Anaesthesia during brachytherapy for cervical cancer can be provided by general, spinal, epidural or combined spinal-epidural (CSE) anaesthesia. However, with CSE anaesthesia, up to 50 mg intravenous (i.v.) morphine rescue opioid requirements and mean pain scores of 5.2 have been reported [1].

We performed a single-arm, prospective study of a modified sacral erector spinae plane block (S-ESPB), to characterise the analgesic effect, dermatomal anaesthesia and radiological spread of injectate. Ten patients were recruited between 15 March 2021 and 23 April 2021 (see Table 1 for patient characteristics). Baseline dermatomal sensory mapping was performed, and patients were positioned prone. A 6–13 MHz linear array ultrasound transducer was placed in the parasagittal orientation with the second sacral foramen (SF-2) in the field. A 21G short bevel needle was inserted in-plane until the needle reached the sacral foramen (Fig. 1A). A distinct loss of resistance was felt once the needle pierced the fibrous covering of SF-2. Twenty millilitres of local anaesthetic solution (1:1 mixture of lidocaine 2% with adrenaline and bupivacaine 0.25%) with 5 ml of iohexol (140 mg.ml^-1) was injected on each side. Patients were turned supine and dermatomal mapping was repeated. Patients received i.v. midazolam 1 mg, and i.v. fentanyl 50 μg if they experienced pain. All patients received i.v. paracetamol 1 g, i.v. dexamethasone 6 mg and i.v. ondansetron 4 mg at the end of the procedure. After brachytherapy, patients underwent a CT scan in which contrast spread was evaluated by a radiologist.

Ten minutes following the S-ESPB, nine patients had no sensation in the L5 dermatome, and all patients had complete loss of sensation in S1–S5 dermatomes. One hour following the S-ESPB, all patients had a loss of sensation in L5–S5 dermatomes. Bilateral loss of sensation in the L4 dermatome was observed in four patients and L3 in three patients. At 6 h, eight patients had a dermatomal sensory loss in S3–S5, seven in S2 and six in the S1 dermatomes. At 12 h, two patients had sensory loss in S1–S5 dermatomes and after 24 h there was no residual sensory loss in any of the patients.

Radiological evidence of contrast spread was found ventral to the sacral vertebrae in all patients (Table 1 and Fig. 1B and C). There was no dorsal spread or spread to the caudal space observed. Four patients received i.v. fentanyl 50 μg intra-operatively. All pain scores reported while the implant remained in situ were 3 out of 10 or less (numeric rating scale). Two patients did not need any supplemental fentanyl in the postoperative period. Median (IQR [range]) cumulative i.v. fentanyl dose overall was 122 (50–250 [0–445]) μg; 60 (50–70 [0–100]) μg 6 h after the block; 170 (50–205 [0–260]) μg 12 h after the block; and 175 (50–260 [0–445]) mcg 24 h after the block. Full details of the dataset including all images are available at https://doi.org/10.6084/m9.figshare.14748381.v2.

Sacral erector spinae plane block has been reported to provide analgesia in the sacrococcygeal and perianal area [2-5]. This was attributed to the dorsal spread of the injectate acting on the dorsal sacral nerve roots. The perineum and labia minora are innervated by the pudendal nerve, which arises from the ventral rami of the second to fourth sacral spinal nerves. The innervation of the upper vagina is autonomic and derived from the uterovaginal plexus, which is a subsidiary of the inferior hypogastric plexus. Only the posterior fifth of the vagina has a somatic nerve supply through the pudendal nerve. To provide anaesthesia for perineal surgery, we wanted to deliver local anaesthetic to the presacral area. We modified the injection endpoint of S-ESPB to place the needle tip at the dorsal opening of the sacral foramen. We hypothesised that the fibrous tissue covering the sacral foramina would inhibit dorsal spread of the injectate when the needle tip was at the dorsal opening of the sacral foramen. The absence of any contrast in the caudal space in our study indicates that the clinical effect was due to anaesthesia of the presacral nerve roots. The injectate could be imaged consistently in the presacral area, along the pudendal and the sciatic nerves, reaching the broad ligament. The spread along the sciatic nerve and broad ligament was unintended and merits further evaluation.

To our knowledge, this is the first imaging report that describes contrast translocation through SF-2 and ventral spread alongside the sacral nerve roots, pudendal nerve and sciatic nerve after S-ESPB. To distinguish our approach from the existing S-ESPB approach, we call it ‘sacral foramen injection’.

宫颈癌近距离放射治疗期间的麻醉可以通过全身麻醉、脊髓麻醉、硬膜外麻醉或脊髓硬膜外联合 (CSE) 麻醉来提供。然而，据报道，对于 CSE 麻醉，高达 50 毫克的静脉内 (iv) 吗啡拯救阿片类药物需求和 5.2 的平均疼痛评分 [ 1 ]。

我们对改良的骶竖脊肌平面阻滞 (S-ESPB) 进行了一项单臂前瞻性研究，以表征注射剂的镇痛效果、皮肤麻醉和放射学扩散。2021 年 3 月 15 日至 2021 年 4 月 23 日期间招募了 10 名患者（患者特征见表 1）。进行基线皮肤感觉映射，并且患者俯卧位。一个 6-13 MHz 线性阵列超声换能器被放置在旁矢状方向，第二个骶骨孔（SF-2）在场中。将一根 21G 的短斜面针插入平面，直到针到达骶骨孔（图 1A）。一旦针刺穿 SF-2 的纤维覆盖物，就会感觉到明显的阻力损失。20 毫升局部麻醉剂溶液（2% 利多卡因与肾上腺素和布比卡因 0 的 1:1 混合物。^-1 ) 在每一侧注射。患者转为仰卧位，并重复进行皮区测绘。如果患者感到疼痛，则接受静脉注射咪达唑仑 1 mg，静脉注射芬太尼 50 μg。所有患者在手术结束时接受静脉注射扑热息痛 1 g、静脉注射地塞米松 6 mg 和静脉注射昂丹司琼 4 mg。近距离放射治疗后，患者接受了 CT 扫描，其中放射科医师对造影剂的扩散进行了评估。

S-ESPB 后 10 分钟，9 名患者在 L5 皮节没有感觉，所有患者在 S1-S5 皮节完全丧失感觉。S-ESPB 后 1 小时，所有患者的 L5-S5 皮节感觉丧失。在四名患者中观察到 L4 皮节的双侧感觉丧失，在三名患者中观察到 L3。在 6 小时时，8 名患者在 S3-S5 中出现皮节感觉丧失，7 名在 S2 中，6 名在 S1 皮节中。在 12 小时时，两名患者在 S1-S5 皮节有感觉丧失，24 小时后，任何患者都没有残留的感觉丧失。

在所有患者的骶椎腹侧发现造影剂扩散的放射学证据（表 1 和图 1B 和 C）。没有观察到背部扩散或扩散到尾部空间。四名患者在手术中接受了静脉注射芬太尼 50 μg。在植入物保持原位时报告的所有疼痛评分均为 3 分（满分 10 分）或更低（数字评分量表）。两名患者在术后期间不需要任何补充芬太尼。静脉注射芬太尼的总剂量中位数（IQR [范围]）为 122 (50-250 [0-445]) μg；60 (50–70 [0–100]) μg 阻滞后 6 小时；170 (50–205 [0–260]) μg 阻滞后 12 小时；阻滞后 24 小时 175 (50–260 [0–445]) mcg。包括所有图像在内的数据集的完整详细信息可在 https://doi.org/10.6084/m9.figshare.14748381.v2 获得。

据报道，骶竖脊肌平面阻滞可在骶尾部和肛周区域提供镇痛 [ 2-5]]。这归因于作用于背骶神经根的注射剂的背侧扩散。会阴和小阴唇由阴部神经支配，阴部神经起源于第二至第四骶脊神经的腹支。上阴道的神经支配是自主的，来自子宫阴道丛，它是下腹下丛的附属。只有阴道后五分之一有通过阴部神经的躯体神经供应。为了为会阴手术提供麻醉，我们想向骶前区域提供局部麻醉剂。我们修改了 S-ESPB 的注射终点，将针尖放置在骶孔的背侧开口处。我们假设当针尖位于骶孔的背侧开口时，覆盖骶孔的纤维组织会抑制注射液的背侧扩散。在我们的研究中尾部空间没有任何对比表明临床效果是由于骶前神经根的麻醉。注射液可以在骶前区、沿着阴部和坐骨神经、到达阔韧带的位置进行一致成像。沿坐骨神经和阔韧带的扩散是意外的，值得进一步评估。沿着阴部和坐骨神经，到达阔韧带。沿坐骨神经和阔韧带的扩散是意外的，值得进一步评估。沿着阴部和坐骨神经，到达阔韧带。沿坐骨神经和阔韧带的扩散是意外的，值得进一步评估。

据我们所知，这是第一个描述 S-ESPB 后通过 SF-2 和沿着骶神经根、阴部神经和坐骨神经的腹侧扩散的造影剂易位的影像报告。为了将我们的方法与现有的 S-ESPB 方法区分开来，我们将其称为“骶孔注射”。