Читать книгу Complications in Equine Surgery - Группа авторов - Страница 100

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 clinical signs of excessive bleeding [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