Puppy Problems: PRAA and Intussusception

Persistent right aortic arch (PRAA) is the most common type of vascular ring anomaly in dogs. It results from the failure of a fetal vessel to regress as the neonate develops. Typically, the right aortic arch regresses after birth; but when it does not, it entraps the esophagus as the neonate matures.¹ The stricture around the esophagus causes esophageal dilation,² leading to regurgitation as the puppy transitions to solid food. The continued presence of the stricture causes proximal dilation of the esophagus, further encouraging regurgitation.³ A genetic predisposition has been shown for German shepherds, Irish setters, and greyhounds.² Affected puppies quickly become malnourished and remain small. A secondary complication is aspiration pneumonia. The sooner this anomaly can be corrected, the sooner the puppy can recover and return to good health.

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Medical management of these anomalies is supportive, involving provision of nutrition through the megaesophagus and stricture, usually via a feeding tube. Surgical treatment consists of vessel ligation with suture or hemoclips; techniques vary slightly according to the specific anomaly.⁴ However, the megaesophagus may persist even after surgery, necessitating continued support throughout the dog’s life. Intussusception is the telescoping of an intestinal segment into an adjoining segment; it can occur at any point along the gastrointestinal (GI) tract. Young dogs with previous GI disease may be affected.⁴ Common clinical signs include vomiting, diarrhea, and abdominal pain.⁵ Correction requires abdominal surgery, which involves applying traction to the affected portion of the intestine to reduce the plication. If the intestinal tissue is necrotic, a resection and anastomosis may be required.⁴

Each of these conditions by itself is serious and requires prompt correction. This article describes a young patient with the misfortune of having both.

The Case

Duncan was a 12-week-old, intact male German shepherd weighing 3.5 kg (7.7 lb). In April 2017, he was referred to our surgery service after his breeder surrendered him to a rescue. He had a history of dysphagia and regurgitation whenever he consumed food or water. In addition, he had a history of diarrhea resulting from coccidiosis.

Initial Assessment

Duncan’s primary care veterinarian had taken a series of barium radiographs, which showed proximal esophageal dilation and distal esophageal narrowing at the heart base. A vascular ring anomaly was suspected. The radiographs also showed a slight infiltrative pattern in the caudal left lung lobe indicative of pneumonia, the suspected result of aspiration of regurgitated esophageal contents. Duncan’s vital parameters were within normal limits; however, he was significantly emaciated (body condition score was 1–2 out of 9).

Treatment

The surgery service recommended surgical ligation of the PRAA. The surgery was scheduled to take place in 2 weeks, which would provide Duncan time to recover from the pneumonia and allow his foster parent time to work on his nutrition, enabling him to gain some weight.

However, 2 days later he was brought to the emergency service for a rectal prolapse. He was obtunded, tachycardic (220 beats/min), dehydrated (10%), hypoglycemic (37 mg/dL), and hypotensive (40 mm Hg). His diarrhea had progressed to hematochezia. During triage he received several IV boluses of 50% dextrose (0.5 mL/kg) and crystalloid fluids (20 mL/kg) to help him become normotensive (80 mm Hg) and euglycemic (102 mg/dL). Diagnostics performed at this time revealed the following:

• Thoracic radiographs showed a resolving pneumonia and esophageal dilation.

• An abdomen-focused assessment with sonography in trauma scan showed slight abdominal effusion and a potential intussusception.

• A complete blood profile showed:

– hypoalbuminemia, probably caused by the chronic diarrhea and malnutrition

– azotemia, probably caused by the dehydration, infection, and stress of disease

– anemia, probably caused by GI blood loss (hematochezia, intussusception)

Duncan’s intussusception and prolapse needed exploratory abdominal surgery; however, his current state put him at high anesthetic risk.⁶ After discussion, the rescue opted to pursue the exploratory surgery. During the procedure, the surgeon found an ileocolic intussusception, which was so distal to the colon that the jejunum was the section of intestine prolapsing out of the rectum. An intestinal resection and anastomosis to remove the necrotic tissue was performed. Because Duncan was chronically hypotensive, the surgical team attempted to place an arterial line for monitoring a constant rate of infusion (CRI) of norepinephrine; unfortunately, placement was not achieved. Placement of an esophageal feeding tube was also attempted, but the tube could not be passed beyond the esophageal stricture. Further attempts to place a feeding tube were aborted and anesthesia was discontinued.

Duncan’s recovery and continued care were managed by the critical care service. Recovery goals focused on trying to achieve a normotensive and euglycemic state, allowing for nutritional gain. During recovery, Duncan regurgitated several times, so metoclopramide
(2 mg/kg/day CRI) was started. His blood pressure was evaluated frequently via a Doppler unit, which allowed for norepinephrine titration until it could be discontinued (maintaining systolic pressure >100 mm Hg) 12 hours after surgery. To maintain his blood glucose at >100 mg/dL, an IV infusion of 2.5% dextrose solution was continued. Supplemental oxygen was delivered at a fraction of inspired oxygen (FiO₂) of 30%. His analgesia was controlled with an IV CRI of fentanyl (3 μg/kg/hr).

Twenty-four hours after surgery, all vital signs were within normal parameters. Whether to pursue the PRAA ligation and/or the placement of a feeding tube at this time was discussed, and it was decided that although he was still at great anesthetic risk, he would not become more stable until he underwent the ligation and placement of a feeding tube. The rescue agreed with the decision to pursue a second surgical event addressing both issues.

A thoracotomy was performed and the vessel was ligated. In addition, a percutaneous endoscopically guided gastrostomy tube (PEGT), which bypassed the shunt location and dilated esophagus, was placed. The anesthesiologist was able to secure an arterial line during recovery so blood pressure could be monitored.

During the next 4 days, Duncan improved each day. However, 5 days after surgery, he became acutely hypotensive (40 mm Hg), hypothermic (96.0˚F/35˚C), tachycardic (180 bpm), hypoxic (pulse oximetry reading 91%), and pale (mucous membranes). Thoracic radiographs showed a moderate amount of pleural effusion, infiltrative pneumonia in the caudal left lung lobe, atelectasis in the right middle lung lobe, and continued esophageal dilation. A slight amount of diffuse edema could be seen on his face and all limbs. As a result of his prolonged nutritional deficits, atelectasis from the pneumonia, and decreased activity, development of hypoproteinemia led to “third spacing” of fluids, in which fluids move into interstitial spaces, leading to pleural effusion and peripheral edema.

Antimicrobial therapy (ampicillin and sulbactam 50 mg/kg IV q8h and enrofloxacin 10 mg/kg IV q24h) was continued. For the hypoproteinemia, Duncan was given an albumin transfusion (0.5 g/kg IV over 8 h). After another 24 hours, he was stable and weaned off supplemental oxygen. He was tolerating increased amounts of food via the PEGT. His initial feeding was 10 kcal of Hill’s Prescription Diet a/d (hillspet.com) slurry (1 kcal/mL) and was increased by 10 kcal at each feeding thereafter (q6h). He remained consistently weak, unable to stand or ambulate. He was not mentally appropriate (depressed to obtunded) and vocalized frequently. His edema was resolving.

Outcome

Because of increasing costs, Duncan was discharged to his foster home the next day. His foster parent was given extensive guidance to help her manage Duncan’s rigorous schedule of medications, feedings, and monitoring needs at home. He was to receive metoclopramide (0.25 mg/kg q6h via PEGT), metronidazole (15 mg/kg q8h via PEGT), and meropenem (30 mg/kg SC q8h).

Two weeks later (May 2017), she brought Duncan back to the surgery service for suture removal (thoracotomy and abdominal incision). His incisions had healed well; however, he was not stable, and his care was resumed by the critical care service. He was hypothermic (<92˚F/32˚C) and anemic (23%) and had a pulse oximetry reading of 85% to 90%. At the time of discharge, Duncan weighed 5.0 kg (11 lbs), but at this evaluation he weighed only 4.4 kg (9.7 lbs). All limbs had become moderately edematous, profound musculoskeletal weakness was still present, and he was displaying new neurologic signs.

The rescue elected to continue care, with the plan of supporting him overnight and determining the cause of his weakness in the morning. However, Duncan continued to neurologically decline overnight, vocalizing more frequently, head pressing, displaying rotary nystagmus and strabismus, and showing periods of limp unresponsiveness. In the early morning, he regurgitated a large amount and became apneic and agonal. Because he had a “Do Not Resuscitate” order, he was allowed to pass.

Discussion

Duncan’s medical situation was layered, starting with the PRAA, progressing to development of intussusception/prolapse, and continuing with musculoskeletal weakness of unknown origin. Although a plan was in place to surgically correct the primary problem (the PRAA), secondary complications associated with malnutrition required immediate care. Given his weakened state, anesthesia was a considerable risk.⁷ To survive his 2 surgical procedures, he needed aggressive anesthesia plans and anesthesia monitoring. His risk factors stemmed primarily from his state of chronic illness and malnourishment (hypoglycemia, hypotension, hypothermia, dehydration).

Duncan’s state of malnutrition was a constant source of concern. Nutrition was essential for Duncan’s recovery, and establishing a functional feeding method was a high priority. The original timeline had allowed him time to gain weight through good nutrition, but when the timeline to anesthesia was accelerated by the intussusception, feeding tube options were considered. When the typically quick placement of an esophageal tube was not successful, the appropriate choice was placement of a PEGT.⁸ Feedings were carefully calculated and administered because Duncan’s extreme malnutrition put him at risk for refeeding syndrome.⁹ Refeeding syndrome can result from the reintroduction of nutrition after profound starvation and can be life threatening. When food consumption is resumed, a rapid shift in electrolytes can lead to profound hypokalemia, hypophosphatemia, and hypomagnesemia. Refeeding syndrome can be avoided by administering calculated feedings and closely monitoring electrolytes.⁸

The root cause of Duncan’s musculoskeletal weakness was never detected. Initially, his weakness was attributed to his advanced malnutrition. When the weakness continued despite supplemental nutrition, workups for other causes (congenital myasthenia gravis, muscular dystrophy, distemper) were needed, but he died before they could be done. Duncan’s recovery in the hospital was eventually limited by finances. Perhaps with unlimited resources, the differentials could have been explored sooner and more thoroughly.

Duncan’s case provides an example of intensive critical care nursing. Although his primary problems clearly required surgical correction, his care didn’t end there. He needed close monitoring for recovery from anesthesia to stabilize and maintain his blood pressure, blood glucose, and other vital parameters. Had Duncan survived, correcting his malnutrition and restoring his health would have remained challenging.