Plus-Hex CLINICAL
The second way in which SC fluids can be delivered is through a sterile giving set with a needle attached to the end. There can still be a small amount of pressure with this method, but instead of using a syringe to force fluids into the SC layer, with the use of a giving set, gravity allows the space to fill with fluid. Whichever method is used, it is usually better tolerated if the fluids have been warmed slightly before administration.
Intraosseous
Where IV access is not available or in cases of severe dehydration, intraosseous( IO) fluid administration may be required. IO catheters allow rapid delivery of a volume of fluid to a patient. This route is often used in critically ill young patients such as kittens and puppies [ 1 ], as their softer bones and small veins can mean catheter placement into the bone is easier than IV placement.
IO catheters can be placed into any bone that has an adequate marrow cavity. The most common site for catheter placement is the medial aspect of the trochanteric fossa, located in the femur; however, the ilium, humerus and tibia can also be used [ 1 ].
One of the main advantages of IO fluid administration is the fast redistribution of fluids, which helps rehydrate and support the patient ' s body systems as quickly as possible. Patient discomfort is common when placing an IO catheter, so local anaesthesia and warming the fluids before administration are recommended [ 6 ].
Assessing hydration status
A patient ' s hydration status can be assessed by either physical examination, measurement of urine concentration or blood work. A combination of these methods can be used to build an accurate interpretation of a patient ' s hydration status.
Physical examination
Physical examination of the patient and assessing features such as skin elasticity, mucous membrane moisuture and capillary refill time can all indicate the level of dehydration. See Table 2( page 55), which lists the typical clinical signs associated with different dehydration percentages.
Blood analysis
Four different parameters can be measured as a way of assessing dehydration in patients. Not all practices will have the ability to check all of these, but they can be useful in creating a treatment plan for dehydrated pets.
Packed cell volume( PCV) is a measure of the proportion of the total blood volume that is occupied by red blood cells. Measurement of PCV is a quick test that can provide information on hydration, anaemia and blood loss. A usual PCV in dogs is between 37 % and 55 %, while in cats it is between 24 % and 45 % [ 8 ].
To measure PCV, blood is taken and placed into a collection tube containing ethylenediaminetetraacetic acid( EDTA), before a sample is drawn into a capillary tube that is then sealed with clay.
After centrifugation at 10,000 rpm for 5 minutes, the PCV can be read, usually with the use of a Hawksley microhaematocrit reader. Haematology machines can also usually provide a PCV value.
Total solids are measured after taking a PCV reading. The plasma from the centrifuged capillary tube is placed on a refractometer to check the concentration of total solids. Plasma contains proteins, and the total solids value provides an estimate of the concentration of total plasma proteins within the circulation.
A normal total solids value in both dogs and cats is in the range of 60 – 75 g / l [ 8 ].
If both the PCV and total solids are raised, this can indicate dehydration, although elevated values for both can also be seen in other illnesses. It is important to fully assess the patient with a VS and evaluate all areas for a full clinical interpretation.
Lactate levels in a patient ' s blood can also be tested in some practices. Lactate is produced when hypoperfusion of the body tissues occurs. Portable lactate monitors are available and work in a similar way to glucometers. A normal lactate level is 0.3 – 2.5 mmol / l. An increased lactate level indicates cause for concern [ 9 ].
Specific gravity( SG) provides a measure of the density of a fluid relative to distilled water [ 8 ]. The SG of a body fluid, such as urine, can be measured using a refractometer.
The usual reference range for urine SG in dogs is 1.015 – 1.045. In cats, the reference range is 1.035 – 1.060. If a urine SG measurement is higher than the reference range for the species, this can indicate dehydration or shock.
Conclusions
IVFT can provide patients with circulatory support in cases of disease, trauma or shock. The use of IVFT can also help support patients that are undergoing anaesthesia and lengthy surgical procedures.
It is important to have a clear understanding of the movement of water throughout the body, as this can aid in selecting the most appropriate type of fluid for each patient.
Volume 41( 1) • February 2026
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