Vet360 Vet 360 Vol 04 Issue 1 February 2017 | Page 17

ANAESTHESIOLOGY
Minimal compression of the air bubble indicates lack of resistance to injection and correct placement in the epidural space . Once the drug has been injected , slowly withdraw the needle from the injection site .
Observe patient response If the epidural injection of a local anaesthetic is successful , relaxation of the external anal sphincter and tail is observed . In an awake patient , hindlimb ataxia , as well as a lack of response to the flexor pinch reflex of the pelvic limbs , develops . Generally , once the toe reflexes have disappeared , anaesthesia adequate for abdominal surgery is present . In anaesthetised patients , a lack of response to surgical stimulation , as well as a lower requirement of inhalant anaesthesia to maintain surgical anaesthesia , is a good indicator of a successful local anaesthetic epidural . Patients receiving epidural opioids alone will still respond to acute pain stimuli and will not exhibit muscle relaxation . Epidural opioid administration often results in reduced requirement for supplemental analgesics in awake patients and reduced requirement for volatile anaesthetics in anaesthetised patients .
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COMMENTS ON THE ARTICLE

Dr Gareth Zeiler BVSc MMedVet ( Anaes ) Department of Companion Animal Clinical Studies , Faculty of Veterinary Science
• The first dozen epidural procedures you perform are expected to have a high failure rate ( up to 60 %). However , as confidence in performing the procedure improves , the success rate will improve . Regardless of administering the drugs in the correct site of administration , a low failure rate , where the patient does not “ block ” in a predictable manner can still be expected ( around 10-20 %).
• Preservative free morphine ( 0.1 mg / kg ) administration into the epidural space provides 12 to 24 hours of opioid induced hypoalgesia . Furthermore , morphine does not cause the vasodilation and decreased sympathetic tone which can result in a relative hypovolemia and hypotension as demonstrated with local anaesthetics . Therefore morphine can be used alone in patients which are at risk of hypotension , or cardiovascular instability . Urine retention and puritis are known , although infrequent , complications .
• Adrenalin based lidocaine formulations are losing popularity . There is evidence that the increased duration of action is due to local vasoconstrictive effects of adrenaline allowing more time for lidocaine to penetrate the nerves . However , it is believed that neural ischemia can result in long term post-epidural complications . Currently , if a longer duration of lidocaine effect is required , adding either medetomidine or dexmedetomidine at very low concentrations ( 1-4 ug / ml of lidocaine ) to the lidocaine formulation results in similar effects as seen when adrenalin is used , without the complications of post-epidural ischemia .
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Issue 06 | FEBRUARY 2017 | 17