Maternal and fetal concentrations of morphine after epidural administration during labor

Side effects of intrathecal and epidural opioids

The purpose of this article is to review the literature on the side effects of intrathecal and epidural opioids. English-language articles were identified through a MEDLINE search and through review of the bibliographies of identified articles. With the increasing utilization of intrathecal and epidural opioids in humans during the 1980s, a wide variety of clinically relevant side effects have been reported. The four classic side effects are pruritus, nausea and vomiting, urinary retention, and respiratory depression. Numerous other side effects have also been described. Most side effects are dose-dependent and may be more common if the opioid is administered intrathecally. Side effects are less common in patients chronically exposed to either intrathecal, epidural, or systemic opioids. Some side effects are mediated via interaction with specific opioid receptors while others are not. It is concluded that the introduction of intrathecal and epidural opioids marks one of the most important breakthroughs in pain management in the last two decades. However, a wide variety of clinically relevant non-nociceptive side effects may occur. All physicians utilizing intrathecal and epidural opioids must be aware of these side effects, for while most are minor, others are potentially lethal.

Influence of epidural analgesia on fetal and neonatal well-being

Epidural analgesia is a frequently used method to reduce the pain of child-bearing. Concerns regarding the safety and potential hazards still persist in the medical community. This review intends to examine how epidural analgesia determines the various factors of fetal and neonatal well-being. Placental drug transfer of opiates like morphine, pethidine and fentanyl is rapid and can lead to neonatal depression. Sufentanil seems to be the safest opiate to administer epidurally. Local anaesthetics are transferred to the fetus in substantial amounts, but the reported effects are subtle and are probably inconsequential. Utero- and fetoplacental blood flow seems to be improved by epidural analgesia with local anaesthetics. Even when using stronger solutions for more extensive blockade in patients for caesarean section, no adverse effects could be demonstrated using pulsed Doppler technique as long as prolonged hypotension (> 2 min) is avoided. Hypotension is best prevented with 20-25 ml/kg crystalloid preload and prompt treatment with ephedrine or etilephrine. Addition of adrenaline to local anaesthetics is considered to be safe for the healthy mother and fetus but it should best be avoided in mothers with pregnancy induced hypertension. Fetal and neonatal acid-base balance and gas-exchange are not adversely affected by epidural analgesia. Many studies show that epidural analgesia can indeed protect the fetus if hypotension is prevented. Neonatal well-being evaluated by APGAR, BRAZELTON, SCANLON and NACS scores is not significantly influenced by local anaesthetics. Neonatal depression can occur however with epidural use of morphine, fentanyl and alfentanil. Sufentanil, again in doses up to 30 micrograms in association with bupivacaine seems to be devoid of depressive effects on the neonate. In summary, the anaesthetist has good arguments to reassure his obstetrical colleagues that providing epidural analgesia for pregnant women in labour is a justifiable intervention to support the natural process of child-bearing.

Risk-benefit assessment of anaesthetic agents in the puerperium

A critical evaluation of anaesthetic agents in the puerperium is difficult because systematic, relevant studies are still lacking. Current knowledge of the effects of different agents used in labour and caesarean section indicates that significant residual effects on the mother and newborn are limited. In the early puerperium, based on physiological and/or hormonal changes, the mother could be more sensitive to inhalational anaesthetic agents and local analgesics. To date there is no evidence that any anaesthetic agent is excreted in breast milk in clinically significant amounts when given as a single dose. The only exception is perhaps in the case of very premature neonates whose mothers have had multidrug therapy before labour. Even then the importance of breast milk should be carefully assessed against possible adverse drug effect. However, repeated administration of long-acting benzodiazepines and continuous epidural administration of pethidine (meperidine) can have adverse effects on the neonate. The essential conclusion of this review is that breast-feeding is best. The different anaesthetic agents are excreted in the milk in amounts so low that detrimental effects on the neonate should not be expected.

Spinal opioids in the management of obstetric pain

Spinal opioids have become increasingly popular agents for providing analgesia during labor, augmenting anesthesia during cesarean section, and providing pain relief after operative delivery. The development of spinal opioids in the management of obstetric pain is reviewed.

[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.

Intrathecal administration of morphine for the relief of pains in labour and estimation of maternal and fetal plasma concentration of morphine

Thirteen healthy women in active labour received an intrathecal injection of morphine 1.0 mg. Eighty-five percent (11 patients) experienced acceptable or good pain relief. Analgesia set in 15-45 min after injection and reached a maximum after 15-120 min and lasted until delivery. Eighty-five percent (11 patients) of the patients developed mild side-effects i.e., pruritus, nausea and emesis. The intrathecal injection of morphine did not adversely affect the condition of the infant. Venous blood samples from the patients and umbilical cords for estimation of plasma morphine showed extremely low concentrations. No patients experienced any discomfort during the injection of morphine. These results indicate that morphine 1.0 mg administered intrathecally decreases labour pains to an acceptable level.

Obstetric analgesia. Clinical pharmacokinetic considerations

All drugs used in obstetric analgesia are more or less lipophilic, their site of action is in the central nervous system, and they have good membrane penetrability in the fetomaternal unit. Thus the dose and method of administration as well as the duration of treatment are important clinical determinants of drug effects in the fetus and newborn. In the past, too much emphasis has been placed on fetomaternal blood concentration ratios of different agents; it is now appreciated that the extent of fetal tissue distribution and the neonatal elimination rate are pharmacokinetically much more important. Extensive fetal tissue distribution is reflected in a low fetomaternal drug concentration ratio, which may be followed by prolonged neonatal elimination of the drug. Currently, the most effective and safest method for obstetric analgesia is regional epidural administration of bupivacaine or lignocaine (lidocaine); only low doses are needed and the newborn is able to handle these agents efficiently. On the basis of pharmacokinetic and neurobehavioural assessments, inhalational anaesthetic agents appear to be more attractive than pethidine (meperidine) or benzodiazepines. Intermittent administration and fast pulmonary elimination of inhalational agents ensure that long-lasting residual effects are unlikely to occur. The kinetics of epidural and intrathecal opiates explain the problems associated with their use in obstetrics. Among the newer drugs used in obstetric analgesia, the properties of meptazinol and isoflurane appear interesting and these agents warrant further study. All drugs used in obstetric analgesia have a potentially detrimental effect on the neonate and, therefore, knowledge of fetal and neonatal pharmacokinetics is of importance to the clinician.

Pharmacokinetic aspects of spinal morphine analgesia

Epidural (E.D.) and intrathecal (I.T.) morphine (M) analgesia were studied in patients with pain after thoracotomy. The role of the pharmacokinetic properties of M. for the associated analgesia was also evaluated. M. concentrations in CSF and plasma were assayed using gas chromatography with EC detection. Analgesia was evaluated as the time postoperative until the patients again required analgetics and were given meperidine intramuscularly (I.M.) for thoracic pain. A lumbar site of E.D. and I.T. injection of M. resulted in a variable but in general longlasting postoperative analgesia although delayed after I.T. administration. The mean duration of analgesia after E.D. administration was dose-related (8.6 +/- 2.0 h, 13.0 +/- 3.5 h, and 15.6 +/- 2.6 h; means +/- SEM for the 2, 4 and 6 mg groups, respectively), which was comparable to that achieved after I.T. administration of 0.25 to 0.50 mg M. M. concentrations in plasma after E.D. administration were comparable in variability and magnitude to those found after I.M. administration. The concentrations of M. in plasma were not related to the long duration of analgesia and may only contribute to analgesia shortly after the E.D. administration. The reported time course of analgesia after E.D. injection with a delayed onset corresponded with the appearance of M. in the CSF. Fifteen min after E.D. administration, M. was found in higher concentrations in CSF than in plasma, but peak levels were not seen until 2 h after the injection. Both the high content of M. in CSF as expressed by AUC, as well as peak concentrations in CSF, were related to the longlasting analgesia after E.D. administration. A protracted clearance of M. from the CSF as a cause of longlasting analgesia was not found, M. was eliminated with a similar half-life from CSF and plasma. The high CSF concentrations of M. seen after E.D. administration were the result of a direct uptake across the dura. In contrast, the appearance of M. in CSF after I.M. administration of 10 mg was slower. Maximal concentration of M. in the CSF was reached after 3 h and the peak levels were on average about 100 times less than those found after E.D. injection of 6 mg morphine. CSF and plasma reached pseudoeliquilibrium at a ratio around 0.9 after I.M. administration. This is to be compared with a CSF/plasma concentration ratio around 100 after E.D. administration. A comparison of M. concentrations in the CSF after thoracic and lumbar E.D. injection showed that spinal CSF rapidly yielded comparable concentrations at the lumbar level.(ABSTRACT TRUNCATED AT 400 WORDS)

Opiates, endorphins and the developing organism: a comprehensive bibliography

A comprehensive bibliography of the literature concerned with opiates, endorphins, and the developing organism is presented. A total of 1378 clinical and laboratory references, with citations beginning in 1875, are recorded. A series of indexed accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics. The clinical section is subdivided into: age of subject examined; maternal aspects; effects on the fetus; pharmacology, physiology, and the withdrawal syndrome; and "other" effects on the offspring. The laboratory section is subdivided into: type of opiate/endorphin studied; species utilized; and major subject areas explored.

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

Interest in the use of epidural narcotics for analgesia has been widespread since the demonstration of opiate receptors in the spinal cord in the mid nineteen-seventies. Recently, several studies have attempted to evaluate the effectiveness of epidural narcotics for the relief of pain in labor and after cesarean section. Using the chronically catheterized maternal-fetal sheep model, we injected 5 mg of preservative-free morphine into the epidural space. No statistically significant changes were observed, neither in maternal or fetal arterial pressure and acid-base status, nor in maternal central venous pressure, systemic and pulmonary vascular resistance, cardiac output, or intrauterine pressure (p greater than 0.05). There was a significant, although small, decrease in maternal heart rate (8%) and uterine blood flow (9%) at 120 minutes (p less than 0.05), and then a return to control values. The maternal levels of morphine peaked at 15 minutes (29 ng/ml) and the fetal levels of morphine peaked at 90 minutes (3 to 4 ng/ml). We conclude that the injection of 5 mg of morphine into the maternal epidural space has no adverse effect on mother or fetus in the sheep model.