Читать книгу Complications in Equine Surgery - Группа авторов - Страница 102

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, pale mucous membranes, and altered mentation can be estimated to have lost approximately 30% of its blood volume [25]. Up to half of the volume lost should be replaced by a whole blood transfusion. In cases of normovolemic anemia, the following formula can be used to estimate transfusion volume:

Blood transfusion volume (ml):

The target PCV will depend on whether the horse is at risk of continued bleeding and whether there are any comorbidities that might decrease perfusion. This author will typically target a PCV of 25%, although the total blood transfusion volume will often be limited by how much blood the donor horse can give.

Donor horses are the most common source of blood for transfusion, but autologous salvaged blood should also be considered. Cell salvage devices can be used to collect blood from surgical sites or drains. Blood is suctioned from the surgical site, filtered, centrifuged, washed, and returned to a bag for reinfusion into the patient [35]. This technique has been reported in canine patients, and could be used in equine patients if the equipment is available [36]. Blood can be collected and transfused directly into the patient without processing, but the cell salvage system reduces contaminants. A leukocyte depletion filter is needed when there may be contamination of blood with neoplastic cells or bacteria.

When blood is lost into a body cavity (hemothorax or hemoabdomen), it can also be left to be reabsorbed by the patient. The immediate hypovolemia must be addressed with IV fluids, but the majority of shed blood may be reabsorbed via lymphatics within 48 hours [37]. If PCV falls below 20% or the horse continues to have signs of shock despite fluid resuscitation, a blood transfusion may still be needed. Allogeneic transfusion from a donor horse is most common, but collection of blood from the abdominal cavity and reinfusion has also been reported [38].