Complications in Equine Surgery. Группа авторов

Types of catheters most commonly used in equine practice are over‐the‐needle stylet catheters and over‐the‐wire catheters. With the exception of intra‐arterial stem cell injections [3] or direct blood pressure monitoring, intravascular catheterization and injection nearly always involves the venous circulation. Complications may occur during catheter placement and venipuncture or while the catheter is indwelling within the vessel.

List of Complications Associated with Intravascular Injection and Catheterization

       Anatomic considerations

       Perivascular swelling and inflammation

       Intra‐arterial injection or catheterization

       Catheter placement/dislodgement/patency

       Thrombophlebitis

       Intravascular foreign bodies

       Vascular air embolism/bleeding

Anatomic Considerations

      The most commonly used site for intravenous injection and catheterization in the horse is the external jugular vein due to large vessel size and ease and convenience of access. The left and right jugular veins are located in the jugular furrows on either side of the neck. The jugular vein is in close association with the trachea on the ventromedial surface and the common carotid artery and vagosympathetic trunk on the dorsomedial surface [1]. The left jugular vein is also closely associated with the esophagus and the left recurrent laryngeal nerve, which are located dorsomedially to the vein [1]. Although venipuncture or catheterization may occur at any site where the vein is visible, the carotid artery is closer to the jugular vein in the lower part of the neck.

      The recommended site for jugular venipuncture and catheterization is the proximal third of the neck, because the omohyoideus muscle traverses between the jugular vein and the carotid artery, placing the jugular vein more superficially and increasing the separation between the two vascular structures [1, 2]. Alternate sites for venous access if the jugular vein is not patent or accessible include the cephalic vein, the lateral thoracic vein, and the saphenous vein [1, 2]. These sites are less preferred because of reduced patient compliance during venipuncture or catheterization (cephalic and saphenous), difficulty in visualizing the vein (lateral thoracic), and increased chance for occlusion or dislodgement of catheters (all sites) compared to the jugular veins [1, 4].

Perivascular Swelling and Inflammation

       Definition

      Perivascular swelling is localized swelling that occurs at the site of intravascular injection, which may be a minor blemish that does not obscure visualization of the vascular structure or it may be severe swelling that prevents further use of the site or causes associated tissue injury.

       Risk factors

       Un‐cooperativeness of the patient

       Inexperience of the person performing the procedure

       Underlying coagulopathies

       Injection of irritating substances, such as phenylbutazone, guaifenesin, tetracyclines, etc.

       Pathogenesis

      Perivascular swelling may be caused by hematoma formation, inflammation of the tissues, or both. Perivascular swelling during intravascular injection or catheterization results from hematoma formation due to trauma to the target vessel or adjacent vessels. The size and rate of hematoma formation will depend on the origin of the bleeding (venous or arterial) and the size of the needle or catheter being used. The second reason for perivascular swelling in the acute setting is a localized inflammatory response to the injection [1, 5, 6]. Perivascular inflammation is most commonly due to perivascular leakage of even miniscule amounts of an irritating medication, but rarely may be caused by individual horses having a hypersensitivity to the silicone coating on most commercial hypodermic needles. If a highly irritating substance is inadvertently given perivascularly, the local reaction may be so severe as to cause necrosis and sloughing of tissues [6]. Irritation or inflammation of the vagosympathetic trunk or the left recurrent laryngeal nerve is an uncommon sequella to jugular venipuncture or catheterization, but is likely related to the causes of perivascular inflammation and swelling.

       Prevention

      Hematoma formation may be minimized by excellent restraint of the patient, good lighting, clear identification of associated anatomy, and sufficient experience with the procedure. Use of smaller gauge needles or catheters will reduce the vascular trauma but may inhibit recognition of inadvertent arteriopuncture. Perivascular administration of a highly irritating substance may be minimized or avoided by placing an intravenous catheter whenever an irritating substance will be injected. A long (5.25”) catheter should be used preferably over a short (3.5”) catheter to reduce risk of the catheter being dislodged from the vein. The intravascular positioning of the catheter should be confirmed by aspirating blood or passively allowing blood to egress through an unclamped extension set prior to injection of the medication. Although injury to the vagosympathetic trunk may occur on either the left or right side, some veterinarians endorse preference for the right jugular vein to avoid risking trauma to the left recurrent laryngeal nerve in performance horses [1].

       Diagnosis

      Perivascular hematoma formation is recognized by swelling that occurs at the injection site during or immediately after needle or catheter placement. Visibly progressing hematoma formation associated with jugular venipuncture or catheterization is indicative of carotid artery injury. Perivascular inflammatory reactions may be differentiated from hematomas because they are more delayed in onset, occurring minutes to hours after the injection. The swellings may be more diffuse and the vein may be thickened when palpated. Knowledge of recent administration of an irritating substance will be an important historical detail in differentiating this type of reaction.

      Perivascular injections may be recognized by the accumulation of injection fluid at the injection site. There may be increased resistance of flow to the intravascular injection; however, if the injection is given through a catheter that is cracked and leaking at the insertion site, there may be no change in resistance. Horner’s syndrome (ipsilateral ptosis, miosis, enophthalmos, protrusion of nictitating membrane, and localized sweating) may develop if the vagosympathetic trunk is injured [7]. Signs of Horner’s syndrome are typically a transient reaction (self‐resolving within 12–24 hours), but it may be permanent. Injury to the left recurrent laryngeal nerve will result in left laryngeal hemiplegia [1]. This neurological deficit is typically not recognized at the time of venipuncture, because the signs are exercise intolerance and inspiratory stridor. Signs of perivascular swelling may or may not be evident.

       Treatment

      Small hematomas will either self‐resolve or resolve with digital pressure. Large, progressing hematomas, especially those associated with carotid injury, require a padded pressure wrap being placed over the area for at least 20–30 minutes and selection of an alternate site for venipuncture or catheterization. Perivascular inflammatory reactions are best treated by avoiding further injection or catheterization of that vessel until the swelling has completely resolved [8]. Local application of warm compresses and topical anti‐inflammatory agents (diclofenac, dimethylsulfoxide) are typically used to hasten resolution and prevent progression. If perivascular nerve injury is noticed at the time of injection, treatment can include local and systemic anti‐inflammatory medication. Oral administration of Vitamin E (10 iu/kg po q24hr) is thought to aid in neurologic healing. Knowledge that a highly irritating substance has been injected perivascularly will guide more aggressive treatment. At the very least, the subcutaneous tissues in the area should be injected with saline or balanced electrolyte solution to help dilute the irritant and the intravascular catheter should be removed from the associated