Anesthesia for Nonobstetric Surgery in the pregnant patient

October 21, 2003

Ri 黃雅萍 卓岱慶 / R3 彭育仁 / VS 王永彬

Basic Data

Name : 粘 x x Age : 39-year-old Gender : Female High and weight: 162 cm & 43 kg Past history: denied any systemic disease Family history: her father was a cancer patient

Brief History (I)

Last menstrual period was on July 6, 2003 Pregnancy with G1P0 was confirmed in July. Sonography:

a left ovarian cystic tumor in size of 9.4cm * 5.4cm. with septum and hair-like and dirty material inside.

Tumor size was enlarged to 11.3cm *6.89cm in Oct. Admission for operation on Oct 13. Operation was performed on Oct 14.

Brief History (II)

Anesthesia Spinal anesthesia with an epidural catheter insert

ed. 麻醉紀錄

Brief History (III)

Operation Left salpingo-oophoectomy Incidental appendectomy.

Pathology Mucinous cystadenoma.

Postoperative analgesia Epidural morphine injection for pain control

She was discharged on Oct 17.

Discussion

Goals

Maternal consideration Maternal safety

Fetal consideration Avoiding fetal asphyxia

Maintain uterine perfusion and fetal oxygenation Anesthesia agent teratogenicity Prevention of preterm labor

Inhibit uterine contraction

Maternal consideration

Maternal safety (I)

Respiratory System ↑Minute ventilation, and ↓RV, FRC

↓Oxygen reserve Develop hypoxia and hypercapnia more rapidly with hypoven

tilation or apnea Airway management by mask, or tracheal intubation c

an be technically difficult. Increased anteroposterior chest wall diameter, breast enlarg

ement, laryngeal edema, and weight gain Affects the soft tissues of the neck

Maternal safety (II)

Cardiovascular System ↓ Blood pressure

↑Plasma volume, cardiac output ↓ Peripheral vascular resistance and placenta resistance

Hypotensive syndrome is associated with supine position since mid-gestation ↑Aortic and venal cava compression Physiologic compensation for aortocaval compression can b

e compromised by anesthetic techniques

Maternal safety (III)

Gastrointestinal System ↑Risk for gastric acid aspiration with anesthetic indu

ction or unconscious sedation. ↓Gastroesophageal sphincter tone Gastric motility is impaired by opioid administration, onset

of labor, pain, trauma, and so forth.

Maternal safety (IV)

Responses to Anesthesia Drugs ↓Anesthetic requirements

↓MAC since 8 or 12 wks gestation ↓Intravenous drugs for induction of GA

↓Dose of spinal or epidural local anesthetics ↓Volume of the spinal or epidural space Higher incidence of dural puncture Maternal never fibers are more sensitive

Fetal considerations

Avoiding fetal asphyxia (I)

Avoided to decrease uterine blood flow or its oxygen content Adequate oxygenation Avoid excessive maternal mechanical hyperventilation Avoid vasoactive medication Fetal and uterine monitor

Avoiding fetal asphyxia (II)

Adequate oxygenation The asphyxiated fetus cannot increase oxygen extr

action Maternal administration of increased inspired oxyge

n will increase fetal oxygenation Fetus is never at risk for hyperoxia.

Avoiding fetal asphyxia (III)

Avoid maternal mechanical hyperventilation Hyperventilation can reduce venous return and

thereby cardiac output, which reduces uterine blood flow.

Avoiding fetal asphyxia (IV)

Avoid vasoactive medication The uterine circulation is not autoregulated and rem

ains sensitive to vasopressors. Vasoactive medication reduces uterine blood flow Uterine displacement, fluid bolus, Trendelenburg po

sition, leg elevation, the use of compression stockings, or any combination of these may be used for maternal hypotension.

Ephedrine remains first choice for maternal hypotension.

Summary (I)

Maternal safety Develop hypoxia and hypercapnia more rapidly with

hypoventilation or apnea Airway management can be technically difficult. Supine Hypotensive syndrome ↑Risk for gastric acid aspiration ↓Anesthetic requirements ↓Dose of spinal or epidural local anesthetics

Summary (II)

Avoiding fetal asphyxia Adequate oxygenation: Fetus is never at risk for hypero

xia. Avoid excessive maternal mechanical hyperventilation Avoid vasoactive medication Fetal and uterine monitor

Teratogenicity (I)

Teratogen: A substance causes an increase in the incidence of a particular defect in a fetus that cannot be attributed to chance.

Congenital anomalies in humans: 3% Most vulnerable period to teratogenic effects: Organ

ogenesis takes place between the 15th to 56th days of gestation.

Exceptions: Central nervous system continues to develop even after birth.

Teratogenicity (II)

Most commonly used anesthetic and sedative drugs are teratogenic in some animal species (in larger doses than used clinically).

Careful, well-controlled human teratogenicity studies are nearly impossible to perform.

All surveys of women who have received anesthesia for operations during pregnancy have failed to indict any anesthetic as a teratogen.

It is not clear whether the hazard is due to the surgery or the anesthetic.

Teratogenicity (III)

Nitrous oxide: Most controversial inhalation anesthetic in terms of safe use during pregnancy.

Nitrous oxide →inhibit methionine synthetase → impair DNA synthesis.

Fetal methionine synthetase ↓, Miscarriage rate ↑, impaired growth and poor skeletal development after maternal exposure to greater than 50% nitrous oxide over prolonged periods in animal model.

Other volatile anesthetics: There is no evidence of teratogenicity.

Teratogenicity (IV)

BZD: Use of BZD during pregnancy also provide conflicting results.

Maternal use of BZD (meprobamate, chlordiazepoxide and diazepam) showed an association with higher incidence of oral clefts, cleft lip and palate in some studies.

Avoid BZD use throughout gestation and most especially during the first trimester.

Teratogenicity (V)

Local anesthetics: No teratogenic effect in human. Local anesthetics may have minor neurobehavioral

effects on the early neonate, but they are not likely to be clinically meaningful.

Opioids: No teratogenic effect in human when used in limited dose in the perioperative period.

The neonate is at risk of respiratory depression, sedation and psychomotor impairment only when delivery occurs at the same time as the surgery.

Teratogenicity (VI)

Muscle relaxants: No teratogenic effect in human and do not cross the placenta to any significant extent.

Induction agents: Thiopental can cause neonatal sedation and decreased fetal heart rate variability. (not likely to be clinically meaningful)

Oxygen and Carbon dioxide: Hypoxia has been showed to be teratogenic in animal model.

Hypercapnia can interfere with fetal development.

Prevention of Preterm Labor

Increased incidence of spontaneous abortion, premature labor, and preterm delivery may be due to surgery itself.

The lowest risk for preterm labor: During the 2th trimester and for surgeries that not manipulate the uterus.

Halogenated anesthetics can produce uterine relaxation and decreased myometrial irritability, may be beneficial.

Prophylactic use of tocolytic agents: No proof of efficacy.

Summary(I)

Specific risk of anesthetic techniques are no able to be defined.

Primary goal: Decrease fetal drug exposure. The drugs for general anesthesia: Should have a

long history of safety. Regional anesthesia are preferred than general

anesthesia. Spinal anesthesia was preferred than epidural

anesthesia due to lower dosage.

Summary(II)

The biggest risk of spinal anesthesia during pregnancy: Hypotension→ Uterus blood flow and perfusion of fetus↓

Ephedrine: Drug of choice for this situation. Elective surgery: Should not be performed. The optimal time for necessary surgery: The 2th

trimester. The primary goal is always to preserve the life of the

mother first. Fetal and uterine monitoring: Intra- and post-op

Thanks for your attention!