Comparison of etomidate and propofol for anaesthesia in microlaryngeal surgery

Propofol and etomidate were compared as hypnotics in total intravenous anaesthesia for microlaryngeal surgery combined with jet ventilation. Two groups of 15 patients were studied. In group 1, propofol 2.0 mg/kg was used for induction. For maintenance a continuous infusion of 12 mg/kg/hour was used for the first 10 minutes, followed by 9 mg/kg/hour for the next 10 minutes and 6 mg/kg/hour thereafter. In group 2, the induction dose of etomidate was 0.3 mg/kg followed by continuous infusion of 1.8 mg/kg/hour for 10 minutes, 1.5 mg/kg/hour for the next 10 minutes and 1.0 mg/kg/hour thereafter. Alfentanil was given for analgesia and suxamethonium for muscle relaxation. The propofol group showed better surgical conditions, more stable anaesthesia and better recovery according to the Steward score. Recovery times to opening eyes on command were comparable for both groups.     

Respiratory disturbance during recovery from etomidate anaesthesia

A case is described in which recovery from the administration of a single dose of etomidate was complicated by periodic episodes of unconsciousness, tremor and apnoea. Subsequent investigations did not reveal any evidence of neurological disease.     

Echocardiographic assessment of the haemodynamic effects of propofol: a comparison with etomidate and thiopentone

The haemodynamic effects of propofol (2 mg/kg), etomidate (0.2 mg/kg) and thiopentone (4 mg/kg) were studied in 30 ASA 1 and 2 patients in whom anaesthesia had been induced with midazolam 0.1 mg/kg, fentanyl 5 micrograms/kg, vecuronium 0.1 mg/kg and atropine 10 micrograms/kg, and maintained with nitrous oxide in oxygen. Arterial pressure was measured directly and left ventricular diameters were determined by transoesophageal echocardiography. Systolic blood pressure after propofol and thiopentone and the end-systolic quotient (systolic pressure/end-systolic diameter), a measure of inotropy, decreased. Fractional shortening (end-diastolic-end-systolic diameter/end-diastolic diameter) decreased only in the thiopentone group. Diastolic blood pressure and end-diastolic diameter (a measure of preload) did not change in any of the groups, and the etomidate group showed no changes in the haemodynamic variables measured. Propofol shows simultaneous negative inotropy and afterload reduction, while thiopentone is exclusively negatively inotropic.     

Comparison of propofol and thiopentone for induction of anaesthesia in premedicated patients

Thirty premedicated ASA I or II patients scheduled for minor gynaecological surgery, were randomly allocated to receive either 1.5 mg/kg or 2 mg/kg propofol of the new emulsion formulation, or 4 mg/kg thiopentone, given over 20 seconds. Anaesthesia was successfully induced in all 30 patients. The mean (SEM) induction times were for propofol 1.5 mg/kg 33.3(3.2) seconds, for 2 mg/kg 30.5(2.7) seconds and for thiopentone 34.6(2.7) seconds. The incidence of apnoea greater than 10 seconds, was respectively 60, 80 and 80%, and the mean duration of apnoea 30.8(5.3), 37.1(5.0) and 23.7(5.0) seconds. The mean systolic blood pressure decreased after propofol 1.5 mg/kg by 16.0 mmHg, after 2 mg/kg by 18.6 mmHg, and increased after thiopentone by 1 mmHg, 2 minutes after injection. Heart rate increased significantly 2 minutes after thiopentone by an average of 15.1 beats/minute, but not after propofol. Pain was not reported during or after the injection. No major adverse reactions occurred at induction or during maintenance of anaesthesia with an inhalation agent. One patient who received 2 mg/kg propofol and isoflurane vomited for 24 hours. The recovery of anaesthesia after propofol induction, was quicker than after thiopentone.     

The effects of speed of injection on induction with propofol A comparison with etomidate

One hundred and eighty female patients received either propofol 2.5 mg/kg or etomidate 0.3 mg/kg injected over 20, 40 or 80 seconds for induction of anaesthesia after premedication with temazepam 20 mg. The mean induction times for both etomidate and propofol were significantly reduced with increasing speed of injection. The mean induction times for etomidate were significantly less than propofol at the slower rates of injection. At each speed of injection, the decrease in systolic, mean and diastolic arterial blood pressures with etomidate were less than with propofol. The decrease in systolic blood pressure was not significantly affected by injection speed for either drug. Apnoea occurred significantly more frequently with propofol than with etomidate at each speed of injection and the incidence of apnoea greater than 60 seconds with propofol was significantly higher when injected over 20 seconds than 80 seconds. The incidence of pain on injection was unaffected by injection speed for either drug. The incidence of myoclonus and (or) hypertonus was significantly higher following etomidate.     

Plasma etomidate levels in mother and fetus

The most commonly used induction agent in anaesthesia for Caesarean section is still thiopentone. The increasing incidence of Caesarean section for delivery of premature babies from a hostile environment may call in question the assumption that the dose of thiopentone received by the neonate will not cause depression in the hours following birth. Previous studies on thiopentone for Caesarean section have shown inconsistency in umbilical vein/maternal vein ratios. We have studied plasma etomidate levels in maternal and umbilical blood at the time of delivery to see whether equilibrium occurs with this agent. We were able to demonstrate an umbilical/maternal vein etomidate ratio of 0.5 (SD 0.18), with no relation to time in the range encountered. Also, the uterine artery/uterine vein etomidate ratio was 0.86 (SD 0.33), suggesting that etomidate uptake into the fetus is effectively complete. Further, in all cases the neonatal plasma etomidate levels were less than half those measured at recovery of consciousness in adults in other studies, despite a larger induction dose than is usually used.     

Adrenocortical function in critically ill patients 24 h after a single dose of etomidate

We compared the effects of single doses of etomidate and thiopentone on adrenocortical function in a randomised controlled clinical trial involving 35 critically ill patients who needed a general anaesthetic. Just before induction of anaesthesia, a baseline blood cortisol sample was taken. Twenty-four hours later we performed a short adrenocorticotrophic hormone stimulation test. No patient had a low cortisol level (< 160 nmol.l-1) at any time during the study. Baseline, pre-ACTH and post-ACTH cortisol levels were similar in the two groups. However, significantly more patients in the etomidate group had an ACTH-stimulated cortisol increment < 200 nmol.l-1. The clinical significance of these findings is not clear, but we conclude that single doses of etomidate may interfere with cortisol synthesis for at least 24 h in the critically ill.     

Cardiovascular instability following bolus dose of etomidate

A patient with alveolar proteinosis developed unexpected cardiovascular instability after broncho-alveolar lavage. He had received two bolus doses of etomidate within an 18-hour period. Serum cortisol concentrations were low and hydrocortisone replacement therapy was necessary to restore arterial pressure. Implications for management of critically ill patients who receive bolus doses of etomidate are discussed.     

Anaphylactoid reaction following the use of etomidate

A 13-year-old female suffered urticaria and severe bronchospasm sufficient to cause hypoxic cardiac arrest after intravenous induction of anaesthesia. Etomidate was strongly implicated in the reaction. The management and mechanism of the reaction are described and discussed, together with consideration of future anaesthesia in the patient.     

Alfentanil supplemented anaesthesia for short procedures

Thirty-nine unpremedicated patients who presented for cystoscopy were given either alfentanil or saline in a random double-blind fashion immediately before anaesthesia with etomidate, nitrous oxide and enflurane. Alfentanil significantly reduced myoclonus associated with etomidate. During anaesthesia, patients who received alfentanil had smaller minute volumes, lower respiratory frequencies, and smaller increases in heart rate. The incidence of apnoea was not significantly increased. After operation, patients who received alfentanil were prescribed significantly more analgesia, possibly because of their reduced uptake of volatile anaesthetic agent. It is concluded that supplementation with alfentanil improves the quality of anaesthesia induced with etomidate.     

Comparison of propofol and thiopentone for induction of anaesthesia for elective Caesarean section

Propofol 2.5 mg/kg was compared with thiopentone 5 mg/kg as an induction agent for elective Caesarean section. Thirty-two healthy women with cephalopelvic disproportion were included in an open randomised study. The placental transfer of propofol was also studied in 10 other mothers given a single dose of 2.5 mg/kg. The induction characteristics and haemodynamic response to propofol and thiopentone were similar. Side effects were rare with both agents, but propofol caused more discomfort on injection compared to thiopentone. Recovery times were shorter after propofol as evaluated by time to orientation, recovery scoring after anaesthesia and measurements with the Maddox wing. Rapid placental transfer and significant fetal uptake were detected for propofol. There was no significant neonatal depression as assessed by Apgar scores and blood gas analyses. Propofol appears to be a suitable alternative to thiopentone as an induction agent for anaesthesia in elective Caesarean section.     

Evaluation of intubating conditions with rocuronium and either propofol or etomidate for rapid sequence induction

We have assessed the effect of two induction agents on tracheal intubating conditions after rocuronium 0.6 mgkg⁻¹ in unpremedicated patients undergoing simulated rapid sequence induction. Following pre-oxygenation, anaesthesia was induced with propofol up to 2.5 mgkg⁻¹ ( n  = 35) or etomidate 0.3 mgkg⁻¹ ( n  = 36), and further increments as required. After loss of verbal contact, cricoid pressure was applied and rocuronium was injected. Laryngoscopy was performed at 45 s and intubation attempted at 60 s after rocuronium had been given. Ninety-four per cent of patients in the propofol group had clinically acceptable (good or excellent) intubating conditions compared to only 75% in the etomidate group (p = 0.025). Owing to coughing, one patient in the etomidate group could not be intubated on the first attempt. A greater pressor response also followed intubation after induction with etomidate. We conclude that etomidate and rocuronium alone cannot be recommended for intubation at 60 s under rapid sequence induction conditions.     

Total intravenous anaesthesia with etomidate-fentanyl

A total intravenous anaesthetic technique using etomidate, fentanyl and neuromuscular blocking drugs with artificial ventilation of the lungs has been used in 90 patients undergoing elective general and gynaecological surgery. A two-step schedule was used, based on a pharmacokinetic model for rapidly eliminated, intravenously administered drugs. Etomidate 100 micrograms/kg/minute with fentanyl 1 microgram/kg/minute were given for 10 minutes, followed by a maintenance dose at a rate of one-tenth this amount. Concurrent evaluation of the technique led to variations in the adjuvant drugs used (atropine, droperidol and neuromuscular blocking agent). The basic dose schedule provided adequate surgical anaesthesia for 76% of patients (although dose adjustments were used in the remainder), with recovery times of 10 minutes or less in 57% of patients. No further opiate analgesia was needed in 40% of patients postoperatively. Those patients given atropine intravenously prior to induction had a significantly lower incidence of nausea and vomiting postoperatively.     

Anti-adrenal action of a subanaesthetic dose of etomidate

The effects of subanaesthetic doses of etomidate on corticosteroid synthesis have been studied in vivo. In the group of patients who received etomidate (n = 10), cortisol and aldosterone responses to adrenocorticotrophic hormone were blunted, while 11-de-oxycortisol response was increased, as compared to a control group (n = 10). These results suggest that a single bolus of 0.04 mg/kg etomidate, which produces sedation, without loss of consciousness, is able to block adrenal 11 hydroxylase.     

Recovery from intravenous anaesthesia. Comparison of disoprofol with thiopentone and methohexitone

Using the endpoints of spontaneous opening of eyes, giving date of birth, sitting up unaided and normal pegboard time, recovery from 2 and 3 mg/kg disoprofol was compared with that from 4 and 6 mg/kg thiopentone and 1.5 mg/kg methohexitone in groups each of 10 unpremedicated patients. The study method differentiated between recovery from the two doses of disoprofol and thiopentone at the first two endpoints only. A between-drug comparison showed early recovery was slightly faster with thiopentone than with equivalent doses of the new drug while no differences were detected between the recovery from equivalent doses of methohexitone and thiopentone. The differences found in this study are felt to be of no clinical significance and recovery from anaesthesia with disoprofol would not be expected to be any slower than that from equivalent doses of thiopentone.