Neuraxial opioids have contributed significantly to improved labor and postcesarean delivery analgesia. In the obstetric population, epidural and intrathecal opioids are associated with a very low risk of clinically significant respiratory depression. Although rare, respiratory depression is a serious risk; patients may die or suffer permanent brain damage as a consequence. This review discusses the mechanism and incidence, as well as the prevention, detection, and management of respiratory depression with morphine, extended-release epidural morphine, and lipophilic opioids in the labor and cesarean delivery setting.

◊ Reviewed by M. Van de Velde, MD, PhD
Department of Anaesthesiology, U.Z. Leuven, Leuven, Belgium

The present review describes in detail the mechanism, incidence and risks of respiratory depression after administration of neuraxial opioids during labor or following Cesarean section. The effects of morphine, slow release morphine and lipophilic drugs are described. The paper also discusses prevention and treatment.

Neuraxial opioids have been involved in causing respiratory depression with serious sequelae (permanent brain damage and death). The incidence of respiratory depression in non-obstetric patients varies between 0.01 to 7% depending on the definition used. In obstetric patients, the reported incidence was 0.2% with lipophilic intrathecal opioids.

Morphine is most likely the substance with the highest risk especially because of late onset respiratory depression. An incidence between 0 and 0.4 % has been described in the cesarean setting. However, the respiratory side effects are dose-dependent. Continuous epidural infusions of lipophilic opioids result in increasing plasma concentrations and may decrease ventilatory response. Apparently, serious respiratory side effects have not been reported.

Dr. Carvalho gives clear dosing advice for the various drugs in use. He correctly points out that increasing the dose does not produce better analgesia but increases the risk of serious side effects. Maximum doses are described for both labor and cesarean section as well as for intrathecal and epidural use.

It is important to be aware of the risk factors such as morbid obesity and associated conditions such as sleep apnea. However, quite correctly, Dr. Carvalho points out that due to the respiratory stimulant effects of progesterone the risk to develop respiratory depression in pregnant women is reduced. However, the reported problems of respiratory depression are common in obese parturients. He also correctly points out that the combination of neuraxial opioids with magnesium or other sedative drugs should be avoided or requires careful monitoring.

In summary, neuraxial opioids are extremely safe and efficacious drugs when given during labor. However, a potential risk of respiratory depression exists. The analgesic benefits outweigh the risks of a rare respiratory event. It is important to stick to recommended doses, to be cautious when parenteral opioids have already been administered, and to be aware of the significantly increased risk of respiratory depression when morbidly obese patients receive neuraxial opioids.