OBSTETRIC ANALGESIA AND ANESTHESIA
The administration of analgesia and anesthesia
requires thorough knowledge of physiologic changes occurring during pregnancy
by those involved in the care of obstetric patients. Special considerations
and precautions regarding administration of analgesics and anesthetics
as well as patient observations are necessary to insure safety of mother
and fetus.
II Policies
A. ACOG Technical Bulletin on Obstetrical Anesthesia and Analgesia includes
the following:
2. The obstetric patient should be anesthetized
only when a qualified physician is immediately available to supervise the
delivery and to deal with any complications that might arise.
3. Safety of obstetric anesthesia depends
principally on the skill of the anesthesiologist. The same level of competence
of anesthesia personnel should be required for obstetric procedures as
for surgical procedures.
4. The director of anesthesia services,
with the approval of the medical staff, must develop and enforce written
policies regarding provision of obstetric anesthesia, i.e., who may do
what and under what circumstances.
5. Those approved to administer obstetric
anesthesia should be approved only for those agents and techniques in which
they have demonstrated competence.
6. For the most part, obstetricians are not qualified to manage the infrequent but occasionally life-threatening complications of major regional anesthesia. Therefore, if major regional anesthesia is administered by an obstetrician, either that individual must be qualified to recognize and manage such complications or a qualified anesthesiologist or nurse anesthetist must be immediately available.
b. Person administering anesthetic should
remain with patient for first 20-30 min. following initiation of block
and following each top up dose. Thereafter, should be readily available.
2) Intermittent or continuous blood pressure
3) Continuous electrocardiographic display
4) Pulse oximeter
5. Regional anesthesia for labor and/or
vaginal delivery requires that the parturient's vital signs and the fetal
heart rate be monitored and documented by a qualified individual. Additional
monitoring appropriate to the clinical condition of the parturient and
the fetus should be employed when indicated. When extensive regional blockade
is administered for complicated vaginal delivery, the standards for basic
intraoperative manitoring should be applied.
6. Regional anesthesia for Cesarean delivery
requires that the standards for basic intraoperative monitoring be applied
and that a physician with privileges in obstetrics be immediately available.
7. Qualified personnel, other than the
anesthesiologist attending the mother, should be immediately available
to assume responsibility for resuscitation of the depressed newborn.
9. All patients recovering from regional
anesthesia should receive appropriate post-anesthesia care. Following Cesarean
delivery and/or extensive regional blockade, the standards for postanesthesia
care should be applied.
o When a site other than the PACU is used,
equivalent post-anesthesia care should be provided.
A. Respiratory
changes
2. Lung volume/capacity
b. Increased minute ventilation
c. Increased respiratory rate
d. Increased tidal volume
b. Hypoxia develops rapidly.
c. Increased likelihood to develop acidosis
as a result of hyperventilation - respiratory alkalosis and compensatory
metabolic acidosis
d. Decreased oxygen reserve - which may be aggravated by increased oxygen consumption during labor
2. Increased plasma volume
3. Increased cardiac output
4. Increased heart rate
5. Decreased peripheral vascular resistance
6. Decreased mean arterial pressure (diastolic
and systolic)
7. Cardiac output changes during labor
b. Active phase: increase of 30%
c. Second stage: increase of 45%
d. With uterine contractions: additional
increase of 10-25%
e. Immediately postpartum: increase of
80% over pre-labor values
2) Aortic compression by the uterus leads to decreased uterine blood flow and potential fetal asphyxia.
3) Patients should not labor in the supine
position (especially with an epidural).
c. Subarachnoid space and epidural spaces
are smaller due to engorged epidural veins. Local anesthetic requirement
is less in pregnant women.
2. Increased plasma volume
3. Increased red cell mass -(physiologic anemia) proportional less when compared to the plasma volume
4. Physiologic anemia: increase of plasma
volume is more than increase of red cell mass
5. Increased clotting factors VII, VIII,
X, XII and fibrinogen
2) Disseminated intravascular coagulation
2. Epidural venous engorgement decreases
the volume of CSF and epidural space: less local anesthetic required
3. Increased sensitivity of nervous fibers
4. Maternal valsalva may lead to increase
in CSF pressure up to 70 cm of H2O.
2. Decreased gastric motility and emptying
time
3. Increased acidity of gastric contents
4. The combination of the above factors
(1, 2 and 3) place the gravida at high risk for pulmonary aspiration during
general anesthesia or impaired consciousness due to any cause.
b. BUN 8-9 mg %
c. Creatinine 0.4 - 0.6 mg %
b. Increased incidence of cystitis and
pyelonephritis in pregnancy
2. Decreased total protein and albumin/globulin
ratio
3. Decreased plasma cholinesterase
B. Late first
stage and second stage of labor: in addition to T10 - L1, also via pudendal
nerve which enters the spinal cord at S2 - S4
C. Third stage
of labor: same as second stage
A. Psychoprophylactic
techniques
b. Lamaze
c. Bradley
d. Harris
3. Very useful in latent phase
4. 20% of prepared patients need nothing
else.
5. 60-65% of prepared patients will reduce
additional analgesics substantially.
6. Hyperventilation may produce acidotic
neonates.
7. Patient should not be advised against
other methods of analgesia but rather consuled to regard them as compatible
and complementary procedures.
a. Barbiturates
2) In presence of pain patient may become excited, disoriented, difficult to manage.
3) Prolonged depressant effect on the neonate
2) Propiomazine (Largon®): 20-40 mg, IM or IV
3) Hydroxyzine (Vistaril®): 50-100 mg, IM
4) Effects: maternal/neonatal
b) Reduces narcotic requirements
c) Controls emesis
d) Produces no neonatal depression
b) Lethargy
c) Decreased feeding
d) Hypothermia
e) Inability to respond to environmental
stimuli
Peak effect 40-50 min 5-10 min
2) Maternal-fetal concentration equilibrates within 6 hours.
3) Neonate requires 3-6 days to eliminate the drug entirely.
4) T 1/2 elimination of meperidine is 23 hours in newborns versus 3-5 hours in normal adults.
5) The most popular narcotic analgesic
used during labor
Dose 50-100 ug 25-50 ug
Onset 7-8 min Immediately
Peak effect 30 min 3-5 min
Duration 1-2 hrs 30-60 min
Dose 5-10 mg 2-3 mg
Peak effect 1-2 hrs 20 min
2) In equianalgesic doses, morphine produces
more respiratory depression of the newborn than meperidine.
Dose 1-2 mg 1/2-1 mg
Onset 10 min Rapidly
2) Duration: 3-4 hrs.
3) Narcotic agonist-antagonist
4) Use cautiously in patients addicted to narcotics.
5) Potential benefit - ceiling effect for respiratory depression
6) Use with caution in women delivering premature infants.
7) May cause significant drowsiness in
mother.
Dose 10-15 mg 5-10 mg
Onset <15 min 2-3 min
2) Narcotic agonist-antagonist
3) Less respiratory depression than meperidine
4) Ceiling effect for respiratory depression
5) Causes maternal sedation and dizziness
6) May cause respiratory depression in the neonate (especially in premature infants).
2) Orthostatic hypotension from peripheral vasodilation
3) Nausea and vomiting by direct stimulation of chemoreceptor trigger zone in medulla. Emetic effects are dose-related
4) Decreased gastric motility
5) During latent phase of labor, may decrease uterine activity; during active phase, may actually shorten labor and correct incoordinate uterine contractions.
6) Reduction in beat-to-beat variability of the fetal heart rate
7) Drowsiness between contractions but loss of the ability to follow instructions during contractions and delivery
8) Neonatal respiratory depression
2) Neonate: 0.1 mg IV, IM, SQ, or IT immediately after delivery
3) Duration: 1-2 hours
4) May need to be repeated since narcotic
action lasts longer than naloxone effect
2) Blocks physiologic effects of enkephalins
3) May cause withdrawal symptoms in patients
addicted to narcotics
2) Low dose ketamine
b) Onset: 30 sec
c) Duration: 4-5 min
d) Uses:
ii) For increased analgesia where regional
analgesia is spotty
b) Emergence delirium and hallucinations in non-premedicated patient
c) Induction agent of choice for patient
with severe hypotension, hypovolemia, or severe asthma
b) Dose-related oxytocic effect on uterine tone
c) Crosses placenta rapidly; at higher
doses may depress Apgar score and cause neonatal muscular hypertonicity
2) Produces profound amnesia and mild sedation within 20 min after IV administration; useful for delivery of macerated fetal demise or severely malformed fetus.
3) No analgesic properties
4) Results in severe agitation, marked excitement, and loss of inhibitions in presence of severe pain
5) "Twilight sleep" once a popular analgesia-amnesia technique, morphine + scopolamine
6) Rarely if ever used in contemporary
management of labor and delivery because of its side effects
c. Caudal
d. Paracervical block
e. Pudendal block
f. Local perineal infiltration
2) Active labor
2) Hypovolemia
3) Coagulopathies
4) Infection at the site of needle injection or septicemia
5) Pre-existing progressive disease of the spinal cord or peripheral nerves
6) Fetal distress
7) Lack of skilled
anesthesiologist
b) Tetracaine (Pontocaine®)
c) 2-Chloroprocaine (Nesacaine®)
b) Short half life
b) Bupivacaine (Marcaine®)
b) Low molecular weight
c) High lipid solubility
d) Freely crosses the placenta
e) Long half-life
4) Fetal distress may occur as a result of decreased uterine blood which falls linearly to the blood pressure.
5) Untreated hypotension may lead to fetal and/or maternal cardiac arrest.
6) Prevention
b) Frequent monitoring of the blood pressure
ii) Every 5-10 minutes thereafter
b) Increase intravenous fluid infusion.
c) Place patient in 10-20 degree Trendelenburg position.
d) Administer oxygen by face mask.
e) If no response by one minute, ephedrine 5-10 mg IV is indicated.
f) Assess fetal status.
b) Overdose
c) Accumulation of local anesthetics during repeated injections overtime
d) Rapid absorption from highly vascular
area
ii) Numbness of lips and tongue
iii) Metallic taste in mouth
iv) Restlessness, nervousness
v) Confusion, blurred vision, nystagmus
vi) Fine tremors of muscles of face and hands
vii) Convulsions
ii) Decreased myocardial contractility, decreased cardiac output and hypotension
iii) Direct vasodilatation - hypotension
iv) As drug levels increase, cardiac arrest
may occur.
ii) Hypoxemia and acidosis
b) Prevention of progression of the reaction
d) Support circulation.
e) Manage cardiac arrest if it occurs.
f) Assess status of the fetus: With maternal
resuscitation the uterine blood flow usually will restore and allow fetal
excretion of local anesthetic via placenta.
2) Clinical manifestations
b) Severe cardiovascular reactions to very
small amounts of local anesthetics
b) Circulatory support
c) Antihistamines
d) Corticosteroid
e) Epinephrine if necessary
b) Following patient movement, coughing,
valsalva, or uterine contraction during injection of subarachnoid block
ii) Inject test dose.
iii) Check for signs of intrathecal placement
of drug prior to administration of full dose.
ii) Monitor vital signs every 1-2 minutes initially.
iii) Monitor vital signs every 10-15 minutes
when stable.
ii) Inject medication immediately after uterine contraction.
iii) Maintain patient sitting up or in
reverse Trendelenburg for at least 30 seconds.
b) Hyperventilation
c) Apnea
d) Hypotension
e) Lethal if not promptly treated
b) Withdraw 10-15 cc of CSF to remove as much local anesthetic as possible.
c) Support circulation.
ii) Intravenous fluids
iii) Ephedrine
2) Prevention
b) Inadvertent dural puncture recognized
during epidural procedure:
ii) Use this catheter to provide anesthesia.
iii) Inject 30-60 cc of normal saline without preservative following delivery.
iv) Leave catheter until the following
day and repeat saline administration, then remove catheter (incidence of
headache will be reduced to 12.5%); or, remove the catheter immediately
after the saline patch.
b) Headache may be associated with nausea,
vomiting, tinnitus and/or diplopia.
b) Hydration
c) Abdominal binder
d) Analgesics
e) Epidural blood patch
f) Intravenous caffeine infusion
2) Epidural hematoma
3) Epidural abscess
4) Meningitis
5) Adhesive arachnoiditis (chemical contaminants
leak into the subarachnoid space)
2) Pre-hydration = 500-1000 ml balanced salt solution in healthy patients
3) Position: lateral decubitus is most commonly used, but sitting position may be useful in very obese patients.
4) Insert epidural needle using proper technique at interspace between L2-L5; then thread epidural catheter 3 cm into epidural space.
5) Position patient with left uterine displacement.
6) Give a test dose of 2 to 3 ml local anesthetic. Ask patient to report any symptoms of intravascular injection (e.g., buzzing or fullness in ears, numbness of lips or tongue). Aspirate carefully before and after injection. Check BP q 1 minute 3 to 5 times after test dose. Wait 3-5 minutes and check for numbness to be sure catheter is not in the subarachnoid space.
7) Give analgesic dose in 3-5 ml increments, usually 10 ml in total.
8) Record blood pressure and pulse every minute for 20 minutes.
9) If blood pressure decreases by 30% or the systolic drops to <100 torr, initiate crystalloid infusion. Treat persistent hypotension with 5-15 mg of ephedrine IV.
10) Analgesia level check after 8 to 10 minutes. If no analgesia develops after 20 minutes, suspect that catheter is misplaced.
11) Fetal/uterine monitoring is important. Monitor throughout the procedure if technically feasible.
12) Evaluate patient at least every 70-90
minutes for need to reenforce block.
2) Inject medication with patient in sitting position.
3) Administer after uterine contraction.
4) Use 25 gauge spinal needle.
5) Usually, patient can still push.
6) Hypotension possible but not frequent
2) High failure rate - more anatomic anomalies in sacrum
3) Requires larger amounts of local anesthetic than other regional techniques
4) Risk of puncturing rectum and fetal
head
2) Place needle through vaginal mucosa lateral to the cervix at the 3 o'clock position.
3) Inject 5-10 cc of 1.5% chloroprocaine or 1% lidocaine after aspirating for blood.
4) Repeat at 9 o'clock if after 5-10 minutes the fetal heart rate is stable.
5) Results in anesthetizing the Frankenhauser ganglion which contains all visceral sensory fibers from uterus cervix and upper vagina
6) Useful during the first stage of labor up to 8 cm dilatation
7) Major disadvantage: Fetal bradycardia
b) Duration: 3-30 minutes
2) Complications:
b) Hematoma
c) Infection spreading from injection site
2. Useful to augment
various regional and psychoprophylactic techniques
3. 40-50% nitrous
oxide in oxygen or low concentration of halothane, enflurane or isoflurane
in air or oxygen
4. Remain in verbal contact with the patient and be reassuring. If the patient becomes confused, drowsy, excited or uncooperative, the inspired
concentration
should be lowered and 100% oxygen administered.
5. The obstetrician
should infiltrate the perineum with a local anesthetic or perform a pudendal
block for added analgesia.
b. Manual removal of the placenta
c. Replacement of inverted uterus
d. Relief of tetanic uterine contraction
during breech delivery, when the uterus has clamped down before the head
is delivered
3. Prevention of regurgitation
b. Antacids to reduce acidity of gastric
contents
c. Skilled endotracheal intubation with
cuffed ET tube
d. Cricoid pressure
e. Extubation with patient awake and lying
on side with head lowered
2. 25 or 26 gauge spinal needle
3. Avoid aortocaval compression (ensure
left uterine displacement).
4. Oxygen by face mask
5. Choice of drugs
b. Lidocaine 5%: 60 - 75 mg
7. Higher incidence of hypotension than
epidural anesthesia
2. Technique is the same as for labor epidural
but additional hydration before the procedure is necessary (1500 -2000
ml of dextrose-free balanced salt solution).
3. T4 level is needed to provide adequate
anesthesia.
4. Choice of drugs
b. Bupivacaine 0.5%
c. Ropivacaina
5. Incidence of hypotension is less than
spinal anesthesia
b. Regional anesthesia contraindication
or refused
c. Need for uterine relaxation
b. Optimal control of airway and ventilation
c. Less hypotension and cardiovascular
instability
b. Fetal depression from drugs
c. Maternal hyperventilation leading to
fetal hypoxemia and acidosis
b. Non-particulate antacid such as sodium
citrate should be administered 15-30 minutes prior to induction.
c. Left uterine displacement by right hip
wedge or table-tilt
d. Pre-oxygenation with 100% oxygen
e. After the abdomen is prepped and draped,
induced with 4 mg/kg thiopental and 1.5 mg/kg succinylcholine
f. Apply cricoid pressure, intubate and
inflate the endotracheal tube cuff before administering positive pressure.
g. Administer 50% O2-N2O
and either 1.0% enflurane, 0.75% isoflurane or 0.5% halothane until delivery.
h. After delivery, volatile inhalation
agents may be discontinued and anesthesia is maintained with a balanced
(N2O/narcotic) technique. Anesthesia can also be maintained
with low concentration of volatile agent supplement with low dose narcotics.
i. Extubate only when patient awake.
b. Aspiration of gastric contents
c. Failed intubation
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Revisado por Dr Francisco Riquelme E.