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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 by advancing the stylet and catheter as a unit together into the vein to overcome skin friction or past valve leaflets or by injecting sterile saline into the catheter as it is being advanced to distend the vein. If the guidewire is verified to be in the vein but cannot be advanced, options include placement of the catheter in a different vein or more distally in the vein or securing an over‐the‐wire catheter without inserting it to its full length (which is allowed by the catheter clamp and fastener included in the kit). Catheter patency may be restored in some of these occluded catheters by aspirating the thrombus from the catheter, if possible. It is important to recognize that this may be an early sign of a more serious problem, such as bending or breakage if the catheter is composed of stiff materials, or early signs of thrombophlebitis. Therefore, catheter removal should be considered in these cases and if the catheter is maintained, strategies should be used to reposition the catheter (resuturing, catheter wraps or bandaging, maintaining the horse’s head in a more elevated position, etc.).

Expected outcome

Use of an alternate site or replacement of the catheter usually resolves the problem. In some cases, hematoma, swelling, thrombophlebitis or infection at the site may develop.