Epidural Waveform Analysis for Thoracic Epidural Blocks

In the EWA-N group, 5 mL of normal saline are injected through the epidural needle after the occurrence of loss-of-resistance (LOR). The needle is connected to the pressure transducer. A satisfactory endpoint is defined as the presence of waveforms synchronized with arterial pulsations. In the absence of pulsatile waveforms, the operator injects an additional 2.5 mL-bolus of normal saline through the epidural needle and reconnects the latter to the pressure transducer. If no waveforms are detected after the second injection, the operator removes the needle and reattempts the epidural block at a different intervertebral level. A maximum of 3 levels is permitted: if waveforms are still absent at the third level, the operator simply accepts LOR as the technical endpoint.

In the EWA-C group, the epidural catheter is advanced 5 cm beyond the needle tip after the occurrence of LOR. Subsequently, the operator injects 5 mL of normal saline through the catheter and the latter is connected to the pressure transducer via the sterile, rigid extension tubing. A satisfactory endpoint is defined as the presence of waveforms. In the absence of pulsatile waveforms, the operator injects an additional 2.5 mL-bolus of saline through the catheter and reconnects the latter to the pressure transducer. If no waveforms are detected after the second injection are still absent at the third level, the operator simply accepts this position for catheter placement (intent-to-treat analysis).