Effect of surgical stimulation on the auditory evoked response.

Previous studies have shown a dose-related effect of a number of general anaesthetic agents on the early cortical waves in the auditory evoked response (AER). In this study the effect of surgical stimulation on these waves was examined in 11 patients anaesthetized with thiopentone, nitrous oxide and halothane and paralysed with pancuronium. The inspired nitrous oxide concentration and end-tidal halothane concentration were held constant at 70% and 0.

Comparison of the respiratory depressant effects of halothane and isoflurane in routine surgery.

Respiratory depression has been studied in 21 patients anaesthetized with either halothane and nitrous oxide, or isoflurane and nitrous oxide while undergoing routine surgery. Spontaneous ventilation was preserved and the end-tidal concentrations of the two volatile anaesthetics were at approximately equal MAC-multiples. The minute volume of pulmonary ventilation was not significantly different for the two anaesthetics, but tidal volume was significantly greater and frequency significantly lower with isoflurane.

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 before elective surgery.

Selective effect of althesin on the auditory evoked response in man.

The auditory evoked response (AER) has been studied in six patients before the induction of general anaesthesia, during anaesthesia with nitrous oxide in oxygen and mechanical ventilation, then with a stepwise increasing rate of infusion of Althesin ranging from 18 micrograms kg-1 min 1 to 90 micrograms kg-1 min-1. The sections of the AER examined in this study were the brainstem waves I, III and V and the early cortical waves Pa and Nb. There were dose-related changes in latency and amplitude of waves Pa and Nb, latency increasing and amplitude diminishing with increasing concentrations of alphaxalone as measured in venous blood.

Effect of isoflurane on bronchomotor tone in man.

Twenty patients were anaesthetized with thiopentone, the trachea intubated and the lungs ventilated with 70% nitrous oxide and oxygen. Normocapnia was maintained and, following control measurements of the specific conductance of the lower airways (s.Glaw), either 1.

Pulmonary gas exchange and diaphragmatic position. Effect of tonic phrenic stimulation compared with that of increased airway pressure.

The influence of diaphragmatic position on abnormal gas exchange has been examined to investigate the theory that the impairment in gas exchange in anaesthetized man is caused by disturbance of diaphragmatic mechanics, resulting in abnormalities of dependent lung ventilation. A gas exchange abnormality, probably caused by airway closure in the dependent regions of the lung, was induced in anaesthetized rabbits by reducing lung volume to residual volume and allowing passive re-expansion. The effects on gas exchange of increases in lung volume produced by two methods--the application of positive end-expiratory pressure (PEEP) and phrenic nerve stimulation (PNS)--were compared.

Effect of etomidate on the auditory evoked response in man.

The effect of etomidate on the auditory evoked response was examined in a double-blind study carried out before the start of surgery. Fourteen patients were anaesthetized with 70% nitrous oxide and oxygen after induction with thiopentone. Ventilation was controlled.

Changes in lung volume and (PAO2-PaO2) during anaesthesia.

The theory, that the decrease in lung volume which occurs after induction of general anaesthesia is the cause of the higher (PAO2-PaO2) during anaesthesia, was examined in 18 patients. Lung volume was increased during anaesthesia by changing the posture of the patient to 30 degrees head-up, but there was no improvement in (PAO2-PaO2). There were no correlations between change in (PAO2-PaO2) and in cardiac output between different postures.

Effects of halothane or enflurane with controlled ventilation on auditory evoked potentials.

The effects of increasing concentrations of halothane and enflurane on selected components of the auditory evoked response were studied in 12 patients; six received halothane and six enflurane. After the induction of anaesthesia with thiopentone, anaesthesia was maintained with 70% nitrous oxide in oxygen. Ventilation was controlled.

End-tidal carbon dioxide during thoracotomy. Its relation to blood level in adults and children.

The concentration of carbon dioxide in end-tidal gas was compared with the tension in arterial or superior vena caval blood during thoracotomy in twelve patients. In six adults requiring pulmonary resection, one-lung anaesthesia did not change the difference between the two measurements. In six children in whom a systemic to pulmonary arterial anastomosis was being created to improve pulmonary blood flow impaired by cyanotic congenital heart disease, occlusion of the pulmonary artery caused in increase in the blood-end-tidal carbon dioxide gradient.

Non-invasive measurement of cardiac output during anaesthesia. An evaluation of the soluble gas uptake method.

A technique for measuring cardiac output which depends on the uptake of an inert soluble gas from the lungs has been evaluated during anesthesia. A respiratory mass spectrometer has been used to follow the concentrations of argon and freon-22 during passive rebreathing in anaesthetized patients before cardiopulmonary bypass. Values for cardiac output obtained with this technique are reproducible, but lower than those recorded using the direct Fick technique before and after the rebreathing manoeuvre.

Morbidity after outpatient anaesthesia. A comparison of two techniques of endotracheal anaesthesia for dental surgery.

A comparison was made of two anaesthetic techniques for outpatient dental surgery; the basis for comparison was symptomatic morbidity. One group of patients was managed with spontaneous breathing of nitrous oxide, oxygen and halothane; the other was ventilated mechanically, and received fentanyl and alcuronium. The latter anaesthetic was associated with a significantly higher incidence of morbidity on the day of operation, but not subsequently.

Measurement of metabolic gas exchange during anaesthesia. A method using mass spectrometry.

A method is described for measuring metabolic gas exchange during general anaesthesia using a respiratory mass spectrometer, a mixing box and two inert tracer gases. Measurement of inspired and expired minute volume is possible to within 2%; oxygen consumption, carbon dioxide output and respiratory quotient can be measured to within 10%.

Respiratory mass spectrometry during general anaesthesia.

The performance of a respiratory mass spectrometer, modified commercially for use during general anaesthesia, has been evaluated. Stability and linearity proved satisfactory for monitoring respiratory gases and accurate measurement was possible when the inspired concentration of all gases was less than 80%. The system has been installed centrally in a three-room operating theatre suite and the selection of long sampling probes which permit an adequate response time for all gases is discussed.

Muscle blood flow and rate of recovery from pancuronium neuromuscular blockade in dogs.

The effect of changes in muscle blood flow on the rate of recovery from neuromuscular block produced by pancuronium was investigated in dogs, and were shown to be independent variables. The significance of this finding in relation to recent work on blood concentrations of the drug and on the pharmacodynamics of the drug is discussed.

A simple ventilator suitable for respiratory gas studies.

A simple ventilator is described where a spring-loaded bellows is filled from a compressed gas supply. The outflow from the bellows to the subjects is controlled by solenoid valves. The device is a minute volume divider and the durations of inspiration and expiration are set by timers that operate the solenoid valves.