POSTGANGLIONIC SYMPATHETIC DISCHARGE AND THE EFFECT OF INHALATION ANAESTHETICS

Postganglionic cardiac, carotid, and hypogastric sympatheticactivity was recorded before and during administration of inhalationanaesthetics, in rabbits ventilated with oxygen and given gallamine.During control periods, when light anaesthesia was maintainedwith pentobarbitone, changes in postganglionic sympathetic dischargepreceded, or responded to, alterations in arterial pressure.Postganglionic activity was increased by cyclopropane, whichraised arterial pressure; by ether, which produced more variablecirculatory changes; and usually by halothane, which loweredarterial pressure. Occasional sympathetic units, identifiedon film, showed partial inhibition during halothane anaesthesia. ^*Addenbrooke's Hospital, Cambridge. Present address: Dept. of Physiology, Australian National University,Canberra.     

PREGANGLIONIC SYMPATHETIC ACTIVITY AND THE EFFECTS OF ANAESTHETICS

Preganglionic cervical and splanchnic sympathetic activity wasrecorded before and during administration of inhalation anaesthetics,in rabbits ventilated with oxygen and given gallamine. Duringcontrol periods; when light anaesthesia was maintained withpentobarbitone, sympathetic discharge responded to changes inarterial pressure. Increased arterial Pco₂ exaggerated the amplitudeof the respiratory sympathetic rhythm, and had a more variableeffect on the mean impulse discharge rate. Preganglionic activitywas increased by 25–50 per cent cyclopropane, which usuallyraised arterial pressure; by halothane, which caused severehypotension; and by diethyl ether, which produced smaller circulatorychanges. These experiments question the concept of "centralvasomotor depression" during inhalation anaesthesia in the rabbit. ^* Addenbrooke's Hospital, Cambridge. Present address: Dept. of Physiology, Australian National University,Canberra.     

OUTCOME AFTER GENRAL ANAESTHESIA FOR REPAIR OF FRACTURED NECK OF FEMUR: A Randomized Trial of Spontaneous V. Controlled Ventilation

One hundred and fifty-two patients undergoing surgery for fracturedneck of femur were randomly allocated to receive either generalanaesthesia with spontanoeous ventilation with nitrous oxideand halothane in oxygen or general anaesthesia with controlledventilation with fentanyl, nitrous oxide and halothane in oxygen.Atracurium was used to provide muscle paralysis in 65% of thelatter group, the remained receiving no neuromuscular blockingagent other than suxamethonium for intubation. Patients werefollowed up for 6 months. Mortality and outcome were not significantlydifferent between the groups. Overall mortality at 4 weeks was5.2% and at 6 months was 15.1%—figures which are considerablylower than in some other comparable studies. This study doesnot support the suggestion that general anaesthesia with controlledventilation is associated with increased postoperative mortality. ^*Department of Anaesthetics, Royal Devon & Exeter (Wonford),Exeter. Acting District Medical Officer, Northampton Health Authority.     

THE EFFECT OF HALOTHANE AND THIOPENTONE ON VENTILATORY RESPONSES MEDIATED BY THE PERIPHERAL CHEMORECEPTORS IN MAN

The activity and responsiveness of the peripheral ventilatorychemoreflex were assessed by the transient depression of ventilationfollowing two breaths of oxygen in air-breathing subjects, andthe differing times of onset of the ventilatory response toi.v. sodium bicarbonate in subjects breathing either air oroxygen. In patients premedicated with pethidine, in whom anaesthesiawas induced with thiopentone, it was found that halothane, inan inspired concentration of 0.7–0.8%, reduced the activityand responsiveness of the peripheral ventilatory chemoreflexmarkedly. When halothane was discontinued and anaesthesia wasmaintained with intermittent injections of thiopentone (0.2mg/kg/min) evidence of peripheral chemoreceptor activity andresponsiveness returned. ^*Departments of Anaesthesia and Physiology, University of Toronto,Toronto, Ontario, Canada. Department of Anaesthetics, Harefield Hospital, Harefield, Middlesex.     

THE INFLUENCE OF DIFFERENT ANAESTHETIC AGENTS ON THE RESPONSE TO RESPIRATORY TRACT IRRITATION

A method is described for comparing the duration of active respiratoryresponses to irritation of the respiratory tract during anaesthesiawith different agents. The reflex responses were more prolongedwith cyclopropane and thiopentone than with nitrous oxide aloneor halothane with nitrous oxide. Each agent was administeredto five patients. Atropine sulphate 1.2 mg given intravenouslyin five cases before stimulation, failed to modify the responsesduring cyclopropane anaesthesia. The differences in the durationsof response are unexplained. It is suggested that they are determinedby the strength and duration of the stimulus, and by the effectof the anaesthetic agent on the sensitivities of the reflexarc and the respiratory centre. ^* At present at the Department of Anesthesia, Western ReserveUniversity, Cleveland, Ohio.     

HAEMODYNAMIC RESPONSES TO ISOFLURANE ANAESTHESIA AND HYPOVOLAEMIA IN THE DOG, AND THEIR MODIFICATION BY PROPRANOLOL

In six dogs chronically implanted with flow and pressure transducers,equipotent inspired concentrations of halothane and isofluranewere determined as the minimum inspired concentration of eachagent which would abolish an individual dog's response to pawclamping. In equipotent concentrations, isoflurane (1.2%, SD0.2%) caused less myocardial depression than halothane (1.0%,SD 0.1%). Dose–response studies were possible up to amean inspired isoflurane concentration of 3.0%, both beforeand after propranolol 0.3 mg kg^-1, i.v. After propranolol, sensitiveindices of myocardial contractility were depressed at all concentrationsof isoflurane, indicating a moderate degree of ß-receptoractivation by isoflurane. The hacmodynamic response to hypovolaemiaduring isoflurane anaesthesia was not modified by propranolol. ^*Present addresses:Department of Anaesthetics, St Vincent'sHospital,Darlinghurst, N.S.W. 2010, Australia. Present addresses:Department of Anaesthesia, University of Bristol,BristolRoyal Infirmary, Bristol BS2 8HW. Present addresses:Department of Anaesthesia, Flinders University,SouthAustralia, Bedford Park, South Australia 5042.     

THE EFFECT OF CYCLOPROPANE, HALOTHANE AND ETHER ON SYMPATHETIC GANGLIONIC TRANSMISSION

The actions of cyclopropane, halothane, and ether on sympatheticganglionic transmission were studied by recording the compoundaction potential evoked in postganglionic nerves by single shockstimulation of the preganglionic pathways. The ganglia investigatedwere the superior cervical and inferior mesenteric in the rabbit,and the superior cervical and stellate ganglia in the cat. Allthree anaesthetics reduced the height of the postganglioniccompound action potential. This effect is interpretable as partialganglion block, but requires further study in view of the increaseddischarge rate measured in both pre- and postganglionic sympatheticnerves during associated studies with inhalation anaestheticsin rabbits. ^*Present address: Department of Physiology, Australian NationalUniversity, Canberra. Addenbrooke's Hospital, Cambridge.     

CARDIAC PERFORMANCE DURING PROLONGED HALOTHANE ANAESTHESIA IN THE CAT: Isolated heart muscle study

The contractile response of papillary muscles, isolated fromnormal cats, to prolonged administration of halothane at minimumalveolar anaesthetic concentration (MAC) was studied. Averagevalues of maximal velocity of shortening (V_max) and maximaldeveloped force (F_m) obtained in 12 muscles during the 1st,2nd and 3rd hour of exposure to halothane anaesthesia were significantlyless than those obtained during the control period and afterrecovery from halothane. There were no significant differencesin values over a 3-h period. When post-extra-systolic potentiationwas induced by paired electric stimulation, average values ofV_max and Fm increased significantly. We conclude that prolongedadministration of halothane at a constant concentration resultedin a sustained depression of myocardial contractility withouttissue tolerance. The myocardium depressed by halothane, however,still retains the ability to respond to additional inotropicstimulation. ^*Present addresses: Department of Anesthesia, University ofIowa College of Medicine, Iowa City, Iowa 52242, U.S.A. Department of Anesthesiology, Tohoku University, Sendai, Japan.     

THE EFFECT OF INTUBATION ON THE DEADSPACE DURING HALOTHANE ANAESTHESIA

Total functional deadspace (including apparatus deadspace) wasmeasured in anaesthetized patients while breathing from masksand after tracheal intubation. The mean VD/VT ratio was 0.18larger during mask breathing and the mean value for the totalfunctional deadspace was 82 ml greater than in the intubatedpatients. The results showed an increase in the VD/VT ratioduring the inhalation of higher concentrations of halothane:the difference closely approached but did not attain the 95per cent confidence limit. Values for VD/VT ratio and VD wereuninfluenced by the duration of anaesthesia up to 120 minutes. ^*Dr. Kain was killed in a motor accident on August9, 1967 Present address: Medical Research Council, Divisionof Anaesthesia,Royal Postgraduate Medical School, London, W.I2     

THE VARIABILITY OF PARTITION COEFFICIENTS FOR NITROUS OXIDE AND CYCLOPROPANE IN THE RABBIT

Partition coefficients were determined for blood, brain, heart,kidney, liver and skeletal muscle. The mean blood/gas coefficientwas 0.461 for nitrous oxide and 0.68 for cyclopropane. The meantissue/blood coefficients which differed significantly fromunity were, for nitrous oxide, heart 0.83, kidney 0.83, liver0.91, muscle 0.76 and, for cyclopropane, brain 1.19, heart 1.25,muscle 0.75. The differences between tissues were significant.Differences between animals were considerable and mostly unsystematic,i.e. a high coefficient in one tissue was not generally associatedwith high coefficients in others. The 95 per cent confidencelimits for nitrous oxide coefficients in the population rangedfrom +6 per cent of the mean for blood to +50 –33 percent for muscle and, for cyclopropane, from +21 –17 percent for blood to less than +89 –47 per cent for muscle. ^*Present addresses: Department of Physiology, University ofManchester,Manchester, M13 9PL. Present addresses: Physiology Department, Marischal College,University of Aberdeen, Aberdeen, AB9 IAS.     

HAEMODYNAMIC RESPONSES TO ENFLURANE ANAESTHESIA AND HYPOVOLAEMIA IN THE DOG, AND THEIR MODIFICATION BY PROPRANOLOL

The haemodynamic responses to minumum equipotent concentrationsof halothane and enflurance were compared in seven dogs. Thehaemodynamic responses to increasing concentrations of enflurane,and to induced hypovolaemia during enflurane anaesthesia, werestudied in the same dogs, both before and after administrationof propranolol 0.3 mg kg^-1 i.v. In equipotent concentrations,enflurane caused marginally greater impairment of left ventricularfunction than halothane, and caused a dose-dependent reductionof arterial pressure, cardiac output and myocardial contractility.Following administration of propranolol, these haemodynamiceffects of enflurane were marked, and withdrawal of 20% of estimatedblood volume was tolerated poorly. ^*Present addresses :Department of Anaesthetics, St Vincent'sHospital,Darlinghurst, N.S.W. 2010, Australia. Present addresses :Department of Anaesthesia, University ofBristol,Royal Infirmary, Bristol BS2 8HW. Present addresses :Department of Anesthesiology, Universityof California,San Francisco Medical Center, San Francisco, U.S.A. Present addresses :Department of Anaesthesia, Flinders Universityof South Australia, Bedford Park, South Australia 5042.     

PRESSURE ANTAGONISM OF ANAESTHETIC-INDUCED CONDUCTION FAILURE IN FROG PERIPHERAL NERVE

Experiments to investigate pressure-induced antagonism of theeffects of general anaesthetics in isolated peripheral nervefrom the frog are described. The doses of four gaseous generalanaesthetic agents required to reduce electrically evoked actionpotentials by 50% (mean ±SEM) were nitrous oxide 490±40.4kPa, ethylene 665±212kPa, dichlorodifluoromethane 108±17.2 kPa³ and cyclopropane 70 ± 5 kPa. The combinationof high pressure and the anaesthetic agent partially or completelyrestored the action potential amplitudes for the gaseous andsome of the volatile agents (chloroform, diethyl ether, halothane).However, reversal of the effects of other volatile agents (ethanol,butanol), sodium pentobarbitone and two local anaesthetic agents(procaine, dibucaine) did not occur. The pressures used to effecta reversal were less than anticipated. This apparent inconsistencywith the critical volume hypothesis for anaesthesia is discussed. ^*Faculty of Medicine, Division of Pharmacology and Therapeutics,University of Calgary, 2920 24th Avenue, N.W., Calgary, Alberta,Canada. Department of Anesthesia, 1386 HSE, University of California,San Francisco, California 94143, U.S.A.     

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.     

QUANTITATIVE EEG AND BRAINSTEM AUDITORY EVOKED POTENTIALS: COMPARISON OF ISOFLURANE WITH HALOTHANE USING THE CEREBRAL FUNCTION ANALYSING MONITOR

We studied EEG and brainstem auditory evoked potentials (BAEP)during routine surgery at various concentrations of isoflurane(12 patients) or halothane (11 patients) or during prolonged(mean 2.5 h, range 1.9–3.5 h) administration of 1% isoflurane(five patients). Recording and analysis was performed with thecerebral function analysing monitor (CFAM). At equivalent MAC,the two agents exhibited distinctive neurophysiological profiles.Increasing concentrations of isoflurane produced a clear sequenceof EEG changes (decreasing fast and increasing slow components)then burst suppression activity suggesting cortical depression.With halothane, changes in EEG amplitude were less pronouncedand those in frequency content less systematic, with no periodsof suppression. Simultaneous BAEP showed greater latency increasewith halothane than with isoflurane. Prolonged administrationof 1% isoflurane was associated with a stable EEG (no periodsof suppression) and BAEP. A preliminary account of this work was presented to the AnaestheticResearch Society, London, November 1986. ^*Present address: Department of Anaesthesia, Hospital for SickChildren, Great Ormond Street, London WCIN 3JH.     

THE MEASUREMENT OF UPTAKE OF NITROUS OXIDE BY PNEUMOTACHOGRAPHY PART II: EXPERIMENTAL PROCEDURE AND RESULTS

The breath by breath uptake of nitrous oxide during the inductionof anaesthesia was measured in two subjects of similar sizeusing the methods described in Part I. Seven measurements weremade with each subject. With Subject A the uptake of nitrousoxide by the pulmonary capillary blood was 2.2±0.6 1.STP after one minute, and with subject B it was 22±0.31. STP. These results are discussed in relation to some theoreticalexpectations, to the results obtained during a previous study,and to measured changes in the pulse rate. Time to loss of consciousnessis also considered in relation to the barometric pressure. ^*Present address: Department of Anaesthesia, University of Leeds. Present address: Department of Anaesthesia, University of Pennsylvania,Philadelphia.     

ULTRASOUND ASSESSMENT OF THE POSITION OF THE TONGUE DURING INDUCTION OF ANAESTHESIA

Tongue position was assessed in 15 female patients at inductionof anaesthesia with either thiopentone or propofol. A videorecording of a midline sagittal section of the tongue was madeusing an ultrasound transducer placed below the chin, and representativefigures analysed by an observer who was not aware of the patient'sstate. In 11 satisfactory recordings, the tongue movement wasinconsistent in direction and not more than 8 mm in the anteriortongue and 6 mm in the posterior tongue. The movements detecteddid not suggest that the tongue is likely to be an importantcause of airway obstruction on induction of anaesthesia. This paper was presented at the Anaesthetic Research Societymeeting at the University of Warwick on April 7, 1989.     

INCREASE IN HALOTHANE CONCENTRATION FOLLOWING REFILLING OF CERTAIN VAPORIZERS

A case of cardiovascular collapse during halothane anaesthesiaraised the question of the halothane concentration deliveredby vaporizers after refilling. The rise in halo thane concentrationfollowing replenishment has been measured in three commonlyused vaporizers; the calibrated Boyle bottle was found capableof delivering a dangerous concentration in certain circumstances. ^* Present addresses: Northampton General Hospital, Northampton. Present addresses: Camborne and Redruth Hospital, Cornwall.     

EFFECTS OF HALOTHANE ON OXYGEN CONSUMPTION OF RAT LIVER SLICES

Normal rat liver slice respiration was studied at 37 °Cby the polarographic technique of Longmuir in the presence ofoxygenated solutions and with addition of clinical concentrationsof halothane to the mixtures. In the presence of halothane,after one exposure of the slices, respiration was significantlyinhibited in all cases when the anaesthetic concentration was23.6 mg/100 ml, in one of four experiments at the 17.7 mg/100ml concentration, but never for a lower halothane concentration.Re-exposure of the tissue to the anaesthetic concentrationswhich were inactive at the first exposure produced significantrespiratory inhibition, presumably because of progressive accumulationin the tissue. One mechanism of the inhibition of tissue respirationby halothane appears to be interference with the oxygen transportmechanism to the mitochondria. Present addresses: ^*Centre d'Anesthesiologie, Hopital UniversitaireSaint Pierre, Bruxelles, Belgique. Department of Biochemistry, North Carolina State University,Raleigh, N.C. 27607, U.S.A.     

DELAYED EXCITATORY REACTION FOLLOWING INTERACTION OF COCAINE AND MONOAMINE OXIDASE INHIBITOR (PHENELZINE)

A case report is presented in which a patient receiving themonoamine oxidase inhibitor, phenelzine, developed a delayedexcitatory reaction following administration of topical cocainespray during anaesthesia for vocal cordsurgery. The pharmacologicalbasis of the drug interaction is discussed. ^*Department of Anaesthesia, St Bartholomew's Hospital, WestSmithfield, London EC1A 7BE. Shackleton Department of Anaesthetics, Southampton General Hospital,Tremona Road, Southampton S09 4XY. Harefield Hospital, Uxbridge, Middx UB9 6JH.     

INTERPLEURAL REGIONAL ANALGESIA: DETECTION OF THE INTERPLEURAL SPACE BY SALINE INFUSION

A saline infusion technique is described for insertion of aninterpleural catheter, to reduce the incidence of pneumothoraxduring conduct of interpleural block, especially if the blockis used as an adjunct to general anaesthesia. Presented in part at the March 1990 meeting, British Section,European Society of Regional Anaesthesia (ESRA).