Obstetric Analgesia and Anesthesia

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Obstetric Analgesia and Anesthesia

• Prof. Dr.Xia Rui
• Head of Department
• Presented by- Dr. Pramee
• Department of Anesthesia
• The First Affiliated Hospital Yangtze University

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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 antacidsH2-blockers (Ranitidine
  100-150mg orally or 50mg IV)
• Metoclopramide 10mg orally or IV
• Sellicks maneuver(cricoid pressure)while
  intubation.

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5.Hematology and coagulation

• Blood volume ? 50, increase in plasma volume gt
  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 15to 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 Ficks law
• Q/TK
• 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
  doesnt 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 blood
  pressure uterine blood flow
• Ketamine uterine hypertonicity
  uterine blood flow.
• 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 cant 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
• Preloading- Ringers Lactate 10ml/kg
• Patient positioning- Sitting or left lateral
• Painting and draping
• Space L2L3 or L3L4
• Needle 25 gauge Quincke or 22 gauge
  Whitacre, Sprotte
• Needle advanced to pierce dura. After free flow
  of CSF,
• Drug used 0.250.5 bupivacaine 2-5mg, with or
  without narcotic (fentanyl 25µg)
• Short onset time
• Duration of action 5070mins

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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
Inject 0.5bupivacaine
Place the catheter
Inject 1.5lidocaine
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Spinal/Epidural Anesthesia Contd..

• General considerations
• Sensory level up to T6 is required for cesarean
  section
• Dose reduction is required due to decreased
  epidural and subarachnoid space.
• Left lateral tilt should be maintained to
  prevent supine hypotension syndrome.
• If there is significant fetal distress, general
  anesthesia must be opted since regional
  anesthesia takes time, esp. epidural anesthesia.
• 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/SpinalAnesthesia

• Hypotension -There can be significant
  hypotension with spinal(less with epidural)
  anesthesia.
• Treatment for hypotension-
• Preloading the patient with 500ml-1000ml of
  Ringers lactate
• Left lateral position
• Oxygen given by face mask .
• Ephedrine 510mg 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 (1200,000) 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 patients airway
• Inject thiopental 50mg,
• midazolam 12mg

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Anesthesia
for Painless laborLumbar 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 sitesL23,
L34
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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
  510min, inject an additional 5ml .In total 10ml
  of anesthetic solution is given to accomplish an
  adequate level of anesthesia.

• ii. Continuous infusion 0.1250.25 of
  Bupivacaine 1012ml/hr with Fentanyl 25µg/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-Coagulopat
  hy, 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 Sellicks 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 1015
  mins.

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Procedure for GA

• Be prepared with antacid
• Preoxygenation Give 100 oxygen with a
  close-fitting mask for 56min
• Patients 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 Sellicks 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

• 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(anticonv
  ulsant 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.