Analgesics for obstetrics: Nursing pharmacology

Analgesics are medications used to relieve pain, and can be used for various reasons in obstetrics, such as during pregnancy to manage headaches, back, or pelvic pain during delivery to help reduce pain from uterine contractions, cervical stretching, and vaginal distension; as well as following vaginal delivery for perineal lacerations, and following cesarean delivery for pain at the incisional site.

Commonly used analgesics in obstetric settings include acetaminophen, which is mainly used during pregnancy; as well as systemic analgesics like opioids and regional analgesics like local anesthetics, which are typically used once the client goes into labor.

However, other analgesics like NSAIDs, such as ibuprofen, should be avoided during pregnancy, since they can cause fetal harm, including fetal renal impairment, oligohydramnios, and premature closure of the fetal ductus arteriosus.

Now, opioids can be full opioid agonists like fentanyl and remifentanil; and partial opioid agonists like butorphanol and nalbuphine; whereas regional anesthetics include bupivacaine and ropivacaine.

Now, in general, analgesics act by blocking neurons that transmit pain sensations. Opioids act on opioid receptors called the mu, kappa, and delta receptors. These receptors are typically located on the pre- and post-synaptic membranes of the pain-conducting neurons in the spinal cord and brain.

Now, opioids are primarily given orally, intramuscularly, and intravenously. When opioids bind to their receptors, they result in a decreased sensitivity to pain by increasing the pain threshold and altering pain transmission.

On the other hand, regional anesthetic medications act by reversibly blocking sodium channels on the neurons and prevent the transmission of pain.

Regional anesthetics can either be injected locally into the pudendal nerve area, called a pudendal anesthesia or nerve block, to numb the lower vagina, vulva, and perineum, which is often used in the repair of episiotomy, or perineal tears.

Now, neuraxial anesthesia, which refers to the injection of opioids combined with a local anesthetic into either the epidural space or the subarachnoid space of the spinal cord, is an effective way to numb larger areas, especially in clients who experience severe labor pains or require a cesarean birth.

Okay, so each class of analgesics has its own set of side effects. Opioids can result in respiratory depression, nausea, vomiting, and constipation, as well as pruritus, hypotension, sedation, euphoria, and confusion.

Additionally, opioids can cause a decrease in the frequency and duration of uterine contractions. Finally, opioids can cross the placenta and cause fetal bradycardia and reduced variability of fetal heart rate, as well as hypotonia, or reduced muscle tone at birth.

On the other hand, side effects of regional anesthetics vary based on the medication and route of administration. Common side effects seen with epidural and spinal anesthesia include accidental injury to the spinal cord, motor weakness, infection, and maternal hypotension, which can further reduce placental blood flow and cause fetal asphyxia.

Occasionally, the anesthetic agent can migrate above the administered level and even reach the brainstem, leading to respiratory depression.

When the client is recovering from spinal anesthesia or if there is an accidental dural puncture during epidural catheter placement, a common side effect is headache.

Lastly, systemic toxicity with a local anesthetic during epidural anesthesia may result in cardiac arrest or even death.

Now, most analgesics are generally avoided after the first trimester of pregnancy and until labor begins. And, due to their addictive potential, prolonged use of opioids can cause neonatal abstinence syndrome.

Opioids are also contraindicated in those with respiratory disorders like asthma, since they may cause respiratory depression.

Moreover, opioids should not be combined with central nervous system or CNS depressants, such as barbiturates or benzodiazepines, since their effects may add up, causing coma or even death.

Lastly, local anesthetics are contraindicated in those with bleeding disorders, or with a skin infection at the catheter insertion site that may spread to the spinal cord and brain.

As a nurse caring for a client in labor, you will be providing non-pharmacological comfort measures and administering medications for pain management.