Ultrasound guided thoracic paravertebral block in breast surgery

Abstract

Thoracic paravertebral block has usually been performed using a loss of resistance technique [1, 2] with the transverse process is an important landmark. However, since the transverse process is neither visible nor palpable, its location is unknown until the block needle encounters the bone. If it is not encountered, the needle tip might advance further causing pleural puncture. Pusch et al. showed that ultrasound scanning of the transverse process and parietal pleura gave an accurate reading of the depth to the paravertebral space [3], but only made the measurements before, not during paravertebral block at T4. Breast surgery is often performed with axillary dissection making additional thoracic paravertebral blocks necessary at several vertebrae. We sought to determine whether visualisation of anatomical landmarks, needle advancement and the spread of local anaesthetic in the paravertebral space as well as knowledge of the distance from the skin to those landmarks using ultrasound imaging could help perform the block at both T1 and T4. With Institutional Review Board approval and written informed consent, 25 healthy patients undergoing unilateral breast surgery received thoracic paravertebral block combined with general anaesthesia. They were placed in the lateral decubitus position with the side to be blocked uppermost. A 3–11 MHz linear array probe (Philips SONOS 5500; Philips Medical Systems, Andover, MA, USA) was applied longitudinally to the paravertebral area. An 18G Tuohy needle was inserted perpendicularly at T4 to hit the transverse process via an out-of-plane approach. This was then directed over the top of the bony structure. The deviation of the needle from the perpendicular line was kept at 15°. The paravertebral space was identified using loss of resistance to normal saline injection without ultrasound. After negative aspiration, 15 ml of 0.5% ropivacaine was administered incrementally under ultrasound guidance. Thoracic paravertebral block at T1 was performed using the same technique with 5 ml of solution. Sensory block was assessed by loss of cold sensation 10 min later. All patients received the block at T4 and 22 at T1. Both parietal pleura and transverse process were successfully visualised at T4 (Fig. 3a) in all patients, while only transverse process visualisation was possible at T1. The distances measured using ultrasound and needle depth are in Table 1. Distances measured using ultrasound correlated well with needle depth. Injection of local anaesthetic was visualised as turbulence at T4 in all patients. Downward movement of pleura was observed at T4 in four patients during injection (Fig. 3b). No accidental pleural puncture occurred. All patients had loss of cold sensation at least between T2 and T4. Ultrasound imaging not only helped determine needle insertion sites, but also provides information on the depth to the paravertebral space. Ultrasound imaging may make thoracic paravertebral block easier to perform and help avoid inadvertent pleural puncture. (a) Measurements of the distances from the skin to the transverse process and pleura on ultrasound longitudinal image at T4. TP = transverse process, PP = parietal pleura, LIG = intertransverse and superior costotransverse ligaments. , distance from the skin to TP; , distance from the skin to PP. (b) Visualisation of local anaesthetic and the downward shift of PP on ultrasound longitudinal image. (A) Before injection, (B) After injection. TP = transverse process, PP = parietal pleura, LA = local anaesthetic.