Complications in Equine Surgery. Группа авторов

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7 Complications Associated with Hemorrhage

       Margaret C. Mudge VMD DACVS, DACVECC

       The Ohio State University, Columbus, Ohio

Overview

      Intra‐ and post‐operative bleeding can occur with many equine procedures. The difference between bleeding and hemorrhage is generally based upon the severity of the blood loss. In many cases, hemorrhage can be predicted based upon the location of the surgical procedure. This chapter will discuss how to treat and prevent intra‐ and post‐operative hemorrhage.

List of Complications Associated with Hemorrhage

       Intraoperative hemorrhageFluid therapy and blood transfusionAdjunctive systemic treatment

       Postoperative hemorrhage

Intraoperative Hemorrhage

       Definition

      Intraoperative hemorrhage is considered a complication if it is unexpected, severe enough to warrant a blood transfusion or leads to moderate/severe anemia, obscures the surgical field, or puts the animal at risk of additional intraoperative or postoperative morbidity. Early consequences of hemorrhage include shock, anemia, and difficulty visualizing the surgical site. Late complications include seroma formation, surgical site infection, and delayed healing.

       Risk Factors

       Patient factors:Highly vascular areas (e.g. tumor removal, gonadectomy, paranasal sinus surgery)Coagulopathy (congenital or acquired)Pre‐existing bleeding (e.g. hemoabdomen, epistaxis) with surgical procedures to explore the cause of bleeding

       Surgical/surgeon factors:Technical failures (ligature slippage, poor choice of hemostatic device, lack of anatomic knowledge)Long duration of surgery in a bleeding area (e.g. complex tumors, sinusotomy)Inadvertent disruption of vasculatureMedications administered (e.g. hemodilution with intravenous fluids, anticoagulation with heparin)

       Pathogenesis

      Bleeding is part of almost every surgery, but is usually well controlled by the patient’s normal mechanisms of hemostasis, along with surgical control of bleeding through pressure and ligation of vessels. The initial response to disruption of a blood vessel is vasoconstriction, followed by platelet activation, adhesion, and aggregation. Activation of clotting factors is initiated by tissue factor, with the end result being a fibrin clot. Platelet abnormalities, coagulation factor deficiencies, and excessive fibrinolysis can all result in abnormal or uncontrolled bleeding.

      The correlation of coagulation profile findings and bleeding complications has been evaluated in dogs and cats after ultrasound‐guided biopsies [1]. Bleeding complications were seen in thrombocytopenic cases, and in cats with prolonged aPTT and dogs with prolonged OSPT. Authors of a retrospective study in horses undergoing percutaneous liver biopsy did not find a correlation between bleeding complications and an abnormal coagulation profile; however, only 3 horses (9% of monitored horses) had a decrease in packed cell volume (PCV) [2].

Hereditary hemostatic defects are uncommon in horses. Platelet dysfunction can occur secondary to Glanzmann thromasthenia, a membrane glycoprotein defect that has been described in a variety of breeds [3]. Von Willebrand disease can also cause prolonged mucosal bleeding times. Coagulation factor deficiencies, such as hemophilia A (factor VIII deficiency) have also been described and result in prolonged bleeding times. Acquired hemostatic defects are more common, and can be related to immune‐mediated destruction of platelets, liver disease, uremia, or bone marrow disease. Transient coagulopathies can occur in horses with gastrointestinal disease or other critical illness, as upregulation of inflammation leads to systemic activation of coagulation [4].

      There is limited information in the veterinary literature regarding risk factors for surgical hemorrhage. There is even less evidence for the efficacy of specific treatments or preventative measures in reducing hemorrhage in veterinary surgical procedures. Size has been shown to be a factor in ovariohysterectomy in dogs, with a 2% intraoperative hemorrhage rate in dogs weighing less than 50 pounds and 79% hemorrhage rate in dogs of 50 pounds or more [5]. The use of active suction drains has been reported as a potential risk factor for postoperative hemorrhage in dogs, but this has not been reported in horses [6].

Patient positioning has been shown to have a significant effect on intraoperative blood loss in humans. Reverse Trendelenburg positioning for human patients undergoing endoscopic sinus surgery resulted in decreased blood loss and improved visualization of the surgical field [7, 8]. Type of anesthesia has also been shown to have an effect on bleeding during endoscopic sinus surgery in human patients, with less bleeding under total intravenous anesthesia compared to inhalation anesthesia [9]. Although the effect of positioning on blood loss has not been evaluated in horses, surgeons have observed decreased blood loss with standing paranasal sinus surgery compared to recumbent surgery in the horse [10]. Reverse Trendelenburg positioning has been used by this author during recumbent paranasal sinus surgery with a subjective decrease in blood loss (Figure 7.1).

      The intravenous or topical administration of tranexamic acid during major human orthopedic surgery is associated with a significant reduction in blood loss and units of blood transfused, without an increase in venous thromboembolic events [11]. Several topical hemostatic agents have been evaluated for use in endoscopic sinus surgery, but none has consistently reduced hemorrhage compared to no treatment [12].

      Surgeon experience may also be a factor in surgical hemorrhage. Involvement of a surgical resident in noncardiac surgeries on humans resulted in higher transfusion rates (56–78% higher) compared to surgeries performed by an attending surgeon without a resident. This may be related to surgeon skill, duration of surgery, or clinical judgment with respect to the need for transfusion [13].

Figure 7.1 A horse is positioned in reverse Trendelenburg in preparation for paranasal sinus surgery.

      Source: Margaret Mudge.

       Prevention

      Coagulopathy is exceedingly uncommon in otherwise healthy equine patients presenting for elective surgery. It would not be cost‐effective to perform coagulation testing on all patients undergoing major surgery, but a thorough patient history, physical examination, and consideration of any underlying disease can help direct further testing. The horse may have a history of excessive bleeding during elective surgery, such as castration, or there may be a history of hematomas or bleeding at venipuncture sites. Medications such as nonsteroidal anti‐inflammatory drugs (NSAIDs) may alter coagulation, although NSAIDs are commonly given prior to surgery in horses without