Epidural fentanyl plus bupivacaine 0.125 per cent for labour: analgesic effects

Comparative efficacy of epidural clonidine versus epidural fentanyl for treating breakthrough pain during labor: a randomized double-blind clinical trial

BACKGROUND

Breakthrough pain during neuraxial labor analgesia is typically alleviated with additional administration of epidural local anesthetics, with or without adjuvants. Sometimes avoiding neuraxial opioids may be warranted and clonidine is an alternative. In a randomized double-blind trial we compared the efficacy of clonidine versus fentanyl, added to bupivacaine, for the management of breakthrough pain.

METHODS

Term parturients (n=98) receiving bupivacaine 0.0625% with fentanyl 2 μg/mL at 12 mL/h, a patient-administered bolus of 5 mL at lockout 6-10 min and a maximum of four boluses per hour, and experiencing breakthrough pain ≥5/10, were randomized to receive a 10 mL bolus containing 12.5 mg bupivacaine and either clonidine 100 μg or fentanyl 100 μg. The primary outcome was 'success' of study drug treatment, defined as a pain score reduction ≥4/10 within 15 min of administration. Maternal hemodynamics and fetal heart rate were documented for two hours after treatment.

RESULTS

There was no significant difference between groups in success rates (66.0% after clonidine (n=47) vs 74.5% after fentanyl (n=51), P=0.48) or in the incidence of hypotension (systolic blood pressure ≤80% of baseline or <90 mmHg) or sedation at 15 min, with 2/51 and 1/47 subjects in the fentanyl and clonidine groups, respectively, receiving phenylephrine.

CONCLUSION

Epidural clonidine 100 μg was not superior to fentanyl 100 μg for decreasing pain scores within 15 min of co-administration with bupivacaine 0.125% for intrapartum breakthrough pain. The analgesic efficacy and hemodynamic side effects did not significantly differ.

A double-blind study on analgesic effects of fentanyl combined with bupivacaine for extradural labor analgesia

Background:

The intermittent technique of labor extradural analgesia has been showing promising results over other techniques. This study was done to assess and compare the efficacy of two different doses of fentanyl mixed with low doses of bupivacaine in intermittent labor extradural analgesia.

Materials and Methods:

90 ASA grade I-II parturients in active labor with a cervical dilatation of 3–7 cm were randomly allocated to three different groups:

Group A: 10 ml bupivacaine 0.125% + fentanyl 10 μg (1 μg/ml)

Group B: 10 ml bupivacaine 0.125% + fentanyl 20 μg (2 μg/ml)

Group C: 10 ml bupivacaine 0.125% (the control group)

All patients were preloaded with 10-15 ml/kg Lactated Ringer's solution. Labor analgesia was maintained by intermittent boluses of the drug combination.

Results:

The mean time of the onset of analgesia was significantly lower (P<0.05) and the duration of analgesia was significantly higher (P<0.01) in Group B when compared with Groups A and C (P<0.001). Patient satisfaction was considerably better in Group B (P<0.01). However, in both groups, the progression of labor was found to be slightly more prolonged than Group C. The level of the sensory and motor block was comparable in both the groups and was at the T8–T10 level; it was comparable and the level of motor blockade (Bromage score = 0, 1) in each group was also not significant (P>0.05).

Conclusion:

The addition of fentanyl (2 μg/ml) to bupivacaine 0.125% decreases the time of the onset of analgesia and increases the duration of analgesia and level of maternal satisfaction during labor as compared to fentanyl (1 μg/ml).

0.2% ropivacaine with fentanyl in the management of labor analgesia: A case study of 30 parturients

BACKGROUND

Epidural infusion of 0.2% ropivacaine is recommended by the manufacturers for labor analgesia.

AIMS

The aim of this study is to evaluate the analgesic efficacy, degree of motor blockade, obstetric outcome in the form of incidence of normal vaginal, assisted vaginal and lower segment cesarean section.

SETTINGS AND DESIGN

Pilot study.

MATERIALS AND METHODS

In this pilot study, 30 nulliparous parturients in active labor had epidural analgesia established using 0.2% ropivacaine with 25 mcg fentanyl for initiation when cervical dilatation was 3-4 cm and then analgesia was maintained with 0.2% ropivacaine at 10 ml/h till the delivery of baby.

STATISTICAL ANALYSIS

It was done by Wilcoxon sign rank test and paired t-test as applicable.

RESULTS

There was a significant difference (P < 0.05) between prebolus, postbolus and postinfusion with respect to visual analog score. There was a significant difference (P > 0.05) between prebolus, postbolus, and postinfusion with respect to Bromage motor score, (Wilcoxon sign rank test). Six out of 30 paturients complained of tingling and heaviness in lower limbs after continuous infusion of 2-2.5 h.

CONCLUSION

We conclude that 0.2% ropivacaine (8 ml) with fentanyl 25 mcg is good for initiation of ambulatory labor analgesia. But for maintenance of labor analgesia lower concentration of ropivacaine may be preferred.

Onset of labor epidural analgesia with ropivacaine and a varying dose of fentanyl: a randomized controlled trial

BACKGROUND

This study was conducted to investigate the onset of labor epidural analgesia using 0.17% ropivacaine with a varying dose of fentanyl. We hypothesized that the onset of analgesia would be shortened in proportion to an increase in fentanyl dose.

METHODS

Women requesting labor epidural analgesia were enrolled in this randomized controlled clinical trial. Each woman was randomly assigned to receive fentanyl 0, 50, 75, or 100 μg with 0.17% ropivacaine 12 mL. The onset and duration of analgesia, the incidence of side effects and patient satisfaction were measured.

RESULTS

Data from 102 women were analyzed. The onset of analgesia (mean ± SD) was shortened with an increasing dose of fentanyl (14.3 ± 5.4, 14.2 ± 6.5, 12.1 ± 5.1, and 8.7 ± 3.8 min with fentanyl 0, 50, 75, or 100 μg, respectively, P=0.001). The duration of analgesia was prolonged with an increasing dose of fentanyl (87.4 ± 20.8, 112.3 ± 19.5, 140.8 ± 18.8, and 143.6 ± 18.6 min with fentanyl 0, 50, 75, or 100 μg, respectively, P<0.001). The incidence of pruritus increased with an increasing dose of fentanyl (P=0.027) but there were no differences for other maternal side effects. There was a significant difference in satisfaction score among groups (P=0.009).

CONCLUSION

The addition of increasing doses of fentanyl to 0.17% ropivacaine contributed to shortened onset as well as prolonged duration of labor epidural analgesia and improved patient satisfaction.

Epidural analgesia during labor and delivery: effects on the initiation and continuation of effective breastfeeding

This prospective cohort study examined the association between epidural analgesia during labor and delivery, infant neurobehavioral status, and the initiation and continuation of effective breastfeeding. Healthy, term infants delivered vaginally by mothers who received epidural analgesia (n = 52) or no analgesia (n = 63) during labor and delivery were assessed at 8 to 12 hours postpartum, followed by a telephone interview with the mothers at 4 weeks postpartum. There was no significant difference between the epidural analgesia and no-analgesia groups in breastfeeding effectiveness or infant neurobehavioral status at 8 to 12 hours or in the proportion of mothers continuing to breastfeed at 4 weeks. Therefore, epidural analgesia did not appear to inhibit effective breastfeeding. There was a positive correlation between infant neurobehavioral status and breastfeeding effectiveness (Spearman rho = 0.48, P = .01), suggesting that neurobehavioral assessment may prove beneficial in identifying infants at greater risk for breastfeeding difficulties.

Comparison of fentanyl with clonidine as adjuvants for epidural analgesia with 0.125% bupivacaine in the first stage of labor: a preliminary report

48 primiparae received epidural analgesia in labor with 10 ml of 0.125% bupivacaine with epinephrine 1:800 000, and then were divided in 4 equal groups (n = 12) to receive one of the following: 5 ml saline (B); 100 mug of fentanyl (BF); 150 microg of clonidine (BC); 75 microg of clonidine and 50 microg of fentanyl (BCF). All the patients had satisfactory analgesia. Onset was similar in the 4 groups but the duration of analgesia was significantly prolonged by the addition of either 100 microg of fentanyl or 150 microg of clonidine (respectively 89.8 min and 92.5 min vs 62.5 min) (P < 0.0001). The addition of both clonidine (75 microg) and fentanyl (50 microg) produced a considerably prolonged analgesia (177.5 min) (P < 0.0001). No episodes of bradycardia were observed. Hypotension, reversed by i.v. ephedrine, occurred in 2 patients of BCF group and in 1 patient of BF and BC groups. Only patients receiving fentanyl had pruritus. Both fentanyl and clonidine produced sedation, but both incidence and severity were greater with the mixture. No differences in neonatal outcome assessed by Apgar scores and NACS, were observed.

Effect of labor analgesia on breastfeeding success

BACKGROUND

The effect of labor analgesia on breastfeeding success is not well defined. Some authors have hypothesized that labor analgesia may affect lactation success. The purpose of this observational study was to determine if intrapartum analgesia influenced breastfeeding success at 6 weeks postpartum in a setting that strongly supported breastfeeding.

METHODS

Healthy women with uncomplicated term pregnancies who planned to breastfeed consented to a telephone interview. We recorded demographic data, labor induction status, delivery mode, and analgesic medications. At between 6 and 8 weeks postpartum, patients were asked to describe breastfeeding use, problems encountered, solutions derived, sources of support and information, and satisfaction. We created a logistic regression model using intrapartum analgesia information and controlling for demographic factors previously correlated with lactation success.

RESULTS

We enrolled 189 women, contacted 177 women postpartum, and obtained complete data on 171 women. Of these, 59 percent received epidural analgesia, 72 percent breastfed fully, and 20 percent breastfed partially (> 50% of infant nutrition) at 6 weeks postpartum. After controlling for demographics and labor outcome, we could not demonstrate a correlation between breastfeeding success at 6 to 8 weeks and labor analgesia.

CONCLUSIONS

In a hospital that strongly promotes breastfeeding, epidural labor analgesia with local anesthetics and opioids does not impede breastfeeding success. We recommend that hospitals that find decreased lactation success in parturients receiving epidural analgesia reexamine their postdelivery care policies.

Determination of the analgesic dose-response relationship for epidural fentanyl and sufentanil with bupivacaine 0.125% in laboring patients

STUDY OBJECTIVE

To establish the analgesic effective doses as defined as a visual analog pain scale (VAS) of at least 10 for 95% of parturients (ED95) receiving either epidural fentanyl or sufentanil with bupivacaine 0.125% for labor analgesia.

DESIGN

Double-blind, randomized controlled study.

SETTING

Two tertiary-care teaching hospitals.

PATIENTS

100 female patients, at full-term pregnancy, in active early labor (< 5 cm cervical dilation) and requesting obstetric anesthesia services for labor analgesia.

INTERVENTIONS

Patients were randomized and equally distributed to receive one of ten epidural dosing regimens of bupivacaine 0.125% alone or with either fentanyl 25, 50, 75, or 100 micrograms or sufentanil 5, 10, 15, 20, or 25 micrograms in a 10-ml bolus after a 3-ml test dose of bupivacaine 0.25%.

MEASUREMENTS AND MAIN RESULTS

VAS scores were obtained from each parturient using a 10-cm plastic VAS slide rule at times 0, 1, 5, 10, 15, 20, 25, and 30 minutes, and then again when the patient requested additional analgesia. Analgesic duration and demographic and obstetric data also were obtained. Using a log-probit dose-response analysis, analgesic success as defined as a VAS of at least 10 with each opioid dose was plotted and an ED95 value of 8 micrograms and 50 micrograms was established for sufentanil and fentanyl, respectively, in bupivacaine 0.125%. No statistical difference was detected for analgesic duration or incidence of side effects between analgesic groups.

CONCLUSIONS

Epidural analgesia with fentanyl and sufentanil in bupivacaine 0.125% behaves in a dose-response fashion allowing for the determination of equipotent dose of each.

Do labor medications affect breastfeeding?

Do labor medications affect breastfeeding? Few studies examine breastfeeding as an outcome of labor medication. While parents may be told that labor medications and epidurals have no effect on newborns, the literature reports significant neurobehavioral effects of these medications on the newborn and the mother-infant relationship.

Quantitative sensory examination of epidural anaesthesia and analgesia in man: combination of morphine and bupivacaine

The effect of epidural administration of a combination of low-dose morphine (2 mg) and bupivacaine (25 mg) on somatosensory and motor functions was examined in 13 healthy volunteers. The study design was a double-blind 4-way cross-over in which combined treatment was compared with either drug used alone or placebo. Every 2nd hour for 10 h effects on nociceptive and non-nociceptive somatosensory functions were quantified with 12 psychophysical measures. In addition knee extension strength, reaction time and skin temperature were examined. Epidural bupivacaine had hypoalgesic effect in all nociceptive tests, whereas epidural morphine only demonstrated hypoalgesic properties in nociceptive test with prolonged stimuli. In comparison with bupivacaine alone the combination treatment had a lesser peak effect but a more prolonged hypoalgesic action. In comparison with morphine alone the combination treatment induced a faster onset and demonstrated a modest increase in hypoalgesic effect in a subset of the test, even beyond the duration of bupivacaine when administered alone. Motor function was not attenuated by any of the treatments. Mechanisms of interaction between morphine and bupivacaine as well as their possible clinical implications are discussed.

Epidural infusions for nulliparous women in labour. A randomised double-blind comparison of fentanyl/bupivacaine and sufentanil/bupivacaine

Sixty nulliparous women received epidural infusions in labour of 0.0625% bupivacaine containing either 2.5 micrograms.ml-1 of fentanyl or 0.25 micrograms.ml-1 of sufentanil, each starting at 12 ml.h-1. The duration of each stage of labour did not differ significantly between the groups nor did the mode of delivery. The quality of analgesia in the first and second stages of labour and at delivery was similar in the two groups and there were no significant differences in the bupivacaine dose requirements. In the fentanyl group, 90% of women required one or no top-ups compared with 87% in the sufentanil group. Five women in the fentanyl group and four in the sufentanil group developed motor blockade, limited to movement of the hip only. Six women (20%) in each group reported pruritus. There were no significant differences in Apgar scores, umbilical cord blood pH levels or neurologic and adaptive capacity scores at 2 or 24 h. Satisfaction with first and second stage analgesia was high with no differences between the groups. There were no significant differences in the incidence of postnatal symptoms with 52% of women reporting perineal pain and 45% localised backache.

Effect of epidural opioids on gastric emptying in labour

The effect of epidural opioids on gastric emptying was studied in 36 women in labour. Women who had received one dose of epidural bupivacaine were randomised to receive 10 ml of bupivacaine 0.25% alone (n = 8) with fentanyl 50 microg (n = 8) or with diamorphine 2.5 mg (n = 8), or 10 ml of bupivacaine 0.125% alone (n = 4) or with fentanyl 100 microg (n = 4) or with diamorphine 5 mg (n = 4) when they first requested a top-up. Mean+/-SD fentanyl concentrations measured at delivery were, in maternal venous plasma (MV) 0.72+/-0.19 ng/ml and in umbilical venous plasma (UV) 0.75+/-0.3 ng/ml. The mean dose-delivery interval was 280 min (range 107-608 min) and there was a negative correlation between UV/MV and dose-delivery interval. Gastric emptying was assessed by measuring paracetamol absorption following an oral dose of 1.5 g given 30 minutes after the study top-up. Time to peak plasma paracetamol concentration was significantly delayed in the groups given fentanyl 50 and 100 microg and diamorphine 5 mg, compared to the groups given bupivacaine alone, and peak concentration was significantly reduced in the group given diamorphine 5 mg. It is concluded that epidural fentanyl 50 and 100 mg and epidural diamorphine 5 mg delay gastric emptying. The addition of 2.5 mg diamorphine has no significant effect.

Analgesic efficacy and safety of a caudal bupivacaine-fentanyl mixture in children

The analgesic efficacy and safety of a single caudal injection of a bupivacaine-fentanyl mixture was investigated in this prospective, controlled, triple-blinded study of 34 children, aged 1-11 yr and of ASA physical status I-II undergoing urological surgery. After induction of anaesthesia and before surgery, the children were randomly assigned to receive a caudal injection of 1.0 ml.kg-1 bupivacaine 0.125% with epinephrine 1:400,000 and either fentanyl 1.0 microgram.kg-1 in 1.0 ml of normal saline or 1.0 ml of normal saline. After completion of surgery, patients were assessed in the recovery room for six hours from the time of the caudal injection and for a further 18 hr on the ward. While in the recovery room arterial oxygen saturation and respiratory rate were monitored continuously and recorded hourly together with end-tidal carbon dioxide, pain and sedation scores. Other complications were also recorded. While on the ward, pain and sedation scores, respiratory rate and side effects were recorded every two hours. Postoperative analgesia was provided by intravenous morphine. Analgesic requirements were recorded for the 24-hr study period. Pain and sedation scores did not differ between groups. Respiratory depression or hypoxia did not occur. The incidences of other side effects did not differ. There were no differences in the numbers of patients requiring morphine within eight hours, the time to first morphine administration or the total morphine requirements. We conclude that a single caudal injection of a bupivacaine-fentanyl mixture with epinephrine administered prior to surgery, while safe, offers no advantage over an injection of bupivacaine 0.125% with epinephrine for paediatric urological surgery.

Epidural pethidine and bupivacaine in labour

A double-blind randomised study was performed to assess the value of the addition of pethidine 50 mg to the initial dose of bupivacaine given for epidural analgesia in labour. Forty-nine patients received either 1 ml of saline (n = 24), or 50 mg of pethidine (n = 25), added to 9 ml of 0.25% bupivacaine as an initial injection for intrapartum epidural analgesia. There was a significant increase in the mean duration of analgesia in the pethidine group. However, pethidine did not increase the speed of onset of analgesia, or improve the quality of analgesia.

The addition of pethidine to epidural bupivacaine in labour--effect of changing bupivacaine strength

The effects of varying the strength of bupivacaine used in epidurals for the relief of labour pain was examined. The trial randomly allocated sixty women in the first stage of labour to one of three groups. All women were of ASA status 1 or 2 and had uncomplicated pregnancies. Subjects in each group received pethidine 25 mg in 10 ml of either 0.125%, 0.1875%, or 0.25% bupivacaine. Pain scores for each patient were then assessed over the following thirty minutes. Duration of analgesia and subsequent dose requirements were examined. No difference in pain scores between groups at thirty minutes after injection of the test solutions was found. The 0.25% solution group did however have a more rapid onset of analgesia with the majority of patients in this group achieving their maximum effect between ten and twenty minutes after injection. Duration of analgesia was not prolonged by using the stronger solutions. This study suggests that when epidural pethidine 25 mg is added to local anaesthetic solutions of bupivacaine, adequate analgesia for the first stage of labour is achieved with the 0.125% bupivacaine solution. The use of stronger solutions of bupivacaine achieves no greater degree of analgesia nor longer duration of action, although the onset of analgesia may be faster with the stronger solutions. Further investigations are needed to determine if 25 mg of pethidine is the best choice of dose to use under these circumstances.

Does combined epidural lignocaine and fentanyl provide better anaesthesia for ESWL than lignocaine alone?

The efficacy of epidural fentanyl combined with lignocaine 1.5% with adrenaline 1:200,000 was studied in a randomised, double-blind, controlled trial of two hundred patients undergoing extracorporeal shock wave lithotripsy with or without ancillary procedures. The quality of anaesthesia was assessed using linear analogue pain scores, the patient's impression, and the rate of intra-operative intervention by the anaesthetist. Postoperative symptomatology was also recorded. The only significant difference lay postoperatively in that the fentanyl-ancillary procedure sub-group had less pain approximately one hour postoperatively (P = 0.01). In the context of this study and in the presence of an adequate autonomic and somatic local anaesthetic blockade, the addition of epidural fentanyl does not appear to confer any significant advantage other than to enhance postoperative analgesia.

Obstetric epidural analgesia with mixtures of bupivacaine, adrenaline and fentanyl

We performed a double-blind comparison of six solutions for epidural analgesia in 90 healthy Chinese women with uncomplicated pregnancies. Patients were randomly allocated to receive 10 ml bupivacaine 0.125% or 0.25% plain, bupivacaine 0.125% with adrenaline 1.25 micrograms/ml, bupivacaine 0.25% with adrenaline 2.5 micrograms/ml or the latter two solutions with added fentanyl 50 micrograms. Analgesia was unsatisfactory in 30% of the bupivacaine 0.125% groups without fentanyl. The addition of adrenaline, compared with bupivacaine 0.25% plain, gave faster onset and longer duration of analgesia (p less than 0.05) which was similar to that found in both fentanyl groups. There were no differences in method of delivery or neonatal Apgar scores among groups. The least concentrated mixture that gave the best analgesia was the combination of bupivacaine 0.125% with adrenaline 1.25 micrograms/ml and fentanyl 50 micrograms.

The addition of fentanyl to epidural bupivacaine in first stage labour

Epidural analgesia was studied in 100 healthy Chinese women with uncomplicated pregnancies in first stage labour. Patients were randomly allocated to receive 8 ml of one of the following five solutions: bupivacaine 0.125% with fentanyl 50 micrograms or fentanyl 100 micrograms, bupivacaine 0.25% plain, bupivacaine 0.25% with fentanyl 50 micrograms or fentanyl 100 micrograms. There was no difference in quality of analgesia among groups as measured by the reduction of visual analogue pain scores 20 minutes after the epidural dose. The duration of analgesia was similar among groups with the overall median duration being 105 minutes. There was no difference in method of delivery or neonatal Apgar scores. The least concentrated mixture providing good quality analgesia for the first stage of labour was the combination of bupivacaine 0.125% with fentanyl 50 micrograms.

Epidural opioids in obstetrics--a review

Epidural opioids have been used in obstetrics since 1980. Various opioids are reviewed in relation to their pharmacology, their efficacy in labour, during caesarean section and for postoperative analgesia, their side-effects and safety. In this patient population it appears safe to administer epidural opioids on the general ward provided that strict monitoring standards are maintained. Practical considerations of nursing management are discussed.

Spinal opioids in the management of obstetric pain

Spinal opioids have become increasingly popular agents for providing analgesia during labor, augmenting anesthesia during cesarean section, and providing pain relief after operative delivery. The development of spinal opioids in the management of obstetric pain is reviewed.

A comparison of lignocaine 2% with adrenaline 1:200,000 and lignocaine 2% with adrenaline 1:200,000 plus fentanyl as agents for caudal anaesthesia in children undergoing circumcision

This randomised double-blind study compares the onset, quality and duration of analgesia in two groups of children (n = 30), aged between two and twelve years undergoing circumcision. Under concurrent general anaesthesia, the children received caudal anaesthesia employing either lignocaine 2% with adrenaline 1:200,000 plus normal saline 0.01 ml/kg, or lignocaine 2% with adrenaline 1:200,000 plus fentanyl 1.0 microgram/kg. The results show no statistical or clinical difference in the onset, duration, quality of pain relief, or side-effects between the two solutions.

A double-blind comparison of epidural bupivacaine and bupivacaine-fentanyl for caesarean section

The effect of adding fentanyl 100 mcg to bupivacaine 0.5% plain to establish epidural anaesthesia for elective caesarean section was investigated in a randomised, double-blind study of sixty healthy women. The quality of intraoperative analgesia as assessed by both patients and anaesthetists was significantly improved with fentanyl. The onset and duration of sensory anaesthesia, degree and duration of motor block, and other characteristics of epidural anaesthesia were unaltered. No adverse maternal side-effects (except mild pruritus) were noted and neonatal outcome was unaffected. The pharmacokinetics of epidural fentanyl administration were investigated by plasma fentanyl assays from maternal and cord blood taken at delivery. Epidural bupivacaine-fentanyl combination is a valuable therapeutic approach to the conduct of epidural anaesthesia for caesarean section in healthy women and foetuses. Further neonatal evaluation of the premature or compromised foetus is suggested before the universal application of this technique.

Onset of action between bupivacaine 0.5% and bupivacaine 0.5% plus fentanyl 75 mcg

This study tested the hypothesis that the addition of fentanyl 75 mcg to bupivacaine 0.5% at the onset of epidural anesthesia for cesarean section reduces the onset time for T4 sensory blockade. The study was conducted in a randomized, double-blind fashion. The same observer performed sensory testing using pain to pinprick. Fourteen ASA I patients scheduled for elective cesarean section had epidural catheters placed. Group 1 (n = 7) received bupivacaine 0.5%, and group 2 (n = 7) received bupivacaine 0.5% plus fentanyl 75 mcg. Patients 5'0'' to 5'4'' in height received 15 ml, and patients 5'5'' to 5'9'' received 20 ml of bupivacaine. There were no adverse effects on the neonate or clinically important changes in maternal hemodynamics. The maternal age, height, weight, and bupivacaine dose did not differ between groups (p greater than 0.05). For group 1, the mean times for sensory loss at T7, T6, T5, and T4 were 13.1 +/- 3.8 minutes, 15.0 +/- 4.0 minutes, 16.9 +/- 4.3 minutes, and 19.3 +/- 4.9 minutes, respectively; for group 2, the mean times were 8.1 +/- 0.9 minutes, 9.9 +/- 1.1 minutes, 11.3 +/- 1.5 minutes, and 12.7 +/- 2.0 minutes, respectively. Two-factor analysis of variance between groups 1 and 2 showed a significant difference (p less than 0.0001), representing a 35% reduction of mean onset time. The coefficient of variation of the mean onset times for group 1 subjects was 26.6% +/- 1.7% and for group 2 subjects 12.7% +/- 2.2% (p less than 0.001), representing a 50% reduction in between-subject variation.(ABSTRACT TRUNCATED AT 250 WORDS)