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new needle. DO NOT inject drugs intended for epidural administration if blood is observed as inadvertent IV injection of LA can cause systemic toxicity (convulsions, cardiovascular depression). Bupivacaine (and to a lesser extent ropivacaine), may cause cardiac arrest due to increased cardiotoxicity. Therefore, it is recommended to always aspirate before injection.
Size differences
The spinal cord typically ends at the level of the L6 vertebra in medium/large adult dogs, however, in cats and in small or young dogs, the spinal cord and meninges may extend to the level of the L7 making piercing of meninges and leakage of CSF more likely compared to medium/large dogs.
Drugs
Adetailed review of current drugs used for epidural anaesthesia and analgesia by Steagall and colleagues (2017)(2) is freely available on-line: https://www.frontiersin. org/articles/10.3389/fvets.2017.00068/full
anaesthetic may spread cranially and potentiate motor blockade of the diaphragm (phrenic nerves).
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Volume Guide:
· Anaesthesia/analgesia caudal to the diaphragm:
 0.2 ml/kg (combined volume opioid + LA)
  The most commonly used drugs for epidural administration are opioids, local anaesthetics or a combination of the two drugs.
· Local anaesthetics: The site of action for local
· Opioid ONLY analgesia to the thorax: 0.3 ml/kg (DO NOT combine with LA at this dose)
Complications
Reported complications with the epidural administration of opioids and local anaesthetic agents are rare, but
may include respiratory depression, pruritus (reported
in humans), hypotension, nausea, vomiting, delayed
hair regrowth and urinary retention. Urinary bladder management should include emptying the bladder at the time of surgery (expression or urinary catheterization) and monitoring bladder size every four to six hours postoperatively until the patient is able to urinate.
Indwelling Epidural Catheter Placement Technique
Catheterization of the epidural space provides the opportunity for repeated or constant delivery of analgesics to the spinal cord, and is usually accomplished by using commercial kits.
STEPS:
· Anatomical landmarks are confirmed and the patient is prepared as previously described.
· The length of epidural catheter to be placed inside the patient is then pre-measured by carefully placing the catheter over the sterile drape against the pa- tient. For severe cranial abdominal pain the tip of the catheter should be advanced to the level of L1-2 or L2-3. For pelvic origin pain, the catheter is advanced only to the level of L5-6. Remember to include the distance from the skin surface to the epidural space in the estimation of catheter length needed. Mark the catheter with a sterile pen (often included in the cath- eter kit) or utilise the reference markings if present on the catheter (brand specific).
· The mark just created will not be visible during placement, so to assist in accurate placement a sec- ond mark exactly the same length of the Tuohy spinal needle is placed on the catheter. The tip of Tuohy spinal needle is placed at the mark created above and a second mark is placed on the catheter at the level of the catheter hub.
· The epidural space that has been chosen for inser- tion is then carefully palpated again and the thumb of the non-needle placing hand is firmly embedded into the depression between L7-S1 or L6-7. The Tuohy spinal needle is then inserted into the desired epidural space. Correct placement is then confirmed using the previously mentioned techniques.
· Once a positive placement has been confirmed, the catheter guide is placed on the epidural catheter and the appropriate tip is inserted into the Tuohy needle hub. The catheter guide is then gently seated into the Tuohy needle hub and the catheter is gently advanced to the tip of the needle. Be careful not to disrupt the placement of the tip of the Tuohy needle. Gentle resistance should be felt as the catheter tip
anaesthetics administered in the epidural space is primarily the spinal nerve roots. Local anaesthetics result in autonomic, sensory and motor blockade. Bupivacaine is the most commonly used local anaes- thetic drugs due to their longer duration of analgesia of two to four hours. Ropivacaine has the advantage of being less arrhythmogenic and toxic for the CNS and cardiovascular system.
· Bupivicaine 0.5% Dosing: 0.5-1.0 mg/kg
· Ropivicaine 0.75% Dosing: 1.0-1.65 mg/kg
· Opioids: The site of action for epidural administered opioids is the opioid receptors in the dorsal horn of the spinal cord. They provide segmental analgesia without sensory, sympathetic or motor blockade. Morphine is the most widely used as it is the least lipid-soluble of the commonly used opioids and, therefore, has the slowest onset of action (30 to 60 minutes) but the longest duration of action (up to 24 hours). Preservative-free morphine is recommended.
· Morphine Dosing: 0.1 mg/kg (diluted with saline to 0.3 mL/kg)
· Local anaesthetic/opioid combinations: The com- bination of opioids with local anaesthetics may be beneficial because affinity of opioid drugs for their receptors in the spinal cord is increased by local anaesthetics
Volume
In small animals, a total epidural volume of injectate that approximates 0.2 mL/kg but does not exceed 6 mL for animals has been recommended.(3) For drugs that do not cause sympathetic or motor blockade, such as the opioids, it is not necessary to adhere to this rule. Volumes greater than 0.2 ml/kg which contain local
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