Analgesics and anestheia

This topic includes Introduction for analgesia and anesthesia used in obstetrics, maternal risk factors for anesthesia, anatomical and physiological considerations, analgesia during labour and delivery, sedatives and analgesia, opioid analgesics, combination of narcotics and antiemetics, inhalation methods, commonly used local anesthesia in obstetrics, spinal anesthesia, infiltration anesthesia, patient controlled anesthesia, psychoprophylaxis, general anesthesia for cesarean section, complication of general anesthesia and its management.

1. ANALGESIA AND ANESTHESIA IN OBSTETRICS BY, MS. PRIYANKA GOHIL MSc (N) OBG PhD SCHOLAR

2. INTRODUCTION Relief of pain during labor and delivery is an essential part in good obstetric care. Choice of anesthesia depends upon the patient’s conditions and the associate disorders. Anesthetic complications may cause maternal death. Anesthesia following full meal may cause maternal death due to vomiting and aspiration of gastric contents.

3. Maternal risk factors for anesthesia are: Short stature S hort neck M arked obesity S evere preeclampsia B leeding disorders P lacenta previa M edical disorders like cardiac, respiratory and neurological disease

4. ANATOMICAL AND PHYSIOLOGICAL CONSIDERATIONS NERVE SUPPLY OF THE GENITAL TRACT :- Uterus is under both nervous and hormonal control. Hypothalamus controls the uterine activity through the reticular formation which balances the effects of the two autonomic divisions.

5. MOTOR NERVE SUPPLY :- The uterus receives both sympathetic and parasympathetic nerve fibers. The sympathetic nerve fibers arise from lower thoracic and upper lumbar segments of the spinal cord. The parasympathetic fibers arise from sacral 2, 3 and 4 segments of the spinal cord.

6. The preganglionic fibers of the sympathetic nerves arising from the spinal cord pass through the ganglia of the sympathetic trunk to aorticorenal plexus where they synapse. The aorticorenal plexus continues as the superior hypogastric plexus or presacral nerve and passes over the bifurcation of aorta and divides into right and left hypogastric nerves. Each hypogastric nerve joins the pelvic parasympathetic nerve of the corresponding side and forms the pelvic plexus (right and left) or inferior hypogastric plexus. The pelvic plexus then continues along the course of the uterine artery as paracervical plexus on each side of the cervix.

7. SENSORY PATHWAY :- Sensory stimuli from the uterine body are transmitted through the pelvic, superior hypogastric and aorticorenal plexus to the 10 th , 11 th and 12 th dorsal and the first lumbar segments of the spinal cord. Sensory stimuli from cervix pass through the pelvic plexus along the pelvic parasympathetic nerves to sacral segments 2, 3 and 4 of the spinal cord.

8. Sensory stimuli from upper vagina pass to 2, 3 and 4 sacral parasympathetic segments and from lower vagina pass through the pudendal nerve. The perineum receives both motor and sensory innervation from sacral roots 2, 3 and 4 through the pudendal nerve. The branches of ilioinguinal and genital branch of genitofemoral nerves supply the labia majora and also carry the impulses from the perineum.

9. NERVOUS CONTROL OF THE UTERINE CAVITY :- Regarding motor innervation of the uterus, the sympathetic nerves rather than the parasympathetic have the influences over the uterine activity.

10. HORMONAL CONTROL :- It is generally agreed that intact nerve supply is not essential for the initiation and progress of labor. Total spinal block does not inhibit uterine activity, provided blood pressure is not allowed to fall, and normal vaginal delivery can occur in the paraplegic patient. It is believed that some hormones are essential for the control of uterine activity.

11. Oxytocin, a hormone derived from posterior pituitary maintains the uterine activity during labor. Progesterone is the pregnancy–stabilizing hormone. Labor commences when it is withdrawn. Adrenaline with its beta activity inhibits the contraction of uterus, while its alpha activity excites it.

12. ANALGESIA DURING LABOUR AND DELIVERY Pain during labor results from a combination of uterine contractions and cervical dilatation. During cesarean delivery incision is usually made around the T12 dermatome anesthesia is required from the level of T4 to block the peritoneal discomfort. Labor pain is experienced by most women with satisfaction at the end of a successful labor. Antenatal (mothercraft) classes, sympathetic care and encouraging environment during labor can reduce the need of analgesia.

13. Drugs have an important part to play in the relief of labor pain but it must not be supposed that they are of greater importance than proper preparation and training for childbirth. The intensity of labor pain depends on the intensity and duration of uterine contractions, degree of dilatation of cervix, distension of perineal tissue, parity and the pain threshold of the subject. The most distressing time during the whole labor is just prior to full dilatation of the cervix.

14. The ideal procedure should produce efficient relief of pain but should neither depress the respiration of the fetus nor depress the uterine activity causing prolonged labor. The drug must be nontoxic and safe for both mother and fetus. But it is regretted that no such agent is available at present that fulfills all these conditions. Every case of labor does not require analgesia and only sympathetic explanation may be all that is required.

15. SEDATIVES AND ANALGESIA The following factors are important to control the dose of sedative and analgesics: Pain threshold : The threshold of pain varies from patient to patient. Some patients experience severe pain though the uterine contractions are relatively weak. In such cases, it is preferable to control the pain adequately.

16. 2. Parity : The multiparous women need less analgesia due to added relaxation of the birth canal and rapid delivery. 3. Maturity of the fetus : Minimal doses of drugs are indicated while the fetus is thought to be premature to avoid neonatal asphyxia.

17. For the purpose of selecting a general analgesic drug, labor has been divided arbitrarily into two phases . The first phase corresponds up to 8 cm dilatation of the cervix in primigravidae and 6 cm in case of multipara. The second phase corresponds to dilatation of the cervix beyond the above limits up to delivery. The first phase is controlled by sedatives and analgesics, and the second phase is controlled by inhalation agents. The idea is to avoid the risk of delivery of a depressed baby.

18. OPOID ANALGESICS PETHIDINE: For a long time pethidine has been used as an analgesic in labor. It has got strong sedative but less analgesic efficacy. Pethidine is generally used in the early first stage of labor and indicated when the discomfort of labor merges into regular, frequent and painful contractions. The initial dose is 100 mg (1.5 mg/kg body weight) IM and repeated as the effect of the first dose begins to wane, without waiting for the reestablishment of labor pain.

19. The side effects of pethidine to the mother are nausea, vomiting, delayed gastric emptying. Ranitidine should be given to inhibit gastric acid production, and emetic effect is counteracted by metoclopramide (10 mg IM) . Pethidine crosses the placenta and accumulates in fetal tissues. Pethidine reduces baseline variability, depresses respiration and suckling of the newborn when administered before delivery.

20. MEPERIDINE Compared to morphine, analgesic effect is one tenth, but respiratory depression effect is less. It is used 25–50 mg (1–3 mg/kg IM) or a PCA (patient controlled analgesia) pump 15 mg every 10 minutes. Repeated use or PCA in labor, infants may need naloxone at delivery. Maximum placental transfer and neonatal depression occur 2–3 hours of use.

21. FENTANYL Fentanyl is a short acting synthetic opioid and is equipotent to pethidine. It has less neonatal effects and less maternal nausea and vomiting. It needs frequent dosing. It can be used as PCA.

22. PHENOTHIAZINES Promethazine (phenergan) is commonly used in labor in combination with an opioid. It does not cause major neonatal depression. Promethazine is a weak antiemetic drug and causes sedation in the mother.

23. NARCOTIC ANTAGONIST Narcotic antagonists are used to reverse the respiratory depression induced by opioid narcotics.

24. NALOXONE Naloxone is given to mother 0.4 mg IV in labor. It may have to be repeated. It is given to the newborn 10 μg/kg IM or IV and is repeated if necessary when the infant is born with narcotic depression. Naloxone is given to a newborn born of a narcotic addicted mother, with proper ventilation arrangement only otherwise withdrawal symptoms are precipitated.

25. BENZODIAZEPINES (DIAZEPAM) It is well tolerated by the patient. It does not produce vomiting and helps in the dilatation of cervix. It is metabolized in the liver. The usual dose is 5–10 mg. It may be used in larger doses in the management of preeclampsia. However, diazepam is avoided in labor.

26. Major disadvantages are: Loss of beat to beat variability in labor, neonatal hypotonia and hypothermia. Flumazenil is a specific benzodiazepine antagonist. It can reverse the respiratory depression effect of benzodiazepines.

27. COMBINATION OF NARCOTICS AND ANTIEMETICS Narcotics may be used in combination with promethazine, metoclopramide or ondansetron. The advantages claimed that the combination potentiates the action of narcotic, produces less respiratory depression and prevents vomiting. But there are also disadvantages like hypotension and delay of second stage of labor.

28. INHALATION METHODS PREMIXED NITROUS OXIDE AND OXYGEN (Entonox): Cylinders contain 50% nitrous oxide and 50% oxygen mixture. Entonox apparatus has been approved for use by midwives. This agent is used in the second phase (from 8 cm dilatation of cervix to delivery). It can be self administered. Entonox is most commonly used inhalation agent during labor in the UK.

29. Hyperventilation, dizziness, hypocapnia are the side effects. The woman is to take slow and deep breaths before the contractions and to stop when the contractions are over. The woman should be monitored with pulse oximetry.

30. COMMONLY USED LOCAL ANESTHESIA IN OBSTETRICS

31. REGIONAL (NEURAXIAL) ANESTHESIA When complete relief of pain is needed throughout labor, epidural analgesia is the safest and simplest method for procuring it. It provides sensory as well as various degrees of motor blockade over a region of the body. But anesthetists/obstetricians have to be trained properly to make use of this very valuable method in normal and abnormal labor.

32. CONTINOUS LUMBAR EPIDURAL BLOCK A lumbar puncture is made between L2 and L3 with the epidural needle (Tuohy needle). With the patient on her left side, the back of the patient is cleansed with antiseptics before injection. When the epidural space is ensured, a plastic catheter is passed through the epidural needle for continuous epidural analgesia. A local anesthetic agent (0.5% bupivacaine) is injected into the epidural space. Full dose is given after a test dose when there is no toxicity.

33. For cesarean delivery a block from T4 to S1 is needed. Repeated doses (top ups) of 4–5 mL of 0.5% bupivacaine or 1% lignocaine are used to maintain analgesia. Epidural analgesia, as a general rule should be given when labor is well established. Maternal hydration should be adequate with normal saline or Hartmann’s solution (crystalloid) infusion prior commencing the blockade.

34. The patient’s blood pressure, pulse and the fetal heart rate should be recorded at 15 minutes interval following the induction of analgesia and hypotension, if occurs, should be treated immediately. The woman is kept in semilateral position to avoid aortocaval compression.

35. CONTINOUS LUMBAR EPIDURAL BLOCK Epidural analgesia is especially beneficial in cases like pregnancy-induced hypertension, breech presentation, twin pregnancy and preterm labor. Previous cesarean section is not a contraindication. Epidural analgesia when used there is no change in duration of first stage of labor. But second stage of labor appears to be prolonged by 15–30 minutes. This might lead to frequent need of instrumental delivery like forceps or ventouse.

36. PARACERVICAL NERVE BLOCK Paracervical nerve block is useful for pain relief during the first stage of labor. Following the usual antiseptic safe guards, a long needle (15 cm or more) is passed into the lateral fornix, at the 3 and 9 o’clock positions. Five to ten milliliter of 1% lignocaine are injected at the site of the cervix and the procedure is repeated on the other side. This dose is quite sufficient to relieve pain for about an hour or two, and injections can be given more than once if necessary.

37. Bupivacaine is avoided due to its cardiotoxicity. Paracervical block should not be used where placental insufficiency is present. Although paracervical block may be used from 5 cm dilatation of the cervix, it is most useful toward the end of the first stage of labor to remove the desire to bear down earlier. Paracervical block can only relieve the pain of uterine contraction and the perineal discomfort is removed by pudendal nerve block. Fetal bradycardia is a known complication.

38. This is due to decreased placental perfusion resulting from uterine artery vasoconstriction or its direct depressant effect on the fetus following transplacental transfer. This method is not commonly used.

39. PUDENDAL NERVE BLOCK It is a safe and simple method of analgesia during delivery. Pudendal nerve block does not relieve the pain of labor but affords perineal analgesia and relaxation. Pudendal nerve block is mostly used for forceps and vaginal breech delivery. Simultaneous perineal and vulval infiltration is needed to block the perineal branch of the posterior cutaneous nerve of the thigh and the labial branches of the ilioinguinal and genitofemoral nerves (vide supra). This method of analgesia is associated with less danger, both for mother and baby than general anesthesia.

40. Technique: The pudendal nerve may be blocked by either the transvaginal or the transperineal route. Transvaginal route: Transvaginal route is commonly preferred. A 20 mL syringe, one 15 cm (6”) 22 gauge spinal needle and about 20 mL of 1% lignocaine hydrochloride are required. The index and middle fingers of one hand are introduced into the vagina, the finger tips are placed on the tip of the ischial spine of one side.

41. The needle is passed along the groove of the fingers and guided to pierce the vaginal wall on the apex of ischial spine and thereafter to push a little to pierce the sacrospinous ligament just above the ischial spine tip. After aspirating to exclude blood, about 10 mL of the solution is injected. The similar procedure is adopted to block the nerve of the other side by changing the hands.

42. COMPLICATIONS Hematoma formation, infection and rarely intravascular injection or allergic reaction. Toxicity may affect: CNS: excitation, ringing in the ears and convulsions. Cardiovascular: tachycardia, hypotension, arrythmias, even cardiac arrest.

43. SPINAL ANESTHESIA Spinal anesthesia is obtained by injection of local anesthetic agent into the subarachnoid space. It has less procedure time and high success rate. Spinal anesthesia can be employed to alleviate the pain of delivery and during the third stage of labor. For normal delivery or for outlet forceps with episiotomy, ventouse delivery, block should extend from T10 (umbilicus) to S1.

44. For cesarean delivery level of sensory block should be up to T4 dermatome. Hyperbaric bupivacaine (5–10 mg) or lignocaine (25–50 mg) is used. Addition of fentanyl (to enhance the onset of block) or morphine (to improve pain control) may be done. Brief or minimal spinal anesthesia is far safer than prolonged spinal anesthesia.

45. The advantages of spinal anesthesia are: less fetal hypoxia unless there is hypotension minimal blood loss. The technique is not difficult and no inhalation anesthesia is required, but postspinal headache occurs in 5–10% of patients. Spinal anesthesia can be obtained by injecting the drug into the subarachnoid space of the third or fourth lumbar interspace with the patient lying on her side with a slight head uptilt.

46. The blood pressure and respiratory rate should be recorded every 3 minutes for the first 10 minutes and every 5 minutes thereafter. Oxygen should be given for respiratory depression and hypotension. Sometimes vasopressor drugs may be required if a marked fall in blood pressure occurs. It is used during vaginal delivery, forceps, ventouse and cesarean delivery.

47. Combined spinal-epidural analgesia (CSE): An introducer needle is first placed in the epidural space. A small gauge spinal needle is introduced through the epidural needle into the subarachnoid space (needle through needle technique). A single bolus of 1 mL 0.25% bupivacaine with 25 μg fentanyl is injected into the subarachnoid space. The spinal needle is then withdrawn.

48. An epidural catheter is thus sited for repeated doses of anesthetic drug. The method gives rapid and effective analgesia during labor and cesarean delivery. It allows women to move (walking epidural) during labor.

49. INFILTRATION ANALGESIA Perineal infiltration: For episiotomy: Perineal infiltration anesthesia is extensively used prior to episiotomy. A 10 mL syringe, with a fine needle and about 8–10 mL 1% lignocaine hydrochloride (Xylocaine) are required. The perineum on the proposed episiotomy site is infiltrated in a fanwise manner starting from the middle of the fourchette. Each time prior to infiltration, aspiration to exclude blood is mandatory. Episiotomy is to be done about 2–5 minutes following infiltration.

50. For outlet forceps or ventouse: (Perineal and labial infiltration): The combined perineal and labial infiltration is effective in outlet forceps operation or ventouse traction. A 20 mL syringe, a long fine needle and about 20 mL of 1% lignocaine hydrochloride are required. The needle is inserted just posterior to the introitus. About 10 mL of the solution is infiltrated in a fanwise manner on both sides of the midline (as for episiotomy). The needle is then directed anteriorly along each side of the vulva as far as the anterior-third to block the genital branch of the genitofemoral and ilioinguinal nerve. Five milliliter is required to block each side

51. Local abdominal for cesarean delivery: This method is rarely used where regional block is patchy or inadequate. Technique :The skin is infiltrated along the line of incision with diluted solution of lignocaine (2%) with normal saline. The subcutaneous fatty layer, muscle, rectus sheath layers are infiltrated as the layers are seen during operation. The operation should be done slowly for the drug to become effective.

52. PATIENT CONTROLLED ANALGESIA Narcotics are administered by mother herself from a pump at continuous or intermittent demand rate through intravenous route. Total dose is limited as there is a lockout interval. This offers better pain control than high doses given at a long interval by the midwife. Maternal satisfaction is high with this method. Drugs commonly used are fentanyl, meperidine or remifentanil.

53. PSYCHOPROPHYLAXIS (Syn: Natural childbirth) It is psychological method of antenatal preparation designed to prevent or at least to minimize pain and difficulty during labor. For most women, labor is a time of apprehension, fear and agony. As a result of suitable antenatal preparation, majority of women have labor that is easy and painless.

54. Relaxation and motivation can reduce the fear and apprehension to a great extent. Patient is taught about the physiology of pregnancy and labor in antenatal (mothercraft) classes. Relaxation exercises are practiced. Husband or the partner is also involved in the management. His presence in labor would encourage the bearing down efforts. Need of analgesia would be less.

55. TRANSCUTANEOUS ELECTRIC NERVE STIMULATION (TENS) It is a noninvasive procedure and is preferred by many women during labor. Electrodes are placed over the level of T10 – L1 and S2 – S4. Current strength can be adjusted according to pain. It works by inhibiting transmitter release through interneuron level. However, no change in pain score was observed when TENS was switched on.

56. GENERAL ANESTHESIA FOR CESAREAN SECTION The following are the important considerations of general anesthesia for cesarean section: Cesarean section may have to be done either as an elective or emergency procedure. Ryel’s tube aspiration of gastric contents is to be done, especially when the stomach contains food materials.

57. A large number of drugs pass through the placental barrier and may depress the baby. Uterine contractility may be diminished by volatile anesthetic agents like ether, halothane. Halothane, isoflurane cause cardiac depression, hepatic necrosis and hypotension. Hypoxia and hypercapnia may occur. Time interval from uterine incision to delivery is related directly to fetal acidosis and hypoxia. Longer the exposure to general anesthetic before delivery the more depressed is the Apgar score.

58. Preoperative preparations: These safety measures should be taken to prevent complications of general anesthesia. Preoperative medication with sedatives or narcotics is not required as they cause respiratory depression of the fetus. Fasting of about 6 hours is preferable for an elective surgery. High-risk women in labor should preferably not be allowed to eat. Ryel’s tube aspiration of gastric contents is to be done when the stomach contains food materials.

59. Preoperative preparations: These safety measures should be taken to prevent complications of general anesthesia. Preoperative medication with sedatives or narcotics is not required as they cause respiratory depression of the fetus. Fasting of about 6 hours is preferable for an elective surgery. High-risk women in labor should preferably not be allowed to eat. Ryel’s tube aspiration of gastric contents is to be done when the stomach contains food materials.

60. H2-blocker (Ranitidine 150 mg orally) should be given night before (elective procedure). H2 receptor blocking agent and metoclopramide is to be given IM especially to women with high risks (obesity). Non-particulate antacid (0.3 molar sodium citrate 30 ml) is given orally before transferring the patient to theater to neutralize the existing gastric acid. While on the theater table, left lateral tilt of the woman is maintained with a wedge on the back. This is to avoid autocaval compression as it is detrimental to both mother and fetus.

61. Metoclopramide (10 mg IV) is given after minimum 3 minutes of preoxygenation to decrease gastric volume and to increase the tone of lower esophageal sphincter. Intubation with adequate cricoid pressure following induction should be done. Uterine incision-Delivery (U-D) interval is more predictive of neonatal status (Apgar score). Prolonged U-D interval of more than 3 minutes results in lower Apgar scores and neonatal acidosis. Awake extubation should be a routine.

62. Preoxygenation with 100% oxygen is administered by tight mask fit for more than 3 minutes. Induction of anesthesia is done with the injection of thiopentone sodium 200–250 mg (4 mg/kg) as a 2.5% solution intravenously. Muscle relaxants: Succinylcholine is commonly used immediately after the induction drug to facilitate intubation. It is a short acting muscle relaxant with rapid onset of action.

63. Intubation: An assistant is asked to apply cricoid pressure as soon as the consciousness is lost. Intubation is done with a cuffed endotracheal tube and the cuff is inflated. Presence of obesity, severe edema, neck abnormalities, short stature or airway abnormalities make intubation difficult.

64. Anesthesia is maintained with 50% nitrous oxide, 50% oxygen and a trace (0.5%) of halothane. Relaxation is maintained with nondepolarizing muscle relaxant (vecuronium bromide 4 mg or atracurium 25 mg). After delivery of the baby, the nitrous oxide concentration should be increased to 70% and narcotics are injected intravenously to supplement anesthesia.

65. Complications of general anesthesia: Aspiration of gastric contents (Mendelson’s syndrome) is a serious and life threatening one. Delayed gastric emptying due to high level of serum progesterone, decreased motilin and maternal apprehension during labor is the predisposing factor. The complication is due to aspiration of gastric acid contents (pH < 2.5) with the development of chemical pneumonitis, lung damage, atelectasis and bronchopneumonia. Right lower lobe is commonly involved as the aspirated food material reach the lung parenchyma through the right bronchus.

66. Clinical presentation: Tachycardia, tachypnea, bronchospasm, rhonchi, rales, cyanosis, decreased PaO2 and hypotension. X-ray chest reveals right lower lobe involvement.

67. Management: Immediate suctioning of oropharynx and nasopharynx is done to remove the inhaled fluid. Bronchoscopy may be needed if there is any large particulate matter. Continuous positive pressure ventilation to maintain arterial oxygen saturation of 95% is done. Pulse oximeter is a useful guide. Antibiotics are administered when infection is evident. Role of corticosteroid is doubtful.

68. Other complications of general anesthesia are: Failure in intubation and ventilation Nausea, vomiting and sore throat.

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