Delayed postoperative bleeding in greyhounds and other sighthounds Figure 1: Postoperative bleeding 48 hours after ovariohysterectomy in a greyhound (bleeding score 3).Photos courtesy C. Guillermo Couto In the early 2000s, we observed what appeared to be a high tendency for bleeding after minor trauma or a simple surgical procedure, such as gonadectomy, dewclaw removal, skin mass biopsy, or laparotomy in RRGs. Some affected dogs required multiple blood transfusions, and several died or were euthanized. In the majority of the patients, the one-stage prothrombin time, activated partial thromboplastin time, and platelet counts (PLTs) were within the reference intervals for the breed. We therefore conducted a web-based health survey that documented the prevalence of diseases and major causes of death in RRGs in North America.20 Bleeding disorders were one of the four most prevalent causes of death reported, accounting for eight percent of all deaths. Overall, hematologic diseases had a prevalence of 3.3 percent, with stroke and spontaneous or postoperative bleeding accounting for 46 percent of these.20 We subsequently conducted a prospective study of 88 RRGs that underwent gonadectomy, and evaluated most clinically relevant hemostatic parameters before surgery, and after a bleeding episode in both “bleeders” and “nonbleeders.”21 The following tests were used to evaluate primary hemostasis: platelet count, platelet function with PFA-100 closure time (CT), von Willebrand factor antigen concentration (vWF:Ag) and von Willebrand factor activity using the collagen binding assay (vWF:CBA). Secondary hemostasis was evaluated with APTT, OSPT, fibrinogen concentration (FIB), antithrombin (AT) activity, and factor XIII. The fibrinolytic pathway was evaluated by measuring plasminogen activity (Plmg), antiplasmin activity (AP), and D-dimer concentration. Although at the time there was no standardized scale to evaluate the severity of bleeding in dogs, we proposed a system with scores ranging from “0 “to “4,” adapted from the one proposed by Buchanan and Adix22 for children with idiopathic thrombocytopenic purpura. The final bleeding score assigned to each RRG corresponded with the highest score recorded during the postoperative period. In dogs with clinical evidence of bleeding (i.e. bleeding score 1 to 4), the assays of hemostatic function performed at baseline were repeated when the bleeding was detected. These assays were also performed in a group of sex-matched greyhounds that underwent surgery at the same time and did not have postoperative bleeding (i.e. bleeding score 0-control dogs).21 None of the dogs developed intraoperative or immediate postoperative bleeding; however, 26 percent of the dogs (23/88) had delayed postoperative bleeding 36 to 48 hours after surgery. The signs of bleeding consisted of cutaneous bruising that extended from the area of the surgical incision toward the periphery (Figure 1). There was no bleeding from mucosal surfaces or in areas distant from the surgical site. None of the dogs required transfusion of blood components and the bleeding was self-limiting; bruising was still present at the time the dogs were discharged four to five days after the surgery.21 There were no significant differences between “bleeders” and “non-bleeders” preoperatively for any of the conventional hemostasis assays. The AP and AT activities, although within the reference interval, were significantly lower in the “bleeder” group than in the “non-bleeders” (p<0.001 and p=0.007, respectively). There were no significant postoperative differences between “bleeders” and the control group for any of the hemostatic parameters evaluated. Figure 2: Severe postoperative bleeding 48 hours after a rear limb amputation in a greyhound with osteosarcoma. In that prospective study, we documented for the first time the development of delayed postoperative bleeding after gonadectomy in RRGs, with a prevalence of 26 percent. In both groups, platelet counts and platelet function were within the reference ranges for the breed and were not significantly different between “bleeders” and “non-bleeders.” Selective or combined clotting factor deficiencies were ruled out on the basis of normal fibrinogen concentration, OSPT, and APTT in the “bleeders.” Factor XIII deficiency was also ruled out on the basis of normal factor XIII assay.21 Both von Willebrand disease and von Willebrand syndrome (vWS) were excluded on the basis of normal vWF and CBA.23 Greyhounds commonly have a high-velocity aortic murmur due to relative aortic stenosis.24 Type 2 vWS—a depletion of high-MW vWF multimers secondary to high shear—has been described in humans with aortic valve mineralization, and in dogs with aortic and subaortic stenosis.25,26 We ruled out type 2 vWS based on the fact the vWF:Ag/vWF:CBA ratio was below two. At the time of the study, we suggested the delayed onset of bleeding (i.e. 36 to 48 hours) in the affected greyhounds could be due to enhanced fibrinolysis, since “bleeders” had lower AP than “non-bleeders” prior to surgery, suggesting activated fibrinolysis and hence, a hypocoagulable state.21 Subsequent studies revealed fibrinolysis does not appear to play a role in the delayed postoperative bleeding of greyhounds.27 Using TEG, fibrinolysis is assessed by the LY30 and LY60 parameters that measure the decreases in MA once fibrinolysis “loosens up” the clot in the cuvette. In a pilot study of 21 dogs, we found no differences in LY60 between “bleeders” and “non-bleeders.”27 Only the TEG variables that represent the fibrin cross-linking of the clot (i.e. angle) and the fibrin to platelet interaction or the strength of the clot (i.e. MA and G) were predictors of the outcome. Hence, we proposed failure to strengthen the clot after surgery was primarily responsible for the bleeding events. However, recent evidence suggests conventional TEG may not be sensitive enough to detect abnormalities in fibrinolysis.28,29 Fletcher et al28 described an in vitro model of TEG using tPA and kaolin activation. Subsequently, the same team further validated this assay in dogs receiving epsilon aminocaproic acid (EACA).30 Considering a routine spay or neuter in a RRG frequently results in hemostatic complications that may lead to readmission to the clinic for treatment, identifying the patients at risk, and/or developing a simple protocol for preventing or minimizing this complication will be extremely valuable. With a prevalence of bleeding of 26 percent, as many as 3,500 to 5,000 RRGs may be readmitted to the clinic and treated after routine surgery every year in the U.S.31 Furthermore, osteosarcoma (OSA) is the most common form of cancer in RRGs, representing 45 percent of all tumors and accounting for approximately 25 percent of the deaths in the breed.20 The standard of treatment in dogs with OSAs is limb amputation followed by postoperative adjuvant chemotherapy; thus, owners of RRGs with OSA who elect amputation face the potential complications, grief, and expenses related to blood component therapy and intensive care for hemostatic complications.31 Figure 2 depicts typical postamputation bleeding in a greyhound. In a retrospective study, we documented 13 of 46 (28 percent) RRGs undergoing amputation for bone tumors bled excessively after surgery, and most required administration of fresh frozen plasma, cryoprecipitate, and or packed red blood cell transfusions.31 Antifibrinolytic agents Fibrinolytic inhibitors such as epsilon aminocaproic acid (EACA) and tranexamic acid (TXA)28,32-35 have proven to be effective in human patients and horses where bleeding complications are associated with enhanced fibrinolysis, but they have also been beneficial in patients with systemic bleeding due to other mechanisms.32 Theoretically, EACA and TXA prevent activation of plasminogen into plasmin on the fibrin surface by preventing the binding of plasminogen to C-terminal lysine residues on partially degraded fibrin, thus blocking the plasminogen binding site, which is essential for efficient plasmin formation (reviewed in 33). Interestingly, EACA neutralizes bleeding states created experimentally in dogs by infusion of plasmin or a plasminogen activator.34 Figure 6: Delayed postoperative bleeding after surgical removal of a small mast cell tumor in a six-year-old Italian greyhound. EACA can either block enhanced fibrinolytic activity, or rapidly restore hyperfibrinolytic states to normal, thus impeding the dissolution of fibrin clots and thereby decreasing RBC transfusion requirements in human patients undergoing surgery.35 EACA has a wide therapeutic index; no relevant adverse effects were reported in toxicologic studies in dogs with doses as high as 0.5 g/kg.36 Since we had anecdotal evidence suggesting EACA had a positive effect in minimizing bleeding, we evaluated the prevalence and severity of postoperative bleeding in 100 RRGs undergoing orchiectomy (OHE) that received either EACA or placebo in a prospective, double-blinded, randomized study. In addition, we aimed to evaluate EACA’s effects on selected TEG and fibrinolysis parameters.33 Dogs were randomized to receive either EACA (500 mg PO q8 hours for five days starting the night of the surgery) or placebo (lactose). The clinicians were blinded as to the type of drug administered. We used the bleeding score previously reported to classify dogs as “bleeders” or “non-bleeders.”33 Venous blood samples were obtained at 24, 48, and 72 hours after surgery for TEG analysis as previously described;13 the residual blood samples were centrifuged and plasma aliquots were used for other hemostasis assays (OSPT, APTT, FIB, plasminogen, and antiplasmin).33 Similar to our previous studies, none of the dogs experienced intraoperative or immediate postoperative bleeding; however, 15 out of 50 RRGs (30 percent) in the placebo group had delayed postoperative bleeding 36 to 48 hours after surgery, compared with five out of 50 RRGs (10 percent) in the EACA group (P=0.012); the use of EACA decreased the odds of bleeding by 79 percent (OR = 0.21, P=0.011). The R and K time shortened (i.e. “hypercoagulability”) over time in the EACA group, while they lengthened (i.e. “hypocoagulability”) in the placebo group (Figure 2). In addition, the angle, MA, and G increased postoperatively over time in the EACA group (i.e. “hypercoagulability”), while they decreased in the placebo group (i.e. “hypocoagulability”). We therefore concluded the clot kinetics were enhanced in dogs receiving EACA when compared with the placebo group.33 Our results are similar to what Hamada et al described in 1995 in 30 human patients undergoing upper abdominal surgery that randomly received placebo or carbazochrome sodium sulfonate (CS) and TXA, a drug similar to EACA.37 They also found significant differences between pre-surgical and postsurgical TEG variables in both groups, and all the patients became hypercoagulable after surgery. The beneficial effects of lysine analogues in bleeding patients were recently reviewed by Hunt.38 Since our early findings, several papers on the use of EACA or TXA have been published in dogs,28,30,39-45 and EACA or TXA are now commonly used in practice. After extensive studies, we concluded administration of EACA at approximately 15 mg/kg, PO, q8h (typically 500 mg per dogs per dose) for five days beginning on the day of the surgery significantly decreases the prevalence of delayed postoperative bleeding in RRGs undergoing surgery by amplifying and strengthening the fibrin clot. We routinely use EACA in greyhounds undergoing major surgery and in those that bleed postoperatively. For major surgeries, we use the EACA preemptively; for minor surgeries (laceration, dental extractions, biopsies, etc.), we send the patient home with a prescription for EACA, and instructions to its owner administer it if the dog bruises in the area or bleeds from the mouth. EACA in tablet or capsule form has become increasingly difficult to obtain or is overly expensive in the U.S. Although, no data on pharmacokinetics or pharmacodynamics are available to my knowledge, I have been using the injectable EACA administered orally at the same dosage via syringe—this appears to be as effective as tablet or capsule form. As a final note, we have recognized a similar syndrome of delayed postoperative bleeding in deerhounds and in Italian greyhounds (Figure 6), and have anecdotal reports of postoperative bleeding in whippets, Afghan hounds, Borzois, and some other sighthound breeds.
