Physiological changes during pregnancy alter the body's response to anesthesia. These changes begin early in pregnancy and progress significantly. By term, there are reductions in MAC values (up to 40%), sensitivity to local anesthetics (up to 30%), and FRC (up to 20%). Pregnant women also experience increased oxygen consumption (20-50%), minute ventilation (40-50%), cardiac output (up to 50%), blood volume (45%), and risk of aspiration. Anesthesia requires accounting for these changes through techniques like left uterine displacement, preoxygenation, and rapid sequence induction.

1. By Yassin M.
15/3/2016 1

2. Anesthesia for parturient
What is the difference?
15/3/2016 2
Physiological
changes
Alter the usual
response
to anesthesia
2 Patients are cared
For simultaneously
Mother Fetus

3. Physiologic changes during pregnancy
 Maternal physiology undergoes many changes during
pregnancy.
 These changes, which are largely secondary to the effects of
progesterone and estrogen, begin as early as 4 weeks gestation and
are progressive.
 In the first 12 weeks of pregnancy progesterone and estrogen are
produced predominately by the ovary and thereafter by the placenta.
These changes both enable the fetus and placenta to grow and
prepare the mother and baby for childbirth.
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4. Central Nervous System Effects
 The minimal alveolar concentration (MAC) progressively
decreases during pregnancy.at term, by as much as 40%—for
all general anesthetic agents; MAC returns to normal by the
third day after delivery.
 Changes in maternal hormonal and endogenous opioid levels
have been implicated.
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5. Cont…
 Progesterone, which is sedating when given in pharmacological
doses, increases up to 20 times normal at term and is probably
at least partly responsible for this observation. A surge in -
endorphin levels during labor and delivery also likely plays a
major role.
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6. Cont…
 At term, pregnant patients also display enhanced sensitivity to
local anesthetics during regional anesthesia; dose requirements
may be reduced as much as 30%.
 This phenomenon appears to be hormonally mediated but may
also be related to engorgement of the epidural venous plexus.
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7. Cont…
 Obstruction of the inferior vena cava by the enlarging uterus
distends the epidural venous plexus and increases epidural
blood volume. The latter has three major effects:
(1) decreased spinal cerebrospinal fluid volume,
(2) decreased potential volume of the epidural space
(3) increased epidural (space) pressure.
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8. Cont…
 The first two effects enhance the cephalad spread of local
anesthetic solutions during spinal and epidural anesthesia,
respectively, whereas the last may predispose to a higher
incidence of dural puncture with epidural anesthesia .
 Engorgement of the epidural veins also increases the likelihood
of placing an epidural catheter in a vein, resulting in an
unintentional intravascular injection
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9. CNS
 Anesthesia Concerns:
 USE Less Volatile
 USE lower concentration for Labor epidural
 USE less Volume for spinal anesthesia. E.g. 1.6cc 0.75%
Bupivicaine
 Beware of High Spinals and High Epidural
 Due to less CSF volume and Higher Epidural Pressure
 Possibility of Intravascular Catheter placement
 Due to engorged, dilated Epidural veins
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10. Respiratory system effects
 Changes in the respiratory system may be categorized as anatomical
and physiological.
 The anatomical changes include capillary engorgement and edema of
the upper airway, pharynx, false cords, glottis and arytenoids.
 There is also an increase in chest diameter, to allow increased minute
ventilation, and an enlargement of the breasts, which can make
laryngoscopy with a standard Macintosh blade more difficult.
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11. Cont…
 Oxygen consumption and minute ventilation progressively
increase during pregnancy. Minute ventilation is increased at
term by about 50% above non pregnant values.
 The increasein minute ventilation is mainly due to an increase
in tidal volume (40%) and, to a lesser extent, to an increase in
the respiratory rate (15%).
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12. Cont…
 By term, oxygen consumption has increased about 20–50% .
 PaCO2 decreases to 28–32 mm Hg; significant respiratory alkalosis
is prevented by a compensatory decrease in plasma bicarbonate
concentration.
 The maternal respiratory pattern changes as the uterus enlarges.
 In the third trimester, elevation of the diaphragm is compensated by
an increase in the anteroposterior diameter of the chest
diaphragmatic motion, however, is not restricted.
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13. Cont…
 Functional residual capacity, expiratory reserve volume, and residual
volume are decreased at term. These changes are related to the
cephalad displacement of the diaphragm by the large gravid uterus.
 Both vital capacity and closing capacity are minimally affected but
functional residual capacity (FRC) decreases up to 20% at term; FRC
returns to normal within 48 h of delivery.
 This decrease is principally due to a reduction in expiratory reserve
volume as a result of larger than normal tidal volumes.
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14. 15/3/2016 14
 ↑Oxygen consumption
20 – 40%
 Progesterone
 ↑ CO2 Production
 ↑Minute Ventilation
40 – 50%
 ↑↑ VT & ↑ RR
 ↑PaO2 & ↑P50 (30 mmHg)
 ↓ PaCo2 (28-32 mmHg)
 Compensatory ↓ HCo3ˉ

15. Cont…
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16. RS
Anesthetic concern
 The combination of decreased FRC and increased oxygen
consumption promotes rapid oxygen desaturation during
periods of apnea.
 Preoxygenation prior to induction of general anesthesia is
therefore mandatory to avoid hypoxemia in pregnant patients.
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17. Cont…
 Pre-oxygenation for the 3-5 full minutes by the clock is vital
because
1-Mothers desaturate more quickly than the non pregnant
patient
2 -The airway is narrower because of venous engorgement
possible edema
3-Intubation is more difficult may take longer
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18. Cont…
 The decrease in FRC coupled with the increase in minute
ventilation accelerates the uptake of all inhalational anesthetics.
 Capillary engorgement of the respiratory mucosa during
pregnancy predisposes the upper airways to trauma, bleeding,
and obstruction.
 Gentle laryngoscopy and the use of small endotracheal tubes
(6–6.5 mm) should be employed during general anesthesia.
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19. Cont…
 Maternal alkalosis associated with decreased PaCO2 values
due to hyperventilation as a result of labor pain causes fetal
acidosis because of
(1) decreased uteroplacental perfusion (with significant
drop of maternal PaCO2) and
(2) shifting of the maternal oxygen dissociation curve to
the left.
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20. Cardiovascular system effects
 Oestrogen and progesterone mediated relaxation of vascular
smooth muscle in pregnancy cause vasodilatation reducing the
peripheral vascular resistance by 20%.
 Consequently systolic and diastolic blood pressures fall.
 A reflex increase in heart rate by 25% together with a 25%
increase in stroke volume, results in a 50% increase in
cardiac output.
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21. Cont…
 During labour cardiac output may increase further by up to
45%.
 The greatest increases in cardiac output are seen during labor
and immediately after delivery.Cardiac contractility remains
unchanged
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22. Cont…
 Up to 20% of women at term develop the supine hypotension syndrome,
which is characterized by hypotension associated with pallor, sweating, or
nausea and vomiting.
 The cause of this syndrome appears to be complete or near-complete
occlusion of the inferior vena cava by the gravid uterus when the mother is
in supine position.
 This will reduce venous return to the heart resulting in a decrease of cardiac
output, maternal blood pressure and placental perfusion. Turning the patient
on her side typically restores venous return from the lower body and
corrects the hypotension in such instances.
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23. Cont…
 The descending aorta can also be compressed by the uterus causing a
reduction in uterine blood flow.
 Aortocaval compression must be considered as a cause of maternal
hypotension from the end of the 1st trimester onwards, though it
typically occurs after 20 weeks gestation.
 Parturients with a 28-week or longer gestation should not be placed
supine without left uterine displacement. This maneuver is most
readily accomplished by placing a wedge (> 15°) under the right hip.
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24. Supine Hypotension syndrome
COP ↓ in supine position after 28th week of gestation.
Occurs in 20% of women at term.
Aortocaval compression
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Compression of IVC Compression of lower aorta
↓ VR → ↓ COP by 24% at term.
↓ blood flow to kidneys,
uteroplacental circulation &
lower extremeties

25. Cont…
 An increase (45%) in plasma volume in excess of an increase
in red cell mass produces dilutional anemia and reduces blood
viscosity.
 At term, blood volume has increased by 1000–1500 mL in
most women, allowing them to easily tolerate the blood loss
associated with delivery; total blood volume reaches 90 mL/kg.
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26. Cont…
 Average blood loss during vaginal delivery is 400–500 mL,
compared with 800–1000 mL for a cesarean section. Blood
volume does not return to normal until 1–2 weeks after
delivery.
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27. CVS
Anesthetic Concerns
 Expect increased HR
 ALWAYS PLACE LEFT LATERAL TILT WITH ALL C-
SECTION PATIENTS
 Increased blood volume compensated for expected blood
loss during delivery
 Prone to Hypotension after spinal or epidural
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28. Hematologic changes
 Pregnancy is associated with a hypercoagulable state that may
be beneficial in limiting blood loss at delivery.
 Fibrinogen and factors VII, VIII, IX, X, and XII concentrations
all increase; only factor XI levels may decrease.
 Accelerated fibrinolysis can be observed late in the third
trimester.
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29. Cont…
 In addition to the dilutional anemia leukocytosis (up to 21,000/
L) and a 10% decrease in platelet count may be encountered
during the third trimester.
 Because of fetal utilization, iron and folate deficiency anemias
readily develop if supplements of these nutrients are not taken.
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30. Cont…
 Cell-mediated immunity is markedly depressed and may
increase susceptibility to viral infections.
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31. Cont…
 Plasma volume increases by 45% and as this increase is
relatively greater than the increase in red cell mass, maternal
hemoglobin concentrations falls from 150 g per litre pre-
pregnancy to 120 g per litre during the 3rd trimester. This is
termed physiological anaemia of pregnancy.
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32. Gastrointestinal Effects
 Upward and anterior displacement of the stomach by the uterus
promotes incompetence of the gastroesophageal sphincter.
 Elevated progesterone levels reduce the tone of the
gastroesophageal sphincter, whereas placental gastrin secretion
causes hypersecretion of gastric acid.
 These factors place the parturient at high risk for regurgitation
and pulmonary aspiration. Intragastric pressure is unchanged.
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33. Cont…
 Data with regard to gastric emptying are conflicting; some
studies suggest normal gastric emptying is preserved until the
onset of labor.
 Nonetheless, nearly all parturients have a gastric pH under 2.5,
and over 60% of them have gastric volumes greater than 25
mL. Both factors have been associated with an increased risk of
severe aspiration pneumonitis.
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34. Cont…
 Opioids and anticholinergics reduce lower esophageal
sphincter pressure, may facilitate gastroesophageal reflux, and
delay gastric emptying.
 These physiological effects, together with recent food ingestion
just prior to labor and any delayed gastric emptying associated
with labor pains, predispose parturients to nausea and
vomiting.
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35. Cont…
 Pregnant women are therefore at risk of developing
Mendelson’s syndrome (aspiration pneumonitis) especially on
induction of general anaesthesia, which reduces upper
oesophageal sphincter pressure.
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36. Cont…
 Strategies for the prevention of this may include the
administration of H2 blocking drugs, neutralization of gastric
contents with non-particulate antacids, e.g. sodium citrate, and
the use of a rapid sequence induction with cricoid pressure,
when administering general anesthesia to pregnant women. At
24 - 48 hours postpartum the changes in the gastro-intestinal
system are thought to have reverted to normal.
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37. Renal Effects
 Renal vasodilatation increases renal blood flow early during
pregnancy which leads to increase in GFR,but autoregulation is
preserved.
 The kidneys often enlarge.
 Increased renin and aldosterone levels promote sodium retention.
 Renal plasma flow and the glomerular filtration rate increase as
much as 50% during the first trimester; glomerular filtration declines
toward normal in the third trimester.
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38. Cont…
 Serum creatinine and blood urea nitrogen may decrease to 0.5–
0.6 mg/dL and 8–9 mg/dL, respectively.
 A decreased renal tubular threshold for glucose and amino
acids is common and often results in mild glycosuria (1–10
g/d) or proteinuria (< 300 mg/d).
 Plasma osmolality decreases by 8–10 mOsm/kg.
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39. Hepatic Effects
 Plasma concentrations of alkalinephosphatase are increased 3-
fold as a result of placental production.
 Succinylcholine may lead to prolonged neuromuscular
blockade secondary to a 25% fall in plasma cholinesterase
concentrations at term and a further 8% fall three days
postpartum (post delivery).
 Pseudocholinesterase activity may not return to normal until up
to 6 weeks postpartum.
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40. Cont…
 High progesterone levels appear to inhibit the release of
cholecystokinin, resulting in incomplete emptying of the
gallbladder.
 The latter, together with altered bile acid composition, can
predispose to the formation of cholesterol gallstones during
pregnancy.
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41. Metabolic changes
 pregnancy is a diabetogenic state; insulin levels steadily rise
during pregnancy. Secretion of human placental lactogen, also
called human chorionic somatomammotropin, by the placenta
is probably responsible for the relative insulin resistance
associated with pregnancy. Pancreatic B cell hyperplasia occurs
in response to an increased demand for insulin secretion.
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42. Cont…
 Secretion of human chorionic gonadotropin and elevated levels
of estrogens promote hypertrophy of the thyroid gland and
increase thyroid-binding globulin; although T4 and T3 levels are
elevated, free T4, free T3, and thyrotropin (thyroid-stimulating
hormone) remain normal.
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43. Mammary Changes:
 Breast engorgement is typical in normal pregnancy and is a
result of human placental lactogen secretion.
 Enlarged breasts in an obese parturient with a short neck may
lead to difficult laryngoscopy and intubation
 Use of a short handled laryngoscope for large breasted
parturient can be extremely helpful.
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44. Seminar topics
 Group one……..utero-placental blood flow
 Group two……..physiology of fetal circulation
 Group three…..substance abuse during pregnancy
 Group four….....smoking and its anesthetic consideration
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