Incidence Of Sinusoidal Fetal Heart Rate After Butorphanol Administration

INTRODUCTION: It is widely accepted that 75% of fetal heart rate tracings show sinusoidal patterns after butorphanol administration. We investigated whether this is true when sinusoidal patterns are defined using the 2008 National Institutes of Health guidelines. METHODS: Case–control study of women who delivered at Froedtert Hospital between June 2010 and December 2011. Inclusion criteria were maternal age older than 18 years, gestational age exceeding 24 weeks, and 60 minutes of interpretable fetal monitoring. Exclusion criteria were multiple gestations, medications that could potentially affect the monitoring strip, or known fetal anomalies. Case patients received 2 mg intravenous butorphanol over 5 minutes. Two faculty physicians reviewed each strip to determine whether it displayed a sinusoidal pattern. Differences of interpretation were resolved through discussion. Power analysis calculated an 80% power to detect 5% significance with 100 patients per group if the true probabilities of sinusoidal changes are 1% and 10%. One hundred fifteen control patients and 95 butorphanol patients were selected. RESULTS: None of the women in the control group, 0% (95% confidence interval [CI] 0.0–3.1%) and one of the butorphanol patients, 1% (95% CI 0.03–5.7%, P=.45) displayed sinusoidal patterns. The staff physicians initially interpreted five strips differently but reached consensus after discussion. The incidence of sinusoidal fetal heart rate after butorphanol administration was 1%. CONCLUSIONS: A sinusoidal pattern is no more likely after butorphanol administration. This contradicts previous data. If a sinusoidal pattern is identified in a mother using butorphanol for analgesia, rapid evaluation for fetal compromise must be performed.