Ketamine was originally synthesized in April 1962 by Calvin Stevens, a consultant for a Parke-Davis/Warner Lambert1 program aimed at finding a safer anesthetic alternative to phencyclidine (PCP). From a clinical point of view, ketamine has been classified as a dissociative anesthetic. The term 'dissociative' suggests that the sensory loss and analgesia as well as amnesia are not accompanied by actual loss of consciousness (Bonta 2004). Sometimes this unique experience incorporates a strong sense of dying. For instance, Barbara Collier, an anesthetist commented: 'Ketamine allows some patients to reason that . . . the strange, unexpected intensity and unfamiliar dimension of their experience means they must have died'2 (Collier 1972).
This characteristic effect is also produced by a few other dissociative anesthetics, such as nitrous oxide (N2O), commonly known as 'laughing gas' for its exhilarating effects. Following his explorations with the substance, Humphry Davy published Researches, Chemical and Philosophical; chiefly concerning Nitrous Oxide (... ) and its Respiration (1800), in which he observed that 'nothing exists but thoughts'. He also noticed other interesting effects such as 'an immediate thrilling, a pleasure in every limb, and an intensification of both vision and hearing'. He wrote:
A sensation analogous to gentle pressure on all the muscles, attended by an highly pleasurable thrilling, particularly in the chest and the extremities. The objects around me became dazzling and my hearing more acute. Towards the last inspirations, the thrilling increased, the sense of muscular power became greater, and at last an irresistible propensity to action was indulged in; I recollect but indistinctly what followed; I know that my motions were various and violent.
William James observed that nitrous oxide can 'stimulate mystical consciousness in an extraordinary degree' and that it reveals 'depth beyond depth of truth' (James 1902: 305). He made these observations in his Gifford Lectures, later published as The Varieties of Religious Experience (1902). One of his conclusions was that human beings have additional 'fields of consciousness':
My impression is . . . that our normal waking consciousness, rational consciousness as we call it, is but one special type of consciousness, whilst all about it, parted from it by the filmiest of screens, there lie potential forms of consciousness entirely different. We may go through life without suspecting their existence.
Other common dissociative anesthetics are DXM (dextromethorphan), a medicine with anti-tussive (cough suppression) properties, PCP (Phency-clidine), and sometimes high doses of alcohol. It is important to observe that dissociation is a broad term that can include the effects of a very wide range of substances. For instance, Meduna in the 1950s used carbon dioxide to induce NDE-like states as an aid to psychotherapy (Meduna 1950).
Ketamine is currently used in many general hospitals around the world, with a recent increase in use in Emergency Departments and in chronic pain clinics (Parke-Davis 1999-2000; Bell et al. 2006; Sehdev et al. 2006). It is often used during severe asthmatic crisis, childbirth, and surgical operations, and occasionally in the treatment of migraine and in anesthesia for children (Jansen 2001). It is relatively safe because it does not usually suppress breathing as much as other anesthetics and it has a short duration of action (30-60 minutes). The substance also has good analgesic and amnesic properties. At small doses (0.1-0.5 mg/kg/hr), it appears to stimulate rather than depress the central nervous system (for instance, Jansen 1989), and it has been used for treatment of pain associated with movement and neuropathic pain. However, as I will discuss later in greater detail, at sub-anesthetic doses (10-25 per cent of a surgical dosage), ketamine can produce effects similar to those described during a near-death experience (Moody 1975; Greyson and Stevenson 1980; Fenwick and Fenwick 1995).
In order to prevent dissociative experiences in surgical settings, the drug is often given together with diazepam (Valium®) and other sedatives (Reich and Silvay 1989). Some authors have suggested that the substance can have beneficial effects as an aid in psychotherapy (Grinspoon and Bakalar 1979; Strassman 1995; Krupitsky 1997; Mills et al. 1998). However, the use of psy-chedelics in therapy remains a highly controversial topic in contemporary psychiatry (Jansen 2001; Arnone and Schifano 2006).
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