Obstetrics Physiologic Changes During Pregnancy

Physiologic Changes During Pregnancy: Respiratory

100

In the parturient patient, vascular engorgement and and soft tissue edema causes the Mallampati Classification to ___. 

✦ Increase
✦ The glottic opening is narrowed: downsized (6.0-7.0) EET should be used. 
✦ Additionally, the tissue in the nasopharynx is particularly friable because of the number of hormonal changes and local edema. Hence why nasal intubation should be avoided in full term mothers.

200

Throughout pregnancy, what happens to the tidal volume and respiratory rate?

✦ Increase
✦ Due to an increase in O₂ consumption and CO₂ production. 

300

The leading cause of death of parturients receiving general anesthesia is due to ___.  

✦ Difficult and failed intubation
✦ In fact, difficult and failed intubation is 8x higher in the full-term patient.
✦ Side Note → Due to the anatomical changes that occur during pregnancy, a short handled laryngoscope (Datta handle) should be considered. This can be especially useful in women with large breasts. 

400

The Minute Ventilation will ___ due to an increase in what hormone?

✦ Increase → Minute Ventilation will increase by up to 50%
✦ Progesterone is a respiratory stimulant, which increases during pregnancy
✦ Decrease in FRC coupled with an increase in Minute Ventilation accelerates the uptake of inhaled anesthetics! 

500

The Oxyhemoglobin Dissociation will shift to the ___ during pregnancy. 

✦ Right

✦ Remember → The oxyhemoglobin dissociation curve tells use the tendency of hemoglobin to bind oxygen.
✦ In a right shift, there is a decreased affinity for O₂ ("Right = Release"), which facilitates O₂ transfer to the fetus.
✦ Maternal Hyperventilation → Leftward shift of the OxyHgb Curve → Uterine artery constriction → Reducing oxygen delivery to the fetus → Increasing the risk of fetal asphyxia

Physiologic Changes During Pregnancy: Cardiovascular

100

Which hemodynamic variables increase during pregnancy? (Select Two)
a. Heart Rate
b. Stroke Volume
c. SVR
d. PAOP 

a. Heart Rate
b. Stroke Volume

✦ Stroke volume is increased as a function of increased intravascular volume, while the HR is increased to satisfy higher metabolic demand.
✦ In the vascular smooth, increase progesterone stimulates nitric oxide release. This reduces SVR.
✦ Additionally, dilutional anemia also contributes to the reduction in SVR.
✦ PAOP is unchanged. 

200

The greatest increase in maternal cardiac output occurs ___.
a. During the first stage of labor
b. During the second stage of labor
c. Immediately after delivery
d. During the first trimester 

c. Immediately after delivery

✦ By term, the cardiac output will increase up to 40% above baseline.
✦ During labor the cardiac output can be be as high as high as 12 to 14L/min.
✦ It reaches its peak (80% above baseline) immediately after delivery.
✦ It is during this time that patients with pre-existing cardiac issues have an increased risk for decompensation.
✦ The cardiac output gradually returns to normal in a timespan of about two weeks.

300

True or False: Left uterine displacement can be accomplished by tilting the mothers right torso by 5- to 10 degrees. 

✦ False! Should be a tilt of about 15- to 30 degrees. 

✦ Aortocaval Compression or "syndrome of supine hypotension" occurs when the maternal patient is in the supine position → the gravid uterus begin to compress both the vena cava and the aorta.
✦ In turn: 

1. This decreases venous return to the heart  as well as arterial flow to the uterus and lower extremities
2. Decreased cardiac output compromises fetal perfusion and can also cause the mother to lose consciousness. 

✦ By displacing the uterus away from the vena cava & aorta, we can reduce its compressive effect.
✦ It should be implemented during the second and third trimester. 

 

400

Due to the systemic alterations that occur in the obstetric population, the mean arterial pressure ___.
a. Increase by 15%
b. Decrease by 15%
c. No change 

c. No change 

✦ Progesterone causes vascular muscle relaxation. Leading to a decrease in SVR and PVR, which creates an increase in blood flow. 

✦ ↑ blood flow + ↓ SVR = Net even effect on MAP 

500

The clotting factors that decrease in the obstetric population include ___. 

✦ 11 & 13
✦ Anticoagulants: ↓ Antithrombin & Protein S, however no change with Protein C.
✦ Clotting factors that increase: 1, 7, 8, 9, 10, & 12
✦ Fibrinogen doubles in mass

✦ Pregnancy creates a hypercoagulable state, however fibrin breakdown occur faster than clot formation. This explains the development of consumption coagulopathy. 

Physiologic Changes During Pregnancy: Gastrointestinal & Renal

100

Pregnancy typically produces:
a. An increase in GFR
b. An increase in serum creatinine level
c. An increase in BUN
d. A decrease in renal blood flow 

a. An increase in GFR
✦ During pregnancy, the GFR increases from about 140 ml/min to 160 ml/min as a result of an increase 

200

In the obstetric population, RSI should be implemented at __^th week of gestation. 

✦ 20^th Week
✦ At the 20^th week: 

1. Lower esophageal sphincter pressure is decreased
2. Gastric volume exceeds 25mL
3. Gastric pH is below 2.5 

✦ Increasing the risk of aspiration and adverse events. 

300

Pseudocholinesterase level __ throughout pregnancy. 

✦ Decreases
✦ It decreases by 30% during the first two trimesters
✦ However, proongation of the DOA of drugs that depend on cholinesterase for metabolism and elimination such as succinylcholine & Ester LA's are uncommon. 

400

In pregnancy, insulin resistance:
a. Increase due to the effects of epinephrine
b. Decrease due to follicle stimulating hormone
c. Decrease due to the effects of estrogen
d. Increase due to the effects of lactogen 

d. Increase due to the effects of lactogen 

✦ Maternal insulin requirements increase in the second and third trimesters, but decrease shortly after.
✦ The increase in insulin resistance is due to the increase in lactogen 

500

Which factors are expected to increase during pregnancy (Choose 3)
a. Creatinine Clearance
b. Lower Esophageal Sphincter Tone
c. Sensitivity to LA
d. MAC
e. Gastric pH
h. Urine Glucose

a. Creatinine Clearance
c. Sensitivity to LA
h. Urine Glucose 

✦ Creatinine Clearance increases as a function of increased intravascular volume and cardiac output → more creatinine is delivered to the kidney per unit time.

The Uterus

100

Uterine blood flow is: (Select two)
a. 20% of the cardiac output
b. 700 ml/min
c. Not autoregulated
d. Reduced by phenylephrine 

b. 700 ml/min
c. Not Autoregulated 

✦ At term, the UBF increases up to 700-900 ml/min
✦ UBF is 10% of CO
✦ UBF is not autoregulated → it dependent on maternal MAP, cardiac output, uterine vascular resistance
✦UBF is not reduced by phenylephrine 

200

Which local anesthetic will cross the placenta the least?
a. Chloroprocaine
b. Ropivacaine
c. Lidocaine 

a. Chloroprocaine
✦ Due to its rapid metabolism 

300

Drug characteristics that favor placental transfer include:
✦ ___ molecular weight
✦ ___ lipid solubility
✦ Ionized or unionized?
✦ Polar or non-polar? 

✦ Low molecular weight → < 500 Daltons
✦ High lipid solubility
✦ Non-ionized
✦ Non-polar (No Charge)

400

The phenomenon of ion trapping explains

a. The lipid-solubility of volatile anesthetics
b. The accumulation of maternally-administered drugs in the fetus
c. The development of sickle cell crisis
d. the compensation of metabolic alkalosis

b. The accumulation of maternally-administered drugs in the fetus

✦ Ion trapping occurs when a pH differences across the membrane result in changes in the distribution of a drug.
✦ For example, administering a weak base like lidocaine to a laboring mother with a physiologic pH of 7.4.
✦ In its unionized state, the drug has the ability to cross through the placenta.
✦ With fetal blood being more acidic (pH of 7.25-7.35), the drug will now become ionized, leaving it unable to cross the placental barrier and back into the maternal circulation → Hence, ion trapping. 

500

True or False: Due to magnesium high lipid solubility, it is easily able to cross the placenta. 

✦ False → Magnesium is not lipophilic, however it is has a low molecular weight making it able to cross through the placenta. 

Stages of Labor, Labor Pain & Neuraxial Anesthesia

100

During the first stage of labor is limited to __ - __ spinal segments. 

✦ T10 to L1 spinal segments 

✦ Associated dilation of the cervix and stretching of the lower uterine segments.
✦ Pain during this stage is carried by visceral afferent C fibers → Slow, diffuse 

✦ During the second stage of labor, stretching of the perineum and pelvic muscles produces pain that is carried by the somatic afferent fibers in the pudendal nerves that derive from the S2 to S4 spinal segments..

200

Which stage of labor begins with the onset of perineal pain? 

✦ Second Stage 

✦ First stage begins with cervical dilation with regular uterine contraction and ends with full cervical (10cm). It is divided into the latent phase and active phase of labor. 

✦ The second stage begins with full cervical dilation and ends with the delivery of the newborn. 

✦ The third stage begins with the delivery of the newborn and ends with the delivery of the placenta. 

300

True or False: A pudendal block is appropriate for pain relief during the first stage of labor. 

✦ False → The perineum is innervated by the pudendal nerve, which derives from S2-S4. Pain during the fist stage of labor derives from T10-L1, which explains why this block is not useful. 

400

This local anesthetic is not commonly used for labor analgesia because its known to reduce the efficacy of morphine. 

✦ 2- Chloroprocaine → Antagonizes the mu & kappa receptors in the spinal cord. 

500

Shortly after an epidural was dosed, the patient becomes hypotensive, dyspneic, and unable to swallow. This is most likely due to:
a. Allergic reaction
b. Eclampsia
c. Subdural injection  

c. Subdural injection → This patient has experienced a total spinal. 

✦ Initial treatment includes vasopressors, IVF, left uterine displacement, and leg elevation.
✦ If the patient lose consciousness and is unable to support their own airway, intubate immediately.