The Efficacy of Propofol in the Prevention on Intrathecal Morphine Induced Pruritus in Cesarean Section Patients

Abstract

The use of a subarachnoid (SAB) block for the patient undergoing cesarean section is the preferred anesthesia practice. The addition of narcotics to the local anesthetic provides a more profound block during the operation and continued analgesia for the patient for up to 24 hours. A disadvantage of this practice is a high incidence (25 - 100%) of pruritus, especially in the parturient who appears to be more vulnerable to this side effect. Current treatments with narcotic antagonists for pruritus are associated with a decreased level of analgesia for the patient. We hypothesize that propofol is an effective treatment for intrathecal opiate induced pruritus in the patient having a cesarean section. Spinal anesthesia with narcotic supplementation can provide post-operative analgesia for up to 24 hours. Pruritus is a common side effect of this technique. The prophylactic administration of propofol 20mg was shown to be effective in preventing pruritus in the general surgical population but this same dose has been shown to be ineffective in cesarean section patients. The purpose of this study was to investigate the efficacy of a 30mg prophylactic dose of propofol in preventing pruritus induced by the subarachnoid administration of morphine in the cesarean section patient. This was a randomized, prospective, double blind study. The study population consisted of 45 ASA I and II parturient patients between the ages of 18 and 40 undergoing elective cesarean section under spinal anesthesia using 0.75% bupivicaine with 0.2 mg morphine. Written, informed consent was obtained at the time of admission. Subjects were randomized by the pharmacy department into two groups. One group received the study drug of propofol 30mg over five minutes. The second group received an equal volume of intralipid (placebo) over five minutes. Patients were assessed on an hourly basis for the presence of pruritus and the need for treatment. The propofol group was estimated to have a 20% need of rescue therapy and the control group had an estimated 60% need for rescue therapy. A 50% difference was considered significant. An 80% power with 22 patients in each group to detect a difference of 1 standard deviation at alpha level 0.05. A p<0.05 will be considered significant. Forty-seven subjects were enrolled in the study with ages ranging from 18-40 years with a mean age of 28 years. The administration of propofol 30 mg over five minutes caused no significant change in heart rate, blood pressure, oxygen saturation, level of sedation or pruritus as compared to the placebo group. Postoperatively, no differences in sedation or pain level were found between groups. Chi-square analysis showed no significant difference between subjects who received rescue therapy (P=0.44). The mean time to rescue therapy was 3 hours. There were no significant differences in the time to onset or the severity of pruritus between groups. Although not statistically significant, the placebo group had a lower incidence of need for rescue therapy. For the patients who received rescue therapy in the propofol group, only 2 out of 11 patients had severe itching, constant scratching (level 4 severity of itch). This represents 18% with this itch level in the propofol group (Figure 1). Also in the propofol group, 9 out of 11 patients had moderate itching, occasional scratching (level 3 severity of itch). This represents 82% of patients at this level of itch (Figure 1). In the patients who received rescue therapy in the placebo group, 4 patients out of 8 demonstrated a level 4 severity of itch and 4 out of 8 patients with a level 3 severity of itch representing 50% of patients. A request for rescue therapy by the patient was considered to be the most reliable indicator of treatment failure. Pruritus is a very subjective experience, therefore it is difficult to measure objectively. Our method of directly questioning the patient each hour on their itch level may have influenced their response due to the power of suggestion. A larger dose of propofol may be required to treat pruritus in the parturient due to an increased volume of distribution and/or hormone changes involved in pregnancy. The obstetric population tends to be more vulnerable to the pruritic effects of opioids due to the effects of estrogens, an increased level of circulating beta-endorphins, and the greater cephalad spread of spinally administered drugs in this population.& In conclusion, our results suggest that prophylactic 30mg intravenous propofol is not successful in preventing intrathecal morphine induced pruritus in the parturient undergoing cesarean section. Clinically, the anesthesia provider should consider proven treatment modalities to reduce the pruritic side effect from intrathecal morphine.