Fluid therapy is one of the most important aspects of critical patient care. Patients are given fluids for so many reasons, and it is crucial to know the different types, what is in them, and why they are prescribed. Types of fluids There are many indications to prescribe intravenous fluid therapy. A few of these are correcting dehydration, correcting electrolyte imbalances, shock, and tissue perfusion. There are two types of fluids that can be used in the ER: crystalloids and colloids. Crystalloids are fluid that is isotonic to the patient’s plasma, which only stay in the vasculature for about 20 minutes and then move out into the cells or out of the body. There are many types of crystalloids. Crystalloid fluids are electrolyte-balanced fluids that can help maintain hydration and correct electrolyte imbalances. They can also be further categorized into replacement fluid, maintenance fluid, hypotonic, isotonic, or hypertonic. This is all based on their osmolality compared to plasma. Determining what type of fluid to use is based on the disease process that is going on. Colloids can consist of synthetic and natural colloids. Synthetic colloid examples are vetstarch, hetastarch, or polysaccharides, which are readily available and can have an extended shelf life. Natural colloids are blood products such as plasma, albumin, and whole blood. These take special care and storage that some clinics do not have readily available. Colloid fluids are large molecules and stay in the vascular space for about one hour. Colloids in emergency and critical care medicine can be controversial. There are side effects that can outweigh prescribing the colloid to a patient. These can consist of acute kidney injury (AKI), coagulopathies, and possible increased mortality. Colloids may be useful in emergent patients to increase perfusion for a short period of time. Patient assessment There are multiple factors to determine how dehydrated a patient is when they come into the emergency room: age, body condition, skin elasticity, mucus membrane moisture, mentation, heart rate, blood pressure, and hypothermia. There are different levels of dehydration based on the physical exam findings. A loss of skin elasticity, or a slight skin tent, and tacky mucous membranes, means the patient is five to six percent dehydrated. A patient with decreased skin turgor, delay of capillary refill time, retracted eyeballs, tachycardia, and dry mucous membranes can be considered six to 10 percent dehydrated. A skin tent that is prolonged, dull corneas, weak pulses, tachycardia, or bradycardia, altered mentation, hypotension, and hyperthermia, a patient can be over 12 percent dehydrated. When a patient comes into the emergency room, the first thing anyone should do is a physical exam that includes temperature, pulse, respiratory rate, weight, and blood pressure. Blood pressure equals cardiac output times vascular resistance. If either of these factors are affected, your blood pressure may be decreased, which can affect perfusion to major organs of the body. Heart rate, arrhythmias, volume status, vessel resistance (shock, medications, systemic disease, etc.). A blood pressure can be taken two ways: direct and indirect. Direct blood pressure consists of placing an arterial line and attaching a transducer to a multiparameter unit. This is the most accurate blood pressure, but it will not be practical in most emergent situations, especially if you do not feel extremity pulses. If you are unable to feel a pulse, it will be very unlikely to obtain an arterial line. Indirect blood pressure uses a doppler or an oscillometric monitor. A doppler blood pressure will measure systolic blood pressure. Oscillometric will measure systolic, diastolic, and mean. Oscillometric is the least accurate of the two because there are multiple factors that can affect its reading. If the patient is moving, or if the patient is too small, it will not be an accurate measurement. Normal blood pressure is 100 to140 systolic, 60 to80 diastolic, and 70 to100 mean. The Rennin Angiotensin-Aldosterone System (RAAS) is activated when the kidneys detect a change in perfusion in the body, it converts the hormone prorenin to renin and releases it into circulation. Renin then converts angiotensinogen to angiotensin I. This hormone then travels to the lungs and angiotensin converting enzyme (ACE), converts angiotensin I to angiotensin II. Angiotensin II works to increase blood pressure by vasoconstricting the blood vessels, increasing sodium retention, and, therefore, increasing blood pressure. Angiotensin II also acts on the adrenal cortex and stimulates the release of aldosterone. Aldosterone also increases sodium reabsorption. If the body does not have enough sodium or blood volume, this hormone system will not be enough to increase blood pressure. Types of shock Shock is defined as poor perfusion that can lead to poor tissue perfusion. This can be caused by multiple reasons. The main types that we see in emergency medicine is hypovolemic, septic, and cardiogenic. Quickly determining what type of shock your patient presents with will increase the chances of that patient leaving the hospital. If a patient comes into the emergency room and diagnosed with cardiogenic shock, fluids should not be started immediately. Hypovolemic shock occurs when the patient has been losing circulating blood volume. This could be due to hemorrhage, vomiting, diarrhea, or third spacing. The RAAS system activates once the kidneys recognize that there is decreased blood volume, but can only do compensate so much when the volume of blood is going out of the body. The severity of hypovolemic shock is determined by multiple factors. How long has the patient been losing fluid? What does their physical exam look like? What is their blood pressure? Crystalloids should be given to a patient with hypovolemic shock. Once a patient loses around 25 to 30 percent of their blood volume due to hemorrhage, they are in hemorrhagic shock, which is a type of hypovolemic shock. It is important to control the hemorrhage first when a patient comes in losing blood volume due to trauma or internal injuries. Administering IV fluids to a patient in hemorrhagic shock when the hemorrhage has not been control, is contraindicated. Patients with hemorrhagic shock should be given natural colloids such as whole blood, packed red blood cells, or plasma. This will increase oxygen carrying capacity, and, therefore, increase perfusion to the organs. Patients diagnosed with septic shock need fluids right away. The goal is to increase intravascular volume to increase cardiac output and increase perfusion in the main organs of the body. These patients may present with hypotension, injected or pale mucous membrane color, poor pulses, and tachycardia. IV fluid therapy must be started immediately. Intravenous access is the quickest way to give fluids to these patients. The cephalic, saphenous, dorsal pedal, medial saphenous, aural vein, jugular, and accessory cephalic vein are just a few veins that an IV catheter can be placed. In theory, the bigger the bore, the shorter the catheter, the faster the fluid can be given. This is also a controversial topic in veterinary medicine. To be practical, if the patient has an IV catheter in, fluids can be given. A jugular catheter should only be attempted in neonates or any patient that is stable enough to undergo this invasive procedure. There are different ways to calculate how much fluid to give to a patient. A bolus of crystalloid is commonly 50 to 90 mls/kg. A quarter of this volume is normally given over 15 to 20 minutes and a blood pressure is taken after. The patient can be placed on maintenance fluids, 40 to 60 mls/kg/day of crystalloids once the patient has had a full bolus of crystalloid and their blood pressure has stabilized. A colloid bolus should be given at 5 to 10 ml/kg over 15 to 20 minutes. Fluid therapy is a dynamic balance that requires a very quick diagnosis, great IV catheter skills, and close nursing monitoring. Depending on the diagnoses, the type of fluid and the prescribed amount is critical to a patient leaving the hospital. Tami Lind, BS, RVT, VTS (ECC), is the current ICU and ER supervisor at Purdue University Veterinary Teaching Hospital. Lind has been at the university for 10 years. She went to veterinary technology school at Purdue and graduated in 2010 with her bachelor’s degree in veterinary technology and has never left. She started as a veterinary technician in the ICU and has been the supervisor at Purdue since 2012. References DiBartola SP, Bateman S. Introduction to fluid therapy. In: DiBartola SP, ed. Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 4th ed. St. Louis, MO: Elsevier-Saunders; 2012:339. Llewellyn, E., Lourenço, M., & Ambury, A. (2020). Recognition, treatment, and monitoring of canine hypovolemic shock in first opinion practice in the United Kingdom. Topics in Companion Animal Medicine, 39. https://doi.org/10.1016/j.tcam.2020.100427 Mandell, D. C., & King, L. G. (1998). Fluid therapy in shock. Veterinary Clinics of North America: Small Animal Practice, 28(3), 623–644. https://doi.org/10.1016/s019A5-5616(98)50059-9 Montealegre, F., & Lyons, B. M. (2021). Fluid therapy in dogs and cats with sepsis. Frontiers in Veterinary Science, 8. https://doi.org/10.3389/fvets.2021.622127 Tello, L. H., & Pardo, M. A. (2022). Fluid and electrolyte therapy during vomiting and diarrhea. Veterinary Clinics of North America: Small Animal Practice, 52(3), 673–688. https://doi.org/10.1016/j.cvsm.2022.01.011
