Obstetric Anesthesia Flashcards
Highest change in CO levels during pregnancy
immediately postpartum: ~75% above pre-labor levels d/t autotransfusion during uterine contractions
*uterine blood flow increases to 600-700ml/min at term (~10% of CO)
Most dangerous time during pregnancy for patients with cardiac disease
During the increase in CO: life-threatening for those with pulmonary hypertension and stenotic valve disease
Which hormone potentiates volatile agents?
Progesterone
Dose adjustment for local anesthetics
~30% lower dose
- increase in plasma volume dilutes total protein & albumin concentration»_space; higher free-fractions of protein-bound drugs
What are the cardiovascular changes observed in pregnancy?
INCREASE: CO, SV, HR
DECREASE: MAP, SVR, PVR
What are the respiratory changes observed in pregnancy?
- cephalad displacement of the diaphragm, increase AP diameter
- lower FRC
- higher O2 consumption
- higher MV, TV, RR
Which pulmonary parameters do not change in pregnancy?
dead space
lung compliance
vital capacity
FEV1
What causes a decrease in SVR?
progesterone INCREASES nitric oxide & prostacyclin = peripheral vasodilation
What causes dilutional anemia?
increase in plasma and RBC volume
Why are pregnant women prone to viral infection?
non-infectious leukocytosis
lower cell-mediated immunity
(to not ‘reject’ the fetus)
What is the normal arterial blood gas in a pregnant patient?
Respiratory alkalosis - secondary to increase in minute ventilation
What is the normal arterial blood gas in a pregnant patient?
Respiratory alkalosis - secondary to increase in minute ventilation
What is the effect of hyperventilation in a pregnant patient?
esp. in labor, further worsens the effects of respiratory alkalosis: uterine vasoconstriction»_space; decrease placental perfusion
Why are pregnant patients considered a difficult intubation?
edematous mucosal surface - friable
(secondary to increase plasma volume»_space; capillary engorgement)
Why are pregnant patients at risk for reflux?
Progesterone lowers GES pressure/tone
Describe aortocaval compression syndrome.
gravid uterus compresses the IVC and aorta»_space; hypotension, tachycardia
* can decrease uteroplacental perfusion
Which drugs cross the placenta?
low molecular weight
non-ionized
lipid-soluble
(*those that also cross the BBB)
How do anesthetic agents cross the placenta?
simple diffusion (agents are lipid-soluble and have low molecular weight)
Give examples of drugs NOT crossing the placenta
NMB (depolarizing & non-depolarizing)
heparin
insulin
glycopyrrolate
What are the types of FHR decelerations?
- early - head compression
- variable - cord compression
- late - uteroplacental insufficiency
What are the parameters measured by APGAR scoring?
HR
respiration
muscle tone
reflex
color
What is the significance of an APGAR score?
evaluate need for resuscitation and success of resuscitation
When is the best time to operate on a pregnant patient?
For non-emergent: avoid during time of organogenesis (as early as 5 weeks AOG)
‘Safest’ at 2nd trimester
How to induce general anesthesia for an emergency CS for fetal distress?
preoxygenate while prepping the abdomen
RSI, verify ETT, cut
Gas: 50% N2O/O2 + 0.5 MAC
Considerations for epidural placement
gravid uterus compresses the IVC»_space; epidural venous distention»_space; ‘smaller’ epidural space
1. check for IV/dural placement
2. higher block - adjust dose
ephedrine vs phenylephrine for maternal hypotension
Ephedrine: 5-10mg (crosses placenta)
- beta-agonist: dose-dependent fetal metabolic acidosis
Phenylephrine: 50-100mcg
- alpha-agonist: peripheral vasoconstriction, increase uterine vascular resistance but no clinical significance on uteroplacental flow
Which levels to block during labor analgesia?
During active labor: target T10-L1
Conversion from analgesia to anesthesia for NSD should block which levels?
Target pudendal nerve S2-S4
What are usual indications for emergency CS?
preeclampsia/eclampsia
non-reassuring fetal status
When do you include fetal monitoring for non-obstetric surgery?
When fetus is deemed viable at 24 weeks AOG
Leading cause of morbidity/mortality
hypertensive disorders: chronic, gestational, preeclampsia/eclampsia
Pathologic features of preeclampsia
1) increased vascular permeability: peripheral edema, pulmonary edema, left-ventricular failure
2) coagulation problems sec to HELLP
Describe HELLP
- Hemolysis, elevated liver enzymes, low platelet count
- Microangiopathic hemolytic anemia
- Immediate delivery if with DIC
Most common cause of mortality in pregnant w/ hypertensive disorder
cerebrovascular accident
Antihypertensives used
labetalol - B>a-antagonist
hydralazine - vasodilator
Anesthetic concerns for MgSO4
- therapeutic range of 4-8 mEq/L
- increased sensitivity to NDMB (even in therapeutic doses)
- crosses placenta: WOF neonatal depression (respiratory & muscle)
Most cardiac disease complicating pregnancy
congenital heart disease
Commonly used tocolytics
indomethacin (NSAID)
MgSO4
terbutaline (b-agonist)
nicardipine (CCB)
Commonly used uterotonics
oxytocin
methylergonovine (ergot alkaloid derivative)
carboprost (prostaglandin analog)
Concerns with the use of uterotonics
Methergine: IV or IM
- CI: hypertension, IHD
Carboprost: IM only
- CI: asthma
Anesthetic concerns in MS
Neuraxial technique is safe
Anesthetic concerns in MG
- resistant to DMB, sensitive to NDMB
- caution w/ opioids, sedatives
- MgSO4 & CCB are not recommended for eclampsia
- epidural analgesia
- vaginal delivery is preferred
Anesthetic concerns in SLE
- preeclampsia vs lupus nephritis as a diagnostic dilemma
- review coagulation profile if for neuraxial technique
- blood crossmatching may be a problem d/t antibodies
