Minimally Invasive Surgery In Cats
Rhett Marshall BVSc MACVSc
The Cat Clinic
189 Creek Road,
Mt Gravatt, 4122.
Minimally invasive surgery (MIS) is a collective term for surgical techniques designed to minimise the extent of an anatomic approach while maintaining precision and efficiency. MIS is a new and rapidly advancing field in veterinary medicine, with new techniques and applications being published in nearly every monthly veterinary journal. The benefits of MIS in decreasing peri-operative pain and decreasing morbidity has well been accepted in human medicine and now also confirmed in animals. Reducing or minimising pain in animals has been a priority for modern veterinary clients and has fueled the pursuit of these veterinary laparoscopic and thoracoscopic techniques that cause minimal invasion.
Laparoscopy
Viewing the internal structures of the abdominal cavity via laparoscopy involves "insufflation’ of the abdominal cavity with carbon dioxide gas. This gas is used because it in non-flammable (when cautery is used), non toxic and inexpensive. Modern CO2 insufflating devices have a pressure limit (12-15mm Hg) that cannot be exceeded so that overdistention of the abdomen is prevented. Insufflation allows displacement of the abdominal wall from the underlying viscera so that instruments may be manipulated without trauma to the abdominal organs. A cannula is placed in the abdominal wall and a rigid telescope (laparoscope) inserted through and into the peritoneal cavity. Once the telescope is in place, biopsy forceps or surgical instruments can be introduced into the abdomen through adjacent cannulas to perform various diagnostic or surgical procedures.
Structures that can be visualized include the liver, gallbladder, kidneys, bladder, stomach, pancreas, spleen, small intestine, cecum, colon, uterus, ovaries, vas deferens, adrenal glands and diaphragm.
The advantages of laparoscopy compared with conventional open surgical exploratory laparotomy include improved patient recovery because of smaller surgical sites and lower postoperative morbidity with a lower infection rate and less postoperative pain. The complication rate of laparoscopy is low. A review of 360 consecutive cases of diagnostic laparoscopy performed by Eric Monnet at Colorado State University found a complication rate of less than 2%. Serious complications include anesthetic- or cardiovascular-related death, bleeding, or air embolism .
Few contraindications exist due to the minimal invasiveness of laparoscopy. Ascites, abnormal clotting times, poor patient condition or obesity are the only relative contraindications. Absolute contraindications to laparoscopy include septic peritonitis or conditions where obvious conventional surgical intervention is indicated. Patients who are a poor anesthetic or surgical risk are not suitable candidates and are even less suitable for conventional surgery.
The basic equipment required for diagnostic laparoscopy include
- telescope (0 or 30°)
- videocamera and monitor
- 2 cannulae (access into abdomen)
- veress needle (for initial safe insufflation)
- light source
- light guide cable
- carbon dioxide insufflator (to continuously inflate the abdomen)
- palpation probe
- oval biopsy forceps
- punch biopsy forceps
- grasping forceps
- scissors
- device for photographic documentation (optional)
Most major video endoscopy equipment required for laparoscopy, thoracoscopy, and arthroscopy may be used interchangeably. Things such as the light source, light guide, monitor, telescope (arthroscope), camera and printer may be interchanged and significantly reduce set up costs if you already have these large ticket items. Purchased new, this basic equipment could cost more than $60,000. Good quality second hand units are readily available from endoscopic suppliers such as Austvet or on e-bay and may cost as little as $10,000.
All types of modern MIS systems involve a video camera, light source and monitor. The video camera will be the most important determinant of your image quality on the monitor and often represents the largest investment. Camera image quality and is determined by how many chips they have. The more chips, the better the image and unfortunately the more expensive. The least expensive single chip cameras are adequate for routine procedures while modern 3 chip cameras provide increased image quality. Xenon fiber optic light sources are most commonly used for MIS as they are brighter and are necessary to provide adequate lighting in body cavities. A single chip camera with a Xenon light source would serve most practitioners well as it can be used for both soft tissue or arthroscopic procedures. The light guide cable connects the telescope to the light source so must also be compatible at both ends.
Telescopes and other minimally invasive surgical instruments (needle holders, curettes, forceps, etc) are more specifically designed for laparoscopy, thoracoscopy or arthroscopy. Telescopes are classified by their diameter and their length; the larger the diameter of the telescope, the more light and the better the image. Telescopes also come in zero-degree (looking straight ahead) to thirty-degree field of view. Angled scopes allow the operator an increased field of view, but can be confusing to beginners. Telescopes cost about $4000-6000 new and $1800-2500 second hand . The diameter of the telescope and instruments must correspond with the trocar-cannula units.
The procedure
The animal is clipped, prepared and draped for abdominal surgery. A Veress needle is used to safely penetrate the abdominal wall, then attached to insufflation tubing which connects to the automatic carbon dioxide insufflator. Carbon dioxide is considered to be the gas of choice for insufflation because of safety in preventing air emboli and spark ignition during cauterisation. After insufflation of the abdominal cavity, the trocar-cannula unit is placed through the abdominal wall and the trocar removed. Most cannulae contain an internal one-way valve that prevents loss of insufflated gas once the trocar is removed after abdominal entry. The cannula remains in place traversing the abdominal wall and creates a portal for the introduction of the telescope or instruments into the abdominal cavity.
The telescope and instruments can then be moved between cannulas as required. When finished, the telescope and instruments are removed, the insufflation tube detached so abdomen decompresses, cannulas removed and sutures placed in the muscle and skin as required.
Whats different in cats?
Their abdominal wall is very thin making it difficult and somewhat dangerous to normally insert a trocar-cannula. The thin muscle wall provides little grip to the cannulas making them easy to accidentally pull out while working. Cats require less intra-abdominal pressure to maintain a good surgical field (4-6mmHg compared to 8-15mmHg in the dog) and more readily develop complications such as reduced cardiac output from pneumo-peritoneum. Maximal insufflation allowed is hence lower for cats (10mHg for cat vs 15mmHg for dogs). The small dimensions of a cats abdomen and thorax requires telescopes and instruments with shorter working lengths (14-18cm compared to 20-30cm for dogs)
To optimise results, we use
- 3.5mm Endotip cannulas – the cannula screws through abdominal wall rather than blindly stabbing a sharp trocar to gain access. These threaded cannulas also resist falling out of muscle wall during use and are simply unscrewed after use leaving undamaged muscle fibres.
- 2.7mm telescope with 14cm working length
- 3mm instruments with uni-polar coagulation
- maximal insufflation of 6mmHg
Is there a place for laparoscopy in cats?
Client acceptance is excellent, the biopsy specimens are high quality and cats clearly benefit from reduced trauma. While the applications of laparoscopic surgical procedures continues to grow, it is likely that the main application of laparoscopy in cats will be diagnostic sampling. Initial set up costs is the major deterrent in veterinary medicine and this can be reduced by purchasing second hand equipment.
Thoracoscopy
Visualisation of lungs, pericardium, heart and major blood vessels, thoracic duct, mediastinum, lymph nodes and the pleural and peritoneal surfaces of the thoracic cavity can be performed with minimal invasiveness by placing a cannula in the chest wall and inserting a rigid telescope.
Thoracoscopy has been used in diagnosing spontaneous pneumothorax, pericardial effusions, pulmonary disease, pleural diseases, neoplasia (including determining margins and respectability), and determining the etiology of refractory pleural effusions. The most common minimally invasive thoracic surgical procedure currently being performed in small animals is creation of a pericardial window. Other thoracic procedures being performed include partial and total lung lobectomies, thoracic duct occlusion, PRAA transection, ligation of PDA, mediastinal mass removal and debridement for pyothorax.
The thorax can be entered trans-diaphragmatically (under xyphoid) or intercostally using a screw in Endo-tip cannula. The trans-diaphragmatic approach allows a long axis view of the thoracic cavity and is best for exploration and biopsy. Once a cannula is introduced, a pneumothorax developes causing the lungs to partially collapse and allows visualisation. Mechanical ventilation is therefore required. Additional cannulas are inserted under thoracoscopic visualisation and instruments inserted as required. Once the telescope is in place, biopsy forceps or surgical instruments can be introduced through adjacent cannulas to perform various diagnostic or surgical procedures within the thorax. Once examination and operative procedures have been completed the instruments and cannulas are removed, air removed from the pleural space and the lungs re-expanded.
Thoracoscopy offers many significant advantages over a conventional open thoracotomy. As such, it will likely become the gold standard for both diagnostic investigations and many surgical procedures performed in the thoracic cavity.
Summary
Minimally invasive thoracic and abdominal surgery is far less invasive than open surgical procedures and has much lower morbidity and mortality yet allows greater visual exploration of the chest and abdomen than can be done with a laparotomy or thoracotomy. General anesthesia is required for performing minimally invasive surgery but the duration and depth of anesthesia can be much less than for open surgery. An owners reluctance for surgery may play an important role in the decision to select a minimally invasive technique.