prepared by dr. mahmoud abdel-khalek august 2015 obstetric anesthesia & analgesia

Prepared byDr. Mahmoud Abdel-Khalek

August 2015

Obstetric Anesthesia&

Analgesia

Physiologic changes of pregnancy

Physiologic and anatomic changes develop

across many organ systems during

pregnancy and the postpartum period

The Metabolic, hormonal and physical

changes all have impact on anesthetic

management

To the anesthesiologist, the most

important changes are those that affect

the respiratory and circulatory systems

Respiratory system

There is an increased risk of difficult or

failed intubation in the parturient:

Mucosal vascular engorgement →

airway edema and friability

Laryngoscopy may be impeded by the

presence of large breasts

Respiratory system

Increased risk of pulmonary aspiration of

stomach contents due to:

Upward displacement of the stomach

Decreased gastric motility and increased

gastric secretions (Progesterone)

Incompetent gastro-esophageal junction

Respiratory system

With the apnea that occurs at induction of

anesthesia, the parturient becomes hypoxic much

more rapidly than the non-pregnant patient due

to 2 main reasons:

Oxygen requirement has increased by 20% by

term

Decrease of FRC, which serves as an “oxygen

reserve” by 20% due to upward displacement

of the diaphragm

Minute ventilation increases to 150% of baseline

leading to a decrease in PaCO2 (32 mmHg)

CVS

Blood volume increases by 40% during pregnancy

in preparation for the anticipated 500-1000 cc

average blood loss during vaginal or Caesarian

delivery, respectively

When the pregnant patient is in the supine

position, the heavy gravid uterus compresses the

major vessels in the abdomen leading to

maternal hypotension and fetal distress (supine

hypotensive syndrome)

Left lateral tilt, usually achieved with a pillow

under the woman’s right hip, is an important

positioning maneuver

PAIN PATHWAYS IN LABOUR AND CAESAREAN SECTION

The pain of the first stage

of labour is referred to the

spinal cord segments

associated with the

uterus and the cervix,

namely T10, 11, 12 and LI

Pain of distension of the

birth canal and perineum

is conveyed via S2-S4

nerves

PAIN PATHWAYS IN LABOUR AND CAESAREAN SECTION

When anesthesia is required for caesarean

section, all the layers between the skin and the

uterus must be anaesthetized

The most sensitive layer is the peritoneum, and

therefore the block should extend up to at least

T4 and also include the sacral roots (S1-S5)

Anatomy& Physiology of Airway in Pregnancy

Incidence of difficult intubation in term

parturients:

1 in 300 cases, compared with 1 in 2200 in the non-

pregnant population

Normal labour

The first stage of labour

Cervix effaces then cervical dilatation begins

Rate of cervical dilatation: Primigravida: 1 cm/ hour Multigravida: 2 cm/ hour

Routine observations: Fetal HR every 15 minutes Maternal pulse and BP every 30 minutes Temperature 4-hourly Urine analysis at each emptying of bladder

Normal labour

The second stage of labour

Commences at full dilatation of the cervix and

terminates at the delivery of the baby

If prolonged more than 1 hour the fetus may

become acidotic

At the delivery of anterior shoulder, IM oxytocin

is given to hasten the delivery of the placenta

and to stimulate the uterine contraction

Normal labour

The third stage of labour

The complete delivery of the placenta&

membranes& contraction of the uterus

Placental blood flow (15% of CO) redistribute to

maternal circulation and may precipitate heart

failure immediately postpartum in women with

cardiac disease

Fetal monitoring

The most commonly used:

Serial ultrasonography

Serial Doppler flow studies

Cardiotocograph (CTG) monitoring

The degree of urgency for the delivery depends

on the condition of the fetus

Routine methods to monitor fetal well-being:

Fetal heart auscultation, Fetal heart cardiotocography,

Color of the liquor& Fetal blood sampling

Normal fetus baseline heart rate: 110- 150beats per

minute

Fetal monitoring

The ability of the fetus to maintain oxygenation is

diminished with each uterine contraction

The normal CTG trace simultaneously records

fetal heart sounds and uterine contractions

Decelerations: Early: Benign Variable: may or may not hypoxemia Late: Pathological

Abnormal trace is an indication for fetal blood

sampling for pH which is more accurate

assessment of fetal well-being

Fetal Monitoring

Color of the liquor may be monitored when the

membranes are ruptured

The liquor color is observed for the presence of

mechonium which may indicate fetal hypoxia

The appearance of new thick mechonium is an

indication for urgent delivery

If mechonium is aspirated into the lungs of the

neonate severe lung damage may ensue

Fetal monitoring

Values for fetal pH:

pH > 7.25: Normal

pH 7.20- 7.25: borderline to be repeated 30

minutes later

pH < 7.20: significant acidosis requiring urgent

delivery of the baby

Urgency of CS delivery

Grade 1. Emergency:

Immediate threat to life of woman or fetus

Grade 2. Urgent:

Maternal or fetal compromise which is not

immediately life threatening

Grade 3. Scheduled:

Needing early delivery but no maternal or fetal

compromise

Grade 4. Elective:

At a time to suit the patient and the maternity team

GI physiology and antacid therapy

During pregnancy an increase in progesterone a

decrease in the tone of the lower esophageal

sphincter and, combined with the increased

abdominal mass, results in an increased possibility of

regurgitation and pulmonary aspiration of gastric

contents

The pH of the gastric contents is low, and therefore

there is an increased incidence of heartburn in

pregnancy

Gastric emptying is not delayed during pregnancy

but is delayed in labour, especially by pain, anxiety

and opioids


Mendelson Syndrome

Mendelson first described the syndrome of aspiration

of gastric contents in 1946 leading to chemical

pneumonitis


Recommendations:

Withhold oral feeding during labour& give parenteral

administration

Use of local anesthetic technique where indicated and

feasible

Alkalinization and emptying of stomach contents before GA

Competent administration of general anesthesia, with

appreciation of the dangers of aspiration during induction

and recovery

Adequate delivery room equipment, including transparent

masks, suction, laryngoscope and tilting table

Anesthetist to remain with the patient until return of

laryngeal reflexes

Reducing the acidity of the stomach contents

Emergency surgery:

immediately before surgery:

30 mL 0.3 molar sodium citrate orally

50 mg ranitidine by slow IV injection

10 mg metoclopramide IV injection

Elective surgery:

150 mg ranitidine orally

10 mg metoclopramide

Pain& Pain Relief in labour

It is only in the last 150 years that effective

methods of pain relief have been available

Pain of labour is amongst the most severe in the

human experience of pain

Studies assessing pain of labour in primigravidae:

9.2% very mild

29.5% mild

37.9% moderate

23.4% severe

The effect of Pain& Analgesia on the mother and fetus

A long painful labour may → an exhausted,

frightened and hysterical mother incapable of

decision making

Pain compromises placental blood flow& renders

uterine contractions less effective

Increase catecholamines secretions results in

increased myocardial work and arterial pressure

and may compromise blood flow to the placenta

by peripheral VC

Activation of adrenocortical hormones may

adversely affect electrolyte, carbohydrate&

protein metabolism


The Ideal Analgesic for Labour:

Rapid-onset , Excellent pain relief in both 1st & 2nd

stages without risk or side-effects to mother or

fetus

Retain the mother's ability to mobilize and be

independent during labour

There is no ideal analgesic at the present time

It can be closely approached by spinal or epidural

techniques which provide effective analgesia

while preserving motor function to a large degree


The Ideal Analgesic for Labour:

Effective epidural (or spinal) analgesia reverses

the adverse physiological effects of labour pain

listed above by blocking the psychological and

biochemical stress response, resulting in

improved maternal well-being and placental

perfusion

labour analgesia

Parenteral (systemic) analgesia

Inhalation analgesia

Regional analgesia for labour

Parentral Analgesia

Pethidine is given by intramuscular injection and

the maximum effect is seen about 1 h after

administration

The analgesic effects are variable and pethidine

may also cause significant side-effects:

maternal sedation, nausea and vomiting,

dysphoria and inhibition of gastric emptying

Fetal respiratory and neurobehavioural

depression

Inhalation analgesia

Entonox, which is 50% nitrous oxide and 50%

oxygen premixed in cylinders

Entonox is administered usually via an on-

demand valve with a face mask or mouthpiece

Although Entonox is a reasonably effective

analgesic, many women feel faint and nauseated

and may vomit or become out of control

Epidural and Subarachnoid Analgesia

This is the most effective form of analgesia in

labour, with up to 90% women reporting

complete or near-complete pain relief

However, it is invasive and patients require

careful monitoring

Regional Analgesia for Labour

Indications for Epidural Analgesia

In addition to relief of pain and distress, there are

several indications for which epidural analgesia

may be helpful in securing a good outcome from

labour

Technique of Epidural Analgesia

Preparation

Informed consent

Intravenous cannulation

Baseline ABP recording

Urinary bladder should be emptied

Clothing

Positioning: sitting or lateral (See table)

Technique of Epidural Analgesia

Conduct of Epidural

Conduct of the Epidural

Regional Anesthesia for the Parturient

Obstetric indications

CS

Forceps and ventouse delivery

Retained placenta

Suturing of trauma to the birth canal

Elective CS

Regional anesthesia is the technique of choice

The woman should be warned about:

Hypotension

Nausea and vomiting

Post dural puncture headache (PDPH)

Possibility of imperfect block

Available techniques:

Spinal anesthesia

Epidural anesthesia

Combined spinal- Epidural anesthesia

Emergency CS

Topping up of an existing epidural

General Anesthesia

Spinal Anesthesia

Complications of Regional Anesthesia in Obstetrics

Shearing of the epidural catheter

Unlikely to cause problems (aseptic, inert)

Post dural puncture headache

Incidence: 0.5- 1%

Bed rest, IV and oral fluids

Simple analgesics

Caffeine infusion

ADH?

Blood patch


Backache

Epidural hematoma

Very rare but potentially disastrous complication

Signs:

Severe back pain

Prolonged profound motor weakness for more than 6

hours

Sudden onset of incontinence

Requires prompt neurosurgical intervention

Epidural abscess or meningitis

Compression of spinal cord and blood supply

(paraplegia)


Systemic toxic reaction

Overdose of LA

Hypotension

Defined as 25% decrease of systolic or MAB OR absolute

decrease of 40 mm Hg

Dizziness, nausea

Vasopressors e.g. phenylephrine, Ephedrine

Neurological deficit

Reassurance that recovery will occur in 3- 6 months

Delivery may be causative and not the epidural

General Anesthesia for the parturient

Safety of anesthesia has increased in obstetrics:

Increasing use of epidural in labour

Increasing use of regional anesthesia for

operative delivery

Improved teaching

Improved assistance to the anesthetist

Currently only 5- 10% of CS In the UK are

performed under GA


Indications

Extreme emergency: severe fetal distress,

maternal hemorrhage

If regional is contraindicated

Patient refuses regional

Emergencies in Obstetrics Anesthesia

Hemorrhage

Failed intubation

Pre-eclampsia and eclampsia

Total spinal block

Amniotic fluid embolism

Maternal r neonatal resuscitation

Failed Inubation

High incidence of airway difficulties in obstetric

patients (approximately 1 in 300 compared with 1

in 2220 in non-pregnant patients)

Causes:

Swollen upper airway mucosa

swollen and engorged breasts and full dentition

The decreasing use of general anesthesia in obstetrics

may lead to a relative lack of experience in this

technique with increased anxiety for both junior and

senior anesthetists

Failed Inubation

Call for help when unexpected difficulty with

laryngoscopy or intubation arises and to avoid

repeated attempts at intubation without

maintaining oxygenation

The placement of a laryngeal mask airway (LMA)

may facilitate ventilation and, if used, cricoid

pressure should be applied continuously

Failed Intubation

Thank you

prepared by dr. mahmoud abdel-khalek august 2015 obstetric anesthesia & analgesia

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