Primary bleeding, caused by the initial traumatic incident itself occurs in all wounds. In contrast, secondary bleeding is the result of renewed damage to the injury or through thrombolysis of clotted vessels. Secondary bleeding can also occur as the result of inadequate hemostasis, or, in surgery, when ligatures have slipped. In cases where infusions or medications raise the blood pressure, new secondary bleeding may occur. The nature and the extent of the bleeding are dependent on the type and size of the injured vessel. If blood cannot adequately drain, it will collect in the (newly-formed) wound or body cavity, such as the thorax or abdomen (internal bleeding). The origin of the bleeding (arterial, venous, or capillary) should be determined because the treatment protocol may differ. The time and method of intervention often is a question of experience and insight into the hemostatic parameters of the patient. In surgery, hemostasis is important to allow a clear overview of the operational field. Additionally, the collection of blood is not beneficial for a good recovery, because it needs to be resorbed and reorganized, and it functions as a medium for bacterial growth. The complete absence of spontaneous hemostasis because of pathological factors such as hemophilia rarely occurs in companion animals. Insufficient clotting and consequently, an increased bleeding tendency can be observed in:
a. patients suffering from hypercapnia (in other words, with an elevated carbon dioxide level in the blood as the result of insufficient ventilation) and;
b. Patients whose clotting factors have been exhausted (for example, in the case of extended bleeding or DIC);
c. Patients with (hereditary) clotting factor deficiencies.
In traumatic wounds, it is sometimes necessary to take measures that temporarily promote blood clotting. The employment of certain interventions can prevent extensive blood loss. These measures include:
a. compression of the supplying vessels by temporarily tying off a body part (extremity, tail) above the bleeding (tourniquet). When an elastic material is not available, it is possible to use cords along with a stick to twist tight. This temporary interruption of the blood supply may not last more than in total 2-3 hours, because tissue necrosis and nerve damage may occur. The same principle is sometimes used in surgery: the so-called artificial bloodlessness according to Esmarch;
b. Direct compression of the wound using digital pressure, a pressure bandage or packing 4×4’s or swabs in the injury or body cavity, for example, nose, ear canal, vagina. This method of hemostasis can also be definitive: after the bleeding has stopped, the pressure bandage or the swabs are removed.
Measures that also lead to definitive hemostasis include the following:
1. compression, bruising, or torsion of blood vessels with hemostatic forceps. For instance, specially-designed, large, compressing clamps (referred to as emasculators) are used during an open castration in equine and farm animals. In many cases, however, a ligature is still needed after clamping;
2. suturing of blood vessels. This gives greater certainty of accurate hemostasis. Generally, resorbable suture material is used to tie off the vascular pedicle. Additionally, hemostatic clips (absorbable or made of inert surgical steel) could be applied to the vessel;
3. the vessel wall may be sutured itself with fragile, atraumatic suture material;
4. pressure bandage or wound cavity packing with swabs (see above);
a. cauterization with hot metal, used to provide a surface with a burnt crust. A modern variant to this method is the use of a hot air gun. This method of coagulation is sometimes used in farm animals, immediately following the removal of large (and, therefore, substantially bleeding) granulomas in a standing animal;
b. electro-coagulation using high-frequency currents (see also Chapter 4). In monopolar electro-coagulation, use is made of a small, active electrode (monopolar thermocautery), where an electric current generates heat. The electric current exits the body via a large passive electrode (a type of grounding plate) that makes contact with a shaven or non-hairy part of the patient. If the vessels are fixated with a metal instrument (hemostat or forceps), the electrode can also contact the instrument and coagulate the vessel indirectly. In bipolar thermocautery, both the passive and active electrodes run isolated from each other in the handle of the instrument. Depending on its form, the thermometer can function as an electric knife, or can be used to coagulate vessels. Thermocautery provides good hemostasis but can delay wound healing if misused by causing too much coagulation or necrosis.
The most secure manner to achieve hemostasis is by compression, which is described above. It is, however, not always possible to approach a hemorrhaging vessel directly (for example, in intracavitary hemorrhage caused by parenchymatous organs). A direct approach to intracavitary haemorrhage can be performed using advanced endoscopic techniques. Pharmaceutical products used to be employed to promote hemostasis in diffuse or difficult to be reached hemorrhages (haemostyptics or haemostatics). None of the systemic acting agents that are now often obsolete assures the desired effect. Most can be used exclusively topically because they are effective through their astringent effect (such as alum, ferric chloride, copper sulfate, and silver nitrate).
Thrombin, prepared from bovine plasma, should be used exclusively topically, because systemic administration may lead to thrombosis and possible emboli. Adrenaline-soaked gauzes or adrenaline in spray-form is used locally to encourage vascular contraction. Along with preventing illness, adrenaline can be combined with a local anesthetic. Uterine haemorrhage can be combated with agents that cause uterine contraction uterotonics or oxytocics. Gelatine was formerly administered intravenously to increase blood viscosity. Presently, it is regularly used in resorbable, locally-applied, gelatine sponges (Spongostan®). Components that have natural blood clotting effects can also be used to improve hemostasis. These can best be administered through blood or plasma transfusion.