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Canadian Journal of Anesthesia 48:A3 (2001)
© Canadian Anesthesiologists' Society, 2001

Abstracts - Monday June 11 8:30 a.m. - 10:00 a.m.

EC80-EC95 OF BUPIV AND ROPIV PLUS FENT FOR LABOUR EPIDURAL ANALGESIA

Rhonda M. Zwack , MD, David C. Campbell , MSc MD, Terrance W. Breen , MD and Ray W. Yip , MD

Department of Anesthesiology, Royal University Hospital, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W8

INTRODUCTION

20 ml of either 0.08% ropivacaine (R) or 0.08% bupivacaine (B) combined with 2 mg/ml fentanyl (F) effectively initiates labour epidural analgesia (LEA) in $95% of parturients (1). The concentrations of 20 ml of either B or R (without F) necessary to initiate effective LEA in "50%" of parturients (EC50 or MLAC) are significantly different, suggesting a difference in potency (2,3). Consequently, the validity of studies comparing equimolar solutions of B and R for LEA is now questioned. However, clinically relevant concentrations (i.e. EC80 - EC95) of R and B combined with F have yet to be determined. The EC50 of 20 ml of B combined with 2 mg/ml F is reportedly 0.05% for initiation of LEA (4). This prospective, randomized, double-blinded study was designed to determine the concentrations of B and R, combined with 2 mg/ml F, that represent their respective EC80-EC95 for initiation of LEA.

METHODS

Following IRB approval and informed consent, labouring women, <= 5 cm dilated, were randomized to receive 20 ml of study solution. Each study solution contained 2 mg/ml F combined with 0.08%, 0.07%, or 0.06% B or R.

Analgesic Outcome was defined as follows:

Analgesic Success:VASP <10/100 at 20 min
Analgesic Failure:VASP >10/100 at 20 min
Unable to Assess:VASP >10/100 at 20 min + Perineal Pressure + Cervix >7 cm
Technical Failure:VASP >10/100 at 20 min +/- Unilat., Patchy or No Block (2% Lido)

RESULTS

98 women have been enrolled. 45 received 0.08%, 4 (1 BF; 3 RF) Unable to Assess and 1 BF Technical Failure with all remaining BF (20/20) and RF (20/20) Analgesic Success (i.e. 0.08% BF = EC100; 0.08% RF = EC100). 41 received 0.07%, 1 BF Unable to Assess with 90% BF (18/20) and 90% RF (18/20) Analgesic Success (i.e. 0.07% BF = EC90; 0.07% RF = EC90). 12 have received 0.06% to date.

DISCUSSION

This ongoing RCT indicates that, at clinically relevant concentrations, BF and RF are equipotent for initiation of LEA.

REFERENCES

1 Anesth Analg 90:1384-9, 2000[Abstract/Free Full Text]

2 BJA 82:371-3, 1999

3 Anesthesiology 90:944-50, 1999[Medline]

4 BJA 78:493-7, 1997





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