Epidural Analgesia & Anesthesia

Position the patient in sternal or lateral recumbency with the hindlimbs pulled forward. Sternal recumbency facilitates locating the lumbosacral space and using the hanging-drop technique; however, it may worsen fracture sites in the pelvis, femur, or tibia. Thus, lateral recumbency might be preferred in those cases.

To avoid causing more damage to fracture sites while the patient is in sternal recumbency, position the patient close to the edge of the table with the affected leg hanging freely off the side. An assistant should stabilize the patient to prevent it from falling off the table.

Clip the hair over the lumbosacral space and prepare the area as you would for surgery.

If there are signs of skin infection or inflammation over the lumbosacral area, do not perform the epidural procedure. Coagulation abnormalities and sepsis are additional contraindications for epidurals.

The depression between L7 and S1 may not be obvious in overweight patients and in certain breeds, such as rottweilers. In these cases, insert the needle at midline just caudal from the imaginary line connecting the iliac prominences.

A Wearing sterile gloves, palpate the iliac prominences (with thumb and middle finger) and draw an imaginary line between them. The lumbosacral space is located just caudal to this line.

B Then palpate the lumbosacral space with the index finger; this space can be felt as a depression just caudal to an imaginary line connecting the iliac prominences.

Insert the spinal needle perpendicular to the skin, directly on midline, and advance it until it passes into the subcutaneous tissue but before it punctures the ligamentum flavum (A). Remove the stylet (B) and fill the hub of the needle with preservative-free saline, sterile water, or the anesthetic solution; this is called the hanging-drop technique (C). For the hanging-drop technique, the stylet needs to be removed before entering the epidural space, but it must be in the needle while penetrating the skin to prevent accidental transplantation of dermal tissue into the epidural space. Carefully advance the needle; a “pop”may be felt when it passes through the ligamentum flavum and reaches the epidural space. The negative pressure in the epidural space draws the solution from the hub of the needle (positive hanging- drop sign), indicating proper epidural placement (D).

In small patients in which the epidural space is small and little negative pressure is present, the solution may not be sucked in from the hub of the needle. Instead, only a slight depression on the meniscus may be noticed as the epidural space is entered. It is critical to slowly advance the needle while carefully observing the meniscus of the hanging drop. Occasionally, the needle may become blocked with tissue because it is advanced without the stylet; this results in a negative hanging-drop sign. In such cases, remove the needle and clear it by reintroducing the stylet. The lack-of-resistance test (see Step 6) can be used instead.

Once the needle is in the epidural space, connect the syringe with the epidural drug solution, aspirate (to assure that the tip of the needle is not in a blood vessel or the subarachnoid space), and slowly inject the drug over a period of 60 seconds. Avoid rapid injections because they may result in a patchy block or cause trauma to epidural tissues.

If a blood vessel is punctured, remove the needle and repeat the technique using a new one. If cerebrospinal fluid is drawn back, remove the needle and repeat the technique, or administer 50% of the intended volume into the subarachnoid space (this is no longer epidural but spinal anesthesia/analgesia).

If the hanging-drop technique fails, the epidural space can be identified by the loss-of-resistance test by using a 3- or 5-mL glass syringe containing 1 mL of air. The advantage of using a glass syringe is that there is negligible resistance from the glass plunge in a glass barrel. Upon injection, resistance should not exist if the needle is in the epidural space. Alternatively, a 3-mL plastic syringe may be used, but the inherent resistance associated with the rubber plunge sliding against the plastic barrel must be considered.

Observation of lack of compression of a small (0.5-mL) air bubble left in the syringe helps confirm that there is no resistance to injection and the needle is correctly positioned in the epidural space. Changes in respiratory pattern during the injection is another indication that the needle is correctly positioned.