Complications in Equine Surgery. Группа авторов
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reconstruct the vein [16, 19].
Expected outcome
Most cases of thrombophlebitis will resolve uneventfully, but may require prolonged antimicrobial therapy. Sequellae may include cosmetic blemish, permanent occlusion of the affected vein, residual edema or varicosities in the area drained by the affected vein, and laryngeal hemiplegia. Septic embolization and dissemination of infection to internal locations may occur and may be associated with additional morbidity and mortality.
Intravascular Foreign Bodies
Definition
Needle emboli, catheter fragmentation, and loss of the guidewire are causes of intravascular foreign bodies during catheter placement and/or management of indwelling catheters [1, 5, 8, 20].
Risk factors
Use of small gauge (20 gauge or smaller) needles, inadequate restraint of a fractious patient, or manufacturer defect. Risk factors for loss of guidewires identified in human medicine and relevant to veterinary medicine are inexperience in the technique or equipment, lack of adequate supervision, distractions during catheter placement, and high workload [21]. Patient restraint and resistant during the procedure would be important in equine settings.
Catheter kinking and breakage should be considered for any catheter type, especially as duration of catheterization increases, and clinicians should be most alert to failure in catheters made of stiffer materials (polytetrafluoroethylene, polyethylene, polypropylene) and over‐the‐needle stylet catheters, because they have to be stiffer to allow insertion.
Figure 3.3 Local abscessation of a jugular thrombophlebitis with complete thrombosis of the right jugular vein at the level of the abscess and 10 cm caudally.
Source: Courtesy of Pablo Espinosa.
Pathogenesis
Catheter fragmentation may occur during placement of over‐the needle stylet catheters if the catheter is advanced and then retracted back over the stylet and the stylet pierces the side of the catheter [1]. Loss of the guidewire during placement of an over‐the‐wire catheter using a Seldinger technique is not uncommon in human or veterinary medicine [21, 22]. The most common reason for loss of the guidewire is not holding onto the guidewire at all times that the wire is in the vein [22]. Catheters may be accidentally transected when the sutures are being cut during catheter removal. Indwelling catheters may bend and break (Figure 3.4), particularly if they are made of more rigid material [1, 2, 20, 23]. In an experimental study evaluating long‐term jugular vein catheterization, 67% of polytetrafluoroethylene catheters kinked, cracked or broke within 14 days, and 100% of polytetrafluoroethylene catheters kinked and broke within 30 days [12]. In the same study, none of the silicone rubber or polyurethane catheters broke, even after 30 days of catheterization [12]. Re‐use of needles is a risk factor in breaking and causing needle emboli in human intravenous drug abuse [24], but re‐use of hypodermic needles is ill‐advised in veterinary practice.
Figure 3.4 Polyurethane catheter removed from a jugular vein 48 hours after being placed. The catheter is seen to have multiple areas of bending and kinking.
Source: Julie E. Dechant.
Diagnosis
Needle emboli can occur when the needle breaks off the hub during placement (Figure 3.5). This will be recognized immediately because the hub and syringe will be free from the needle. Catheter fragmentation will not be recognized until the catheter is removed and found to be incomplete. Loss of the guidewire is typically recognized immediately in veterinary medicine [22]; however, delayed recognition is common in human medicine [21]. Catheter breakage is immediately evident if it occurs at the time of catheter removal; however, if the failure occurs in an indwelling catheter, it may not be recognized. During aspiration or injection of the catheter, any evidence that air bubbles are being aspirated or bubbling under the skin during injection is strongly suggestive that there is a defect in the catheter at or near the insertion site. Intravascular foreign bodies should be localized by radiographs starting at the site of penetration and proceeding along the vein toward the thorax (Figure 3.5) [1, 20]. Ultrasound may be needed to evaluate the site of insertion (although manipulation of the tissues makes ultrasound less desirable than radiographs) or to evaluate if the intravascular foreign body is in the heart [1, 20].
Figure 3.5 Lateral radiograph of the cranial cervical region (cranial to the left of the image) in a horse that was referred for treatment and removal of a needle fragment that broke off during attempted venipuncture of the left jugular vein. An intravenous catheter was placed in the contralateral (right) jugular vein. The needle fragment was located medial to the jugular vein in the cranial cervical region.
Source: Courtesy of the University of California, Davis Veterinary Medical Teaching Hospital Diagnostic Imaging Service.
Treatment
For any intravascular foreign bodies, immediate steps to be taken would be occlusion of the vein on the cardiac side of the insertion point to try to prevent migration into the heart and pulmonary vasculature [5]. Defective catheters should be removed immediately. During removal, the vein should be occluded on the cardiac side of the vein so that any catheter fragments can be trapped at the site and prevented from embolization [5]. If the intravascular foreign body is accessible, it should be removed to prevent complications, assuming the risks of removal do not outweigh the benefits [8, 20, 25]. Direct approaches can be made to the jugular vein, but this should be done under general anesthesia with radiographic control to guide dissection. Endovascular retrieval is preferred in humans [25]; however, horse size will be limiting to this technique unless the patient is a foal or pony‐sized or the intravascular foreign body is located in the jugular vein or cranial vena cava [20, 22]. In an experimental study, 5 out of 6 horses with experimental catheter transection had the transected catheter located in the proximal or distal pulmonary arteries at necropsy 30 hours later [26].
Expected outcome
In general, it is believed that intravascular foreign bodies located within the pulmonary vasculature carry a low risk of complications [1, 8].
Vascular Air Embolism/Bleeding
Definition
Vascular air embolism is the aspiration of a significant amount of air from the