Pocket ObGyn – Gynecologic Anesthesia
See Abbreviations

• 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; fol- lowed 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

 

Common local anesthetics
Mech: Block voltage-gated Na channels, prevent nerve depolarization/action potential High lipid solubility = favors entry into cells = more potent, longer duration
Anesthetic	Type	Lipid solubility	Concentration	Max dose w/o epi	Max dose w/ epi
Lidocaine	Amide	++	1% 10 mg/mL	4 mg/kg	7 mg/kg
Bupivacaine	Amide	++++	0.25% 2.5 mg/mL	2.5 mg/kg	3 mg/kg
2-chloroprocaine	Ester	+	2% 20 mg/mL	11 mg/kg	14 mg/kg
Ropivacaine	Amide	+++
Mepivacaine	Amide	++
From Hawkins JL, Bucklin BA. Obstetrical anesthesia. In: Gabbe SG, ed. Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Saunders, Elsevier; 2012:362.

• 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 hys- terectomy 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 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 metabo- lites, 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

 

Parenteral opioids
Opioid	Onset	Neonat half-life	Disadvantages
Fentanyl Remifentanil – also fast acting	1 min IV	5.3 h	Short duration; may not control labor pain well
Morphine	5 min IV 40 min IM		Longer duration can result in prolonged sedation
Nalbuphine	2–3 min IV 15 min IM	4.1 h	Partial agonist/antag: Antag properties limit side effects but may also limit relief
Meperidine Historic 1st choice in labor, no longer widely used	5 min IV 30–45 min IM	13–22 h, 63 h for active metabolite	Both drug & active metabolite normeperidine cross placenta: Prolonged fetal sedation; risk of lethal serotonin syn in pts taking MAOIs limits use
From Obstet Gynecol 2002:100:177.

 

Methods of administration of parenteral opioids
Method	Advantages	Disadvantages
Intermittent administration Administered by nurse Short to medium acting opioids	No pump req, no staff needed to set up apparatus RN oversight of fetal status for administrations	Less autonomy, more delays, more total opioid used
Patient-controlled analgesia Programmed to deliver on-demand boluses Short acting (eg, Fentanyl)	Pt autonomy, less delay in administration; results in less total opioid used	Requires pump apparatus, anesthesia staff for setup Risk of self-administration during period of fetal distress

See Abbreviations