HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT

Review of Fluid Therapy in Acute Blood Loss

Michele L. Frazer, DVM, Diplomate ACVIM, ACVECC

Permissive and increased use of plasma and fresh, warm, instead of crystalloid fluids may benefit equine patients with acute blood loss. Author’s address: Hagyard Equine Medical Institute, 4250 Iron Works Pike, Lexington, KY 40511; e-mail: [email protected]. © 2013 AAEP.

1. Introduction This eventually leads to organ dysfunction and car- Acute blood loss in the veterinary patient is an diovascular collapse. emergency that many practitioners must manage in Patients with blood loss can be placed into one of the field or hospital setting. Diagnosis may be ob- four categories as defined by the American College of 1 vious in cases of external blood loss, whereas inter- Surgeons. Category 1 is loss of Յ15% of blood nal blood loss may be more difficult to determine. volume. Transcapillary refill typically compen- Acute hemorrhage can occur into the peritoneal, sates for this loss and maintains blood volume and pleural, or pericardial cavities; reproductive tract; blood pressure. Category 2 is loss of 15% to 30% of gastrointestinal tract; guttural pouches; joints; and blood volume. Compensatory mechanisms such as muscle tissue. In the equine patient, common tachycardia and tachypnea occur, and sympathetic causes include trauma, rupture of a vessel in the vasoconstriction can typically maintain blood pres- reproductive tract in pre- or post-foaling mares, frac- sure. Category 3 is loss of 30% to 40% of blood tured ribs in foals, and inadequate hemostasis volume. Compensatory mechanisms can no longer during surgery. History, physical examination, ul- maintain blood pressure, and decompensated hypo- trasound examination, and blood work aid in diag- volemic shock occurs. Organ dysfunction, such as nosing acute hemorrhage as well as assessing the acute renal failure, may occur from decreased tissue severity and determining the cause. oxygenation. Decreased urine production and hy- In hemorrhage, the number of circulating red potension occur. Category 4 is loss of Ͼ40% of blood cells decreases, and the oxygen-carrying ca- blood volume. Patients in this category require im- pacity of the blood is compromised. Initially, phys- mediate emergency treatment, and changes in blood iological responses are able to compensate and pressure and perfusion may not be reversible. maintain blood pressure with transcapillary refill, The goal of treatment in patients with acute blood tachycardia, tachypnea, and systemic vasoconstric- loss is preventing hemorrhagic shock while also tion. When significant volume is lost, the body can no preventing further loss of blood. Two areas of longer compensate for the blood loss, and hemorrhagic controversy have occurred as to how best to accom- shock occurs. In this situation, adequate tissue plish this goal: fluid type and volume to be perfusion and oxygenation cannot be maintained. administered.

NOTES

458 2013 ր Vol. 59 ր AAEP PROCEEDINGS HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT 2. Materials and Methods 4. Discussion A review of literature from the past 10 years describ- Different strategies are used to treat acute blood ing fluid for acute blood loss in human loss in veterinary patients. Some clinicians limit medicine was undertaken. Current trends in fluid intravenous fluid therapy in an attempt to maintain choice and volume of fluid administered were low blood pressure and limit further hemorrhage. reviewed. The risk of limiting fluid therapy is and subsequent cardiovascular collapse. 3. Results Without appropriate fluid volume, organs do not In human medicine, a strategy has been developed receive adequate perfusion and oxygenation. In op- called Damage Control Resuscitation (DCR) to re- position, some clinicians advocate more liberal use suscitate patients with acute hemorrhage.2,3 The of crystalloid and fluids to maintain blood goal of DCR is early prevention and/or treatment of pressure in a range closer to normal to preserve the lethal triad. The lethal triad consists of coagu- organ perfusion and prevent hypovolemic shock. lopathies, hypothermia, and acidosis.3 Metabolic The risk with this method is that further hemor- acidosis occurs from hypoperfusion leading to organ/ rhage may occur. tissue damage from decreased oxygenation and a Veterinarians also vary in what fluid should be switch to anaerobic metabolism. Hypothermia re- used in resuscitation. Crystalloid fluids are typi- sults from hypoperfusion and, if used in treatment, cally inexpensive, easy to administer, and readily the use of cold resuscitation fluids. Coagulopathies available to most practitioners. However, the primarily occur from hypoperfusion and tissue majority of the fluid rapidly leaves the vascular trauma. Other factors including loss of procoagu- compartment and moves to the interstitial space. lant proteases, dilution of blood from fluid resusci- Colloid fluids are more expensive and require spe- tation, and organ dysfunction from acidosis and cialized equipment to administer. Fresh, whole hypothermia also potentiate coagulopathies.4–6 blood requires the presence of a donor and ideally, a One of the key points in the DCR resuscitation laboratory to perform a cross-match. Plasma re- plan is . A minimum vol- quires refrigeration for storage. Both require spe- ume of intravascular fluid replacement is adminis- cialized IV lines with a filter designed for tered at a rate to maintain mean arterial blood administration of blood products. Anaphylactic re- pressure at 50 mm Hg and systolic blood pressure at actions may occur with either. Hydroxyethyl 80 mm Hg. These pressures are considered suffi- starch, a synthetic colloid, does not require refriger- cient to maintain organ perfusion without potenti- ation or specialized equipment to administer, but it ating hemorrhage. Proponents of DCR cited a 40% has been associated with coagulopathies. Also, col- survival rate in DCR-resuscitated patients versus a loids may increase the blood pressure more than 16% survival rate in patients not undergoing DCR 7–10 desired and may potentiate further . resuscitation strategies. DCR is now the stan- Extrapolating data and strategies from human dard of care for resuscitating patients with blood 7 medicine and applying it to veterinary medicine may loss in human medicine. The DCR strategy has assist the veterinarian in establishing a treatment emerged over the past decade and is in opposition to plan for resuscitative fluids in acute hemorrhage the strategy used during the past century, when cases. Application of DCR strategy to veterinary rapid volume expansion with crystalloid fluids was medicine will guide the practitioner in choice of re- used in cases of hemorrhagic shock. suscitative fluid in hemorrhagic shock. Plasma Permissive hypotension should not be confused with prolonged hypoperfusion. Prolonged hypoper- and potentially warm whole blood should be the fusion and failure to maintain blood pressure at initial resuscitation fluid. Plasma provides addi- DCR-recommended levels results in decreased per- tional clotting factors. Warm blood is used to pre- fusion to vital organs and tissues leading to meta- vent hypothermia because the coagulation cascade bolic acidosis, hypothermia, and coagulopathies. is less effective at lower body temperatures. Fresh, Coagulopathies are associated with increased mor- whole blood is preferred over . tality in patients with hemorrhagic shock.11–13 Interestingly, this practice is already routinely per- The second key point in DCR resuscitation is the formed in equine medicine because a type of fluid chosen for initial resuscitation. The with packed red cells from equids is not available. DCR strategy recommends the use of plasma as the DCR protocol recommends minimal administra- initial resuscitation fluid. This early use of plasma tion of crystalloid fluids because they dilute coagu- aids in prevention of a coagulopathy, one component lation factors and may increase coagulopathies. of the lethal triad.14 Human studies claim a 46% However, in the equine patient, financial con- reduction in mortality rate when plasma was used straints and availability of may prevent ad- in equal parts with whole blood as opposed to the use ministering the volume of plasma and whole blood of more blood than plasma.14 Also, fresh, warm, needed to maintain mean arterial blood pressure at whole blood has been advocated over packed red 50 mm Mg. Crystalloid fluids, therefore, are re- blood cells.7,15,16 quired in these cases.

AAEP PROCEEDINGS ր Vol. 59 ր 2013 459 HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT Historically, and hematocrit levels blood to equine patients with acute hemorrhage may have been utilized to determine when blood trans- assist the veterinary practitioner in successful treat- fusions should be administered. However, these ment of these cases. Limiting factors with this clinical parameters are not reliable transfusion trig- strategy are having the appropriate equipment to gers because they are unreliable indicators of blood monitor blood pressure and having access to plasma loss severity. In acute blood loss, red blood cells or whole blood. However, physical examination and plasma are both lost; therefore hematocrit and and blood work parameters may compensate for lack hemoglobin do not change until transcapillary refill of equipment. The DCR strategy needs further and other compensatory mechanisms occur. In ad- evaluation in equine medicine, but it may become dition, treatment with intravenous fluids will dilute the standard of care in resuscitation of equine pa- but not alter the total number of circulating red tients with hemorrhagic shock. blood cells. Therefore, the hematocrit decreases even if the number of red blood cells remains un- References changed. In species that have a large reservoir of 1. Marino PL. The ICU Book. 3rd edition. Philadelphia: Lippincott William & Wilkins; 2007:213–214. red blood cells in the spleen (such as the horse), the 2. Halcomb JB. Damage control resuscitation. J Trauma hematocrit alters rapidly with splenic contraction 2007;62:S36–S37. and may initially increase even in patients with 3. Moore EE, Thomas G. Stated laparotomy for the hypother- severe blood loss. mia, acidosis, and coagulopathy syndrome. Am J Surg 1996; 172:405–410. Application of DCR strategy will also aid in deter- 4. Brohi K, Cohen MI, Ganter MT, et al. Acute traumatic mining the volume of fluid to administer in hemor- coagulopathy: initiated by hypoperfusion: modulated rhagic shock. The goal of DCR is permissive through the protein C pathway? Ann Surg 2007;245:812– hypotension. A volume of fluid is administered 818. that maintains the mean arterial blood pressure at 5. Brohi K, Cohen MI, Ganter MT, et al. Acute coagulopathy of trauma: hypoperfusion induces anticoagulation and hyper- 50 mm Hg or the systolic blood pressure at 80 mm fibrinolysis. J Trauma 2008;64:1211–1217. Hg. Measuring blood pressure in the equine pa- 6. Hess JR, Brohi K, Dutton RP, et al. The coagulopathy of tient to obtain the ideal pressure readings is diffi- trauma: a review of mechanisms. J Trauma 2008;65:748– cult. Many field or hospital practitioners will not 754. 7. Gerhardt RT, Strandenes G, Cap AP, et al. Remote damage have equipment to accurately measure blood pres- control resuscitation and the Solstrand Conference: defin- sure. If a practitioner rarely encounters a case of ing the need, the language , and a way forward. Transfusion hemorrhagic shock, justifying the cost of the equip- 2013;53(Suppl 1):9S–16S. ment may be challenging. Even when equipment is 8. Holcomb JB, Jenkins D, Rhee P, et al. Damage control re- available, obtaining frequent, reliable blood pres- suscitation: directly addressing the early coagulopathy of trauma. J Trauma 2007;62:307–310. sure readings may be impossible and potentially 9. Shaz BH, Dente CJ, Nicholas J, et al. Increased number of dangerous to the veterinarian or techni- coagulation products in relationship to red blood cell products cian. Horses with blood loss may exhibit colic transfused improves mortality in trauma patients. Trans- signs, ataxia, or change in mentation. Therefore, fusion 2010;50:493–500. 10. Hodgetts TJ, Mahoney PF, Kirkman E. Damage control the blood pressure cuff may not be maintained in the resuscitation. J R Army Med Corps 2007;153:299–300. correct position, and readings may be unreliable. 11. Brohi K, Singh J, Heron M, et al. Acute traumatic coagu- Even if blood pressure readings are not obtained, lopathy. J Trauma 2003;54:1127–1130. other parameters may be utilized to determine if 12. MacLeod JB, Lynn M, McKenney MG, et al. Early coagu- lopathy predicts mortality in trauma. J Trauma 2003;55: fluid resuscitation is adequate to maintain organ 39–44. perfusion. DCR strategy advocates fluid therapy 13. Maegele M, Lefering R, Yucel N, et al. Early coagulopathy until the radial pulse can be palpated. In the in multiple injury: an analysis from the German Trauma equine patient, lack of peripheral pulses and cold Registry on 8724 patients. Injury 2007;38:298–304. extremities suggest hypoperfusion. Abnormalities 14. Borgman MA, Spinella PC, Perkins JG, et al. The ratio of blood products transfused affects mortality in patients receiv- in creatinine, blood nitrogen, and ing massive transfusions at a combat support hospital. are indicators of potential renal dysfunction. When J Trauma 2007;63:805–813. these parameters are altered from the reference 15. Kauvar DS, Holcomb JB, Norris GC, et al. Fresh whole range, renal damage from hypoperfusion should be : a controversial military practice. J Trauma 2006;61:181–184. considered and fluid therapy must be adjusted. 16. Repine TB, Perkins JG, Kauvar DS, et al. The use of fresh Applying the DCR strategy of permissive hypoten- whole blood in massive transfusion. J Trauma 2006; sion and administration of plasma and fresh, warm 60(Suppl 6):S59–S69.

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