SHPB was routinely done by fluoroscopy-guided bilateral posterior approach (Plancarte et al. 1997). Newer techniques were used like trans-discal and CT-guided approaches (Waldman et al. 1991; Cariati et al. 2002). The newer ultrasound-guided anterior approach minimizes the radiation exposure risks (Mishra et al. 2008; Mishra et al. 2013). The main concern of this technique is the potential injury to structures overlying the plexus such as common iliac arteries, bowel and bladder, and the risk of infection form bowel perforation. Preoperative bowel and bladder preparation, Trendelenburg position, and smaller size Chiba needle helped to avoid the visceral injury by collapsing the viscera away from the needle path. Avoidance of vessel injury by guidance and following negative aspiration of blood. The use of colored doppler sonography helped to avoid the needle injury complications.

In the present study we studied the efficacy and safety of preemptive US-guided anterior approach of SHPB in pelvic surgery. We found that it markedly reduced the total 24 h morphine consumption with lower VAS score at all time intervals starting from 2 h postoperative. Vital signs (HR and MBP) although showed some statistical significance but with no clinical significance.

Our primary outcome morphine consumption was less in SHPB group, and these results agreed with results of Rapp et al. after abdominal hysterectomy (Rapp et al. 2017), De Silva et al. in minimally invasive robotic gynecological surgeries (Silva et al. 2022) and Peker et al. during cesarean section (Peker et al. 2021).

VAS was significantly reduced in our present study in SHBP group through all time intervals from 2 till 24 h. These results coincide with those of De Silva et al. (2022), Peker et al. (2021), and Aytuluke et al. (2019). They found improvement in VAS score with SHBP, however they measured the VAS score till 48 h postoperative.

Nausea and vomiting showed no difference between the two groups and these results are similar to those of Rapp et al. and Aytuluk et al. (Rapp et al. 2017; Aytuluk et al. 2019). Also, no major complications were reported like local anesthetic toxicity, bowel injury, and vascular injury. These results coincide with those of Mishra et al. (2013).

Postoperative pain has a visceral and a somatic component. SHPB is mainly used to control the visceral pain (Sindt and Brogan 2016). Accordingly, adding other nerve block techniques for somatic pain control (i.e., transversus abdominis plane block, ilioinguinal and iliohypogastric block) is recommended for more effective pain relief. In this regard, Carney et al. suggested transversus abdominis plane block as a method for postoperative pain relief in patients undergoing hysterectomy (Carney et al. 2008).

There were studies that investigated SHPB in the perioperative period despite still little in comparison with the studies investigating it in chronic pelvic pain. However, the intervention in these studies was done surgically either open or during laparoscopy in pelvic surgeries. In addition, in these studies the SHPB was performed after surgical stimulus. The novelty and the main strength point of our study is that this is the first study, up to our knowledge, that investigated preemptive ultrasound-guided SHPB in perioperative analgesia in a randomized, controlled trial.

The limitations and weak points of our study include the limited number of patients and limited follow-up time (24 h). We recommend further studies to involve a larger sample of patients and follow them for longer times.