incidental surgery during pregnancy

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2. Anesthesia for non-obstetric surgery during pregnancy
By Misganaw M.( BSC, MSC in Anesthesia)
May, 2023
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3. Outline
 Introduction
 Choice of anesthesia for non-obstetric surgery during pregnancy
 Maternal and fetal safety
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4. Introduction
 During pregnancy, surgery for non-obstetric procedures occurs in up
to 2% of women
 This figure may be considerably higher in the first trimester as
pregnancy may go undetected at the time of surgery
 Approximately 42% of procedures occur in the first trimester, 35%
during the second and 23% during the third
 The range and incidence of procedures are similar to the non-
pregnant group of young women
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5.  Acute abdominal problems are most common, with appendicectomy
ranking first followed by cholecystectomy
 Pregnancy predisposes to cholelithiasis and approximately 3% of
pregnant women develop gallstones, however only a limited number
require surgery
 Other common problems include adnexal disease (e.g. ovarian cysts
which may rupture or become torted) and trauma
 Anaesthetists who care for pregnant patients undergoing non-
obstetric surgery must provide safe anaesthesia for both the mother
and the foetus
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6.  To maintain maternal safety the physiological and anatomical
changes of pregnancy must be considered
 Anaesthetic techniques and drug administration modified
accordingly
 Foetal wellbeing is related to avoidance of foetal asphyxia,
teratogenic drugs and preterm labour
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9. Anesthetic goals
 Optimize or maintain normal maternal physiological function
 Optimize or maintain utero-placental blood flow and oxygen
delivery
 Avoid unwanted drug effects on the foetus
 Avoid stimulating the myometrium (oxytocic effects) - uterine
contractions
 Prevent hypotension, hypovolemia, hypoxia and hypothermia
 Avoid awareness during general anaesthesia
 Preferential use of regional anaesthesia
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11. Anesthesia and gestation
 Elective surgery should not be performed at all during pregnancy, and
only tubal ligation should be performed during the first 6 weeks
postpartum to allow the physiological changes of pregnancy to resolve
 Emergency surgery must proceed regardless of gestational age and the
primary goal is to preserve the life of the mother
 Where feasible, surgery is often delayed until the second trimester to
reduce the risk of both teratogenicity and miscarriage
 Anaesthetic management when the fetus is dead or non-viable should
follow the same principles as for the pregnant patient
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12. Anesthesia in the first trimester
 The ideal anaesthetic technique should not interfere with
fertilization or early embryo development and should result in
minimal postoperative nausea, sedation, pain and psychomotor
impairment
 Most procedures can be performed with small doses of midazolam
and opioids
 Continuous propofol sedation and patient-controlled sedation are
becoming popular
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13.  It is recommended that the use of propofol is always supervised by
Anesthetist
 Nitrous oxide should be avoided as animal studies provide evidence
that it is a potent inhibitor of methionine synthase
 However, currently, there is no evidence in human beings to suggest
that this is clinically significant
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14.  After 6–8 weeks gestation, cardiac, respiratory, metabolic and
pharmacological parameters are considerably altered
 With the increase in minute ventilation and oxygen consumption,
decreased FRC, pregnant women become hypoxemic more rapidly
 Supplementary oxygen must always be given during vulnerable
periods to maintain oxygenation
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15.  Airway management by a face mask, a laryngeal mask or tracheal
intubation can be technically difficult because of increased
anteroposterior chest wall diameter, breast enlargement, laryngeal
oedema and weight gain affecting the soft tissues of the neck
 Nasal tube airways should be avoided in pregnancy because of
increased vascularity of mucous membranes
 Marked reduction of plasma cholinesterase concentrations(30%
reduction) theoretically cause succinylcholine, ester local
anaesthetics and certain other drugs to have prolonged effects
 However, this is counterbalanced by increased volumes for drug
distribution
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16.  Neuromuscular drug monitoring is recommended
 Aspiration prophylaxis is recommended from the beginning of the
second trimester
 Pregnancy is associated with lower anesthetic requirements
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17.  The minimum alveolar concentration(MAC)for inhalation
anesthetics is reduced by 30% as early as 8–12 weeks of gestation
 I.V drugs that induce general anaesthesia should also be given in
lower doses
 Fetal well-being should be assessed by ultrasound or Doppler before
and after anesthesia/surgery
 Because of the increased risk of hypoxaemia, difficulties with
intubation, acid aspiration and risks to the fetus, regional anaesthesia
can be selected over general anaesthesia whenever feasible
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18. Anesthesia in the second trimester
 Aortocaval compression is a major hazard from 20 weeks onwards
(and sometimes even earlier); this compromises uterine blood flow
and, in some women, results in supine hypotension
 This effect may be exacerbated by regional or general anaesthesia
when normal compensatory mechanisms are attenuated or abolished
 Aortocaval compression is only effectively avoided by the use of the
lateral position
 It can be decreased by uterine displacement through wedging or
manual displacement
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19.  Venacaval compression results in distension of the epidural venous
plexus, increasing the risk of intravascular injection during regional
blockade
 The capacity of the epidural space is reduced, which probably
contributes to the enhanced spread of local anaesthetics in
pregnancy
 Pregnancy is associated with a hypercoagulable state because of
increased pro-coagulant factors
 The incidence of thromboembolic complications is at least five
times greater during pregnancy; thromboprophylaxis is essential
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20. Anesthesia for the third trimester
 At this gestation, delivery by caesarean section before major surgery
is often recommended
 Where possible, surgery should be delayed 48 h to allow steroid
therapy to enhance fetal lung maturation
 It may be appropriate to deliver the baby under regional anaesthesia
and then convert to a general anaesthesia for the definitive surgery
 Anaesthesia post delivery should be tailored to surgical
requirements, with the precaution that volatile agents should be
discontinued or used only in small doses (<0.5 MAC) along with
oxytocics to minimize the risk of uterine atony and haemorrhage
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21.  Surgery, stress and perhaps anaesthesia may suppress lactation, at
least temporarily
 Most drugs are excreted into breast milk; however, only a few are
absolutely contraindicated during breast feeding (e.g. radioactive
substances, ergotamine, lithium, psychotropic agents)
 The possible neonatal effects of other drugs such as opioids and
sedatives should be explained to the mother
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22. Issues approved by ASA and American College of Obstetricians
and Gynecologists (ACOG) 2011
 No currently used anaesthetic agents have been shown to have any
teratogenic effects in humans when using standard concentrations at
any gestational age
 Foetal heart rate monitoring may assist in maternal positioning and
cardiorespiratory management, and may influence a decision to
deliver the foetus
 Surgery should be done at an institution with neonatal and
paediatric service
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23.  A pregnant woman should never be denied indicated surgery,
regardless of trimester
 Elective surgery should be postponed
 If possible, non-urgent surgery should be performed in the second
trimester when preterm contractions and spontaneous abortion are
least likely
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24. Anesthetic technique
 No studies have shown a beneficial effect on the outcome of
pregnancy after regional compared with general anaesthesia
 However, regional anaesthesia minimizes fetal drug exposure,
airway management is simplified, blood loss may be decreased, and
overall risks to the mother and fetus are less
 The largest risk of regional anaesthesia is hypotension resulting
from sympathetic nerve blockade, which reduces uterine blood flow
and perfusion to the fetus
 Attention to maternal fluid volume and blood pressure is critical
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25.  Ephedrine has traditionally been the vasopressor of choice in this
situation because of its a- and b-receptor stimulating properties and
lack of effect on uterine blood flow
 More recent research has shown that it is more important to treat the
hypotension effectively than to worry about the choice of agent
 Therefore, drugs which have previously been contraindicated (e.g.
phenylephrine) are now considered safe
 General anaesthesia should only be given by a suitably trained
anaesthetist experienced in administering general anaesthesia to
obstetric patients
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26. Choice of anesthesia
Choice of Anaesthetic technique depends on
 Patient’s present surgical status (site and nature of surgery)
 Present gestational age of the foetus
 Pregnancy induced physiological changes and other co morbidities
 No technique has been proven to have superiority over the other in
foetal outcomes
 Regional techniques may be preferable
 Safe anaesthetic management is more important than particular
agent or technique
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27. General anesthesia
 Maintain left uterine displacment to prevent aortocaval compression
 Pre-oxygenation
 Rapid sequence induction (Thiopent. sod. & succinylcholine,
cricoid pressure and tracheal intubation using cuffed E.T. tube)
 Maintenance: muscle relaxant, an opioid and/ or inhalational agent (
≤ 2 MAC) is recommended
 The use of nitrous oxide should be limited in first trimester
 Opioids and induction agents decreases FHR variability to greater
extent than volatile agents
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28.  Ketamine increases uterine tone (in early pregnancy) and should not
be used
 Positive pressure ventilation may reduce UBF
 Avoid hyperventilation to maintain end tidal CO2 in normal
pregnancy range
 Patients on magnesium for tocolysis – reduce dose of NMBs
 Extubation when fully awake after return of protective airway
reflexes
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29. Regional anesthesia
 Minimal foetal drug exposure
 Avoidance of complications of general anaesthesia
 If no sedative or narcotics are supplemented, no change in FHR
variations
 Post operative analgesia
 Avoid hypotension i.e. adequate preloading, maintain left uterine
tilt, choice of vasopressor
 Patients on magnesium are more prone to hypotension
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30. Fetal safety
Prevention of foetal asphyxia
 One of the most serious risks to the foetus during maternal surgery
is intrauterine asphyxia
 This must be avoided by maintaining maternal oxygenation and
haemodynamic stability
 It is extremely important to avoid hypoxia, extreme hyper and
hypocarbia, hypotension and uterine hypertonus
 Maternal hypoxaemia causes uteroplacental vasoconstriction and
decreased perfusion, causing foetal hypoxia, acidosis and ultimately
death
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31.  Uteroplacental circulation is not autoregulated and hence perfusion
is entirely dependant on the maintenance of an adequate maternal
blood pressure and cardiac output
 Hypotension can be caused by anaesthetic drugs, central neuraxial
blockade, hypovolaemia or aortocaval compression
 Maternal hypotension needs to be treated by ensuring left lateral tilt
and bolus of IV fluids
 Additional vasopressors may be required and currently it is felt
alpha agonist like phenylephrine that produce a better foetal acid
balance than indirect sympathomimetic agent such as ephedrine
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32. Drugs and teratogenicity
 Teratogenicity is defined as the observation of any significant change
in the function or form of a child secondary to prenatal treatment
 The teratogenicity of a drug depends upon the dose administered, the
route of administration and the timing of foetal exposure
 During the 1st two weeks of human gestation the teratogens have an all
or none phenomenon; the foetus is lost or is preserved fully intact
 The period from the 3rd to the 8th week of gestation, represents the
most important time for organogenesis during which drugs can exert
their most serious teratogenic effects
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33.  After this, drug exposure should not cause organ abnormalities, but
foetal growth retardation may occur
 Although most anaesthetic drugs are known teratogens in certain
species, most agents are safe in humans
 The foetus is at more risk from asphyxia than the teratogenic effect
of anaesthetic drugs
 Studies looking at the outcomes of women who underwent surgery
during pregnancy suggest no increase in congenital anomalies in
their offspring but an increase in foetal loss, growth restriction and
low birth weight attributed to the requirement for surgery (not
anaesthetic administration)
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34.  Nitrous oxide inhibits methionine synthetase, and therefore there is
concern it could affect DNA synthesis in the developing foetus
 It has also been shown to be teratogenic during peak organogenesis
in rodents, but there is no evidence in humans
 Anaesthesia can be safely delivered without nitrous oxide and
therefore many would avoid its use during non-obstetric surgery in
the pregnant woman
 Another drug of concern is ketamine, this causes increased uterine
tone and foetal asphyxia, so that it should not be used in the first two
trimesters but the effect is not seen in the third trimester
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35.  Benzodiazepines have been associated with a cleft lip and palate in
animal studies
 The association in humans is controversial
 A single dose has not been associated with teratogenicity and single
doses may be useful to provide anxiolysis preoperatively
 Long term use should be avoided as neonatal withdrawal may also
occur
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36. Prevention of pre-term labour / foetal monitoring
 Surgery during pregnancy increases the risk of spontaneous
abortion, preterm labour and preterm delivery
 This risk is increased with intra-abdominal procedures
 Uterine manipulation should be kept to a minimum and drugs that
increase uterine tone (e.g. ketamine) should be avoided
 Prophylactic tocolytic therapy is controversial as there are
associated maternal side effects and efficacy during nonobstetric
surgery has not been proven
 Perioperative foetal monitoring is also an area of controversy
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37.  From 18-22 weeks foetal heart rate (FHR) monitoring is feasible
and from 25 weeks heart rate variability can be observed
 Continuous monitoring may be technically difficult during
abdominal operations or in cases of maternal obesity
 Anaesthetic agents reduce both baseline FHR and FHR variability
and therefore interpretation is difficult and may lead to unnecessary
interventions
 Anaesthetic agents do not cause decelerations or persistent foetal
bradycardia and these changes may indicate foetal distress
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38.  Monitoring may enable swift action to be taken such as the
optimisation of maternal haemodynamics, oxygenation and
ventilation
 Although perioperative foetal monitoring has not been shown to
improve foetal outcome, a sensible approach would be to use
cardiotocography (CTG) monitoring where possible and practical
when the foetus is of a viable age
 If the foetus is not of a viable age or perioperative CTG monitoring
is not possible / practical, FHR monitoring should occur pre and
post-operatively and staff should be alert to the signs of premature
labour
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39. Laparoscopic surgery
 There were previous concerns regarding foetal safety during laparoscopic
surgery
 These included fears of direct uterine and foetal trauma, foetal acidosis due
to absorbed carbon dioxide and decreased maternal cardiac output
secondary to the increased intra-abdominal pressure and positioning with a
subsequent decrease in uteroplacental perfusion
 There are advantages to laparoscopic surgery for both the mother and the
foetus such as decreased post-operative pain (and therefore less need for
analgesics), shorter recovery times and a lower risk of thromboembolic
events
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40.  A study done in Sweden involving more than 2 million deliveries,
favoured laparoscopic surgery compared with an open procedure
 The advantages include less exposure of the fetus to possibly toxic
agents, smaller incisions, decreased pain, less need for analgesics,
more rapid recovery and mobilization
 Pregnancy should therefore not be seen as a contraindication to
laparoscopic surgery if surgery is required
 Certain precautions should be taken, pneumatic stockings should be
used to promote venous return and the lowest pressure
pneumoperitoneum (<12mmHg) should be used where possible
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41.  Carbon dioxide pneumoperitoneum is associated with an increased
risk of hypoxaemia, hypercarbia and hypotension because of the
physiological and anatomical changes of pregnancy
 PaCO2 should be closely monitored by the routine use of end tidal
carbon dioxide monitoring and consideration of arterial blood gas
analysis in selected cases
 Aortocaval compression should be avoided
 FHR monitoring may be advisable to detect foetal compromise early
allowing optimisation of maternal haemodynamics
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42. Postoperative care
 As previously stated pregnancy induces a hypercoaguable state and the
risk of thromboembolic disease is further increased by venous stasis
 Attention to thromboprophylaxis is therefore essential
 This should include early mobilisation, maintaining adequate hydration,
stockings, other calf compression devices and consideration of
pharmacological prophylaxis (low molecular weight heparin)
 Adequate analgesia is important as pain will cause increased circulating
catecholamines which will impair uteroplacental perfusion
 Analgesia may mask the signs of early preterm labour and therefore
tocometry is useful to detect contractions
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43. References
 Millers anesthesia ,8th edition
 Oxford anesthesia,4th edition
 E safe anesthesia
 Morgan's clinical anesthesia, 4th edition
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44. THANK YOU!
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