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OBSTETRIC ANESTHESIA

Intrathecal Morphine for Postpartum Tubal Ligation Postoperative Analgesia

Department of Anesthesiology, Royal University Hospital, Saskatoon, Saskatchewan, Canada

Address correspondence and reprint requests to David C. Campbell, MD, MSc, FRCPC, Associate Professor, College of Medicine, University of Saskatchewan, Department of Anesthesiology, Royal University Hospital, 103 Hospital Dr., Saskatoon, Saskatchewan, Canada S7N 0W8. Address e-mail to campbelld{at}sdh.sk.ca

	Abstract

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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 µg ITM for postoperative PPTL analgesia. Sixty-six women received spinal anesthesia with 60 mg (1.2 mL) of 5% hyperbaric lidocaine, 10 µg (0.2 mL) of fentanyl, and either 0.2 mL of 0.9% saline (normal saline; NS) or 100 µg (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 µg 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 µg) of intrathecal morphine to obviate this pain with minimal adverse effects.

	Introduction

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Postpartum tubal ligation (PPTL) surgery is often performed with regional anesthesia in our institution. Performing PPTL surgery in the postpartum period offers several advantages, including surgical ease, reduced complications, and avoidance of hospital readmission (1,2). In dedicated obstetric hospitals or units, PPTL surgery can be performed without disruption of scheduled cases performed in the main operating room. Unfortunately, women undergoing PPTL surgery often experience considerable postoperative incisional and crampy abdominal pain. Although several investigations have attempted to reduce immediate (2- to 8-h) postoperative pain (3–5), none has evaluated women throughout the first 24 h. Recently, several reports have indicated that intrathecal morphine (ITM), 100 to 200 µg, provides adequate postoperative pain relief after cesarean delivery (6–10). In our institution, 200 µg of ITM is routinely administered to provide effective postoperative cesarean delivery analgesia. We performed an initial open-labeled, nonrandomized, pilot study in women undergoing PPTL surgery, by using 100 µg of ITM. Of note, the women who received the ITM reported effective postoperative analgesia and did not use the patient-controlled IV analgesia (PCIA) morphine provided. Therefore, this prospective, randomized, double-blinded study was designed to determine the efficacy of 100 µg ITM for postoperative analgesia after PPTL surgery, with the primary outcome being 24-h PCIA morphine consumption.

	Methods

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After IRB approval and obtaining informed, written consent, 66 ASA physical status I or II women scheduled to undergo spinal anesthesia (SA) for PPTL surgery within 72 h of an uncomplicated, vaginal, term, singleton delivery were enrolled. To facilitate the study, only women with surgery scheduled between 7:00 AM and 4:00 PM were enrolled. Exclusion criteria included not speaking English, history of opioid abuse, contraindication to oral naproxen, chronic pain syndromes, third- or fourth-degree perineal lacerations, an epidural catheter in situ immediately before proposed PPTL surgery, height <150 cm, obesity (postpartum body mass index >35), or previous major abdominal surgery. Once enrolled, women would be excluded either if local anesthetic skin infiltration was administered by the surgeon immediately before skin incision or if general anesthesia (GA) was required for prolonged surgical time.

Sixty minutes before surgery, per standard institutional protocol, all women received 500 mg of naproxen (Apotex Inc., Weston, Ontario, Canada) orally. No other form of premedication was permitted except for 30 mL of sodium citrate (0.3 M) upon arrival to the operating room. Before the initiation of SA, each woman received at least 20 mL/kg of an IV balanced salt solution. Women were then randomized, by using a computer-generated randomization table, to receive one of the two intrathecal study solutions, each consisting of 60 mg (1.2 mL) of 5% hyperbaric lidocaine (Astra Pharma, Mississauga, Ontario, Canada), 10 µg (0.2 mL) of fentanyl (Abbott Laboratories, Montreal, Quebec, Canada), and either 0.2 mL of 0.9% saline (normal saline, NS; n = 33) or 100 µg (0.2 mL) of 0.5 mg/mL preservative-free morphine sulfate (MS; n = 33) (Sabex Inc, Boucherville, Quebec, Canada). Each study solution consisted of a total volume of 1.6 mL and was prepared by an anesthesiologist or research assistant not involved in the study.

SA was performed in the sitting position at either the L3-4 or L4-5 interspace at the discretion of the blinded anesthesiologist, by using either a 25- or 27-gauge atraumatic Whitacre (Becton-Dickinson, Rutherford, NJ) spinal needle. After the identification of clear, free-flowing cerebrospinal fluid, the study solution was injected into the subarachnoid space. Aspiration of cerebrospinal fluid was required at the completion of the injection of the study solution. Each woman received one of the two study solutions in a double-blinded fashion. Immediately after the injection of the study solution, the woman was placed in the supine position in preparation for surgery.

Noninvasive blood pressure, heart rate, and respiratory rate were determined every 3 min, and oxygen saturation was continuously monitored. Hypotension, defined as a 20% decrease in systolic blood pressure from the preoperative level, was treated with incremental doses of IV ephedrine (5–10 mg) and a bolus of a balanced salt solution. The most cephalad level of sensory loss to ice in the midclavicular line was recorded immediately before the surgical incision. Supplementary intraoperative analgesia was limited to IV fentanyl and was administered by a blinded anesthesiologist as required. Intraoperative anxiolytics were not permitted.

Each participant was assessed with a 100-mm visual analog scale pain (VASP) score for both incisional and crampy pain by an investigator blinded to the study solution. The 100-mm VASP was labeled at either end only with "No Pain" at one end and "Worst Imaginable Pain" at the other. VASP scores for crampy pain were assessed by a blinded investigator immediately before the administration of the study solution. During surgery, the efficacy of anesthesia was assessed with VASP scores at the time of surgical incision, as well as during manipulation of each fallopian tube. After surgery, both incisional and crampy VASP scores were assessed by a blinded investigator upon arrival to the recovery room and subsequently 4, 8, 12, and 24 h after SA. Incisional pain was assessed with the woman in bed at rest (supine) and with movement (sitting). During each assessment, oxygen saturation, respiratory rate, nausea, vomiting, pruritus, and ability to void spontaneously were evaluated.

Postoperative analgesia was strictly controlled and limited to IV morphine delivered by PCIA for 24 h after SA. All women received the identical PCIA morphine protocol of a 2-mg dose with a lockout period of 6 min and no 4-h limit, which was initiated upon arrival in the recovery room. No other forms of analgesics, anxiolytics, or hypnotics were permitted during the 24-h study period. If necessary, IV diphenhydramine (25–50 mg) and IV dimenhydrinate (25–50 mg) were administered at the discretion of the blinded postpartum nurse to treat pruritus and nausea/vomiting, respectively.

Times of arrival in the postanesthesia recovery room, initial ambulation and discharge home were recorded. During the final assessment at 24 h, women were assessed regarding satisfaction, by using a 100-mm VAS. Discontinuation of breast-feeding during the first 24 h after surgery was also recorded. Each participant was contacted daily for 5 days for evidence of a postdural puncture headache or transient radicular irritation (TRI).

Data were analyzed with the unpaired t-test for continuous data (demographics and times) and ² and Fisher’s exact probability test for nominal data (breast-feeding, Filschie clips, and postoperative adverse effects). Dermatomal levels were reported as median and range and analyzed with Wilcoxon’s ranked sum test. A P < 0.05 was considered significant except where repeated sampling of interval data was undertaken (VASP scores and cumulative PCIA morphine); in these cases, Bonferroni’s correction was applied.

	Results

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Six women were excluded because of major protocol violations. These were local anesthetic infiltration before skin incision (one NS and one MS), GA because of prolonged difficult surgery (one NS), and discontinuation of PCIA morphine before the completion of the study (one NS and two MS). In the remaining 60 women, NS (n = 30) and MS (n = 30), there were no statistical differences as to demographic data, gestational age at delivery, parity, preoperative VASP scores for crampy abdominal pain, birth weight, and breast-feeding before surgery (Table 1). There were also no differences in the time from delivery to SA, duration of PPTL surgery, the number of women receiving Filshie clips, and time from SA to arrival in the postoperative recovery room (Table 1). Time to first ambulation, however, was slightly delayed in the MS group (248 vs 328 min, P < 0.03).

All 60 women reported VASP scores for spasmodic (crampy) and incisional pain in the recovery room as 0. After surgery, VASP scores for crampy (Fig. 1) and incisional pain, at rest (Fig. 2) and with movement (Fig. 3), were significantly higher in the NS group compared with the MS group at 4, 8, 12, and 24 h (P < 0.001). In the NS group, VASP scores for crampy and incisional pain with movement were significantly higher than incisional pain at rest at 4, 8, 12, and 24 h (P < 0.02). Mean time to the first dose of PCIA morphine was 238 min in the NS group, compared with 720 min in the MS group (P < 0.03). Cumulative PCIA morphine use (Fig. 4) was significantly more in the NS group compared with the MS group at 4, 8, 12, and 24 h (P < 0.0001). At 24 h, cumulative PCIA morphine consumption (mean ± SD) was 1.1 ± 2.5 mg in the MS group, compared with 39.6 ± 19.6 mg in the NS group (P < 0.0000001).

View larger version (18K): [in this window] [in a new window]   Figure 1. Crampy abdominal pain. Visual analog scale pain (VASP) scores for crampy abdominal pain are shown on the y axis and time (h) after spinal anesthesia (SA) on the x axis. Initial represents VASP scores immediately before the induction of SA. PAR represents the VASP scores while in the postanesthesia recovery room. NS = normal (0.9%) saline; MS = morphine sulfate. Data are expressed as mean± SD. *P < 0.001 compared with MS.

View larger version (17K): [in this window] [in a new window]   Figure 2. Incisional pain at rest. Visual analog scale pain (VASP) scores for incisional pain at rest are shown on the y axis and time (h) after spinal anesthesia on the x axis. PAR represents the VASP scores while in the postanesthesia recovery room. NS = normal (0.9%) saline; MS = morphine sulfate. Data are expressed as mean ± SD. *P < 0.001 compared with MS.

View larger version (16K): [in this window] [in a new window]   Figure 3. Incisional pain with movement. Visual analog scale pain (VASP) scores for incisional pain with movement are shown on the y axis and time (h) after spinal anesthesia on the x axis. PAR represents the VASP scores while in the postanesthesia recovery room. NS = normal (0.9%) saline; MS = morphine sulfate. Data are expressed as mean ± SD. *P < 0.001 compared with MS.

View larger version (19K): [in this window] [in a new window]   Figure 4. Cumulative patient-controlled IV analgesia (PCIA) morphine use. Cumulative PCIA morphine use (mg) is shown on the y axis and time (h) after spinal anesthesia on the x axis. PAR represents the VASP scores while in the postanesthesia recovery room. NS = normal (0.9%) saline; MS = morphine sulfate. Data are expressed as mean ± SD. *P < 0.0001 compared with MS.

	Discussion

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Assessment of postoperative analgesia after PPTL surgery has been reported as a secondary outcome in the majority of published investigations, most of which have been primarily concerned with the efficacy of intraoperative anesthesia (3–5). These investigations have reported that the majority of women require some form of opioid analgesics within two to four hours after surgery. Specifically, Norris et al. (4) reported that the mean time to a patient’s request for additional postoperative analgesia was less than eight hours when intrathecal meperidine (70 mg) was used. Malinow et al. (5) reported that the majority of women receiving intrathecal lidocaine (70 mg) combined with fentanyl (10 µg) and epinephrine (200 µg) requested additional analgesia by five hours. It is important to note that neither study controlled the type, timing, or amount of postoperative analgesia administered. Consequently, direct comparisons with this investigation are not possible. In this study, postoperative analgesia was strictly controlled and self-titrated by the patient-determined method of PCIA. The results of this investigation indicate that 100 µg of ITM produced effective postoperative analgesia with mean VASP pain scores <5 of 100 for the entire 24-hour study period. In addition, 70% (21 of 30) of women receiving ITM did not use any PCIA morphine during the entire 24-hour study period.

Naproxen was previously shown to provide preemptive analgesia in women undergoing laparoscopic tubal ligation (11). The American Academy of Pediatrics considers naproxen to be safe during breast-feeding (12). Because both study groups received preoperative naproxen, it is not possible to determine the effect of naproxen alone (if any) on postoperative analgesia. Perhaps the profound postoperative analgesia observed in the MS group was, in part, caused by the preemptive analgesic effect of naproxen. However, it is unlikely that naproxen alone had a significant preemptive analgesic effect, because women in the NS group experienced significant postoperative pain and required PCIA morphine.

In this study, SA was achieved with intrathecal hyperbaric 5% lidocaine (60 mg) and fentanyl (10 µg). In an evaluation of 70 mg of hyperbaric 5% lidocaine alone, Norris et al. (4) reported effective intraoperative anesthesia in only 90% of women, with 10% (1 of 10) requiring GA for inadequate SA. The authors, however, did not describe the reason for anesthetic failure (i.e., prolonged surgery, low block, ineffective anesthesia with fallopian tube manipulation). In contrast, in this investigation, only 1 (1.5%) evaluable woman of the 66 enrolled required GA, because of a prolonged difficult surgery. Profound anesthesia (intraoperative VASP = 0 of 100) was observed in the remaining 98% (65 of 66) women enrolled in this study. The one exception required only one dose of 50 µg of IV fentanyl. The use of local anesthesia combined with intraperitoneal lidocaine was reported to produce adequate intraoperative anesthesia for PPTL in a group of women from Thailand (13). Unfortunately, the authors found that many women also required intraoperative IV ketamine and fentanyl to produce intraoperative mean VASP scores of approximately 10 of 100. Of note, a recent ASA Task Force report questioned the adequacy of intraoperative anesthesia with local anesthesia for PPTL surgery (1).

One of the secondary outcomes of this study was to determine the adequacy of intraoperative anesthesia by evaluating VASP scores at specific critical times of painful surgical stimuli. At these predetermined times (i.e., incision, manipulation of each fallopian tube, and skin closure), 98% (59 of 60) of women reported intraoperative VASP scores of 0 of 100. The addition of 10 µg of fentanyl to intrathecal lidocaine may have produced the profound intraoperative anesthesia observed; however, the study design did not permit such a determination, and, therefore, further evaluation is required.

No woman in either group experienced either respiratory depression (<8 breaths/min) or oxygen saturation <95% during the 24-hour study period. The incidence of nausea, although more in the NS group, did not achieve statistical significance between groups, probably because of an inadequate power to adequately evaluate this secondary outcome. Of importance, only 10% (95% confidence interval [CI], 0%–20%) of women in the MS group reported postoperative nausea, with 7% (95% CI, 0%–14%) requiring treatment. Although 77% (95% CI, 63%–91%) of women in the MS group reported pruritus, only 10% (95% CI, 0%–20%) required treatment. These results concur with an investigation comparing similar small doses of ITM (0.025–0.1 mg) with PCIA morphine in obstetric patients. This investigation reported no difference in the incidence of nausea, vomiting, pruritus, or treatment for pruritus (8).

None of the 66 women enrolled (95% CI, 0%–4.5%) complained of symptoms of TRI throughout the five-day postoperative assessment period. The 95% CI was calculated by using the "rule of three" (14,15). This is consistent with recent reports of no observed incidence of TRI after intrathecal hyperbaric 5% lidocaine in the obstetric population (15,16).

Although a threefold difference in breast-feeding discontinuation in the first 24 hours after surgery was observed, 12% NS (95% CI, 1%–23%) vs 4% MS (95% CI, 0%–12%), this difference did not achieve statistical significance, suggesting that the power of the investigation was probably inadequate to detect differences in this secondary outcome. The effect, if any, of the effective postoperative analgesia on the ability of women to continue breast-feeding requires further evaluation.

An unexpected secondary outcome was the observation that women in the MS group had a significantly prolonged time to initial ambulation after surgery (Table 1). This was surprising considering that, in the NS group, incisional pain with movement was significantly more intense than incisional pain at rest at 4, 8, 12, and 24 hours after surgery. However, many women receiving MS reported that, for the first time since delivery, they were able to rest comfortably and chose not to ambulate. It is important to note that this outcome was simply determined by asking evaluable women to record when they actually ambulated for the first time of their own volition. It was, therefore, not a determination of the time to complete resolution of motor blockade. The clinical relevance of this statistically significant difference is unclear.

The observation of similar times to discharge home between groups was probably the result of the predetermined study protocol that required all women to remain in hospital for the entire 24-hour study period. Consequently, the possibility that the profound postoperative analgesia afforded by ITM might result in women being discharged home sooner cannot be evaluated.

In conclusion, the addition of 100 µg of morphine to intrathecal hyperbaric 5% lidocaine (60 mg) and fentanyl (10 µg) provides profound intraoperative anesthesia and postoperative analgesia for 24 hours after PPTL surgery.

	Acknowledgments

 
This investigation received no pharmaceutical financial support. Dr. Campbell received research funding for this investigation from the Clinical Teaching and Research Fund of the College of Medicine at the University of Saskatchewan as well as from the Research Equipment Fund of the Royal University Hospital Foundation at the Royal University Hospital in Saskatoon, Saskatchewan, Canada. Dr. Campbell was awarded protected research time to complete this investigation from the Department of Anesthesiology, College of Medicine at the University of Saskatchewan. Dr. Riben received funding from the College of Medicine at the University of Saskatchewan to complete the Bachelor of Science in Medicine program under the supervision of Dr. Campbell.

	Footnotes

 
Presented in part at the annual meeting of the Canadian Society of Anesthesiology in Toronto, Ontario, Canada, June 16, 1998.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999