Veterinary Medicine - March 2009 - (Page 132)

Anesthesia techniques PEER-REVIEWED 2. Positioning of the needles for a preoperative intercostal block. in patients with rib fractures.1,2,8 The intercostal nerves descend in the intercostal space along the caudal border of each rib, associated with the ventral branches of the intercostal artery and vein. For a lateral thoracotomy, the block can be performed immediately after anesthetic induction and surgical preparation of the chest wall (preemptive analgesia) (Figure 2), or it can be performed before closing the chest wall, allowing visualization of the nerves and blockade of both the dorsal and ventral branches (Figure 3). Conscious patients that require an intercostal nerve block for analgesia of rib fractures will likely require sedation with appropriate systemic drugs, such as opioid and benzodiazepine combinations. The block is performed as dorsally as possible, near the intervertebral foramen. With the patient in lateral recumbency and the needle perpendicular to the lateral aspect of the body, advance the needle onto the rib, and then walk it caudally until it enters the tissues behind the rib’s caudal border. After aspirating the syringe to avoid intravascular administration, inject the local anesthetic. Repeat this procedure to block three intercostal nerves in front of the incision (or fractured ribs) and three caudal to it, in addition to the site of interest.1,2,8,9 INTRAPLEURAL ANALGESIA Local anesthetics can be administered into the pleural cavity (between the visceral and parietal pleura) to provide analgesia after a lateral or sternal thoracotomy, in patients with thoracic trauma, and in patients with cranial abdominal pain, such as that associated with acute pancreatitis.1,8-10 The mechanism of analgesia has been suggested to be due to diffusion of local anesthetic through the parietal pleura, causing intercostal nerve block, blockade of the thoracic sympathetic chain and splanchnic nerves, and diffusion of the anesthetic into the ipsilateral brachial plexus, resulting in blockade of the parietal peritoneum.8-11 Because cranial abdominal nerves enter the spinal cord at the level of the thorax, intrapleural administration of a local anesthetic blocks the cranial abdominal nerves, and this technique may be useful for acute pancreatitis or cranial abdominal surgical procedures.9 Local anesthetics and adjunctive agents can be administered through a chest tube, if present. Follow the anesthetic drugs with 3 to 5 ml of sterile saline solution to ush the tube. If a chest tube is not in place, a hypodermic needle, butter y catheter, or intravenous catheter can be used. Systemic analgesics and sedatives should be considered for conscious patients. After sterile preparation and in ltration of the site of interest with 3. An intraoperative intercostal block in a dog after lateral thoracotomy. The surgeon has visualized and palpated both the dorsal and ventral branches of the intercostal nerves on the caudal aspect of the ribs near the intervertebral foramen and is depositing a mixture of lidocaine and bupivacaine near the nerves. 0.2 to 0.5 ml of 2% lidocaine, penetrate the chest wall between the ribs with the stylet and catheter. Once the pleural space has been reached, advance the catheter off the end of the stylet to avoid lung laceration. Attach a three-way stopcock and syringe to the catheter as soon as the stylet is removed to avoid inducing a signi cant pneumothorax, and make sure the catheter is never left open to the environment. A hypodermic needle or butter y catheter should have the stopcock attached, closed to the needle, before penetration of the chest wall. Local anesthetic administered intrapleurally is rapidly and extensively absorbed systemically, so be sure to avoid using toxic doses. In ammation and the resulting tissue acidity may reduce the ef cacy of local anesthetics and result in increased systemic absorption. If possible, place the patient with the incision site down, and maintain the patient in that position during needle placement and drug injection and for at least 10 minutes afterward, as this 132 March 2009 VETERINARY MEDICINE

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Veterinary Medicine - March 2009 Contents Letters Correction Author Guidelines Hot Literature Idea Exchange A Challenging Case Local and Regional Anesthesia Techniques The Latest Scoop on Litter Product Preview CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - March 2009

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