Patients with CPA should not have fluids administered unless they have or are suspected to have hypovolemia. In patients with spontaneous circulation but are hypovolemic, fluid therapy can help increase the mean arterial pressure (MAP) and improve cardiac output. In a patient with CPA, euvolemic (proper amount of blood) fluids are not likely to increase cardiac output. Fluids may accumulate in the veins causing an increase is central venous pressure or CVP). This will result in a decrease in blood flow and a decrease in oxygen delivery to the tissues. In such patients, fluid therapy should be used very conservatively if at all. If ROSC is achieved and the heart is contracting spontaneously, then fluid therapy can be utilized more readily. For patients that are in CPA and are also hypovolemic, boluses of fluids may be beneficial; this will provide additional circulatory volume. Even though CVP will increase, the ventricles will stretch leading to improved cardiac output. This, in turn, increases MAP which improves blood flow to the tissues. If your patient has undergone severe trauma, severe vomiting and/or diarrhea or hemorrhage they are more likely to benefit from fluids.  Intravenous (I.V.) fluids have many purposes in veterinary medicine. They can be used for routine procedures such as a spay or for the life-threatening emergencies such as a major trauma. Prior to administering fluids, you must have venous access and assess the patient to determine their needs. There are several types of fluids that are designed to be given intravenously. They are broken down in to two categories: crystalloids and colloids.
Crystalloids include: Lactated Ringer’s Solution (L.R.S.), Normosol-R, Plasmalyte-A, and Sodium Chloride (NaCl). While all of these are suitable to be given intravenously, they are all used to treat different conditions. If a specific fluid type is not available, they can be made up in the clinic to meet the patient’s needs. For example: You need a 2.5% dextrose in 0.45% sodium chloride solution to give a patient, but only have bags of 0.45% sodium chloride and sterile bottles of 50% dextrose. You would need to follow the guidelines based on the size of the patient, the size of the fluid bag and what the Veterinarian specifies and/or the clinic guidelines. Lactated Ringer’s is an isotonic solution that is made up for 130 mEq/L of sodium, 109 mEq/L of chloride, 4 mEq/L of potassium, 3 mEq/L of calcium, and is a slightly acid solution with a pH of 6.7. This is commonly used in patients with hypocalcemia, such as lactating or pregnant animals. Normosol-R is an isotonic solution as well. It contains: 140 mEq/L of sodium, 98 mEq/L of chloride, 5 mEq/L of potassium, 0 mEq/L of calcium, and is a slightly alkaline solution with a pH of 7.4. This is used to help restore electrolyte imbalances in dehydrated patients or maintain their hydration levels and blood pressure when undergoing a surgical procedure.
Plasmalyte-A is another isotonic solution. It contains: 140 mEq/L of sodium,103 mEq/L of chloride, 5 mEq/L of potassium, and 0 mEq/L of calcium, and is also a very slightly alkaline solution with a pH of 7.4. This is also used to help restore electrolyte imbalances in dehydrated patients or maintain their hydration, electrolyte levels, and blood pressure when undergoing a surgical procedure. It is compatible with blood and blood components and can be administered at the same time if needed.
Sodium Chloride is a very versatile fluid. The sodium chloride (0.9%) contains: 154 mEq/L of sodium, 154 mEq/L of chloride, 0 mEq/L of potassium, and 0 mEq/L of calcium, and is acidic with a pH of 5.4. This fluid is often used to dilute other medications prior to being administered intravenously such as Antivenin, dextrose, or packed red blood cells. Sodium chloride can also be used to flush I.V. catheters, it can be used to safely flush body cavities, and it can be used to keep delicate tissues moist during extended procedures, along with several other things. While the 0.9% sodium chloride is a commonly stocked fluid in clinics, there are other concentrations, such as 0.45% sodium chloride. This contains different amounts of electrolytes, a different tonicity, and a different pH level.
Colloids include both natural and synthetic solutions. These work by expanding the plasmaor bloodvolume. Hydroxyethylstarch (H.E.S) is a common synthetic fluid, while whole blood is consider edanatural solution. Hydroxyethyl starch is sold under the names “Hetastarch” and“Vetastarch”,and is able to begin given the patient without having to perform any diagnostic blood tests and is best to use in the event of an emergency as it can be given right away. With whole blood, that is sometimes not the case, and blood type testing may be required prior to administering the blood. Once the patient is stabilized, and they need other blood components such as whole blood or plasma, they can be easily tested if needed and switched to the preferred fluid.