This study explained that the Posterior approach TAP block (PTAP) provided a sensory block that involved a greater number of dermatomes and involvement of more cephalad dermatome blocked to sharp touch as compared to the Lateral approach TAP block (LTAP) under US guidance. The posterolateral spread of the local analgesic agent to the paravertebral space might be linked to the high number of dermatomes.

Ultrasound (US)-guided transversus abdominis plane (TAP) block is used as a part of a multimodal analgesic regimen in the postoperative period. Lateral approach TAP block (LTAP) has been widely used for postoperative analgesia after lower abdominal surgeries. Posterior approach TAP block (PTAP), which is achieved by more posterior blockade of the anterior ramus of the spinal nerve, also provides profound postoperative analgesia after transverse lower abdominal incision. The study investigated the dermatomal sensory block following LTAP and PTAP under US guidance.

Twenty-seven adult female patients undergoing the laparoscopic resection of ovarian tumours under general anaesthesia were randomly divided into two groups, those receiving LTAP (Group L, n = 14) and those receiving PTAP (Group P, n = 13). Before induction of general anaesthesia, all patients were given bilateral TAP blocks with 15 ml of 0.25% levobupivacaine on each side under US guidance, and the sensory blockade was evaluated.

The data are expressed as median (interquartile range [IQR]). PTAP produced a median sensory blockade to sharp touch of three dermatomal segments (IQR 3–4), the most cephalad being T-10 (IQR T-9–T-10), whereas LTAP produced blockade of a median of two segments (IQR 2–2, P = 0.002), the most cephalad being T-10 (IQR T-10–T-10, P = 0.005).

PTAP produced a sensory block that involved a greater number of dermatomes and involvement of more cephalad dermatome blocked to sharp touch, compared with LTAP under US guidance.