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Extracorporeal shock wave lithotripsy (ESWL) is a non-invasive procedure that allows urinary stones to be fragmented using acoustic shock waves. The impact of the shock waves causes transient stinging pain at the entry site as well as deep visceral discomfort, requiring analgesia during the procedure. The objective of this study was to compare the clinical efficacy of Entonox and pethidine for pain relief during outpatient ESWL. We randomized 150 outpatients undergoing elective ESWL into three groups of 50 patients, each group receiving inhalational Entonox, intravenous pethidine, or inhalational compressed air during ESWL. Quantitative evaluation of pain was performed according to a visual analogue scale (VAS), before and after the intervention. Analysis of variance (ANOVA) and paired t tests were used to compare VAS scores in the three groups, before and after the intervention. Entonox and pethidine decreased the pain score significantly, while compressed air did not. There was no significant difference between pain relief by Entonox and pethidine. This study demonstrates for the first time that inhalational Entonox is an effective analgesic regimen for ESWL. Entonox can be regarded as an appropriate alternative to analgesics like opioids in relieving pain during ESWL.

The paper develops a new theory of chronic pain and pain relief by extracorporeal shock wave treatment. Chronic pain without underlying anatomical disorder is looked at as a pathological control function of memory. Conditioned reflexes are considered to be engraved memory traces linking sensory input of afferent signals with motor response of efferent signals. This feature can be described by associative memory functions of the nervous system. Some conditioned reflexes may cause inappropriate or pathological reactions. Consequently, a circulus vitiosus of pain sensation and muscle and/or vessel contraction is generated when pain becomes chronic (pain spiral). The key feature is a dedicated engram responsible for a pathological (painful) reaction. The pain memory may be explained by the concept of a holographic memory model published by several authors. According to this model it is shown how nervous systems may generate and recall memory contents. The paper shows how extracorporeal shock wave treatment may reorganize pathologic memory traces, thus giving cause to real and permanent pain relief. In a generalized manner, the idea of associative memory functions may help in the understanding of conditioning as a learning process and explain extracorporeal shock wave application as an efficient treatment concept for chronic pain. This concept may open the door for new treatment approaches to chronic pain and several other disorders of the nervous system.