T. E. J. Healy

The extra work of breathing through adult endotracheal tubes

A sinusoidal flow generator was connected to adult endotracheal tubes of sizes 5–10 and was used to simulate human ventilation. Measurement of the changes in pressure and flow allowed calculation of the work imposed on breathing by endotracheal tubes. The work of breathing increased with increasing ventilatory rate, tidal volume, and decreasing tube diameter. We discuss the suggestion that the work imposed on breathing by an endotracheal tube is a more appropriate unit for comparison than resistance to air flow.

Reducing the haemodynamic responses to laryngoscopy and intubation. A comparison of alfentanil with fentanyl.

The effects of alfentanil and fentanyl on controlling the haemodynamic responses to laryngoscopy and intubation have been compared. Five groups of ten patients were studied. Induction was with thiopentone 4 mg/kg. Thirty seconds later group 1 received 1 ml/20 kg saline, group 2 received 15 micrograms/kg alfentanil, group 3 received 30 micrograms/kg alfentanil and group 4 received 5 micrograms/kg fentanyl one minute before induction. Suxamethonium was given 60 seconds after induction and intubation of the trachea was performed 150 seconds after the start of induction. Heart rate and mean arterial pressure were recorded every minute throughout and compared with pre-induction control values. Control patients (group 1) showed significant increases associated with tracheal intubation in all haemodynamic variables. No increases were noted in groups receiving 30 micrograms/kg alfentanil or 5 micrograms/kg fentanyl. The heart rate, but not blood pressure, increased with intubation after 15 micrograms/kg alfentanil. The mean time to movement in 50% of the control patients was 7 minutes. In those given 15 and 30 micrograms/kg alfentanil it was 11 and 12 minutes respectively. In those given 5 micrograms/kg fentanyl it was greater than 15 minutes. Alfentanil is shown to reduce the cardiovascular responses to laryngoscopy and intubation and the effect appears to have a shorter duration than that of fentanyl.

Reducing the haemodynamic responses to laryngoscopy and intubation

The effects of alfentanil and fentanyl on controlling the haemodynamic responses to laryngoscopy and intubation have been compared. Five groups often patients were studied. Induction was with thiopentone 4 mg/kg. Thirty seconds later group 1 received 1 ml/120 kg saline, group 2 received 15μg/kg alfentanil, group 3 received 30 μg/kg alfentanil and group 4 received 5 μg/kg fentanyl. Group 5 received 5 μg/kg fentanyl one minute before induction. Suxamethonium was given 60 seconak after induction and intubation of the trachea was performed 150 seconds after the start of induction. Heart rate and mean arterial pressure were recorded every minute throughout and compared with pre‐induction control values.

Profile of recovery after general anaesthesia.

The duration of impairment of mental functioning after anaesthesia was studied in 55 patients undergoing hernia repair who were divided into three groups in which the method of induction of anaesthesia (intravenous or inhalational) and ventilation (spontaneous or controlled) was varied. Performance in a five minute serial reaction time test and subjective estimates of coordination were assessed four times a day for two complete postoperative days and were compared with those in a control group of orthopaedic patients in hospital. After considerable impairment initially, reaction times in all groups gradually returned towards control values, but in patients breathing spontaneously during anaesthesia impairment recurred during the second postoperative day. These results suggest that such patients should be advised not to undertake hazardous tasks such as driving a car for at least 48 hours after a general anaesthetic. Discrepancies between subjective and objective assessments of impairment also suggest that patients should not rely on their own assessments of fitness to drive.

Hygienic practices of consultant anaesthetists: a survey in the North-West region of the UK

Questionnaires were distributed to all 213 consultant anaesthetists in the North‐West region of the UK with a response rate of 68%. These questionnaires were designed to assess the hygienic precautions taken to reduce the potential for transmission of infectious agents to and from the patients under their care. Face masks and gloves were always used by 35.2% and 14.5%, respectively, while only 36.4% washed their hands between cases. Most respondents have changed their practice since the recognition of HIV transmission (74.8%) and hepatitis B and C (69.8%). A high proportion of anaesthetists continue to administer anaesthesia despite suffering from respiratory (94%), gastrointestinal (42.9%) or herpes simplex (32.6%) infections. The anaesthetic breathing system was changed at the end of each day or following a high‐risk case by 33.3% of the respondents, while just over 25% changed it following a known infected case. Bacterial filters were used by 17% and changed after each case by 7.2%. On a scale of 0–10 (10 = significant) anaesthetists rated their potential for transmitting or contributing to patient infection as a median of 3 (interquartile range: 2–6). The results of this study show that, although anaesthetists are well aware of proper hygienic practices, their performance falls short of accepted recommendations.

Anaesthesia and demyelinating disease

The demyelinating diseases are classified and the current concepts of the aetiology and pathophysiology of the most common of these diseases, multiple sclerosis, are described. The effects of the impaired function, local responses and known complications of the disease on the choice of anaesthetic, drugs and techniques are discussed.

The effect of sufentanil on the cardiovascular responses to tracheal intubation

The effects of sufentanil 0.5 or 1 μg/kg, given intravenously after induction of anaesthesia, on the cardiovascular responses to tracheal intubation were examined in a controlled, randomised, double‐blind investigation. The control group of patients exhibited significant rises in arteriat blood pressure and heart rate for 4 minutes after tracheal intubation. Heart rate exceeded 100 beats/minute and systolic pressure increased by over 20% in every patient. All patients moved or breathed within 10 minutes of the administration of suxamethonium. Sufentanil 0.5 μg|kg prevented increases in the me an values of heart rate and arterial blood pressure, although increases were observed in five patients. Significant falls in the mean values of heart rate and arterial pressure occurred from 4 minutes after intubation until observations ended 15 minutes after induction of anaesthesia. Two patients moved or breathed during this time, although movement in response to nerve stimulation occurred in all patients 10 minutes after administration of suxamethonium. Sufentanil 1 μg/kg was effective in suppressing a rise in heart rate or arterial pressure in every patient. Significant falls in these variables occurred from 2 minutes after tracheal intubation onwards. No patient moved or breathed for 15 minutes after induction of anaesthesia, although neuromuscular transmission was present 10 minutes after giving suxamethonium in each case.

The role of new anesthetic agents

The three anesthetic drugs introduced most recently to the market are sevoflurane, desflurane, and ropivacaine. Sevoflurane and desflurane are both inhalational anesthetic agents and ropivacaine is a local anesthetic agent. Sevoflurane provides a rapid onset and offset of action; it is well tolerated with little airway irritation. It is hemodynamically stable, with low potential for toxicity. Concerns about its interaction with soda lime during low-flow anesthesia with the production of Compound A have not proved to be a clinical problem. While desflurane also provides rapid onset and recovery from anesthesia, it is not as hemodynamically stable as sevoflurane, and also causes airway irritation. Ropivacaine is a unique local anesthetic in that it is supplied as the pure S-enantiomer. It is at least as effective as bupivacaine, with lower toxicity and less motor block for the same degree of sensory block.

Electromyography in anaesthesia A comparison between two methods

Two instruments measuring evoked compound muscle action potentials (EMG) produced by train of four stimulation of the ulnar nerve were compared. The neuromuscular transmission section of a Datex Anaesthesia and Brain Monitor (ABM), which utilises an integration technique to measure the EMG, and the Medelec MS6, by which amplitude of the EMG was recorded and measured were attached to the same electrodes placed over adductor pollicis. Eight patients scheduled for surgery requiring non‐depolarising neuromuscular blockade were studied. The changes in neuromuscular transmission measured by the two methods correlated well, with no statistically significant difference in results. The ABM provides a simple and accurate automatic measurement of evoked EMG for use in the study of neuromuscular transmission.

A comparison of the antibacterial properties of six local analgesic agents

The effect of six local analgesic drugs on bacterial growth is reported. Amethocaine proved to be the only effective antibacterial agent.