Introduction:
Anesthesia role will be there in all surgical specializations in those Obstetrics is important one. But in obstetrical anesthesia there are some controversial issues also.
Anesthesia role will be there in all surgical specializations in those Obstetrics is important one. But in obstetrical anesthesia there are some controversial issues also.
Giving
anesthesia in a obstetrical patient is not as easy as in general people
because nobody knows when the labor begins, and anesthesia may have to
be given within short time of a full meal. Patient may vomit and
gastric contents may be aspirated leading to maternal morbidity and
sometimes mortality.
Along
with normal physiological adaptations of pregnancy which will affect
the type of analgesia and anesthesia, the associated risk factors like
preeclampsia, placental abruption, and chorioamnionitis etc will also
affect the choice.
Though
obstetrical anesthesia is serving patients in relieving their pain but
the complications should not be ignored as these are responsible for 1.6
percent of pregnancy-related maternal deaths.
Nowadays
anesthesia-related maternal mortality has declined significantly
because of the measures using to increase the safety. Among them first
to mention is increased use of regional analgesia, rather than general
anesthesia. Second one is the increased availability of in-house
anesthesia coverage.
But
still inadequate anesthesia services have been are remaining as a
leading and potentially preventable cause of maternal deaths in some
developing countries.
General principles followed in obstetrical anesthesia services:
Obstetrical
anesthesia can be given either on request of the woman or as a
responsibility of the obstetrician to help her as much as possible in
relieving the pain.
Actually
there should be combined effort of the obstetrician and the
anesthesiologist in managing the patient. Before planning to give
anesthesia patient should be examined to identify any risk factors and
to plan according to them. By this we can minimize the need for
emergency anesthesia as it may become hazardous.
The risk factors are,
If
patient is morbidly obese it will become difficult to keep her in
position to give spinal or local anesthesia and also the dose of the
drugs also changes.
In
case of any anatomical abnormalities or edema of the face or neck
intubation during general anesthesia will become a problem. If spinal
abnormality is there giving spinal or epidural anesthesia will become a
problem. Any prior surgeries or trauma can also lead to these
abnormalities. So, verifying the previous medical and surgical history
of the patient is important.
In
case of general anesthesia patients with short neck or with arthritis
of neck or having goiter will create problems whereas in woman with
extreme short stature giving spinal will become a problem as identifying
the inter vertebral space will become a problem.
In
woman with medical conditions like pulmonary or cardiac or neurological
problems or bleeding disorders or with severe pre-eclampsia , sudden
untoward effects can occur during anesthesia better to take physician
consultation and he should be informed about the posting of the case.
If
the woman is having any prior history of anesthetic complications,
through history to be taken regarding it and measures to be taken to
prevent them.
If
planning for normal delivery, the chances of converting into operative
delivery to be kept in mind like in cases of malpositions, bigbaby,
placenta previa, high-order multiple gestation etc.
If a hospital is said to be having good obstetrical anesthesia services, ideally should have,
-
A 24 hours availability of a licensed obstetrical practitioner, who is
also trained to administer an appropriate anesthetic and to maintain of
vital functions in case of an obstetrical emergency. The obstetrician
should be proficient in giving local and pudendal analgesia. In case of
emergency, regional analgesia may be administered by the properly
trained obstetrician but anesthesiologist is preferred, so that the
obstetrician can concentrate on laboring woman and her fetus. As per general anesthesia is concerned it should be administered only by those with special training.
- A 24 hours availability
of anesthesia personnel, so that cesarean delivery can be started
within 30 minutes of the decision or if the patient to be shifted
immediately to caesarean section from the labor board and he should take
responsibility of all the drugs he has administered.
- A 24 hours availability
of a qualified physician with obstetrical exposure to take care of
emergencies that can occur during vaginal or cesarean delivery or during
administration of anesthesia.
- Availability of good equipment, facilities, and supporting team to the obstetrician and anesthesiologist in the surgical suite.
- Immediate availability of pediatrician personnel to look after the baby if resuscitation is needed as depressed newborn.
Individual pain tolerability:
How the woman experiences the labor pain is entirely based
individual’s pain tolerability and response to variable stimuli. This
is modified by emotional, motivational, cognitive, social and cultural
circumstances. It also depends on the ability of the woman and her
caregivers to anticipate her pain experience prior to labor. So, in
deciding the method of pain control individualization is desirable.
Non pharmacological methods used for control of pain:
The pain during labor is aggravated by fear
and imaginations by the woman. If before delivery the woman receives
counseling regarding the events that take place during delivery and the
measures available to relieve the pain and if she gains confidence on
the obstetrical staff that cares for her, the intensity of the pain can
be decreased. This is psycho prophylactic method.
Pain
can be decreased by teaching pregnant women to practice relaxed
breathing and to her labor partners psychological support techniques.
By these techniques the need for potent analgesic, sedative, and
amnestic drugs during labor and delivery has decreased.
A
well motivated women with supportive spouse or other family member and
with a considerate obstetrician who instils confidence can easily pass
through the labor and delivery normally.
Analgesics and sedatives used during labor:
Analgesia
during labor can be started when uterine contractions and cervical
dilatation starts causing discomfort. To give pain relief a narcotic can
be used such as meperidine along with one tranquilizer drug such as
promethazine.
Successful
analgesia and sedation means which allow the mother to rest quietly in
between contractions. So, the discomfort usually is felt at the peak of
an effective uterine contraction but the pain is generally not
unbearable.
The other parenteral drugs used for labor pain are Fentanyl, Nalbuphine, Butorphanol, Morphine etc.
Parenteral agents:
Meperidine and Promethazine:
For intramuscular injection Meperidine
is given in dose of 50 to 100 mg with promethazine in dose 25 mg at
intervals of 2 to 4 hours. By intravenous injection of meperidine in
doses of 25 to 50 mg every 1 to 2 hours more rapid effect can be
achieved.
Analgesic effect is maximum after 30 to 45 minutes of an intramuscular injection but
Immediate effect can be seen after intravenous administration.
Meperidine
will cross the placenta and its half-life is around 13 hours, it is
longer in the newborn. It is having depressant effect in the fetus
which occurs after the peak maternal analgesic effect. Sometimes it
needs treatment with naloxone in 3 percent of newborns.
Butorphanol (Stadol):
This is a synthetic narcotic and given in 1- to 2-mg doses either IV or IM.
The
major side effects are somnolence, dizziness, and dysphoria. In some
cases neonatal respiratory depression is reported but in low incidence
than with meperidine. And a sinusoidal fetal heart rate pattern noted in
some cases following butorphanol administration.
These two drugs should not be given are contiguously, as butorphanol antagonizes the narcotic effects of meperidine.
Fentanyl:
Fentanyl is a short-acting and very potent synthetic opioid. It can be given in doses of 50 to 100 µg intravenously every hour.
The main disadvantage is a short duration of action. So, it requires frequent dosing or patient-controlled intravenous pump.
Compared with fentanyl, butorphanol provides better initial analgesia.
As per the efficacy of the parenteral agents is concerned, meperidine is found to be the most common opioid used worldwide for obstetrical analgesia. The parenteral opioids will not influence the length of labor or need for obstetrical intervention. Compared with them epidural analgesia provides superior pain relief.
And
intravenous and intramuscular sedatives are not without risks. Among
129 maternal anesthetic-related deaths 4 were estimated from this type
of sedation, in that one
is from aspiration, two are from inadequate ventilation and one from
over dosage. And also respiratory depression in newborn can occur due to
meperidine or other narcotics.
Narcotic Antagonists:
Naloxone: The antagonist normally used to reverse the respiratory depression induced by opioid narcotics is nalaxone.
It acts by displacing the narcotic from specific receptors in the central nervous system.
Naloxone, along with proper ventilation should be given to reverse respiratory depression in a newborn.
Naloxone
is contraindicated in a newborn of a narcotic-addicted mother because
of the fear that withdrawal symptoms may become precipitated.
Nitrous oxide:
Nitrous oxide is
used in obstetrical analgesia along with oxygen in the form of a
self-administered mixture of 50-percent nitrous oxide (N2O) and oxygen.
In
it two type of preparations are there, one is both gases premixed in a
single cylinder called Entonox, and in the other form a blender mixes
the two gases from separate tanks called Nitronox.
A breathing circuit is used to which the gases are connected through a valve that opens only when the patient inspires.
The suggestions for the use of nitrous oxide are:
The woman
should take slow deep breaths and she has to inhale the gas 30 seconds
before the next anticipated contraction and to stop when the
contraction starts to recede.
She has to breathe normally in between contractions by removing the mask. Either the patient or a person who is having knowledge about the circuit should hold the mask.
The attendant should be in verbal contact with the patient to monitor her conscious levels.
The
patient should be previously instructed that the pain will not become
completely eliminated but some amount of relief can be obtained.
During the process intravenous access to be secured.
Pulse oximetry used to measure the level of oxygen saturation and scavenging of exhaled gases to be maintained.
If previously opioids are administered additional
caution to be taken as the combination of opioids and nitrous oxide can
make the woman unconscious and unable to protect her airway.
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