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Original Articles – Regional

Intraabdominal local anaesthetics for postoperative pain relief following abdominal hysterectomy: a randomized, double-blind, dose-finding study

Perniola, Andreaa; Gupta, Anila,d; Crafoord, Kristinab; Darvish, Bijana; Magnuson, Andersc; Axelsson, Kjella

Author Information
European Journal of Anaesthesiology: May 2009 - Volume 26 - Issue 5 - p 421-429
doi: 10.1097/EJA.0b013e3283261b53

Abstract

Introduction

Abdominal hysterectomy with or without salpingo-oophorectomy is associated with moderate-to-severe postoperative pain [1]. Poor pain control in the postoperative period can lead to increased postoperative morbidities and poor quality of life [2,3]. Furthermore, an emerging clinical study suggests that acute pain may rapidly evolve into chronic pain if poorly treated [4]. A meta-analysis of the literature found that more than 30% of patients had chronic pain 1 year after abdominal hysterectomy [5]. Therefore, efficient postoperative pain management is imperative for the patient and is one of the new pain management standards recommended recently [6].

Local anaesthetics have been infiltrated subcutaneously, infused intraabdominally, as well as injected into the peritoneal cavity as a single dose at the end of the operation following abdominal hysterectomy with variable effects [1,7,8]. When injected as a single dose, analgesia is limited to approximately 2–4 h because of the short duration of action of local anaesthetics [1]. In one recent study, the authors used a catheter inserted intraabdominally and local anaesthetic or placebo infusion into the abdominal cavity for 24 h postoperatively and found a reduction in postoperative analgesic requirements by 40% during 4–24 h [9]. The dose of levobupivacaine used as a continuous infusion in that study was 12.5 mg h−1, which resulted in plasma concentration of local anaesthetics far below known toxic concentrations in humans [10]. It remains unclear whether increasing the dose of local anaesthetics would further reduce pain intensity or rescue analgesics postoperatively.

This study was performed with the primary aim of assessing whether increasing doses of levobupivacaine infused intraabdominally postoperatively would reduce analgesic requirements. The secondary aims were to assess pain intensity, the incidence of nausea and vomiting, expiratory muscle function, time to mobilization and home readiness, plasma concentration of local anaesthetics and health-related quality of life at 1 and 3 months after abdominal hysterectomy.

Methods

Following approval from the Institutional Review Board at the University Hospital, Orebro, Sweden, informed consent was obtained from 60 patients ASA I or II in the age group 40–65 years undergoing elective abdominal hysterectomy with or without salpingo-oophorectomy. Patients undergoing surgery for suspected gynaecological cancer were excluded, as were those on chronic analgesic medication and those with known allergy to local anaesthetics.

Randomization and blinding

The hospital pharmacy, which also randomized patients into three groups using computer-generated randomized numbers, prepared two syringes and one bag. The syringes contained 20 ml of the study drug, whereas the bag contained 500 ml of levobupivacaine, which was delivered at 10 ml h−1 in a dose of 7.5 mg h−1 (group L), 12.5 mg h−1 (group M) or 17.5 mg h−1 (group H) in a double-blind, randomized method as described in detail below. The blinding to patient group was maintained until all patients completed the study.

Anaesthesia and surgery

All patients were premedicated with diazepam (10 mg) orally 1 h before planned surgery. Paracetamol (1 g) was given orally every 6 h, starting with the first dose at the time of premedication. Following intravenous access, anaesthesia was induced with fentanyl (1–2 μg kg−1) intravenously and propofol (1–2 mg kg−1). Tracheal intubation was performed after muscle relaxation with rocuronium (0.5 mg kg−1), and anaesthesia was maintained with 1–3% sevoflurane and 33% oxygen in nitrous oxide. Mechanical ventilation was used in a low-flow system in order to maintain an end-tidal CO2 of 4.5–5.5 kPa. Monitoring included noninvasive blood pressure, pulse frequency, peripheral oxygen saturation, end-tidal gas monitoring, ECG and train-of-four stimulation. Sevoflurane concentration was adjusted to maintain mean arterial pressure and heart rate within 20% of the preinduction value. We did not use any monitoring devices for assessment of anaesthetic depth but relied upon clinical assessment. Intravenous fentanyl was given intermittently as an analgesic when required during the operation. At the end of surgery, muscle relaxation was reversed using glycopyrrolate and neostigmine. Hysterectomy was performed in a standardized way using either a lower-abdominal midline incision or a Pfannenstiel's incision depending on the choice of the operator and expected degree of surgical difficulty.

Catheter placement and postoperative pain management

Prior to closing the peritoneum, a multihole catheter (ON-Q Pain Relief System; I-Flow Corporation, Lake Forest, California, USA) was inserted percutaneously about 1 cm away from the edge of the incision, and the tip of the catheter was placed supravaginally. No attempt was made to fix the catheter intraperitoneally. The catheter was attached to an elastomeric infusion pump (ON-Q Pain Relief System). This infusion pump consists of a disposable 500 ml elastomeric reservoir that delivers a continuous infusion at a fixed rate of 10 ml h−1 through a catheter. A one-way valve prevents any backflow. Forty millilitres of the study drug (levobupivacaine 0.75 mg ml−1, 1.25 mg ml−1 or 1.75 mg ml−1) was injected; 20 ml subcutaneously along the incision prior to skin closure and 20 ml via the catheter into the abdominal cavity in groups L, M and H, respectively. An infusion of the study drug was then started via the intraabdominal catheter immediately after skin closure at 10 ml h−1 over 48 h in all groups according to the randomization procedure described earlier. During the first 4 h postoperatively, patients received intravenous ketobemidone (a narcotic analgesic equipotent with morphine) (1–2 mg) intermittently for pain relief by the nurses in the postanaesthesia care unit (PACU) in order that the numeric rating scale (NRS) (0, no pain; 10, worst imaginable pain) was 3 or less. Thereafter, and when the patient was fully awake, a patient-controlled analgesia pump with ketobemidone (1 mg bolus with 6 min lock-out time) was connected intravenously as rescue medication, and the patients were instructed in its use preoperatively. All patients were observed in the PACU for 4 h before being transferred to the general gynaecological ward.

Recording and measurements

For all measurements, the time at which the infusion of the study drug was started was considered to be time zero (t = 0). In addition to the routine postoperative protocols, the following measurements were recorded.

Pain intensity

Patients were first asked to enumerate the pain at the incision site, ‘deep’ (visceral) pain and pain on coughing at 1, 4, 12, 24 and 48 h, using the NRS. Mild pain was defined as an NRS 3 or less, whereas moderate and severe were defined as NRS 4–6 and NRS more than 6, respectively.

Rescue analgesic (ketobemidone) consumption

Rescue analgesic (ketobemidone) consumption was recorded during 0–4, 4–24 and 24–48 h.

Recovery parameters

The ability to sit and walk with and without support, gastrointestinal function (time to start drinking, eating and intestinal motility) and postoperative home readiness were recorded. Standardized home readiness criteria were used as described in an earlier study [11] (see Appendix 1).

Expiratory muscle function

Expiratory muscle function was measured before and 4, 24 and 48 h after the operation using maximum expiratory pressure (PEmax) (MicroMedical, Moreton-in-Marsh, Gloucestershire, UK) in a similar way to that described in a previous study [11] and with an attachment that provided a leakage of 0.3 l min−1 to minimize the effect of buccal muscles on the generated expiratory pressure [12]. PEmax was measured twice by asking the patient, who was in the semi-reclining position, to blow rapidly using full abdominal force after a maximal inspiration. The better of the two measurements was recorded.

Side effects

Nausea or vomiting (0–4, 4–24 and 24–48 h) or both, pruritus and all other complications were recorded.

Health-related quality of life

Health-related quality of life was measured using the short form (SF-36) questionnaire before and 1 and 3 months after the operation in all groups. The SF-36 is a validated health survey consisting of 36 questions that measure eight health concepts and has been translated and validated into the Swedish language [13,14]. The scores are calibrated so that a higher score indicates an improved level of function; for example, a higher score in body pain indicates a low level of body pain, whereas a higher score in social functioning indicates improved level of social functioning.

Surgical complications

A gynaecologist inspected the incision site and a nurse changed the dressing before home discharge. Staples were used for wound closure, which were removed after about 1 week by a district nurse. If there was any discharge from the wound, the patient was asked to contact the hospital for culture and sensitivity testing of the fluid. Blood was taken for analysis of white cell count and C-reactive proteins (CRPs) to rule out any evidence of systemic infection at 24 h. After 48 h, the catheter was removed, and the catheter tip was sent for bacterial culture.

Plasma levobupivacaine concentration

Blood (7 ml) was taken in heparinized tubes after 24, 48 and 52 h in all patients who agreed to participate in this part of the study. The blood was centrifuged in order to separate the plasma, which was frozen to −20°C. After completing the study, analysis of total and free levobupivacaine concentration was performed by liquid gas chromatography as described in detail in a previous study [9].

Statistics

The number of patients required for the study was calculated on the basis of total ketobemidone consumption over 24 h, which was found to be 30 ± 15 mg in a previous study [9]. We were interested in a reduction in ketobemidone consumption by 50% in group H compared with group L (from 30 to 15 mg) and by 30% (from 30 to 20 mg) in the intermediate group M. We used a one-way analysis of variance (ANOVA) and, assuming α = 0.05, we calculated that we would need 60 patients (20 in each group) in order to achieve a power of 80% (β = 0.2). For the analysis of ketobemidone consumption and recovery variables, a one-way ANOVA was used. The incidence of side effects and complications were analysed with the chi-squared test or Fischer's exact test as appropriate. Pain at the incision site, deep pain and pain on coughing were analysed using the Kruskal–Wallis test at 1, 4, 12, 24 and 48 h after the operation, and the dimensions in SF-36 were analysed in a similar way at 1 and 3 months after the operation. At each time point, we used the Mann–Whitney U test to compare the three study groups pairwise, corrected for multiple comparisons by the method described by Holm [15]. The sign test was used to test differences in the dimensions in SF-36 between preoperative scores and after 1 and 3 months. PEmax and total and free plasma concentration of levobupivacaine were analysed using the repeated measurement ANOVA, with study group as the between subject factor and postoperative time points (4, 24 and 48 h) as the within subject factor. We assumed an autoregressive correlation structure between time points and made Tukey's adjustment to correct for multiple comparisons. The computations were performed as a mixed model and implemented in Statistical Analysis Software, version 9.1 (SAS Institute Inc., Cary, North Carolina, USA). All other statistical analyses were done using SPSS for windows version 14 (SPSS Inc., Chicago, Illinois, USA). Statistical significance was considered for P values of less than 0.05.

Results

Of the 60 patients assigned into the study after randomization, one patient was subsequently excluded because of withdrawal of informed consent (group H), and one patient was excluded after 24 h because of reoperation for bleeding (group H). Thus, a total of 58 patients (20 in group L, 20 in group M and 18 in group H) successfully completed the study.

Patients' characteristics, duration of operation and anaesthesia and the type of surgery performed as well as the type of incision are shown in Table 1. No differences were found between the groups in the number of patients undergoing different types of surgery (Table 1). There was a statistically significant difference in the duration of surgery between group L and group H (P = 0.0012).

Table 1
Table 1:
Patients' and operation characteristics

The supplemental requirements of ketomebidone were similar at all time points between the groups: 28.0 ± 12.5, 30.1 ± 11.7 and 34.4 ± 18.0 mg during 0–24 h, respectively, in group L, group M and group H (Table 2). Four patients (two in group M, one in group L and one in group H) received 20 mg parecoxib each, two because of persistent nausea, which was thought to be opiate induced, and two because of a protocol violation. Patients in group L had a ‘lower’ consumption of ketobemidone than those in group H (28.0 ± 12.5 vs. 34.4 ± 18.0). This difference, however, did not reach statistical significance (P = 0.374). The difference between groups L and H was 6.4 mg [95% confidence interval (CI) −3.7 to 16.6]. Combining the results of all patients in the three groups who had a similar operative procedure (total hysterectomy ± salpingo-oopherectomy vs. subtotal hysterectomy ± salpingo-oopherectomy), ketobemidone consumption during 0–24 h was found to be 31 ± 20 and 29 ± 19 mg, respectively (P = 0.7). When pooling the results from all patients, there was no significant statistical difference in ketomebidone consumption in patients who had a lower midline abdominal incision (28.9 ± 11.8 mg) vs. Pfannenstiel (37.6 ± 20.2 mg).

Table 2
Table 2:
Analgesic consumption

The intensity of postoperative pain on the NRS is shown in Fig. 1a–c. Median pain scores were less than 5 in all groups, except during coughing when the scores were less than 8 in the early postoperative period. Median pain scores decreased with time so that, after 4 h, NRS was less than 3 on incision and deep pain and 5–6 on coughing in all groups. No differences were found between the groups in NRS pain score at any time point during the 48 h study period.

Fig. 1
Fig. 1

The incidence of postoperative nausea (PON) was more than 50% during 0–4 h and similar between the groups (Table 3). The incidence of PON was also similar between the groups during the period of 4–48 h. The incidence of postoperative vomiting was 0–10% during 0–24 h, with no differences between the groups. The number of patients who received antiemetics during 0–24 h was 16 (80%) in group L, eight (40%) in group M and 13 (68%) in group H (P = 0.027, group L vs. M). After 24 h, the number of patients given antiemetics was similar between the groups (10% in each group).

Table 3
Table 3:
Side effects and complications

The recovery times and time to home readiness are shown in Table 4. The times to sitting, standing, drinking, eating and return of gastrointestinal function were similar between the groups. The mean time to home readiness was 3.5–4.5 days with no significant differences between the groups.

Table 4
Table 4:
Postoperative functional recovery

Expiratory muscle function, measured as PEmax, decreased at 4 h compared with preoperative values and gradually recovered with time over 48 h (Fig. 2). However, no statistically significant differences were found between the groups.

Fig. 2
Fig. 2

No patient had any evidence of systemic infection (increase in CRP or white blood count or fever). Inspection of the surgical wound did not reveal redness of the wound in any patient. Furthermore, no positive cultures for bacterial growth were obtained from the catheter tip in any patient.

The results of the SF-36 questionnaire are shown in Table 5. No differences were seen between the groups in any of the factors in the health-related quality of life questionnaire after 1 or 3 months. However, significantly higher scores were seen at 3 months after the operation compared with preoperative values as well as after 1 month in most variables, including body pain, and in all three groups.

Table 5
Table 5:
Health-related quality of life (SF-36) sign test

Nine samples from group L, eight from group M and eight from group H at each time period were sent for analysis of plasma concentration. The total and free plasma concentration of levobupivacaine at 24, 48 and 52 h in the three groups are shown in Fig. 3a and b, respectively. A higher free concentration of local anaesthetics was seen with increasing dose of local anaesthetics (group H > group M > group L) (P < 0.01). Pairwise comparison after Tukey's adjustment showed statistically significant differences between groups L and H at 24 h (P = 0.022). A similar pattern was seen even with free concentration of local anaesthetics. There was no significant increase in total or free concentration of levobupivacaine at 24 h compared with 48 h. The median (range) total and free concentrations of levobupivacaine obtained after 48 h of infusion in group H were 1.055 (0.286–2.113) and 0.019 (0.006–0.038) μg ml−1, respectively. No clinical evidence of local anaesthetic toxicity was seen in any patient.

Fig. 3
Fig. 3

Discussion

We found no evidence of a dose-dependent effect when local anaesthetics were infused intraabdominally following abdominal hysterectomy, and both ketobemidone consumption and NRS during the 48 h observation period were similar between the groups. The recovery parameters, expiratory muscle strength, discharge times, side effects as well as health-related quality of life questionnaire showed no differences between the groups. The plasma concentration of local anaesthetics was lower than known toxic concentrations in humans, and no evidence of systemic toxicity of local anaesthetics was seen in any patient.

Postoperative pain and analgesic consumption

The injection of local anaesthetics peripherally for postoperative pain management is attractive because of its simplicity and low risk of side effects. However, certain factors have limited the use of local anaesthetics for postoperative pain management. These include the short effect duration when injected as a single dose, the absence of satisfactory methods to deliver these drugs, the risk of infection when using catheters placed peripherally as well as the uncertain efficacy of this method. Although local anaesthetics have been injected successfully via catheters along peripheral nerves, their injection and infusion into tissue planes has been somewhat controversial [16–20]. Specifically, the single-dose injection of local anaesthetics subcutaneously or intraperitoneally has provided only very limited analgesia of short duration [1,21] or none at all [17]. In one double-blind randomized study on patients undergoing abdominal hysterectomy, which was methodically identical to the present study, we demonstrated a reduction in rescue analgesic medication from 44.3 mg in the placebo group to 30.5 mg in patients receiving 12.5 mg h−1 levobupivacaine as an intraabdominal infusion [9], which was comparable to the results of the present study in which patients in the medium-dose group required 30.1 mg morphine. The absence of a dose-dependent effect of local anaesthetics in the present study could be due to several reasons. First, the slow and continuous infusion of local anaesthetics may not provide sufficient drug concentration locally intraabdominally at the pain sites to produce analgesia, and a larger dose given intermittently may result in higher local anaesthetic concentrations locally to provide improved analgesia. Second, it is possible that the local anaesthetic infused intraperitoneally is absorbed systemically, and the effects seen by us were due to its systemic absorption, which has been shown by several authors using intravenous local anaesthetic infusion [22,23]. Other explanations for the lack of differences between groups could include: the difference between the doses of local anaesthetics infused between the groups was too small, the abdominal wall rather than the peritoneum is the site of maximal pain following abdominal hysterectomy or that the power of the study was not adequate to detect small differences in analgesic consumption between the groups.

Recovery and discharge

No differences were found in the recovery parameters between the groups. PEmax has previously been shown to be a good and objective measure of pain relief following abdominal surgery [11]. Because forced expiration, as during coughing, is primarily achieved by the abdominal muscles, any factor that reduces muscle function would result in a low PEmax, for example abdominal pain. This was evident in the present study when PEmax decreased at 4 h (when pain was intense) and gradually recovered with time over 48 h. However, no differences were found between the groups in PEmax probably because pain intensity was similar. With improved pain relief, as after epidural analgesia, PEmax has been shown to be numerically higher [11].

We found a high incidence of PONV in the present study, which is not surprising as these patients are at high risk for PONV. However, this study was not powered to assess differences in PONV. Good pain relief and minimization of opiate consumption in the postoperative period as well as the absence of PONV are important requirements for quicker home readiness as these ensure earlier mobilization and, possibly, even earlier discharge. Home readiness was somewhat longer in our study than in another study [24], which could reflect on healthcare practices in different institutions and countries. This needs to be explored further.

Health-related quality of life

No differences were found between the groups in the health-related quality of life questionnaire (SF-36) after 1 or 3 months. However, there was a significant improvement in the experienced quality of life in most dimensions, including body pain and physical component score, after 3 months compared with both preoperative values and after 1 month. In our study, patients in all three groups experienced improved physical function score and reduction in body pain after 3 months compared with preoperative values. Several studies have shown that the SF-36 is sensitive in detecting residual effects of surgery and postoperative pain [25]. As surgery was standardized in the present study and postoperative pain was similar in all groups, the lack of differences in SF-36 between the groups may not be surprising.

Plasma concentration of levobupivacaine

The median total and free plasma concentration of levobupivacaine was found, in general, to be about 50% of that reported to produce mild central nervous system (CNS) symptoms in healthy volunteers [10]. There was a dose-dependent increase in plasma concentration of local anaesthetics, and a statistically significant increase was seen in the high-dose group compared with the low-dose group, which would confirm that the amount of local anaesthetics absorbed depends on the amount administered. In the high-dose group, three patients had a median total plasma concentration of levobupivacaine that was slightly higher than that known to produce mild CNS symptoms in humans [10]. Although no patient had any symptom of local anaesthetic toxicity, it is unlikely that increasing the dose of local anaesthetics via continuous infusion would reduce pain intensity or analgesic requirements as a plateau effect seems to be achieved already at the lower doses of local anaesthetics. Significantly, there was no increase in plasma concentration of local anaesthetics at 48 h compared with 24 h, suggesting a lack of accumulation of local anaesthetics.

Limitations of the study

One limitation of the present study is the absence of a blinded control group. This study was designed identically to a previous blinded and randomized study in which we included a control group and found a significant reduction in ketobemidone consumption during 0–24 h postoperatively [9], and, therefore, we did not feel that it was necessary to include a control group in the present study. Another limitation of this study could be the narrow range of doses of local anaesthetics studied by us. As doses higher than 17.5 mg h−1 have never previously been studied intraabdominally, we felt that the risks to patients may exceed any significant potential benefit by increasing the dose further. The resulting plasma concentration as well as the absence of any significant reduction in analgesic consumption or pain relief with higher doses would support our initial argument. A final limitation of this study could be that we expected a major reduction (50%) in rescue analgesic requirement between the high-dose and low-dose groups. Thus, a difference of less than 50% would either reduce the power of the study or require a higher number of patients to be recruited for statistical significance. The final results showed that ketobemidone consumption (the primary end-point) was 6.4 mg (95% CI, −3.7 to 16.6) (P > 0.05) higher in group L than in group H, which was opposite to our hypothesis. Thus, there was only a 2.5% chance that the rescue ketobemidone consumption in group H could be more than 3.7 mg compared with group L. Therefore, we believe that our results are valid, and increasing the size of the groups in order to find small differences would not only be futile but also ethically questionable.

In conclusion, no dose-dependent effect was found in this study, with low doses of levobupivacaine compared with higher doses resulting in similar analgesic consumption and pain intensity. Consequently, no differences were found between the groups in the time to recovery and discharge or in the health-related quality of life up to 3 months postoperatively. Median plasma concentrations of levobupivacaine were below known toxic concentrations in humans but increased in a dose-dependent manner with no accumulation over 24–48 h. Future studies should focus on the mode of intraabdominal administration of local anaesthetics, the site of catheter placement as well as the mechanism of local anaesthetic action when administered intraabdominally.

Acknowledgements

We would like to thank the personnel in the operating theatres as well as those in the postoperative and gynaecological wards for their constant attention and help during the various phases of this study. Special thanks to Jill Kjellberg for her help with the data collection and Ingegärd Wilhelmsson for help with patient recruitment.

References

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Appendix 1

Home readiness

The criteria for home readiness were:

  1. full mobilization without assistance,
  2. return of gastrointestinal function (eating/drinking/bowel movement) to normal,
  3. mild pain adequately controlled by oral analgesics,
  4. no PONV,
  5. no evidence of infection locally (redness, tenderness) or systemically (fever, rise in CRP or white blood cell),
  6. no other on-going complications (bleeding, respiratory problems, deep vein thrombosis, etc.).
25 Wu C, Naqibuddin M, Rowlingson AJ, et al. The effect of pain on health-related quality of life in the immediate postoperative period. Anesth Analg 2003; 97:1078–1085.
Keywords:

abdominal hysterectomy; local anaesthetics; opiates; postoperative

© 2009 European Society of Anaesthesiology