal perfusion)
what kind of fluids are required if HR, Bp, pulses, CRT etc are normal?
maintenance phase fluids required
signs of volume depletion
-weak, rapid pulse
-pale, dry/tacky mucous membranes
-poor skin elasticity
-reduced urine output
-small heart (radiographically)
signs of volume overload
-increased respiratory rate
-serous nasal discharge
-increased urine output
- electrolyte solutions
-pass easily out of the vascular space (75 - 85% within 1 hour)
-used for short term intravascular volume expansion and replacement of interstitial deficits.
- may be hypotonic, hypertonic or isotonic
-similar in electrolyte composition to plasma
-can be given in large volumes rapidly IV if needed
-Indicated for use in mixed electrolyte and water loss situations
•Haemorrhage (mild to moderate)
0.9 % sodium chloride
- normal saline solution
- Contains sodium, chloride and water
Indications for treatment of;
•short term gastric vomiting
•Suitable for intraoperative fluid therapy
(compound sodium lactate)
- Isotonic replacement solution
-electrolyte composition similar to plasma
-contains Na, Cl, K, Ca and lactate
used for electrolyte losses;
-siutable for intraoperative fluid therapy
take care in;
- liver disease
-not useful in hypercalcaemia as contains calcium
similar to hartman's but without lactate
7.2% saline (hypertonic)
-high osmotic potential => draws fluid into the intra-vascular space with a small infused volume.
-Dose: 4 ml/kg
-Effective within 5 minutes
-Lasts about 30 mins
-ALWAYS follow with isotonic fluids
-Can be combined with colloids
-lower sodium load
-Dextrose or glucose makes them isotonic as infused but can be thought of as providing a hypotonic solution
-Not commonly used
- rapidly passes out the vascular space
-ineffective to treat hypovolaemia
-excessive/overly rapid infusion may lead to electrolyte disorders.
-Suitable for treating free water losses (e.g. dog trapped in hot car)
0.18% saline & 4% glucose
-Mainly water with small amounts Na and Cl
-If used for maintenance, potassium is required
-Suitable for treating free water loss
-Natural or synthetic
-Large macromolecules (larger = longer retention in vascular space)
-Increase oncotic pressure
-Retained within circulation longer than crystalloids (unless capillaries are abnormally leaky)
albumin & plasma
often not readily available
synthetic colloid solutions
more commonly used
uses of colliods
- volume expansion of the intravascular space in hypovolaemia
-oncotic support in patients with hypoalbuminaemia
risks of colloids
- potential for interference with coagulation
- may interfere with measurement of total solids or urine SG
types of colloids
gelatin based colloids
-small molecule (c.f starches) size hence shorter duration but larger oncotic pull
-rapid effect - useful during anaesthesia
-minimal clotting effect
-electrolyte composition varies (some have high potassium)
- different molecular weight modified starches
-hetastarch larger molecule than pentra than tetra
(hetastarch > pentra > tetra)
-useful for long term hypovolaemia or support for hypoalbuminaemic patinets.
-larger molecules are less likely to leak through capillaries
-derived from bovine haemoglobin
-can be considered a blood product
- whole blood
-packed red blood cells
-fresh frozen plasma
- contains RBCs, proteins, clotting factors, some platelets
- treatment of choice in acute blood loss
-may be used in anaemia/coagulopathies
-up to 28 day storage, although protein degradation occurs after 12-24 hours
-PCV will be raised by 1% for each 2 ML/Kg whole blod administered.
packed red blood cells
- whole blood centrifuged to concentrate the red cells
- PCV high; 60-90%
- needs resuspension in 0.9% NaCl
- uses; normovolaemic anaemia & whole blood loss where other fluid produccts given simultaneously.
fresh frozen plasma (FFP)
- contains clotting factors and other plasma proteins.
-must be frozen within 6 hours of collection & stored in domestic freezer for 2/3 months.
-doses approx 10-30 ml/kg over 4 hours
-animals with prologed clotting times undergoing surgical procedures
-sometimes used to increase patient plasma albumin, but large volumes required.
- frozen for longer time after collection
- contains vit K-dependent factors (II, VII, IX, X) but does not contain factors V, VIII, vWF or plasma proteins.
anticoagulant forms of rodenticide toxicity
- produced from the plasma fraction of blood
20% fibrinogen; 50% factor VII; and 30% factors VIIc, XIII & vWF
-must be stored at -18C (up to 1 year)
inherited clotting factor deficiencies - haemophilia A and von Willebrands disease (absence of vWF)
- polymerised bovine haemoglobin
-acts as colliod due to large protein molecules (Hb)
- care with vol. overload (especially in cats)
- does not need cross-matched
-can be stored for up to 3 years
- mucous membrane colour alteration common and may interfere with colorimetric lad assays
to increase O2 carring capacity in anaemi animals.
Useful if there is concurrent hypovolaemia.
-inappetant patients may not receive adeqaute potassium via food.
-hypokalaemia causes muscle weakness
-some disease remote potassium loss e.g. renal failure
-NEVER administer > 0.5 mmol/kg/hour- risk of
cardiac arrhythmias arrest or death
-Mix well (can settle in the bag)
-Ensure renal and cardiac function adequate
-Always check infusion rates and monitor
response (especially when correcting quickly)
usually fluid therapy is enough to correct acidaemia, but occaionally bicarbonate is indicated.
Respiratory function MUST be adequate to
DO NOT mix with fluids containing calcium (e.g.
-Give a small amount then reassess (e.g. third or
half estimated requirement, over 30 mins
-Estimated requirement (mmol)
= 0.3 x BE x weight (kg)
- If using 8.4% solution, 1 mmol = 1 mL
routes of fluid administration
oral route of fluid administration
- can cary in electrolyte intake, calorific valve etc
- not suitable in GIT dysfunction
-not suitable in extreme losses (e.g. shock)
-can include assisted methods such as feeding via oesophagostomy tube or other feeding tube, stomach tubing.
subcutaneous route of fluid administration
- useful in exotics & v.small animals
-may be limited absorption if vasoconstricted (not suitable for hypotension for this reason)
-only isotonic fluids are suitable
-takes 6 to 8 hours to reach extracellular space
- max 10ml/kg
- ocasionaly used for home treatment e.g chronic liver failure
intravenous route of fluid administration
- route of choice in most situations
-in cats & dogs, often cephalic, saphenous, jugular veins
- rabbits; ear
-large animals - jugular vein
- use aseptic technique and change catheter approx. every 72 hours
-can use hypertonic or isotinic fluids
intraosseous route of fluid administration
- useful if peripheral venous access impossible (e.g. circulatory collapse, some exotics, multiple damaged veins)
-can use proximal humerus, tibial tuberosity, wing of ileum
- care re possible injection or leakage if needle moved
intraperitoneal fluid administration
-not as rapid absorption as intraosseus
-risk of organ penetration
-more often in exotics than dogs & cats
assessing existing losses
- body weight (if known)
-estimated dehydration from table;
e.g dog 10kg, 7% dehydration
10 x 0.07 = 7 litres (to replace existing loss)
replace over 24-48 hours (usually)
add maintenance requirements & provide for ongoing losses
for ease of use many people use a multiple of maintenance requirements
e.g. 2 or 3 x maintenance requirements calculated for that animal
rate of fluids
-assess patients clinically & with labroatory tests if appropiate.
-if in shock, need rapid fluids initially
- in extreme give fluids rapidly but ensure you reassess
-consider low volume resuscitation in ongoing haemorrhage
-supply maintenance approx 2 ml/kg/hr
-generally repid loss needs raid replacement
calculating fluid rate
Example: you want to give a 22kg dog 2 x maintenance fluids
maintenance = 2 mL/kg/hr
for 22kg dog maintenance;
22 x 2 =44 mL/hr
2 x maintenace = 44 x 2 = 88 ml/hr (round up tp 90)
(to get in minutes) 90/60 = 1.5 ml/minute
for a standard giving set, 20 drops = 1ml.
to get drops per min; 20 x 1.5 = 30 drops per minute
30/60 = 0.5 drops per second
= 1 drop every 2 seconds
Have you done enough?
-patient can be reassessed as aboer
-may depend on situation - may be possible to fully correct a deficit before anaesthesia
however if there are ongoing losses (e.g. bleeding splenic mass) this may not be possible without progressing to surgical correction.
- you are seeking an optimal state where you have created as much improvement in the patient's state as is possible without further intervention (e.g. surgery)
- reduced homeostatic control mechansims
- vasodilation caused by anaesthesic agents, fluids will support intravascular volume to maintain organ perfusion.
-may be continuing to correct pre-existing deficits
-replace evaporative losses
-replace fluid from 'third space' losses
- replace haemorrhagic blood loss from during surgery
- intravenous in most cases.
fluid choice and rate depends on patient status and losses
5 to 10 to 15 mL/kg/hr
3 to 6 to 9 mL/kg/hr
lower rates for healthy patients, with no pre-existing losses & limited ongoing loss.
higher rates may be required but monitor patient during anaesthesia.
intra-operative blood loss
-estimate blood volume of the animal
88mL/kg - dog
66mL/kg - cat
70-90mL/kg equids (dep on breeds)
-estimate blood loss
e.g. look at suction, weight swabs
1mL blood weighs 1.3g
estimate percentage of blood vol lost
- up to 10% replace w/crystalloids
- 10-20% use colliods
- 20% + use product w/oxygen carrying capacity
-guidelines only - may depend on patient status to start with
post-operative fluid therapy
The plan should be formulated to include maintenance requirements and account for ongoing losses.
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