Complications in Equine Surgery. Группа авторов

[14]. Herbal supplements have been shown to alter platelet function and coagulation in human patients. Commonly used mediations that increase the risk of bleeding include garlic, ginkgo biloba, green tea, and fish oil [15].

      Physical exam may reveal mucous membrane petechiation, which should prompt a complete blood count, and potentially platelet function testing. Ideally, any anemia should be corrected before surgery, especially if blood loss is anticipated. Although erythropoietin will increase red blood cell production, the administration of recombinant human erythropoietin has led to development of erythropoietin antibodies and severe anemia in horses, so cannot be recommended [16]. Delaying the surgery or administering whole blood or packed RBC transfusions are the best methods for correcting preoperative anemia.

      Clinicopathologic findings of hepatic failure (e.g. icterus, photosensitization, abnormal liver enzymes, increased serum bile acids) should cause the clinician to delay surgery, perform coagulation testing, and consider transfusion with fresh frozen plasma. Horses with colic, especially with obstructive surgical or inflammatory medical conditions, frequently have clinicopathologic evidence of coagulopathy with increased d‐dimer and prolonged PT/PTT [17]. While there is no definitive treatment to prevent hemorrhage in these horses, consideration should be given to avoiding large volumes of synthetic colloids, and instead treating with fresh frozen plasma if colloids are needed.

The surgeon should be prepared with appropriate hemostatic equipment. Surgical stapling devices such as the LDS™ and electrothermal bipolar vessel‐sealing device (Ligasure™, Medtronic, Minneapolis, MN) can occlude vessels up to 7 mm in diameter [18]. Other stapling devices, such as the TA™ staplers (Medtronic), can be used to compress larger bundles of tissue. Electrocautery is effective for vessels up to 2 mm diameter [19]. For distal limb surgeries, especially extensive wound or foot debridements, the use of a tourniquet should be considered to provide better visualization and limit blood loss Figure 7.2). Patient positioning should also be considered, for example, reverse‐Trendelenburg or standing position for paranasal sinus surgery.

      Preparation for intraoperative hemorrhage also includes securing blood products or blood donor horses. In cases of known red blood cell alloantibodies or previous transfusion reactions, preoperative autologous donation (PAD) should be considered [20]. PAD involves collecting the patient’s blood 2–4 weeks prior to surgery. Approximately 15–20% of the patient’s blood volume can be collected (6–8 liters for a 500 kg horse). Acute normovolemic hemodilution is another technique that could be considered when allogeneic blood is not available. This technique involves removal of the patient’s blood just before anesthesia with replacement of volume by crystalloid fluids [21].

Figure 7.2 A tourniquet is applied over the metatarsophalangeal joint to limit blood loss and improve visualization during surgery of the digit.

      Source: Courtesy of Frank Nickels.

      Human patients who require blood transfusion during surgery have an increased risk of death, and are more likely to have septic and wound complications [22]. Hemorrhage during trauma surgery carries a high risk of transfusion and death, so in many cases, “damage control surgery” is advocated. An initial laparotomy is performed to control the damage (e.g. intestinal leakage, devitalized bowel, bleeding vessel), and packing with temporary closure are performed until the patient is stable enough to undergo definitive repair [23].

       Diagnosis and monitoring

      The diagnosis of intraoperative hemorrhage is based on the volume of blood loss, along with changes in vital signs (tachycardia, hypotension, prolonged capillary refill time) and decreasing PCV and TS. Intraoperative blood loss is usually readily apparent, but can be overlooked if it is not collected and measured. Suction canister volume should be recorded, and PCV of the fluid can be measured to determine the volume of blood lost. Careful monitoring under anesthesia is necessary, as the heart rate and hematocrit may not change, even with severe blood loss. Arterial blood pressure and PaO₂, along with mucous membrane color and capillary refill time, may be more accurate reflections of blood loss [24]. Central venous pressure and blood lactate concentration have also been shown to correlate with acute blood loss in standing, unsedated horses [25].

       Treatment

       Local treatment

      The initial response to intraoperative hemorrhage should be to apply firm pressure to the bleeding area. Direct mechanical pressure is a very effective way to limit blood loss during and after surgery. If bleeding vessels can be visualized, they should be clamped and ligated. Collagen sponges, microfibrillar collagen, gelatin sponges, oxidized regenerated cellulose, and bone wax are all topical mechanical hemostatic agents that apply pressure to the area of bleeding [26]. Topical thrombin and fibrin‐based sealants promote formation of fibrin clots, and are applied onto the bleeding areas [27]. Surgical sealants such as polyethylene glycol polymers are used as an adjunct for vascular reconstruction, but are quite expensive [28].

      A tourniquet can be used on the distal limb in order to improve visualization of transected vessels. In the case of diffuse bleeding, such as after debridement of exuberant granulation tissue, pressure bandages can be used on the distal limb. If substantial bleeding is encountered during paranasal sinus surgery, the sinus should be packed firmly with gauze packing and the sinusotomy bone flap can be temporarily stapled closed [29]. Chilled saline and topical vasoconstrictive agents such as epinephrine or phenylephrine can also be used as topical adjuncts (alone or on gauze packing) in sinus surgery to promote local vasoconstriction and reduce bleeding [30]. When blood loss from the paranasal sinuses cannot be controlled with direct pressure, temporary bilateral carotid artery occlusion can be used to limit blood loss ([31].

      One of the most important factors in limiting blood loss is making a quick decision to limit blood loss and postpone the remainder of the surgery until bleeding is controlled. In the case of paranasal sinus surgery, the packing can be removed during a standing procedure 24 to 48 hours later, with reevaluation of the sinus and completion of the procedure under better visualization.

       Fluid therapy and blood transfusion

      Initial stabilization for acute blood loss is accomplished with intravenous crystalloid fluids. A starting point for resuscitation should be an initial bolus of approximately 20 ml/kg. Overzealous resuscitation can result in further bleeding due to an increase in blood pressure and dilution of clotting factors. The goals of fluid therapy should be to bring the mean arterial blood pressure to within a range of 60–70 mmHg, and maintain tissue perfusion [25]. Blood lactate can be used to help determine response to fluid therapy, with the aim to normalize lactate (<2 mmol/l) within 24 hours [32]. Synthetic colloids have been shown to cause platelet dysfunction and reduced von Willebrand factor and factor VIII, and have been associated with increased blood loss during surgery in human patients [33]. In healthy ponies treated with gelatin and hydroxyethyl starch, hemodilution occurred but there were no clinically significant effects on hemostasis [34]. Despite the lack of evidence of adverse effects in horses, the use of synthetic colloids is not recommended in the acutely bleeding patient.

      Blood transfusion is recommended for acute blood loss of greater than 20% blood volume, especially if there are concerns about continued blood loss. Additional parameters that indicate a need for transfusion include signs of shock (heart rate >60/min, CRT >3 sec, cold extremities, depressed mentation) despite adequate volume resuscitation, oxygen extraction ratio greater than 40%, lactate greater than 4 mmol/l, and acute hemorrhage with a PCV less than 20%.

      In acute blood loss situations, the volume of blood lost can be estimated based on the severity of shock. For example, a horse that is severely tachycardic with decreased pulse pressure,