Ex1 OB 1 Flashcards
CVS system changes in pregnancy
increased HR, SV
therefore increased CO
Respiratory system changes in pregnancy
- displacement of diaphragm superiorly
- decreased FRC
- increased risk of apnea/dyspnea
- hyperventilation
GI changes during pregnancy
- N/V
- heart burn + acidity
Major cardiovascular changes during pregnancy
- increased intravascular volume
- increased cardiac output
- decreased vascular resistance
- supine HOTN
Changes to the heart during pregnancy
heart enlarges, displaces upward + to Left
Why does CO change during pregnancy?
Increase in both HR, SV
Decrease in SVR
Decreased SVR is due to
initiating factor: estrogens, progesterone, prostacyclin
CO is greatest when?
Right after delivery
When does moms CO return to baseline?
~ 2 weeks after delivery
What compensates for the blood loss during delivery?
contractions of engorged uterus provide 300-500mL autotransfusion into maternal circulation –> increased CO
Common cause of moms HOTN
While laying flat on back: weight of placenta + amniotic sac can compress IVC
Increased risk of ____ in mom d/t decreased vascular resistance/venodilation?
epidural vein puncture
While placing epidural, what should be ensured?
Remaining midline (avoid epidural veins)
90% of pregnant women have a ____
late systolic or ejection murmur
Common murmurs in pregnant women are attributable to
increased stroke volume
decrease in blood viscosity
At term, what may be seen on the CXR?
Larger cardiac silhouette d/t diaphragm shifting heart up + Left
What changes may be seen in 3rd trimester on EKG?
Increased incidence of dysrhythmias (PAC, PVC, SVT) d/t Left Axis shift on ECG
Second trimester
20-28 weeks gestation
important but preventable cause of fetal distress
aortocaval compression
-after 20-28w gestation
aortocaval compression
gravid uterus obstructs aorta + inferior vena cava (while supine) –> no blood supply to placenta (uteroplacental circulation) –> no blood supply to baby –> asphyxia
What will be seen on the fetal heart monitor if aortocaval syndrome occurs?
Late decelerations
How to avoid aortocaval syndrome?
Tilt parturient to left side
3rd trimester
29-40 weeks
Cause of LE edema, venous stasis
Chronic partial caval obstruction in 3rd trimester
Beginning location of aortic compression
L3-L4
upper body BP may remain normal
Changes in blood volume during pregnancy are due to
increased mineralocorticoid activity –> sodium retention + increased body water content
Blood volume changes during pregnancy
increased:
plasma volume ( +50%
total blood volume (+45%)
red cell volume (+25%)
Which increases more during pregnancy: plasma volume or red cell volume?
Plasma volume
Changes in blood volume lead to ____ during pregnancy
relative dilutional anemia
TBV at term
85-100 mL/kg
Healthy parturients can tolerate up to _____ mL blood loss without a transfusion
1500mL
High Hgb levels may indicate
Normal Hgb > 11
High Hgb = > 14
*may indicate low volume state caused by preeclamsia, HTN, or inappropriate diuresis
Approximate intravascular volume change
1000-1500 mL
*helps compensate for EBL
EBL vaginal
300-500 mL
EBL section
800-1000mL
Coagulation changes during pregnancy
- coagulation factors + fibrinogen increase
- platelets remain same or decrease 10% during 3rd trimester
Factors that increase during pregnancy
I, VII, VIII, IX, X, and XII
Factors that decrease during pregnancy
XI and XIII
Coagulation lab changes in pregnancy
PT -20%
PTT -20%
No change: platelets or bleeding time
Coagulation lab changes in pregnancy: thromboeleastography
hypercoagulable
Coagulation lab changes in pregnancy: antithrombin III
decreased
Coagulation lab changes in pregnancy: fibrin degradation products
increased
Coagulation lab changes in pregnancy: plasminogen
increased
What may worsen airway edema in pregnancy?
- preeclampisa
- trendelenberg position
- Tx w/ tocolytics
Average size ETT in pregnancy
6-6.5
changes in airway during pregnancy
- capillary engorgement of mucosal lining
- mucous membranes = friable
- swelling of false vocal cords (narrowed glottis)
- weight gain/breasts = hinder laryngoscopy
key for successful airway placement
- proper axis alignment (via positioning)
- short laryngoscopy handles
- know where glidescope is at all times (video laryngoscope)
What does diaphragmatic elevation cause?
- less negative intrathoracic pressure
- decreased FRC, ERC, RV (20%)
significant PFT changes
compensatory increase in thoracic anterior-posterior diameter
What change in moms body causes the majority of respiratory changes?
Hormones (increased progesterone)
+
Enlarged Uterus
What physical changes in moms body causes respiratory changes?
Enlarged uterus –> ribcage becomes wider, back broader (+ diaphragm pushed up)
Why is mom at a higher risk of rapid oxygen desaturation during periods of apnea?
Combo:
decreased FRC + increased O2 consumption
What is mandatory prior to GA in pregnant patients?
Preoxygenation
Risk of pain/anxiety during labor in relation to respiratory system
increased RR –> hypocapna, faintness, perioral numbness
–> fetal hypoxia/distress
What occurs to 2,3-DPG during pregnancy?
Why does this change?
- 2,3-dpg concentration increases
- lowers affinity of maternal Hgb for O2
Reason for change of 2,3-dpg
Lowers moms affinity of Hgb for O2 –> facilitates dissociation of oxygen from Hgb thru intervillous space in placenta, enhances delivery of O2 to growing fetus
Dissociation curve is affected during pregnancy how?
increased 2,3-DPG shifts O2 Hgb dissoc. curve to the Right (P50 increases from 27-30 mmHg)
Most significant Respiratory changes
Decreased FRC
No change in VC
Increased TV
Decreased ERV
When does mom’s minimal alveolar concentration return to normal?
3 days post-partum
Effect of pregnancy on MAC
decreases by up to 40%
Cause of changed MAC during pregnancy
Progesterone + B-endorphin
Pregnant patients reaction to local anesthetics + cause
enhanced sensitivity d/t increased spread of LA in epidural/subarachnoid spaces (occurs d/t epidural venous engorgement)
Parturient is highly dependent on _____ for blood pressure control
SNS
D/t increased SNS role in parturient, what occurs after regional anesthesia?
significant decrease in BP
When does SNS return to normal?
36-48 hours postpartum
cause of constipation during pregnancy
progesterone –> slowed GI motility –> enhanced water absorption
All moms after ______ (time) are at risk for what?
12 weeks +
increased risk for aspiration
RSI
If GA is administered to parturient, what should also be given?
- nonparticulate antacid (Bicitra)
- H2 blocker
- Reglan (consider)
What occurs to GFR during pregnancy?
- Increased by 50% in 1st trimester
- declines to normal in 3rd trimester
Hepatic effects during pregnancy
Serum cholinesterase activity decreases by ~ 30%
NOT clinically relevant for sux/mivacurium
When does pseudocholinesterase activity return to normal?
6 weeks postpartum
Effect of pregnancy on urine labs
Mild glucosuria (1-10g/dL) or proteinuria (<300mg/dL) d/t decreased renal tubular threshold for glucose/amino acids
What joins the mother and fetus?
Placenta
Uterine blood flow receives how much CO?
10% CO at term (600-700mL/min)
nongravid = 50mL/min
T/F: the uterus is capable of autoregulation
False
Uterine perfusion is dependent on
- adequate driving pressure (uterine arterial pressure)
- low uterine venous pressure
- low uterine vascular resistance
Increased uterine venous pressure _____ uterine blood flow
lowers
Increased uterine venous pressure is d/t
Caused by: Vena caval compression Uterine contractions Drug-induced hypertonus (oxytocin, LA) Skeletal muscle hypertonus (seizures, valsalva)
Increased uterine venous resistance ______ uterine blood flow
lowers
Causes of increased uterine venous resistance
- endogenous vasoconstrictors
2. exogenous vasoconstrictors
Endogenous vasoconstrictors that may cause increased UVR
- catecholamines (stress)
- vasopressin (in response to hypovolemia)
Exogenous vasoconstrictors that may cause increased UVR
- epinephrine
- vasopressors (phenyl, ephedrine)
- local anesthetics in high concentrations
Transfer of oxygen from mom to baby is dependent on
ratio of maternal UBF to fetal blood flow
oxygenated blood from placenta has PaO2 of
40mmHg (80% saturated)
fetal Hgb O2 dissociation curve is shifted ____
to the Left
HgbF > affinity for O2 than HgbM
Fetal Hgb vs. Mom Hgb
Fetal ~ 15 g/dL
Mom ~ 12 g/dL
transport of anesthetics from mom to baby occurs via
passive diffusion
The rate of transfer of anesthetics from mom to baby occurs based on
Fick Principle
Factors that promote rapid diffusion (anesthetics from mom to baby)
- most anesthetics
- NOT muscle relaxants
- low molecular weight (<500 daltons)
- high lipid solubility
- low degree of ionization
- low protein binding
Ion trapping
fetal acidosis/low pH –> Rx = greater tendency to exist in ionized form, unable to diffuse back across placenta into maternal plasma –> Rx trapped in fetus (larger amounts)
Rx used to stimulate/strengthen uterine contractions
oxytocics
Rx used to delay/stop premature labor
tocolytics
Oxytocics indications
- induce/augment labor
- control PP bleeding/uterine atony
- induce therapeutic abortion
Oxytocics
- Oxytocin (pitocin)
- Ergot alkaloids: Ergonovine (ergotrate), Methylerogonovine
- Prostaglandin 15-methyl F2a
Oxytocin MOA
Acts on uterine smooth muscle to stimulate the frequency and force of contractions; potent vasodilator
Oxytocin S/E
CV effects: vasodilation, HOTN, tachycardia, arrhythmias
-high doses: may have antidiuretic effect + produce water intoxification, cerebral edema, convulsions
Oxytocin dosage
- diluted (20-40 u/L)
- IV infusion
- NEVER BOLUSED/PUSHED
Risk of Oxytocin
Added preservative (chlorbutanol) = vasodilatory + negative inotropic effects
Mom complains of N/V after oxytocin given, what can you assume?
BP will drop soon, even if it doesn’t show it yet. Slow down drip.
Ergot Alkaloids - MOA
small doses: increase force + frequency of uterine contractions
high doses: contractions more intense, prolonged, resting tone increased, tetanic contractions occur
Ergot Alkaloids - Rx
Most commonly used: methergine (methylerogonivine)
Methergine A/E
CV: vasoconstriction, HTN augmented in presence of pressors
Ergot Alkaloids: restrictions
Administration is restricted to 3rd stage of labor to control postpartum bleeding
Methergine Administration
- ONLY IM, 0.2mg
* prefer to give in thigh if spinal/epidural given
Methergine - avoid in
PVD, HTN, CAD
Methergine - why not IV?
associated with severe HTN, convulsions, stroke, retinal detachment, pulm edema
Prostaglandin 15-methyl F2a
Hemabate
“carboprost tromethamine”
Hemabate
3rd line Tx for uterine atony
goal: achieve uterine contraction
Hemabate SE
transient HTN, severe bronchospasm, increased PVR
Hemabate avoid in
asthmatics
Hemabate administration
0.25mg IM
or intramyometrially (OB)
*must be refrigerated, $$$$
Tocolytics are used for
delay or stop premature labor
- used for fetuses gestational age 20-28 weeks
- cervical dilation < 4cm + effacement < 80% associated with greater likelihood of terminating premature labor
Tocolytics C/I
- chorioamnionitis
- fetal distress
- intrauterine fetal demise
- severe or chronic pregnancy-induced HTN
- severe hemorrhage
Terbutaline
Selective B2-adrenergic agonist
-used to inhibit preterm labor by producing myometrial inhibition by directly relaxing uterine smooth muscle
Terbutaline SE
maternal bronchodilation vasodilation tachycardia hyperglycemia hypokalemia hyperinsulinemia metabolic acidosis
What is magnesium sulfate used for in OB?
Preeclampsia + tocolytic agent
MOA Mag Sulfate
- reduces presynaptic release of Ach, which decreases hyperactivity at neuromuscular junction, thus weakening contractions
- physiologic calcium antagonist, prevents increase of free intracellular calcium
Mag Sulfate Administration
- Loading dose (4gm over 20 min)
Followed by - Infusion (2-4g/hr)
Mag Sulfate SE
sedation, flushed face, hypotension, heart block, skeletal muscle weakness, respiratory depression, cardiac arrest
*flushed, weak, tired, soft, mushy
Mag Sulfate Safety Precautions
Soft, boggy uterus –> high risk for PPH.
*have blood available, may need methergine, make sure T&C
Other agents used to delay preterm labor
Indomethacin
Nifedipine
Indomethacin MOA
NSAID that inhibits prostaglandins
Nifedipine MOA
CCB
most common drug given systemically to mother
opioids
Opioids AE
- cross placental circulation freely (RR depression in newborn), limited to early stages of labor OR regional not available
- maternal SE: RR depression, N/V, altered MS
If regional not available, best option?
Remifentanil bolus PCA
Duramorph
preservative free morphine used in spinal/epidural
Which opioid is not used and why?
- Morphine not used
- excessive RR depression in neonate
Duramorph administration
10mg/10mL (1mg/mL)
or
5mg/10mL (0.5mg/mL)
Duramorph administration for spinal vs epidural
Spinal: use TB syringe (small amount)
Epidural: use normal syringe (bigger volume)
Fentanyl use in OB
-adequate labor analgesia with minimal neonatal depression
Maternal effects from Fentanyl
Maternal respiratory depression outlasts analgesia
-do NOT give near delivery
Neonatal effects from Fentanyl
- transient decrease in FHR variability noted
- doses of 1mcg/kg no adverse effects
Fentanyl administration
25-50 mcg IV peak 3-5 min DOA 30-60min Best: epidural/spinal Not-ideal: IV/PCA
Reason for using Butorphanol or Nalbuphine
produce less N/V than other opioids
Butorphanol MOA
“Stadol”
kappa-agonist + mu-antagonist, minimal affinity for delta receptors
Butorphanol administration
1-2mg IV/IM
DOA up to 4h
Nalbuphone MOA
“Nubain”
partial kappa-agonist + mu-antagonist, minimal delta activity
Nalbuphone administration
10mg IV/IM
DOA up to 6h
Nalbuphone Equipotent dose
10mg morphine = 10mg Nalbuphone
Remifentanil compared to epidural
Remifentanil less effective than standard epidural
PCA remifentanil dosage
0.25 mcg/kg q2 minutes
Remifentanil characteristics
- ultra-short acting with context sensitive 1/2t = 3.2 minutes
- crosses placenta readily, rapidly redistributed + metabolized by fetus
When is ketamine used?
Adjunctive, used for “hot spot”, subanesthetic doses = result in analgesia w/o LOC or loss in reflexes
Disadvantages of Ketamine
HTN, emergence delirium
Advantages of Ketamine
Maintains maternal CVS + uterine blood flow
Ketamine dose
0.25-0.5 mg/kg IV
or
10 mg q2-5min IV
High doses of ketamine may cause
High doses ( > 2mg/kg)
psychomimetic effects
increased uterine tone (+ low Apgar score)
Typical duration of C/S
45 minutes
Most frequently used inhalational technique
outside of US: 50:50 N2O + O2