Ob1 Lec - Analgesia

OBSTETRICS I – OB Analgesia – Anesthesia Lecture by Irma A. Lee, F.P.O.G.S. USTMED ’07 Sec C - AsM

ANALGESIA DURING LABOR 1. Epidural Analgesia / Anesthesia

GOALS OF CHILDBIRTH PREPARATION • Patient education concerning pregnancy, labor and delivery • Relaxation training • Instruction in breathing techniques • Husband (support person) participation • Early parental bonding

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NONPHARMACOLOGIC ANALGESIC TECHNIQUES A. Minimal Training • Emotional support • Touch & massage • Therapeutic use of heat & cold • Hydrotherapy • Vertical position B. Specialized Training • Biofeedback • TENS • Acupuncture • Hypnosis

Most effective method of intrapartum pain relief Uses local anesthetics (Bupivacaine, Lidocaine, Ropivacaine, 2 chloroprocaine, Epinephrine)

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Other Indications for Epidural Analgesia o Vaginal delivery of twins o Vaginal delivery of preterm infants o Pre-eclampsia o Patient with medical complications (mitral stenosis, spinal cord injuries, intracranial neurovascular disease, asthma)

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A. Visceral pain • From uterine contractions and cervical dilatation • Via visceral afferent fibers entering spinal cord at T10-T12 and L1

Contraindications of Epidural Analgesia o Patient refusal or inability to cooperate o Increase intracranial pressure o Infection at the site of needle puncture o Coagulopathy o Uncorrected maternal hypovolemia o Inadequate training or experience in the technique

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B. Somatic pain • from distention of pelvic floor, vagina, perineum • Via somatic nerve fibers transmitted from pudendal nerve to S2-S4

Complications of Epidural Analgesia o Hypotension o Inadequate analgesia o High or total spinal o Urinary retention o Headache o Postdural puncture seizures o Meningitis o Back pain

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Bupivacaine o Oftenly used local anesthetic for epidural analgesia o 8-10mL of 0.25% to 0.5% for 2 hrs o Peak effect achieved in 20 mins. o Provide excellent sensory blockade with minimal motor blockade

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Maintenance of Epidural Analgesia a. Intermittent Bolus Injection Supplemental doses of local anesthetics given for the duration of labor Results in blockade of sacral segments, intense motor blockade or both

OBSTETRIC PAIN PATHWAYS

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Continuous Infusion More popular for maintaining epidural analgesia Benefits:  Easy to maintain level of analgesia  More stable maternal VS

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Decrease risk of systemic anesthetic toxicity

2. Spinal Analgesia / Anesthesia • Low spinal block or saddle block • For vaginal delivery requiring perineal anesthesia • Other indications: delivery of preterm fetuses, low forceps delivery, cerclage, completion curettage • All local anesthetics can be used o Lidocaine – short duration

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Tetracaine Bupivacaine

intermediate to long duration

3. Alternative Regional Anesthetic Techniques a.

Paracervical Block o Used during first stage of labor o No sensory or motor blockade

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b.

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Analgesia for spontaneous vaginal delivery and outlet forceps delivery Complications (systemic local anesthetic toxicity, hematoma)

Perineal Infiltration o Most common local anesthetic technique for vaginal delivery o Anesthetic for episiotomy and repair

4. Systemic Analgesia

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Risks for epidural anesthesia

a.

Opioids

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Lipid soluble with low molecular weight easily crosses the placenta Causes neonatal respiratory depression Result in decrease beat-to-beat variability of FHR

Pudendal Nerve Block o Pudendal nerve provides sensory innervation for the lower vagina, vulva and perineum; motor innervation to perineal muscles and external anal sphincter

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c.

Blocks transmission of impulse through the paracervical ganglion(Frankenhausen’s ganglion) Fetal complications: bradycardia Maternal complications (hematoma, systemic local anesthetic toxicity, vasovagal syncope) Agent of choice: 2-chloroprocaine

Used when conditions contraindicated the use of regional (hemorrhage, coagulopathies) Epidural anesthesia is not available

(1) Meperidine (Demerol) o Most widely used opioid for labor analgesia o Given at 25-50 mg IV or 50-100 mg IM every 24 hrs. o Onset of analgesia 5 minutes after IV and 45 minutes after IM o Often used with Phenothiazines to decrease nausea and vomiting o To prevent neonateal respiratory depression, delivery should be within the 1st hr. or more than 4 hrs. after IV administration o Decrease FHR variability 25 minutes after IV or 40 minutes after IM administration but recovers within 60 minutes (2) Nalbuphine (Nubain) o Demonstrate ceiling effect for respiratory depression at 30 mg dose o 10-20 mg every 4-6 hrs. o Onset within 2-3 minutes after IV and within 15 minutes after IM o Less maternal nausea and vomiting o More maternal sedation and dizziness (3) Naloxone ( Narcan) o Opioid antagonist to reverse neonatal respiratory depression o Given at 0.1mg/kg of a 1mg/mL IV or IM

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Inhalational Analgesics o

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Nitrous Oxide  Gas anesthetic  Given intermittently as 50% nitrous oxide in 50% oxygen(NITRONOX) by mask or mouthpiece  For forceps delivery  Part of balanced general anesthesia Halogenated Agents  Volatile anesthetics  Causes dose related uterine smooth muscle relaxation (halothane, enflurane, isoflurane)  For internal podalic version of the 2nd twin, breech decomposition and replacement of acute uterine inversion  With cardiodepressant and hypotensive effects  Hepatotoxic

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Problems Regarding Use of Inhalational Anesthetics o Need for specialized vaporizers o Concern regarding pollution of labor and delivery room o Incomplete analgesia o Potential for maternal amnesia o Potential for loss of protective airway reflexes and pulmonary aspiration of gastric contents

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Intravenous Drugs During Anesthesia o

THIOPENTAL(PENTOTHAL)  Short-acting barbiturate  Used with a muscle relaxant (succinylcholine) prior to tracheal intubation  Induces sleep, poor analgesic  Causes neonatal respiratory depression  Used during second stage of labor, short minor gynecologic procedures

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KETAMINE (KETALAR)  Sedative, good analgesia prior to delivery  Avoid in hypertensive patients  Induces delirium and hallucinations

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PROPOFOL(DIPRIVAN)

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CONTRAINDICATIONS o Hypotension o Coagulopathies o Neurologic disorders o Infection on sites of skin puncture

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MANAGEMENT OF SPINAL BLOCK COMPLICATIONS o Hypotension  Uterine displacement  Hydration with 0.5 to 1 L of NSS  Ephedrine 5-10 mg/IV o

Total spinal block  Treat associated hypotension  Tracheal intubation  Ventilatory support

2. Continuous lumbar epidural block • block is from T8-S5 dermatomes • Opiates are added to avoid motor block 3. COMBINED SPINAL - EPIDURAL TECHNIQUES • Provide effective analgesia for labor and cesarean delivery 4. BALANCED GENERAL ANESTHESIA • Uses nitrous oxide, thiopental and succinylcholine • Causes maternal and fetal CNS depression • Major hazard is aspiration pneumonitis • PROPHYLAXIS FOR ASPIRATION DURING GENERAL ANESTHESIA o Fasting for 8 hrs o Histamine H2 antagonists to reduce gastric activity (Cimetedine) o Sellick maneuver – skillful tracheal intubation with pressure on cricoid cartilage to occlude esophagus • NGT • Awake extubation 5. LOCAL ANESTHETIC BLOCK • emergency CS in the absence of anesthesiologist • to augment patchy regional block given in an emergency

Sedation for short surgical procedures

ANESTHESIA FOR CESAREAN SECTION 1. Spinal • • •

Total spinal blockade due to excessive dose of analgesic Spinal headache due to CSF leakage Convulsions Bladder dysfunction

block For elective cesarean sections Level of sensory block up to T8 dermatome Larger dose of anesthetic agent o Tetracaine 8-10 mg o Bupivacaine 12 mg o Lidocaine 50-75 mg COMPLICATIONS o Hypotension due to vasodilatation from sympathetic blockade and veno-caval compression

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