Emergency and critical care applications of interventional radiology (Proceedings)

Following the trends in human medicine, there is an ongoing effort to adapt and develop minimally invasive therapeutics for the management of various problems facing veterinary patients. Minimally invasive therapeutics offer the advantages of smaller incisions, decreased pain, shortened anesthesia times and shorter length-of-stay compared to traditional open surgical approaches. Currently in veterinary medicine, laproscopy, thoracoscopy, minimally invasive orthopedic procedures, endourology, and interventional radiology (IR) are meeting this demand.

Interventional radiology (IR) involves the use of contemporary imaging modalities such as fluoroscopy, endoscopy, ultrasound, CT, and MRI (or combinations thereof) to gain access to different structures in order to deliver materials for therapeutic purposes. IR is a subspecialty of radiology in human medicine. IR techniques have been widely utilized in human medicine for the past 20-30 years to effect minimally invasive diagnostic and therapeutic outcomes. Applications of IR in veterinary medicine are just being realized. The purpose of these proceedings is to present current applications of IR in veterinary medicine with an emphasis on applications of IR in Emergency and Critical Care Settings.

Equipment & Training:

Many IR procedures require advanced imaging modalities. Fluoroscopy is a critical tool for performing most IR procedures. In IR, an array of guide wires with various properties, catheters specifically adapted for individual procedures, stents composed of different materials and configurations, embolic coils, embolic particles, drainage devices, surgical glue, oils, chemotherapeutic agents, occlusion devices, balloons, etc. replace the standard surgical pack.

Because IR is so new to veterinary medicine, there are only few formal IR programs in the country. They are at Michigan State University and the Animal Medical Center in New York City. However, many training opportunities exist for specific procedures through various continuing education meetings and organizations.

IR Applications in the Emergency and Critical Care Setting:

Tracheal collapse: Tracheal collapse is a common affliction of small breed dogs. Traditional management of tracheal collapse is centered on medical management (cough suppressants, corticosteroids, management of concurrent problems). Surgical management using prosthetic rings placed around the cervical trachea is an option in patients with cervical tracheal collapse that fail medical management. Surgical management of tracheal collapse tends to be invasive and is associated with a significant incidence of acute complications and limitations including but not limited to disruption of the tracheal blood supply, injury to the recurrent laryngeal nerve causing laryngeal paralysis, and the inability to access the intrathoracic trachea.

Tracheal stent placement involves the placement of an intraluminal self-expanding metallic stent that holds the trachea open.1 Placement requires the use of fluoroscopy. Tracheal stenting offers a very rapid, non-surgical (everything is done through the airway) treatment option for animals with tracheal collapse. The incidence of acute complications is very low when compared to prosthetic ring placement provided the stent is sized and deployed appropriately. Long-term complications may include shortening of the stent as it expands to its nominal diameter with subsequent collapse cranial to the stent, stent fracture (likely precipitated by coughing and excessive over sizing of the stent during placement), and inflammatory tissue formation at the ends of the tracheal stent. As a result, ongoing medical management is still important although most patients require a much less rigorous medication protocol.

In the emergency setting, some dogs with acute respiratory embarrassment secondary to tracheal collapse require intubation and positive pressure ventilation when traditional measures to stabilize them fail (sedatives, oxygen therapy, corticosteroid therapy, and cough suppression). In this setting, attempts are generally made to extubate the dog while facilitating a slow recovery from anesthesia in an effort to minimize respiratory effort. When the patient is unable to be extubated, definitive care is necessary. Placement of a tracheal stent is a technique that provides this patient population with a rapid, minimally invasive, and effective technique to restore the patency of the tracheal lumen.

Overall, the author recommends tracheal stent placement for dogs with tracheal collapse that are not having good quality of life in the face of medical management, those with intrathoracic tracheal collapse, and those whose owner does not wish to pursue a surgical treatment option. Dogs with intrathoracic tracheal collapse and mainstem bronchial collapse often benefit significantly from tracheal stent placement although they often continue to cough due to the mainstem bronchial collapse. Cervical tracheal collapse may be treated through traditional surgical techniques or placement of a tracheal stent. The entire procedure takes approximately 30minutes and usually requires only 24 hours total hospitalization. It is important for clients to recognize that tracheal collapse is a progressive condition. This being said, tracheal stent placement offers an excellent palliative treatment option. Tracheal stent placement also offers an excellent palliative treatment for animals with airway obstruction due to neoplasia.2

Tracheobronchial Foreign Body Retrieval: Large airway foreign bodies are rare and dogs and cats. When present, however, they most often cause manifestations of fixed airway obstruction. If the foreign object is mobile, dynamic airway obstruction may also result. Non-cardiogenic pulmonary edema may be a sequelae. With the aid of general anesthesia, an endotracheal tube can be positioned just beyond the larynx. Using a bronchoscope adapter to maintain insufflations of inhaled anesthetic in oxygen, a stone basket commonly utilized for endoscopic retrieval of uroliths may be passed down the endotracheal tube to "capture" the foreign body. Alternatively, various grabbing instruments or a foley catheter passed beyond the foreign object and inflated and withdrawn slowly may help facilitate mobilizing the object proximally. The author has had the most success with the stone basket. Careful manipulation of instruments and the foreign object must be performed to minimize the chance of tracheal trauma.

Retrograde Bladder Access / Antegrade Urethral Access / Percutaneous Cystostomy: Numerous clinical conditions necessitate placement of a urinary catheter in the critical care setting. However, on rare occasion, retrograde access using a urinary catheter is not possible due to urethral damage/disruption, very small patient size, complex anatomy, or the presence of a diverticulum(s) associated with prostatic neoplasia or infection. In this patient population, using fluoroscopic guidance, retrograde guide wire (0.035in standard stiffness, angled tip, hydrophilic guide wire)a access to the bladder can be accomplished in some cases and a urinary catheter placed over the guide wire. The angled tip of the guide wire allows it to be directed across areas of complex anatomy and regions of partial urethral disruption or stenosis.

In some instances, however, retrograde access with a urinary catheter or a guide wire is unsuccessful. In this patient population, antegrade urethral access is very often possible. The patient is sedated in lateral recumbency and the abdomen is clipped and prepared as if for surgery. The entire procedure is performed with the aid of fluoroscopic guidance. Cystocentesis is performed using an 18g catheter near the apex of the bladder. A small amount of urine is withdrawn and replaced with 5-10mL of sterile iodinated contrast agent (200-300mgI/mL) to help illustrate the bladder. Through this catheter, a 0.035in standard stiffness, angled tip, hydrophilic guide wirea is passed. The slight angle at the tip of the guide wire allows it to be directed. The guide wire is directed down the urethra. Most times, with the exception of complete urethral transection, the guide wire will traverse areas of the urethra that are damaged or disrupted, obstructed, and those that display complex anatomy and will be exteriorized at the level of the penis or vulva. A urinary catheter can then be placed retrograde over the guide wire and the guide wire removed. This technique is not expected to be useful in cats with urethral obstruction due to urethral plug or stones. Standard techniques for dislodging the plug/stone should be undertaken.

As an added measure of security, once guide wire access to the bladder is achieved, following serial dilation, a locking loop pigtail drainage catheter 6F-10F can be placed percutaneously over the guide wire and into the bladder as a percutaneous cystostomy tube.

Malignant Urethral Obstruction: Transitional cell carcinoma, prostatic carcinoma, and other intrapelvic neoplasia may result in urethral obstruction. Traditional therapy has been centered on diverting urine via surgical placement of a cystostomy tube while pursuing traditional tumor-directed therapies. Cystostomy tube placement requires surgery and requires significant owner maintenance for the duration of the pet's life. In addition, complications including tube dislodgement and recurrent urinary tract infection are not uncommon. Using IR techniques, an intraluminal self-expanding metallic urethral stent can be placed (non-surgically) via the vulva or penis to open the urethral lumen. Note that stents for this purpose are very different than those used for tracheal applications. Using fluoroscopy, the length and width of the obstruction can be very precisely measured and a stent of an appropriate length and width to span the obstruction chosen. The stent is deployed from a delivery system introduced via the urethral orifice. The entire procedure takes approximately 1hour and is associated with little to no patient discomfort. Patients are able to urinate immediately after stent placement. The greatest complication of the procedure is incontinence. Incontinence results from the stent spanning the urethral sphincter and at times, a significant portion of the urethra. The overall incidence of incontinence after stent placement is <20%. Females logically may have greater problems with this than males. In a case series by Weisse et al. and based on the MSU experience, no patients died in the short or long term due to recurrent urethral obstruction.3 With the symptom of the neoplastic condition palliated, chemotherapy, radiation therapy or other adjunctive treatments may be utilized to address the tumor directly.

Nasojejunal / Esophagojejunal Tube Placement: Enteral nutritional support is associated with decreased length of stay, fewer infective complications, and significant cost savings when compared to parenteral nutritional support in people with critical illness. Nasogastric and nasoesophageal tube placement is quick and the procedure is generally well-tolerated in small animal patients. However, many of these patients demonstrate nausea or vomiting associated with feeding into the stomach. Feeding distal to the stomach allows for the provision of enteral nutritional support in this patient population. Traditional surgical jejunostomy is invasive (requires surgery or laproscopy) and is associated with significant complications including ostomy complications and septic peritonitis. We describe a technique also utilizing fluoroscopy in which a combination of a 5F berenstein catheter and 0.035in 260cm hydrophilic, straight, flexible tip guide wire are utilized to gain guide wire access to the jejunum. Once this is achieved, a feeding tube is placed over the guide wire and sutured adjacent to the nasal planum. In our experience, ability to achieve transpyloric access is 100%. Ability to gain jejunal access is 84%. Oral migration is very rare. This technique has become standard of care in our service in patients with pancreatitis, septic peritonitis, and conditions associated with protracted vomiting or gastric motility disorders. Other enteral feeding access devices (EJ, G, GJ) may also be placed with the aid of fluoroscopic guidance.

Percutaneous Nephrostomy Tube Placement: Percutaneous nephrostomy may be performed for the stabilization of patients with ureteral obstruction allowing for diversion of urine while definitive diagnosis and treatment is undertaken for the underlying disease process. Ureteral obstruction most often results from stones, infection, and tumors of the bladder. The procedure is performed under a short anesthesia and eliminates the need for emergency surgery in these often critically-ill patients until a time when they are more stable and better surgical candidates.

Vascular Obstruction (Malignant and Thrombotic): Vascular thrombosis requiring thrombolytic therapy may be accomplished using systemic fibrinolytic therapy (TPA). Systemic thrombolysis requires high doses of thrombolytic agents and may result in unintended bleeding. Catheter directed thrombolysis uses the same fibrinolytic agents, but is performed locally, thus allowing for the delivery of a high dose of thrombolytic agent locally, theoretically resulting in a lower risk of bleeding and a more effective rate of thrombolysis. The author has also effectively dealt with malignant vascular obstruction resulting in cranial vena cava syndrome or a Budd-Chiari syndrome utilizing intravascular stent placement. All of the aforementioned procedures are performed utilizing fluoroscopic imaging.

*Significant portions of these proceedings were previously published for various veterinary continuing education conferences.

References

Moritz A, Schneider M, Bauer N. Management of advanced tracheal collapse in dogs using intraluminal self-expanding biliary wallstents. J Vet Intern Med 2004;18:31-42.

Culp WT, Weisse C, Cole SG et al. Intraluminal tracheal stenting for treatment of tracheal narrowing in three cats. Vet Surg 2007;36:107-13.

Weisse C, Berent A, Todd K et al. Evaluation of palliative stenting for management of malignant urethral obstructions in dogs. J Am Vet Med Assoc 2006;229: 385-8.