Anesthesia for Nonobstetric Surgery during Pregnancy

1
Anesthesia for Nonobstetric Surgery during
Pregnancy

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

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Nonobstetric Surgery during Pregnancy Special
Concerns

• 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.

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Physiologic Changes of PregnancyCardiovascular

• 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.

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Physiologic Changes of PregnancyAorto-Caval
Compression

• 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)

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Physiologic Changes of PregnancyAorto-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

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Physiologic Changes of PregnancyRespiratory

• 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

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Physiologic Changes of PregnancyRespiratory 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

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Physiologic Changes of PregnancyRespiratory 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
  breathing
• perfusion of unventilated alveoli (shunting) ?
  hypoxemia
• Hypoxemia worsened by aorto-caval compression

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Physiologic Changes of PregnancyGastrointestinal

• 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

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Physiologic Changes of PregnancyGastrointestinal
II

• It is recommended that pregnant women
• gt18-20 weeks gestation or
• with reflux symptoms
• be treated as at risk for pulmonary
  aspiration
• 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

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Physiologic Changes of PregnancyNeurologic

• 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

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Physiologic Changes of PregnancyRenal

• 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.

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Risks to the FetusAlterations in Uterine Blood
Flow

• 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

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Risks to the FetusAlterations in Uterine Blood
Flow

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

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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

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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).

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Risks to the Fetus Teratogenicity

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

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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

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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

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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.

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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
  administration.
• ? Due to sympathetic NS stimulation by N2O, among
  many other possibilities

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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.

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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.

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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

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Occupational Exposure to Anesthetic Agents in
Pregnancy

• 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.

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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.

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Fetal Outcome of Nonobstetric Surgery during
Pregnancy

• 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

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Fetal Outcome of Nonobstetric Surgery during
Pregnancy

• 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

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Fetal Outcome of Nonobstetric Surgery during
Pregnancy

• 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

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Fetal Outcome of Nonobstetric Surgery during
Pregnancy

• 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.

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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.

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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

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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.

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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

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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
  output.

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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
  1997177673-9
• 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

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Gasless Laparoscopic TechniqueAkira, 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

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Recommendations for Administering Anesthesia for
Surgery during Pregnancy

• 1. Do not perform elective surgery during
  pregnancy
• 2. Query regarding possibility of pregnancy.
  Universal preoperative pregnancy testing is not
  standard.
• 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
  needed.
• 5. Local or regional anesthesia is favored, if
  feasible, to avoid manipulation of maternal
  airway minimize fetal drug exposure.

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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
  anesthesia.
• 8. Normal maternal ventilation should be
  maintained, including normal PaCO2 for pregnancy
  (ETCO2).

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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)

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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)

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Conclusions

• 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
  pregnancy)

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Conclusions

• 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.