Mod VII: Anesthesia Considerations for Physiologic Changes of Pregnancy

Question 1

_{Anesthetic Considerations: Respiratory}

The combination of which two variables is responsible for Rapid desaturation (hypoxemia) during periods of apnea/hypoventilation at induction/intubation?

Answer 1

↓ FRC and ↑ O2 consumption

_{Preoxygenation (denitrogenation) prior to induction of general anesthesia is therefore mandatory to avoid hypoxemia in pregnant patients​}

Question 2

_{Anesthetic Considerations: Respiratory}

What could Exacerbate ↓ FRC + ↑ O2 consumption, and lead to Rapid desaturation (hypoxemia) with periods of apnea/hypoventilation at induction/intubation?

Answer 2

Parturient with pre-existing alterations in closing volumes

^{(smoker, obese, scoliosis)}

Supine/T-burg position

Question 3

_{Anesthetic Considerations: Respiratory}

What are closing volumes?

Answer 3

Closing volumes = Closing capacity - Residual volume

Increased closing volumes are bad

_{Closing capacity<strong> </strong>(CC) is the volume in the lungs at which its smallest airways, the respiratory bronchioles, collapse. It is defined mathematically as the sum of the Closing volumes and the Residual volume}

_{<strong>Closing capacity (CC) = Closing volumes + Residual volume</strong>}

^{<u>Residual Volume</u> (RV), is the amount of gas that normally remains in the lungs during respiration, and specifically, after forced expiration}

Increase in the closing capacity occurs with age and with certain condition and it means that the small airways begin to collapse at a higher volume/before expiration is complete

Ideally, you want your small airways to only collapse when they are almost empty

So, smaller closing volumes are good, and increased closing volumes are bad

Question 4

_{Anesthetic Considerations in Pregnancy: Respiratory}

Why is Preoxygenation (denitrogenation) prior to induction of general anesthesia mandatory in pregnant patients?

Answer 4

To avoid hypoxemia from ↓ FRC + ↑ O2 consumption

_{[The combination of decreased FRC and increased oxygen consumption promotes rapid oxygendesaturation during periods of apnea. Preoxygenation (denitrogenation) prior to induction of general anesthesia is therefore mandatory to avoid hypoxemia in pregnant patients]}

Question 5

_{Anesthetic Considerations in Pregnancy: Respiratory}

Why must supplemental O2 be provided to supine parturient?

Answer 5

↓ FRC + ↑ O2 consumption

Closing volumes > FRC

^{(in some pregnant women at term when they lie supine)}

Under these conditions, atelectasis and hypoxemia readily occur

Question 6

_{Anesthetic Considerations in Pregnancy: Respiratory}

How do ↓ FRC + ↑ alveolar ventilation affect uptake/elimination of inhaled anesthetics?

Answer 6

The decrease in FRC coupled with the increase in minute ventilation accelerates the uptake of all inhalational anesthetics

The reduction in dead space narrows the arterial end-tidal CO2 gradient.

Question 7

_{Anesthetic Considerations in Pregnancy: Respiratory}

During labor, how could hyperventilation (pain/prepared child birth methods) affect acid/base balance?

Answer 7

worsens already existent alkalemia

Question 8

_{Anesthetic Considerations in Pregnancy: Respiratory}

Why should Hypocapnia (low PaCO2) be avoided during labor?

Answer 8

Hypocapnia → vasoconstriction uterine vasculature → ↓ placental perfusion = FETAL COMPROMISE

Question 9

_{Anesthetic Considerations in Pregnancy: Respiratory}

Which anesthetic techniques are helpful in circumventing the deliterious effects of hyperventilation and hypocapnia during labor?

Answer 9

Regional techniques

Regional techniques obviate the need for breathing methods and eliminate pain

Help circumvent the hyperventilation and the hypocapnia

Question 10

_{Anesthetic Considerations in Pregnancy: GI}

Increase levels of which hormone is responsible for the Reduction in lower esophageal sphincter tone during pregnancy?

Answer 10

↑ Progesterone

_{Progesterone is a hormone released by the corpus luteum in the ovary. It plays important roles in the menstrual cycle and in maintaining the early stages of pregnancy. It may also be involved in the growth of certain cancers}

Question 11

_{Anesthetic Considerations in Pregnancy: GI}

Decreased levels of which hormone is responsible for the ↑ Gastric acidity during pregnancy?

Answer 11

↓ Gastrin (placental origin)

_{a hormone which stimulates secretion of gastric juice and is secreted into the bloodstream by the stomach wall in response to the presence of food}

Question 12

_{Anesthetic Considerations in Pregnancy: GI}

Which factors increase the risk of Risk for Aspiration (Mendelson’s Syndrome) during pregnancy?

Answer 12

Gastric pH < 2.5 in almost all pregnant women

Gastric volume > 25 ml in 60%

↓ Gradient between LES tone (↓) & ↑ intragastric pressure (↑)

Pain, narcotics, anxiety, maternal barring down, lithotomy

Question 13

_{Anesthetic Considerations in Pregnancy: GI}

Which anesthetic interventions could Minimize risk for aspiration w/ pregnancy?

Answer 13

P.O. intake

^{Modest amounts clear liquids in uncomplicated laboring pts.}

^{Clear liquids 2hrs. prior to induction GETA in uncomplicated C-section}

^{Further restrictions in pts. with added risks}

Pharmacologic interventions

^{Nonparticulate antacid - H2 antagonist - Metoclopramide}

RSI with Sellick maneuver

^{> 20 wks. gestation}

^{Earlier if symptoms of reflux}

Use regional technique

Question 14

_{Anesthetic Considerations in Pregnancy: GI}

RSI with Sellick maneuver to prevent aspiration - What is it? Who could benefit from it?

Answer 14

Same as RSI with Cricoid pressure

> 20 wks. gestation

Earlier if symptoms of reflux

Question 15

_{Anesthetic Considerations in Pregnancy: GI}

What effect does succinylcholine have on the lower esophageal sphincter tone?

Answer 15

Succinylcholine increases the LES

The increase in the LES exceeds the increase in intragastric pressure

This result in increase in Barrier pressure which is protective

[Esophageal Barrier pressure] = [Lower esophageal sphincterpressure] – [Intragastric pressure]

Question 16

_{Anesthetic Considerations in Pregnancy}

Why is there an Altered Drug Response in pregnancy?

Answer 16

Effects of the pregnancy on the CNS

Question 17

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

How does pregnancy affect Local anesthetic requirements?

Answer 17

Local anesthetic requirements ↓↓ (30%)

Question 18

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why are Local anesthetic requirements ↓↓ (30%) in pregnancy?

Answer 18

Epidural venous engorgement

^{↓ Epidural space volume → ↑ rostral spread of LA epidural space}

^{↑ Epidural space pressure → ↑ PDPH}

^{Greater risk for placing catheter into vein → intravascular injection}

↓ CSF volume in 2nd/3rd trimester

^{↓ CSF volume in 2nd/3rd trimester<strong> </strong>→ enhanced spread of LA in subarachnoid space}

Low CSF protein

^{Low CSF protein → ↑ unbound fraction LA}

Elevated CSF pH

^{Elevated CSF pH → ↑ unionized fraction of LA}

Hormonally mediated

^{Hormonally mediated (progesterone ↑ neural sensitivity)}

Question 19

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

How does the decreased epidural space volume in pregnancy affect spread of LA in the epidural space?

Answer 19

Causes Increased rostral spread of LA in the epidural space

^{(Rostral spread means towards the head, especially the front of the head)}

Question 20

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is there increased incidence of PDPH w/ LA administration during pregnancy?

Answer 20

Increased epidural space pressure

Question 21

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is pregnancy a/w a greater risk for placing epidural LA catheter into a vein which could result in intravascular injection of LA?

Answer 21

Epidural venous engorgement

Question 22

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is there enhanced spread of LA in subarachnoid space in pregnancy, especially in 2nd/3rd trimester?

Answer 22

Decreased CSF volume

Question 23

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is the unbound fraction of LA increased in pregnancy?

Answer 23

Low protein in the CSF

Question 24

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is the unionized fraction of LA increased in pregnancy?

Answer 24

Elevated CSF pH

^{(CSF is alkalotic)}

Question 25

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

How does pregnancy affect MAC of inhalation agents?

Answer 25

Pregnancy is a/w Progressive decrease of Minimum Alveolar Concentration (MAC)

Begins as early as 8-12 weeks gestation w/ ↓↓ of 25%

Max ↓↓ (40%) by term

Return to normal apprx 3 days after delivery

Question 26

_{Anesthetic Considerations in Pregnancy - Altered Drug Response}

Why is MAC of inhalation agents decreased in pregnamcy?

Answer 26

Pregnancy-induced analgesia

Related to ↑ progesterone levels and endorphin concentrations

Which increase pain threshold => pregnancy-induced analgesia