Observations on extradural morphine analgesia in various pain conditions

Clinical studies that initiated the use of spinal opioids for the treatment of pain: A new approach to historical review

Opioids administered into the spinal space by intrathecal or epidural routes can provide potent and prolonged selective analgesia. Compared to the systemic administration of opioids, spinal administration can bring about analgesia with fewer central and systemic adverse effects. For the past 40 years, spinal opioid analgesia has achieved great popularity in various fields of pain treatment. The aim of this work is to identify clinical studies that initiated the use of spinal opioids for the treatment of pain. To determine the historical role of each of the review's studies we used the combination of two factors: the study priority in terms of the time of its publication and the degree of its acknowl-edgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the count of citations indicated a sufficient acknowledgement by the other authors. The citation impact was assessed as the initial citation count - for period of five years after the year of article publication - and the total count. The selection of studies most important for the introduction of spinal opioids to clinical practice was based on two factors - the study priority in terms of the time of its publication and the degree of acknowledgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the citation count was indicative of sufficient acknowledgement by other authors. Analysis of the related data shows that the clinical studies initiating the use of spinal opioids for the treatment of pain belong to two groups of authors - Wang et al. and Behar et al. Both studies were published in 1979 and described delivery of morphine into the spinal space, although the techniques of administration were different: Wang et al. injected morphine intrathecally, Behar et al. administered morphine epidurally. The response to these studies was overwhelming -- close to a dozen reports on this topic were published in 1979 and more than a hundred - in 1980-1981. The total citation response to the Wang et al. article reached 699, and that to Behar et al. - 518. Two earlier records (1900-1901) of the use of intrathecal morphine, by Nicolae Racoviceanu-Pitesti and Otojiro Kitagawa, found no following in medical literature for more than three quarters of a century.

Comparison of hemodynamic response and postoperative pain score between general anaesthesia with intravenous analgesia versus general anesthesia with caudal analgesia in pediatric patients undergoing open-heart surgery

Context:

Regional anesthesia may attenuate adverse physiological stress responses associated with cardiothoracic surgery. In this study, hemodynamic stress response at the different time of surgical stimuli was compared between patients receiving general anesthesia (GA) along with caudal epidural analgesia with GA with intravenous analgesia in pediatric population undergoing open-heart surgery.

Aims:

This study aims to compare the hemodynamic response at the different time of surgical stimuli and postoperative pain score, in pediatric patients undergoing open-heart procedures.

Settings and Design:

We designed a prospective randomized controlled trial to study hemodynamic effects between Group I and Group II. Fifty patients were randomly allocated equally into Group I (GA + caudal epidural) and Group II (GA + intravenous analgesia) by sealed envelope technique.

Subjects and Methods:

After obtaining approval from Institutional Ethical Committee, this prospective study was conducted in 50 American Society of Anesthesiologist Classes II and III pediatric patients aged between 1 and 12 years posted for cardiac surgery in our institution.

Statistical Analysis:

ANOVA, two-way ANOVA, and Student's test.

Results:

The heart rate, systolic blood pressure, diastolic blood pressure and mean blood pressure variations were compared between Groups I and II at different time intervals. The variations were found to be significantly higher at the time of skin incision and 2 min after skin incision in Group II as compared to Group I. Pain score was compared between the groups and was found to be significantly lower with Group I (2.5 ± 1.2) as compared to Group II (4.6 ± 1.7), P = (0.004).

Conclusions:

Caudal analgesia with GA (Group I) was found to have better hemodynamic control and significantly better postoperative pain relief in the first 24 h after awakening.

Pain Relief in the Intensive Care Unit

Treatment of severe pain in the intensive care unit first requires an assessment of pain type: nociceptive, cen tral, visceral, or referred. Narcotics given parenterally are the most commonly used agents for severe nocicep tive pain. Attention to potency, lipophilicity, route of administration, and side effects are all important. Cen tral nervous system pain may require nonnarcotic adju vants, anticonvulsants, or monoamine altering drugs for effective analgesia. The concomitance of emotional suf fering with the pain is an important problem to recog nize so that psychiatric disorders are properly treated.

A review of intrathecal morphine therapy related granulomas

The development of catheter associated granulomatous masses in intrathecal morphine therapy is an uncommon, but potentially serious problem. While these systems have historically been used in patients with short life expectancies, more recently patients with pain from a benign source have benefited from this therapy, and new complications are being encountered secondary to the patients' longer life spans. Morphine is the most commonly used intrathecal opioid and evidence exists that the formation of granulomatous masses are related to the use of higher doses. When the patients' requirement of morphine increases significantly, the physician should be alert for signs of spinal cord compression, such as new neurological deficits, myelopathy, or radiculopathy. Patients that require these higher doses should be properly informed of the association with granulomas and their associated risks. Indolent infection may also be the etiology of granulomatous masses, and the presence of organisms, both aerobic and anaerobic, should be routinely investigated. Patients with catheter-associated granulomas appear to share several features. They exhibit the onset of symptoms several months following the initiation of intraspinal opioids and commonly present with an increase in pain that precedes signs and symptoms of neurological deterioration. While MRI might be the preferred method of detection of intrathecal granulomas, its cost and availability are prohibitive for routine screening. CT myelogram via pump side port injection of contrast can also be performed to detect catheter tip related granulomas/obstructions. Serial neurological examinations for new deficits may be performed and recorded during pump refill visits to recognize a granulomatous mass in its early stages. If an abnormality is identified, imaging studies are appropriate. Awareness of the condition and vigilance are the keys to successful management of this complication.

Reduced analgesic effect of acupuncture-like TENS but not conventional TENS in opioid-treated patients

Evidence from recent animal studies indicates that the analgesic effect of low-frequency transcutaneous electrical nerve stimulation (TENS) is reduced in opioid-tolerant animals. The aim of the present study was to compare the analgesic effect of conventional (high frequency) and acupuncture-like (low frequency) TENS between a group of opioid-treated patients and a group of opioid-naive patients in order to determine if this cross-tolerance effect is also present in humans. Twenty-three chronic pain patients (11 who took opioids and 12 who did not) participated in the study. Participants were assigned in a randomized crossover design to receive alternately conventional and acupuncture-like TENS. There was a significant reduction in pain during and after conventional TENS when compared to baseline for both the opioid and nonopioid group (P < .01). For acupuncture-like TENS however, the analgesic effect of TENS was only observed in the nonopioid group (P < .01), with opioid-treated patients showing no change in pain scores during and after TENS when compared to baseline (P > .09). The reduced analgesic effect of acupuncture-like TENS in opioid-treated patients is coherent with previous animal studies and suggests that conventional TENS should be preferred in patients taking opioids on a regular basis.

PERSPECTIVE

This study shows that patients taking opioids on a regular basis are less susceptible to benefit from acupuncture-like TENS. This phenomenon is probably attributable to the fact that the analgesia induced by acupuncture-like TENS and opioids are mediated by the same receptors (ie, μ opioid receptors).

The site of action of epidurally administered opioids and its relevance to postoperative pain management

The use of epidurally administered opioids to control postoperative pain is a well established and widely accepted technique. However, despite this longstanding use, there is still an ongoing debate concerning the site of action of the opioids used. Some argue that analgesia is mediated by a spinal mechanism and others that a supraspinal mechanism is responsible. On close inspection of the evidence it becomes apparent that epidural opioids act predominantly spinally when administered as a bolus, and predominantly supraspinally when administered as a continuous infusion. A concentration of 10 microg x ml(-1) appears to be the threshold at which epidurally administered fentanyl can elicit segmental analgesia, a value which may have significant clinical applications. The evidence supporting a synergistic relationship between epidural opioids and local anaesthetics is weak and unsupported by a plausible physiological mechanism. Thus the 'threshold concentration' of approximately 10 microg x ml(-1) is unlikely to be lowered by co-administering opioids with local anaesthetics.

Buprenorphine-Soaked Absorbable Gelatin Sponge: An Alternative Method for Postlaminectomy Pain Relief

There have been several reports of instillation of buprenorphine in the intact epidural space in an attempt to control postoperative pain, but none in which an absorbable gelatin sponge soaked with buprenorphine is placed directly in the epidural space. In the present study, carried out on 30 patients (study group) undergoing noncervical laminectomies, 0.3 mg buprenorphine diluted to 5 mL with normal saline soaked into an absorbable gelatin sponge was placed in the epidural space under direct vision. In 30 other patients (control group) undergoing laminectomies, absorbable gelatin sponge soaked with 5 mL normal saline was placed in the epidural space. Pulse rate, mean arterial pressure, respiratory rate, pain score by visual analog scale, duration of analgesia, and adverse effects, if any, were noted preoperatively and postoperatively at 1, 2, 3, 4, 5, 6, 12, 18, and 24 hours. The presence of any neurologic symptoms was also assessed at these time intervals as well as on the seventh postoperative day. The authors observed that changes in pulse rate, mean arterial pressure, and respiratory rate were not statistically significant between the control and the study groups. The pain relief score, duration of pain relief (14.8 +/- 0.77 hours in the study group vs. 0.66 +/- 0.15 hours in the control group), and sedation were significantly better in the study group. No patient demonstrated any respiratory depression (respiratory rate <12/min), bradycardia, pruritus, or neurologic pressure symptoms, although the incidence of nausea was higher in the study group.

The site of action of epidural fentanyl in humans: the difference between infusion and bolus administration

Most published studies suggesting that epidural fentanyl acts predominantly at spinal sites administered the drug as a bolus injection, whereas most studies suggesting that it acts predominantly at supraspinal sites administered the drug as an infusion. In this study we tested the hypothesis that the mode of administration (bolus versus infusion) of epidural fentanyl determines its site of action. Ten healthy volunteers were enrolled in this randomized, double-blinded, cross-over study. On separate study days fentanyl was administered into the epidural space as a bolus (0.03 mg followed by 0.1 mg 210 min later) and as an infusion (0.03 mg/h followed by 0.1 mg/hr 210 min later for 200 min). Using a thermal and electrical experimental pain model, the heat ( degrees C) and electrical current (mA) causing maximum tolerable pain were assessed repetitively over a period of 420 min. The analgesic efficacy measures were obtained at a lumbar and a cranial dermatome. Plasma fentanyl concentrations were determined throughout the study. Epidural bolus administration of fentanyl resulted in segmental analgesia (leg > head), whereas the epidural infusion of fentanyl produced nonsegmental analgesia (leg = head). There was a significant linear relationship between the analgesic effect and the plasma concentration of fentanyl for the epidural infusion but not for the epidural bolus administration of fentanyl. These findings support our hypothesis and might explain the apparent conflict in the literature regarding the site of action of epidural fentanyl.

IMPLICATIONS

In an experimental pain study in volunteers, epidural fentanyl caused segmental analgesia when administered as a bolus and nonsegmental systemic analgesia when administered as a continuous infusion. This finding may help resolve the long-standing controversy surrounding the site of action of epidural fentanyl.

Postoperative analgesia in dogs receiving epidural morphine plus medetomidine

This investigation was carried out to compare the postoperative analgesia and plasma morphine concentrations in dogs given epidural morphine or epidural morphine combined with medetomidine prior to surgery. Twelve dogs (seven males and five females) with ruptured cranial cruciate ligaments presented to the Washington State University Veterinary Teaching Hospital. Six dogs received an epidural injection of morphine (0.1 mg/kg) and six dogs received epidural morphine (0.1 mg/kg) combined with medetomidine (0.005 mg/kg). Numeric rating scale (NRS) pain scores and cumulative pain scores (CPS) were assigned to 10-min segments of video. Video segments, heart rates and respiratory rates were recorded prior to premedication and at 4, 8, 12, 18 and 24 h after epidural injection. Blood was sampled from the cephalic vein at each of these times and during anesthesia at 0.5, 1, 2 and 3 h after epidural injection. Data were analyzed using either Friedman's test or one-way anova for repeated measures. In the morphine group, significant increases compared with premedication values were detected at 4, 8 and 12 h after epidural injection for NRS and at 4 and 12 h after epidural injection for CPS. In the morphine plus medetomidine group, NRS was significantly higher at 4 and 8 h whereas there were no differences from baseline values for CPS. Plasma morphine concentrations were not significantly different between treatment groups, but were significantly increased compared with preinjection values at 0.5, 1, 12, 18, and 24 h in the morphine plus medetomidine group. Epidurally administered morphine combined with medetomidine was associated with only minor benefits based on subjective pain scoring when compared with morphine alone in these dogs undergoing repair of a ruptured cranial cruciate ligament.

The state of implantable pain therapies in the United States: a nationwide survey of academic teaching programs

The purpose of this questionnaire survey was to provide an overview of anesthesiology pain fellowship programs in the United States with regard to implantation of spinal cord stimulators (SCS) and opioid infusion devices. Of the 95 programs solicited, 80% responded to questions pertaining to the prevalence of use and technical considerations of implantation. Of the responding programs, 87% report implanting SCS, and 84% report implanting neuraxial infusion pumps. All programs perform a stimulation or infusion trial before implantation, although the duration varied from a trial in the operating room at the time of implantation to 25 days. Of the programs, 83% implant cylindrical leads, and 17% implant flat leads via laminectomy for their nonrevision SCS implants. Morphine, bupivacaine, hydromorphone, and baclofen are the most commonly used drugs and are used in implanted pumps by >50% of respondents. The question of industry-sponsored pain fellow education in implantable techniques is addressed.

IMPLICATIONS

Of the pain teaching programs in the United States, 80% responded to a questionnaire eliciting information about the implantation of spinal cord-stimulating and opioid infusion devices. The range and diversity of responses imply a lack of agreement about implantation techniques, drugs, and protocols.

Pharmacology and mechanisms of opioid analgesic activity

Opiates by an action at specific receptors can induce a highly selective alteration in the response of humans and animals to strong and otherwise aversive chemical, mechanical or thermal stimuli. Specific investigations in a variety of species from rodent to primate using microinjection techniques to examine the pharmacology of local drug action have shown potent antinociceptive actions to be mediated by a receptor specific action at a number of sites within the brain, including the periaqueductal gray (PAG: mu receptor), the rostral ventral medulla (mu/delta receptor) and the substantia nigra (mu receptor) and within the spinal dorsal horn (mu/delta/kappa receptor). Mechanistic studies have shown these actions in the different sites to be mediated by several discrete mechanisms. For example, in the PAG, the local opiate effect is likely mediated by the indirect activation of bulbospinal pathways, rostral projections to forebrain sites and by a local alteration in afferent input into the brainstem core. In the spinal cord, this effect is mediated by an action presynaptic to the primary afferent and by a post-synaptic effect to hyperpolarize projection neurons. In addition, it is now appreciated that mu and kappa receptors in the periphery can modulate the sensitized state of the small afferent terminal innervating inflamed tissue and exert an anti-hyperalgesic action. After systemic delivery of an opiate, it is thus clear that a wide array of central and peripheral systems serve to explain the powerful analgesic effect exerted by this class of agents.

Morphine does not affect laser induced warmth and pin prick pain thresholds

The aim of this double-blind, placebo-controlled study was to evaluate the effect of intravenously administered morphine in humans using an argon laser to induce experimental pain. Thirty volunteers were randomised to receive a total of 0.15 mg.kg-1 morphine intravenously or saline. The argon laser was used to determine the possible change in warmth thresholds and pin prick pain thresholds. Measurements were performed before and at 10, 20, 30 and 40 min after the injection. During the observation period the warmth thresholds increased 20.7% (P < or = 0.05) from baseline (0.82 W +/- 0.42 W) in the morphine group while an increase of 14.3% (P > or = 0.05) was seen in the placebo group (Baseline: 0.91 +/- 0.37). The pinprick pain thresholds of the morphine group increased 9.4% (P < or = 0.05) from baseline (1.39 W +/- 0.7 W) while the corresponding thresholds of the placebo group was 4.6% (P > or = 0.05) (baseline: 1.73 W +/- 0.44 W). The differences seen between the morphine group and the placebo group were not statistically significant and thus it was demonstrated that morphine had no effect of either the feeling of warmth or the pain elicited by the argon laser. The present study supports other investigations and clinical experience suggesting that intermittent pain is not relieved by morphine unlike continuous pain, which can be relieved by morphine.

Chronic pain in the spinal cord injured: statistical approach and pharmacological treatment

We include in this article the results of a postal inquiry into chronic pain in SCI patients in Valencia (Spain), and our experience with their management. A mailed questionnaire including lesion and chronic pain data was sent to all of the 380 SCI patients who live in the region of Valencia. We received 202 answers, with 145 questionnaires being accurately answered and these were analysed for this study. The results show that chronic pain (that is, lasting more than 6 months) is very common (65.5%). The most frequent type was deafferentation pain (phantom pain), described as burning or a painful numbness. Since 1988 we have been treating a sample of 33 patients suffering from resistant pain according to the following therapies: 1 amitriptyline + clonazepam+NSAID (nonsteroidal antiinflammatory drugs); 2 amitriptyline + clonazepam + 5-OH-tryptophane + TENS (transcutaneous electrical nerve stimulation); 3 amitriptyline + clonazepam + SCS (spinal cord stimulation); 4 morphine, by continuous intrathecal infusion. After almost 4 years using these therapies we can affirm that the results regarding analgesia reached 80% in all cases, and that morphine used by intrathecal route is very safe and useful in selected patients.

Are poor metabolisers of sparteine/debrisoquine less pain tolerant than extensive metabolisers?

It has recently been shown that O-demethylation of the opioid drug codeine to morphine depends on the sparteine/debrisoquine oxygenase (CYP2D6) which in man exhibits genetic polymorphism. Morphine may be an endogenously formed substance in mammalians. Therefore, it may be hypothesized that the final step in an endogenous synthesis of morphine from codeine also depends on CYP2D6. CYP2D6, which is present in the liver and presumably also in the brain, is not expressed in subjects who are poor metabolisers of the sparteine/debrisoquine type. We have determined sensitivity to painful stimuli in 94 extensive metabolisers and 82 poor metabolisers of sparteine in 2 phasic (pain thresholds to heat and pressure) and 1 tonic (cold pressor test) experimental pain model. Extensive and poor metabolisers did not differ significantly in the 2 phasic pain models neither with respect to pain detection nor pain tolerance thresholds. However, for the cold pressor test, peak pain ratings and area under the pain rating-time curve during 2 min were significantly higher in poor than in extensive metabolisers (P = 0.0024 and 0.044). Furthermore, a substantially higher fraction of poor metabolisers prematurely withdrew their hand from the ice water during the cold pressor test due to intolerable pain (32 vs. 18%, P = 0.0545). We conclude that poor metabolisers of sparteine may be less tolerant to tonic pain than extensive metabolisers, and we hypothesize that this may be related to an inherited defect in endogenous synthesis of morphine via CYP2D6 in the brain.

Dose changes in long- and medium-term intrathecal morphine therapy of cancer pain

Intrathecal morphine analgesia for the treatment of cancer pain was administered using implanted ports and drug delivery systems (DDS) in 79 patients. Effective control of the pain was achieved in nearly all patients; in only two patients was the use of the DDS discarded because of relative ineffectiveness. Fifty-three manual drug release systems (41 lumbar, 12 ventricular) and 26 lumbar ports were used. Forty patients survived more than 2 months; the maximum survival time was 560 days (mean survival time, 80 days with a port system, 100 days with a manual DDS). Patients still alive at the time of this study, i.e., with unknown survival time, were excluded. The initial mean daily dose was 8.5 mg in lumbar ports, 2.75 mg in lumbar DDS, and 0.2 mg with intraventricular application. Dose change patterns disclosed no alteration of the initial dose in 18 of 26 port patients, an initial increase in 4, a preterminal increase in 3, and a single intermittent increase in 1 patient. Of 40 lumbar DDS patients, 13 showed a constant dose, 9 an initial, 3 a preterminal, and 5 an intermittent increase. Three patients with less than 2 months' survival time had a rather continuous increase. All long-time survivors (i.e., with more than 2 months' survival time) reached a plateau and remained there until a preterminal if any increase occurred. These findings suggest the morphine dosage to be indicative of the progress of the disease rather than of a drug tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal sufentanil in rats: Part I: Epidural versus intrathecal sufentanil and morphine

Male Wistar rats were injected epidurally or intrathecally with increasing doses of sufentanil or morphine in order to determine differences in potency, onset and duration of analgesia and supra-spinal side-effects. For sufentanil, only small differences in the lowest ED50-values for analgesia and supra-spinal side-effects were observed between the two spinal routes. Given intrathecally, sufentanil had a somewhat faster onset but a shorter duration of action than did epidural sufentanil. However, intrathecal morphine when compared to epidural morphine had a faster onset with a greater potency and a longer duration of action. The stronger opioid activity of intrathecal morphine was also reflected in a reduced safety ratio for the blockade of the cornea reflex. These differences between the two opioids, with regard to their optimal route of spinal administration, are discussed in terms of lipophilicity and optimal clinical use.

Perioperative complications of anesthesia

An overview of several perioperative complications and their management strategies is presented. Operative hypothermia, malignant hyperthermia, bronchospasm, and side effects of spinal opioid agents are discussed. Ramifications of these complications may extend well beyond the operative period and influence patient outcome. Therefore, it is necessary that the surgeon have a fundamental understanding of the pathophysiology and modalities of treatment in the context of anesthesia and surgery.

Posttraumatic reflex sympathetic dystrophy: Mechanisms and medical management

Reflex sympathetic dystrophy (RSD) refers to a symptom complex of posttraumatic pain associated with a wide and varying spectrum of vasomotor and neurologic changes. The diagnosis of reflex sympathetic dystrophy is made almost entirely on clinical grounds, and is often confirmed by observation of the results of diagnostic local anesthetic nerve blocks. Laboratory and radiographic investigations are useful adjuncts to diagnosis. The key to successful management is early recognition, as delays in treatment are associated with worse outcome. A multimodal approach to treatment is recommended that may include nerve blocks, rehabilitation, and pharmacologic and behavioral pain management. The role of other modalities including surgery and electrical stimulation remains controversial.

Epidural fentanyl effect on cardiac output and hepatic blood flow

Epidural opioids provide high quality analgesia with no clinically apparent effect on the circulation or on specific organ blood flow. Little investigative data is available to support these impressions of circulatory stability. Ten patients presenting for thoracotomy were studied at rest preoperatively to determine if epidural fentanyl had any effect on the systemic circulation or hepatic blood flow. Intravascular pressure measurements, cardiac output estimation using the dye-dilution technique and estimation of altered hepatic blood flow by measuring the clearance of indocyanine green were performed. No significant changes in heart rate, perfusion pressure, cardiac output or hepatic blood flow were detected following the administration of fentanyl 50 micrograms into the epidural space.

Epidural methadone for analgesic management of patients with conservatively treated proximal femoral fractures

Epidural methadone analgesia was initiated soon after admission to emergency room in elderly patients who sustained osteoporotic proximal femoral fracture and who were considered to be high surgical risks. The severe pain was significantly reduced, enabling early mobilization of the patients. The analgesia was discontinued only when nonnarcotic analgesia sufficed. The treatment lasted for about 3.5 weeks. One minor complication was observed during the treatment period. We concluded that patients who have femoral neck fracture who are at high risk for operation and have to be observed and stabilized before operation can be managed by continuous epidural methadone analgesia.

Postoperative epidural morphine analgesia in Papua New Guinea

In order to introduce the technique of epidural narcotics for pain relief in Papua New Guinea, fifty patients were given low doses of epidural morphine and thereupon the quality of analgesia and morbidity evaluated. The lowest effective epidural morphine dose was determined by considering the patient's characteristics and height of surgical incision. Pain relief was provided for three postoperative days in the surgical or gynaecological wards. The quality of analgesia thus provided was excellent in all the patients with no incidence of clinically significant respiratory depression or hypotension. Minor complications such as nausea, vomiting, pruritus and retention of urine were also relatively uncommon.

Clinical differences in spinal opioid efficacy

The case report describes a patient who presented with two simultaneously-occurring but distinct pain syndromes. Epidural morphine controlled the pain from the abdominoperineal resection, while the pain from a deep venous thrombosis was not masked. Such differential effects of epidural morphine on pain of varying origin supports physiological observations on the specificity of the site of action of spinal opioids.

[Use of epidural and intrathecal opiates in obstetrics]

The discovery of opiate receptors and naturally occurring opiate-like substances in the central nervous system started a new era in pain control. Epidural and spinal opiates have been increasingly used since 1979. However, applying these analgesic techniques in obstetrics has been criticized because of possible side-effects on the mother and foetus. In this literature survey, their advantages and disadvantages are analyzed. Maternal side-effects include pruritus, nausea, urinary retention, and, most of all, respiratory depression. As a general rule, these side-effects are greater with the intrathecal route, high doses, and the use of morphine. The effects on the course of labour are small, and neonatal status is not altered. Spinal and epidural opiates are efficient analgesic techniques for labour and caesarean section. They provide a dose-related, but not surgical, analgesia. Currently, there is a great deal of interest in mixtures of a diluted local anaesthetic agent and a lipophilic drug for use during labour or caesarean section. An opiate alone may not consistently provide satisfactory analgesia during labour, and it cannot be recommended for routine use, except for patients in whom the cardiovascular effects of routine regional anaesthesia are to be avoided. The choice of a lipid-soluble opiate like fentanyl is safe. However, when considering new drugs, great care must be taken to avoid unforeseen problems. A good knowledge of the problem and a cautious approach combined with careful monitoring of the respiratory rate and adequacy of ventilation are the keys to the safe use of spinal and epidural opiates.

Itching after epidural and spinal opiates

When opiates are administered by the epidural and spinal routes, itching occurs as a side effect. We reviewed 52 reports in the literature of the use of epidural and spinal opiates to assess the incidence of itching and found an overall incidence of 8.5% in patients receiving epidural opiates, and 46% in patients receiving spinal opiates. The symptom is a recognised, though rare, side effect of systemically administered opiates, and in the case of systemic administration the itching is generalised. In the case of epidural and spinal administration, the itching may be generalised. But often a segmental distribution is demonstrable, centred on the level of injection, or the itching is localised to a particular area such as the nose and face. It is likely therefore, in the latter case, that there is an effect upon the spinal cord itself. Although occasionally spinal opiate-induced itching is extremely troublesome and lessens the value of spinal opiate pain relief, in the majority of cases, the itching is not severe and is treatable with naloxone. However, the frequent occurrence of the symptom and the likelihood of a spinal cord mechanism do provide valuable information about opioid actions, and benefit may be derived from better understanding the phenomenon. This paper states a hypothesis to explain spinal opiate-induced itch and explores the possible mechanisms of the effect.

Lack of analgesic effect of opioids on neuropathic and idiopathic forms of pain

The aim of the present study has been to assess the responsiveness of various types of chronic pain to opioids given i.v. and tested against placebo in a double-blind, randomized fashion. Pain classified as primary nociceptive was effectively alleviated (P greater than 0.001) while neuropathic deafferentation pain was not significantly influenced by morphine or equivalent doses of other opioids. Also 'idiopathic' pain, defined as chronic pain with no or little demonstrable pathology, failed to respond. The results were not related to whether the patients were regular users of narcotic analgesics or not. The outcome of our double-blind opioid test has proved useful to justify a continued, or discontinued, use of narcotic medication in individual patients. It may also support the indication and choice of invasive stimulation procedures (spinal cord or brain). The results of the study illustrate the misconception of chronic pain as an entity and highlight the importance of recognizing different neurobiological mechanisms and differences in responsiveness to analgesic drugs as well as to non-pharmacological modes of treatment. The opioid test has thus become a valuable tool in pain analysis and helpful as a guide for further treatment.

Epidural administration of opiates by a new device

Epidural administration of opiates as a long-term treatment of cancer pain, even for out-patients, is now well established. Most reports describe intermittent injections given several times a day, which may have technical and personal disadvantages. Continuous epidural infusion may be preferable. This report describes 16 patients who were treated with epidural opiates delivered by plastic infusion pumps. Pain relief was effective, the equipment was inexpensive and home treatment was easily accomplished.

Drug delivery for intractable cancer pain. Use of a new disposable parenteral infusion device for continuous outpatient epidural narcotic infusion

Administration of narcotic analgesics through the epidural route has proven useful for treating pain of acute and chronic nature. This route of narcotic administration is frequently chosen for cancer patients with intractable pain that may be refractory to treatment by conventional oral or parenteral therapy. Implantable constant infusion devices have been commonly described as an alternative drug delivery system for this type of patient. This case report describes the use of the Travenol Infusor (Travenol Laboratories Inc., Deerfield, Illinois) an external, lightweight, disposable, drug delivery device for delivering continuous epidural morphine infusion to a patient with severe cancer pain. The patient has achieved stable pain relief for greater than 8 months without hospital admission for pain control, or management of complications due to the drug delivery system. The Travenol Infusor may prove to be an alternative drug delivery system for patients requiring continuous epidural narcotic infusion.

Intraspinal morphine for cancer pain

From a survey of the recent literature on chronic intraspinal morphine administration for cancer pain concerning 412 cases, the present authors observe that: 1. data regarding follow-up on pain relief and complications are lacking; 2. continuous administration by closed systems shows more efficacy in long-term pain relief; 3. tolerance, although not reported by all authors, is present and becomes remarkable in prolonged administration; 4. serious side-effects are less frequent with the epidural administration technique. These data are confirmed by the present authors' clinical experience of 22 patients treated with epidural morphine administration and 53 patients treated with intrathecal morphine. The widespread use of these methods is limited not only by technical complications but also by the existence of certain types of pain which do not respond to morphine and which may develop, as part of the evolution of the neoplastic disease, even during treatment with intraspinal morphine.

Intraspinal analgesia: an historical overview

The application of opioids in the proximity of the spinal cord is a recent addition to the forms of treatment available for pain relief. During the last 20 years we have learned more about the intimate mechanisms of the action of opiates then we had in the preceding 5 millennia. Opium, in fact, has been used for medical purposes from prehistoric times. On the basis of the newly acquired knowledge, we are now applying opioids in more effective ways and providing more patients with long overdue relief of their pain.

Buprenorphine vs. morphine via the epidural route: a controlled comparative clinical study of respiratory effects and analgesic activity

Twelve patients with intense or very intense pain of the non-incident type, secondary to neoplasia, were divided at random into two groups and treated with an epidural dose of 3 mg of morphine in 10 ml of glucose solution (6 patients = group M) or with 0.3 mg of buprenorphine in the same vehicle (6 patients = group B). None of the patients had previously been treated with opioids by any route. After first determining basal values, the following assessments were carried out: (1) evaluation of the analgesic effect of the drugs with checks at 30 min and at 1, 2, 3, 4, 6 and 18 h after administration, using a visual analogue scale, a numerical rating scale and a simple descriptive scale; and (2) evaluation of effects on respiration by means of checks at 30 and 90 min and at 6 and 18 h, on control of breathing indices (P0.1; VE; VA; Ti/Ttot; VT/Ti; RR), gas exchange indices (delta(A-a)O2; VD/VT; pAO2; R) and blood gas and acid-base indices (paO2; paCO2; pH; HCO3-). The data obtained were analyzed statistically using analysis of variance and Student's t test. The study results showed very similar analgesic efficacy for both treatments at a single dosage level of morphine (3 mg) compared to buprenorphine (0.3 mg), which was approximately 3 times greater than an equivalent parenteral dose of morphine (10 mg). Analysis of the results revealed statistically, though not clinically, significant changes in respiratory function indices, only in the buprenorphine-treated group. The effects of buprenorphine on respiratory function, when administered epidurally at the above dosage, are less favourable than those of morphine in the early measurements, probably because of its greater systemic absorption; nevertheless, the risk of delayed respiratory depression appears to be less after buprenorphine than after morphine.

Role of epidural and intrathecal narcotics and peptides in the management of cancer pain

The spinal administration of opioids may provide analgesia of long duration to patients with bilateral or midline lower abdominal or pelvic cancer pain. However, cross-tolerance to orally and parenterally administered narcotics and the rapid development of tolerance to spinal narcotics have limited their usefulness. Opioids have extensive distribution in the CSF and plasma when administered into the epidural or intrathecal space, and delivery of drug to brain stem sites may account for many of the toxic and therapeutic effects of spinal opioids. Further clinical and pharmacokinetic studies are required to provide the information regarding: the optimal opioids for use as spinal analgesics; equieffective dose ratios of spinal opioids in comparison to parenteral or oral opioids; strategies useful to forestall the development of tolerance of spinally administered opioids; the analgesic efficacy of this therapy in opioid-tolerant patients; and the role of spinally administered nonopioid analgesics in the management of cancer pain in the tolerant patient. These questions will need resolution before this therapy can be recommended for routine use in the management of cancer pain.

Therapeutic progress--review XXIII. Morphine analgesia in terminal care

Pain as a problem in terminal care is considered in this review with particular emphasis on the use of opiates. The choice of routes of administration is discussed in detail and the role of combination of opiates with anti-emetics and steroids is considered.

Opioid ligand binding sites in the spinal cord of the guinea-pig

The properties of opioid binding sites in membranes from the spinal cord of the guinea-pig were analyzed in experiments employing radiolabeled opioid ligands, selective or partially selective for mu, delta and kappa-type binding sites. Incubation was conducted at 37 degrees C in a quasi-physiological modified Krebs medium, containing sodium and magnesium. The types of binding sites were discriminated on the basis of their affinities for [3H-D-Ala2-MePhe4-Gly5-ol]enkephalin ([3H]DAGO), [3H-D-Ala2-D-Leu5]enkephalin, and [3H]ethylketocyclazocine and the relative potencies of the displacing ligands, DAGO, [D-Ser2-Leu5]enkephalyl-Thr and trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]benzeneacetamide methanesulfonate hydrate (U50488H), which are selective for mu, delta and kappa type binding sites respectively. In membranes from whole spinal cord, kappa type sites comprised about 60%, mu about 30% and delta about 10% of the total of mu, delta and kappa binding sites. Binding sites of the mu type were also found in the lumbo-sacral region of guinea-pig spinal cord, in contrast to earlier reports of their absence from this tissue. Morphine showed a better than 500-fold selectivity for mu over kappa sites in spinal cord, while nalbuphine and (-)1-cyclopentyl-5-(1,2,3,4,5,6-hexahydro-8-hydroxy-3,6,11- trimethyl-2,6-methano-3-benzazocin-11-yl)3-pentanone methanesulfonate (WIN 44441-3) showed about a 10-fold selectivity for mu sites. The drug U50488H had about a 150-fold greater affinity for kappa than mu-type binding sites.

The action of intrathecal morphine and methadone on the lower urinary tract in the dog

The effects of intrathecally administered morphine and methadone on lower urinary tract dynamics were investigated by cystometrograms and urethral pressure profiles in 16 anesthetized dogs. The examinations were performed before and 30, 60 and 90 minutes following intrathecal injection of 0.03 mg./kg. morphine or methadone. Intrathecal normal saline was used for control studies. Significant relaxation of the detrusor was noted after intrathecal morphine as expressed by a decrease in mean intravesical pressure (p less than 0.05) and by a rise in the calculated detrusor compliance. These effects were reversed by intravenously injected naloxone. As opposed to morphine, methadone caused an increase in detrusor tone. No appreciable effects were observed on the urethra after intrathecal morphine or methadone. Neither intravenous injection of the opiates nor intrathecal administration of saline caused alterations in bladder tone. The result may imply a spinal, albeit opposing, effect of the two opiates on bladder dynamics.

Cardiac effects of thoracic epidural morphine caused by increased vagal activity in the dog

This study was carried out in order to investigate possible side-effects of thoracic epidural morphine on cardiac electrophysiology, haemodynamics and metabolism. In pentobarbital-anaesthetized dogs, intracardiac conduction times were determined by His bundle electrography, and refractoriness by programmed electrical stimulation; monophasic action potential recordings were obtained from the right ventricle by the suction electrode technique. Cardiac output, left ventricular and aortic blood pressures were measured, as well as plasma concentrations of morphine, free fatty acids, glycerol, glucose and lactate. Thoracic epidural morphine (0.12 mg X kg-1) reduced spontaneous heart rate, prolonged atrioventricular nodal conduction time and refractoriness, and reduced left ventricular dP/dt max. Bilateral vagotomy reversed these effects. Intra-atrial, His Purkinje and intraventricular conduction times, atrial and ventricular refractoriness and action potential duration, stroke volume and mean aortic blood pressure, as well as the metabolic variables, were not significantly influenced by thoracic epidural morphine with or without vagotomy. Peak plasma morphine levels of 12-25 ng X ml-1 were measured 10 min after morphine injection. In conclusion, this study demonstrates depressive side-effects of epidural morphine on cardiac function, mediated by an increased vagal activity.

Urinary function during epidural analgesia with methadone and morphine in post-cesarean section patients

Urinary function was assessed in 120 women after cesarean section under epidural anesthesia. Postoperative analgesia was obtained by means of epidurally administered methadone (40 patients) or morphine (40 patients). In the remaining 40 women, no narcotic drugs were given and postoperative pain was treated with intramuscular or oral non-opiate analgesics and sedatives. Both methadone and morphine provided potent postoperative pain relief. Following epidural methadone, mean urine volumes of the first two postoperative voidings were increased (543 +/- 38 ml and 571 +/- 31 ml) as compared with those after epidural morphine (219 +/- 25 ml and 218 +/- 18 ml) and with those of patients receiving non-opiate analgesics (319 +/- 28 ml and 414 +/- 30 ml). The mean time interval between the end of surgery and first voiding following methadone analgesia was shorter (336 +/- 27 min) than after morphine (582 +/- 18 min) or after non-opiate (448 +/- 28 min) analgesic drugs. Difficulty in micturition and the need for bladder catheterization were also decreased in the group with epidural methadone (2.5%) in comparison with the groups receiving morphine (57.5%) or non-opiate analgesic medicaments (12.5%). The use of epidural methadone for postoperative pain relief is advocated, both in view of its analgesic potency and of the low incidence of urinary disturbances.

Continuous infusion of spinally administered narcotics for the relief of pain due to malignant disorders

The INFUSAID model #400 totally implantable drug delivery system was implanted in 17 patients for the continuous infusion of spinally administered preservative-free morphine sulfate. Sixteen patients had pain of malignant origin, and one patient had pain secondary to meningomyelocele. Over time, there was a consistent mean improvement in analgesia scores ranging from 50% to 70% of the control levels for 16 of the patients with cancer-related pain. This form of pain therapy was not successful in treating the benign pain of the patient with meningomyelocele. Overall, the patients with cancer were pleased with their pain therapy, experienced few complications, and reported improved quality of life. Continuous infusion of spinally administered narcotics using a totally implantable drug delivery system such as the INFUSAID model #400 is a safe, complication-free procedure for the control of cancer-related pain.

Postoperative pain treatment after upper abdominal surgery with epidural morphine at thoracic or lumbar level

Thirty patients undergoing upper laparotomy were entered into a randomized trial, comparing the effect of midthoracic (T) and lumbar (L) epidural morphine on postoperative pain and pulmonary function. Five mg morphine was injected through the catheter at the end of the operation, and subsequently three times a day. Six, 30 and 54 h postoperatively, the following tests were performed: linear analogue pain score, arterial gas tensions (PaO2, PaCO2 and pH), forced ventilatory capacity (FVC), forced expiratory volume in 1s (FEV1) and peak expiratory flow rate (PEF). The changes in pain score (increase of the median): T: 21, 6, 5, and L: 24, 15, 8 per cent of full scale), PaO2 (decrease of the tension: T: 1.7, 2.1, 2.4, and L: 2.0, 2.8, 2.0 kPa), PaCO2, pH, FVC (decrease of the volume: T: 1.3, 1.1, 0.9, and L: 1.3, 1.3, 1.21), FEV1 and PEF from the preoperative tests were not significantly different. It is concluded that the clinical effect of epidural morphine for postoperative pain treatment is the same or little different whether the administration takes place at the thoracic or lumbar level.

Epidural morphine prophylaxis of postoperative pain: report of a double-blind multicentre study

In a double-blind placebo-controlled trial, 154 subjects, having intraperitoneal surgery or Caesarean section, and 53 patients undergoing lower limb orthopaedic surgery, received epidural morphine, 5 mg in 10 ml 0.9 per cent NaCl, or placebo, 10 ml 0.9 per cent NaCl, intraoperatively to determine duration of action and efficacy in preventing postoperative pain. Epidural morphine gave significantly longer postoperative analgesia (greater than 11 h) than placebo (3-6 h) in both groups (p less than 0.05) and patients who received morphine required less postoperative analgesic. Obstetric subjects experienced longer pain relief (18.3 +/- 1.3 h) than patients undergoing non-obstetric intraperitoneal surgery (9.2 +/- 1.2 h) (p less than 0.001). Generally mild pruritus affected more than 40 per cent of those receiving morphine, but over 90 per cent of obstetric patients receiving morphine. Respiratory depression occurred in 2-7 per cent of subjects who received morphine; unpredictable in onset, it responded rapidly to naloxone. Epidural bupivacaine, if employed for the surgical procedure, appeared to prolong epidural morphine analgesia. We consider epidural morphine useful in preventing postoperative pain, but its use demands close observation of respiratory rate in a high density nursing area.