1
History of Interventional Pain Medicine

Formative Years

The contemporary era in pain management really began with the discovery of nitrous oxide and its analgesic properties in the late 18th century. This was soon followed by scientific investigation of the anesthetic properties of nitrous oxide and ether on animals, and the use of these substances in human patients. Surgical anesthesia was first publicly demonstrated at Massachusetts General Hospital in 1845 and 1846. The discovery and use of anesthetics changed the perception of pain (Fig. 1.1). In the 1850s Charles Gabriel Pravaz, a French surgeon, and Alexander Wood of Edinburgh independently invented the syringe (Fig. 1.2a,b), which allowed injections of morphine. By the 1860s the efficacy of locally applied opiates, especially morphine, directly to the skin or nerves for pain relief was widely accepted. The effects of pre- and intraoperative administration of morphine to the area of incision or amputation were investigated. When cocaine became available as a local anesthetic, owing to the work of Sigmund Freud and, especially, Karl Koller, this soon resulted in its use as a local anesthetic in diverse procedures (Fig. 1.3a,b).

Figure 1.1 The first surgical anesthesia in Massachusetts General Hospital in 1845.

Figure 1.2 (a) Gabriel Pravaz, courtesy of Wellcome Library, London. (b) Alexander Wood, reproduced with permission from Peter Stubbs (www.edinphoto.org.uk).

Figure 1.3 (a) Sigmund Freud, (b) Karl Koller (courtesy of the Wood Library Museum of Anesthesiology, Park Ridge, IL, USA).

Surgical techniques for pain relief represented another great medical advance during the 19th century. With the advent of antiseptic surgery, procedures became less life threatening, allowing investigation of pain relief techniques involving permanent interruption of afferent pathways. Innovative techniques were developed for treating trigeminal neuralgia, in addition to procedures such as retrogasserian neurectomy and cordotomy, ablation of the sympathetic nervous system, sympathectomy for visceral pain and angina pectoris, and surgical management of neuralgia.

Pain Mechanisms

Little was understood about pain mechanisms at the beginning of the 19th century. Many questions such as how sensibility related to movement, whether separate sensory and motor nerves existed, and whether single nerves could perform different functions were still unanswered. Early researchers tried to explain pain by concentrating on the specialization of functions in different parts of the brain. Animal experiments investigating the function of spinal nerve roots were more successful, significantly contributing to medical knowledge during this period. Investigators such as Claude Bernard, Charles Bell, and Francois Magendie developed innovative experimental procedures that allowed differentiation of sensation from movement and between functions of anterior and posterior spinal nerve roots. A significant impetus to the perception of the nervous system as a system involving the transmission of sensations from the periphery to the center through a system of complex relays was provided by the work of German physiologist and comparative anatomist Johannes Muller (Fig. 1.4).

Figure 1.4 Johannes Muller.

Muller proposed a connection between the anatomic pathway of a fiber and perception of sensation, stimulating further research on specific fibers for pain and nociception. As a result of such work, an entirely new school of physiologic research was founded. Soon nerve structures were identified in the dermis, leading to investigation of dissociation of sensations in that region, such as sensation of touch, pressure, and pain; and the spinal cord was more realistically appraised as a central processor with the ability itself to affect the transmission of sensations. Other noteworthy contributions were made by Waller, who developed a sectioning technique allowing observation of fatty degeneration of a fiber, leading to an awareness of ascending and descending pathways and the origin of nerve fibers.

There were many other pioneers who, through work with patients in pain or self-experimentation, contributed to the general body of medical knowledge: Weir Mitchell's work with neuritis, neuralgia, and causalgia, Henry Head's discovery of two different types of nerve fiber, and Sherrington's notion of an integrated nervous system were major advances establishing a firm foundation for an understanding of pain mechanisms and more effective approaches to treatment (Fig. 1.5).

Figure 1.5 Weir Mitchell. (Courtesy of the Clendening History of Medicine Library, University of Kansas Medical Center.)

We are indebted to Melzack and Wall for perhaps the most significant leap in understanding, the gate control theory. This explanation located both facilitators and inhibitory influences on the cells of the substantia gelatinosa of the spinal cord; with large-diameter, fast-conducting touch fibers suppressing, and smaller-diameter, slower-conducting pain fibers increasing, central output. Because nerve lesions usually involve smaller fibers, they result in over-activity of the substantia gelatinosa. Scar formation at the site of nerve injury causes complications, increasing nerve excitability at the site of the lesion (Fig. 1.6).

Figure 1.6 R. Melzack and P. Wall. (Courtesy of Dr. Ronald Melzack.)

Establishment of Interventional Pain Medicine

Greater understanding of pain mechanisms has resulted in the development of devices offering innovative therapeutic approaches. For instance, dorsal column stimulators were a direct result of the gate control theory. The efficacy of treatment relies on stimulation of low-threshold primary afferent fibers, which causes central inhibition of pain signals. Dorsal column stimulators are now an effective means of treating patients with chronic neuropathic and vascular pain. In addition, peripheral nerve stimulators have been used to manage chronic pain after peripheral nerve injury. Deep brain stimulation is a newer technique, still somewhat uncertain in terms of efficacy of pain relief.

New treatment techniques represent another beneficial byproduct of pain-related research. For instance, the discovery of opioid receptors in the central nervous system provided a rationale for the development of intrathecal and epidural administration of opioids. These now active techniques have resulted in the formation of a new sub-specialty under the umbrella of primary specialists of pain medicine. This sub-specialty has been called interventional pain medicine.

Biotechnology allows drugs targeted towards specific physiological processes to be developed, sometimes designed for compatibility with the body to reduce side effects. Genomics and knowledge of human genetics is having some influence on medicine, as the causative genes of most monogenic disorders have now been identified. In addition, the development of techniques in molecular biology and genetics is influencing medical technology, practice, and decision-making.

Evidence-based medicine is a contemporary movement to establish the most effective algorithms of practice through the use of systematic reviews and meta-analysis. The movement is facilitated by modern global information science, which allows all evidence to be collected and analyzed according to standard protocols, which are then disseminated to healthcare providers. One problem with this "best practice" approach is that it could be seen to stifle novel approaches to treatment. The Cochrane Collaboration leads this movement.

Defining a Pain Specialist

John Bonica was the first anesthesiologist who experienced the difficulties of pain management during his years in the army as he was treating the wounded soldiers from the Pacific. He felt strongly that no one particular physician is capable of looking after a patient with pain. He proposed the first concept of multidisciplinary approach to pain management.

What defines a "pain specialist?" Rollin Gallagher stated, "specialties define themselves [in] many ways: by age group (pediatrics), organ system (cardiology), specific constellation of illnesses or diseases (infectious diseases), type of procedure (surgery), or practice setting (emergency medicine)." Held to this definition, pain management becomes a unique specialty indeed. Although pain management is concerned with the diagnosis, treatment, and rehabilitation of a singular sensory symptom, it is essential that practitioners undertake a multidisciplinary approach to achieve these ends. They must also be well versed in the study of pain and its prevention. Although more than 60% of pain specialists originate from the field of anesthesiology, they can also come from a variety of other disciplines such as interventional radiology, physical therapy, psychiatry, primary care medicine, and neurology. In addition, pain specialists must possess a keen understanding of the variety of conditions and causes associated with pain. This broad range of training and knowledge allows the practitioner to achieve their ultimate goal: the management of a patient's pain. Despite these extensive requirements, pain management remains classified as only a subspecialty of anesthesiology under the...