Hypotensive anaesthesia for microsurgery of the middle ear. A comparison between isoflurane and halothane

Fifty patients undergoing microsurgery of the ear were anaesthetised using thiopentone, nitrous oxide, oxygen and either halothane or isoflurane, via a low flow circle system with carbon dioxide absorption. Systolic blood pressure was reduced to approximately 70 mmHg by the additional use of increments of labetalol; the patients breathed spontaneously. The degree of haemostasis was assessed by the surgeon who was unaware which volatile agent was being used to supplement anaesthesia. Isoflurane, although it is a potent vasodilator produced operating conditions which were indistinguishable from halothane. Isoflurane is thus a safe and reliable alternative to halothane as a volatile agent used to supplement anaesthesia when using induced hypotension for middle ear surgery.     

Single breath induction of anaesthesia, using a vital capacity breath of halothane, nitrous oxide and oxygen

Inhalational induction of anaesthesia, using a single vital capacity breath of 4% halothane in 66% nitrous oxide and 33% oxygen was evaluated in 100 unpremedicated outpatients. The technique was found to be acceptable to most (91%) of the patients studied, with a mean (SD) induction time (measured from beginning of inspiration to loss of 'eyelash reflex') of 83(21) seconds. Relative cardiovascular stability was a notable finding of the technique, with a slight decrease in the mean arterial pressure of only 10%. Anaesthetic induction time was unaffected by age, weight or smoking habits. The technique of single breath induction is therefore proposed as a safe and acceptable alternative to intravenous induction in co-operative adult patients.     

A comparison of halothane and trichloroethylene with isoflurane. A study of drawover air anaesthesia with the Triservice anaesthetic apparatus

Induction and recovery times were not significantly different between two groups that received halothane with trichloroethylene and isoflurane, respectively. Maintenance of anaesthesia and analgesia was also satisfactory. Isoflurane resulted in a higher heart rate (p less than 0.01), a lower respiratory rate (p less than 0.01) and a higher inspired oxygen concentration (p less than 0.05). Respiration may be more efficient. Other potential advantages of isoflurane for anaesthesia in the field are discussed. Despite the fact that it is 15 times more expensive, the use of isoflurane as sole agent is recommended.     

Anaesthetic induction time for tracheal intubation using sevoflurane or halothane in children

The current study was designed to determine the anaesthetic induction time required for tracheal intubation (Time_EI) with equipotent inspired concentrations of 5% sevoflurane and 2.5% halothane in oxygen. Time_EI that prevents 50% and 95% of patients from coughing and gross purposeful muscular movements after intubation was defined as Time_EI50 and Time_EI95, respectively. Thirty-six patients aged 1–7 years were enrolled in the study. Anaesthesia was induced via mask and when Time_EI attained a predetermined value, intubation was performed using an uncuffed tube. Each Time_EI at which tracheal intubation was attempted was predetermined according to the up-and-down method. When intubation was accomplished without gross purposeful muscular movements, it was considered a smooth intubation. Determination with this method revealed that Time_EI50 and Time_EI95 for the sevoflurane/halothane groups were 147/214 s and 194/255 s, respectively. In conclusion, it is possible to determine Time_EI using an inspired sevoflurane concentration of 5% and halothane 2.5% in oxygen. The technique with 5% sevoflurane seems more practical for paediatric anaesthesia induction in busy clinical situations.     

Comparison of conventional and rapid inhalational induction of anaesthesia with enflurane

Inhalational induction of anaesthesia using either a conventional method or a vital capacity breath of 4% enflurane in 67% nitrous oxide was compared in 30 adult surgical patients. Induction time was significantly faster in patients who took a vital capacity breath (71, SD 22 versus 132, SD 18 seconds, p less than 0.01). There were no significant differences between groups in respect of systolic blood pressure, heart rate, arterial oxygen saturation or incidences of excitement or coughing. The vital capacity breath method was acceptable to 87% of patients.     

Renin Release during Controlled Hypotension with Sodium Nitroprusside, Nitroglycerin and Adenosine: A Comparative Study in the Dog

The haemodynamic effects of i.v. infusions of sodium nitroprusside (SNP), nitroglycerin (TNG), and adenosine were studied in dogs in parallel with quantitative determinations of plasma renin activity (PRA) by radioimmunoassay. The drugs were given for controlled hypotension, and the mean arterial blood pressure (MABP) was decreased to approximately 50 mmHg (6.7 kPa). Arterial blood samples for PRA were collected at 10-min intervals. During the last interval the dogs were subjected to haemorrhagic shock. SNP-induced hypotension could be maintained only with a stepwise increase in infusion rate, from 11.8 to 16.0 micrograms X kg-1 X min-1 (P less than 0.05). TNG could not produce the desired blood pressure level, but gradually increasing doses induced a gradually decreasing MABP (80-60 mmHg) (10.7-8.0 kPa). During adenosine-induced hypotension, a perfectly stable blood pressure level was maintained without dose adjustments. Both SNP and TNG induced blood pressure-dependent increases in PRA, while no changes in PRA were seen during adenosine-induced hypotension. Nor could haemorrhagic shock, which induced further increases in PRA during SNP- and TNG-induced hypotension, alter PRA during adenosine infusions. We conclude that adenosine differs markedly from conventional hypotensive drugs such as SNP and TNG with respect to stability of action and dose requirements, and that this stability is related to an inhibited increase in renin release.     

Anaesthesia in the field. Spontaneous ventilation–a new technique

In recent years the British Army has used the Triservice Anaesthetic Apparatus in the field. Trichloroethylene is no longer manufactured in the United Kingdom and halothane is not recommended for closely repeated anaesthetics. A method based on existing equipment is described for patients breathing spontaneously. A background infusion of ketamine, midazolam and alfentanil supplements the inhalation of isoflurane in oxygen-enriched air.     

A comparison of isoflurane and halothane in anaesthesia for intra-ocular surgery

Isoflurane 0.75% was compared with halothane 0.5% as the volatile supplement in a normocapnic technique for intra-ocular surgery. Both agents gave satisfactory conditions for operation with a comparable reduction in intra-ocular pressure during the procedure. Systolic arterial pressure, however, was significantly lower in the isoflurane group at the end of surgery and after tracheal extubation than in the halothane group. Isoflurane provides a useful alternative to halothane in anaesthesia for intraocular surgery.     

Volatile agent use: perception and practice A survey of agent use over a 3-year period

We calculated the quantity, as MAC hours and MAC hours anaesthetic, of halothane, enflurane and isoflurane, used in this Health District over a 3-year period. Halothane accounted for 77% of anaesthesia in the first year and for 57% in the final year. Overall usage of volatile agents decreased. Fifteen consultants and 19 senior registrars perceived, in a survey of practice, only a change in relative use of volatile anaesthetic agents with a large swing from halothane to both enflurane and isoflurane. Half the anaesthetists stated that the medicolegal consideration was the prime reason for their change. The perceived total demise of halothane does not appear to have been realised, despite individual anaesthetist's perceptions.     

Recovery after single-breath halothane induction of anaesthesia in daycase patients

A single-breath technique of inhalational induction of anaesthesia allows intravenous induction agents to be avoided. We have investigated recovery from anaesthesia in 40 daycase patients, using tests of psychomotor function. Patients anaesthetised with inhalational induction awaken earlier than those who receive thiopentone, but not significantly earlier. There were no significant differences in postoperative psychomotor function between patients who received thiopentone and those who had inhalational inductions. Single-breath halothane, nitrous-oxide, oxygen induction is an alternative to intravenous induction in cooperative adults, but does not confer significant benefits in terms of recovery.     

Nitrous oxide solubility in halothane and its effect on the output of vaporizers

The absorption of nitrous oxide in halothane was studied by bubbling nitrous oxide and nitrous oxide/oxygen gas mixtures through a halothane bottle, using 100% oxygen as a control. The gas volume emerging from the halothane bottle was measured each minute, over a period of up to 15 minutes. When oxygen was used as a control gas, the averaged flow rate dropped slightly over the experimental period, due to the cooling of the halothane. However, in the presence of nitrous oxide, the initial flow rate of the gas emerging from the halothane bottle was greatly diminished, but then accelerated rapidly to reach that obtained with oxygen. The results suggested that nitrous oxide dissolved in large quantities in halothane, and the data are consistent with an Ostwald coefficient in excess of 4.0.     

Haemodynamic Changes during Sodium Nitroprusside Induced Hypotension and Halothane/Nitrous Oxide Anaesthesia

The haemodynamic effects of nitroprusside (SNP) were studied in six patients undergoing surgery for intracranial aneurysm under controlled hypotension in endotracheal anaesthesia with halothane-nitrous oxide during hypocapnia. Mean arterial pressure was reduced with SNP from mean 12.25 kPa to mean 8.29 kPa (32%). There were concomitant statistically significant decreases in systemic vascular resistance (-21%), cardiac index (-17%), stroke index (-23%), pulmonary arterial mean pressure (-27%) and pulmonary capillary wedge pressure (-27%). Heart rate, central venous pressure and pulmonary vascular resistance did not change significantly. After the infusion of SNP was discontinued all parameters, except cardiac index and heart rate, returned to values not significantly different from the control values. The hypotension induced by SNP resulted from reductions in cardiac index and systemic vascular resistance. The reduction in cardiac index did not reach a critical level in any of the patients.     

Central and Splanchnic Haemodynamics in the Dog During Controlled Hypotension with Sodium Nitroprusside

The effects of controlled hypotension induced by sodium nitroprusside (SNP) on central and splanchnic haemodynamics were studied in ten artificially ventilated dogs under neurolept anaesthesia. SNP was given intravenously as a continuous infusion in order to maintain a mean arterial blood pressure (MABP) of about 50 mmHg. Observations were made before (control) and at 20 and 60 min after the start of the SNP infusion. The mean SNP dosage was 13.7 micrograms X kg-1 X min-1. Systemic vascular resistance (SVR) decreased by 47%. After 20 min there was a 17% decrease in cardiac output, while the hepatic arterial blood flow was diminished by 39%, and portal venous blood flow by 16%. Cardiac output and portal venous blood flow tended to return towards control values at 60 min, while the hepatic arterial blood flow remained depressed. The total oxygen uptake was unaltered after 20 min, but slightly decreased after 60 min. There were no changes in hepatic or preportal tissue oxygen consumption, nor in hepatic lactate uptake. It is concluded that SNP-induced hypotension was achieved primarily by a profound reduction of SVR, and initially also by a slight decrease in cardiac output. Although splanchnic and hepatic blood flows decreased, there were no signs of hypoxia in the preportal tissues or in the liver.     

Anaesthesia and the QT intervalEffects of isoflurane and halothane in unpremedicated children

The effects of isoflurane and halothane on the QT interval were investigated during induction of anaesthesia. Fifty-one unpremedicated, ASA grade 1 children were studied. Anaesthesia was induced with either isoflurane ( n  = 25) or halothane ( n  = 26) and was maintained to the end of the study with end-tidal concentrations of between 2.5% and 3%. Recordings of the electrocardiograph, heart rate and systolic arterial pressure were obtained at the following times: before induction of anaesthesia; 1 min and 3 min after stable end-tidal concentrations of anaesthetic agent had been reached; 1 min and 3 min following vecuronium administration; at the time of tracheal intubation and 1 min and 3 min later. Isoflurane significantly prolonged the QT interval (p < 0.001), in contrast to halothane which shortened it (p < 0.01). Heart rate remained largely unchanged during isoflurane anaesthesia but it decreased in the presence of halothane (p < 0.001). In both groups, systolic arterial pressure decreased significantly after induction of anaesthesia (p < 0.001) and remained so to the end of the study. In the isoflurane group, 12 children developed ECG repolarisation abnormalities and in one child an arrhythmia was noticed. In the halothane group, one child developed repolarisation changes while arrhythmias were observed in 10 children. There were no adverse sequelae. It is concluded that halothane may be a better anaesthetic agent than isoflurane for use in children with a prolonged QT interval.     

Total intravenous anaesthesia with propofol or inhalational anaesthesia with isoflurane for major abdominal surgery: Recovery characteristics and postoperative oxygenation—an international multicentre study

Two hundred and ten adult patients undergoing open cholecystectomy, vagotomy or gastrectomy were included in a randomised multicentre study to compare postoperative nausea and vomiting, oxygen saturations for the first three postoperative nights, time to return of gastrointestinal function, mobilisation, and discharge from the hospital following induction and maintenance of anaesthesia with propofol and alfentanil or with thiopentone, nitrous oxide, isoflurane and alfentanil. Recovery from anaesthesia was significantly faster in the propofol group (mean (SD) times to eye opening and giving correct date of birth of 14.0 (SD 13.8) and 25.5 (SD 29.5) minutes, and 18.5 (SD 14.8) and 35.5 (SD 37.2) minutes in the propofol and isoflurane groups respectively). There was significantly less nausea in the propofol group (15.4%) than in the isoflurane group (33.7%) in the first two postoperative hours (p < 0.003) but not thereafter. There were no significant differences between the groups in any other recovery characteristics. The incidence of hypoxaemia (arterial oxygen saturation less than 93%) was close to 70% in both groups for the first three postoperative nights, indicating the need for oxygen therapy after major abdominal surgery.