Sonographic measurement of needle insertion depth in paravertebral blocks in women

Single-injection paravertebral block offers adequate unilateral analgesia f or thoracic and upper abdominal surgery. This technique is easy to learn bu t there is a risk, albeit low, of pleural puncture. The aim of the study wa s to determine whether sonographic measurements of the distances from the s kin to the transverse process and to the parietal pleura are useful for cal culating the required depth of needle insertion. Before puncture of the par avertebral space, the distances from the skin to the transverse process and to the parietal pleura were measured by sonography. The deviation of the n eedle from the horizontal plane was measured and an angle correction for th e insertion depth was calculated. Twenty-two women undergoing elective unil ateral breast surgery were studied. Sonographic visualization of the transv erse process and the parietal pleura and measurement of their distances fro m the skin was successful in all women. Puncture of the paravertebral space failed in one obese woman. There was a very close correlation between need le insertion depth from the skin to the transverse process and the distance measured by ultrasound if angle correction was used (adjusted r(2) = 0.95) . Similarly, there was excellent correlation between the angle-corrected ul trasound distance from the skin to the parietal pleura and the distance fro m the skin to the paravertebral space (adjusted r(2) = 0.92).