Fluid therapy
Fluid therapy is a critical part of patient care, both during anaesthesia as well as for hospitalised patients. Current recommendation suggests that all anaesthetic patients be offered intravenous fluid therapy (there may be situations where fluids are not recommended, but for the majority of our patients, we should be supporting them with fluid therapy).
See below for the current guidelines for different fluid rates for different species.
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Recommended fluid rates:
Canines
Maintenance
There is some variation in set recommendation of daily maintenance rates for a hospitalised patient. AAHA guidelines suggest 2-6ml/kg/hr. This doesn't account for any losses such as via vomiting or dihorrhoea. These losses need to be considered and replaced gradually. Patients should be monitored closely to ensure that they are receiving an appropriate amount of fluid. The formula for this over 24 hours is:
(132 x body weight (kg))^0.75 = volume in ml per 24hr
Surgical Maintenance
During anaesthesia, we want to continue to replace ongoing losses as well as account for effects that anaesthetic medications will have on the patient. The below rate is the starting rate for fluid therapy during anaesthesia but should be reassessed throughout. Once 1hr of anaesthetic time is reached this rate can be dropped by 25% every hour until normal maintenance is reached.
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5 x body weight (kg)
= volume in ml for the 1st hour
Shock rate
Hypovolaemic shock can occur for a number of reasons such as major haemmorhage, severe dehydration, and vasodilation and needs careful correction. Care must be taken to not over perfuse with shock rates. It is recommended to work out the shock rate volume and start with 25% of this over 10-15 minutes. Reassess the patient and, if needed, give the next 25%.
85 x body weight (kg)
= total shock rate volume in ml
Bolus
If your patient is becoming hypotensive under anaesthetic, it may be necessary to provide a bolus of fluid to increase circulating volume. Ensure hypotension is due to hypovolaemia before administering fluids by assessing anaesthetic depth, medications given, etc. Take care to not rely solely on fluid therapy to correct anaesthetic-related hypotension. Give the bolus over 10-15 minutes and reassess. This can be repeated once if needed.
5 x body weight (kg)
= bolus volume in ml
Felines
Maintenance
Feline patients require lower volumes of fluids than canines and are more susceptible to fluid overload so care should be taken always. AAHA guidelines suggest 2-3ml/kg/hr. This doesn't account for any losses such as via vomiting or dihorrhoea. These losses need to be considered and replaced gradually. Patients should be monitored closely for overloading of fluids. The formula for this over 24 hours is:
(80 x body weight (kg))^0.75 = volume in ml per 24hr
Surgical Maintenance
During anaesthesia, we want to continue to replace ongoing losses as well as account for effects that anaesthetic medications will have on the patient. The below rate is the starting rate for fluid therapy during anaesthesia but should be reassessed throughout. Once 1hr of anaesthetic time is reached this rate can be dropped by 25% every hour until normal maintenance is reached.
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3 x body weight (kg)
= volume in ml for the 1st hour
Shock rate
Hypovolaemic shock can occur for a number of reasons such as major haemmorhage, severe dehydration, and vasodilation and needs careful correction. Note that tachycardia may not appear in hypovolaemic felines. Care must be taken to not over perfuse with shock rates. It is recommended to work out the shock rate volume and start with 25% of this over 10-15 minutes. Reassess the patient and, if needed, give the next 25%.
55 x body weight (kg)
= total shock rate volume in ml
Bolus
If your patient is becoming hypotensive under anaesthetic, it may be necessary to provide a bolus of fluid to increase circulating volume. Ensure hypotension is due to hypovolaemia before administering fluids by assessing anaesthetic depth, medications given, etc. Take care to not rely solely on fluid therapy to correct anaesthetic-related hypotension. Give the bolus over 10-15 minutes and reassess. This can be repeated once if needed.
3 x body weight (kg)
= bolus volume in ml
Rabbits
Maintenance
The current fluid guidelines for a rabbit's daily maintenance suggest a volume of 100ml/kg per 24hrs or just over 4ml/kg/hr. In some cases this can be doubled but care must be taken as overload can easily happen. Rabbits are susceptible to hypothermia as well, so some recommend use of fluid warming for these patients too.
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100 x body weight (kg) = volume in ml per 24hr
Surgical Maintenance
Due to the faster loss of fluids for rabbits via evaporation and metabolism compared to canines and felines, they require higher surgical fluid rates. The general recommendation is 10ml/kg/hr to account for these losses. Fluid warming is strongly advised as well.
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10 x body weight (kg)
= volume in ml per hour
Shock rate
Rabbits have a circulating blood volume of 55-60ml/kg. Due to high metabolism and fluid losses, hypovolaemia can happen rapidly. Care must be taken to not over perfuse. Shock rates are generally recommended at 10ml/kg/hr but rates of up to 100ml/kg/hr have been suggested. As with canines and felines, start with 25% over 15min and reassess.
10 x body weight (kg)
= shock rate volume in ml
Bolus
I am currently unaware of any literature demonstrating evidence-based numbers for bolus rate fluids to correct hypotension in rabbits.
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If you are aware of a figure please let me know.
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Please let me know if you know of any studies with hypotension bolus rates