Let US Guide You in Epidural Injections

In veterinary medicine, most epidural injections are performed blindly. Tests such as the hanging drop and the loss of resistance are used to determine correct placement, but failure rates range from 7% to 12% and 25% to 30%. Human medicine has now described many types of ultrasound (US)-guided epidural injection techniques that could greatly benefit veterinary clinical practice.

In this study, 20 dog cadavers and 5 live dogs were used to establish parameters for a similar technique. Radiographs were used to classify each dog as normal or having lumbosacral (LS) abnormalities. Epidural injections of contrast media were performed on all subjects and CT used to determine success and subarachnoid leakage. Only 1 operator was used in this study, introducing a possible limitation. The US-guided technique was done with a parasagittal approach, using L7, the iliac wings, and S1 as landmarks.

Spinal needles and epidural catheters were both used, with greater risk of subarachnoid contamination when using the spinal needles (though contamination was not severe in any of the cases). Visualizing the necessary landmarks tended to be more difficult in obese patients or those with LS radiographic abnormalities. CT imaging confirmed successful epidural injections in all test cases.

Epidural injections are a blind technique with success or failure influenced by several factors, including patient obesity, vertebral anatomic variations, and operator experience. This study corroborated other recent investigations of the feasibility of the US-guided regional techniques. However, using these techniques in daily clinical practice requires a high level of US equipment and a high training degree. This may be a limitation for general practitioners. Also, further studies should evaluate this technique in clinical practice.—Amalia Agut, DVM, PhD, DECVDI