Ultrasound-Guided Central Neuraxial Blocks

Abstract

Central neuraxial blocks (CNBs; spinal and epidural) are techniques that are frequently used for anesthesia or analgesia in the perioperative period and for managing chronic pain. Success of these techniques depends on one’s ability to accurately locate the epidural or the intrathecal space. Traditionally, CNBs are performed using surface anatomical landmarks, fascial clicks, visualizing the free flow of cerebrospinal fluid (CSF) and “loss of resistance.” Although anatomical landmarks are useful, they are often difficult to locate or palpate in patients with obesity [1], edema in their backs, and underlying spinal deformity or after spinal surgery. Even in the absence of the above, a given intervertebral space is accurately identified in only 30% [2, 3] of cases, and anesthesiologists very frequently incorrectly identify a space higher than intended [2, 4, 5], which has been attributed as a cause for injury of the conus medullaris [4] or spinal cord [6] after spinal anesthesia. This error is exaggerated by obesity [2] and as one tries to locate an intervertebral space in the upper spinal levels [2, 4, 5]. Therefore, the Tuffier’s line, a surface anatomical landmark that is ubiquitously used during CNB, is not a reliable landmark [5]. Moreover, because of the blind nature of the landmark-based techniques, it is not possible for the operator to predict the ease or difficulty of needle placement prior to skin puncture. Data from the United Kingdom indicate that 15% of spinal anesthetics are technically difficult [7], 10% require more than five attempts [7], and a failed CNB can occur in 5% of patients below the age of 50 [8]. Multiple attempts at needle placement can lead to pain and discomfort to the patient and injury to soft tissue structures that lie in the path of the advancing needle and may rarely result in complications, such as dural puncture, postdural puncture headache, or epidural hematoma. Therefore, any method that can reduce technical difficulties or assist the operator during CNB is desirable.