Stephen J. Birchard DVM, MS, Diplomate ACVS

Tuesday, September 18, 2018

How To Repair Diaphragmatic Hernias in Dogs and Cats

   Hernias of the diaphragm can be either congenital or acquired. Acquired hernias are most commonly due to blunt trauma to the abdomen.  Increased intra-abdominal pressure causes the diaphragm to stretch and rupture.  Liver, spleen and intestines are the organs most commonly herniated into the thoracic cavity.(1)  The muscular portion of the diaphragm, at its ventral and lateral aspects, is the most frequently torn area. Congenital hernias include the pericardial peritoneal diaphragmatic hernia (PPDH).

   Clinical Signs  
   Signs of respiratory distress, e.g., tachypnea, dyspnea, or abdominal breathing, are most common.  The animal may have a "tucked-up" appearance to the abdomen due to shifting of viscera into the pleural space.  In chronic cases, weight loss and lethargy may be the only signs the owners describe.(2) Exercise intolerance is also usually seen. In rare cases, the owner may describe signs referable to other organ systems.  For example, herniation of the intestine can cause obstruction of bowel, resulting in vomiting.  Herniation of the liver and biliary system can cause extrahepatic biliary obstruction, causing elevated serum bilirubin and icterus. 
   Auscultation of the thorax reveals decreased lung sounds ventrally, and muffled heart sounds.  The thorax is dull on percussion.  Reportedly, auscultation of borborygmus in the thorax is a sign of diaphragmatic hernia, but this is not a consistent finding and should not be depended upon to make the diagnosis.
   Radiographic examination of the thorax may reveal fluid densities and/or bowel loops in the thorax. (Fig 1) Loss of continuity of the diaphragm is also seen. 
Fig. 1: Lateral thoracic radiograph of a dog with a diaphragmatic hernia and
several loops of bowel in the thoracic cavity. 
Hydrothorax may be the only radiographic sign if the liver is the only organ herniated into the thorax.  This fluid appears serosanguineous and is a transudate or modified transudate.  Ultrasonographic examination of the cranial abdomen can help confirm the hernia. 
   Preoperative Care  
   Diaphragmatic herniorraphy is usually considered an emergency operation. Although historically some authors advocated delaying surgical repair for several hours (3), a more recent study found that patients operated within the first 24 hours after presentation had very good outcomes (90% survival) (4). If the animal with diaphragmatic hernia does not stabilize with initial supportive care or if stomach or strangulated bowel is in the thorax the repair must be done immediately.(5) Stomach in the thorax can become dilated with air and cause life threatening hypoventilation. (Fig. 2) 
Fig. 2: Lateral thoracic radiograph of a dog with diaphragmatic hernia and stomach in the thorax cavity.
The stomach is severely dilated with air. 
If this occurs, pass a stomach tube to initially decompress the stomach If a stomach tube cannot be passed perform gastrocentesis percutaneously by placing a needle or over the needle catheter into the stomach through the chest wall.  When respiratory parameters have improved, anesthesia and surgery can then be performed.
   Since these patients have markedly reduced ventilatory capacity, anesthetic induction and intubation must be rapid and smooth.  Pre-oxygenation of the patient in an oxygen cage or with an anesthetic mask is helpful to prevent hypoxia during the stress of anesthetic induction.  Rapidly acting intravenous induction agents, such as propofol, allow prompt intubation.  Begin positive pressure ventilation as soon as the endotracheal tube is placed.  Inhalant anesthetics, such as isoflurane, are acceptable for maintenance of anesthesia.
   During the clipping and prepping of the animal for surgery, the prep table can be tilted so that the head is elevated and the hindquarters lowered.  This helps prevent movement of abdominal viscera into the thorax.  
   Key Point: It is important to realize that when the abdominal cavity is surgically opened in an animal with diaphragmatic hernia, the animal will no longer be able to ventilate on its own. The rent in the diaphragm allows air to enter the thoracic cavity when the abdomen is open, eliminating the negative intrathoracic pressure that is necessary for normal ventilation. Intermittent positive pressure ventilation (IPPV) is therefore necessary during the surgical repair of the diaphragm. 
   The ventral midline abdominal approach is indicated for most diaphragmatic hernias. (Fig. 3) 
Fig. 3: Intraoperative appearance of a left diaphragmatic hernia
exposed via a ventral midline abdominal approach.
(arrows indicate edges of the ruptured diaphragm).
The liver is present in the thoracic cavity.
Balfour retractors and large malleable retractors facilitate the exposure.  Grasping the edges of the diaphramatic defect with Babcock forceps or stay sutures can help in closure of the defect.  In many cases, the diaphragmatic defect must be enlarged to allow the viscera to be pulled back (reduced) into the abdomen.  When enlarging the defect, be sure to make the diaphragmatic incision in an accessible portion of the diaphragm to simplify closure. Chronic hernias may be associated with adhesions between the herniated organs and the lungs or mediastinum.(2) Break these down carefully to avoid injury to lung or other organs.  After reducing herniated organs back to the abdominal cavity carefully examine the lungs for evidence of atelectasis.  If atelectasis is found it is best not to acutely re-expand those lung lobes since re-expansion pulmonary edema can occur.  This is especially true in chronic hernias.  Place a thoracic drain tube before closure of the diaphragm to allow for re-establishment of negative pressure in the pleural space once the diaphragmic rent is repaired.  
   A variety of techniques for herniorrhaphy have been described.  The author prefers a continuous suture pattern using 2-0 or 3-0 PDS depending on patient size. Suturing is begun at the most inaccessible area of the defect (usually the dorsal aspect) progressing to the most accessible.(Fig 4) 
Fig. 4: Same dog as in figure 3 after suture closure of the diaphragmatic hernia.
Be very careful when working around the central part of the diaphragm because of the caudal vena cava.  Take care to not make the closure too tight around the caval hiatus.  Incorporation of the ribs with the soft tissues during suturing is sometimes necessary for those hernias that occur along the costal arch.
   In rare cases there is not enough diaphragmatic tissue to permit primary closure.  For example, chronic hernias in which the diaphragmatic tissue tears directly off the costal arch or dorsally from the spine.  In these cases reconstruction of the defect with a mesh implant such as Marlex mesh can be used.  The mesh is sutured in place with non-absorbable sutures such as monofilament polypropylene.  Prophylactic antibiotics are indicated in these cases.
   Once closure of the diaphragm is completed, remove residual air from the thorax.  This can be done either directly through the diaphragm using a needle or over the needle catheter or by placing a thoracostomy tube. When postoperative pneumothorax is a potential problem, such as those cases with lung adhesions, an indwelling thoracic drain tube should be placed and left in for as long as necessary to ensure stable negative intrapleural pressure. As previously mentioned in animals with chronic hernias and lung atelectasis, slowly evacuate the air in the pleural space over several hours to prevent re-expansion pulmonary edema. 
   Postoperative Care 
   Close observation of the patient is mandatory postoperatively.  If available the patient is kept in an oxygen cage until recovered.  In most cases recovery is unremarkable.  Acute, severe pulmonary edema can occur in some animals postoperatively and must be treated aggressively using diuretics, oxygen, and assisted ventilation.  In general the prognosis for postoperative survival is very good for patients with either acute or chronic diaphragmatic hernias. (2,4)
1. Wilson GP, Newton CD, Burt JK. A review of 116 diaphragmatic hernias in dogs and cats. J Am Vet Med Assoc 1971; 159:1142-1145
2. Minihan AC, Berg J, Evans KL. Chronic diaphragmatic hernia in 34 dogs and 16 cats.
J Am Anim Hosp Assoc. 2004 Jan-Feb;40(1):51-63. 
3. Boudrieau RJ: Pathophysiology of Traumatic Diaphragmatic Hernia, in Bojrab MJ (ED): Disease Mechanisms in  Small Animal Surgery, ed 2. Philadelphia, Lea & Febiger, 1993, pgs 103–108
4. Gibson TW1, Brisson BA, Sears W. Perioperative survival rates after surgery for diaphragmatic hernia in dogs and cats: 92 cases (1990-2002).J Am Vet Med Assoc. 2005 Jul 1;227(1):105-9.
5.Bjorling DE. Thoracic Trauma, in Birchard SJ, Sherding RG, ed. Saunders Manual of Small Animal Practice. St. Louis, Elsevier, 2006, pgs. 1721-1722.