Transcript Obstetrics Anesthesia

Obstetric Analgesia and
Anesthesia
Prof. Dr.Xia Rui
Head of Department
Presented by:- Dr. Pramee
Department of Anesthesia
The First Affiliated Hospital
Yangtze University
2015/7/18
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Objectives
Anesthetic implications according to physiological changes
in parturients
Effects of anesthetic agents in uteroplacental circulation
Anesthesia for Cesarean section: Regional and GA
Side Effects of Epidural/Spinal Anesthesia
Anesthesia for Painless labor
Analgesia and anesthesia for abnormal obstetrics
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Analgesia denotes the state in which only modulation of
pain perception is involved. It may be local and affect
only a small area of the body; regional and affect a larger
portion ; or systemic.
Anesthesia is a triad of hypnosis, analgesia and areflexia
by the virtue of anesthetic agents.
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In obstetrics , regional anesthesia  more commonly
performed for cesarean delivery
local anesthetics (spinal , epidural)
 general anesthesia
systemic medication and endotracheal intubation
Difficulty with intubation , aspiration, and hypoxemia
leading to cardiopulmonary arrest are the leading causes
of anesthesia related maternal death.
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Physiological changes during
pregnancy
There are considerable physiological changes in
parturient which can affect the anesthesia technique
Cardiovascular system
Respiration and metabolism
Center nervous system
Gastrointestinal Tract
Hematology and coagulation
Uterus
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1. Cardiovascular system
The anesthetic implication is that these patients due to
hyperdynamic circulation can go in congestive heart
failure.
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2. Respiration and metabolism
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Anesthetic implications of
Respiratory Changes
Due to increased minute ventilation, induction with inhalational agents
is faster and dose requirement is less, making pregnant patients more
susceptible to anesthetic overdose.
Due to decreased FRC,ERV and increased oxygen requirement these
patients are vulnerable to go in hypoxia.So,preoxygenation of 5-6 min
is required. This is the time required for maternal fetal equilibrium.
Due to capillary engorgement in upper airway chances of trauma and
bleeding during intubation is high.
Laryngeal edema can be the prominent feature of PIH patients,
making intubation difficult.
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3. Center nervous system
Progesterone has got sedative effect
decreasing
the anesthetic requirement by 25-40%.
MAC ↓ by 20-40%
↓ Vasopressor response
There is decrease in local anesthetic requirement by
30-40% for spinal and epidural anesthesia.
More chances of high spinal and epidural in
pregnancy.
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4.Gastrointestinal Tract
Parturients are very vulnerable for aspiration due to
following reasons:
Gastric emptying is delayed due to progesterone.
Gravid uterus changes the angle of gastroesophageal
junction making the lower esophageal sphincter (LES)
incompetent.
Progesterone relaxes the LES.
Gastric contents are more acidic.
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Anesthetic implications
A pregnant patient should always be considered as
full stomach even if she is fasting.
The minimum fasting period for elective CS is
recommended to be 6 hrs for light meals and 8 hrs for
heavy meals.
Preoperative antacids—H2-blockers (Ranitidine 100150mg orally or 50mg IV)
Metoclopramide 10mg orally or IV
Sellick’s maneuver(cricoid pressure)while intubation.
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5.Hematology and coagulation
 Blood volume ↑ 50%, increase in plasma volume ＞
increase in RBC mass → relative anemia
 Plasma cholinesterase level is decreased by 25%
prolonging the effect of succinylcholine.
 Hypercoagulable state in pregnancy:↑ platelet
turnover, clotting and fibrinolysis
↑ 2,3-DPG→right shift of oxyhemoglobin curve →
↑O2 delivery
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6.Uterus
 In supine position the gravid uterus compresses the
inferior vena cava and aorta, decreasing the cardiac
output and blood pressure causing Supine
hypotension syndrome(SHS) which can cause severe
hypotension after spinal anesthesia.
To prevent this patient should be kept in left lateral
position by:
Putting a 15˚ wedge under the right hip
Tilting the operation table by 15˚to left
Manually displacing the uterus to left
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Passing through the maternal-fetal barrier
Drugs with molecular weighs ﹤600 cross the placenta
easily
By simple diffusion according to the principles of
Fick’s law:
Q/T=K[
A(CM  CF)
D
]
Q/T: rate of diffusion
A: the surface area available for drug transfer
CM: maternal drug concentration
CF: fetal drug concentration
D: membrane thickness
K : the diffusion constant of the drug
At term, transfer of drugs across the placenta↑
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Placental transfer
 The rate of drug transfer into the fetus is governed
mainly by:
Lipid solubility of drug
Degree of drug ionization
Molecular weight of the drug
Dose administered
Placental blood flow
Placental metabolism
Protein binding.
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Placental blood flow and effects of anesthetic
agents in uteroplacental circulation
Uterine blood flow is 500-700 ml/min(10% of cardiac
output)
Placental blood flow is directly dependent on
maternal blood flow.
Effects of anesthetic agents in uteroplacental circulation
Hypotension and drugs causing vasoconstriction can
severely compromise fetal well being.
- Ephedrine is drug of choice for treating spinal
induced hypotension in pregnancy since it doesn’t
decrease placental flow.
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Effects of anesthetic agents in uteroplacental
circulation Contd..
Positive pressure ventilation
cardiac output by
venous return
compromise placental flow.
Inhalational agents(higher conc.)
hypotension ,
cardiac output
compromise uterine flow
IV agents:
 Sodium thiopentone and Propofol
uterine blood flow
Ketamine
uterine hypertonicity
flow.
blood pressure
uterine blood
Spinal/epidural anesthesia
hypotension
compromise uterine blood flow.
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Fetal distribution
All anesthetic drugs except muscle relaxants and
glycopyrrolate can be transferred to fetus from maternal
circulation. So, all drugs should be used in minimum
concentration and dosage.
A large fraction of drug coming from placenta to fetal
liver(75% of umbilical vein blood flows through liver), so less
drug reaches the fetal vital organs(brain, heart).
Drugs like local anesthetics and opioids which are bases,
crosses the placenta in non-ionized form and becomes ionized
in the fetal circulation(low pH) and can’t come back to
maternal circulation leading to accumulation of drugs in the
fetus.
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Distribution of drugs between maternal and fetal compartments
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The techniques in obstetric analgesia and anesthesia
1. Regional
Spinal anesthesia
For Cesarean section
Combined Spinal-Epidural
Anesthesia (CSEA)
Lumbar epidural block
For painless labor
 Caudal block
2. Systemic
 General anesthesia
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Anesthesia for Cesarean section
Spinal anesthesia
Procedure:
1)Preloading:- Ringer’s Lactate 10ml/kg
2) Patient positioning:- Sitting or left lateral
3)Painting and draping
4)Space: L2~L3 or L3~L4
5)Needle: 25 gauge Quincke or 22 gauge
Whitacre, Sprotte
6)Needle advanced to pierce dura. After free flow of
CSF,
7)Drug used: 0.25~0.5% bupivacaine 2-5mg, with or
without narcotic (fentanyl 25μg)
Short onset time
Duration of action: 50~70mins
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Combined Spinal-Epidural Anesthesia(CSEA)
Immediate onset of
analgesia by spinal
anesthesia
After giving spinal
anesthesia , an epidural
catheter is placed
immediately prior the
surgery
Drug can be re-injected
according to the need
during the surgery
Most common used in
cesarean section delivery
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Puncture the spinal needle,
fluid from the subarachnoid
space
Place the catheter
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Inject 0.5%bupivacaine
Inject
1.5%lidocaine
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Spinal/Epidural Anesthesia Contd..
General considerations:
1)Sensory level up to T6 is required for cesarean section
2) Dose reduction is required due to decreased epidural and
subarachnoid space.
3) Left lateral tilt should be maintained to prevent supine
hypotension syndrome.
4) If there is significant fetal distress, general anesthesia must
be opted since regional anesthesia takes time, esp. epidural
anesthesia.
5) Onset of epidural takes time (15-20 mins) so reserved for
elective cases only or for condition like PIH.
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Advantages of regional anesthesia over
general anesthesia
Risk of pulmonary aspiration is bypassed.
Effect of anesthetic drugs on fetus is not seen.
Awake mother can interact with her newborn
immediately.
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Side Effects of Epidural/Spinal
Anesthesia
 Hypotension :-There can be significant hypotension with
spinal(less with epidural) anesthesia.
Treatment for hypotension:Preloading the patient with 500ml-1000ml of Ringer’s
lactate
Left lateral position
Oxygen given by face mask .
Ephedrine 5~10mg iv to sustain a mild vasopressor effect.
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Side Effects of Epidural/Spinal
Anesthesia
 Nausea and vomiting
Due to rapid onset of hypotension and parasympathetic
stimulation of the gastrointestinal tract
Treatment:Antiemetics: Inj Ondansetrone 4 mg iv
Fluid
 Bradycardia
Treatment:Inj.Atropine or Inj.Glycopyrrolate
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Side Effects of Epidural/Spinal
Anesthesia
 Postdural puncture headache(PDPH)
Due to leakage of cerebrospinal fluid through the
needle hole in the Dura
Treatment:Use a small-caliber needles (25G)
 Recumbent position (bed sore)
 Hydration
 sedation
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Side Effects of Epidural/Spinal Anesthesia
 Time taken is more than General Anesthesia , so not ideal for
fetal distress.
 Difficulty in controlling sensory level with spinal
anesthesia( chance of high spinal is more in parturient)
Cardiopulmonary arrest
 Inadvertent intravascular injection of local anesthetic (toxic
reaction) or intrathecal injection of anesthetic (total spinal)
The pregnant patient is more likely to have an intravascular
drug injection because of the venous distention in the
epidural space
Injection of the drug into a highly vascularized area will
result in rapid systemic absorption
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Side Effects of Epidural/Spinal Anesthesia
 Cardiopulmonary arrest(contd..)
Full cardiopulmonary resuscitation (CRR) is indicated
(establish a patent airway, intubate the trachea, O2supply,give
vasopressors, treat arrhythmias, provide external cardiac
massage)
Then, immediate cesarean section delivery to savage fetus.
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Prevention and treatment of local anesthetic
overdose
Maximum doses of local anesthetics used in
obstetrics
Lidocaine: 5 mg/kg
Bupivacaine: 1.5 mg/kg
Ropivacaine: 3.0 mg/kg
Add epinephrine (1:200,000) to produce local
vasoconstriction: prevent too-rapid absorption and
prolong the anesthetic effect.
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Prevention and treatment of local anesthetic
overdose
If manifested by central nerve system toxicity
(convulsion):
Recognize the prodromal sings:
ringing in the ears, diplopia, perioral numbness,
slurred speech
 100 % Oxygen supply
 protect the patient’s airway
 Inject: thiopental 50mg,
midazolam 1~2mg
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Anesthesia for Painless labor
Lumbar Epidural Block
Well suited to obstetric anesthesia: vaginal
delivery, or cesarean surgery
After evaluation of patient, Epidural catheter is
placed once labor is established.
The catheter can be used for surgery and
postoperative analgesia
 Satisfactory results of analgesia
The fetal outcome is not adversely affected
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Procedure: After putting the patient in sitting or left
lateral position. puncture sites:L2~3, L3~4
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Puncture with the epidural needle and place
the catheter
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Lumbar epidural block
i. Inject 3ml of a 1.5%
Lidocaine as a test dose. If
spinal anesthesia dose not
result after 5~10min, inject
an additional 5ml .In total
10ml of anesthetic solution
is given to accomplish an
adequate level of anesthesia.
ii. Continuous infusion
0.125%~0.25% of
Bupivacaine
10~12ml/hr with
Fentanyl 2~5μg/ml in
the epidural mixture
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Caudal block
An epidural block approached through the
caudal space
Seldom used
Hard to perform (the landmarks of the sacral
hiatus is obscured , and the fetus might be
injured by the needle )
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General Anesthesia for Cesarean Section
General considerations:
 Usually considered for fetal distress or if contraindication to regional
anesthesia-Coagulopathy, infection (at site for spinal), hypovolemia,
moderate to severe vulvular stenosis, progressive neurologic disease
 Due to high chances to aspiration, prophylaxis should be taken.
 Intubation with Sellick’s maneuver (cricoid pressure).IPPV with bag and
mask avoided
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 Difficult intubation should be anticipated and ready for
management.
 Patient should be nursed in left tilt position.
 All drugs should be given in minimal doses as all drugs
crosses the placenta and attain equilibrium between
mother and fetus in 10~15 mins.
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Procedure for GA
 Be prepared with antacid
 Preoxygenation: Give 100% oxygen with a close-fitting mask
for 5~6min
 Patient’s abdomen is surgical scrubbed (disinfection) and draped
for surgery (anesthetics act on the fetus ↓)
 Induction: Thiopental 2-5mg/kg iv or Ketamine 1-2mg/kg
 Muscle relaxant: Succinylcholine 1.5 mg/kg
 Endotracheal intubation with Sellick’s maneuver
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Procedure for GA(Contd..)
 Maintenance: 50% Nitrous oxide, 50% oxygen,
(0.5%)halothane or 0.75% isoflurane or 1% Sevoflurane.All
inhalational agents relax the uterus and may cause Postpartum
Hemorrhage(PPH).So, low concentration to be used.
Induction to delivery time under 10 mins …..fast!!!
 After delivery of the fetus ,the nitrous oxide concentration
may be increase to 70%, intravenous narcotics and
benzodiazepines injected for supplemental anesthesia
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Analgesia and anesthesia for
abnormal obstetrics
1) The trapped head in breech delivery
 If an epidural block is in place, no further
analgesia will be required (forceps?)
 General anesthesia is acceptable
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2) Fetal distress
Fetus development of bradycardia and appearance of
meconium
Uterine perfusion is correlated with BP. Hypotension
will aggravate fetal distress
Regional anesthesia can cause hypotension , so
usually contraindicated if fetal distress exist.
GA might be required for speedy delivery.
Neonatal resuscitation is needed .
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3) Pregnancy Induced Hypertension
(PIH)/Preeclampsia
Composed of hypertension, generalized edema, and
proteinuria.
The primary pathologic characteristics is generalized
arterial spasm
Regional and general anesthesia are used
Contraindications to regional anesthesia include
coagulopathy, urgency for fetal distress
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Pregnancy Induced Hypertension
(PIH)/Preeclampsia (Contd..)
 If coagulation profile is normal epidural anesthesia
is anesthesia of choice because:
These patients can manifest severe, uncontrollable
hypotension with Spinal anesthesia( hypertensives are more
prone to hypotension after Spinal).
Intubation may be very difficult due to laryngeal edema.
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Pregnancy Induced Hypertension
(PIH)/Preeclampsia(Contd..)
 If coagulation profile is abnormal GA should be
administered.
 Extra considerations besides the protocol for C/S to be taken
in case of PIH which are:
 Intubation to be done by expert hands with minimum trauma
 Attenuation of cardiovascular response to intubation to be
blunted, otherwise intracranial hemorrhage can occur.
 These patients are on Magnesium which potentiates the action of
non-depolarizing muscle relaxants(NDMR).so, dose of NDMR
should be reduced.
 Patients with PIH have decreased levels of cholinesterase,
prolonging the effect of succinylcholine
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4) Eclampsia
Patient presenting with hypertension, generalized edema,
proteinuria and seizure.
Induction should be done with thiopentone(anticonvulsant
activity) and followed by GA protocols same as PIH
5) Hemorrhage and shock
Placenta previa and aruptio placenta are accompanied
by serious maternal hemorrhage.
Treatment of shock must be formulated.
Ketamine can support BP for induction
Regional block is contraindicated in the presence of
hypovolemia
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Anesthesia for surgeries during
pregnancy
Elective surgeries should be deferred until delivery
Urgent surgeries should be done during second
trimester.
First trimester
high chances of abortion and
congenital abnormalities.
Third trimester
high chance of preterm labor
Only Emergency surgeries should be taken in first
and third trimester.
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Choice of Anesthesia
If possible surgery to be performed under local/
regional anesthesia.
Avoid GA as much as possible.
If GA must be opted ,do not use nitrous oxide.
minimum use of inhalational and intravenous agents.
If Spinal anesthesia is to be given, avoid hypotension.
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