Pocket Obstetrics and Gynecology

OB ANESTHESIA

GYNECOLOGIC ANESTHESIA

• Many office procedures & selected transvaginal operations may be performed under local anesthesia, w/ or w/o sedation/analgesia

Examples: Loop electrosurgical excision procedures, 1st trimester dilation & curettage, hysteroscopy, endometrial ablation

Technique: Paracervical block or intracervical block

• Local anesthetic toxicity

Tox usually occurs following inadvertent intravascular injection

CNS effects typically precede CV effects

CNS: Prodrome of excitation, ringing in ears, perioral numbness, confusion; followed by convulsions; followed by coma

CV: Initial HTN, tachy; followed by HoTN, arrhythmias, cardiac arrest

Exception: Bupivacaine-cardiotoxicity predominates; prolonged Na+ channel blockage

Epi may be added to ↓ overall uptake & allow increased local effect.

Contraindications to use of epi exist. Cardiac: HTN, CHF, arrhythmias, MI. Other relative contraindications: Tricyclic antidepressant use, MAOI use, beta blockade, cocaine use, hyperthyroidism, asthma, diabetes

• Laparoscopic & prolonged gynecologic surgeries usually performed under GA

Laparoscopic procedures require complete relaxation of abdominal wall (ie, paralysis)

Std anesthesia techniques & precautions apply

Many laparoscopic procedures require prolonged Trendelenburg positioning for access to pelvis; in some pts, this may cause hemodynamic compromise, difficulty ventilating

• Transvaginal procedures & many abdominal procedures may be performed under neuraxial anesthesia/sedation, particularly if pt not candidate for GA due to medical comorbidities (though precludes use of paralytics)

Examples: Dilation & curettage/evacuation, operative hysteroscopy, vaginal hysterectomy or abdominal hysterectomy in pts not candidates for GA

• Both minilaparotomies & some laparoscopic procedures (most commonly sterilization) may be performed under sedation w/ local anesthesia only

PARENTERAL ANALGESIA IN OBSTETRICS

• All nonneuraxial methods provide only partial relief of labor pain.

May help laboring women cope w/ pain

Useful in cases of absolute contraindication to or pt refusal of neuraxial anesthesia

• Opioids act as opioid receptor agonists: Mu, kappa, delta

G-protein–coupled receptors → ↓ intracellular Ca → inhibition of release of pain neurotransmitters. Distributed through brain, terminal axons of spinal cord afferents

• Xfer across the placenta is rapid & signif; fetal effects may limit use

Drug xfer affected by prot binding capacity, size, ionization

In general, all local anesthetics & opioids transfuse freely across the placenta

Fetal acidosis results in ion trapping → fetal drug accum

• Side effects of systemic opioids

Maternal: Sedation, respiratory depression, N/V

Fetal: Decreased fetal HR variability during labor; pseudosinusoidal HR pattern, respiratory depression at birth. Use short-acting opioid w/ no active metabolites, if poss. Monit fetus continuously during administration of systemic opioids. Avoid administration shortly before deliv.

• Sedatives: Do not provide analgesia; typical use is for sleep/relaxation in latent labor

NEURAXIAL ANESTHESIA IN OBSTETRICS

• Most effective method for labor pain

• Also std for C/S, postpartum tubal ligations, urgent postpartum procedures whenever poss

• Indications for spinal/epidural anesthesia in labor

Maternal request

Anticipation of operative vaginal deliv or shoulder dystocia; breech extraction; high risk of C/S; Risk of hemorrhage; difficult intubation

Maternal condition where signif pain or stress would create medical risk (eg, sev respiratory or cardiac dz)

Maternal condition which could worsen & potentially limit use of neuraxial anesthesia later in labor course (eg, worsening thrombocytopenia or coagulopathy)

• Contraindications to spinal/epidural anesthesia in labor

Absolute: Maternal refusal, uncooperative pt; soft tissue infxn of site; uncorrected hypovolemia; uncorrected therapeutic anticoagulation; Lovenox w/i 24 h; certain spinal conditions (eg, ependymoma); sev thrombocytopenia (<50 K)

Relative: Certain spinal conditions (eg, discectomy, rod fusion); mod thrombocytopenia (<75 K); LP shunt, some neurologic dzs (ie, multiple sclerosis); fixed ­cardiac output conditions (ie, AS)

• Types of neuraxial blocks: Spinal, epidural, & CSE

Spinal:

Anesthetic/opioid delivered directly into spinal fluid w/ needle through dural puncture

Benefits: Rapid onset (2 min); 1/20 epidural dose used so less risk tox

Disadvantages: Limited duration (1–1.5 h)

Epidural:

Anesthetic/opioid delivered into epidural space via continuous infusion through catheter

Benefits: Ability to continuously infuse & adjust dosage as needed; pt controlled

Disadvantages: Slower onset (20 min), larger doses used (20× spinal doses)

CSE:

Meds delivered directly into spinal fluid, then catheter placed in epidural space

Benefit: Combination of rapid onset & ability to continuously infuse

Disadvantages: More technically challenging than epidural or spinal alone; increased risk of PDPH compared to spinal alone

Figure 4.1 Epidural block

LOCAL ANESTHETICS IN OBSTETRICS

• Indications for local anesthetics

Skin infiltration for episiotomies/assisted deliveries (nonemergent settings), laceration repair

Nerve blocks: Pudendal, paracervical (close proximity to large vessels → higher potential for tox)

Spinal & epidural anesthesia

• In an emergent setting where access to general anesthesia will be delayed, local anesthetics may be administered in large amts to perform C/S, followed by general anesthesia when available

Figure 4.2 Pudendal block

NONPHARMACOLOGIC ANALGESIA IN OBSTETRICS

• Advantages: Empowering, few side effects, may improve overall satisfaction w/ labor experience

• Disadvantages: Incomplete relief, pts may perceive eventual pharm rx as failure

• Evid: Many nonpharmacologic methods have not been well studied

GENERAL ANESTHESIA IN OBSTETRICS

• Rarely indicated for vaginal deliv except for emergent, unanticipated procedures (eg, breech extraction, internal version, shoulder dystocia)

• In US, 10% of C/S are performed under general anesthesia (Anesthesiology 2005;103:645)

Emergent (“crash”) C/Ss are the most common setting for general anesthesia

Other situations include nonemergent C/S in a pt w/ absolute contraindications to neuraxial anesthesia

Advantages: Rapid, complete anesthesia; ability to administer 100% oxygen

Disadvantages: Risk of difficult intubation; risk of aspiration; small risk of infant respiratory depression; anesthetics cause uterine atony, leading to more bld loss

• Other uses:

Uterine inversion: Obstetric emergency where body of uterus inverts following deliv

Nitric oxide or halogenated anesthetics relax uterus & facilitate replacement. Nitroglycerine may be given IV/sublingually if delay in general anesthesia is anticipated.

Can be considered in cases of retained placenta due to bandl’s ring or head entrapment for breech extraction; must balance w/ risk of uterine atony

POSTOPERATIVE PAIN MANAGEMENT

• Post C/S pain include visceral (uterus) & somatic pain (abdominal wall).

• Multimodal rx regimens

Goals: (1) Adequate pain control, (2) ↓ opioids to ↓ assoc side effects such as N/V, ileus, sedation, & effects on infant via secretion of active compounds into breast milk

• Oral pain meds – preferred mgmt once pt is tolerating PO

Opioids – carry above side effects

NSAIDs – important adjuvant therapy to reduce opioid exposure

Esp effective on visceral pain from uterine involution

Also available as 12 h IV formulation (ketorolac) for up to 4 doses postop

Breast-feeding: Opioids & NSAIDs considered generally compatible w/ breast-feeding

Exception: Meperidine – prolonged infant sedation by active metabolite normeperidine

• Postpartum bilateral tubal ligation:

Avoid long-acting intrathecal/epidural opioid/local anesthetic if goal is discharge soon after procedure. Infiltration of skin, fallopian tubes w/ local anesthetic shown to ↓ total analgesic use, ↑ time to analgesic use postoperatively. Sufentanil, bupivacaine, lidocaine all effective.