Subcutaneous Fluid Therapy in Rodents
Fluid therapy is indicated whenever surgery is performed, or if the rodent becomes dehydrated due to illness. Decreased water intake may occur due to pain, disease, or inability to access the water bottle. Hydration status can be checked by pinching up or “tenting” the skin over the nape of the neck. The skin should immediately relax into its normal position. If the skin remains tented longer than normal, the rodent is dehydrated. The eyes may also appear sunken.
| % Dehydration | Detectable Signs |
| <5% | Not detectable |
| 5% | Subtle loss of skin elasticity |
| 6-8% | Definite delay in return of skin to normal position |
| 10-12 % | Tented skin stands in place, eyes are sunken |
| 12-15% | Signs of collapse and severe depression; on the verge of death |
Rodents that are dehydrated often do not eat well, become depressed, and will not heal well following surgery. Fluid replacement therapy is quick and easy to perform, and can be lifesaving. Either lactated Ringer’s solution or sterile saline for injection may be used as replacement fluids. These are both inexpensive and readily available.
Fluid Therapy During Surgery
- Animals lose fluid during surgery, especially if the abdominal cavity is opened, or there is unexpected bleeding.
- The standard rate of fluid administration during surgery is 10ml/kg/hr, which is usually given through an intravenous catheter in dogs and cats.
- It is difficult to place an intravenous catheter in rodents, so fluids can be given by the subcutaneous route.
- For surgeries of 1 hour or less, the fluids can be given immediately after the surgery is finished, while the rat is recovering.
- For surgeries longer than 1 hour, the fluids should be given after 1 hour, then every half hour afterwards until the end of the surgery. If this is not possible, the fluid can be given in divided doses during recovery.
- Fluids can be injected under the skin in any part of the body, but the easiest location to use is the loose skin over the shoulders, as illustrated.
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- A 25 gauge needle should be used, and the fluids should be warmed to body temperature.
- Care must be taken not to overheat the fluids or burns will occur.
- The following calculations outline fluid therapy for a 300 gm rat undergoing a surgery of 45 minutes, and a surgery of 2 ½ hours.
Example 1: Length of surgery = 45 minutes.
Fluid rate = 10ml/kg/hr of surgery
Weight of rat = 300 gms
| 10 ml | = x ml | = 3 ml |
| 1000 gm | 300 gm | 300 gm |
The rat needs 3 ml fluid for 1 hour surgery, so needs 2.25 ml for 45 minutes. This is injected at the end of the surgery, while the rat is recovering.
Example 2: Length of surgery = 2 ½ hours
Fluid rate = 10ml/kg/hr of surgery
Weight of rat = 300 gm
10 ml
= x ml
= 3 ml
1000 gm
300 gm
300 gm
The rat needs 3 ml fluid for 1 hour surgery, so needs a total of 7.5 ml for 2 ½ hrs.
After 1 hour of surgery, give the rat 3 ml warmed fluids subcutaneously
After 1 ½ hours give 1.5 ml warmed fluids
After 2 hours give 1.5 ml warmed fluids
After 2 ½ hours give 1.5 ml warmed fluids
Total given = 7.5 ml
Or
Give 3.8 ml fluid at the end of the surgery, and another 3.8 ml approximately ½ hr later.
Fluid Therapy Due to Dehydration Caused by Pain, Disease, or Debility
- Rodents may not eat or drink because of pain, disease, or inability to access the water bottle.
- The standard rate of fluid therapy for maintenance in mammals is 60ml/kg/24hr. If an IV catheter can be placed, such as in a dog or cat, this is given as a constant drip. With rodents, since it is difficult to place an IV catheter, the fluids are divided into thirds and given every 8 hours.
- With dehydrated rodents, an additional 5 - 10% of body weight should be given, depending on the degree of dehydration.
- The following calculations outlines fluid therapy in a 300 gm rat that is severely (10%) dehydrated, and mildly (5%) dehydrated.
Example 1: Severely dehydrated rat
Daily (24hr) Maintenance:
60 ml
= x ml
= 18 ml
1000 gm
300 gm
Plus 10% of body weight: 10% of 300gm
= 30 ml
Total fluids required over 24 hours
48ml
One third of the fluid requirements (ie 16 ml) is given under the skin in 2 or 3 sites every 8 hours for the first 24 hours, after which the hydration status is re-evaluated.
Example 2: Mildly dehydrated rat
Daily (24hr) Maintenance:
60 ml
= x ml
= 18 ml
1000 gm
300 gm
Plus 5% of body weight:5% of 300 gm
= 15 ml
Total fluids required over 24 hours
33ml
One third of the fluid requirements (ie 11 ml) is given under the skin in 2 or 3 sites every 8 hours for the first 24 hours, after which the hydration status is re-evaluated.
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