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Intrathecal Hydromorphone for Post Cesarean Delivery Analgesia – Impact of Lowering the Dose on the Amount of Rescue Pain Medication
Abstract Number: T-50
Abstract Type: Original Research
Cesarean section (C/S) is usually performed under spinal using bupivacaine and intrathecal morphine (ITM). With the critical shortage of ITM in 2012, we empirically used 200-mcg intrathecal hydromorphone (ITH) and undertook a dose finding study. We found the minimum concentration of ITH to be 60-mcg and the ED 80 to be 130-mcg (1). This study assesses the effect this lower dose has had on post-operative medication usage.
After IRB approval, a chart review was conducted to identify 120 matched patients who had primary or repeat C/S under spinal, 60 using 200-mcg ITH and 60 using 130-mcg ITH. The amount of post-operative oxycodone/acetaminophen (5-mg/325-mg), oxycodone, and morphine (via PCA) were converted to oral morphine mg equivalents and totaled for each patient's hospital stay (2). Ibuprofen and acetaminophen amounts were also tallied.
54 subjects per group were necessary for 80% power to detect a 15% difference in morphine mg equivalents. Statistical significance was determined using the Student t-test (age, LOS, BMI), Mann Whitney U (number C/S, MSO4 mg equivalents), Pearson Chi-Square (race).
We found no difference in post-operative opioid use (p=0.877), age, length of stay, or number of C/S per patient; BMI was higher in the 130-mcg group.
In light of our prior study's results (minimal dose, 60-mcg ITH, ED 80, 130-mcg), we have switched from 200-mcg ITH to 130-mcg. This study's goal was to validate the lower dose by comparing post-operative pain medication use before and after the change. We found no difference in opioid consumption and little variability in ibuprofen and acetaminophen use. This implies that a 130-mcg dose is clinically as effective as 200-mcg. Other literature suggests 130-mcg ITH may be too high and an additional dose finding study may be indicated (3, 4).
As with any chart review, we could have introduced selection bias; our sample may not be representative of, or generalizable to, our whole population. We hoped to lessen this using a relatively large sample size and group matching of patients. We acknowledge the difference in BMI, however long acting IT opioids are not routinely dosed based on patient weight.
(1) ASA Abstract A-3109,2015
(2) Calculating Total Daily Dose of Opioids for Safer Usage. http://www.ced.gov/drugoverdose/pdf/calculating_total_daily_dose-a.pdf
(3) Beatty NC, et al. JCA 2013;25:379-383
(4) Sviggum HP, et al. A&A 2016;123:690-7