Pharmacological treatment of bowel obstruction pain is indicated for inoperable patients and aims to relieve abdominal continuous pain as well as intestinal colic. The prescribed analgesics are mainly strong opioids, but for refractory colic hyoscine butylbromide or hyoscine hydrobromide, two anti-cholinergic drugs, may be used in association to opioids. The preferred routes of administration are subcutaneous, intravenous and transdermal [121].

Interventional techniques consist of invasive approaches that provide temporary or permanent interruption of nerve transmission. Even when optimal pharmacological therapy is provided, it is estimated that 10 % of patients suffer from refractory pain [122]. This corresponds, in most cases, to neuropathic and bone pain. For these patients, as well as for those who experience major adverse effects from analgesic therapy, those techniques may be useful, as part of a multimodal approach [123].

Many patients undergoing these procedures are being treated with high dose opioids. This implies the risk for respiratory depression and excessive sedation as a result of a successful intervention. Careful monitoring of respiratory function is therefore mandatory and an appropriate reduction of opioid doses must be performed. Often, half the usual dose is administered immediately after the procedure and a subsequent further reduction is performed in order to avoid a withdrawal syndrome [123]. Peripheral nerve blocks, neurolytic sympathetic blocks, neuraxial analgesia, vertebroplasty and kyphoplasty are the main interventional procedures for cancer pain relief.

Peripheral nerve blocks with local anaesthetics have a limited use in the management of cancer pain. However, they may be useful for acute pain control or to provide short-term analgesia while other therapeutic approaches are implemented. Acute pain control may be needed on the perioperative setting or for other acute events, such as pathological rib fractures, when an intercostal nerve blockade, by means of a bolus injection of local anaesthetics, may be beneficial. Alternatively, catheter infusions adjacent to nerve plexuses, such as the brachial plexus, or other peripheral nerves may provide pain relief for days or weeks. Implantation of catheters into the intrapleural space to anaesthetise the intercostal nerves, and, additionally, the thoracic sympathetic chain, is used, especially for post-thoracotomy pain control, although there are early reports of its use for pain control in the terminally ill patient, with good results in a selected population of patients [124, 125]. The onset of pneumothorax and the risk for local anaesthetic toxicity limits its use [126]. Furthermore, the presence of advanced malignant disease often distorts the normal neuroanatomy and, consequently, poses technical difficulties.

Neurolytic blockade of peripheral nerves, mainly intercostal nerves, although providing a prolonged pain relief, is associated with a high incidence of neuritis. This can trigger pain that is much more difficult to control than the original one and, thus, should be reserved for patients with a very short life expectancy when other strategies have failed [127].

Clinical reports on the use of peripheral nerve blocks are limited and the lack of comparative studies compromises the establishment of recommendations for clinical practice [127].

Autonomic nerve blocks consist of the blockade of sympathetic nervous system fibres, which carry pain afferents from the viscera. The most commonly performed procedures are celiac plexus ablation, superior hypogastric plexus block and ganglion impar block.

Celiac plexus and splanchnic nerves block is often used to control pancreatic cancer or other upper abdominal malignancies related pain. Although there is no robust statistical evidence of a better pain control than that offered by analgesic therapy only, the fact that this technique enables lower opioid doses and, consequently, fewer side effects justifies its importance [128].

The celiac plexus lies retroperitoneally at the level of the T12 and L1 vertebrae and anterior to the aorta and carries afferent fibres from several abdominal organs including the pancreas, liver, biliary tract and bowel up to the first part of the transverse colon. The most common access route is posterior with fluoroscopy guidance, although other approaches may be useful. The ultrasound-guided anterior approach is a minimally invasive technique with increasing popularity and is believed to be a safer procedure. Nonetheless, no randomized controlled trial has shown its superiority over other methods yet [128, 129].

Contra-indications to the use of this technique include severe refractory coagulopathy or thrombocytopenia, aortic aneurysm or mural thrombosis, local or intra-abdominal infection and bowel obstruction. Large masses making anatomical structures position difficult to visualize are a relative contraindication [130].

Possible complications of these methods include diarrhoea, temporary postural hypotension, back pain and dysaesthesia. More severe side effects, including permanent motor deficit, are rare [123]. Four cases of paraplegia were reported in a review of 2,730 coeliac blocks, three of which with associated loss of anal and bladder sphincter function. These major complications were attributed to either direct spinal cord injury during the procedure or to spinal ischaemia secondary to anterior spinal artery spasm [131].

Superior hypogastric plexus block enables reduction of pain with lower abdominal or pelvic viscera origin. It carries afferents from the bladder, uterus, prostate, vagina, testes, urethra, descending colon and rectum. The hypogastric plexus lies retroperitoneally at the level of L5 and S1 vertebrae and its approach is most commonly posterior, with the patient in the prone position, under computed tomography and fluoroscopy guidance. However, an ultrasound-guided anterior approach may be useful since it can be performed with the patient lying supine and avoids radiation exposure [132]. A transdiscal approach has also been described as a safe, equally effective and easier procedure compared to the classic posterior approach [133, 134]. Potential complications of a superior hypogastric plexus block include bleeding, infection, nerve structures and visceral damage and sexual dysfunction [135].

The ganglion impar, also known as ganglion of Walther, corresponds to the distal termination of the sympathetic chains as they merge. It is generally located on the ventral aspect of the sacrococcygeal junction but may lie ventral to the coccyx. It has shown to provide pain relief for patients with pelvic and perineal cancer and effectiveness in treating radiation proctitis pain has been reported [136, 137]. The ganglion impar can be accessed via the anococcygeal ligament, in a midline or paramedian approach; via the sacrococcygeal or intercoccygeal joint spaces or via a lateral approach. A lateral approach seems to reduce the risk of perforating the rectum and avoids needle breakage when bent or inserted through ossified structures [138], but literature is contradictory regarding the best approach.

The appropriate timing for carrying out a neurolytic plexus block should be further investigated but it may be advantageous to perform it before the second step of the WHO analgesic ladder rather than the fourth step [139].

Vertebroplasty and kyphoplasty are vertebral augmentation procedures consisting of an injection of bone cement into the cancellous or spongy bone of the vertebral body to alleviate pain caused by a vertebral compression fracture. In kyphoplasty, a modification of vertebroplasty, a balloon is previously inserted and inflated in order to create a cavity and only then the bone cement is injected. There is no clear evidence indicating that one of the procedures is superior to the other [145].

Contraindications for these procedures include overt instability, cord compression with clinical myelopathy, infection at the fracture site, bleeding disorders and low platelet count. When cord compression is present without neurological symptoms, neuromonitoring or local anaesthesia with an anterior delivery of cement is advisable [145].

Serious complications are rare with polymethyl methacrylate extravasation being the most common. However, it is asymptomatic and is less frequent in kyphoplasty [145].

In spite of many technical and pharmacological advances, cancer pain remains a major cause of suffering resulting in poor quality of life for the patients. Cancer pain management presents many difficulties such as lack of pain assessment and education in opioids prescription including fear of side effects. New medications and invasive techniques may increase pain relief for cancer patients. However the healthcare provider should always have in mind the complexity of the total pain to find the better approach of its different dimensions contributing not only to the relief of pain, but also allowing exceedingly better quality of life to the patients consequently reducing healthcare and socio-economic burdens.