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or tissue debridement may be necessary if necrosis is evident.

       Expected outcome

      Perivascular hematomas and mild inflammatory reactions will resolve without further treatment, although local application of warm compresses and topical anti‐inflammatory medications may speed resolution. Severe inflammatory reactions may result in temporary or permanent loss of patency of the vein and associated nerve function. Injury or inflammation of the vagosympathetic trunk or left recurrent laryngeal nerve is usually temporary, assuming there are no other clinical signs, but may be permanent, especially if there is severe associated, perivascular inflammation.

Intra‐Arterial Injection or Catheterization

       Definition

      Accidental arterial penetration during venipuncture or catheterization will result in a significant hematoma formation but no other consequences if quickly recognized. Administration of medications into the arterial circulation is associated with severe and violent reactions when it involves the cerebral circulation or may be associated with arteriospasm and tissue necrosis if it involves a peripheral artery.

       Risk factors

       Anatomical location: The common carotid

       Poor lighting

       Fractious or insufficiently restrained patient

       Inability or inexperience to recognize anatomic landmarks, and accessing the vein in the lower part of the neck [2]

       Use of smaller gauge needles

       Pathogenesis

      The needle is advanced and placed into the arterial lumen inadvertently and the solution injected. The common carotid artery is the most common artery to be accidentally punctured, especially in the caudal two‐thirds of the neck, because of the close proximity of the carotid artery to the jugular vein and common use of the jugular vein for venous access [1, 2]. Risk of inadvertent arterial injection or catheterization is less with the cephalic vein, lateral thoracic vein, and saphenous veins, because there are no adjacent arteries. Smaller gauge needles prevent recognition of inadvertent arteriopuncture.

       Prevention

      Adequate knowledge of anatomy is required; inject into the cranial aspect of the jugular vein whenever possible. Adequately restrain the patient and perform injection in areas with adequate lighting. Use needles not smaller than 18–20 gauge, although these calibers also show weak or absent pulsations [9].

       Diagnosis

      Accidental penetration of the artery is typically associated with pulsatile and projectile ejection of bright red blood from the catheter or needle; however, projectile arterial blood is not always apparent [9, 10]. Smaller gauge (18–20 gage and smaller) needles are associated with weak or absent pulsations [9]. Placement of the bevel against the arterial wall or incomplete seating of the needle in the vessel may also prevent forceful ejection of blood. The most serious consequence of arterial catheterization is injection of medications into the arterial system. Intracarotid injections are the most severe and serious of these accidental injections because of the typically immediate and violent reactions by the patient. Clinical signs can range from disorientation to hyperexcitability to seizures and death.

       Treatment

      If arterial puncture is recognized, the needle or catheter should be removed and firm direct pressure applied to the site immediately. Reactions to accidental intracarotid injections can be immediate and violent. Personnel and patient safety should be prioritized. Immediate treatment of accidental intracarotid injection includes sedation and/or anticonvulsive medications (alpha‐2 agonists, benzodiazepines, and phenobarbital) and provision of neuroprotective treatments (dimethylsulfoxide, corticosteroids, and mannitol) [10].

       Expected outcome

The severity of intracarotid injections depends on the amount and type of medication administered. Oil‐based formulations, such as phenylbutazone, are associated with fatal reactions [10]. Outcome may also be affected by injuries incurred subsequent to the injection (e.g. head trauma, etc.). Although systemic reactions are not pronounced with accidental injection of other arteries, ischemia and necrosis of the tissues supplied by the artery may occur if the artery thromboses.

Catheter‐Related: Difficult or Incorrect Placement, Dislodgement and Loss of Patency

       Definition

       Inability to advance catheter or guidewire is a technical complication that can occur during placement of either an over‐the‐needle stylet catheter or an over‐the‐wire catheter.

       Blockage, bending or removal of catheter.

       Risk factors

       Use of alternate venous access sites to jugular vein (cephalic, lateral thoracic, saphenous) [2].

       Type of catheter material: more pliable catheter materials (polyurethane, silastic) can be compressed as they traverse the skin.

       Foals are prone to removing the intravenous catheters from their dams.

       Pathogenesis

      Inability to advance the catheter or guidewire may be caused by friction from the skin against the catheter (especially in thick skinned animals), perivascular placement or inadequate seating of the stylet needle or guide needle into the vein, or obstruction by valve leaflets or changes in diameter or direction of the vein [1, 2]. Premature removal of a catheter results from a failure to adequately secure the catheter. The alternate catheter sites of the cephalic, lateral thoracic, and saphenous veins are prone to premature removal because of increased mobility of these areas and ability of the horse to bite at these sites [1, 4]. Even if a catheter is well sutured, some patients are highly adept at removing them, either through rubbing the neck or scratching with a hind foot. Reasons for low flow may be due to kinking of the catheter under the skin or as the horse’s position changes or it may be caused by early development of a thrombus at the catheter tip.

       Prevention

      To prevent premature catheter removal, it is advisable to always securely suture in the intravascular catheters unless they are intended for very short‐term use and under predictable circumstances. Bandaging the catheter site, use of a low‐profile catheter (such as an over‐the‐wire catheter), and frequent monitoring may reduce this complication but does not entirely prevent it. Catheter patency can be assured by maintaining a continuous flow of fluids through the intravascular catheter or regularly flushing or heparin locking the catheter if it is being used infrequently. In general, flushing the catheter with heparinized saline (2–10 iu/ml) every 6 hours is adequate in healthy horses, but more often may be prudent in patients at higher risk for coagulopathies, such as colic patients [1, 4, 8]. Catheters should be carefully inspected and palpated every day with a gloved hand to determine if the catheter is kinking under the skin.

       Diagnosis

      Problems occur when the stylet catheter cannot be advanced off the stylet needle into the vein or when the guide wire cannot be passed through the needle. Trouble‐shooting of this problem can be done by aspirating blood from the needle or stylet to verify that the tip of the needle or stylet is in the vein. Low flow through the catheter may be recognized by a catheter that is positional or has resistance to flow [8]. No flow, which persists despite manipulation of the catheter, is caused by thrombus formation within the catheter.

       Treatment

For stylet catheters, placement can be facilitated

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