Time course of ventilatory depression following induction doses of propofol and thiopental

The Modulation by Anesthetics and Analgesics of Respiratory Rhythm in the Nervous System

Rhythmic eupneic breathing in mammals depends on the coordinated activities of the neural system that sends cranial and spinal motor outputs to respiratory muscles. These outputs modulate lung ventilation and adjust respiratory airflow, which depends on the upper airway patency and ventilatory musculature. Anesthetics are widely used in clinical practice worldwide. In addition to clinically necessary pharmacological effects, respiratory depression is a critical side effect induced by most general anesthetics. Therefore, understanding how general anesthetics modulate the respiratory system is important for the development of safer general anesthetics. Currently used volatile anesthetics and most intravenous anesthetics induce inhibitory effects on respiratory outputs. Various general anesthetics produce differential effects on respiratory characteristics, including the respiratory rate, tidal volume, airway resistance, and ventilatory response. At the cellular and molecular levels, the mechanisms underlying anesthetic-induced breathing depression mainly include modulation of synaptic transmission of ligand-gated ionotropic receptors (e.g., γ-aminobutyric acid, N-methyl-D-aspartate, and nicotinic acetylcholine receptors) and ion channels (e.g., voltage-gated sodium, calcium, and potassium channels, two-pore domain potassium channels, and sodium leak channels), which affect neuronal firing in brainstem respiratory and peripheral chemoreceptor areas. The present review comprehensively summarizes the modulation of the respiratory system by clinically used general anesthetics, including the effects at the molecular, cellular, anatomic, and behavioral levels. Specifically, analgesics, such as opioids, which cause respiratory depression and the "opioid crisis", are discussed. Finally, underlying strategies of respiratory stimulation that target general anesthetics and/or analgesics are summarized.

Geriatric Pharmacology: An Update

An aging worldwide population demands that anesthesiologists consider geriatrics a unique subset of patients requiring customization of practice. This article reviews the current literature investigating physiologic changes of the elderly that affect pharmacokinetics and pharmacodynamics. Changes in drug absorption, distribution, metabolism, and excretion are discussed as well as the ultimate effects of medications. Implications for practice regarding specific anesthetic and analgesic drugs are addressed. Despite the immense body of research that contributes to understanding of geriatric pharmacology, elderly patients often are excluded from rigorous research trials, and further scientific investigation to inform best practices for this group of patients is needed.

A Phase 1, Single-center, Double-blind, Placebo-controlled Study in Healthy Subjects to Assess the Safety, Tolerability, Clinical Effects, and Pharmacokinetics–Pharmacodynamics of Intravenous Cyclopropyl-methoxycarbonylmetomidate (ABP-700) after a Single Ascending Bolus Dose

Background

Cyclopropyl-methoxycarbonylmetomidate (ABP-700) is a new “soft” etomidate analog. The primary objectives of this first-in-human study were to describe the safety and efficacy of ABP-700 and to determine its maximum tolerated dose. Secondary objectives were to characterize the pharmacokinetics of ABP-700 and its primary metabolite (cyclopropyl-methoxycarbonyl acid), to assess the clinical effects of ABP-700, and to investigate the dose–response and pharmacokinetic/pharmacodynamic relationships.

Methods

Sixty subjects were divided into 10 cohorts and received an increasing, single bolus of either ABP-700 or placebo. Safety was assessed by clinical laboratory evaluations, infusion-site reactions, continuous monitoring of vital signs, physical examination, adverse event monitoring, and adrenocorticotropic hormone stimulation testing. Clinical effects were assessed with modified observer’s assessment of alertness/sedation and Bispectral Index monitoring. Pharmacokinetic parameters were calculated.

Results

Stopping criteria were met at 1.00 mg/kg dose. No serious adverse events were reported. Adverse events were dose-dependent and comprised involuntary muscle movement, tachycardia, and ventilatory effects. Adrenocorticotropic hormone stimulation evoked a physiologic cortisol response in all subjects, no different from placebo. Pharmacokinetics were dose-proportional. A three-compartment pharmacokinetic model described the data well. A rapid onset of anesthesia/sedation after bolus administration and also a rapid recovery were observed. A quantitative concentration–effect relationship was described for the modified observer’s assessment of alertness/sedation and Bispectral Index.

Conclusions

This first-in-human study of ABP-700 shows that ABP-700 was safe and well tolerated after single-bolus injections up to 1.00 mg/kg. Bolus doses of 0.25 and 0.35 mg/kg were found to provide the most beneficial clinical effect versus side-effect profile.

Is propofol an optimal agent for procedural sedation and rapid sequence intubation in the emergency department?

Objective:

We conducted a qualitative systematic review to evaluate the efficacy and safety of propofol for direct current cardioversion (DCC), rapid sequence intubation (RSI) and procedural sedation in adult emergency department (ED) patients.

Data source:

MEDLINE (1966 to September 2000), PubMed (to September 2000), EMBASE (1988 to September 2000), Database of Systematic Reviews (to September 2000), Best Evidence (1991 to September 2000) and Current Contents (1996 to September 2000) databases.

Study selection:

English-language, randomized, comparative evaluations of propofol for procedures routinely conducted in adults (>18 years) were included. Direct current cardioversion, RSI and procedural sedation were considered.

Data extraction:

Efficacy and safety endpoints were evaluated for all trials. For DCC and procedural sedation trials, efficacy measures included induction and recovery times, as well as the association for successful procedure. For the RSI trials, optimal intubating conditions were evaluated as the primary efficacy endpoint. Safety measures included hemodynamic changes, apnea rates and adverse effects.

Data synthesis:

In the setting of DCC, efficacy and safety outcomes were similar for propofol, thiopental, etomidate and methohexital. All of these agents provided markedly shorter induction and recovery times than midazolam. Patients who were pre-medicated with fentanyl exhibited prolonged recovery times and greater decreases in blood pressure. When used for RSI, propofol administration was associated with satisfactory intubating conditions that were comparable to those seen with thiopental and etomidate. Blood pressure reductions were seen in both DCC and RSI studies. Apneic episodes (>30 seconds) occurred in 23% of propofol recipients, 28% of thiopental recipients and 7% of etomidate and midazolam recipients. Apart from the DCC studies described, no procedural sedation studies met our predefined review eligibility criteria.

Conclusion:

The body of literature evaluating propofol for DCC and RSI in the ED is limited. There is evidence to support the use of propofol for DCC and RSI, but this evidence comes from stable patients in non-ED settings. Further ED-based randomized comparative trials should be conducted before propofol is adopted for widespread use in the ED.

Total intravenous anesthesia will supercede inhalational anesthesia in pediatric anesthetic practice

Inhalational anesthesia has dominated the practice of pediatric anesthesia. However, as the introduction of agents such as propofol, short-acting opioids, midazolam, and dexmedetomidine a monumental change has occurred. With increasing use, the overwhelming advantages of total intravenous anesthesia (TIVA) have emerged and driven change in practice. These advantages, outlined in this review, will justify why TIVA will supercede inhalational anesthesia in future pediatric anesthetic practice.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Intravenous boluses of fentanyl, 1 μg kg⁻¹, and remifentanil, 0.5 μg kg⁻¹, give similar maximum ventilatory depression in awake volunteers

BACKGROUND

The relative respiratory effects of fentanyl and remifentanil, administered as i.v. bolus, have not previously been studied. We determined what remifentanil bolus dose gave the same maximum depression of ventilation as 1 µg kg(-1) of fentanyl.

METHODS

Twelve healthy volunteers rebreathed in a system designed to dampen variations in end-tidal carbon dioxide tension PE'CO2 so that measurements would be obtained at similar levels of CO(2) stimulation. The minute ventilation was measured before (V(preinj)) and after injection (V(nadir)) of fentanyl, 1 µg kg(-1), and remifentanil, 0.25, 0.5, and 1 µg kg(-1). The remifentanil doses were plotted against V(nadir)/V(preinj) in a log-probit diagram to determine what amount gave the same maximum ventilatory depression as the fentanyl dose.

RESULTS

V(nadir) was [median (inter-quartile range)] 51 (38-64)% of V(preinj) after fentanyl, and 70 (61-77), 50 (46-56), and 29 (24-38)%, respectively, after remifentanil. The nadir occurred 5.0 (4.4-7.0) min after fentanyl, and 3.8 (2.7-4.6), 2.9 (2.7-3.2), and 3.0 (2.7-3.2) min after remifentanil injection. PE'CO2 at ventilation nadir was 6.26 (5.98-6.62) kPa after fentanyl, and 6.18 (6.12-6.50), 6.11 (5.91-6.45), and 6.11 (5.93-6.45) kPa after remifentanil 0.25, 0.5, and 1 µg kg(-1), respectively. A remifentanil dose of 0.47 (0.42-0.62) µg kg(-1) was equidepressant to 1 µg kg(-1) of fentanyl. Fifteen minutes after fentanyl injection, the median minute ventilation was 30-40% less than after injection of remifentanil, 0.25 and 0.5 µg kg(-1) (P<0.05).

CONCLUSIONS

Fentanyl, 1 µg kg(-1), and remifentanil, 0.5 µg kg(-1), gave similar maximum ventilatory depression. The onset of and recovery from ventilatory depression were faster with remifentanil.

Anesthetics and control of breathing

An important side effect of general anesthetics is respiratory depression. Anesthetics have multiple membrane targets of which ionotropic receptors such as gamma-aminobutyric acid-A (GABA(A)), glycine, N-methyl-D-aspartate and nicotinic acetylcholinergic (nACh) receptors are important members. GABA, glutamate and ACh are crucial neurotransmitters in the respiratory neuronal network, and the ability of anesthetics to modulate their release and interact with their receptors implies complex effects on respiration. Metabotropic receptors and intracellular proteins are other important targets for anesthetics suggesting complex effects on intracellular signaling pathways. Here we briefly overview the effects of general anesthetics on protein targets as far as these are relevant for respiratory control. Subsequently, we describe some methods with which the overall effect of anesthetics on the control of breathing can be measured, as well as some promising in vivo approaches to study their synaptic effects. Finally, we summarize the most important respiratory effects of volatile anesthetics in humans and animals and those of some intravenous anesthetics in animals.

Tracheal intubating conditions and apnoea time after small-dose succinylcholine are not modified by the choice of induction agent

BACKGROUND

In a randomized, double-blind clinical trial, we studied the effect of different i.v. induction drugs on tracheal intubation conditions and apnoea time after small-dose (0.6 mg kg(-1)) succinylcholine used to facilitate orotracheal intubation at an urban, university-affiliated community medical centre.

METHODS

One hundred and seventy-five ASA I and II adult patients scheduled to undergo surgical procedures requiring general anaesthesia and tracheal intubation were allocated to one of five groups according to i.v. anaesthetic induction drug used. General anaesthesia was induced by i.v. administration of lidocaine 30 mg and propofol 2.5 mg kg(-1) (Group 1), thiopental 5 mg kg(-1) (Group 2), lidocaine 30 mg and thiopental 5 mg kg(-1) (Group 3), etomidate 0.3 mg kg(-1) (Group 4), or lidocaine 30 mg and etomidate 0.3 mg kg(-1) (Group 5). After loss of consciousness, succinylcholine 0.6 mg kg(-1) was given i.v. followed by direct laryngoscopy and tracheal intubation after 60 s. Measurements included intubation conditions recorded during laryngoscopy 60 s after succinylcholine administration, and apnoea time.

RESULTS

Overall, clinically acceptable intubation conditions were met in 168 out of the 175 patients studied (96%). They were met in 35/35 patients in Group 1, 33/35 patients in Group 2, 34/35 patients in Group 3, 33/35 patients in Group 4, and 33/35 patients in Group 5. Mean (SD) apnoea time was 4.0 (0.4), 4.2 (0.3), 4.2 (0.6), 4.1 (0.2) and 4.1 (0.2) min respectively in Groups 1-5. There were no differences in the intubation conditions or apnoea times between the groups.

CONCLUSIONS

The use of succinylcholine 0.6 mg kg(-1) produced the same favourable intubation conditions and a short apnoea time regardless of the induction drug used.

Anesthetic protocols for common emergencies

Anesthesia, sedation, and pain management should be taken seriously in the emergency patient. Proper knowledge of the drugs available and their pharmacokinetics and pharmacodynamics are necessary to administer anesthesia safely to critical patients. A proactive approach regarding monitoring, titration of anesthetic drugs, and anticipation of life-threatening complications helps in achieving successful anesthetic outcomes.

GABAA receptors mediate postnatal depression of respiratory frequency by barbiturates

We tested the hypothesis that barbiturates depress respiratory motor output by actions on the GABAA receptor. We examined the influence of pentobarbital sodium on nerve activity recorded from a fourth cervical (C4) ventral root (phrenic motoneuron output) in the in vitro brainstem-spinal cord preparation of neonatal rats aged 1-3 days. Bath application of pentobarbital slowed the respiratory rhythm but this effect could be reversed by drug washout or by simultaneous application of 8 microM bicuculline methiodide, a GABAA receptor antagonist. Pentobarbital up to a concentration of 80 microM (or 20 mg/l) did not change the magnitude of C4 nerve bursts. The GABAA receptor agonist muscimol evoked similar changes. The results support the hypothesis that respiratory depression by barbiturates is due to GABAA receptor-mediated inhibition, with the principal effects on rhythm generation. In the light of recent studies suggesting that GABAA receptors may be excitatory in the early neonatal period, we examined postnatal changes in the GABAergic slowing of respiratory rhythm. Stimulation of GABAA receptors slowed respiratory rhythm from the first postnatal day, with no change in efficacy over the first 3 days of life.

Application of nasal bi-level positive airway pressure to respiratory support during combined epidural-propofol anesthesia

STUDY OBJECTIVE

To examine whether nasal bi-level positive airway pressure (BiPAP) can be used as an airway during combined epidural-propofol anesthesia.

DESIGN

Prospective, consecutive case series study.

SETTING

Operating room at a general hospital.

PATIENTS

213 ASA physical status I and II adult patients undergoing lower extremity or lower abdominal gynecology surgery.

INTERVENTIONS

After epidural anesthesia, propofol was infused at 20 mg/kg/hr (P20) for 4 to 5 minutes followed by 5 mg/kg/hr (P5), and nasal continuous positive airway pressure (CPAP) 8 cm H(2)O and BiPAP 14/8 cm H(2)O was applied. In clinical situations, BiPAP with respiratory rate (RR) 10 breaths/min was applied. Furthermore, tidal volume (V(T)) during anesthesia, the effect of changing pressure support levels, and evaluation of pressure-controlled ventilation without spontaneous breathing were examined.

MEASUREMENTS AND MAIN RESULTS

CPAP resulted in a high RR, marked increased PaCO(2), and slightly decreased PaO(2), whereas BiPAP showed no change or a slightly decreased RR, slightly increased PaCO(2), and no change in PaO(2) or a great increase in PaO(2) with oxygen delivery. In clinical applications, similar results were found and anesthetic conditions were sufficient. Tidal volume increased after induction and maintained increased values under BiPAP 14/8 cm H(2)O. Of V(T) at 2, 6, or 10 cm H(2)O of pressure support levels, the 6 cm H(2)O was appropriate. Vecuronium injection showed a slight decrease and then increase in V(T) and PaCO(2), but the values were within normal (safe) limits. Respiration after rapid and high-dose infusion of propofol showed a markedly decreased RR, but the V(T) was maintained, and PaCO(2) and PaO(2) were at safe values. Rapid induction with 2.0 mg/kg propofol followed by P5 showed satisfactory results, in all but the obese patients.

CONCLUSIONS

BiPAP 14/8 cm H(2)0 with RR at 10 breaths/min during combined epidural-propofol anesthesia can be used to provide ventilatory support in lower extremity or lower abdominal gynecology surgery.

Propofol anesthesia

Although questions may still remain regarding the use of this unique sedative-hypnotic drug with anesthetic properties in high-risk patients, our studies have provided cardiopulmonary and neurological evidence of the efficacy and safety of propofol when used as an anesthetic under normal and selected impaired conditions in the dog. 1. Propofol can be safely and effectively used for the induction and maintenance of anesthesia in normal healthy dogs. Propofol is also a reliable and safe anesthetic agent when used during induced cardiovascular and pulmonary-impaired conditions without surgery. The propofol requirements to induce the safe and prompt induction of anesthesia prior to inhalant anesthesia with and without surgery have been determined. 2. The favorable recovery profile associated with propofol offers advantages over traditional anesthetics in clinical situations in which rapid recovery is important. Also, propofol compatibility with a large variety of preanesthetics may increase its use as a safe and reliable i.v. anesthetic for the induction and maintenance of general anesthesia and sedation in small animal veterinary practice. Although propofol has proven to be a valuable adjuvant during short ambulatory procedures, its use for the maintenance of general anesthesia has been questioned for surgery lasting more than 1 hour because of increased cost and marginal differences in recovery times compared with those of standard inhalant or balanced anesthetic techniques. When propofol is used for the maintenance of anesthesia in combination with a sedative/analgesic, the quality of anesthesia is improved as well as the ease with which the practitioner can titrate propofol; therefore, practitioners are able to use i.v. anesthetic techniques more effectively in their clinical practices. 3. Propofol can induce significant depression of respiratory function, characterized by a reduction in the rate of respiration. Potent alpha 2 sedative/analgesics (e.g., xylazine, medetomidine) or opioids (e.g., oxymorphone, butorphanol) increase the probability of respiratory depression during anesthesia. Appropriate consideration of dose reduction and speed of administration of propofol reduces the degree of depression. Cardiovascular changes induced by propofol administration consist of a slight decrease in arterial blood pressures (systolic, mean, diastolic) without a compensatory increase in heart rate. Selective premedicants markedly modify this characteristic response. 4. When coupled with subjective responses to painful stimuli, EEG responses during propofol anesthesia provide clear evidence that satisfactory anesthesia has been achieved in experimental dogs. When propofol is used as the only anesthetic agent, a higher dose is required to induce an equipotent level of CNS depression compared with the situation when dogs are premedicated. 5. The propofol induction dose requirement should be appropriately decreased by 20% to 80% when propofol is administered in combination with sedative or analgesic agents as part of a balanced technique as well as in elderly and debilitated patients. As a general recommendation, the dose of propofol should always be carefully titrated against the needs and responses of the individual patient, as there is considerable variability in anesthetic requirements among patients. Because propofol does not have marked analgesic effects and its metabolism is rapid, the use of local anesthetics, nonsteroidal anti-inflammatory agents, and opioids to provide postoperative analgesia improves the quality of recovery after propofol anesthesia. 6. The cardiovascular depressant effects of propofol are well tolerated in healthy animals, but these effects may be more problematic in high-risk patients with intrinsic cardiac disease as well as in those with systemic disease. In hypovolemic patients and those with limited cardiac reserve, even small induction doses of propofol (0.75-1.5 mg/kg i.v.) can produce profound hypotens

Pharmacokinetics and pharmacodynamics of eltanolone (pregnanolone), a new steroid intravenous anaesthetic, in humans

Eltanolone, a new intravenous steroid anaesthetic agent was administered intravenously in a dose of 0.6 mg.kg-1 over 45 s to eight healthy male volunteers to evaluate some of its pharmacokinetic and pharmacodynamic effects. Drug concentration-time data were analysed by PCNONLIN, a non-linear regression programme, showing data consistent with a three-compartment model with initial distribution half-life t1/2 lambda 1 between 0.3 and 2 min, intermediate distribution half-life t1/2 lambda 2 between 12 and 29 min and terminal half-life t1/2 lambda z between 72 and 212 min. The total body clearance of eltanolone was rapid and with individual values in the range 1.6-2.3 l.h-1.kg-1. Eltanolone was initially distributed into a relatively large central compartment V1 between 0.09 and 0.98 l.kg-1 and then extensively further distributed (Vss between 1.80 and 5.44 l.kg-1 and V between 4.87 and 11.87 l.kg-1). The excretion of unchanged of eltanolone in urine was very small, the renal clearance was less than 0.5% of the total clearance. Induction of anaesthesia was trouble free with onset and duration of anaesthesia between 1-2 min and 6-13 min, respectively. There was slight respiratory depression, a small transient increase in heart rate, and a maximum reduction in arterial blood pressure of 23%, as compared with the resting level. Pain on injection and venous sequelae were not seen. Involuntary movements were seen in one subject. We conclude that eltanolone has a favourable pharmacokinetic profile with relatively rapid half-lives, large distribution volumes and rapid total body clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Pediatric analgesia and sedation

Sedation and analgesia are essential components of the ED management of pediatric patients. Used appropriately, there are a number of medications and techniques that can be used safely in the emergency care of infants and children. Emergency physicians should be competent in the use of multiple sedatives and analgesics. Adequate equipment and monitoring, staff training, discharge instructions and continuous quality management should be an integral part of the ED use of these agents.

[Recovery after anesthesia with Diprivan]

In view of the rapid and complete recovery, the low incidence of hangover, nausea or vomiting, propofol can be considered as first choice agent for minor surgery, short operations and/or day-case surgery. For long and major procedures it is of no advantage over the thiopental-isoflurane technique. For a rapid recovery, the dose should be titrated, particularly during the closing stage of the procedure. As propofol has some amnesic properties, any instructions given to the patient postoperatively should be in writing. Sexual thoughts resulting from disinhibition may occur during emergence; therefore, it is recommended to have a third party present to avoid any implications of misconduct.

[Use of Diprivan for digestive system endoscopy]

After evaluation of the patient's clinical condition and appropriate premedication is seems reasonable to suggest for: 1. Endoscopic procedures involving the gastro-intestinal tract: slow, titrated induction, using 0.5 to 1 mg.kg-1 of propofol, until the required level of sedation has been achieved; this may or not be preceded by the injection of a low dose of midazolam (0.02 to 0.03 mg.kg-1) or of alfentanil (5 micrograms.kg-1); maintenance is achieved by bolus injections of 20 mg (up to 0.5 mg.kg-1); maintenance of spontaneous ventilation, with oxygen administration is the rule; SpO2 is monitored routinely; anaesthesia has to be performed according to the recommendations of the French Society of Anaesthesia and Intensive Care (SFAR) and the anaesthetist must be prepared to manage any incident during the endoscopy and the recovery period. 2. Procedures involving the biliary tract and the oesophagus, which require deeper anaesthesia: induction should again be titrated using a very slow infusion, with doses ranging from 0.9 to 2.2 mg.kg-1); the maintenance requires a continuous infusion, doses ranging from 4 to 6 mg.kg-1.h-1 when propofol is administered alone and from 4 to 12 mg.kg-1.h-1 when combined with an opioid; continuous oxygenation is necessary using a nasal airway; the need for intubation depends on the type of procedure and the status of the patient; the same monitoring devices and similar safety measures are required during and after procedure as for any anaesthetic or sedation, especially when it is performed in day-case patients or outside the operating theatre.

[Use of Diprivan in chronic respiratory insufficiency]

Propofol may be recommended as an anaesthetic agent in patients with chronic respiratory insufficiency since: it prevents the increase in bronchial resistances resulting from the administration of opioids; it possesses a bronchodilator effect, comparable with that of flunitrazepam; it ensures rapid recovery, which would favour patient's co-operation postoperatively. The effects of propofol on respiratory drive should not be neglected, as they may persist even after complete recovery. In pulmonary surgery, propofol may be recommended in patients with one-lung ventilation, since it does not depress the hypoxic vasoconstriction reflex. Some procedures may be carried out in spontaneous ventilation or, preferably, using jet ventilation, provided that propofol is given by means of an infusion pump.

[Use of Diprivan in gynecology]

1. Propofol as an induction agent At a dose of 2 to 2.5 mg.kg-1, as a bolus injection over 30 to 60 seconds, for gynaecological procedures of short duration (abortion, D and C), propofol can be characterized as follows when compared with other induction agents: ADVANTAGES OVER METHOHEXITONE AND ETOMIDATE: decreased incidence of hiccups and abnormal movements, increased quality of induction, similar to that obtained with thiopentone, decreased postoperative nausea and vomiting. ADVANTAGES OVER THIOPENTONE: shorter recovery period, more rapid recovery of consciousness and orientation. DISADVANTAGES WHEN COMPARED WITH THIOPENTONE: more frequent pain at the injection site, however its prevention is possible, more frequent apnoea, but may be avoided by slowly injecting the drug, higher cost. The main advantage of propofol over thiopentone (shorter recovery period), makes day-case gynaecological procedures one of its major indications. This concerns young, healthy women, whose professional and family lives are important and who may benefit from minimal disruption in their way of life. 2. Propofol as a maintenance agent Propofol is given as a continuous infusion at a dose ranging from 6 to 12 mg.kg-1.h-1 for maintenance of prolonged procedures (abdominal surgery, hysterectomy) and can be characterized as follows with respect to halogenated anaesthetics: ADVANTAGES OVER ENFLURANE AND ISOFLURANE: decreased postoperative nausea and vomiting, increased recovery scores (1st hour). COMPARED WITH DESFLURANE: shorter induction time than desflurane, less respiratory problems at induction, similar recovery period, same incidence of nausea and vomiting. The administration of propofol for maintenance of anaesthesia has the main advantage of reducing the incidence of postoperative nausea and vomiting when compared to conventional halogenated anaesthetics. Respective costs of the various techniques, using propofol or the new halogenated anaesthetics, may be a criterion for choice in the future.(ABSTRACT TRUNCATED AT 250 WORDS)