ANAESTHESIOLOGY nal recumbency , with the hindlimbs flexed at the hips and stifles and hocks extended so the legs are positioned alongside the body ( Figure 1 ). This position makes the lumbosacral space easier to identify .
Figure 1 . The lumbosacral space is easier to identify if you place the patient in sternal recumbency with the hindlimbs flexed at the hips , the
stifles and hocks extended , and the legs alongside the body .
Palpate the space Locate the lumbosacral space by palpating the most anterior aspect of both iliac crests with your thumb and middle finger ; the imaginary line connecting them passes through the lumbosacral intervertebral space . With your index finger , palpate the space as a depression immediately caudal to the dorsal spinous process of L7 and immediately cranial to the fused dorsal spinous processes of the sacrum ( Figure 2 ).
Figure 2 . To identify the lumbosacral space , palpate the iliac crests , dorsal spinous process of L7 , and the lumbosacral space immediately caudal to L7 and cranial to the sacrum .
Prepare the site Once you have identified the lumbosacral space , clip the hair , and surgically prepare the area . Place a sterile transparent drape over the area , tear a small opening in the drape at the injection site , and use a sterile disposable 2.5- to 7.5-cm , 20- to 22-ga spinal needle and sterile gloves . If the procedure is being performed in an awake but sedated patient , inject 0.5 to 1 ml 2 % lidocaine ( with sodium bicarbonate solution added to the local anaesthetic in a 1:9 ratio of bicarbonate to lidocaine to reduce the pain of injection ) subcutaneously at the site of the spinal needle insertion and wait five to 10 minutes before inserting the spinal needle at this site .
Figure 3 . Once the injection site area is prepared and draped , palpate the lumbosacral space , tear a small opening in the drape at the injection site , and insert the needle until you penetrate the ligamentum flavum
Insert the needle Using your nondominant hand to confirm the landmarks and the lumbosacral space , position the spinal needle over the midline with your dominant hand ( Figure 3 ). Midline positioning is critical to avoid contact with the transverse processes of the L7 vertebra . Direct the needle bevel cranially , and advance the needle , with stylet in place , perpendicular to the skin . Position your dominant hand so that it is in contact with the animal when penetrating the skin to provide counterpressure and to avoid pushing the needle in too far . It is often helpful to hold the stylet with the index finger of your dominant hand to keep it from being pushed out of the spinal needle by the subcutaneous tissues . If the needle encounters bone , withdraw it slightly , redirect it caudally or cranially , and advance it again . You may need to adjust the needle angle to facilitate correct placement in the epidural space .
The diameter of the lumbosacral epidural space is 2 to 4 mm in medium-sized dogs and < 3 mm in cats . 4 As the needle is advanced , you usually feel a popping sensation as the skin is penetrated and then a second pop as the needle penetrates the ligamentum flavum and enters the epidural space . Advance the needle no farther since most of the blood vessels lie in the ventral part of the spinal canal and it is more likely that a vessel will be penetrated if advanced too far . In cats , the spinal dura mater frequently extends to S1-S2 , so it is more likely that the dura and arachnoid will be punctured if the needle is advanced too deeply , entering the subarachnoid space . Occasionally , you will see the tail twitch or hindlimb movement as the epidural space is entered , indicating the needle has contacted the cauda equina . In this case , the drug may be injected without redirecting the needle .
Confirm needle placement Once the epidural space has been entered , remove
Issue 06 | FEBRUARY 2017 | 15