Spinal process landmark as a predicting factor for difficult epidural block: A prospective study in Taiwanese patients

Although epidural anesthesia is a common practice in neuraxial blockade, difficult access to the epidural space is a frequent problem in operating theaters. We designed this study of epidural blocks to determine if the spinal landmark grading system is valuable in predicting a difficult epidural block. Before the epidural block, we collected the following data: demographics, body habitus (normal, thin, obese, pregnant), spinal anatomy (normal, deformed), spinal level (lumbar, thoracic), and spinal landmark grade (grade 1: spinous processes visible; grade 2: spinous processes not seen but easily palpated; grade 3: spinous processes not seen and not palpated but the interval between them is palpated as a low landmark under the thumb; grade 4: other). We performed all 848 epidural blocks initially using a midline approach and an 18-gauge Touhy needle. We evaluated the technical difficulty of the epidural block using three methods: whether the epidural block was accomplished at the spinal level (first-level success); the total number of attempts at skin puncture (attempts-S); and total number of attempts to change ligament puncture direction (attempts-L) required to complete the epidural block. Of all examined factors, spinal landmark grade correlated best with technical difficulty as measured by all three methods. Deformed spinal anatomy and body habitus both correlated with difficulty, merely from the total numbers of attempts (attempts-S and attempts-L). Thoracic epidurals were more difficult than lumbar epidurals by all three measures of difficulty. We concluded that this spinal landmark grading system is valuable in predicting a difficult epidural block and advocate its use as a predictor by anesthesiologists.