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PAIN AND AWARENESS DURING GENERALANAESTHESIA

SIR,-Although about 1% of patients experience awarenessduring general anaesthesial the subject is poorly documented andprevious investigations have not generated enough cases for theexperience to be characterised. To investigate this further I placed asmall advertisement in the personal columns of three Britishnewspapers asking readers to report instances of awareness duringgeneral anaesthesia. Further details of this investigation will bepublished elsewhere2 but three aspects deserve particular mention.27 reports of awareness were obtained, relating to events up to 59

years previously (average 18 years); the experiences were clearlyenduring. 21 patients found the experience disturbing and 9 of themthought it the worst experience of their lives; surprisingly, the other6 did not. 20 of the 21 patients who found awareness disturbing hadfelt pain while only 2 of the 6 patients who were not disturbed hadfelt pain. This is consistent with the observation that patients whoare aware during high-dose narcotic anaesthesia, as often used foropen heart surgery, do not appear to report awareness in terms of

any great distress; in contrast, almost all patients who take legalaction in respect of awareness have experienced severe pain (L.Hargrove, personal communication). Thus the perception of painduring periods of awareness may cause patients very much distress.

3 reports described experiences during childhood, at the ages of 4,4, and 7 years. Could awareness be more common in children thanin adults? Anaesthesia requirements increase with decreasing ageduring most of childhood, and children are often lightlyanaesthetised. In the only study of awareness in children McKieand Thorps found dreams and awareness reported in 11 % of cases,5 % experiencing awareness.Thus the provision of adequate analgesia during anaesthesia

should not only counter the physiological stress of surgery (asdiscussed in your Sept 5 editorial) but also guard againstpsychological stress and sequelae during periods of awareness; thismay be especially important for children. The practical applicationof this policy presents a dilemma. Anaesthesia based largely uponnarcotic analgesics is generally held to carry a greater risk ofawareness-but the patient may be pain-free. On the other hand,anaesthesia based upon volatile agents is thought to have a lower riskof awareness but, for those patients who are aware, the experiencemay prove painful and unpleasant.Nuffield Department of Anaesthetics,Radcliffe Infirmary,Oxford OX2 6HE JOHN M. EVANS

1 Breckenndge JL, Aitkenhead AR Awareness during anaesthesia: a review Ann RoyColl Surg Engl 1983; 65: 93-96.

2 Evans JM. Patients’ expenences of awareness during general anaesthesia. In: RosenM, Lunn JN, eds. Consciousness, awareness and pain in general anaesthesia.London: Butterworths (in press)

3 Hilgenberg JC. Intra-operative awareness during high-dose fentanyl-oxygenanesthesia. Anesthesiology 1981, 54: 341-43.

4. Mummaneni N, Rao TLK, Montoya A. Awareness and recall with high-dose fentanyloxygen anesthesia Anesth Analg 1980; 59: 948-49.

5. McKie BD, Thorp EA. Awareness and dreaming dunng general anaesthesia in apaediatric hospital. Anaesth Intens Care 1973; 1; 407-14.

HYPERVENTILATION AND ANAESTHETIC

REQUIREMENT IN BABIES

SiR,—Your Sept 5 editorial, which discusses the provision ofadequate anaesthesia for premature and newborn infants, states thathyperventilation reduces the minimum alveolar concentration

(MAC), a measure of anaesthetic potency, of nitrous oxide inbabies. However, there is no evidence to support this statement. Incontrast, studies contradict this supposition.

In dogs, halothane MAC is not altered by reducing PCO from42 to 14 mm Hg.1 In adults, halothane MAC does not differ innormocapnic cases (PaC02 38 mm Hg) compared with hypocapnicpatients (PaC02 21 mm Hg) The influence of hyperventilation orinitrous oxide MAC has not beeri determined in adults or babies.Measurement of nitrous oxide MAC (1-04 atm absolute) in youngadult volunteers under non-hyperventilating conditions requiredthe use of a hyperbaric chamber.3 Nitrous oxide MAC in babies isnot known.

Hyperventilation does not alter MAC in adults. Although babiesmay be different from adults in this regard, studies demonstrating adecrease in nitrous oxide MAC in babies with hyperventilation havenot yet been done.

Department of Anesthesia,University of California, San Francisco,California 94121, USA DONALD D. KOBLIN

1. Eger EI II, Saidman LJ, Brandstater B. Minimum alveolar anesthetic concentration: astandard of anesthetic potency. Anesthesiology 1965; 26: 756-63.

2. Bridges BE, Eger EI II. The effect of hypocapnia on the level of halothane anesthesiain man. Anesthesiology 1966, 27: 634-37.

3. Hornbein TF, Eger EI II, Winter PM, Smith G, Wetstone D, Smith KH. Theminimum alveolar concentration of nitrous oxide in man. Anesth Analg 1982; 61:533-36.

SiR,—The misapprehensions of those who reacted against DrAnand and colleagues’ study are regrettable. But in another respect,it is impossible to use language too hyperbolic or excessive to-describe the practice which, though prevalent, was not discussed atlength in your editorial-that of conducting major surgery of alltypes on premature and term infants with no pain relief or

anaesthesia whatsoever, not even nitrous oxide.In 1985 our severely premature son had a ’Broviac’ catheter

implanted and patent ductus arteriosus surgery over a period of 1 V2hours. He was not moribund. He was not comatose. He was in noimmediate danger from symptoms caused by his open ductus;rather the surgery was scheduled to increase his chances of asuccessful outcome over the long run. On the morning of theoperation, planned 3 days in advance, his blood pressure was lowand he became unstable when being taken to the theatre. Instead ofwaiting until he was stable the anaesthetist paralysed him, and heunderwent thoracotomy with only oxygen and paralysing agents. Iwas later told that pain relief had been withheld not only because oflow blood pressure but also because it had never been demonstratedthat babies can feel pain. My son died 5 weeks later after a"worst-case" clinical course comparable with that described byAnand and colleagues for infants unprotected from surgical stress.What happened to my son meets the dictionary definition of

vivisection. Even so I delayed going to the media for 7/2 monthswhile trying to work with hospital staff, local and national

associations, and regulatory bodies. If any one of them had takenaction, I never would have "gone public". But not one did act, andthe local medical society declared that the anaesthetist had done agood job. Thus public disclosure1 offered the only hope forpromoting change in our medical community. Some reporting hasbeen inaccurate. This happens when lay people are forced to enterthe technically difficult world of physicians to defend their children.You may label some of their efforts inaccurate, inappropriate, orwhatever-just please continue to help us.

9404 Piney Branch Road, Apt 205,Silver Spring, Maryland 20903, USA JILL R. LAWSON

1 Lawson JR. Letter to the editor Birth 1986; 13: 125-26

MONITORING FOR ANAESTHESIA

SIR,-Your Sept 26 editorial on monitoring during anaesthesiadid not discuss monitor design. Anaesthetists may welcome

guidance on the mass of devices (and information derived fromthem) now on offer from equipment manufacturers.

Monitors designed for use in theatre usually contain

microprocessors which can perform a variety of functions. Self-testing apart, the machines provide a range of alarms andinformation from basic data to complex trend analyses. Ifanaesthesia is progressing smoothly these displays can be examinedat leisure. However, if the monitor detects a problem, the alarm anddisplay systems are often so complex that a significant amount oftime can be spent trying to find out what has changed and turningoff the alarms, which can be distracting. Occasionally essentialinformation has to be obtained by interrogating the monitor via akey system, which means more time and attention being deflectedfrom the patienti