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control such as forced warm air and warm water blankets. It can be difficult to place a warm air blanket around a small patient. These devices blow warm dry air, so pay particular attention to keeping the cornea lubricated to reduce the risk of creating corneal ulcers. This is especially important with small patients where the head is hard to visualize under the blanket. It is considered beneficial to use more than one patient warming device. For example combine a circulating warm water blanket under the patient and a forced warm air device around and over the patient where possible. For most small exotic animals set the circulating warm water blanket and forced warm air device at 104 °F (40 °C) because these patients have a high body temperature. Drape the patient as quickly as possible to help hold heat in under the drapes.
Use warm (101–103 °F; 39–40 °C) saline for abdominal and thoracic lavage. Fill the body cavity with the warm saline and do not immediately remove it. Allow it to dwell within the body for several minutes. Repeat this process until the body temperature begins to rise. Once the downward trend in body temperature reverses and the body cavity has been closed, in most cases, the temperature will continue to rise assuming other patient warming devices are in place. For most species, if the body temperature drops below 96 °F (35.5 °C) during the surgery, stop the procedure and instill warm saline into the body cavity before continuing the procedure. Repeat the process before closing.
Instrumentation and Equipment
Hemostatic Aids
The average cotton‐tipped applicator (CTA) holds approximately 0.1 ml of blood when completely soaked and a 4 × 4 gauze sponge holds 10 ± 2 ml (Hughes et al. 2007). The total blood volume of small mammals is 57 ml/kg of body weight (Jenkins 2000; Bennett 2009). If a patient loses 10–15% of total blood volume (approximately 1% of body weight), it is generally considered safe. Most mammals experience hypovolemic shock and release large amounts of catecholamines with loss of 15–20% of the total blood volume. Loss of 20–30% of the total blood volume can have life‐threatening consequences (Jenkins 2000; Bennett 2009). As an example, if a 50 g mouse loses more than five CTAs full of blood, it is equivalent to more than 20% of the blood volume (Harkness 1993). Table 1.1 shows approximately 20% of the blood volume of common rodent pets.
Magnification is an aid for hemostasis (see Chapter 3). What would seem a small amount of blood to the naked eye observer appears to be major blood loss when magnified drawing the surgeon's attention to the hemorrhage and the need to arrest it. Additionally, small vessels can be identified and controlled more easily when working under magnification.
Hemostatic clips are available in various sizes including microclips. These are very useful for controlling hemorrhage in small patients, where it is difficult to accurately place a ligature. Additionally, they can be applied in deep, hard‐to‐reach locations. With some types of hemostatic clips, both straight and right‐angled appliers are also available (Figure 1.3). This applier makes it easier to get under a hemostat to apply a clip to a severed vessel.
Table 1.1 Loss of approximately 20% of total blood volume results in cardiovascular compromise with potentially life‐threatening consequences.
Source: Harkness (1993), Jenkins (2000), Harkness et al. (2010).
| Species | 20% of blood volume (ml) |
|---|---|
| Gerbil | 1.2 |
| Hamster | 1.4 |
| Rat | 4.0 |
| Guinea pig | 4.5 |
Twenty percent of the approximate blood volume of rodents.
Sterile CTAs are useful for atraumatic tissue dissection and manipulation. They can be used to apply pressure to damaged vessels allowing a clot to form. Use moistened CTAs when using them for tissue manipulation and dissection and dry ones to absorb fluids.
Absorbable gelatin sponge is made from treated purified gelatin solution. It is capable of absorbing many times its weight in blood and also provides a scaffolding for clot formation. It is completely absorbed in 4–6 weeks. Surgicel (Ethicon, Inc., Sommerville, NJ) is oxidized regenerated cellulose resembling cloth. It is a hemostatic aid that adheres nicely to moist tissues, but is not capable of absorbing much fluid and does not adhere well to dry tissue. Gelatin sponges are thick and absorb more fluid than oxidized regenerated cellulose but are prone to becoming dislodged from the tissue.
Topical thrombin is commercially available and when applied uses the patient's fibrinogen to form a fibrin clot. It is most useful for oozing and minor bleeding from capillaries and venules where standard surgical techniques are ineffective at halting the hemorrhage. It can be applied directly to the source of hemorrhage or can be applied onto gelatin sponge that is then placed over the site of hemorrhage. A hemostatic “taco” can be made of gelatin sponge wrapped in oxidized regenerated cellulose and soaked in topical thrombin and is very effective for controlling hemorrhage (Figure 1.4).
Electronic Hemostatic Devices
Electrocautery
Electrocautery uses direct current electricity to heat metal until it is red hot. The red hot tip is applied to the source of hemorrhage to heat and coagulate tissues. Electrocautery causes heat damage to adjacent tissues that then undergo necrosis minimizing its value in many situations. Cautery pens (Convenient Cautery Kit; Jorgensen Labs; www.jorvet.com) may be useful to cauterize small vessels in small exotic mammals if electrosurgery is not available. They have a fine wire tip and are battery‐operated. Keep in mind that the longer the heat is applied to the tissue, the more thermal necrosis occurs.
Figure 1.3 Straight and right‐angled hemostatic clip appliers are available. Compared with the standard applier (a), the right‐angled appliers (b) can be inserted into a small body cavity to place a hemostatic clip at nearly a right angle, while the standard applier requires the handles to be almost perpendicular to the vessel, making it difficult to place through a small approach into a body cavity.
Figure 1.4 A “hemostatic taco” made of gelatin sponge (G) wrapped in oxidized, regenerated cellulose (S) and soaked in topical thrombin has been applied to the caudal vena cava (arrow) after right adrenalectomy.
Electrosurgery
Electrosurgery uses high‐frequency alternating current to generate energy. There is an active electrode and an indifferent electrode or ground.