Correlation between spinous process dimensions and ease of spinal anaesthesia

BACKGROUND: Neuraxial anaesthesia, despite being a common technique, may pose some technical challenges leading to complications such as post-dural puncture headache, trauma to neural structures and neuraxial haematoma. We hypothesised that the interspinous gap (ISG) and the spinous process width (SPW) could be used as objective measures to predict ease of access to the neuraxial space. METHODS: Two hundred and two consecutive patients scheduled to have spinal anaesthesia for various surgical procedures were enrolled prospectively after institutional approval. Following proper positioning for the neuraxial blockade, the ISG and SPW at the intended level were measured with calipers. The number of attempts, and redirections at the selected spinal level, and the number of levels required for successful needle placement were also recorded. RESULTS: Group-wise analysis of the data into patients requiring >1 attempt, >1 level and ≥3 redirections showed that the single independent predictor of a difficult neuraxial block was the ISG. Twenty-three percent of the patients required more than one attempt, with a mean gap of 6.35 (±1.2) mm, in contrast to 8.15 (±2.4) mm in those with a single attempt (P=0.000). In addition, 16% of the patients needed more than one level, with a mean gap of 6.03 (±2.01) mm in contrast to 8.07 (±2.37) mm for a single level (P=0.000). CONCLUSIONS: The single independent predictor of ease or difficulty during spinal anaesthesia was the ISG (P=0.000).