Thoracoscopy is a minimally invasive operative procedure for the examination of the pleural cavity and its organs. With the development of high-resolution microcameras, video optics, and fiberoptic light delivery systems, clear magnified images of the surgical field can be transferred to a video screen. The ability to perform diagnostic and advanced therapeutic procedures is possible with minimally invasive video-assisted endoscopy in combination with minimally invasive surgical instruments.
Instrumentation
The basic equipment to perform a thoracoscopy includes a surgical telescope, trocar-cannulas, a basic set of thoracoscopic surgical instruments, a light source, a video camera and a video monitor. Thoracoscopy does not require CO2 insufflation since the rib cage is maintaining the thoracic cavity expanded.
Telescopes used for thoracoscopy are most commonly of 5 mm in diameter. This size of scope can be used in a wide range of animals. Telescope comes with different angles. The most commonly used telescopes are the forward-view 0°-degree and the forward oblique 300-degree. The 0° degree telescope allows a natural field of view and a normal perspective to organ orientation. The 300-degree telescopes give a better visualization of part of the thoracic cavity difficult to access. However, the orientation and the manipulation are more difficult with the angled scopes.
The trocar-cannulas used during thoracoscopy are usually 12 mm in diameter. They allow introduction of instruments and surgical stapling devices within the thoracic cavity. The trocar has a blunt tip. The cannula is short which increases the maneuverability of the thoracoscope and the instruments. The cannula for thoracoscopy does not have a valve at the end. When those cannulas are used, mechanical ventilation is necessary because of the open communication between the thoracic cavity and the atmosphere. Laparoscopic cannulas with an airtight seal can be used and a control pneumothorax is then established during the procedure. Mechanical ventilation might not be required. However, the risk of tension pneumothorax is higher.
A standard laparoscopic light source is used for thoracoscopy. The light source provides illumination to the telescope via a light cable. Light sources typically range from 150 to 300 W. The most powerful light sources are necessary in the large breed dog to be able to visualize the entire thoracic cavity.
Numerous instruments are available for endoscopic exploration and surgery. The basic instrument set consists of grasping forceps, scissors, biopsy forceps and a palpation probe. Forceps and scissors are isolated for electrocautery. Electrocautery can be used to cauterize small blood vessels during resection of mediastinum or the pericardium. Pre-tied ligatures are available for lung biopsy. They eliminate the need for knot tying inside the thoracic cavity. Surgical stapling devices are available for thoracoscopic procedures. Vascular clips and EndoGIA are the 2 most common stapling equipment used. Vascular clips come in medium (5 mm), and medium large (10 mm) sizes. EndoGIA comes in three different lengths for the cartridges: 30, 45, and 60 mm. Staples are 2.0, 2.5, 3.5 or 4.8 mm long before closure. The EndoGIA places 6 rows of staples and cut in between.
Thoracoscopy technique
Gas inhalation and mechanical ventilation are recommended for thoracoscopy. Lung volume and motion during ventilation is interfering during thoracoscopy. It is recommended to reduce the tidal volume of the ventilation and to increase the frequency of ventilation to compensate. The lungs are not going to occupy the entire thoracic cavity, which will allow a better visualization of the rest of the organs. One-lung ventilation technique with selective intubation of either the left or the right lungs will allow a better exposure of specific area of the thoracic cavity. One lung ventilation is strongly recommended when a surgical procedure (i.e., lung lobectomy, vascular ring dissection) have to be performed. One entire lung is going to be excluded during the procedure. A bronchial blocker can be used instead of selective intubation to achieve one-lung ventilation. The blocker will be placed in the lung lobe that needs to stay deflated. When one-lung ventilation is used, the non-ventilated lung is going to collapse. The non-ventilated lung is then creating a shunt, which results in severe hypoxemia. Arterial blood gases are needed to monitor oxygenation of the patient. Positive end expiratory pressure can be applied to improve oxygen saturation during one lung ventilation.
The thoracic cavity can be approached by a trans-diaphragmatic or an intercostal technique. The trans-diaphragmatic approach allows visualization of both hemi-thoraces with a long axis view. Trans-diaphragmatic approach allows exploration of the ventral part of the thorax, the pericardium and the cranial mediastinum. The caudal part of the thorax can be visualized if the thoracoscope is inserted through one of the intercostal cannula. The intercostal approach allows the exploration of only one hemi-thorax. It provides better visualization for a surgical intervention during thoracoscopy.
Transdiaphragmatic sub-xyphoid approach
The patient is positioned in a dorsal recumbent position. First, a screw-in cannula is inserted in a sub-xyphoid position in a cranial direction. Before insertion of the screw in cannula, a small skin incision is performed caudal to the xyphoid. The cannula is screwed in the thoracic cavity under thoracoscopic visualization. The cannula should be directed toward one the hemithorax at a 300-degree angle from the xyphoid. If the cannula is too perpendicular to the skin the cannula will penetrate in the abdomen between the diaphragm and the liver. After penetration in the thoracic cavity by the cannula, the thoracoscope is advanced in the thoracic cavity. After a first exploration of the thoracic cavity, two other cannulas are placed under thoracoscopic visualization to allow utilization of instruments. Cannulas are placed in intercostal spaces according to the pathology to explore or treat. Cannulas need to be placed as ventral as possible to allow maximum mobility of the instruments. Internal thoracic arteries should be visualized before placing the cannulas. A palpation probe can be introduced to move lung lobes and to allow exploration of the hilus of the lungs.
Intercostal approach
The patient is positioned most commonly in a lateral recumbent position. The trocar for the thoracoscope is usually introduced in the 9th or 10th intercostal space at the junction of the dorsal and middle third of the thoracic wall. Additional cannulas are placed in a triangular fashion in the 4th or 5th intercostal space. Cannulas are inserted after small skin incision and dissection of the sub-cutaneous tissue with a hemostat. The cannula and the blunt trocars can then safely be introduced under thoracoscopic visualization. Hilar lymph node biopsy, lung lobectomy and pericardectomy can be performed through this approach. Intercostal thoracoscopy on the right side allows a good inspection of the right atrial appendage after pericardectomy.
After completion of the procedure, a thoracic drain is placed under thoracoscopic control. The cannulas are removed and the site of introduction inspected for bleeding. The cannula used for the thoracoscope is removed last. The deep muscle layer is closed with a monofilament absorbable suture in a cruciate pattern. The intercostal muscles do not need to be closed after an intercostal approach. An intercostal nerve block is performed with bupivacaine. The skin is closed in a routine fashion. Negative pressure is established after removal of the cannulas. The thoracic drain is maintained for 12 to 24 hours.
Indications
Thoracoscopy is indicated for thoracic exploration, pleural effusion of unknown origin, pericardial effusion, lung resection and vascular ring anomaly. Biopsy of the pleural surface, lymph nodes and lungs can be performed during exploration of the thoracic cavity.
Biopsy of the pleural surface is performed with a biopsy forceps. Lymph nodes biopsy can be performed either with a biopsy forceps for hilar lymph nodes or after dissection and ligation of blood vessel for mediastinal lymph nodes. Ligation of blood vessels is better performed with endoclips. Careful sharp dissection should be done for mediastinal lymph node biopsy. Identification of the internal thoracic artery and cranial vena cava will be required prior to any dissection. Lung biopsies are best performed with an Endoloop suture. The tip of the lung is introduced in the loop and the sutured is tied using the knot pusher. The fragment of lung is then dissected with Metzenbaum scissors. Staples can be used to get a lung biopsy. A transdiaphragmatic sub xyphoid approach is recommended for thoracic exploration and biopsy.
Lung lobectomy is best performed in lateral recumbency and with an intercostal approach. Cannulas are placed in a triangulation fashion. Special stapling equipment (Endo GIA) is used to perform a lung lobectomy. The Endo GIA is placed perpendicular to the bronchi and blood vessels of the lung lobe to resect. Therefore, a cannula has to be placed in a location to allow the correct positioning of the Endo GIA. After dissection of the lung lobe, the Endo GIA is introduced in the thoracic cavity and placed at the hilus of the lung lobe. After placement of the staples, the lung lobe will be exteriorized through a small intercostal thoracotomy. The tissue sample can be placed in an Endopouch prior to exteriorization to prevent seeding of neoplastic cells. EndoGIA 45 3.5 is recommended for lung lobectomies in dogs.
Pericardial window is performed with either a trans-diaphragmatic sub-xyphoid approach or an intercostal approach. Transdiaphragmatic approach allows a complete thoracic exploration. Intercostal approach provides a better exposition of the right atrium. The thoracoscope is introduced through the diaphragm. The 2 cannulas for instruments are placed in the in the right hemithorax. The phrenic nerves should be localized before starting the partial pericardectomy or the pericardial window. A grasping forceps with small sharp teeth is used to get a good bite in the pericardium. Pericardial fat may need to be dissected away in order to get a good bite in the pericardium. If the pericardium is under too much tension it might be interesting to partially drain the effusion to be able to get a better bite in the pericardial sac. After tenting the pericardium, Metzenbaum scissors with electrocautery are used to perform a pericardial window. The grasper is holding the pericardium away from the myocardium to prevent electrical stimulation of the myocardium with the cautery. A 4x4 centimeters window should be sufficient to drain adequately a chronic pericardial effusion without increasing the risk of herniation of the heart through the window. After completion of the window sternal lymph nodes should be biopsied.
Thoracoscopy is a safe and effective method for evaluating pathology without the expense and the morbidity of open thoracotomy. The view obtained via thoracoscopy is often superior to that obtained via open thoracotomy because the telescope can be placed directly on the lesion.