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Anesthesia for Nonobstetric Surgery during Pregnancy


Normal physiologic changes of pregnancy may increase maternal risk & alter management. ... Questionnaire study: 7000 dental assistants, 1995 ... – PowerPoint PPT presentation

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Title: Anesthesia for Nonobstetric Surgery during Pregnancy

Anesthesia for Nonobstetric Surgery during
  • Anita M. Backus, MD
  • Associate Clinical Professor
  • Director of Obstetric Anesthesia
  • UCLA Medical Center
  • Los Angeles, California

Nonobstetric Surgery during Pregnancy Special
  • Normal physiologic changes of pregnancy may
    increase maternal risk alter management.
  • The pregnancy may result in a delay in diagnosis
    causing ? mat. morbidity mortality.
  • There are risks to the fetus, including
    teratogenicity, alterations in uterine blood
    flow, and preterm labor.
  • Fetal needs may conflict with those of the mother.

Physiologic Changes of Pregnancy Cardiovascular
  • Cardiac output ? by 50 by 2nd trimester due to ?
    heart rate and stroke volume.
  • Blood volume ? 45 during pregnancy.
  • Colloid oncotic pressure ? from 27?22 mm Hg (?
    risk of pulmonary edema).
  • Hypercoagulable state due to ? clotting factors
    (? risk of perioperative thromboembolic events).
  • Small changes in blood pressure
  • SBP ? lt 10 DBP ? 20 in mid-pregnancy
  • Both back to pre-pregnancy levels by term.
  • No change in filling pressures SVR ? 20.

Physiologic Changes of Pregnancy Aorto-Caval
  • Frank supine hypotensive syndrome in 15-20 of
    term pregnant women when supine
  • hypotension, pallor, nausea
  • Uterine blood flow may be compromised even
    without maternal hypotension due to ? UPP
  • ? arterial BP in lower body (? UAP) or
  • ? UVP 2 to IVC compression
  • Exacerbated by agents which impair maternal
    compensatory efforts
  • vasodilators (potent inhalational agents)
  • sympathectomy (spinal, epidural)

Physiologic Changes of Pregnancy Aorto-Caval
Compression II
  • With a T4 sympathectomy, 70-80 of supine, term
    pregnant women will become hypotensive without
    lateral uterine displacement.
  • All women gt 20 wks gestation need lateral uterine
    displacement during anesthesia in order to avoid
    ? uterine blood flow and maternal hypotension
  • usually left uterine displacement (LUD), however
    RUD is better in 10 of patients

Physiologic Changes of Pregnancy Respiratory
  • Early in pregnancy respiratory alkalosis with
    partial metabolic compensation develops
  • results in ? buffering capacity
  • P50 is ? during pregnancy from 26 to 30 mm Hg
  • promotes offloading of oxygen to fetus
  • Oxygen consumption ? 60 during pregnancy.
  • No ETCO2-PaCO2 gradient is present in pregnancy
    due to ? alveolar dead space 2º ? CO

Physiologic Changes of Pregnancy Respiratory II
  • Respiratory changes arise due to hormonal,
    metabolic, and mechanical alterations.
  • Minute ventilation ? 45 by term due to ? TV
  • Begins early in gestation due to hormonal
    stimulation later added metabolic stimulus
  • RR essentially unchanged during gestation
  • Functional residual capacity (FRC) falls 20
  • Supine position ? additional 30 decrease

Physiologic Changes of Pregnancy Respiratory III
  • ? FRC and ? oxygen consumption result in marked ?
    safe duration of apnea
  • PaO2 in first minute of apnea after pre-O2
  • ? 30 in a pregnant woman
  • ? 10 in a non-pregnant woman
  • The reduced FRC, especially when compromised by
    the supine position, commonly falls below the
    closing capacity in late pregnancy
  • small airway closure during normal tidal
  • perfusion of unventilated alveoli (shunting) ?
  • Hypoxemia worsened by aorto-caval compression

Physiologic Changes of Pregnancy Gastrointestinal
  • Pregnancy causes changes in gastric orientation
    resulting in intrathoracic displacement of the
    intraabdominal portion of the esophagus
  • reduces the tone effectiveness of the LES
  • Addition of ? intragastric pressure as pregnancy
    progresses ? ? gastroesophageal reflux
  • 22 first trimester
  • 39 second trimester
  • 72 third trimester

Physiologic Changes of Pregnancy Gastrointestinal
  • It is recommended that pregnant women
  • gt18-20 weeks gestation or
  • with reflux symptoms
  • be treated as at risk for pulmonary
  • of gastric contents
  • non-particulate antacid prophylaxis
  • If GA required rapid sequence induction with
    cricoid pressure and intubation
  • Some anesthesiologists would treat any pregnant
    patient as at risk for aspiration

Physiologic Changes of Pregnancy Neurologic
  • MAC
  • reduced from early in pregnancy by 30 probably
    due to ? progesterone levels
  • Additional ? near term due to endorphins
  • The ? MAC ? FRC ? minute ventilation increase
    the likelihood of the pregnant woman
    unintentionally losing consciousness when
    inhalational analgesia is being administered.
  • Spinal dose requirements ? 25 starting 2nd trim
  • Increased spread of a small dose of epidural
    anesthetic in pregnancy no change w/ large dose

Physiologic Changes of Pregnancy Renal
  • Renal blood flow ? 75 during pregnancy
  • Glomerular filtration rate ? 50
  • Blood urea nitrogen (BUN) and creatinine levels
    fall to 8-9 mg/dL and 0.5-0.6 mg/dL, respectively.

Risks to the Fetus Alterations in Uterine Blood
  • Single greatest risk to the fetus perioperatively
    is asphyxia.
  • Oxygen delivery to the baby is determined by
  • maternal oxygen-carrying capacity (hematocrit)
  • oxygen saturation
  • gradient between maternal fetal P50
  • maternal 30 mm Hg and fetal 19 mm Hg
  • uteroplacental blood flow

Risks to the Fetus Alterations in Uterine Blood
  • Maternal hyperventilation
  • Oxyhemoglobin curve is shifted to the left,
    reducing the gradient for offloading O2 to the
  • Increased alkalosis may also cause
    vasoconstriction, reducing fetal blood flow.
  • Maternal acidosis produces fetal acidosis which,
    if severe, results in fetal myocardial depression.

Determinants of Uterine Blood Flow
  • Uterine artery pressure - uterine venous pressure
  • uterine vascular resistance
  • Maternal hypotension (hemorrhage, aorto-caval
    compression, sympathectomy, vasodilators,
    myocardial depression) ? UBF by ? UAP.
  • Aorto-caval compression can also ? UBF by ? UVP.
  • Uterine vascular resistance ? with
  • ? uterine tone (ketamine ? 2 mg/kg, ?-agonists)
  • uterine contractions
  • vasoconstrictors

Determinants of Uterine Blood Flow
  • Ephedrine is the drug of choice for hypotension
    however, small doses of phenylephrine have
    negligible adverse effects on UBF and are
    acceptable when medically indicated by the
    mothers condition.
  • If the mother is in extremis, any drug which is
    indicated to restore maternal circulation may and
    should be given (e.g., ACLS protocol drugs).

Risks to the Fetus Teratogenicity
  • Teratogen an agent/condition which causes
  • intrauterine death
  • congenital anomaly (birth defect)
  • functional deficit
  • intrauterine growth restriction (IUGR)

Risks to the Fetus Teratogenicity
  • Etiology of birth defects
  • Genetic 20
  • Chromosomal 3-5
  • Maternal viral infection 2-3
  • Drug/chemical exposure 2-3
  • Maternal metabolic disorder small
  • Unknown 65-70

Risks to the Fetus Teratogenicity
  • Only a small percentage of exposed
    embryos/fetuses may manifest adverse effects.
  • Timing of exposure is critical
  • 1st 2 weeks of gestation (before implantation)
    will either die (pregnancy never recognized) or
    live and develop normally
  • Weeks 3-8 (organeogenesis) exposure most likely
    to cause congenital anomalies
  • Week 8 onward functional defects or IUGR
  • Dose or degree of exposure is also very important

Anesthetic Agents Animal Studies
  • Extensive animal studies have been carried out.
  • Early work was confounded by effects of
    hypoventilation and decreased feeding.
  • More recent studies of opioids have shown no ?
    risk of congenital anomalies, although morphine
    administration was associated with IUGR ?
    mortality in rats.
  • Halogenated agents, when administered so as to
    minimally affect sleep and feeding patterns, are
    not teratogenic in rats.

Nitrous Oxide Animal Studies
  • At ? 50 concentration is teratogenic in rodents
  • fetal resorptions, skeletal visceral anomalies
  • N2O inhibits methionine synthetase activity.
  • Does resultant interference with DNA synthesis
    cause teratogenicity?
  • Appears not, because folate administration
    (bypassing methionine synthetase step) does not
    prevent anomalies
  • Coadministration of halogenated anesthetic averts
    most of teratogenic effects, as does methionine
  • ? Due to sympathetic NS stimulation by N2O, among
    many other possibilities

Injected Anesthetic Agents Humans
  • There is no evidence of teratogenicity of any
    commonly used anesthetic induction agent or local
    anesthetic in humans, except cocaine.
  • Cocaine, when used chronically during pregnancy,
    may be a structural behavioral teratogen.
  • Muscle relaxants no evidence that limited
    exposure during anesthesia is teratogenic.
  • Prolonged exposure (weeks) in utero may have
    adverse structural effects.

Diazepam Exposure in Early Pregnancy
  • Received much attention as a cause of cleft lip
    and palate
  • The evidence is conflicting and much of the
    exposure has been polypharmaceutical
  • Careful consideration is warranted before
    prescribing chronic use during pregnancy
  • Small doses of a benzodiazepine given during the
    course of an anesthetic have not been implicated
    in teratogenesis.

Studies of Anesthetic Agents as Human Teratogens
  • Subject to many confounding variables
  • Fetal outcome has been examined using two main
    study designs
  • Women chronically (occupationally) exposed to
    subanesthetic concentrations of anesthetic agents
    during pregnancy
  • Women who have undergone surgery during pregnancy
  • very difficult to separate out the effects of
    type of surgery maternal surgical illness

Occupational Exposure to Anesthetic Agents in
  • There is some evidence that chronic occupational
    exposure to nitrous oxide in an unscavenged
    environment may ? risk of spontaneous abortion.
  • Questionnaire study 7000 dental assistants, 1995
  • No ? abortion risk for those working in scavenged
    environment vs. non-exposed group
  • Relative risk of 2.6 for those with ? 3 hours/wk
    exposure to unscavenged N2O vs. non-exposed
  • However, no dose-response relationship data
    based on only 13 abortions in high-risk group
  • Rowland, et al., Am J Epidemiol 1995141531-8.

Nonobstetric Surgery during Pregnancy
  • About 0.16-0.75 of pregnant women require
    nonobstetric surgery each year
  • Most commonly performed procedures
  • Appendectomy
  • Resection of adnexal mass
  • Cholecystectomy
  • Laparoscopy, as a means of performing these
    procedures, is rapidly gaining in popularity.

Fetal Outcome of Nonobstetric Surgery during
  • Mazze and Kallen study, Swedish Health Registry
  • 5405 operated pregnant women, 1973-81
  • No ? congenital anomalies, even w/1st trim op
  • gt50 received general anesthesia, including N2O
    in gt98 of cases, without ? adverse outcomes.
  • Similar results when 1st trimester ops analyzed
  • ? risk of low very-low BW (prematurity/IUGR)
  • ? incidence of babies dying in 1st 7 days
  • Data were not available on spontaneous abortions
  • Type of anesthesia surgery not linked to outcome

Fetal Outcome of Nonobstetric Surgery during
  • Case-control study from Hungary
  • Cseizel, et al., Gynecol Obstet 1998261193-9.
  • 20,830 women who delivered babies with congenital
    anomalies (1980-94)
  • Confirmed lack of association between 1st
    trimester surgery and birth defects

Fetal Outcome of Nonobstetric Surgery during
  • Kort (North Carolina, 1980-89), 78 gravidae opd
  • Kort, et al. Surg Gynecol Obstet 1993177371-6
  • ? preterm labor in operated cohort 21 vs 12
  • Greatest risk was timing of surgery
  • 3rd trimester 25
  • 2nd trimester 8.2
  • Also proximity of operative site
  • Adnexal surgery 22
  • Appendectomy 11
  • Cholecystectomy 0
  • No ? perinatal mortality

Fetal Outcome of Nonobstetric Surgery during
  • Delay in diagnosis due to the pregnancy with
    visceral perforation and peritonitis is one of
    the greatest surgical dangers to the fetus.
  • May lead to as great as 100 fetal wastage with
    ruptured appendicitis
  • Al-Mulhim, et al., Int Surg 199681295-7
  • Appendicitis is notoriously difficult to diagnose
    in pregnancy due to lack of specificity of
    physical signs and laboratory findings
  • Negative appy rate of 50 is common.

Prophylactic Tocolytic Agents
  • Controversial
  • Threshold should be lower in 3rd trimester when
    risk of preterm labor is greatest.
  • There is agreement that patients should be
    monitored closely post-operatively and treated
    therapeutically with tocolytics if preterm labor
    should develop.

Laparoscopy during Pregnancy
  • Proposed advantages over open surgery
  • more rapid return to normal diet ?
    ? nutritional stress for the fetus
  • ? post-operative pain ? ? need for pain meds
  • more rapid mobilization ? ? risk of
    thrombo-embolic events
  • ? uterine manipulation exposure to air
  • ? risk of incisional hernias
  • Major concern with the technique
  • fetal effects of pneumoperitoneum

Laparoscopy Effects of Pneumoperitoneum
  • Initial studies in pregnant ewe, in which ETCO2
    was kept constant, showed maternal fetal
    acidosis and fetal tachycardia with
    intraabdominal CO2 insufflation.

Laparoscopy Effects of Pneumoperitoneum
  • However, if maternal PaCO2 was held constant by ?
    minute ventilation during insufflation, no
    changes in fetal HR, acid-base status, PaO2 or
    blood pressure were seen. No fetal deaths, PTL
  • Cruz, et al., Anesthesiology 1996851395-1402
  • Intraabdominal insufflation pressure limited to
    15 mm Hg.
  • Marked ? in PaCO2-ETCO2 gradient was observed
    with insufflation (6 ? 16 mm Hg)
  • attributed to ? pulmonary compliance, ? airway
    pressures, ? deadspace ventilation

Laparoscopy Effects of Pneumoperitoneum
  • Insufflation pressure must also be limited due to
    adverse effects on venous return
  • Venous return further impaired by pressure of
    gravid uterus on IVC in Trendelenberg position
    often needed during laparoscopy
  • Left uterine displacement must be maintained in
    order to preserve venous return and cardiac

Laparoscopy during Pregnancy
  • Equivalent or improved maternal fetal outcomes
    have been observed with laparoscopy vs.
    laparotomy during pregnancy
  • Swedish Health Registry data, 1973-93
  • Reedy, et al., Am J Obstet Gynecol
  • 2181 laparoscopies vs. 1522 laparotomies
  • No difference in fetal survival up to 1 year
  • No difference in fetal malformations
  • No difference in duration of gestation or BW

Gasless Laparoscopic Technique Akira, et al., Am
J Obstet Gynecol 1999180554-7
  • Ovarian cystectomy during pregnancy
  • 12-16 weeks gestation
  • Epidural anesthesia
  • Gasless laparoscopy using subcutaneous lift
    system (17 pts) vs laparotomy (18 pts)
  • Gasless technique avoids ? intraabdominal
    pressure ? CO2 absorption.
  • ? blood loss, analgesic use, tocolytic need
  • No preterm deliveries or abortions in scope group
  • 1 abortion in laparotomy group

Recommendations for Administering Anesthesia for
Surgery during Pregnancy
  • 1. Do not perform elective surgery during
  • 2. Query regarding possibility of pregnancy.
    Universal preoperative pregnancy testing is not
  • 3. If possible, delay surgery until the 2nd
    trimester to avoid the period of organeogenesis
    (1st trim) the highest risk of preterm labor
    (3rd trim).
  • 4. Excessive maternal catecholamine release
    should be avoided. Light premedication may be
  • 5. Local or regional anesthesia is favored, if
    feasible, to avoid manipulation of maternal
    airway minimize fetal drug exposure.

Recommendations for Administering Anesthesia for
Surgery during Pregnancy
  • 6. For general anesthesia aspiration prophylaxis
    rapid sequence induction of anesthesia with
    cricoid pressure and intubation are recommended
    for women at gt 18-20 weeks gestation or any
    pregnant woman with symptomatic GE reflux.
  • 7. Left uterine displacement is indicated for any
    pregnant woman gt 20 weeks gestation undergoing
  • 8. Normal maternal ventilation should be
    maintained, including normal PaCO2 for pregnancy

Recommendations for Administering Anesthesia for
Surgery during Pregnancy
  • 9. Laparoscopy consider checking maternal PaCO2,
    in addition to continuous monitoring of ETCO2,
    especially if surgery is prolonged or FHR tracing
    suggests fetal stress. Maintain intraabdominal
    insufflation pressure lt 15 mm Hg.
  • 10. Maternal oxygen delivery should be generous
    (preferably at least 50).
  • 11. Continuous FHR monitoring is recommended
    intraoperatively (as the operative site allows)
    post-operatively beginning at 20 wks gestation,
    if possible (technically easier at gt 22 wks)

Recommendations for Administering Anesthesia for
Surgery during Pregnancy
  • 12. Tocodynamometric monitoring of uterine
    activity is recommended post-operatively to allow
    early detection and treatment of preterm labor.
  • 13. Measures to prevent perioperative
    thrombo-embolic events should be taken
    (compression stockings, pneumatic compression
    devices, early post-operative mobilization)

  • When necessary, surgery may be performed during
    pregnancy with maternal safety.
  • Potential adverse effects for the fetus include
  • spontaneous abortion (maximal in 1st trimester)
  • preterm delivery (maximal in 3rd trimester)
  • intrauterine growth restriction (anytime in

  • There is no clear evidence that congenital
    anomalies are associated with surgery or
    anesthesia during pregnancy
  • All efforts should be made to minimize adverse
    perturbations of the fetal environment.
  • No anesthetic technique has been shown to improve
    fetal outcome.