Analgesia & Anesthesia
Contribution of the departments of Obstetrics and Gynecology and Anesthesiology of St. Elizabeth’s Medical Center (Boston) and Women’s Health & Education Center (WHEC).
The terms analgesia and anesthesia are sometimes confused in common usage. Obstetric analgesia is the loss or regulation of pain perception during labor. It may be local and affect only a small area of the body; regional and affect a larger portion; or systemic. Analgesia is achieved by the use of hypnosis (suggestion), systemic medication, regional agents, or inhalation agents. Anesthesia is the total loss of sensory perception, and may include loss of consciousness. It is induced by various agents and techniques. In obstetrics, regional anesthesia is accomplished with local anesthetic techniques (epidural, spinal) and general anesthesia with systemic medication and endotracheal intubation. Maternal mortality relating to anesthesia has reduced 10-fold since the 1950s, largely due to an enhanced appreciation of special maternal risks associated with anesthesia. Ideally, obstetric deliveries today should be conducted only in hospitals where equipment and specially trained personnel are available.
The purpose of this document is to help obstetricians and gynecologists understand the available methods of pain relief to facilitate communication with their colleagues in the field of anesthesia, there-by, optimizing patient care. It is helpful in decreasing maternal and neonatal mortality and morbidity. Labor results in severe pain for many women. Pain management should be provided whenever it is medically indicated. The use of techniques and medications to provide pain relief in obstetrics requires and expert understanding of their effects to ensure the safety of both mother and fetus.
Anatomy of Pain:
Uterine contractions and cervical dilatation result in visceral pain (T-10 through L-1). As labor progresses, the descent of the fetal head and subsequent pressure on the pelvic floor, vagina, and perineum generate somatic pain transmitted by the pudendal nerve (S2-4). The evolution of pain in the first stage of labor was originally described as involving spinal segments T11 and T12 (Cleland J). Subsequent research has determined that segments T10-L1 are involved (Bonica, 1972). Discomfort is associated with ischemia of the uterus during contraction as well as dilatation and effacement of the cervix (1). Sensory pathways that convey nociceptive impulses of the first stage of labor include the uterine plexus, the lumbar and lower thoracic sympathetic chain, and the T10-L1 spinal segments. Pain in second stage of labor undoubtedly is produced by distention of the vagina and perineum. Sensory pathways from these areas are conveyed by branches of the pudendal nerve via the dorsal nerve of the clitoris, the labial nerves, and the inferior hemorrhodial nerves. These are the major sensory branches to the perineum and are conveyed along nerve roots S2, S3, S4.
Dystocia, which is usually painful, may be due to feto-pelvic disproportion; tetanic, prolonged, or dysrhythmic uterine contractions; intrapartum infection; or many other causes. Substantial advances in the quality and safety of obstetric anesthesia have been made in the past 3 decades. Outdated techniques such as “twilight sleep” and mask anesthesia have been recognized as ineffective or unsafe and have been replaced by epidural infusion of narcotic/local anesthesia mixtures, patient-controlled analgesic during labor, and postoperatively. When required general anesthesia is provided using short-acting drugs with well-known fetal effects, and careful attention is focused on airway management.
Techniques of analgesia without the use of drugs:
Three distinct psychological techniques have been developed as a means of facilitating the birth process and making it a positive emotional experience: “natural childbirth”, psychoprophylaxis, and hypnosis. So-called natural childbirth was developed by Grantly Dick-Read in early 1930s and popularized in his book Childbirth Without Fear. Dick-Read’s approach emphasized the reduction of tension to induce relaxation. In Russia in the mid 1950s, it became evident that obstetric psychoprophylaxis was a useful substitute for poorly administered or dangerously conducted anesthesia for labor and delivery. This method later induced in France by Lamaze. Hypnosis for pain relief has achieved periodic spurts of popularity since the early 1800s and depends on the power of suggestion.
It should be obvious that none of the psychophysical techniques should be “forced” on a patient, even by a skillful practitioner. The patient must not be made to feel that she will fail if she does not choose to complete her labor and delivery without analgesic medication. It must be made clear to her from the outset that she is expected to ask for help if she feels she wants or needs it. All things considered, psychophysical techniques should be viewed as adjuncts to other analgesic methods rather than substitutes for them.
Psychoprophylaxis:
A currently popular technique of “psycho-physiologic preparation” involves educating the patient about her body functions and physiology of labor. Positive attitudes and the need for good medical care are stressed. The goal of this technique is to use few if any drugs during first and second stages of labor. Under optimal circumstances the need for narcotic drugs in the first stage of labor is reduced or eliminated altogether. When combined with certain analgesic “regional techniques” for late first-stage pain relief and second-degree analgesia - it approaches the ideal in management of pain relief for the childbirth experience. For maximum effectiveness, the husband should be instructed and included in the management of pain of the first and second stages of labor. His presence alone is reassuring, and the “coach”. These techniques can significantly reduce anxiety, tension, and fear. They also provide the parturient with a valuable understanding of the physiologic changes that occur during labor and delivery (2).
The effectiveness of hypnosis is partially due to the well-known, although incompletely understood mechanisms by which emotional and other central processes can influence a person’s total responses to the pain experience. Verbal suggestion and somato-sensory stimulation may help to alleviate discomfort associated with the first stage of labor. In addition, hypnotic stage may provide apparent analgesia and amnesia for distressing, anxiety-provoking experiences. Finally, hypnotic techniques may substantially improve the patient’s outlook and behavior by reducing fear and apprehension. However, there are certain practical points to consider in regard to hypnosis because the time needed to establish a suitable relationship between physician and patient is often more than can be made available in the course of a busy medical practice.
Analgesic & Anesthetic Agents:
The general comments and precautions are:
- If the patient is prepared psychologically for her experience, she will require less medication. Anticipate and dispel her fears during the antenatal period and in early labor. Never promise a painless labor.
- Individualize the treatment of every patient, because each one reacts differently. Unfavorable reactions to any drugs can occur.
- Know the drug you intend to administer. Be familiar with its limitations, dangers, and contraindications as well as its advantages.
- All analgesics given to the mother will cross the placenta. Systemic medications produce higher maternal and fetal blood levels than regionally administered drugs. Many drugs have central nervous system depressant effects. Although they may afford the desired effect on the mother, they may exert a mild to severe depressant effect on the fetus or newborn.
- The ideal drug will have an optimal beneficial effect on the mother and a minimal depressant effect on the fetus or newborn. None of the presently used narcotic and sedative medications used in obstetrics has selective maternal effects.
- The regional administration of local anesthetics accomplished this goal to a large extent because the low maternal serum levels that are produced expose the fetus to insignificant drug mass.
Parenteral Agents for Labor Pain:
Various opioid agonists and opioid agonist-antagonists are available for systemic analgesia. These agents can be given in intermittent doses on patient’s request or via patient-controlled administration. Recent reports suggest that the analgesic effect of parenteral agents used in labor is limited, and the primary mechanism of action is heavy sedation. Although regional analgesia provides superior pain relief, some women are satisfied with the level of analgesia provided by narcotics when large enough doses are used. However, patients exposed to doses of this magnitude are at increased risk of aspiration and respiratory arrest. The use of shorter-acting agents, such as patient-controlled administration of fentanyl, may decrease some of the neonatal risks posed by meperidine. The decision to use parenteral agents to manage labor pain should be made in collaboration with the patient after a careful discussion of the risks and benefits (4).
Commonly used parenteral agents are (3): Abbreviations; IM (intramuscularly), IV (intravenously).
- Fentanyl – 50-100 micro g (IV) dose, frequency 1 hour; onset of pain relief is in 1 minute and neonatal half-life is 5.3 hours.
- Meperidine – 25-50 mg (IV) dose, frequency every 1-2 hour; onset of pain relief in 5 minutes and neonatal half-life is 13-22.4 hours. OR - 50-100 mg (IM) dose, frequency every 2-4 hour; onset of pain relief in 30-45 minutes and neonatal half-life 63 hours for active metabolites.
- Nalbuphine – 10 mg (IV or IM) dose, every 3 hours; onset of pain relief in 2-3 minutes (IV) and 15 minutes (IM) and neonatal half-life is 4.1 hours.
- Butorphanol – 1-2 mg (IV or IM) dose, every 4 hours; onset of pain relief in 1-2 minutes (IV) and 10-30 minutes (IM) and neonatal half-life for IV dose not known, for IM dose it is similar to nalbuphine in adults.
- Morphine – 2-5 mg (IV) or 10 mg (IM) every 4 hours; onset of pain relief in 5 minutes (IV) and 30-40 minutes (IM) and neonatal half-life is 7.1 hours.
In summary, the rate of placental transfer of a drug is governed mainly by (1) lipid solubility, (2) degree of drug ionization, (3) placental blood flow, (4) molecular weight, (5) placental metabolism, and (6) protein binding.
Regional Analgesia:
In obstetric patients, regional analgesia refers to a partial to complete loss of pain sensation below the T8 to T10 level. In addition, a varying degree of motor blockade may be present, depending on the agents used. Regional anesthesia is achieved by injection of a local anesthetic around the nerves that pass from spinal segments to the peripheral nerves responsible for sensory innervations of a portion of the body. More recently, narcotics have been added to local anesthetic to improve analgesia and reduce some side effects of local anesthetics. Regional nerve blocks used in obstetrics include the following; (1) lumbar epidural and caudal epidural block, (2) subarachnoid (spinal) block, and (3) pudendal block. Paracervical block is no longer considered a safe technique for the obstetric patient. In the past, paracervical anesthesia was used to relieve the pain of the first stage of labor. Many now consider paracervical block to be contraindicated in obstetrics because of the potential adverse side effects like fetal bradycardia and suggested incidence is about 20%-25%.
Local Infiltration Analgesia:
Local tissue infiltration of dilute solutions of anesthetic agents generally yields satisfactory results because the target is the fine nerve fibers. This is commonly used at episiotomy site. The dangers of systemic toxicity are seen when large areas are anesthetized or when re-injection is required. It is a good practice, therefore, to calculate in advance the milligrams of drug in the volume of solution that may be required to keep the total dosage below the accepted toxic dose. Infiltration in or near an area of inflammation is contraindicated. Injections into these zones may be followed by rapid systemic absorption of the drug due to the increased vascularity of the inflamed tissues. Moreover, the injection may introduce or aggravate infection.
Epidural:
Epidural analgesia offers the most effective form of pain relief and is used by most women in the United States. In most obstetric patients, the primary indication for epidural analgesia is the patient’s desire for pain relief. The advantage of this method is that medication can be titrated over the course of labor as needed. In addition, epidural catheters placed for labor analgesia can be used for cesarean delivery or postpartum tubal ligation. Modern epidural preparations that combine a low-dose local anesthetic, such as bupivacaine, levobupivacaine, or ropivacaine, with an opioid agonist are preferred because they decrease motor blockade and result in an increased rate of spontaneous vaginal delivery. Some women who receive epidural analgesia may be candidates for ambulation (5).
Common complication of epidural anesthesia are: hypotension, fever >100.40 (excess rate over women treated with narcotics), post-dural puncture headache, transient fetal heart decelerations, pruritis (with added opioid only) and inadequate pain relief.
Spinal:
Single-shot spinal analgesia provides excellent pain relief for procedures of limited duration, such as cesarean delivery, the second stage of labor, rapidly progressing labor, and postpartum tubal ligation. A long-acting local anesthetic often is used, with or without and opioid agonist. The duration of anesthesia is approximately 30-250 minutes depending on the drugs used. However, because of its inability to extend the duration of action, single-shot spinal analgesia is of limited use for the management of labor. The advantages of spinal anesthesia are that no fetal hypoxia ensues unless hypotension occurs, blood loss is minimal and the mother remains conscious to witness delivery, no inhalation anesthetics or analgesic drugs are required. The technique is not difficult and good relaxation of the pelvic floor and lower birth canal is achieved. Prompt anesthesia is achieved within 5-10 minutes and there are fewer failures than with epidural anesthesia. Complications are fewer and easy to treat. Hypotension is rare with the doses used. Spinal headache occurs in 1-2% of patients, however, and operative delivery is more often required because voluntary expulsive efforts are eliminated. Respiratory failure may occur if the anesthetic ascends within the spinal cord due to rapid injection or straining by the patient.
General Anesthesia:
Because general anesthesia results in a loss of maternal consciousness, it must be accompanied by airway management by trained anesthesia personnel. Nitrous oxide may be supplemented with halogenated hydrocarbons, such as isoflurane, desflurane, and sevoflurane, at low concentrations. The use of intravenous agents, such as sodium pentothal, followed by rapid sequence induction is used to minimize the risk of aspiration. All inhaled anesthetic agents readily cross the placenta and have been associated with neonatal depression. Ideally, induction-to-delivery time should be minimized when general anesthesia is used. Fetal exposure of more than 8 minutes can be associated with increased neonatal depression (6). Loss of airway reflexes and aspiration are causes of maternal mortality. Halogenated agents are potent uterine relaxants when administered in high inhalation concentrations. This property can be useful for internal podalic version or fetal entrapment (either during vaginal or cesarean delivery). Increased relaxation, however, is a concern because of its potential for increasing blood loss during cesarean delivery (7). For both elective and indicated cesarean delivery, agents to decrease gastric acidity should be used. Sodium citrate with citric acid has been shown to neutralize the gastric contents of 88.5% of women undergoing cesarean delivery and should be administered when the decision is made to perform cesarean delivery. A fasting period of 6-8 hours is preferable before general anesthesia is administered to reduce gastric aspiration.
Summary:
Complications of anesthesia remain an important and often preventable cause of pregnancy-related mortality, accounting for more than 5% of maternal deaths. Anesthesia-related maternal mortality has decreased with time and is currently estimated at 1.7 per 1,000,000 live births. The increased safety of regional analgesia has increased the relative risk of general anesthesia; the case fatality rate of general anesthesia for cesarean delivery is estimated to be approximately 32 per 1,000,000 live births compared with 1.9 per 1,000,000 live births for regional anesthesia (8). Regional analgesia provides a superior level of pain relief during labor when compared with systemic drugs and therefore should be available to all women. Parenteral pain medications for labor pain decrease fetal heart rate variability and may limit the obstetrician-gynecologist’s ability to interpret the fetal heart rate tracing. Consideration should be given to other drugs in the setting of diminished short- or long-term fetal heart rate variability.
References:
- Bonica JJ. Principles and Practice of Obstetric Analgesia and Anesthesia. FA Davis, 1994.
- American College of Obstetricians and Gynecologists. Pain relief during labor. ACOG Committee Opinion 231. Washington DC: 2000 (Level III)
- ACOG Practice Bulletin. Obstetric Analgesia and Anesthesia. Clinical management guidelines for obstetricians and gynecologist. Number 36, July 2002.
- Howell CJ. Epidural versus non-epidural analgesia for pain relief in labour. (Cochrane Review). In: The Cochrane Library, Issue 2, 2002. Oxford: Update Software (Meta-analysis).
- American College of Obstetricians and Gynecologists. Task Force of Cesarean Delivery Rates. Evaluation of cesarean delivery. Washington DC: ACOG, 2000 (Level III).
- Datta S, Ostheimer GW, Weiss JB et al. Neonatal effect of prolonged anesthetic induction for cesarean section. Obstet Gynecol, 1981; 58:331-335.
- Cunningham FG, Gant NF, Levno KJ, Gilstrap LC, Hauth JC, Wenstrom KD. Analgesia and anesthesia. In: Williams Obstetrics. 21st ed. New York: McGraw-Hill, 2001:361-383 (Level III).
- Panchal S, Arria AM, Labhetwar SA. Maternal mortality during hospital admission for delivery: a retrospective analysis using a state-maintained database. Anesth Analg. 2001;93:134-141 (Level II-3).
Published: 30 September 2009
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