Spinal Hydromorphone Versus Morphine for Post-Cesarean Delivery Analgesia

Spinal Hydromorphone Versus Morphine for Post-Cesarean Delivery Analgesia: A Non-Inferiority Trial

Morphine is usually used for pain relief after cesarean delivery. However, sometimes it is not available, the patient might be allergic to morphine or intolerant to its side effects. Hydromorphone, another drug from the same class, might be used alternatively, but we need to prove that it is not inferior to morphine.

Spinal or intrathecal (IT) morphine is the most commonly used opioid for post-cesarean delivery analgesia. Factors that contribute to its widespread use include a favorable pharmacokinetic profile with duration of action up to 24 hours, ease of administration (during spinal block for surgical anesthesia) and low cost. Most providers administer 100 to 200 mcg of IT morphine for cesarean delivery analgesia with excellent analgesic results. Nevertheless, subarachnoid use of morphine is not without adverse events. While dose-dependent respiratory depression is the most worrisome complication, other side effects such as pruritus, nausea, vomiting and urinary retention can be bothersome during early puerperium. Furthermore, shortages of preservative free morphine in the United States has led clinicians to seek a reasonable alternative.

For the last 20 years, spinal hydromorphone has been successfully used for chronic pain associated with neoplasms. Its use for post-cesarean analgesia has been successfully reported. However, data regarding its efficacy in the IT space for post-cesarean analgesia is scarce. In the past, doses of 40 to 100 mcg have been reported to provide adequate postoperative pain relief with minimal side effects. In a recent study, the Effective Dose in 90% of patients has been established for both Hydromorphone and Morphine to be 75 mcg and 150 mcg, respectively.

No prospective studies have been conducted to specifically establish non-inferiority of hydromorphone when compared to morphine for post- cesarean analgesia. In addition, while all opioids share the same side effect profile, the frequency of those events are unknown for IT hydromorphone.

The current proposal is a blinded randomized controlled trial of intrathecal hydromorphone versus morphine in term pregnant women undergoing elective cesarean deliveries under spinal anesthesia.

Inclusion Criteria:

• Age > 18 years; American Society of Anesthesiologist's Physical Status (ASA-PS) < 3; Term pregnancy (> 37 weeks gestational age); Elective cesarean delivery; Spinal Anesthesia;

Exclusion Criteria:

• Documented allergy or severe intolerance to opioids; Intra-operative conversion to a general anesthetic technique; Chronic pain syndrome with baseline pain levels >3 on a visual analogue scale (0-10 cm); History of opioid use during this pregnancy; Allergy or intolerance to NSAIDS or acetaminophen; Morbid obesity- Body Mass Index (BMI) >40.