Demand analgesia to assess pain relief from epidural opiates

Current Status and Future Directions of Pain-Related Outcome Measures for Post-Surgical Pain Trials

Background: Clinical trials remain vital in order to: A) develop new treatment interventions, and also, B) to guide optimal use of current interventions for the treatment and prevention of acute and chronic postsurgical pain. Measures of pain (e.g. intensity and relief) and opioid use have been validated for the settings of postsurgical pain and continue to effectively guide research in this field..

Methods: This narrative review considers needs for innovation in postsurgical pain trial outcomes assessment.

Results: Future improvements are needed and include: A) more widespread measurement of movement-evoked pain with validation of various procedure-relevant movemen-tevoked pain maneuvers; B) new validated analytical approaches to integrate early postoperative pain scores with opioid use; and, C) closer attention to the measurement of postoperative opioid use after hospital discharge. In addition to these traditional measures, consideration is being given to the use of new pain-relevant outcome domains that include: 1) other symptoms (e.g. nausea and vomiting), 2) recovery of physiological function (e.g. respiratory, gastrointestinal, genitourinary and musculoskeletal), 3) emotional function (e.g. depression, anxiety) and, 4) development of chronic postsurgical pain. Also, there is a need to develop pain-related domains and measures for evaluating both acute and chronic post-operative pain. Finally, evidence suggests that further needs for improvements in safety assessment and reporting in postsurgical pain trials is needed, e.g. by using an agreed upon, standardized collection of outcomes that will be reported as a minimum in all postsurgical pain trials.

Conclusions: These proposed advances in outcome measurement methodology are expected to improve the success by which postsurgical pain trials guide improvements in clinical care and patient outcomes.

Analysis of individual patient data from clinical trials: epidural morphine for postoperative pain

BACKGROUND

Individual patient information from clinical trials is infrequently available, but can provide insights for clinical trials and practice.

METHODS

We analysed individual patient information from five randomized trials (913 patients) of i.v. patient-controlled analgesia (IVPCA) plus epidural placebo, morphine sulphate (MS) 5 mg, or extended-release epidural morphine (EREM; DepoDur) at doses of 5-30 mg, to explore effects of a range of epidural morphine doses. Pain and opioid requirement on first and second postoperative days, dose-response, clinically relevant comparisons of IVPCA without epidural morphine, 5 mg MS, and 10 mg EREM, and relationship between patient rating and other measures were described.

RESULTS

There were three strong findings. Epidural morphine resulted in greater patient satisfaction, despite higher rates of adverse events. Those describing their analgesic medication as 'very good' or 'excellent' used IVPCA opioid less and had pain scores significantly below the global mean, whereas those describing their medication as 'poor' or 'fair' had pain scores significantly above the mean. Epidural morphine meant less need for postoperative IVPCA opioid than epidural placebo. The therapeutic gain with EREM was lower pain scores with less IVPCA opioid. Moderate or severe pruritus was more common with IVPCA plus epidural morphine, whatever the formulation, compared with IVPCA plus placebo.

CONCLUSIONS

Analysis of individual patient data from high-quality clinical trials provides important insights into characteristics of new agents not immediately apparent from original trials, and also informing clinical practice. Prophylactic epidural morphine provides a better patient experience than IVPCA alone.

Study of the prophylactic effect of droperidol, alizapride, propofol and promethazine on spinal morphine-induced pruritus

BACKGROUND

We have compared the use of alizapride, propofol, droperidol and promethazine for the prevention of spinal morphine-induced pruritus.

METHODS

Three hundred ASA I or II women undergoing Caesarean section under spinal anaesthesia, in which morphine 0.2 mg was added to a local anaesthetic, were assigned randomly to receive i.v., in the operating room, just after delivery of the baby, alizapride 100 mg, propofol 20 mg, droperidol 1.25 mg, promethazine 50 mg or saline 2 ml (control group). In the postoperative period, the women were assessed for pruritus (absent, mild, moderate or severe) or other untoward symptoms by blinded observers. We used 95% confidence limits (95% CI) for the cumulative incidence of moderate and severe pruritus to compare the groups, and the NNT and 95% CI to compare droperidol, propofol and alizapride as for their effectiveness in preventing pruritus. For other untoward effects, the chi(2)-test was used, results being considered significant when P<0.05.

RESULTS

The droperidol, propofol and alizapride groups had significantly lower incidences of pruritus compared with the control and promethazine groups, while the incidence of pruritus was similar among the patients assigned to the promethazine and control groups. As for the prevention of moderate and severe pruritus, droperidol had the lowest NNT (3.52; 95% CI: 3.37-3.67), followed by propofol (4.61; 95% CI: 4.45-4.77) and alizapride (5.43; 95% CI: 5.27-5.59). As for untoward effects, droperidol and promethazine increased the incidence of somnolence, which seemed more severe with promethazine. Otherwise, there were no differences between the groups.

CONCLUSION

Droperidol, propofol and alizapride, in a decreasing order of effectiveness in the doses used in this study, reduced the incidence of pruritus induced by the use of morphine 0.2 mg intrathecally. On the other hand, promethazine 50 mg was shown to be ineffective.

The effect of intravenous tenoxicam on pruritus in patients receiving epidural fentanyl

In this prospective randomised study, pruritus and pain were evaluated in patients undergoing abdominal surgery during which epidural fentanyl was administered. All patients had an epidural catheter inserted at the time of surgery. Epidural fentanyl 100 micrograms was administered intra-operatively and infused at a concentration of 2 micrograms.ml-1 for 48 h postoperatively. All patients received a standard anaesthetic and, in addition, the study group had a 20 mg bolus of tenoxicam intravenously, intra-operatively. Patients receiving tenoxicam demonstrated significantly lower pruritus and pain scores at 30 min, 2, 4, 8 and 24 h postoperatively as well as reduced pethidine requirements for breakthrough pain in the first 24 h. In conclusion, tenoxicam 20 mg significantly reduces the incidence and severity of postoperative pruritus in patients who received peri-operative epidural fentanyl. In addition, it significantly reduces pain and further analgesic requirements postoperatively.

2-Chloroprocaine antagonism of epidural morphine analgesia

BACKGROUND

2-Chloroprocaine (2-CP) used for lumbar epidural anesthesia (LEA) reportedly decreases the efficacy of epidural morphine (EM) administered for post-cesarean section (CS) analgesia. The amount of supplemental i.v. morphine self-administered by the patient via the patient-controlled analgesia device (PCA) is used to study the interaction between EM and 2-CP.

METHODS

Forty-two patients scheduled for elective CS were randomly divided into 3 equal groups, and received 2-CP, 2-CP + epinephrine (Epi, 5 micrograms.ml-1) or 2% lidocaine (Lido) with Epi for LEA. All patients received 5 mg EM and i.v. PCA morphine for postoperative pain. Cumulative amount of i.v. morphine used in the first 24 hours as well as the amount of the drug used during each 2-h period were noted. Nonparametric analysis of variance and Chi-squared analysis were used for statistical comparisons.

RESULTS

The mean cumulative 24-h i.v. PCA morphine requirement in the 2-CP, 2-CP+Epi and Lido+Epi groups respectively was 20.5 +/- 24, 33.1.5 +/- 27 and 4.07 +/- (mean +/- SD). The Lido + Epi group used significantly less morphine (P = 0.01) compared to either of the 2-CP groups with no significant difference between the 2-CP groups. The maximum i.v. PCA morphine use occurred in the first 4 hours following surgery in all three groups.

CONCLUSION

Analgesic efficacy of EM is decreased when 2-CP is used for LEA compared to when Lido + Epi is used.

Efficacy of bupivacaine delivered by wound catheter for post-Caesarean section analgesia

A prospective, randomized, double-blind trial was conducted to assess contribution to postoperative analgesia of intermittent instillation of 0.25% bupivacaine beneath the rectus sheath in 70 women delivered by lower uterine segment Caesarean section. The operations were performed via a Pfannenstiel incision under spinal anaesthesia. Background intravenous narcotic analgesia was provided with a patient controlled analgesia system (PCAS) using a standard morphine regimen. Overall (44 hr) mean morphine consumption was significantly greater in the placebo (saline) group compared to the treatment group (84.2 mg versus 63.3 mg. Two tailed t test p < 0.001). The most significant intergroup differences in narcotic use were found in the first 4 hours and between 24 and 36 hours after commencing PCAS (Two tailed t test p = 0.014 and 0.003 respectively). Subjective pain scores were assessed with a 10 cm visual analogue scale (VAS). The mean peak VAS score was greater in controls (5.37) than the treatment group (4.25) between 18 and 24 hours postoperatively (Mann-Whitney U = 424, p = 0.027). There were no intergroup differences in pain scores for any other time period. The overall incidence of nausea was lower in the treatment group compared to the control group (Chi squared with Yates' correction p = 0.046) and a lower degree of sedation was seen in those receiving bupivacaine between 4 and 8 hours after commencing PCAS (Mann-Whitney U = 427, p = 0.028). No differences in other narcotic related side-effects (vomiting and pruritus) were shown between groups. Regular instillation of 0.25% bupivacaine beneath the rectus sheath of women delivered by Caesarean section reduces their morphine requirements by 25% in the 44 hours after operation, with an associated reduction in both nausea and early sedation.

Epidural fentanyl does not influence intravenous PCA requirements in the post-caesarean patient

Forty ASA physical status I or II patients scheduled for elective Caesarean delivery were studied to determine the effect of epidural fentanyl on post-Caesarean delivery analgesic requirements as administered by intravenous patient-controlled analgesia (PCA). Following delivery of the infant, under epidural anaesthesia with lidocaine 2% with 1/200,000 epinephrine, patients were randomly assigned to receive either 10 ml of preservative-free normal saline via the epidural catheter or 100 micrograms of fentanyl with 8 ml preservative-free normal saline in a double-blinded fashion. On arrival in the post-anesthesia recovery room (PAR), patients were provided with intravenous PCA meperidine 12.5 mg every eight minutes as needed. Patients were visited at intervals over the next 24 hr to determine if any differences in narcotic requirements, demands for narcotics, or severity of pain were noted. No differences were observed in any values between the groups. It is concluded that a single bolus of epidural fentanyl does not provide an advantage for postoperative pain relief in this patient population.

Wound infiltration of local anaesthetic after lower segment caesarean section

The analgesic efficacy of subcutaneous wound infiltration with 20 ml of 0.5% bupivacaine after elective lower segment section Caesarean section was studied in 28 patients in a double-blind randomised controlled manner using a patient-controlled analgesia system. The mean 24-hour morphine consumption of the placebo group and the bupivacaine group was similar (76 mg and 68 mg respectively). Analysis of the cumulative hourly morphine consumption failed to show any statistically significant differences between the groups. However, on a weight-adjusted basis statistically significant differences in morphine consumption were demonstrated, although these may not be clinically important. Subjective experiences of pain, nausea and drowsiness assessed by linear analogue scoring were similar in both groups.

The development and clinical use of patient-controlled analgesia

Patient-controlled analgesia has successfully made the transition from research tool to clinical acceptability. Reliable and sophisticated patient-controlled analgesia systems are commercially available. The technique has been most used for control of postoperative pain but has been successfully used during labour, after burns and other trauma and in terminal care. Virtually every opioid has been administered by patient-controlled analgesia using almost every route of administration. It is more effective than the traditional techniques of pain control after surgery but is not automatically so. Choice of opioid and the settings chosen for demand dose and lockout interval greatly influence effectiveness. Patient-controlled analgesia requires active participation by the patient but the psychology of patient-controlled analgesia has generally been under-estimated. Patient-controlled analgesia has developed empirically and many assumptions have been made; there is a need for fundamental research.

The morphine sparing effect of ketorolac tromethamine. A study of a new, parenteral non-steroidal anti-inflammatory agent after abdominal surgery

A randomised, double-blind study of patients after upper abdominal surgery was undertaken to assess the analgesic efficacy of ketorolac tromethamine, a new, parenteral non-steroidal anti-inflammatory agent. Postoperatively, patients received a 24-hour intramuscular infusion of either saline (n = 20), ketorolac 1.5 mg/hour (n = 21) or ketorolac 3.0 mg/hour (n = 20). Cumulative morphine requirements were measured using a patient-controlled analgesia system which delivered intravenous increments of morphine on demand. Pain was assessed by visual analogue scores. Arterial blood gas analyses were performed pre-operatively and on the first postoperative day. Patients who received low and high dose ketorolac infusions required less morphine than the control group (p less than 0.05 and p = 0.06, respectively). This was associated with significantly lower pain scores. Patients who received the higher ketorolac dose had significantly less postoperative increase in arterial carbon dioxide tensions than controls. This study suggests that ketorolac tromethamine is a useful analgesic drug with significant morphine sparing properties.

The maternal and fetal cardiovascular effects of epidural fentanyl in the sheep model

Since the demonstration of opiate receptors in the spinal cord in the mid-1970s, investigators have been looking for the most effective epidural narcotic. With the use of the chronically catheterized maternal sheep model, we injected two different doses of preservative-free fentanyl (50 and 100 micrograms) into the epidural space. No statistically significant changes were observed, either in maternal or fetal arterial pressure and acid-base status or in maternal central venous pressure, systemic and pulmonary vascular resistance, cardiac output, and intrauterine pressure (p greater than 0.05). With a dose of 50 micrograms of fentanyl, maternal levels of fentanyl peaked at 60 minutes (50 pg/ml) and the fetal levels of fentanyl peaked at 45 minutes (20 pg/ml). With the 100 micrograms dose of fentanyl, maternal levels of fentanyl peaked at 45 minutes (230 pg/ml) and the fetal levels peaked at 15 minutes (110 pg/ml). We conclude that the injection of 50 and 100 micrograms of fentanyl into the maternal epidural space has no adverse effects on mother or fetus in the sheep model.

Pruritus following spinal anaesthesia

A case report of severe pruritus following spinal anaesthesia in an 80-year-old man is presented. The pathophysiology of pruritus is discussed and the possible causes in the case reported are outlined.

Intradural morphine and diamorphine. Dose response studies

This open study of 81 patients having major orthopaedic surgery reviews the duration of analgesia and side-effects of 0.625, 1.25 or 2.5 mg of morphine or 1.25 or 2.5 mg of diamorphine given intradurally in combination with 7.5 mg of cinchocaine at induction of anaesthesia. A significant dose-response relationship for duration of analgesia measured by time to first requirement of postoperative analgesic was found with morphine; 1.25 and 2.5 mg of morphine produced analgesia of longer duration than 0.625 mg. No such dose-response was found for side-effects. There was no significant difference in duration of analgesia between diamorphine 1.25 and 2.5 mg, and the duration was similar to that seen with the higher doses of morphine. An intradural dose of between 0.625 mg and 1.25 mg of either morphine or diamorphine used with cinchocaine and without additional parenteral opiate, may be appropriate.

Spinal opiate analgesia and facial pruritus: a neural theory

Facial pruritus associated with spinal opiate analgesia in man is thought to result either from release of histamine or from imbalance of sensory modulation secondary to spread of opiate to the medulla or fourth ventricle. There is another possibility: the sensory imbalance may be secondary to rostral spread of opiate effect by nervous transmission. Evidence is adduced in support of possible anatomical pathways, and in support of a medullary ‘itching centre’ in man.

Extradural diamorphine in the control of pain following lumbar laminectomy

Catheters were inserted into the extradural space under direct vision at the time of surgery for prolapsed intervertebral disc or lumbar canal stenosis. In the post-operative period, diamorphine (3 mg in 5 ml water) was injected through the catheter when patients requested analgesia. In only four of 49 patients was significant pain relief not achieved after extradural diamorphine injection. In four other patients it was not possible to use this method of analgesia throughout the two post-operative days as planned. As judged by the improved mobility and by grading on a linear analogue pain scale, the quality of analgesia achieved was better than after intramuscular papaveretum (10-20 mg) and extradural diamorphine was requested less frequently. There were no serious side-effects in the patients studied, although the technique was not used in patients over 55 years of age. Extradural diamorphine appeared to be less effective in two patients who had undergone re-explorations.