Analgesics and anestheia

BY, MS. PRIYANKA GOHIL
MSc (N) OBG
PhD SCHOLAR

Relief of pain during labor and delivery is an essential part in
good obstetric care.
Choice of anesthesia depends upon the patient’s conditions
and the associate disorders.
Anesthetic complications may cause maternal death.
Anesthesia following full meal may cause maternal death due
to vomiting and aspiration of gastric contents.

 Maternal risk factors for anesthesia are:
Short stature
Short neck
Marked obesity
Severe preeclampsia
Bleeding disorders
Placenta previa
Medical disorders like cardiac, respiratory and neurological
disease

NERVE SUPPLY OF THE GENITAL TRACT:-
Uterus is under both nervous and hormonal control.
Hypothalamus controls the uterine activity through the reticular
formation which balances the effects of the two autonomic
divisions.

MOTOR NERVE SUPPLY:-
The uterus receives both sympathetic and parasympathetic
nerve fibers.
The sympathetic nerve fibers arise from lower thoracic and
upper lumbar segments of the spinal cord.
The parasympathetic fibers arise from sacral 2, 3 and 4 segments
of the spinal cord.

The preganglionic fibers of the sympathetic nerves arising from
the spinal cord pass through the ganglia of the sympathetic trunk
to aorticorenal plexus where they synapse.
 The aorticorenal plexus continues as the superior hypogastric
plexus or presacral nerve and passes over the bifurcation of aorta
and divides into right and left hypogastric nerves.
Each hypogastric nerve joins the pelvic parasympathetic nerve of
the corresponding side and forms the pelvic plexus (right and
left) or inferior hypogastric plexus.
The pelvic plexus then continues along the course of the uterine
artery as paracervical plexus on each side of the cervix.

SENSORY PATHWAY:-
Sensory stimuli from the uterine body are transmitted through
the pelvic, superior hypogastric and aorticorenal plexus to the
10th, 11th and 12th dorsal and the first lumbar segments of the
spinal cord.
Sensory stimuli from cervix pass through the pelvic plexus along
the pelvic parasympathetic nerves to sacral segments 2, 3 and 4
of the spinal cord.

Sensory stimuli from upper vagina pass to 2, 3 and 4 sacral
parasympathetic segments and from lower vagina pass through
the pudendal nerve.
The perineum receives both motor and sensory innervation
from sacral roots 2, 3 and 4 through the pudendal nerve.
The branches of ilioinguinal and genital branch of genitofemoral
nerves supply the labia majora and also carry the impulses from
the perineum.

NERVOUS CONTROL OF THE UTERINE CAVITY:-
Regarding motor innervation of the uterus, the sympathetic
nerves rather than the parasympathetic have the influences over
the uterine activity.

HORMONAL CONTROL:-
It is generally agreed that intact nerve supply is not essential for
the initiation and progress of labor.
Total spinal block does not inhibit uterine activity, provided
blood pressure is not allowed to fall, and normal vaginal delivery
can occur in the paraplegic patient.
It is believed that some hormones are essential for the control of
uterine activity.

Oxytocin, a hormone derived from posterior pituitary maintains
the uterine activity during labor.
Progesterone is the pregnancy–stabilizing hormone.
Labor commences when it is withdrawn.
Adrenaline with its beta activity inhibits the contraction of
uterus, while its alpha activity excites it.

Pain during labor results from a combination of uterine
contractions and cervical dilatation.
During cesarean delivery incision is usually made around the T12
dermatome anesthesia is required from the level of T4 to block
the peritoneal discomfort.
Labor pain is experienced by most women with satisfaction at
the end of a successful labor.
Antenatal (mothercraft) classes, sympathetic care and
encouraging environment during labor can reduce the need of
analgesia.

 Drugs have an important part to play in the relief of labor pain
but it must not be supposed that they are of greater importance
than proper preparation and training for childbirth.
The intensity of labor pain depends on the intensity and
duration of uterine contractions, degree of dilatation of cervix,
distension of perineal tissue, parity and the pain threshold of the
subject.
The most distressing time during the whole labor is just prior to
full dilatation of the cervix.

 The ideal procedure should produce efficient relief of pain but
should neither depress the respiration of the fetus nor depress
the uterine activity causing prolonged labor.
The drug must be nontoxic and safe for both mother and fetus.
But it is regretted that no such agent is available at present that
fulfills all these conditions.
Every case of labor does not require analgesia and only
sympathetic explanation may be all that is required.

The following factors are important to control the dose of
sedative and analgesics:
1. Pain threshold:
The threshold of pain varies from patient to patient.
Some patients experience severe pain though the uterine
contractions are relatively weak.
In such cases, it is preferable to control the pain adequately.

2. Parity:
The multiparous women need less analgesia due to added
relaxation of the birth canal and rapid delivery.
3. Maturity of the fetus:
Minimal doses of drugs are indicated while the fetus is
thought to be premature to avoid neonatal asphyxia.

 For the purpose of selecting a general analgesic drug, labor has
been divided arbitrarily into two phases.
The first phase corresponds up to 8 cm dilatation of the cervix in
primigravidae and 6 cm in case of multipara.
The second phase corresponds to dilatation of the cervix beyond
the above limits up to delivery.
The first phase is controlled by sedatives and analgesics, and the
second phase is controlled by inhalation agents.
The idea is to avoid the risk of delivery of a depressed baby.

OPOID ANALGESICS
PETHIDINE:
For a long time pethidine has been used as an analgesic in labor.
It has got strong sedative but less analgesic efficacy. Pethidine is
generally used in the early first stage of labor and indicated when
the discomfort of labor merges into regular, frequent and painful
contractions.
The initial dose is 100 mg (1.5 mg/kg body weight) IM and
repeated as the effect of the first dose begins to wane, without
waiting for the reestablishment of labor pain.

The side effects of pethidine to the mother are nausea,
vomiting, delayed gastric emptying.
Ranitidine should be given to inhibit gastric acid production, and
emetic effect is counteracted by metoclopramide (10 mg IM).
Pethidine crosses the placenta and accumulates in fetal tissues.
Pethidine reduces baseline variability, depresses respiration and
suckling of the newborn when administered before delivery.

MEPERIDINE
Compared to morphine, analgesic effect is one tenth, but
respiratory depression effect is less.
It is used 25–50 mg (1–3 mg/kg IM) or a PCA (patient controlled
analgesia) pump 15 mg every 10 minutes.
Repeated use or PCA in labor, infants may need naloxone at
delivery.
Maximum placental transfer and neonatal depression occur 2–3
hours of use.

FENTANYL
Fentanyl is a short acting synthetic opioid and is equipotent to
pethidine.
It has less neonatal effects and less maternal nausea and
vomiting.
It needs frequent dosing.
It can be used as PCA.

PHENOTHIAZINES
Promethazine (phenergan) is commonly used in labor in
combination with an opioid.
It does not cause major neonatal depression.
Promethazine is a weak antiemetic drug and causes sedation in
the mother.

NARCOTIC ANTAGONIST
Narcotic antagonists are used to reverse the respiratory
depression induced by opioid narcotics.

NALOXONE
Naloxone is given to mother 0.4 mg IV in labor.
It may have to be repeated.
It is given to the newborn 10 μg/kg IM or IV and is repeated if
necessary when the infant is born with narcotic depression.
Naloxone is given to a newborn born of a narcotic addicted
mother, with proper ventilation arrangement only otherwise
withdrawal symptoms are precipitated.

BENZODIAZEPINES (DIAZEPAM)
It is well tolerated by the patient.
It does not produce vomiting and helps in the dilatation of
cervix.
It is metabolized in the liver.
The usual dose is 5–10 mg.
It may be used in larger doses in the management of
preeclampsia.
However, diazepam is avoided in labor.

Major disadvantages are: Loss of beat to beat variability in labor,
neonatal hypotonia and hypothermia.
Flumazenil is a specific benzodiazepine antagonist.
It can reverse the respiratory depression effect of
benzodiazepines.

COMBINATION OF NARCOTICS AND ANTIEMETICS
Narcotics may be used in combination with promethazine,
metoclopramide or ondansetron.
The advantages claimed that the combination potentiates the
action of narcotic, produces less respiratory depression and
prevents vomiting.
But there are also disadvantages like hypotension and delay of
second stage of labor.

INHALATION METHODS
PREMIXED NITROUS OXIDE AND OXYGEN (Entonox):
 Cylinders contain 50% nitrous oxide and 50% oxygen mixture.
Entonox apparatus has been approved for use by midwives.
This agent is used in the second phase (from 8 cm dilatation of
cervix to delivery).
 It can be self administered.
Entonox is most commonly used inhalation agent during labor in
the UK.

Hyperventilation, dizziness, hypocapnia are the side effects.
The woman is to take slow and deep breaths before the
contractions and to stop when the contractions are over.
The woman should be monitored with pulse oximetry.

COMMONLY USED LOCAL ANESTHESIA IN OBSTETRICS

REGIONAL (NEURAXIAL) ANESTHESIA
When complete relief of pain is needed throughout labor,
epidural analgesia is the safest and simplest method for
procuring it.
It provides sensory as well as various degrees of motor blockade
over a region of the body.
But anesthetists/obstetricians have to be trained properly to
make use of this very valuable method in normal and abnormal
labor.

CONTINOUS LUMBAR EPIDURAL BLOCK
 A lumbar puncture is made between L2 and L3 with the epidural
needle (Tuohy needle).
With the patient on her left side, the back of the patient is
cleansed with antiseptics before injection.
When the epidural space is ensured, a plastic catheter is passed
through the epidural needle for continuous epidural analgesia.
 A local anesthetic agent (0.5% bupivacaine) is injected into the
epidural space.
Full dose is given after a test dose when there is no toxicity.

 For cesarean delivery a block from T4 to S1 is needed.
Repeated doses (top ups) of 4–5 mL of 0.5% bupivacaine or 1%
lignocaine are used to maintain analgesia.
Epidural analgesia, as a general rule should be given when labor
is well established.
Maternal hydration should be adequate with normal saline or
Hartmann’s solution (crystalloid) infusion prior commencing the
blockade.

 The patient’s blood pressure, pulse and the fetal heart rate
should be recorded at 15 minutes interval following the
induction of analgesia and hypotension, if occurs, should be
treated immediately.
The woman is kept in semilateral position to avoid aortocaval
compression.

CONTINOUS LUMBAR EPIDURAL BLOCK
 Epidural analgesia is especially beneficial in cases like
pregnancy-induced hypertension, breech presentation, twin
pregnancy and preterm labor.
Previous cesarean section is not a contraindication.
Epidural analgesia when used there is no change in duration of
first stage of labor.
But second stage of labor appears to be prolonged by 15–30
minutes.
This might lead to frequent need of instrumental delivery like
forceps or ventouse.

PARACERVICAL NERVE BLOCK
 Paracervical nerve block is useful for pain relief during the first
stage of labor.
Following the usual antiseptic safe guards, a long needle (15 cm
or more) is passed into the lateral fornix, at the 3 and 9 o’clock
positions.
Five to ten milliliter of 1% lignocaine are injected at the site of
the cervix and the procedure is repeated on the other side.
 This dose is quite sufficient to relieve pain for about an hour or
two, and injections can be given more than once if necessary.

Bupivacaine is avoided due to its cardiotoxicity.
Paracervical block should not be used where placental
insufficiency is present.
Although paracervical block may be used from 5 cm dilatation of
the cervix, it is most useful toward the end of the first stage of
labor to remove the desire to bear down earlier.
 Paracervical block can only relieve the pain of uterine
contraction and the perineal discomfort is removed by pudendal
nerve block.
Fetal bradycardia is a known complication.

This is due to decreased placental perfusion resulting from
uterine artery vasoconstriction or its direct depressant effect on
the fetus following transplacental transfer.
This method is not commonly used.

PUDENDAL NERVE BLOCK
It is a safe and simple method of analgesia during delivery.
Pudendal nerve block does not relieve the pain of labor but affords
perineal analgesia and relaxation.
Pudendal nerve block is mostly used for forceps and vaginal breech
delivery.
Simultaneous perineal and vulval infiltration is needed to block the
perineal branch of the posterior cutaneous nerve of the thigh and
the labial branches of the ilioinguinal and genitofemoral nerves
(vide supra).
This method of analgesia is associated with less danger, both for
mother and baby than general anesthesia.

Technique:
The pudendal nerve may be blocked by either the transvaginal or
the transperineal route.
Transvaginal route:
Transvaginal route is commonly preferred.
A 20 mL syringe, one 15 cm (6”) 22 gauge spinal needle and about 20
mL of 1% lignocaine hydrochloride are required.
The index and middle fingers of one hand are introduced into the
vagina, the finger tips are placed on the tip of the ischial spine of one
side.

 The needle is passed along the groove of the fingers and guided to
pierce the vaginal wall on the apex of ischial spine and thereafter
to push a little to pierce the sacrospinous ligament just above the
ischial spine tip.
After aspirating to exclude blood, about 10 mL of the solution is
injected.
The similar procedure is adopted to block the nerve of the other
side by changing the hands.

COMPLICATIONS
Hematoma formation, infection and rarely intravascular
injection or allergic reaction.
Toxicity may affect:
a. CNS: excitation, ringing in the ears and convulsions.
b. Cardiovascular: tachycardia, hypotension, arrythmias, even
cardiac arrest.

SPINAL ANESTHESIA
Spinal anesthesia is obtained by injection of local anesthetic
agent into the subarachnoid space.
It has less procedure time and high success rate.
Spinal anesthesia can be employed to alleviate the pain of
delivery and during the third stage of labor.
For normal delivery or for outlet forceps with episiotomy,
ventouse delivery, block should extend from T10 (umbilicus) to
S1.

 For cesarean delivery level of sensory block should be up to T4
dermatome.
Hyperbaric bupivacaine (5–10 mg) or lignocaine (25–50 mg) is
used.
Addition of fentanyl (to enhance the onset of block) or morphine
(to improve pain control) may be done.
 Brief or minimal spinal anesthesia is far safer than prolonged
spinal anesthesia.

The advantages of spinal anesthesia are:
a. less fetal hypoxia unless there is hypotension
b. minimal blood loss.
The technique is not difficult and no inhalation anesthesia is
required, but postspinal headache occurs in 5–10% of patients.
Spinal anesthesia can be obtained by injecting the drug into the
subarachnoid space of the third or fourth lumbar interspace with
the patient lying on her side with a slight head uptilt.

The blood pressure and respiratory rate should be recorded
every 3 minutes for the first 10 minutes and every 5 minutes
thereafter.
Oxygen should be given for respiratory depression and
hypotension.
Sometimes vasopressor drugs may be required if a marked fall in
blood pressure occurs.
It is used during vaginal delivery, forceps, ventouse and cesarean
delivery.

Combined spinal-epidural analgesia (CSE):
An introducer needle is first placed in the epidural space.
A small gauge spinal needle is introduced through the epidural
needle into the subarachnoid space (needle through needle
technique).
A single bolus of 1 mL 0.25% bupivacaine with 25 μg fentanyl is
injected into the subarachnoid space.
The spinal needle is then withdrawn.

An epidural catheter is thus sited for repeated doses of
anesthetic drug.
The method gives rapid and effective analgesia during labor and
cesarean delivery.
It allows women to move (walking epidural) during labor.

INFILTRATION ANALGESIA
Perineal infiltration:
For episiotomy: Perineal infiltration anesthesia is extensively used
prior to episiotomy.
A 10 mL syringe, with a fine needle and about 8–10 mL 1%
lignocaine hydrochloride (Xylocaine) are required.
The perineum on the proposed episiotomy site is infiltrated in a
fanwise manner starting from the middle of the fourchette.
Each time prior to infiltration, aspiration to exclude blood is
mandatory.
Episiotomy is to be done about 2–5 minutes following infiltration.

For outlet forceps or ventouse: (Perineal and labial infiltration):
The combined perineal and labial infiltration is effective in outlet
forceps operation or ventouse traction.
A 20 mL syringe, a long fine needle and about 20 mL of 1%
lignocaine hydrochloride are required.
The needle is inserted just posterior to the introitus. About 10 mL
of the solution is infiltrated in a fanwise manner on both sides of
the midline (as for episiotomy).
The needle is then directed anteriorly along each side of the vulva
as far as the anterior-third to block the genital branch of the
genitofemoral and ilioinguinal nerve.
Five milliliter is required to block each side

Local abdominal for cesarean delivery:
This method is rarely used where regional block is patchy or
inadequate.
Technique:The skin is infiltrated along the line of incision with
diluted solution of lignocaine (2%) with normal saline.
The subcutaneous fatty layer, muscle, rectus sheath layers are
infiltrated as the layers are seen during operation.
The operation should be done slowly for the drug to become
effective.

PATIENT CONTROLLED ANALGESIA
Narcotics are administered by mother herself from a pump at
continuous or intermittent demand rate through intravenous
route.
Total dose is limited as there is a lockout interval.
This offers better pain control than high doses given at a long
interval by the midwife.
Maternal satisfaction is high with this method.
Drugs commonly used are fentanyl, meperidine or remifentanil.

PSYCHOPROPHYLAXIS
(Syn: Natural childbirth)
It is psychological method of antenatal preparation designed to
prevent or at least to minimize pain and difficulty during labor.
For most women, labor is a time of apprehension, fear and agony.
As a result of suitable antenatal preparation, majority of women
have labor that is easy and painless.

Relaxation and motivation can reduce the fear and apprehension
to a great extent.
Patient is taught about the physiology of pregnancy and labor in
antenatal (mothercraft) classes.
Relaxation exercises are practiced.
Husband or the partner is also involved in the management.
His presence in labor would encourage the bearing down efforts.
Need of analgesia would be less.

TRANSCUTANEOUS ELECTRIC NERVE STIMULATION (TENS)
It is a noninvasive procedure and is preferred by many women
during labor.
Electrodes are placed over the level of T10 – L1 and S2 – S4.
Current strength can be adjusted according to pain.
It works by inhibiting transmitter release through interneuron
level.
However, no change in pain score was observed when TENS was
switched on.

GENERAL ANESTHESIA FOR CESAREAN SECTION
The following are the important considerations of general
anesthesia for cesarean section:
Cesarean section may have to be done either as an elective or
emergency procedure.
Ryel’s tube aspiration of gastric contents is to be done, especially
when the stomach contains food materials.

A large number of drugs pass through the placental barrier and
may depress the baby.
Uterine contractility may be diminished by volatile anesthetic
agents like ether, halothane.
Halothane, isoflurane cause cardiac depression, hepatic necrosis
and hypotension.
Hypoxia and hypercapnia may occur.
Time interval from uterine incision to delivery is related directly
to fetal acidosis and hypoxia.
Longer the exposure to general anesthetic before delivery the
more depressed is the Apgar score.

Preoperative preparations:
These safety measures should be taken to prevent complications
of general anesthesia.
Preoperative medication with sedatives or narcotics is not
required as they cause respiratory depression of the fetus.
Fasting of about 6 hours is preferable for an elective surgery.
High-risk women in labor should preferably not be allowed to eat.
Ryel’s tube aspiration of gastric contents is to be done when the
stomach contains food materials.

H2-blocker (Ranitidine 150 mg orally) should be given night
before (elective procedure).
H2 receptor blocking agent and metoclopramide is to be given IM
especially to women with high risks (obesity).
Non-particulate antacid (0.3 molar sodium citrate 30 ml) is given
orally before transferring the patient to theater to neutralize the
existing gastric acid.
While on the theater table, left lateral tilt of the woman is
maintained with a wedge on the back.
This is to avoid autocaval compression as it is detrimental to both
mother and fetus.

Metoclopramide (10 mg IV) is given after minimum 3 minutes of
preoxygenation to decrease gastric volume and to increase the
tone of lower esophageal sphincter.
Intubation with adequate cricoid pressure following induction
should be done.
Uterine incision-Delivery (U-D) interval is more predictive of
neonatal status (Apgar score).
Prolonged U-D interval of more than 3 minutes results in lower
Apgar scores and neonatal acidosis.
Awake extubation should be a routine.

Preoxygenation with 100% oxygen is administered by tight mask
fit for more than 3 minutes.
Induction of anesthesia is done with the injection of thiopentone
sodium 200–250 mg (4 mg/kg) as a 2.5% solution intravenously.
Muscle relaxants: Succinylcholine is commonly used immediately
after the induction drug to facilitate intubation.
It is a short acting muscle relaxant with rapid onset of action.

Intubation:
An assistant is asked to apply cricoid pressure as soon as the
consciousness is lost.
Intubation is done with a cuffed endotracheal tube and the cuff is
inflated.
Presence of obesity, severe edema, neck abnormalities, short
stature or airway abnormalities make intubation difficult.

Anesthesia is maintained with 50% nitrous oxide, 50% oxygen and
a trace (0.5%) of halothane.
Relaxation is maintained with nondepolarizing muscle relaxant
(vecuronium bromide 4 mg or atracurium 25 mg).
After delivery of the baby, the nitrous oxide concentration should
be increased to 70% and narcotics are injected intravenously to
supplement anesthesia.

Complications of general anesthesia:
Aspiration of gastric contents (Mendelson’s syndrome) is a
serious and life threatening one.
Delayed gastric emptying due to high level of serum
progesterone, decreased motilin and maternal apprehension
during labor is the predisposing factor.
The complication is due to aspiration of gastric acid contents (pH
< 2.5) with the development of chemical pneumonitis, lung
damage, atelectasis and bronchopneumonia.
Right lower lobe is commonly involved as the aspirated food
material reach the lung parenchyma through the right bronchus.

Clinical presentation:
Tachycardia, tachypnea, bronchospasm, rhonchi, rales, cyanosis,
decreased PaO2 and hypotension.
X-ray chest reveals right lower lobe involvement.

Management:
Immediate suctioning of oropharynx and nasopharynx is done to
remove the inhaled fluid.
Bronchoscopy may be needed if there is any large particulate
matter.
Continuous positive pressure ventilation to maintain arterial
oxygen saturation of 95% is done.
Pulse oximeter is a useful guide.
Antibiotics are administered when infection is evident.
Role of corticosteroid is doubtful.

Other complications of general anesthesia are:
a. Failure in intubation and ventilation
b. Nausea, vomiting and sore throat.

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