Managing diaphragmatic hernias (Proceedings)

A hernia is an abnormal protrusion of an organ or part of it through the containing wall of its cavity, beyond its normal confines. A diaphragmatic hernia is a protrusion of the abdominal viscera through the diaphragm. In the dog and cat, traumatic diaphragmatic hernias are common, whereas the congenital type is infrequently seen. The diaphragm is not essential for life as the entire diaphragm can be removed in a newborn cat or dog and the animal will survive.

Applied anatomy

The diaphragm is a musculotendinous structure that separates the thoracic and the abdominal cavities. The diaphragm projects into the thoracic cavity like a dome. On the thoracic side it is separated from the pleura by the endothoracic fascia and on the abdominal side, is separated from the peritoneum by the transversalis fascia. The fascia and serosa are so thin in the dog that over the tendinous portion they can only be visualized microscopically. Diaphragm attaches to the lumbar vertebrae, the ribs, and the sternum. Contraction of the diaphragm is a major force contributing to ventilation. The diaphragm is composed of a U shaped central tendon and 4 muscle groups: the pars sternalis, the pars lumbalis and the paired pars costalis. The pars lumbalis of the diaphragmatic musculature is formed by the right and left diaphragmatic crura, the right crus being considerably larger than the left. Seen from the abdominal cavity each crus of the diaphragm is a triangular muscular plate whose borders produce the tendinous portions. The musculature of the crus medial is the thickest (5-6 mm). The pars costalis on each side consists of fibers radiating from the costal wall to the tendinous center. The pars sternalis is an unpaired medial part unseparated from the bilateral costal portions. The diaphragm is composed of only one layer of muscle and two layers of tendon and therefore is weaker than the multilayered abdominal wall. The central tendon of the diaphragm of the dog is relatively small. In its tendinous portion, transverse fibers course from one side to the other as a reinforcing apparatus. The motor innervation of the diaphragm is supplied by the paired phrenic nerves. The phrenico abdominal arteries are the principal blood supply to the diaphragm. Several structures traverse the diaphragm through one of the three foramens. The caval foramen is located in the central tendon and allows passage of the caudal vena cava. The esophageal hiatus and aortic hiatus are located in the pars lumbalis of the diaphragm. The esophageal hiatus allows passage of the esophagus and vagal trunks. The aortic hiatus is bordered by the paired crural tendons and permits passage of the aorta, azygous vein, and thoracic duct.

The stomach and liver attach by ligaments to the concave peritoneal surface of the diaphragm.

Types of diaphragmatic hernias

     • Congenital pleuroperitoneal hernia

     • Congenital peritoneopericardial hernia: most common congenital diaphragmatic defect, may remain asymptomatic, associated with other midline defects: ventricular septal defect, abdominal hernia.

     • Traumatic diaphragmatic hernia: the most common form in dogs and cats: 80% of the cases. Nature of the trauma, multisystem injury, and shock are potential complications in traumatic diaphragmatic hernia

     • Hiatal hernia: usually congenital, common in Sharpei, sliding (Figure 1) or paraesophageal.

Figure 1

Diagnosis

Diaphragmatic hernia often is missed during the initial assessment after trauma, so a high index of suspicion for this condition should be maintained in animal that had experienced significant trauma. Clinical findings that suggest diaphragmatic hernia include dyspnea, tachypnea, cyanosis, paradoxical breathing, and muffled heart and lung sounds. The abdomen may appear empty on palpation. Auscultation may reveal muffled heart and lung sounds on one side of the chest. Radiographic findings that support a diagnosis of diaphragmatic hernia include loss of the diaphragmatic silhouette, pulmonary atelectasis, and presence of fluid dense structures in the chest or the pericardial sac. A gastric or bowel gas pattern within the thoracic cavity or the pericardial sac confirms the diagnosis. An upper gastrointestinal study might be required to confirm the diagnosis. Megaesophagus is commonly associated with a hiatal hernia.

Chronic diaphragmatic hernia occurs as a delayed presentation or failure of diagnosis after trauma. Presentation for chronic diaphragmatic hernia can occur years after the original trauma. Usually presentation is due to entrapment of a liver lobe that produces significant pleural effusion.

Preoperative considerations

Immediate surgical intervention for the repair of a diaphragmatic hernia is rarely indicated. Traumatic diaphragmatic hernia is a life threatening condition. It causes several concurrent pathophysiologic derangements. Ventilation is impaired by loss of diaphragm contraction and pleuropulmonary coupling. Gas exchange is impaired by pulmonary atelectasis as well as reduced resting lung volume. Ventilation perfusion mismatch and shunt are present. Oxygen delivery is impaired by decreased cardiac output resulting from impingement of venous return. Patients may also be compromise by trauma to other abdominal organs. Acute distension of a herniated stomach will further compromise the ventilation function and cause death in few minutes. Initial therapy of diaphragmatic hernia is primarily supportive, consisting of supplement oxygen, shock therapy, and treatment of concurrent injuries. Surgical correction should be undertaken early, usually within several hours after presentation. Delaying surgery beyond a few hours only increases the likelihood of cardiopulmonary decompensation and death. Some animals present with severe cardiopulmonary depression that will not stabilize with oxygen and other supportive therapies. In this case surgical correction should be undertaken without delay.

Surgical approaches

The dog or cat is positioned in dorsal recumbency The midline abdominal approach is the easiest and most versatile approach and is therefore the most commonly used. In some cases of congenital hernias or chronic diaphragmatic hernia where thoracic adhesions and/or complicating thoracic injuries are suspected the surgeon should be prepared to perform a median sternotomy. By far the most common approach used is the abdominal midline.

Surgical procedure

Diaphragmatic and peritoneopericardic hernias.

Using the abdominal approach, an incision is made from the xiphoid cartilage to the umbilicus. This incision can easily be extended if necessary. Once the peritoneal cavity is opened, the diaphragm is exposed and the situation evaluated. Some hernias, especially in the area of the dorsal attachments of the crura and the aortic hiatus are not easily visualized; therefore, this area should be carefully inspected even when another laceration is present. The herniated contents are replaced in their proper position and inspected for damage. Some of the complicating injuries that the surgeon must be prepared for a torsion of one or more liver lobes, ruptured viscus, intestinal intussusception, costal abdominal hernia, and others. If adhesions exist, they should be broken down using blunt dissection so as to avoid excess hemorrhage and inadvertent damage to a vital structure. Occasionally, in chronic cases, the hernial ring has to be excised because of adhesions between it and herniated structure. Those parts of the hernial ring that might be adhered to the liver should be dissected free from the diaphragm rather than stripping them from the liver and creating a raw bleeding surface.

Using large sponges or laparotomy pads moistened with warm saline, the liver and bowel are retracted laterally and posteriorly. The diaphragmatic tear is now more easily visualized so that a careful examination of the thorax can be done both visually and manually. All thoracic fluid should be aspirated. The lungs should be expanded to remove atelectasis and to inspect for pulmonary tears and persistent areas of collapse. The re-expansion of the lung parenchyma should be slow. Pulmonary edema could be a complication during re-expansion especially in cat after chronic diaphragmatic hernia. If the hernia is more than 48 hours old, the edges of the tear should be debrided. The hernia is closed using a single layer of absorbable material or nonabsorbable material. The suture size should be 4-0 in cats and small dogs and 3-0 in medium and larger breed dogs. It might be necessary to preplace the most dorsal sutures for better visualization of the tear during suturing. It is also helpful to reconstruct the tear with several simple interrupted sutures to facilitate visualization of the rent. When tears around the caudal caval foramen are sutured, larger stitches are to be avoided so as to prevent constriction of the vena cava. The same principle applies to the aortic and esophageal hiatus. When beginning the continuous suture line, this author finds it helpful to begin dorsally and work ventrally. Chronic diaphragmatic hernia may require a muscle flap (transverse abdominalis muscle) or an omentum flap to close the defect.

A thoracostomy tube should be placed for evacuation of the pleural space should be placed prior to complete closure of the diaphragm. The most convenient placement for the thoracostomy tube is the subcostal position just lateral to midline. Closure of the diaphragm is completed. With the use of a 3-way stop cock and 60 cc syringe, air is evacuated from the thorax until a gentle negative pressure is obtained. The celiotomy incision is closed in a routine fashion. When the celiotomy closure is complete, the tube is again aspirated. The patient should then be placed through a series of positional changes (ventral recumbency, right lateral recumbency, left lateral recumbency, and dorsal recumbency) while attempting to aspirate air. The patient is monitored carefully for the next six to eight hours.

Hiatal hernia

The purpose of the procedure is to bring back the lower esophageal sphincter in the abdominal cavity. Using the abdominal approach, an incision is made from the xiphoid cartilage to the umbilicus. This incision can easily be extended if necessary. Once the peritoneal cavity is opened, the diaphragm is exposed and the situation evaluated. The hernia is reduced by gentle traction on the stomach and the esophagus. The omentum, small intestine, and liver lobes can also be herniated. After reduction of the hernia the redundant phrenicoesophageal ligament is excised while preserving the vagal trunks.(Figure 2) The esophageal hiatus is reduced by mattress sutures placed in the medial diaphragmatic crura.(Figure 3) The hiatus is reduced to size of a finger. A simple esophagopexy is performed by placing interrupted sutures between the ventral esophagus and the diaphragmatic crura. A tube gastrostomy is then performed between the gastric fundus and the left abdominal wall. A thoracostomy tube should be placed for evacuation of the pleural space should be placed prior to complete closure of the hiatus.

Figure 2

Postoperative care

Post-surgical care includes systemic antibiotics and careful monitoring of the patient's breathing, temperature, and color. Small dogs and cats should be kept on a warming device for at least 24 hours. If complete bandaging of the chest is done, it should not be applied tightly because of the restriction of breathing. Analgesics may be used to relieve pain so that the animal can breathe more freely. The thoracostomy tube is checked every hours for the first 4 hours and then every 4 hours. The thoracostomy tube can usually be removed 24 hours after the surgery.

Figure 3

The gastrostomy tube after hiatal hernia is kept for at least 7 days. The stomach can be decompressed with the tube every 4 to 6 hours. Medications such as famotidine, sucralfate and metoclopramide can be administered through the tube.