EFFECT OF SURGICAL STIMULATION ON THE AUDITORY EVOKED RESPONSE

Previous studies have shown a dose-related effect of a numberof general anaesthetic agents on the early cortical waves inthe auditory evoked response (AER). In this study the effectof surgical stimulation on these waves was examined in 11 patientsanaesthetized with thiopen-tone, nitrous oxide and halothaneand paralysed with pancuronium. The inspired nitrous oxide concentrationand end-tidal halothane concentration were held constant at70% and 0.3%, respectively, and baseline AER recordings weremade. Following surgical stimulation there was a progressiveand significant increase in the amplitude of waves Nb and Pb/Pc.Unambiguous autonomic responses were seen in three patients,but these were not significantly correlated with changes inthe AER. We conclude from this, and previous studies, that theamplitude of cortical waves in the AER are sensitive not onlyto anaesthetic concentration but also to surgical stimulation.The may, therefore, provide a useful index of depth of anaesthesia,that is the balance between the effects of surgical stimulationand anaesthetic depression on central nervous system activity. Present address: University Department of Anaesthesia, 24 HydeTerrace, Leeds LS2 9LN.     

ENFLURANE ANAESTHESIA CAUSES GRADED CHANGES IN THE BRAINSTEM AND EARLY CORTICAL AUDITORY EVOKED RESPONSE IN MAN

The effect of increasing end-tidal enflurane concentration onthe auditory evoked response was studied in six patients. Aftera standard induction, anaesthesia was maintained with 70 nitrousoxide in oxygen and the end-tidal enflurane concentration wasincreased gradually from 0 to 1 over a period of 30 min. Theaveraged auditory evoked response was derived from the electroencephalogramand measurements were made of the latencies and amplitudes ofwaves I, HI, V, Pa and Nb within the auditory evoked response.The latencies of all waves and the interpeak latencies I toV and HI to V showed significant linear increases and the amplitudesof Pa and Nb showed significant linear decreases with increasingend-tidal enflurane concentration. These results could not beexplained by changes in deep body temperature or end-tidal carbondioxide concentration. The study demonstrated a dose-relateddirect effect of enflurane on the brainstem and early corticalcomponents of the auditory evoked response.     

THE EFFECT OF TUBOCURARINE ON ULNAR NERVE CONDUCTION VELOCITY

Nerve conduction velocity was studied in the ulnar nerve ofhuman subjects during general anaesthesia. An increase in velocityof between 1.9 and 4.8 per cent occurred following the administrationof paralytic doses of tubocurarine to subjects receiving nitrousoxide, oxygen and halothane anaesthesia in whom ventilationwas controlled. This increase in velocity did not appear tobe related to a change of subcutaneous temperature.     

Reduced Levels of Serum Haemolytic Complement and Renal Lesions in Ovum-Fusion-Derived Tetraparental Mouse Chimaeras

Tetraparental mice of the NZB↔CFW chimaeras were examined for: [I] the degree and location of antibody and complement deposition in the kidneys; [2] the origin of the complement deposited in the kidneys; and [3] serum haemolytic complement levels These data were compared with similar observations on pa rental-strain mice and other chimaeric combinations The renal lesions showed hath quantitatively and specially increased deposition of antibody and complement in the NZB↔CFW chimaeras compared with the controls In addition, the complement in the kidneys was shown to induce C5 of CFW origin. Finally, serum haemolytic complement in the chimaeras was undetectable despite the fact that CFW mice have rather high levels of haemolytic complement. It is argued that one explanation for these findings could be the presence of chronic allogeneic disease in the chimaeras. Other evidence for the existence of such a state it cited, but it is noted that such findings are not seen in all chimaeric combinations.     

EARLY CORTICAL AUDITORY EVOKED RESPONSE IN ANAESTHESIA: COMPARISON OF THE EFFECTS OF NITROUS OXIDE AND ISOFLURANE

Previous studies showing graded changes in the early corticalwaves Pa and Nb of the auditory evoked response (AER) with increasingconcentration of volatile anaesthetic agents demonstrated highamplitudes of these waves in the period immediately followinginduction of anaesthesia and tracheal intubation, when the patientbreathed nitrous oxide alone. These high amplitude waves werenot consistent with extrapolation of the data or observationsof patients under steady-state nitrous oxide anaesthesia. Inorder to discriminate between effects in the period immediatelyfollowing induction of anaesthesia and tracheal intubation,and effects caused by nitrous oxide alone, a randomized cross-overstudy was performed. Eight patients breathed either nitrousoxide or isoflurane at 0.6 MAC for three consecutive 10-minperiods following intubation and before surgery. The amplitudesof Pa and Nb were significantly less for isoflurane with respectto the same MAC fraction of nitrous oxide in all periods, butfor both agents the amplitudes were significantly greater inthe 10 min following intubation than in subsequent periods,presumably as a result of stimulation. ^*Present address: Hospital for Sick Children, Great Ormond Street,London WC1.     

EFFECT OF ISOFLURANE ON THE AUDITORY EVOKED RESPONSE IN MAN

We have examined the effects of isoflurane (0.6–2.9% end-tidal)on the auditory evoked response (AER) in six patients beforeelective surgery. Isoflurane produced significant dose-relatedchanges in the AER: reductions in amplitude and increases inlatency of the cortical waves Pa and Nb, and increases in thelatency of the brainstem waves III and V. When isoflurane wascompared with halothane and enflurane using an MAC-based comparison,we found no differences in the effect of the three agents onthe amplitude of the early cortical waves, although the latenciesshowed significant differences. The consistent dose-relatedeffect on the amplitudes of the cortical waves implies thatthe AER could be a promising index of the depth of anaesthesia.     

THE AUDITORY EVOKED RESPONSE AS AN INDICATOR OF AWARENESS

The latency of the early cortical wave Nb of the auditory evokedresponse (AER) was compared with responses to Tunstall's isolatedforearm test, while, the concentration of nitrous oxide wasprogressively reduced during light anaesthesia in seven patients.A threshold Nb latency of 44.5 ms was chosen to discriminatebetween an early cortical AER containing three waves and thatwith two waves of longer latency. When Nb latency decreasedbelow this threshold, four of the patients has positive responses,indicating awareness. The addition of a volatile anaestheticabolished any response, and increased Nb latency to more than44.5 ms. The three wave AER pattern, therefore, is associatedwith a depth of anaesthesia at which awareness occurs.     

Sexual Risk Cognitions Questionnaire: A reliability and validity study

The Sexual Risk Cognitions Questionnaire was designed to assess the type and frequency of cognitions associated with unsafe sex. It consists of 22 core items (SRCQ-22) with six subsections. Each subsection consists of 8-12 items designed for specific subgroups defined by gender, sexual orientation and HIV serostatus. Data on reliability and validity are presented based on a sample of 344 respondents in London. Reliability for all sections of the questionnaire was high but sample numbers were relatively small for some subsections. Validity for the SRCQ-22 was assessed in terms of its relationship with self-reported sexual behaviour among men who have sex with men who made up the largest proportion (70%) of the sample. The results indicate that the SRCQ-22 is a reliable measure for assessing cognitions related to HIV risk sexual behaviour in this population and supports the view that they are important determinants of safe and unsafe behaviour.     

Diagnostic model for local temporal thermal change at the skin of the breast during extended application of diagnostic ultrasound

A biophysical model is derived to account for the temporal thermalchange at the skin of the breast as a result of ultrasound stimulationat the suspect lesion for seven minutes, with responses recordedusing an infrared camera. Twenty-two patients were studied.The observed temporal responses for malignant cases have a differentpattern from those of the benign cases studied and a mathematicalmodel is used to investigate the controlling parameters. A newmethod is used to estimate the coefficients of the resultingdifference equation which allows more useful diagnostic parametersto be computed than the corresponding continuous bioheat equation.The model is used to fit the experimental data. The resultssuggest that this method might be a rapid and noninvasive aidfor distinguishing between benign and malignant breast tumours.     

In vivo'Purging' of residual disease in CLL with Campath-1H

We assessed the role of human CD52 antibody (Campath-1H) in six patients with chronic lymphocytic leukaemia (CLL) treated to maximal response with purine analogues (fludarabine/deoxycoformycin) in whom persistent leukaemic infiltration of blood and bone marrow had precluded autologous stem cell transplantation. Five patients achieved haematological and histological complete remission following Campath-1H and one had minimal focal residual CLL in a trephine biopsy. Autologous transplantation was performed in two patients without complications and with rapid haemopoietic engraftment. Treatment with Campath-1H may be of value in eradicating residual disease in CLL and may facilitate high-dose therapy in young patients.