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

GOALS OF CHILDBIRTH PREPARATION Patient education concerning pregnancy, labor

and delivery Relaxation training Instruction in breathing techniques Husband (support person) participation Early parental bonding

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

OBSTETRIC PAIN PATHWAYS

A. Visceral pain From uterine

contractions and cervical dilatation

Via visceral afferent fibers entering spinal cord at T10-T12 and L1

B. Somatic pain from distention

of pelvic floor, vagina, perineum

Via somatic nerve fibers transmitted from pudendal nerve to S2-S4

ANALGESIA DURING LABOR

1. Epidural Analgesia / Anesthesia Most effective

method of intrapartum pain relief

Uses local anesthetics (Bupivacaine, Lidocaine, Ropivacaine, 2

chloroprocaine, Epinephrine)

Other Indications for Epidural Analgesiao Vaginal delivery of twinso Vaginal delivery of preterm infantso Pre-eclampsiao Patient with medical complications (mitral

stenosis, spinal cord injuries, intracranial neurovascular disease, asthma)

Contraindications of Epidural Analgesiao Patient refusal or inability to cooperateo Increase intracranial pressureo Infection at the site of needle punctureo Coagulopathyo Uncorrected maternal hypovolemiao Inadequate training or experience in the

technique

Complications of Epidural Analgesiao Hypotensiono Inadequate analgesiao High or total spinalo Urinary retentiono Headacheo Postdural puncture seizureso Meningitiso Back pain

Bupivacaineo Oftenly used local anesthetic for epidural

analgesiao 8-10mL of 0.25% to 0.5% for 2 hrso Peak effect achieved in 20 mins.o Provide excellent sensory blockade with

minimal motor blockade

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

b. Continuous Infusion- More popular for maintaining

epidural analgesia- Benefits:

Easy to maintain level of analgesia

More stable maternal VS 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 durationo Tetracaine intermediate too Bupivacaine long duration

3. Alternative Regional Anesthetic Techniques

a. Paracervical Blocko Used during first stage of laboro No sensory or motor blockade

o Blocks transmission of impulse through the paracervical ganglion(Frankenhausen’s ganglion)

o Fetal complications: bradycardiao Maternal complications (hematoma,

systemic local anesthetic toxicity, vasovagal syncope)

o Agent of choice: 2-chloroprocaine

b. Pudendal Nerve Blocko Pudendal nerve provides sensory

innervation for the lower vagina, vulva and perineum; motor innervation to perineal muscles and external anal sphincter

o Analgesia for spontaneous vaginal delivery and outlet forceps delivery

o Complications (systemic local anesthetic toxicity, hematoma)

c. Perineal Infiltrationo Most common local anesthetic technique

for vaginal deliveryo Anesthetic for episiotomy and repair

4. Systemic Analgesia Used when conditions contraindicated the use of

regional (hemorrhage, coagulopathies)

Epidural anesthesia is not available Risks for epidural anesthesia

a. Opioidso Lipid soluble with low molecular weight

easily crosses the placentao Causes neonatal respiratory depressiono Result in decrease beat-to-beat variability

of FHR

(1) Meperidine (Demerol)o Most widely used opioid for labor

analgesiao Given at 25-50 mg IV or 50-100 mg IM

every 2-4 hrs.o Onset of analgesia 5 minutes after IV and

45 minutes after IMo Often used with Phenothiazines to

decrease nausea and vomitingo 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 doseo 10-20 mg every 4-6 hrs.o Onset within 2-3 minutes after IV and

within 15 minutes after IMo Less maternal nausea and vomitingo More maternal sedation and dizziness

(3) Naloxone ( Narcan)o Opioid antagonist to reverse neonatal

respiratory depressiono Given at 0.1mg/kg of a 1mg/mL IV or IM

b. Inhalational Analgesics

o 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

o 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

Problems Regarding Use of Inhalational Anesthetics

o Need for specialized vaporizerso Concern regarding pollution of labor and

delivery roomo Incomplete analgesiao Potential for maternal amnesiao Potential for loss of protective airway

reflexes and pulmonary aspiration of gastric contents

c. 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

o KETAMINE (KETALAR) Sedative, good analgesia prior to

delivery Avoid in hypertensive patients Induces delirium and

hallucinations

o PROPOFOL(DIPRIVAN) Sedation for short surgical

procedures

ANESTHESIA FOR CESAREAN SECTION

1. Spinal block For elective cesarean sections Level of sensory block up to T8 dermatome Larger dose of anesthetic agent

o Tetracaine 8-10 mgo Bupivacaine 12 mg

o Lidocaine 50-75 mg

COMPLICATIONSo Hypotension due to vasodilatation from

sympathetic blockade and veno-caval compression

o Total spinal blockade due to excessive dose of analgesic

o Spinal headache due to CSF leakageo Convulsionso Bladder dysfunction

CONTRAINDICATIONSo Hypotensiono Coagulopathieso Neurologic disorderso Infection on sites of skin puncture

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 ANESTHESIAo Fasting for 8 hrso 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

-fin-

audrey_cl@yahoo.com