Determination of an Effective Dose of Intrathecal Morphine for Pain Relief After Cesarean Delivery

Randomized study of postcesarean analgesia with intrathecal morphine alone or combined with clonidine

STUDY OBJECTIVE

To investigate the efficacy of the combination of intrathecal morphine with clonidine in comparison with 2 doses of intrathecal morphine alone for postcesarean analgesia.

DESIGN

Prospective, double-blinded, randomized clinical trial.

SETTING

Maternity ward of Hospital Santa Cruz, Curitiba, Paraná, Brazil (operating room and ward).

PATIENTS

The study included 195 American Society of Anesthesiologist I to III singleton parturients undergoing elective cesarean section.

INTERVENTIONS

The patients were randomized into 3 groups (M50, M100, and M/C). Patients were anesthetized intrathecally with 12 mg of 0.5% hyperbaric bupivacaine and 50 μg or 100 μg morphine (groups M50 and M100, respectively) or 50 μg morphine and 75 μg clonidine (group M/C).

MEASUREMENTS

The patients were subsequently assessed for pain levels and side effects at 9 to 11 hours and 22 to 24 hours after the injection.

MAIN RESULTS

There was no difference in the quality of pain relief among the groups. In all 3 groups, pain was more intense during the first assessment. Pruritus and nausea were more frequent in group M100, and dizziness was more frequent in group M/C; however, these results were statistically insignificant. The group receiving clonidine showed a significantly lower incidence of shivering compared with the other groups.

CONCLUSIONS

At these doses, there was no benefit of associating clonidine with morphine to improve postcesarean analgesia. Considering that higher doses of morphine were associated with more side effects, 50 μg of intrathecal morphine alone seems to be a better option for analgesia. The use of clonidine to reduce postoperative shivering must be balanced against the potential risks of hypotension, bradycardia, dizziness, and sedation.

Accuracy in obtaining 100 μg from 10 mg of morphine for spinal anesthesia

STUDY OBJECTIVE

Dilution is often required to obtain appropriate concentrations of intrathecal morphine for analgesia. We compared techniques of diluting by measuring the quantity of morphine actually obtained in the final solution.

DESIGN

This is an experimental study by 3 experienced anesthesiologists.

SETTING

The setting is at a university teaching hospital.

PATIENTS

There are no patients.

INTERVENTIONS

There are no interventions.

MEASUREMENTS

Five techniques for obtaining 100 μg from 10 mg/mL were compared: technique 1 (T1) = extraction up to 0.1 graduation on a 1-mL syringe, followed by simple dilution (SD). Technique 2 (T2) = As for T1 but syringe was shaken to mix solution. Technique 3 (T3): SD with 10-mL syringe. Technique 4 (T4): Double dilution with 10-mL syringe. Technique 5 (T5): Extraction up to the 0.1 graduation of a 1-mL syringe, then SD, then shake solution by hand. Three tests using high-performance liquid chromatography with ultraviolet were performed on each syringe prepared 3 consecutive times, namely, at the first (beginning, B), fifth (middle, M) and last (end, E) milliliter or 0.1 mL (depending on syringe type).

MAIN RESULTS

Average overall concentrations were 208 ±19, 199 ±24, 120 ±13, 136 ±9, and 119 ±16 μg/0.1 mL, T1-T5, respectively. By Kruskal-Wallis test, we classified the techniques according to the magnitude of the difference between the observed concentration of morphine and the desired (theoretical) concentration of 100 μg/0.1 mL. In ascending order, techniques ranked as follows: T5 (smallest difference), T3, T4, T2, and T1 (greatest difference) (P = .0001).

CONCLUSIONS

There is significant variability in the concentration of morphine actually contained in final solutions after dilution. Morphine presented in different premixed concentrations increases the risk of error. We advocate technique 5 as described above, whereas technique 1 should be prohibited.

Definitions of "respiratory depression" with intrathecal morphine postoperative analgesia: a review of the literature

PURPOSE

To review the postoperative intrathecal morphine (ITM) analgesia literature for their definitions of "respiratory depression" (RD).

SOURCE

Medline (1966 - June Week 5 2001) and reference lists were searched for original studies involving bolus-dose ITM for postoperative analgesia, which used "respiratory depression" or similar terms.

PRINCIPLE FINDINGS

The search identified 209 studies. These were included if ITM use was appropriate (bolus dose, postoperative analgesia) and the term "respiratory depression" was used, which left 96 studies remaining. Forty-four (46%) did not define "RD" despite using this term. A further 24 (25%) defined RD with respiratory rate (RR) alone. Only 28 (29%) defined RD with more than RR alone. There was no statistically significant association between the presence of a definition for RD with study design, study size or publication period. Also, no significant association existed between rigorousness of RD definitions and the above factors.

CONCLUSION

The term "respiratory depression" has no clear definition from a review of the literature on ITM use for postoperative analgesia. While defining RD with bradypnea is superior to having no definition, this is still inadequate. In future research, the consistent use of terms with specific meanings will facilitate understanding the true incidence of ITM's respiratory effects. If "respiratory depression" is used, then an explicit definition of its meaning should be provided. Future research must also address what is clinically significant respiratory impairment from intrathecal opioids, and how to optimally monitor for this. Further delineating their risks vs benefits will allow for more optimal dosing.

Intrathecal morphine for postpartum tubal ligation postoperative analgesia

Intrathecal morphine (ITM) provides effective postoperative cesarean delivery analgesia but has not been reported for postoperative postpartum tubal ligation (PPTL) analgesia. We designed this prospective, randomized, double-blinded study to determine the efficacy of 100 microg ITM for postoperative PPTL analgesia. Sixty-six women received spinal anesthesia with 60 mg (1.2 mL) of 5% hyperbaric lidocaine, 10 microg (0.2 mL) of fentanyl, and either 0.2 mL of 0.9% saline (normal saline; NS) or 100 microg (0.2 mL) of morphine (morphine sulfate, MS). Postoperative analgesia was limited to patient-controlled IV analgesia morphine. Six women (three NS and three MS) were excluded because of major protocol violations. Twenty-four-hour patient-controlled IV analgesia morphine use was (mean +/- SD) 39.6 +/- 19.6 mg in the NS group and 1.1 +/- 2.5 mg in the MS group (P < 0.0000001). Visual analog scale scores for crampy and incisional pain (rest and movement) were significantly higher in the NS group compared with the MS group at 4, 8, 12, and 24 h (P < 0.001). The adverse effect profile was similar between groups. Visual analog scale satisfaction scores (mean +/- SD) were 96.6 +/- 16.0 in the MS group and 84.2 +/- 23.6 in NS group (P < 0.05). The results of this study indicate that women experience significant postoperative pain after PPTL surgery, and this pain is effectively obviated by 100 microg ITM.

IMPLICATIONS

This investigation documents the extent of the significant postoperative pain experienced by women after routine postpartum tubal ligation surgery and demonstrates the efficacy of a small dose (100 microg) of intrathecal morphine to obviate this pain with minimal adverse effects.