OB Anesthesia Flashcards
What is the leading direct cause of pregnancy related deaths in the United States?
Hypertensive disorders of pregnancy
What is the normal fetal heart rate?
120 to 160 beats per minute
What is the p50 of fetal hemoglobin?
21
Why are magnesium infusions used on the OB floor? What are some potential side effects? How is hypermagnasemia treated?
Magnesium is used as an anticonvulsant in patients with preeclampsia as well as a tocolytic to prevent pre-term labor
Potential side effects :
- Sedation
- Loss of deep tendon reflexes (via decreased release of ACh)
- Respiratory depression
- Cardiac arrest
- Antagonizes a-adrenergic agents
- Antagonizes NMDA receptors (not clinically relevant)
Treatment:
1) Stop source
2) Calcium
3) Furosemide
4) Dialysis
When is the fetus most susceptible to teratogenic agents?
3 to 8 weeks
What is the oxygen consumption of a normal sized term fetus?
7 mL/kg/min
Describe amniotic fluid embolism
AFE occurs when amniotic fluid and constituents enter the maternal circulation, leading to an immune response secondary to immune mediators
Criteria for AFE:
1) Acute hypotension or cardiac arrest
2) Acute hypoxia (due to pulmonary vasospasm)
3) Coagulopathy
4) Occurs at the onset of labor, during c-section, or within 30 minutes post-partum
Treatment is resuscitative and involves controlling the airway, stabilizing hemodynamics, and correcting the coagulopathy
Describe the Apgar Score
The Apgar Score is a subjective scoring system used to evaluate the newborn and is performed at 1 and 5 minutes after delivery
A value of 0, 1, or 2 is given in 5 categories: - Heart rate 0 = absent 1 = 100 2 = >100 - Respiratory effort 0 = absent 1 = slow and irregular 2 = good, crying - Reflex irritability 0 = no response 1 = grimace 2 = cough - Muscle tone 0 = floppy 1 = some flexion 2 = actively moving - Color 0 = blue 1 = pink body with blue extremities 2 = completely pink
Describe the normal changes seen in respiratory parameters during pregnancy
Minute ventilation increases (primarily due to increased TV rather than RR)
Results in decreased PaCO2
pH stays normal or slightly elevated (respiratory alkalosis)
Bicarbonate decreases (to compensate for alkalosis)
Base excess decreases
PaO2 increases due to increased minute ventilation
Describe the causes of decelerations seen in fetal heart rate monitoring
Early decelerations occur with uterine contractions and are caused by head compression
Late decelerations occur 10 to 30 seconds after a contraction and are due to uteroplacental insufficiency
Variable decelerations vary in shape, size, and timing, and are caused by umbilical cord compression
What are normal umbilical cord blood values?
Arterial: 7.25/50/20/22
Venous: 7.35/40/30/20
Define Pre-Eclamspia
New onset hypertension (>140/90) during pregnancy with some evidence of end organ dysfunction:
- Proteinuria
- Thrombocytopenia
- Renal dysfunction with elevated Cr
- Visual disturbance or cerebral symptoms
- Pulmonary edema
- Liver dysfunction
Why is GA sometimes preferred over neuraxial anesthesia for cerclage placement?
GA with volatiles causes uterine relaxation which can help when you have cervical dilation and bulging membranes
What is the most common presenting sign of uterine rupture? What are other signs/symptoms? What are the risk factors?
Most common sign is non-reassuring FHR patterns (fetal bradycardia)
Other symptoms include abdominal pain, vaginal bleeding, and recession of fetal presenting part
Risk factors include prior c-section, multiparity, and induction of labor
How does placental abruption present? What are the risk factors?
Typically presents with painful vaginal bleeding, uterine tenderness, and non-reassuring fetal tracings
Risk factors include hypertension, cocaine/tobacco use, trauma, advanced maternal age, and multiparity
What are the risks of non-obstetric surgery during pregnancy? During which trimester is it the safest? When can intraoperative FHR monitoring be used?
Risks include fetal loss, preterm labor, low birth weight, and teratogenicity
2nd trimester is safest
- lowest risk of premature labor and abnormal organogenesis
FHR monitoring can be done beginning at 18-20 weeks
How does pregnancy affect the concentration of serum constituents?
Albumin concentration decreases
- due to plasma expansion
Fibrinogen, Transferrin, and globulins all increase
- due to hormonal changes
How does a combined spinal epidural (CSE) compare to a continuous lumbar epidural (CLE)?
More rapid onset of analgesia
Decreased incidence of failed epidural analgesia
- may take 1-2 hours after placement of CSE to really confirm epidural is working (CSE is relatively contraindicated in patients where a functioning epidural is critical to safety)
Higher risk of opioid induced pruritis
What are the risk factors for GERD during pregnancy? What physiologic changes during pregnancy make GERD more common?
Risk factors for GERD during pregnancy:
- gestational age
- GERD prior to pregnancy
- mulitparity
- BMI and weight gain are NOT risk factors
Gastric emptying of both solids and liquids is slowed during labor, but NOT throughout pregnancy
Esophageal peristalsis and intestinal transit are slowed during pregnancy due to elevated progesterone and decreased motilin levels
What dermatomes need to be blocked during Stage I of labor? What about stage II?
Stage I - T10-L1 dermatomes
Stage II - addition of S2-S4
How are coagulation factors affected by pregnancy?
All factors increase, EXCEPT:
- Factor XI
- Factor XIII
- Protein S
What are the side effects to common uterotonic drugs?
Oxytocin - hypotension
Hemabate (Carboprost) - bronchoconstriction
Methergine (Methylergonovine) - hypertension
Terbutaline/Ritodrine - risk of uterine atony, hyperglycemia, and hypokalemia
What characteristics allow a drug to pass through the placenta?
Small
Unionized
Lipophilic
Low protein binding
What are the advantages and disadvantages of adding dilute epinephrine to a LA/opioid epidural for labor analgesia?
Advantages:
- more rapid onset and longer duration of analgesia
- enhanced analgesia due to a-1 receptor stimulation
- decreased LA/opioid requirements
Disadvantages:
- increased intensity of motor blockade
- increased cost
- additional risk of drug error
What are the risk factors for increased maternal mortality?
Advanced maternal age (>35 years old)
African-American or Hispanic race
Obesity (BMI >29)
Multifetal gestation
Which local anesthetic is most prone to “ion trapping” and what does that mean?
Lidocaine
“Ion trapping” may result in higher ratios of local anesthetic accumulating in an acidotic fetrus
- As pH drops, the ionized form of lidocaine is preferentially formed
- Charged form is unable to cross the placenta and gets trapped
Can present with a baby that has poor tone and slow heart rate when delivered
