Thoracic paravertebral space location. A new method using pressure measurement.

The major drawback of paravertebral space location using the traditional method of loss of resistance to air or saline is a failure rate of at least 10%. We investigated whether pressure measurement during needle advancement could improve reliability. Twenty-nine blocks in 14 awake adult patients undergoing treatment for chronically painful neuralgic conditions of the chest or abdominal wall were studied. In erector spinae, the mean inspiratory pressure (29.5 mmHg, SD 14.2), exceeded the expiratory pressure (19.4 mmHg, SD 9.7). However, upon traversing the superior costo-transverse ligament, there was a sudden lowering of pressures and the mean expiratory pressure (7.6 mmHg, SD 3.7) exceeded the inspiratory pressure (3.3 mmHg, SD 2.9). No negative pressures were recorded. Correct needle placement was confirmed by X ray screening and contrast injection. All blocks were successful and uncomplicated. Location of the paravertebral space by this objective method of 'pressure inversion' improves sensitivity and specificity and should lead to an improvement in the success rate of thoracic paravertebral analgesia.