Plasma concentration of fentanyl, with 70% nitrous oxide, to prevent movement at skin incision

The Haemodynamic Response to Endotracheal Intubation at Different Time of Fentanyl Given During Induction: A Randomised Controlled Trial

Endotracheal intubation elicits huge spectrum of stress responses which are hazardous in high-risk patients. Numerous drugs and techniques have been applied to attenuate the stress responses. In this double-blind study, one hundred and forty-five patients over 20 years old, ASA physical status I and II, undergoing elective surgeries requiring general anaesthesia with endotracheal intubation were included. Patients were randomly divided into three groups which fentanyl 2 mcg/kg was given at either 1, 2, 3 minutes before intubation. All groups received midazolam 0.05 mg/kg, lidocaine 0.5 mg/kg, propofol 2 mg/kg and rocuronium 1 mg/kg before intubation. Haemodynamic parameters were recorded for 10 minutes after induction. Two-level longitudinal hierarchical linear models were used for data interpretation and P < 0.05 was considered statistically significant. The study demonstrated significantly lower haemodynamic responses in the group who received fentanyl 2 minutes before intubation (P < 0.05). Confounding factors such as smoking, hypertension, diabetes mellitus and preoperative intravenous fluid supplement were analysed. In conclusion, fentanyl injection 2 minutes before intubation is recommended in order to obtain the most stable haemodynamic status.

Bupivacaine caudal epidural anesthesia: assessing the effect of general anesthetic technique on block onset

BACKGROUND

The primary objective of this prospective, randomized trial was to compare the effect of propofol and sevoflurane on effectiveness of regional anesthesia. As a secondary objective, we aimed at evaluating the influence of age on neuraxial block profile.

METHODS

One hundred and thirteen healthy children aged <10 years, scheduled for general or urological surgical procedures were randomly allocated to receive either propofol or sevoflurane induction and maintenance. Children received caudal or lumbar epidural block depending on their weight and expected surgery. Time to onset of surgical anesthesia, intraoperative analgesic effectiveness, residual motor blockade, postoperative pain, and adverse effects were evaluated. To assess the influence of age on these measures children were further divided into three age groups: 0-24, 25-60 and >60 months.

RESULTS

The mean time to onset of surgical anesthesia was significantly shorter in the sevoflurane group than the propofol group (3.1 vs 4.7 min, P < 0.01), independent of the type of regional technique employed. Distress on arousal in recovery was increased in children receiving sevoflurane (P = 0.03). There was no significant difference in residual motor blockade between the groups but children between 0 and 24 months receiving sevoflurane had a higher incidence of residual motor blockade 3 h after local anesthetic injection (P = 0.01).

CONCLUSIONS

This study has demonstrated that general anesthesia with sevoflurane decreases the time to onset of surgical anesthesia relative to propofol anesthesia. This effect was most marked when sevoflurane anesthesia preceded caudal epidural blockade. The basis for this effect is most likely to be related to differential binding of the two anesthetic agents to receptors in the spinal cord that mediate immobility in response to surgical stimuli.

Inter-patient variability upon induction with sevoflurane estimated by the time to reach predefined end-points of depth of anaesthesia

BACKGROUND AND OBJECTIVES

A difficult issue in anaesthesia is its titration for an individual patient to avoid over- and underdosage. Common practice is to use an initial dose and increase it subsequently if the defined end-point is not reached. This assumes that the end-point is reached after a similar interval of time in all patients given a similar dose. In order to test this hypothesis we measured the time to reach end-points such as loss of consciousness (LOC), a bispectral index (BIS) value of 60, the minimal BIS and the minimal mean arterial pressure (MAP) values.

METHODS

Thirty patients aged 18-60 yr scheduled for general surgery were included in this observational study. After preoxygenation, induction was performed with 6% inspired concentration of sevoflurane in 6 Lmin-1 oxygen using the SiBI connector and the tidal volume technique. Remifentanil was administered when the BIS value was 60 and tracheal intubation was performed 4 min later.

RESULTS

Time (median, minimum-maximum) to LOC, a BIS value of 60, the minimal BIS and MAP values were, respectively, 75 (45-135), 120 (75-270), 300 (120-720) and 450 (120-1200) seconds. The time to the minimal BIS value was significantly (P < 0.05) shorter than the time to reach the minimal MAP value.

CONCLUSIONS

These results demonstrate large inter-patient variability for the time necessary to reach defined end-points of depth of anaesthesia when a similar dose of anaesthetic is given. Measuring the time to reach a predefined BIS value would allow application of nociceptive stimuli only at adequate levels of hypnosis and would facilitate titration.

Ceasing routine use of nitrous oxide-a follow up

BACKGROUND

The role of nitrous oxide in modern anaesthesia is questioned. The routine use of nitrous oxide was almost completely stopped in our department after November 1, 2000, and we now report some consequences.

METHODS

Staff completed a questionnaire after 6 months, and we analysed the use of hypnotics and opioids after 12 months. The cost of drugs for the year after stopping nitrous oxide was compared with the cost 2 yr before.

RESULTS

Less than half of the 55 staff members who answered the questionnaire used nitrous oxide in the 6 months after the stop, and they did so on only a few occasions. Half of the staff members thought the benefit of nitrous oxide was small. Most supported the change. The use of opioids was stable during the study period, and there was an annual increase of 12-14% in the use of hypnotics during the 3 yr.

CONCLUSIONS

The staff questionnaire showed a strong acceptance of the new policy, and the use of other anaesthetic agents did not increase as expected. Has the value of nitrous oxide been overestimated?

Sevoflurane requirements during coloproctologic surgery: difference between two different epidural regimens

STUDY OBJECTIVE

To examine the influence of epidural morphine on the end-tidal sevoflurane concentration titrated to maintain bispectral index (BIS) values between 40 and 50.

DESIGN

Prospective, double-blinded clinical trial.

SETTINGS

Anesthesia department of a university hospital.

PATIENTS

40 ASA physical status I, II, and III patients scheduled for elective coloproctological surgery.

INTERVENTIONS

Patients were randomized to receive via a thoracic epidural catheter either a) bupivacaine 0.25% (10 mL) and saline 0.9% (2 mL) as a bolus followed by an infusion of bupivacaine 0.25% (5 mL/hr) or b) bupivacaine 0.25% (10 mL) and morphine 0.1% (2 mL) as a bolus followed by an infusion of bupivacaine 0.25% plus morphine 0.025% (5 mL/hr). Anesthesia was induced with propofol, fentanyl 2 microg kg(-1) and atracurium and maintained with sevoflurane and nitrous oxide in oxygen. Sevoflurane level was titrated to maintain a BIS value between 40 and 50. After extubation, patients were asked about the presence of pain.

MAIN RESULTS

There was no significant difference between groups of end-tidal sevoflurane concentrations at identical BIS values and hemodynamic values at any time in the study. However, the morphine group had a lower pain score level at extubation than did the plain bupivacaine group (no pain on movement, 79% vs. 31.5%, p < 0.01).

CONCLUSIONS

Adding morphine to the bupivacaine epidural solution did not reduce sevoflurane requirements but did provide high-quality postoperative analgesia, mainly just after tracheal extubation.

Propofol anesthesia for craniotomy: a double-blind comparison of remifentanil, alfentanil, and fentanyl

For patients undergoing craniotomy, it is desirable to have stable and easily controllable hemodynamics during intense surgical stimulation. However, rapid postoperative recovery is essential to assess neurologic function. Remifentanil, an ultra-short-acting mu-opioid receptor agonist, may be the ideal agent to confer the above characteristics. In this prospective randomized study, we compared the hemodynamic stability, recovery characteristics, and the dose of propofol required for maintaining anesthesia supplemented with an infusion of remifentanil, alfentanil, or fentanyl in 34 patients scheduled for supratentorial craniotomy. With routine monitors in place, anesthesia was induced with propofol (2-3 mg/kg), atracurium (0.5 mg/kg), and either remifentanil (1 microg/kg), alfentanil (10 microg/kg), or fentanyl (2 micro/kg). The lungs were ventilated with O2/air to mild hypocapnia. Anesthesia was maintained with infusions of propofol (50-100 microg/kg/min) and either remifentanil (0.2 microg/kg/min), alfentanil (20 microg/kg/h), or fentanyl (2 microg/kg/h). There were no significant differences among the groups in the dose of propofol maintenance required, heart rate, or mean arterial pressure. However, the time to eye opening (minutes) was significantly shorter in the remifentanil compared to the alfentanil group (6+/-3; 21+/-14; P = 0.0027) but not the fentanyl group (15+/-9). We conclude that remifentanil is an appropriate opioid to use in combination with propofol during anesthesia for supratentorial craniotomy.

Isoflurane, nitrous oxide, and fentanyl pharmacodynamic interactions in surgical patients as measured by effects on median power frequency

STUDY OBJECTIVE

To identify and quantify the simultaneous interactions of isoflurane, nitrous oxide (N2O), and fentanyl during surgical procedures. The slowing of the EEG to a median power frequency of 2 Hz to 3 Hz was chosen as the measure of pharmacodynamic drug effect.

DESIGN

Prospective, randomized, open label.

SETTING

Operating room of a university hospital.

PATIENTS

65 ASA physical status I and II patients undergoing gynecological laparatomies.

INTERVENTIONS

25 patients received no fentanyl. 20 patients received a loading dose of 100 micrograms fentanyl and a continuous infusion of 70 micrograms.h-1 fentanyl. Calculated effect compartment concentrations were 0.7 ng.ml-1 between the first and second hours after induction of anesthesia. Another 20 patients received a loading dose of 200 micrograms fentanyl and a continuous infusion of 150 micrograms.h-1 fentanyl; the respective effect compartment concentrations were 1.5 ng.ml-1. N2O was randomly administered in concentrations of 0, 20, 40, and 60 vol%; in the group that did not receive fentanyl, we additionally investigated 75 vol% N2O. Each patient received two different N2O concentrations, with each combination of N2O and fentanyl finally applied to ten patients. Isoflurane vaporizer settings were chosen so that the median power frequency was held between 2 Hz and 3 Hz. The type and degree of interaction among the three anesthetic drugs was analyzed based on a generalized isobole approach.

MEASUREMENTS AND MAIN RESULTS

The interaction of isoflurane, N2O, and fentanyl is compatible with additivity. A model with regard to the relative potencies and age dependency is given by: [formula: see text] with C0,iso = 1.30 vol%, C0,N2O = 177 vol%, C0,fen = 10.6 ng.ml-1, and a = -0.0031 yr-1. where conc. = end-tidal or effect compartment concentrations.

CONCLUSION

The potency of N2O and fentanyl to substitute isoflurane in maintaining a median power frequency of 2 Hz to 3 Hz during surgery is less than anticipated from minimum alveolar concentration studies.

Esmolol potentiates reduction of minimum alveolar isoflurane concentration by alfentanil

Esmolol, a short-acting beta1-receptor antagonist, decreases anesthetic requirements during propofol/N2O/morphine anesthesia. This study was designed to determine whether esmolol affects the volatile anesthetic (isoflurane) required to prevent movement to skin incision in 50% patients (minimum alveolar anesthetic concentration [MAC]) with or without an additional opioid (alfentanil). One hundred consenting adult patients were randomly divided into five treatment groups: isoflurane alone (I), I with continuous large-dose (250 microg x kg(-1) x min(-1)) esmolol (E), I with alfentanil (effect site target of 50 ng/mL) via a continuous computer-controlled infusion (A), A plus continuous small-dose (50 microg x kg(-1) x min(-1)) esmolol (A1), or A plus large-dose esmolol (A2). Anesthesia was induced via a face mask, and steady-state target end-tidal isoflurane concentrations were maintained before incision. The MAC of isoflurane alone was 1.28% +/- 0.13%. Large-dose esmolol did not significantly alter the isoflurane MAC (1.23% +/- 0.14%). Alfentanil alone significantly decreased isoflurane MAC by 25% (0.96% +/-0.09%). Adding small-dose esmolol did not further decrease MAC with alfentanil (0.96% +/- 0.13%). However, large-dose esmolol significantly decreased isoflurane MAC with alfentanil (0.74% +/- 0.09%). Esmolol and alfentanil both significantly reduced the increases in heart rate and mean arterial pressure associated with endotracheal intubation and incision. The mechanism of this effect is unknown.

IMPLICATIONS

Most anesthetic techniques rely on a balance of several highly selective medications. The current results define a new anesthetic-sparing effect when volatile anesthetic, analgesic, and beta-adrenergic blocking drugs are combined.

Awareness in anaesthesia: incidence, consequences and prevention

Awareness during anaesthesia is a state of consciousness that is revealed by explicit or implicit memory of intraoperative events. Although large clinical surveys indicate an incidence of explicit awareness of < 0.3% during anaesthesia for general surgery, this adverse effect should be a great concern, because patients may be permanently disabled by the experience of being awake during surgery. Prevention of awareness during anaesthesia starts with an appropriate preoperative visit to the patient. The anaesthetic delivery machines must be properly checked before and during anaesthesia. The anaesthetic depth should be assessed by observation of movement responses, and consequently a minimum of muscle relaxants used. Because the anaesthetic depth can be controlled by determination of endtidal drug concentration, volatile inhaled anaesthesia may be associated with a lower frequency of awareness than other anaesthetic regimens.

Remifentanil: a new opioid

Remifentanil appears to have pharmacodynamic properties similar to other potent mu opioid agonists. It does, however, have unique pharmacokinetic properties, with a rapid onset and rapid offset of effect, irrespective of the duration of its administration. With this property, remifentanil appears to be a very titratable opioid that will make it suitable for administration for either very brief periods, in which analgesia is required, or over prolonged periods, without the concern for prolonged recovery.

Concentrations of desflurane and propofol that suppress response to command in humans

The anesthetic concentration just suppressing appropriate response to command (minimum alveolar anesthetic concentration awake [MAC-awake] for volatile anesthetics or plasma concentration to prevent a response in 50% of patients [Cp50]-awake for intravenous anesthetics) provides three important measures. First, along with pharmacokinetics, the ratio of the awakening concentration to the anesthetizing concentration (MAC-awake/MAC or Cp50-awake/Cp50) determines time to awakening. Second, a correlation between MAC-awake and the anesthetic concentration sufficient to prevent learning suggests MAC-awake provides a surrogate measure of amnestic potency. Third, population values for MAC-awake provide evidence for or against commonality in anesthetic mechanisms. We studied 22 male volunteers twice to determine both MAC-awake for desflurane (2.60% +/- 0.46%) and Cp50-awake for propofol (2.69 +/- 0.56 microgram/mL). Awakening with desflurane occurs at a concentration closer to its anesthetizing concentration (36% of MAC) than propofol (18% of Cp50); that is, 1) desflurane requires less of a decrement in anesthetic concentration at the effect site for arousal; and 2) if MAC-awake (Cp50-awake) values reflect the concentrations providing amnesia, propofol is a more potent amnestic. Of interest, the dose response curves of desflurane and propofol were equivalently steep, a finding consistent with a common mechanism of action. In contrast, sensitivity of each volunteer to desflurane did not correlate with sensitivity to propofol (r2 < 0.01, P = 0.98) arguing against a common mechanism.

Pharmacokinetic-pharmacodynamic relationships for opioids in balanced anaesthesia

The pure mu-receptor opioid agonists fentanyl, sufentanil and alfentanil are commonly used to provide the specific anti-nociceptive component of a balanced anaesthesia technique. Trefentanil and remifentanil are new opioids with a very short duration of action. Remifentanil has an ester structure and is very rapidly metabolised by blood and tissue esterases. Different perioperative stimuli require different plasma concentrations to suppress responses of the patient. The ability of the anaesthesiologist to select a precise dosage scheme for the individual patient is impeded by the large interindividual pharmacokinetic and pharmacodynamic variability. In addition, the combination of opioids and other drugs used to produce the desired components of balanced anaesthesia may exert additive, synergistic or antagonistic effects. Knowledge of factors influencing the pharmacokinetics and pharmacodynamics is still fragmentary and often controversial. Consequently, the opioid dose needs to be adjusted according to the responses of the patient during surgery to ensure adequate anaesthesia and rapid recovery. The duration of action is not predicted by the elimination half-life alone. The decline in effect-site concentration is dependent on the complex entity of infusion duration, and pharmacokinetic and pharmacodynamic parameters. Computer simulations of infusions of varying duration have been extremely useful when selecting an opioid for a specific clinical scenario on a rational basis. Traditionally, opioids are still administered by intermittent bolus injections. A disadvantage of this method of administration is that plasma concentrations fluctuate above and below the level required for adequate anaesthesia. Computer-assisted infusion pumps make it possible to target a particular drug concentration in plasma and to maintain or change this concentration as needed. This technique provides more stable anaesthesia and a more rapid recovery of the patient.