Analgesic supplementation of light general anaesthesia

General anaesthesia for major surgery requires narcosis, relaxation and freedom from the harmful response to the trauma of operationl.This latter was termed 'analgesia' in a publication by Gray & Rees2 in which the now-accepted benefits from hyperventilation were extolled.The use of intravenous analgesics as supplements in anaesthetic techniques was introduced by Neff, Mayer & Perales3 in 1947 in America and by Mushin & Rendell-Baker4 in 1949 in Britain and has achieved wide popularity.This is based on the assumption that they will obviate the harmful effects of reflex autonomic stimulation during light anaesthesia.While very light planes of narcosis with specific analgesic and relaxant drugs have the advantage of reducing the need for large doses of potent agents such as ether, their use may expose the patient to other risks, including untoward effects on the circulation5.This had been first suggested by Loder 6 , who condemned light general anaesthesia with relaxants as being inadequate for major surgery.He described hypotension with bradycardia, pallor and sweating following traction on abdominal viscera and showed that these could be overcome by blocking autonomic ganglia with local anaesthetics.Davies7 suggested that similar beneficial effects could be obtained by intravenous supplementation with thiopentone or pethidine during anaesthesia.On the contrary, Heller, Watson & Storrs 8 found 'light plane analgesia' (thiopentone-nitrous oxide oxygen-relaxan t, with occasional early use of small amounts of pethidine) was not harmful to cardiovascular function 'by virtue of non-suppression of traumatic autonomic reflexes'.Thus, the present position with regard to the benefits of analgesic supplementation of nitrous oxide-oxygen-relaxant anaesthesia is by no means clear.Gray1 states that 'there is no real evidence that powerful narcotic agents . . .such as pethidine influence these reflexes other than by a general central nervous depression similar to, and sometimes longer