Surgical Management of Idiopathic Spontaneous Pneumothorax Ashley A. Magee, DVM, DACVS DoveLewis Annual Conference Speaker Notes

Transcription

1 Surgical Management of Idiopathic Spontaneous Pneumothorax Ashley A. Magee, DVM, DACVS DoveLewis Annual Conference Speaker Notes Introduction Spontaneous pneumothorax is an acute, life threatening disease of dogs and cats. It must be recognized swiftly and managed aggressively to effect a good outcome in these patients. This lecture will discuss the etiology of the various forms of spontaneous pneumothorax but then focus on the idiopathic form of the disease. The signalment, history and presenting clinical findings of patients affected with this condition and the appropriate diagnostic tests and differential diagnoses for patients with a pneumothorax will be reviewed. We will touch on medical management and then focus on surgical management of the disease, followed by a discussion of aftercare and prognosis. Case examples will be presented throughout the lecture as well as the conclusion of the lecture, time permitting. Etiology Spontaneous pneumothorax can be defined into two categories, primary and secondary. Primary spontaneous pneumothorax is defined is defined as an air leak from the lungs in a patient not associated with trauma or underlying airway disease. Secondary spontaneous pneumothorax occurs in association with a preexisting disease process mass, abscess, or chronic lower airway disease, for example. While the etiology of secondary pneumothorax is related directly to the underlying disease process (pneumonia resulting in necrosis or abscessation, asthma, etc.), in primary spontaneous pneumothorax the cause is usually the rupture of a bulla or bleb. When evaluated histologically, no obvious cause for bulla formation is found; hence the name idiopathic or primary spontaneous pneumothorax. No definitive cause for bulla or bleb formation has been found in dogs, other than when they form secondary to chronic severe lower respiratory disease. Bulla formation as a latent result of trauma has been postulated but not proven and some feel that these lesions may be congenital in nature. In humans, mutations associated with alpha-1 antitrypsin have been reported, but so far, this has not been identified in canines. In cats, primary spontaneous pneumothorax is exceedingly rare and in one retrospective all 35 cases reviewed had underlying lung disease. A bulla is defined as a rupture of alveoli resulting in a confluence of alveolar space trapping air, and a bleb is localized air trapped within the visceral pleura. In general, bulla are larger then blebs. Bulla tend to be found near the base of the lungs within the pulmonary parenchyma, and blebs are often found at the periphery. Bullae/blebs can form secondary to chronic upper and lower airway disease, as well as secondary to parasite migration (d. immitis, p. kellicotti) and have been noted as an incidental finding in patients with a history of previous thoracic trauma. 1

2 In the case of either form of spontaneous pneumothorax, the result is a closed, bilateral pneumothorax that rapidly worsens due to continued air accumulation as the patient breathes (tension pneumothorax). Trapped pleural air causes compression and collapse of the lung parenchyma and of the great vessels resulting in decreased ventilation and perfusion, with onset of hypoxia, metabolic and respiratory acidosis and shock. Thus this condition is often rapidly fatal if not detected and treated appropriately. Signalment: Primary spontaneous pneumothorax predominately occurs in large, deep chested canine breeds. The Siberian Husky appears to be overrepresented. Males and females are equally represented and no age predilection has been reported. History: An acute onset of respiratory distress is usually reported, with onsets of as short as one hour to as long as three days reported. Occasionally a brief period of coughing is noticed along with restlessness and reluctance to lay down. Physical examination findings: Patients present with varying degrees of tachypnea and dyspnea, often with abdominal effort. Pale, muddy or cyanotic mucous membranes are noted and oxygen saturation as measured by pulse oximetry is low. Lung sounds are decreased predominately dorsally and usually bilaterally. Tachycardia, thready pulses and hypotension are usually found. Patients are often anxious and can become distressed if restrained in lateral recumbency. Diagnosis: Confirmation of pneumothorax is made with thoracocentesis and thoracic radiography. In distressed patients thoracocentesis should be performed as soon as the index of suspicion arises as it is highly therapeutic as well and restraining and sedating patients with a severe pneumothorax can have devastating consequences. Computed tomography of the thorax is another imaging modality used in these cases when the origin of the leak cannot be ascertained by plain radiographs but its reliability in effectively detecting bulla and blebs has been questioned. Differential diagnosis: Once the diagnosis is of a pneumothorax is confirmed, all other causes of pneumothorax are ruled out before a diagnosis of primary idiopathic pneumothorax is made. Differentials include traumatic causes (blunt or penetrating thoracic trauma), iatrogenic causes (recent endotracheal intubation, thoracic surgery or lung biopsy), or pneumothorax secondary to preexisting pulmonary pathology (ruptured mass, abscess, migrating foreign body, parasite migration, or chronic lung disease). Sometimes a bulla can be seen on initial radiographs but more often they are collapsed and not detected. Therefore, diagnosis of primary spontaneous pneumothorax is often a diagnosis of exclusion. The patient should be evaluated carefully for any evidence of occult trauma or wounding over the thorax and radiographs reviewed for evidence of pulmonary pathology or pleural fluid accumulation. A complete blood count, serum chemistry panel, urinalysis and blood gas measurements are also helpful in assessing the current status of the patient and ruling in or out concurrent disease. Coagulation tests should be run in severely compromised patients. Stabilization and initial management: 2

3 Patients presenting in respiratory distress should have immediate access to flow by 100% oxygen administered by mask, nasal prongs or oxygen cage. Low doses of reversible opioid sedation can be used for pain and anxiety control if needed. Bilateral thoracocentesis to negative pressure should be performed aseptically after clip and prep. IV catheter placement and fluid therapy can help counteract hypovolemic shock and any electrolyte and acid base derangements. Shocky patients should be kept warm to prevent further hypotension and other systemic derangements (coagulopathy, worsening acidosis) resulting from hypothermia. Thoracocentesis is performed as needed determined by patient s clinical status. Medical management: In contrast to the more typical traumatic closed pneumothorax, repeated thoracocentesis is unlikely to be effective in evacuating the large volumes of air entering the thorax in patients diagnosed with primary spontaneous pneumothorax. Because the leak is in an abnormal area of lung (bulla or bleb) and rupture is not associated with bleeding or inflammation, sealing of the leak is unlikely with intermittent evacuation alone and thoracostomy tubes are indicated for more complete and rapid removal of accumulating air. Applying continuous negative pressure (Pleuravac) to the tubes can be very beneficial but it requires an increased level of intensive nursing to maintain. In patients with pneumothorax due to a presumed or documented bulla or bleb, reported success with medical management with thoracostomy tubes is sub optimal, with only about 50% of patients achieving resolution of the pneumothorax and of those about half will have a recurrence in their lifetime. Methods that have been reported to improve the success of medical management include placement of pleural access ports (50% success) and autologic blood patch treatment (87% success) but the reported case numbers were quite small. Therefore, surgery is currently recommended for patients with a documented bulla or bleb, or in patients with no pathology detected that fail a period of medical management. Anesthesia: Perhaps one of the most challenging aspects of of these patients is anesthetic management for diagnostics and surgery. While these patients may seem stable if their pleural space is evacuated of air and they are awake, once they are anesthetized, recumbent and being ventilated, they can rapidly deteriorate without careful management. Anesthesia and surgery requires a team of experienced technicians and DVMS in order to efficiently and safely process the patient through induction, additional imaging and surgery. Every effort to minimize anesthetic time and maximize the patient s vital parameters during this time must be made. Anesthetic protocols require multimodal anesthesia, a combination of gas anesthetic and intravenous drugs to allow precise control of depth while minimizing loss of systemic vascular resistance. Chest tubes must be kept evacuated during positive pressure ventilation to as air accumulation in the pleural cavity rapidly prevents adequate ventilation and perfusion. Once the thorax is opened and until leaks are corrected, total IV anesthesia is used to avoid operating room personnel exposure to inhalant gasses. Surgery: Surgical resolution of primary spontaneous pneumothorax requires a thorough exploration of the chest and lung parenchyma. Median sternotomy allows access to the entire thoracic cavity and all the lung lobes, but access to the base of the lobes is challenging, especially in large, deep chested dogs. A fifth or sixth intercostal thoracotomy allows access to all lung lobes and the lung hilus for complete lobectomy but does not allow concurrent exploration of the opposite 3

4 hemithorax. Because blebs and bulla are often found in multiple lobes, bilateral exploration is usually recommended, especially in light of recent evidence that CT can be misleading with the respect of the number of detected bulla and blebs. If an intercostal thoracotomy is performed to remove a lobe with a documented lesion, exploration of the other hemithorax can be done with a second intercostal thoracotomy after repositioning the patient, or thoracoscopy can be performed. Unfortunately, use of video assisted thoracic surgery in the diagnosis and treatment of bulla and blebs also has its limitations and is associated with a high rate of conversion to open surgery due to failure to identify leaking lung tissue. If a lesion is suspected in the area being evaluated but cannot be directly visualized, conversion to an open procedure is required. Regardless of surgical approach, the goals of surgery are to identify and remove leaking lung tissue, and remove any abnormal non leaking tissue to minimize chances for a second event. All lung surfaces should be carefully explored and lungs submerged in saline to detect both major and minor leaks. Often when the correct hemithorax with the major leak is opened, anesthetic gas will immediately be detected. The patient is then switched to total IV anesthesia until the leak can be controlled. Partial or complete lung lobectomy is performed depending on size, location and number or lesions. Rarely, diffuse disease is found and when complete resection would require removal of greater than 50% of the lung volume, pleurodiesis can be attempted to encourage fibrosis of the visceral and parietal pleura. Abrasion with a dry sponge and instilling blood into the pleural cavity both have reported successes when paired with continuous pleural evacuation in patients with non-resectable lesions or that are otherwise not candidates for surgery. Post-operative management: The patient is recovered with oxygen supplementation and this is continued for the first 12 hours after surgery when possible. Bilateral thoracic drainage tubes are maintained post-operatively for hours. This allows for removal of residual trapped pleural air and fluid as well as instillation of local anesthetic for post-operative pain control. Other methods of pain control include intercostal nerve blockade, opioid and other analgesic infusions and oral medications, transdermal systems of opioid or local anesthetics, and NSAIDS. When using local anesthetics with multiple modes of delivery, care must be taken not to exceed the recommended total dose in order to avoid overdose complications. Patients are maintained on intravenous fluids and electrolytes until eating and drinking. Antibiotics started in the preoperative phase at the time of chest tube placement are continued until return of culture results taken at surgery or at time of thoracic tube removal. Bacterial culture is important especially in patients undergoing repeated thoracocentesis and prolonged thoracostomy tube management because infection either from the airways or introduced via skin or tubes is a potentially devastating complication. The thorax is protected under a bandage from surgery to suture removal in most cases to provide protection, cleanliness and compression. Strict exercise restriction is instituted for 4-6 weeks depending on the surgical approach. Follow up radiographs are taken immediately post-operatively and recommended again in 4-6 weeks post-op prior to return to full activity. Healing of the sternum as well as evaluation of the lung fields is required in patients that underwent median sternotomy. 4

5 Reported complications: Adverse events associated with thoracic surgery for primary spontaneous pneumothorax are varied and include anesthetic complications, hemorrhage, anemia/hypoproteinemia, failure to resolve the pneumothorax, aspiration or hospital acquired pneumonia, pleuritis, recurrent pneumothorax, surgical site seroma, infection and/or dehiscence. In patients that sustained a significant hypoxemic and/or hypotensive event prior to or during surgery, multiorgan dysfunction, SIRS, ARDS or DIC are significant risks. Outcome: While data in veterinary species is limited, reported prognosis is good for long term survival in patients managed surgically, with recurrence reported between 0% and 25%. In patients where their condition was initially managed successfully medically, reported recurrence rates are close to 50%. References: Puerto DA, Brockman DJ, et. al. Surgical and nonsurgical management of and selected risk factors for spontaneous pneumothorax in dogs: 64 cases ( ). J AM Vet Med Assoc 2002 Jun1;220(11): Maritato K, Colon JA, Kergosien D. Pneumothorax. Compendium 2009 May; 31(5). Reetz JA, Caceres AV, et. al. Sensitivity, positive predictive value, and intraobserver variability of computed tomography in the diagnosis of bullae associated with spontaneous pneumothorax in dogs:19 cases ( ). J Am Vet Med Assoc 2013 Jul 15;243(2): Case JB, Mayhew PD, Singh A: Evaluation of video-assisted thoracic surgery for treatment of spontaneous pneumothorax and pulmonary bullae in dogs. Vet Surg 2015 Jul; 44 Suppl. 1:31-8 Lipscomb VJ, Hardie RJ, Dubielzig RR: Spontaneous pneumothorax caused by pulmonary blebs and bullae in 12 dogs. J Am Anim Hosp Assoc 2003 Sept-Oct; 39(5): Jerram RM, Fossum TW, et.al The efficacy of mechanical abrasion and talc slurry as methods of pleurodiesis in normal dogs. Vet Surg 1999 Sept-Oct;28(5): Oppenheimer N Klainbart S et. al. retrospective evaluation of the use of autologous blood-patch treatment for persistent pneumothorax in 8 dogs ( ). J Vet Emerg Crit Care (San Antonio) 2014 Mar-Apr;24(2): Cahalane AK, Flanders JA: Use of pleural access ports for treatment of recurrent pneumothorax in two dogs. J Am Vet Med Assoc Aug 15;241(4): Grubb T: Anesthesia for patients with respiratory disease and/or airway compromise. Top Companion Anim Med 2010 May;25(2): Mooney ET, Rosanski EA, et.al. Spontaneous pneumothorax in 35 cats ( ). J Feline Med Surg 2012 Jun; 14(6):

6 Trempala CL, Herold LV: Spontaneous pneumothorax associated with Aspergillus bronchopneumonia in a dog. J Vet Emerg Crit Care (San Antonio) 2013 Nov-Dec; 23(6): Boudreau B, Nelson LL, et.al. Spontaneous pneumothorax secondary to reactive bronchopneumopathy in a dog. J Am Vet Med Assoc Mar 1;242(5): Oliviera C, Rademacher N, et. al. Spontaneous pneumothorax in a dog secondary to Dirofilaria immitus infection. J Vet Diagn Invest Nov;22(6):