Intrathecal morphine tied to high pruritus incidence in parturients
A high incidence of pruritus was found among parturients (ie, women about to give birth) following the administration of intrathecal morphine during spinal anaesthesia for Caesarean section (CS), according to a Singapore study.
More than half of the 124 women evaluated (57 percent) had moderate-to-severe pruritus (score 4–10) after receiving 100 μg of intrathecal morphine, with 4 as the worst mean score recorded. [Proceedings of Singapore Healthcare 2018;doi:10.1177/2010105818760340]
The most common locations of itch were the back, chest, abdomen, and face which affected 48, 46, 42, and 41 percent of parturients, respectively. Less affected sites were the upper and lower extremities and the neck (33, 25, and 29 percent, respectively).
Despite the high pruritus incidence, only seven patients (5.6 percent) required treatment, which contradicts a previous study that demonstrated a high need for pruritus treatment (64 percent) in a similar population. [Anaesthesia 1997;52:270-275] However, this could have been due to the higher intrathecal morphine dose used in the previous study (200 μg), noted the researchers.
Moreover, the researchers said the low treatment rate could be associated with the routine use of prophylactic ondansetron and dexamethasone for prevention of postoperative nausea and vomiting (PONV) at the hospital where the subjects delivered.
“[However,] the effect of ondansetron on the rates of pruritus is debatable as there have been conflicting results from previous studies,” they added. Several studies showed that treatment with ondasentron had no effect on pruritus prevention, while others demonstrated a reduced incidence of severe pruritus. [Int J Obstet Anesth 2014;23:222-226; Anesth Analg 2007;104:421-424; Anesth Analg 2009;109:174-182]
Compared with patients who had no/mild pruritus, those with moderate-to-severe pruritus had a significantly higher mean score for distress and bother from itching 24 hours after intrathecal morphine administration (2.5 vs 0.7; p<0.0001).
Only 14 patients reported nausea, vomiting, and dry-retching, six of whom reported nausea that interfered with daily activities. Only four cases of PONV were deemed clinically significant based on the PONV Intensity Scale. Rescue treatment rate was also low, with only seven patients requiring antiemetics.
Intrathecal morphine is usually added to hyperbaric bupivacaine in spinal anaesthesia for CS to support postoperative analgesia, said the researchers. However, it usually entails adverse events such as pruritus and PONV, which may lead to maternal distress and dissatisfaction that may eventually affect delivery, they added.
“This study allowed us to better understand and advise patients undergoing [CS] under spinal anaesthesia and improve their childbirth experience,” said the researchers.
The findings may also serve as a groundwork when evaluating the effectiveness of medications for the prevention and treatment of pruritus and PONV, and for determining risk factors for these conditions in the local obstetric population to establish preventive and therapeutic guidelines, they added.