Nerve blocks, synonymous with regional anesthesia, refer to the reversible interruption of nerve signal transmission with the use of various drugs (local anesthetics). This interruption of potential transmission can occur in any area where nerves are accessible to an external approach. It is the only pharmacological approach capable of stopping the pain. This is due to the exclusive ability of local anesthetics to cause a strong blockade of aesthetic perception. Based on correct indications and agreed therapeutic approaches they can be used for surgical anesthesia, perioperative analgesia, as well as for the diagnosis, prognosis and treatment of chronic painful conditions.
Surgical blocks: Nerve blocks of spinal nerves have long been used in clinical anesthetic practice but increasingly in recent years. Either as simple one-off blocks or as continuous blocks using infusion catheters, they are used in upper and lower extremity and trunk surgeries, either alone or more often in combination with a basic general anesthesia or sedation.
Their main advantages over regional spinal anesthesia techniques are the avoidance of serious neurological complications, greater hemodynamic stability and less impact on motor function. A recent systematic review concluded that the majority of locoregional techniques are beneficial to patients and hospital operations by reducing postoperative pain and opioid consumption and/or increasing patient satisfaction.
The use of ultrasound guidance over the last decade has been found in recent systematic reviews to improve their performance and clinical outcomes, and to reduce the risk of local anesthetic toxicity. Regional anesthesia may potentially limit central pain sensitization and influence the development of chronic postoperative pain. Mechanisms that have been proposed include 1) Decreased postoperative nociceptive neural activity 2) Decreased changes in synaptic neuroplasticity in the CNS and 3) Altered interaction properties of non-nociceptive cells such as microglia in the CNS.
Local anesthetic injection for a nerve block has been shown to reduce acute inflammation, baseline cytokine production, and central markers of pain sensitization, as well as acute postoperative pain.
Based on a detailed literature review, an interdisciplinary team led by Chou, Gordon, de Leon-Casasola et al. issued recommendations for their use in clinical practice in 2016 with a strong recommendation based on high-quality evidence for the use of peripheral blocks depending on the surgical site in adults and children, as well as for the use of continuous nerve block techniques where the need for analgesia likely exceeds the effective duration action of the single injection.
Diagnostic blocks: Many chronic pain conditions do not have specific morphological features detectable by clinical examination or imaging. For some of these, nerve blocks can be used to identify the source of pain. The basis for this is that if a structure is the source of pain, then if its innervation is anesthetized or blocked the pain will cease and vice versa. Nerve blocks cannot identify the pathological process behind the painful condition. But they can tell if an anatomical structure is the main source of pain. For example, analgesia after a ilioinguinal and iliohypogastric nerve block in patients with inguinal pain cannot differentiate between neuropathy of these nerves and damage to the tissues they innervate. However, reports point out that it can act therapeutically. The best documented diagnostic blocks are median branch blocks in relation to zygopophyseal joint pain.
Prognostic blocks: Blocks used to draw conclusions regarding the possible efficacy of semi-permanent blocks, neurolysis or surgical sympathectomy are called prognostic and can be used to prepare the patient for the results of a permanent block.
Therapeutic blocks: The use of therapeutic blockades has a long tradition and literature. At first, it seems strange to expect a therapeutic effect from local anesthetic injection, as its effect on nerve transmission is short-lived. Still, various publications report effects that extend beyond the duration of nerve transmission blockade, such as greater occipital nerve (GON) blockade for the treatment of headache, one of the best-studied therapeutic blockades, as well as sphenoparietal ganglion blockade in chronic migraine.
Usually these blockades are carried out with a combination of local anesthetic, steroid agents and other drugs, which in themselves have beneficial effects such as for example corticosteroids which provide analgesia in neuralgia through their anti-inflammatory action but also through the stabilization of nerve membranes’ action potential and the reduction of their ectopic depolarizations.
At least three phenomena concerning the response to nerve blocks are described in the literature. 1) Analgesia may last much longer than the duration of the nerve block. 2) Blockade distal to the area of the lesion responsible for the pain may stop or reduce the pain and 3) Blockade of a nerve innervating a large part but not the entire area of pain, it can provide analgesia to the entire area. These phenomena have strengthened the therapeutic potential of nerve blocks in the treatment of chronic painful conditions.
One of the proposed mechanisms for the prolonged duration of the effect is the facilitation of functional and psychological rehabilitation of patients through the temporary reduction of pain from nerve blocks. Patients who achieve analgesia may be able to increase their activity and improve their mood, resulting in a long-lasting effect on pain intensity. Besides, it is suggested that one of the mechanisms of pain chronicity is the hyperactivity of peripheral neurons which is limited by nerve blocks.
The literature over the past five years has focused primarily on performing ultrasound-guided nerve blocks, with few case reports on therapeutic usage of nerve blocks in chronic pain conditions, and those for newer blocks such as fascial plane blocks. Publications report positive results, with their usage in cases of neuralgia being an alternative solution in over half of patients. In modern clinical practice indeed, even empirically and despite the absence of Evidence Based evidence, this happens. A critical element is the pre-existing time of neuralgia.
A large retrospective study by Gergen, Fritzsche, Denke, Schafer and Tafelski published in July 2020 evaluated the results of a series of ganglionic and peripheral nerve blocks as a treatment option in patients with chronic intractable neuropathic pain, with the aim of evaluating their effectiveness. 4960 patients attending a university hospital pain clinic between 2009 and 2016 were evaluated. Age, months of pain before the first infusion, and improvement in pain after the first two injections were identified as predictors of clinical response in the block series. The results of the study showed an overall improvement during the first 6 injections. The researchers acknowledged several limitations of the study but concluded that their retrospective study demonstrated a beneficial effect of blocks as a treatment for intractable pain syndromes, with the treatment effects being significant and of clinical relevance, as treatment options in these patients are limited.
Several publications over the past twenty years, involving case reports and patient series (16 publications involving 79 patients) have reported the successful use of peripheral nerve blocks in selected patients with cancer pain. The most commonly used blocks were paraspinal blocks, brachial plexus blocks, and intercostal nerve blocks. Sympathetic blocks such as block of splachnic nerves, celiac plexus, hypogastric plexus are prooved in studies a useful and effective intervention in cancer pain. The reduction in pain and the amount of opioid drugs in cases of intractable cancer pain demonstrate them as a convenient solution that is underutilized, probably due to the small percentage, only 3-4%, of cancer patients whose pain is treated by a pain specialist, who should also be trained in interventional techniques. Besides, 80% of cancer patients experience pain, 50% of which is not effectively controlled by pharmacotherapy, while 25% of these patients die with pain.
