THE LABOUR IS REPORTED TO BE ONE OFTHE MOST PAINFUL EXPERIENCES IN AWOMAN’S LIFE.
Pain Pathways- First stage of labour- uterine contraction + cervical dilatation. Afferent- visceral afferent from uterus (symathetic) T 10, 11, 12, L 1 posterior segments. Second stage- distension of pelvic floor, vagina and perineum by descending head Afferent- sensory fibres of S 2, 3, 4 (pudendal nerve)
EFFECTS OF PAIN AND STRESS release of adrenocorticotropic hormone, cortisol, catecholamines, and b-endorphins. b-adrenergic agents have uterine relaxant effects and higher epinephrine levels are associated with anxiety and prolonged labour. animal studies indicate that both epinephrine and nor-epinephrine can decrease uterine blood flow in the absence of maternal heart rate and blood pressure changes, contributing to occult fetal asphyxia.
Maternal psychological stress (induced by bright lights or toe clamp) can detrimentally affect uterine blood flow and fetal acid-base status (animal studies) Postpartum women suffer objective deficits in cognitive and memory function when compared with nonpregnant women.
Analgesia for Labor and Delivery Always controversial! “Birth is a natural process” Women should suffer!! Concerns for mother’s safety Concerns for baby Concerns for effects on labor
Analgesia for Vaginal Delivery Psychoanalgesic techniques Acupuncture TENS (transcutaneous electric nerve stimulation) Systemic narcotics Tranquilizers / hypnotics Inhalation analgesia
ANALGESIA FOR LABOURPsychoprophylaxis- nonpharmacologic method Relaxation, concentration on breathing, acupuncture, gentle massage, and partner participation. may be used alone, or in conjunction with parenteral or regional techniques. efficacy of these techniques is largely unproven because of a lack of randomized clinical trials. there are no serious safety concerns with any of these techniques.
Acupuncture Acupuncture alleviates labour pain and reduces use of both epidural analgesia and parenteral opioids. Arranging to have a qualified provider available at the time of delivery may be challenging.
Under Water Delivery No advantage in labour outcome or in reducing the need for analgesia. The request for epidural analgesia was delayed by about 30 minutes. Lack of trials demonstrating safety and the rare but reported unusual complications such as fetal infection or asphyxia.
Others- Intracutaneous sterile water injections- similar gating mechanism as acupuncture. transcutaneous electrical nerve stimulation during labour- made the pain less disturbing, doesn’t decrease it.
Placental Transfer of Drugs:Maternal, Drug, Placental and Fetal Factors Lipid solubility Molecular size Total dose of drug Concentration gradient Maternal metabolism and excretion Degree of ionization pKa of drug, maternal and fetal pH Protein binding - mother and fetus Uterine blood flow
Sedatives Do not possess analgesic qualities. Used early in labour to relieve anxiety or to aid in sleep. Cross the placenta freely. Barbiturates, Phenothiazines, and Benzodiazepines. Barbiturate and benzodiazepines are not used routinely in obstetrics.
Phenothiazines Promethazine (Phenargan) Dose- 25 mg Antagonists are not available. Weak antiemetic. Routine use of promethazine is unnecessary.
Systemic Opioid Analgesia Morphine-like pharmacological activity. Natural- morphine and codeine Semisynthetic- hydromorphone and heroine Synthetic- meperidine and fentanyl Provide sedation and a sense of euphoria. Analgesic effect in labour is limited. Primary mechanism of action is sedation.
Advantages- Easy administration. Inexpensive. Avoids complications of regional block. Does not require skilled personnel. Few serious maternal complications.
Disadvantages- All drugs easily cross placenta. Pain relief inadequate in most cases Maternal sedation Nausea, vomiting, gastric stasis Fetal heart rate effects: Loss of beat-to-beat variability Sinusoidal rhythm Dose-related maternal / neonatal depression Newborn neurobehavioral depression
Treatment of respiratory depression- ventilation, oxygenation, gentle stimulation, naloxone.
Tramadol Centrally acting opioid analgesic used in treating severe pain. Route- IV or IM Dose- 50 mg Emetic. Should be given with antiemetic. Maximum respiratory depression and low apgar score occur in newborns that are delivered within- 3 hours after an IM administration 2 hours after an IV administration.
Meperidine Meperidine 100 mg is roughly equi-analgesic to morphine 10 mg. Side effects- tachycardia, nausea and vomiting, and a delay in gastric emptying. Normeperidine - active metabolite of meperidine, potentiating meperidines depressant effects in the newborn. Concentrations increase slowly, therefore, exerts its effect on the newborn during the second hour after administration. Multiple doses of meperidine = greater accumulation of both meperidine and normeperidine in fetal tissues.
Fentanyl Fast-onset, short-acting synthetic opioid. Requires frequent redosing or the use of a patient- controlled intravenous infusion pump. Fewer neonatal effects and less maternal sedation and nausea. Other opioids are nalbuphine, pentazocine, buprenorphine and butorphanol
Inhalational analgesia Easy to administer (no needles) Nitrous oxide is administered in subanaesthetic concentrations. (N2O 30-50%) Analgesia without loss of consciousness. Crosses the placenta but is eliminated efficiently, no untoward neonatal effects. No effects on uterine contractions. Most effective for short term (1-2 hrs) pain relief Most beneficial in late first stage of labour.
Local and regional techniques Local infiltration Pudendal block Paracervical block Paravertebral (lumbar sympathetic block) Epidural - lumbar (caudal) Spinal Combined spinal-epidural (CSE)
Perineal Infiltration Direct infiltration of 1% lignocaine is used for perineal and lower vaginal lacerations. Advance the needle and inject and aspirate to avoid intravascular injection. Dose of lignocaine is 3-4 mg/kg plain solution, and 7-8 mg/kg with added epinephrine. 1% solution = 10 mg/ml For 6O kg woman total dose should not exceed 200 mg or 20 ml. After local infiltration one should wait 3 minutes before proceeding.
Paracervical block 5 to 6 ml of a dilute solution of local anesthetic without epinephrine (e.g., 1 percent lidocaine or 1 or 2 percent 2-chloroprocaine) is injected into the mucosa of the cervix at the 3- and 9-oclock positions fetal bradycardia that follows in 2 to 70 percent of applications fetal acidosis and death have been reported Paracervical block should be used cautiously at all times and should not be used at all in mothers with fetuses in either acute or chronic distress.
mechanism of postparacervical block bradycardia- local anesthetic injected close to the uterine artery passed to the fetus uterine artery vasoconstriction secondary to a direct effect of the local anesthetic on the uterine artery local anesthetic injected directly into the uterine musculature increases uterine tone
Pudendal nerve block minor regional block, effective and very safe. Using a 20-gauge needle, inject 5 to 10 ml of local anesthetic just below the ischial spine. Because the hemorrhoidal nerve may be aberrant in 50 percent of patients, some prefer to inject a portion of the local anesthetic somewhat posterior to the spine. Although a transperineal approach to the ischial spine is possible, most prefer the transvaginal approach. One-percent lidocaine or 2-percent 2-chloroprocaine can be used
satisfactory for all spontaneous vaginal deliveries and episiotomies, and for some outlet or low operative vaginal deliveries. The potential for local anesthetic toxicity is higher with pudendal block compared with perineal infiltration because of large vessels proximal to the injection site. Aspiration before injection is particularly important.
Regional Analgesia for Labor Epidural (LA or opioids) Spinal (LA ± opioids) CSE- combined spinal epidural (opioids ± LA)
Fetal / Neonatal Effects of RegionalAnalgesia in Labor Uterine perfusion maintained. Profound hypotension & possible fetal compromise. LA toxicity - extremely rare. FHR changes: baseline variability periodic decelerations (due to maternal catecholamine) Neurobehavioral effects absent with current agents.
Epidural Analgesia Epidural block is the most effective and least depressant (pharmacologic option) allowing for an alert, participating mother. (guidelines American College of Obs & gynae) Primary indication is the patients desire for pain relief. Medical indications during labor- selected forms of cardiovascular and respiratory disease, and prevention or treatment of autonomic hyperreflexia in parturients with a high spinal cord lesion.
Epidural analgesia prevents increases in both cortisol and 11-hydroxycorticosteroid levels during labor, but systemically administered opioids do not. Epidural analgesia also attenuates elevations of epinephrine, norepinephrine, and endorphin levels.
Contraindications- Coagulopathy Sepsis Patient’s refusal Fixed cardiac output disease History of allergy to local anaesthetics Thrombocytopenia Hypovolemia
Types- Lumbar- routinely done Caudal- not favoured
Lumbar- Low concentrations of local anesthetic are injected at L2-L5. Affecting the small easily blocked sympathetic nerves that mediate early labour pain. Sparing the sensation of pressure and motor function of the perineum and lower extremities. Dose can be adjusted according to patient’s response.
Choice of epidural local anaestheticLignocaine- rapid onset, dense motor block, risk of cumulative toxicity with repeated doses.Bupivacaine- good sensory block with minimal motor effect. No adverse effect on labour with 0.0625% concentration Highly protein bound, fetal blood concentrations are lower than with other local anaesthetics.
Epidural Opioids in Labour Inadequate analgesics used alone Synergistic with local anesthetics Speedy onset of analgesia Improves quality of analgesia Permits use of very dilute LA solutions Help relieve persistent perineal pain and unblocked segments
Fentanyl and Sufentanil Rapid onset, few side effects Sufentanil slightly more effective No significant fetal drug accumulation No serious adverse neonatal effects with either
Side effects of epidural- hypotension local anesthetic toxicity allergic reaction high or total spinal anesthesia neurologic injury spinal headache. Fetal bradycardia
The effect of epidural analgesia on labour progression, fetal position, and risk of cesarean delivery is controversial. Randomized studies support the conclusion that epidural analgesia results in a modest prolongation of both the first and second stages of labour. Significant increase in the use of oxytocin for labour augmentation.
Increased rate of instrumental delivery. Several well-designed randomized studies suggest that, in settings with baseline low rates of caesarean delivery, epidural analgesia does not increase the risk of caesarean delivery.
Epidural analgesia during labor is associated with an increase in maternal temperature. Dependent on the duration of exposure. Possible mechanisms- noninfectious inflammatory activation, changes in thermoregulation, and acquired intrapartum infection.
Combined spinal epidural Opioids ± LA Rapid onset of intense analgesia. Ideal in late or rapidly progressing labour. Very low failure rate. Less need for supplemental boluses. Minimal motor block (“walking epidural”) Walking epidural- Use of opioid only to allow parturients to ambulate during labour because there is little or no interference with motor function.
Early intrathecal opioids followed by continuous epidural infusion in active labour may be a good option for women desiring regional analgesia, offering superior pain control until active labour has been achieved.
One randomized study found that use of intrathecal opioids increased speed of cervical dilatation and decreased length of labour when compared with conventional epidural. The use of intrathecal opioids improved pain control in early labor without increasing the risk of caesarean delivery. avoids maternal sedation , decreases nausea and vomiting. comparisons of intrathecal opioid analgesia versus epidural or parenteral opioids in labour found the use of intrathecal opioids significantly increases the risk of fetal bradycardia .
Fetal heart rate should be monitored during and after the administration of either epidural or intrathecal medications to allow for timely intrauterine resuscitation. No increase in emergency caesarean delivery.
Conclusions Individualize technique to patient’s goals and stage of labour. Optimize management for spontaneous delivery. Provide safe, cost-effective analgesia.