3. Non-Obstetric Surgery during pregnancy Flashcards
A 28-year-old woman presents for acute appendicectomy – she is 22 weeks pregnant.
a) List the risks to the fetus during anaesthesia for the mother. (5 marks)
- > > Hypoxia, hypercarbia:
failure to adequately manage maternal airway
and ventilation can result in
uterine artery constriction,
hypoxia, hypercarbia and myocardial depression
of the fetus.
- > > Hyperventilation of mother
causing hypocarbia can cause uterine
artery vasoconstriction,
poor perfusion and leftward shift of maternal
oxyhaemaglobin dissociation curve. - > > Hypoperfusion:
Fetoplacental unit entirely dependent
on maternal perfusing pressure.
Therefore, it is necessary to maintain
maternal blood pressure and
manage aortocaval compression.
- > > neuronal apoptosis
As yet unconfirmed/unquantified
anaesthetic-induced neuronal apoptosis
in developing brain. - > > Risk of miscarriage –
unquantified. Likely to have more to
do with the disease process necessitating
the surgery or the surgery itself.
b) How can the risks to the fetus be minimised? (10)
> > Defer surgery until after delivery
unless absolutely necessary.
> > Multidisciplinary approach,
involve obstetricians in the assessment of
pre- and postoperative maternal and fetal well-being.
> > Airway and respiratory:
• RSI after antacid premedication,
rapid securing of airway.
Extubate awake, sitting up.
• Ventilation targeted to
end-tidal carbon dioxide
and oxygen saturations to reduce
the possibility of hypoxia and
hypercarbia in the fetus.
> > Cardiovascular:
• Left lateral tilt, adequate filling,
and maintenance of maternal
blood pressure at normal levels all
help minimise risk of placental
hypoperfusion.
Ensure adequate analgesia as
Raised circulating catecholamines will
compromise placental perfusion.
> > Neurological:
• Shortest duration of anaesthesia possible
reduces the exposure of
fetal brain to anaesthetic agents.
• Avoidance of general anaesthesia
through the use of regional
or neuraxial technique, where possible.
Not an option for appendicectomy.
c) What additional pre- and intraoperative steps would you take to ensure fetal safety if she was 27 weeks
pregnant? (5 marks)
> > Discussion with neonatologists preoperatively:
fetus is now viable and preparations
for consequences of premature labour are necessary.
If NICU cot not available, consideration
should be given to in utero transfer
to hospital where cot is available,
if maternal condition permits.
> > Discussion with obstetricians regarding
possible need for tocolysis and
steroids for fetal lung maturation
(urgency of surgery may not allow time
for this to be fully effective).
> > Pre-, intra- and postoperative
cardiotocographic fetal monitoring.
> > Ensure liaison between obstetricians
and surgeons regarding planned
surgical approach:
open versus laparoscopic approach,
consideration of site of laparoscope insertion.
> > Avoid NSAIDs due to risk of
premature closure of ductus arteriosus.
32/40
Key anaesthesia-relevant timings in obstetrics:
> > Risk of teratogenesis in
first trimester when main organ systems are
being developed, especially 2–8/40.
> > Consider need for antacid premedication
and RSI from approximately 12/40.
> > Risk of aortocaval compression f
rom approximately 20/40.
> > Surgery and anaesthesia confer i
ncreased risk of miscarriage in the
middle trimester and increased risk
of early labour later in pregnancy.
> > The fetus is potentially viable
from 24/40 onwards, sometimes earlier
BJA article additional points
1 1st trimester
Commonly used preoperative medications, including benzodiazepines or opioids, may be safely offered without concern for fetal cleft palate
2 Second trimester (weeks 13–26)
The second trimester is preferred for non-elective surgery. Patients are considered to be at the lowest risk for preterm delivery, surgical exposure is enhanced as the uterus is lower in the abdomen, and major embryonic development is complete by the eighth week
3 the following are helpful: fetal monitoring can alert you if optimisation of maternal positioning, oxygenation or blood pressure is needed.
4 Increased minute ventilation, driven mostly by increased tidal volumes, leads to compensated respiratory alkalosis with a pH nearing 7.44
5 Renal
Renal changes impact fluid and electrolyte balance, and drug metabolism and elimination. Renal blood flow and glomerular filtration rate increase by 75% and 65% above baseline
Serum creatinine decreases by the end of the first trimester; therefore, elevated creatinine levels should be investigated and can alter drug dosing strategies
6
However, rapid sequence induction with aspiration prophylaxis should be considered in any trimester if the patient is experiencing nausea, vomiting, pain, infection, and gastro-oesophageal reflux; has a history of hiatus hernia; or has a full stomach.
7
Although laparoscopy is considered safe during pregnancy and has reduced morbidity compared with open procedures, CO2 insufflation confers a higher risk of hypercarbia.7 Hypercarbia, hypotension and hypoxaemia may lead to vasoconstriction and subsequent reduction in uteroplacental perfusion, which may lead to fetal distress.
8
Reversal of neuromuscular block
Unless confronted with a ‘cannot intubate, cannot ventilate’ scenario, the 2019 Society for Obstetric Anesthesia and Perinatology consensus statement on sugammadex recommends against its use during pregnancy because of concerns about progesterone binding.
BJA
Newly postpartum
Neonatal (breastfeeding) considerations
Many mothers will ask when they can resume breastfeeding after surgery. The old recommendation of discarding breast milk while in the PACU is not supported by the ASA or the Association of Anaesthetists.9,10 Although all anaesthetic medications transfer to breast milk to some degree, the vast majority are in very low concentrations,
Some exceptions to this are
opioids that have genetic variants for metabolism
(e.g. codeine and pethidine [meperidine]),
certain antibiotics (e.g. tetracycline)
and cardiovascular agents (e.g. amiodarone and statins)
Maternal considerations
The return to maternal physiological baseline is gradual and often takes place over weeks.
Cardiac output may reach values 150% above pregnancy baseline immediately postpartum and may take up to 24 weeks to return to normal.5
Maternal heart rate stabilises within 2 weeks. The dilutional anaemia seen throughout the pregnancy resolves by 3 weeks postpartum.
Gastric emptying, volume and pH return to pre-pregnancy levels at 18 h postpartum
Incidence
Non-obstetric surgery is required in 0.5–2.0% of women (the incidence varies
with the survey). Acute appendicitis occurs in 1 in 2,000 confinements, and other
surgical procedures include ovarian cystectomy and cervical cerclage. Maternal
trauma may also necessitate surgery. The anaesthetic considerations vary according
to gestational age.
General Principles
Maternal safety considerations are as for any general anaesthetic. In respect of the fetus,
the timing of surgery should be such as to maximize fetal viability. The techniques used
should minimize the risks of teratogenesis or the onset of premature labour, and
prevent uterine hypoxia or hypoperfusion. The same principles apply to postoperative
analgesia and to fluid and oxygen therapy
First Trimester
The major concerns are of teratogenesis and of spontaneous abortion. Up until
15 days of gestation the embryo is either lost or preserved intact, and so anaesthesia
during this period cannot be teratogenic. The developing fetus thereafter is most
vulnerable up to around 60 days (8–9 weeks) of gestational age.
more
recent meta-analysis concluded that non-obstetric surgery and anaesthesia did not
increase the risk of birth defects and spontaneous abortion
offered regional anaesthesia where this is appropriate and/or elective
surgery should be deferred. The teratogenic effects of nitrous oxide have been
demonstrated only in rats, and risks to theatre personnel are negligible with modern
gas scavenging systems.
Factors Which Affect Placental Drug Transfer
The placenta is in effect a lipid bilayer.
Some nutrients cross this membrane by active
transport processes, but drugs cross only by passive diffusion.
Small hydrophilic molecules (up to a molecular weight of around 100) will diffuse
across the placenta, but transfer of larger compounds that are poorly lipid-soluble
depends largely on the concentration gradient (according to Fick’s law of diffusion),
on the permeability and on the area available for transfer. Permeability is inversely
proportional to molecular weight.
Transfer depends on the diffusion gradient, and this in turn is affected by the degree
of protein binding and ionization on either side of the membrane.
Local anaesthetics, for example, may concentrate on the fetal side of the circulation, due to ion trapping.
The relative fetal acidaemia increases the proportion of drug in the ionized form,
thereby reducing its transfer back across the placental membrane. The same is true of
opioids such as pethidine and alfentanil.
Lipophilic substances will cross the placenta according to flow-dependent transfer
according to the rate at which they are delivered to the placental circulation.
Communicating Risks to the Mother
Teratogenesis:
major organogenesis is completed by the eighth week of pregnancy
and, although the risk of other malformations persists briefly beyond that period, a
mother who was 10 weeks into pregnancy can be reassured that the risks are
negligible.
Were she to require an anaesthetic in very early pregnancy, you could
explain that you would use agents whose risks of causing fetal defects were extremely
small. In practice, this would mean using the older agents which have been in long established use.
You would, however, recommend regional or neuraxial anaesthesia if
feasible, as this effectively reduces any risk of congenital anomaly to zero.
Spontaneous abortion:
the increased risk of miscarriage is also very small, and
probably bears no relation to anaesthesia. It is more likely that direct surgical stimulation
might provoke premature uterine activity, but in practice this is unusual, even after
pelvic surgery. The exception is following cervical cerclage, but in this case it should be
the obstetric team rather than the anaesthetist who explains the risks and benefits.
General anaesthesia and developmental delay: the concerns about neuronal damage
associated with general anaesthesia in young children (see under ‘Mechanisms of have extended to the fetus. In the
context of non-elective surgery for the mother, however, there is little that can be
done to offset any potential risks, which do at the moment remain suggestive but
unproven.
