2.5 Hemostasis: Chemical and Topical Agents

While energy devices and mechanical methods (like ligatures and clips) address macro-bleeding from distinct vessels, the Surgical First Assistant frequently encounters generalized oozing from capillary beds or highly vascular organs. In these situations, chemical and topical hemostatic agents are deployed. These agents work by either providing a physical matrix for clot formation or by actively participating in the physiological coagulation cascade.

Absorbable Gelatin Sponges

Absorbable gelatin (most commonly known by the brand name Gelfoam) is derived from purified porcine skin gelatin. It is available in various forms, including sponges, powders, and films.

• Mechanism of Action: Gelatin is primarily a mechanical hemostat. It absorbs blood and swells to several times its original size, creating a structural matrix that traps platelets and allows the natural coagulation cascade to proceed.
• Application: Gelatin sponges can be applied dry or saturated in sterile saline. Crucially, they are frequently soaked in topical thrombin to provide both a physical matrix and an active clotting accelerant.
• Considerations: Gelatin is absorbed by the body over 4 to 6 weeks. However, because it swells significantly, it should be used with extreme caution or avoided in confined spaces (such as the spinal canal or near the optic nerve), where expansion could cause dangerous pressure necrosis.

Oxidized Cellulose

Oxidized cellulose (common brand names include Surgicel, Surgicel Nu-Knit, and Surgicel Fibrillar) is a plant-based material manufactured in knit or fibrillar formats.

• Mechanism of Action: When oxidized cellulose contacts whole blood, it swells into a brownish, gelatinous mass that serves as an artificial clot. It also has a low pH (acidic), which provides a mild bactericidal effect against many gram-positive and gram-negative organisms.
• Application: It must be applied dry. If it is moistened before application, it loses its hemostatic efficacy. The Assistant should apply only the minimal amount necessary and remove excess material once hemostasis is achieved, although small amounts left in situ will be absorbed in 7 to 14 days.
• Contraindications: Because of its acidic nature, oxidized cellulose inactivates topical thrombin. Therefore, oxidized cellulose should never be combined with thrombin. Furthermore, it should not be left on nerve tissue due to the risk of low-pH induced neuropathy, and it can interfere with bone regeneration if packed into bony defects.

Microfibrillar Collagen Hemostat (MCH)

Microfibrillar collagen (e.g., Avitene, Arista) is derived from purified bovine corium (connective tissue).

• Mechanism of Action: Unlike gelatin or cellulose, MCH acts directly on the physiological clotting process. When it contacts blood, its unique structure powerfully attracts platelets. The platelets adhere to the collagen fibrils and degranulate, releasing factors that trigger the intrinsic coagulation cascade.
• Application: MCH must be applied strictly dry, using dry forceps, to a dry field. If it contacts wet gloves or instruments, it instantly becomes a sticky, unmanageable mass. Once applied, firm pressure is held over the agent using a dry sponge.
• Precautions: Because it is an animal derivative, there is a risk of allergic reaction. It should not be used in grossly contaminated wounds due to the risk of promoting abscess formation, and it is contraindicated in the closure of skin incisions as it may interfere with healing.

Topical Thrombin

Thrombin is an enzyme extracted from bovine blood, or increasingly, derived from recombinant human sources (recombinant thrombin).

• Mechanism of Action: Thrombin catalyzes the conversion of fibrinogen into fibrin, the final step in the clotting cascade, thereby rapidly accelerating clot formation regardless of the patient's intrinsic clotting factor levels.
• Application: Thrombin is typically supplied as a dry powder that the surgical technologist or circulating nurse reconstitutes with sterile saline just prior to use. It can be sprayed directly onto oozing surfaces, or more commonly, it is used to soak an absorbable gelatin sponge (Gelfoam).
• CRITICAL SAFETY WARNING: Thrombin is strictly for topical use. It must NEVER be injected intravascularly. Intravenous injection of thrombin will cause massive, sudden, and potentially fatal disseminated intravascular coagulation (DIC) or thromboembolism. Ensure it is clearly labeled on the sterile field and kept physically separated from injectable medications.

Bone Wax

Bone wax is a sterile mixture of beeswax, isopropyl palmitate, and a softening agent.

• Mechanism of Action: It provides purely mechanical hemostasis. It is physically kneaded to soften it and then smeared forcefully across the cut edge of cancellous bone (e.g., the sternum in cardiac surgery, or cranial flaps) to plug the osteons and stop marrow bleeding.
• Considerations: Bone wax is non-absorbable. Because it remains in the body indefinitely as a foreign body, it can inhibit bone osteogenesis and increase the risk of infection. It should be used sparingly.

Fibrin Sealants

Fibrin sealants (e.g., Tisseel, Evicel) are biological tissue adhesives. They are supplied in a dual-syringe system containing human fibrinogen in one syringe and human thrombin in the other.

• Application: When the two components are expelled simultaneously through a mixing tip, the thrombin instantly acts on the fibrinogen to form a stable fibrin clot. They are used for hemostasis, to seal tissue planes, and to prevent fluid leaks (such as cerebrospinal fluid or biliary leaks).