Today's VETgirl online veterinary continuing education blog is by Dr. Lisa Powell, DACVECC. She is a senior consultant for Critical Consults, LLC. In this two-part blog, she'll review the importance of fluid therapy in veterinary medicine! If you missed part 1, check it out here.
Fluid Therapy for the Emergency Patient (Part 2)
Authored by Dr. Lisa Powell, DACVECC
Shock is defined as a physiological state characterized by a significant, systemic reduction in tissue perfusion, resulting in decreased tissue oxygen delivery and insufficient removal of cellular metabolic products, resulting in tissue injury. Hypovolemic shock, caused by trauma, severe dehydration, or third spacing of fluids, requires volume resuscitation with intravenous fluids to prevent end-organ damage and failure. The most common fluid type used to resuscitate patients with hypovolemic shock is crystalloids +/- additional colloids. If the fluid loss is blood due to hemorrhage or coagulopathy, specific blood products can be used for volume resuscitation.
When administering crystalloid fluids to treat hypovolemic shock, a replacement fluid should be used, and small aliquots should be administered while monitoring patient response. For example, a dose of 30 ml/kg of crystalloid fluid should be administered over 20-30 minutes (or faster), then perfusion parameters re-assessed to decide if more fluids are necessary. Perfusion parameters to monitor include heart rate, respiratory rate, mucous membrane color, mentation, pulse quality, and blood pressure. If the patient remains in a shock state despite crystalloid fluid resuscitation, a bolus of synthetic colloids can be administered, with a starting dose of 5-10 ml/kg. When administering large amounts of crystalloids and colloids, one must be aware of the potential for volume overload, third spacing of fluid, or worsening of hemorrhage from active bleeding sites.
Traumatic Brain Injury
Dogs and cats presenting with traumatic brain injury (TBI) often require fluid resuscitation due to decreased cerebral blood flow, but are more prone to cerebral edema from cerebral vascular injury. Therefore, fluids should be administered judiciously, and the patient must be monitored for worsening CNS signs. Hypertonic crystalloid fluids in combination with an artificial colloid are very effective in resuscitating patients with TBI using lower volumes of fluid. In addition, the intravascular COP increases, decreasing the redistribution of fluid into the cerebral interstitial space. Patients with TBI should be monitored for increased intracranial pressure, evidenced by the presence of the Cushing’s Reflex or worsening of neurologic signs (use serial modified Glasgow Coma Scores, or MGCS). The Cushing’s Reflex is defined as systemic hypertension with reflex bradycardia, as the body is attempting to increase cerebral perfusion against the increase in intracranial pressure. In these cases, mannitol is usually indicated to relieve the cerebral edema and improve CNS function.
Severe, Acute Hemorrhage
Acute hemorrhage can occur due to traumatic injuries, coagulopathies (especially anticoagulant rodenticide toxicity), or ruptured vascular tumors (e.g., splenic or hepatic tumors). Patients presenting with acute blood loss are often mentally dull, tachycardic, tachypneic, have pale mucous membranes, and have hyperdynamic femoral pulse quality. These signs are due to the severe tissue hypoxia that occurs with low circulating red blood cell volume. When resuscitating these patients, IV crystalloid therapy can be used initially; however, crystalloid dose should be lowered, as blood clots forming at bleeding sites could be dislodged if fluid administration is too aggressive. Ideally, blood products should be used to resuscitate patients with significant blood loss resulting in cardiovascular shock and tissue hypoxia.
Hypotensive resuscitation is a strategy used in many human trauma patients, especially combat injury, that targets a systemic blood pressure of no more than 90 mmHg with resuscitative fluids and blood products. This assures adequate tissue perfusion while maintaining blood clot stability.
When resuscitating these dogs and cats with blood products, component therapy is ideally used. Patients presenting with blood loss due to coagulopathies should be administered plasma components; if blood loss is significant, packed red blood cell transfusions may also be indicated. In these patients, if component therapy is not available, whole blood transfusions can be administered as well. Care must be taken when using whole blood transfusions to avoid volume overload. The dose of pRBCs or FFP ranges from 10-20 ml/kg.
A 3 year old, 45 kg, MN German Shepherd presents with a GDV. His heart rate is 200 bpm, RR 45 bpm, mucous membranes are pale, his abdomen is quite distended, and femoral pulse quality is poor. Lactate is 8 mg/dl (normal < 2 mg/dl), PCV is 56%, and serum TP is 6.5 mg/dl. Systolic blood pressure is 60 mmHg, measured on the front leg with Doppler. Following intravenous access in both cephalic veins, fluids are administered based on the following fluid plan:
Initial crystalloid fluid dose: 30 ml/kg over 20 minutes (total = 1.35 L)
Reassess vitals: HR 160 bpm, RR 35 bpm, mm pale, pulses still poor. The stomach is trocharized, and a large amount of air is released. Systolic BP remains at 60mmHg.
A second 30 ml/kg bolus of crystalloids is administered, along with 5 ml/kg hetastarch over 30 minutes (1.35 L crystalloids + 225 ml hetastarch).
Reassess vitals and lactate: HR 130 bpm, RR 30 bpm, mm pale pink, stronger femoral pulse quality. Systolic BP 85 mmHg. Lactate 4.5 mg/dl.
Due to improvement in vitals and perfusion parameters, fluids are administered at a slower rate, and continued as the dog is prepared for more diagnostics and definitive therapy.
Fluid therapy is a mainstay of treatment for veterinary patients presenting to an emergency room with severe dehydration and cardiovascular shock. The fluid type, amount, and frequency administered depends on the underyling disease process, severity of signs, and manifestation of tissue hypoxia. Use of a fluid plan tailored to the specific patient, and with continued monitoring of response to therapy, will lead to resolution of tissue hypoxia and an improved outcome.