OB Flashcards
What is the minimum fasting for elective c-section?
6 hours
The diaphragm is displaced cephalad about 4 cm by the expanding uterus. Why is this significant?
FRC decreases by 20%
May lead to small airway closure
What lung volumes are not changed during pregnancy? Increased? Decreased?
NO change: VC, CV, CC, lung compliance, FEV1, FEV1/FVC, diffusion capacity
Increased: IRV, TV, IC, dead space, MV, diaphragm excursion, O2 consumption
Decreased: ERV, RV, FRC, TLC, chest wall excursion, chest wall compliance, total system compliance, airway resistance, pulmonary resistance
Ventilatory changes produce respiratory ________ (PaCO2 = 30 mmHg) yet the compensation by metabolic ______ (excretion of bicarbonate) will keep the pH normal.
Alkalosis (pH 7.44)
Acidosis (HCO3 20-21)
Would you anticipate the PaO2 to be higher in the pregnant or non-pregnant?
Pregnant
Non-pregnant: 100, 1st: 107, 2nd: 105, 3rd: 103
Would you anticipate the PaCO2 to be higher in the pregnant or non-pregnant?
Non-pregnant
Non-pregnant: 40, pregnant: 30
Describe the changes in alveolar ventilation.
70% increase in alveolar ventilation
TV increases by 40%
RR increases by 15%
What enhances the maternal uptake of inhaled anesthetics?
Increase in alveolar ventilation
Decrease in FRC
*Faster induction
Airway edema d/t engorgement is most evident during what trimester?
3rd
*Use smaller ETT
Why will any episodes of apnea lead to maternal hypoxia quickly?
Increase in oxygen consumption
Decrease in FRC
Rapid airway obstruction
Is it ok to allow the mother to hyperventilate?
NO
Uterine vasoconstriction - decreased placental perfusion
Left shift - increased affinity of maternal Hgb for O2
Is MAC increased or decreased in pregnancy?
Decreased 15-40%
Begins 8-12 weeks
Changes in CV System
No change? Increased? Decreased?
NO change: CVP, PADP, PCWP, LVSWI, LVESV
Increased: BV, plasma volume, RBC volume, CO, SV, HR, EF, femoral venous pressure, LVEDV
Decreased: total peripheral resistance, SVR, MAP, SBP, DBP
When does CO increase the most?
Postpartum - increases 80%
Increase in SV - uterus no longer obstructs
30-40% during 1st trimester
15% latent
30% active
45% second stage
Why is there an anemia? H/H 11.6/35.5%
Blood volume increases by 33-40%
Plasma volume increases by 45%
RBC volume increases by 20%
CO to the uterine vasculature is approx…
700 mL/min
Explain maternal supine hypotensive syndrome.
Compression of IVC decreases VR - decreased SV and BP
Further compression will decrease uterine perfusion - fetal distress
Maternal response - tachycardia, vasoconstriction of LE
LUD - 15 deg, 15 cm wedge
Why is there an increased incidence of accidental epidural vein puncture?
Venodilation
Healthy parturient will tolerate up to _____mL of blood loss.
1500
What should you think if you see a high Hgb level (> 14)?
Low-volume state
Preeclampsia
HTN
Inappropriate diuretics
Changes in Coagulation Factors
No change? Increased? Decreased?
NO change: Factor 2 and 5
Increased: all other factors
Decreased: Factor 11 and 13
Changes in Coagulation
No change? Increased? Decreased?
NO change: plt count, bleeding time
Increased: fibrin degradation products, plasminogen
Decreased: PT, PTT, AT
*Hypercoagulable
Changes in GI System
Increased gastric emptying time
Decreased gastric motility
Decreased LES tone
*All d/t elevated levels of progesterone
Increased intragastric pressure
Increased secretion of gastric acid
*D/t elevated gastrin
Caution: narcotics, valium, and atropine all decrease LES tone further
*Prone to gastric reflux - FULL stomach at week 12
Changes in Renal System
No change? Increased? Decreased?
Increased: RBF, GFR, creatinine clearance
Decreased: BUN, creatinine
What 2 factors cause decreased uterine blood flow?
- Decreased perfusion pressure — decreased uterine arterial pressure + increased uterine venous pressure
- Increase uterine vascular resistance
endogenous vasoconstrictors + exogenous vasoconstrictors
Uterine artery pressure is determined by…
Maternal systemic arterial pressure
*Maternal BP is the ONLY factor that influences blood flow through the placenta
How does maternal blood circulate through the placenta?
Uterine artery
Intervillous space
Fetal villi
Veins
How many microscopic tissue layers are found in the placental membrane?
3
- Fetal trophoplasts
- Fetal connective tissue
- Endothelium of the fetal capillaries
Pharmacology Considerations
MAC reduced 15-40% ED50 of thiopental reduced Elimination 1/2 life of thiopental prolonged Propofol unaltered Sux unaltered, sensitivity reduced Increased sensitivity to Vec and Roc Response diminished to chronotropic agents Subarachnoid dose of LA reduced by 25%
Regional Effects on Uterine BF
Increased BF: pain relief, decreased SNS activity, decreased hyperventilation
Decreased BF: hypotension, IV injection of LA
First Stage of Labor
Cervical effacement and dilation
Latent phase: onset of labor to the point at which the cervix begins to rapidly change
Active phase: begins at 2-3 cm dilation, cervix undergoes its max rate of dilation
Second State of Labor
Begins at full cervical dilation (10 cm)
Ends with delivery of the fetus
Third Stage of Labor
Delivery of the placenta
First Stage Labor Pain
Pain source: cervical distention, stretching of the lower uterine segment, and possibly, myometrial ischemia
Pain type: visceral
Fibers: unmyelinated C fibers
Enter the cord at: T10, T11, T12, and L1
Second Stage Labor Pain
Pain source: compression and stretching of the pelvic musculature and perineum
Pain type: somatic
Fibers: myelinated A-delta fibers
Enter the cord at: S2, S3, and S4 via pudendal nerves
When should Meperidine be given?
Give early in labor (4 hours before delivery)
Max maternal and fetal depression are seen 10-20 min after IV and 1-3 hrs after IM
10-25 mg IV
25-50 mg IM
Total 100 mg
Name 2 partial agonists that can be used.
- Butorphanol 1-2 mg IV or IM
2. Nalbuphine 10-20 mg IV or IM
What dose of Ketamine is associated with fetal depression?
> 1 mg/kg
And can cause hypertonic uterine contractions
Doses of Intrathecal and Epidural Opioids
Intrathecal/Epidural Morphine: 0.5-1 mg/7.5-10 mg Meperidine: 10-20 mg/100 mg Fentanyl: 10-25 mcg/50-100 mcg Sufentanil: 3-10 mcg/10-30 mcg
What is the most common SE of regional anesthesia?
Hypotension
Bupivacaine-induced cardiovascular collapse may be treated with…
Bretylium
Amiodarone may be useful in reversing the decreased threshold for LV tachycardia
Umbilical Cord Prolapse
Causes: excessive cord length, malpresentation, low birth weight, graviparity, multiple gestations, artificial rupture of membranes
Diagnosis: sudden fetal bradycardia or profound decelerations
Treatment: immediate steep T-burg or knee-to-chest position, manual pressure against the presenting part, uterine relaxation, emergency cesarean section
List 3 causes of antepartum hemorrhage.
- Placenta Previa
- Placenta Abruption
- Abnormal Placental Implantation
Placenta Previa
What is it?
What is the concern?
Placenta implanted on the lower uterine segment – either partially or completely covers the opening of the cervix
Results in PAINLESS vaginal bleeding (preterm, no contractions)
Potential for sudden loss of large amounts of blood
Significant bleeding may follow manual examination of the cervix
Increases postpartum bleeding
Placenta Previa
Risk Factors?
Tx?
Associated with what other risks?
Risk factors: multiparity, age, previous C-section, previous previa
Tx: Bedrest and observation
Increased risk for - accrete if history of previous C-section, VAE, asymmetric intrauterine growth restriction
What type of placenta previa increases the risk of excessive bleeding for c-section?
Anterior lying placenta previa
Placental Abruption
What is it?
Results in…
Incidence is higher in women with what?
Separation of the placenta from the deciduas basalis
Results in hemorrhage, uterine irritability, abdominal pain, fetal hypoperfusion
Incidence higher in women with HTN
What is the most common cause of DIC?
Placental Abruption
Placental Abruption Significance of bleeding? Candidates for regional anesthesia? Risk factors? How do these patients present? Associated with what other risks?
Bleeding may be concealed – large volumes, uterus may contain 2500 mL of blood
Contraindication to regional anesthesia
Risk factors: HTN, increased age, tobacco use, cocaine use, trauma, PROM, history of previous abruption
Presentation: painful vaginal bleeding, uterine tenderness, increase uterine activity, fetal distress
AFE, DIC
Abnormal Placental Implantation
Placenta normally implants into the endometrium
Placenta accreta – on the myometrium, 78%
Placenta increta – into the myometrium, 17%
Placenta percreta – completely through the myometrium, 5%
What is the most common indication for obstetric hysterectomy?
Abnormal Placental Implantation
Abnormal Placental Implantation
Associated with what?
May be unforeseen…why?
Associated with placenta previa, previous c-sections
MRI and ultrasonography have poor predictive capability for the diagnosis
Amniotic Fluid Embolism
Mortality rate?
S/S?
Tx?
86%, 50% during first hour S/S - hypotension, dyspnea Tx - supportive care, A-OK Associated with placental abruption Prone to develop DIC
What is the 3rd leading cause of maternal death?
AFE
What is the most common fetal HR changes seen during labor?
Variable decels
What is the most common serious side effect of mag sulfate?
Pulmonary edema
What is the most common cause of postpartum hemorrhage?
Uterine atony
What is the most common severe morbidity complicating OB anesthesia?
Maternal hemorrhage
What is the most common cause of maternal death in pregnancy-induced HTN?
Cerebral hemorrhage
2nd: pulmonary edema
What % of the CO perfuses the gravid uterus at term?
10%
800 mL/min
When does CO return to baseline?
14 days postpartum
Rank the amides local anesthetics from greatest to least according to their ability to cross the placenta.
Mepivcaine > etidocaine > lidocaine > ropivacaine > bupivacaine
“Maternal Elevated Locals are Risky to Baby!”
Methergine
Ergot alkaloid Dose: 0.2 mg IM Potent vascular effects - Increase in BP, CVP, and PCWP NOT administered IV - Arterial and venous constriction, coronary artery constriction, severe HTN, cerebral bleeding Metabolized and eliminated by liver Onset: 3-5 min Half-life: 2 hrs
Hemabate
Prostaglandin F2a
Dose: 250 mcg IM, Q15 min, max 2 mg
Potent stimulator of uterine contraction
Strong and painful!
Caution with asthmatics
Frequent side effects: N/V/D, bronchospasm, flushing, bradycardia, hypotension
Onset: 5 min
Magnesium Sulfate
Relaxation of vascular, bronchial, and uterine smooth muscle
Anticonvulsant
Increased uterine BF, renal BF
Increased prostacyclin release by endothelial cells
Decreased plasma renin activity
Decreased plt aggregation
What is the therapeutic serum level of Mag?
4-8 mg/dL
Review serum levels of Mag and associated symptoms.
Normal level = 1.8-3 mg/dL PQ interval prolonged, wide QRS = 5-10 Loss of deep tendon reflexes = 10 Heart block = 15 Respiratory depression with levels > 15 Cardiac arrest with levels > 25
Where does Mag work?
NMDA receptor
The neuromuscular blocking effects of Mag can be a least partially antagonized by what?
Calcium
Preeclampsia
New onset HTN (>160/110), proteinuria (>5 G/day), and after 20 weeks gestation
Affects 5-7% of pregnancies
Plasma volume is normal in mild disease but may be reduced by up to 40% in severe disease.
How long do mothers remain at risk for eclampsia?
Usually resolves w/in 48 hrs
Up to 2 weeks postpartum
DIC
Associated with what 3 obstetric problems?
- Intrauterine fetal demise
- Placental abruption
- Amniotic fluid embolism
Lab studies:
Decreased: fibrinogen, platelets
Increased: PT, PTT, fibrin degradation products
Definitive treatment = elimination of the cause
Evacuate the uterus
Early Decels Type I
Occur with each contraction Start and end with the contraction Uniform in appearance Beat-to-beat variability not present Vagal stimulation from compression of the fetal head
Late Decels Type II
Occur with each contraction
Begin late in the contraction
Lowest point occurs after the peak of the contraction
Uniform in appearance
Beat-to-beat variability may or may not be present
Uteroplacental insufficiency
Variable Decels Type III
Abrupt onset and recovery
Irrespective of contractions
Vary in appearance, duration, depth, and shape
Beat-to-beat variability present
Baroreflex-mediated response from umbilical cord compression
List 2 non-cutting point needles.
- Sprotte
2. Whitacre
Subarachnoid Block for C-section
Dose Requirements and Duration (w/Epi)
Tetracaine 7-10 mg - 2.5-3 hrs
Lidocaine 60-75 mg - 1.5-2 hrs
Bupivacaine 11.25-15 mg - 3-3.8 hrs
How much of the total uterine blood flow goes to the intervillous space?
550 mL/min
What is the PaCO2 and PaO2 in the normal fetus?
PaCO2 48 mmHg
PaO2 30 mmHg
Give the formula for uterine blood flow.
Mean uterine artery pressure -uterine vein pressure / uterine vascular resistance
*Uterine artery pressure depends on maternal BP
Placental blood flow is directly dependent on the pressure in the uterine artery…therefore, placental blood flow depends solely on…
Maternal blood pressure
Is uterine blood flow autoregulated?
NO
What is the predominant adrenergic receptor in the uterine vasculature?
Alpha-adrenergic receptors
Which maternal hemodynamic parameter shows the greatest decrease during normal gestation?
SVR (-20%)
Which maternal hemodynamic parameter shows the greatest increase during normal gestation?
CO (+50%)
What is the normal FHR?
What is normal beat-to-beat variability?
120-160 bpm
3-6 beats/min
What is the most serious fetal risk associated with maternal surgery during pregnancy?
Uterine asphyxia
The effect of progesterone on the respiratory system.
Acts as a direct respiratory stimulant
Increase in chemoreceptor sensitivity
Steep and left shift of CO2 ventilatory response curve
Does pregnancy mimic restrictive or obstructive disease?
Restrictive
What does HELLP stand for?
Hemolysis
Elevated liver enzymes
Low platelets
*Usually occurs b4 36 weeks gestation
What does the diagnosis of HELLP call for?
Immediate delivery regardless of gestation d/t high maternal and fetal mortality
In the pre-eclamptic patient, what are the best tests to evaluate bleeding?
PT and PTT
What is the mainstay therapy for HTN in the pre-eclamptic patient? Why?
Hydralazine
Lowers BP and increases uteroplacental BF
What drug should be avoided in the treatment of HTN in the pre-eclamptic patient?
Esmolol
Also avoid: Clonidine, Nifedipine, ACE-I
What is the most common cause of morbidity and mortality in pregnancy?
Pre-eclampsia and eclampsia
How do you convert mEq/L to mg/dL?
Divide mEq/L by 0.8 to convert to mg/dL
How does Mag work as an anticonvulsant?
Decreases the presynaptic release of Ach
Reduces the sensitivity of postsynaptic membranes to Ach
What is the earliest sign of Mag toxicity?
Marked depression of DTR
Mag toxicity is treated with IV…
Calcium gluconate
How is Mag administered in the pre-eclamptic patient?
Loading dose: 4-6 G over 20-30 min
Gtt: 1-2 G/hr for up to 24 hours postpartum
What is Ritodrine used for?
Stop premature labor
Beta 2 agonist
SE: hyperglycemia, hypokalemia, tachycardia - crosses the placenta so could cause these SE in fetus
What are the benefits of chloroprocaine?
Rapid onset
Crosses the placental barrier in the smallest amount
Rapidly hydrolyzed by pseudocholinesterase
Safest and least toxic
What vasopressor has a minimal effect on uterine blood flow?
Ephedrine
Is prilocaine appropriate for OB use?
NO - ortho-toluidine causes methemoglobinemia
Why does bupivacaine pass less readily across the placental barrier than the other amides?
Greatest protein binding (95%)
What is the major concern for a patient who is scheduled for tubal ligation in the early post-partum period?
Risk of aspiration
When regional anesthesia has not been used, wait 8-12 hours postpartum to allow the patient to reach CV stability and increase the likelihood of gastric emptying
What should you try to avoid in a pregnant patient presenting for nonobstetric surgery?
Avoid N2O and benzos
Most organogenesis occurs in the 1st trimester
What is the most common surgical emergency procedure during pregnancy?
Appendicitis
What is the most common cause of maternal death during OB general anesthesia?
Hemorrhage
NOT airway
Ideally, the uterine-to-delivery interval is less than…
3 min
At what state of labor is a pudendal block given?
Just before delivery (end of second stage)
Paracervical block
First stage of labor
NOT effective during the second stage
8-40% incidence of fetal bradycardia that develops 2-10 min after injection
Disadvantages of Chloroprocaine
NOT a suitable agent for use with opioids
Can use opioid agonist-antagonist
Can develop tachyphylaxis
What do you want to maintain in the healthy pregnant patient: SBP, DBP, or MAP?
SBP
Prevent a decrease of 20-30% OR falling below 100 mmHg
APGAR
- HR
- Respiratory effort
- Reflex irritability
- Muscle tone
- Color
What is the neonatal dose of epinephrine for treatment of asystole?
0.01-0.03 mg/kg
Given for HR < 60
What is the appropriate drug for the neonate with an APGAR score of 3 after 5 min?
Sodium bicarbonate
What general anesthetic factors most depress the APGAR score at 1 min?
Low FiO2
High N2O
A pregnant patient receives a caudal block…
- and suddenly becomes agitated, dyspneic, and her legs thrash.
- and suddenly becomes agitated, dyspneic, and unable to move her legs.
- Intravascular injection
2. High spinal
What 2 drugs are used in the situation of uterine inversion/inverted uterus?
- Inhaled agents
2. Nitroglycerine (50-100 mcg)
Should severe maternal hypotension exist, what IV anesthetic would you use for induction and intubation?
Ketamine
Damage to which of the 3 layers of the uterus is of greatest concern to the anesthetist?
Middle, muscular layer, myometrium
Treatment of LA toxicity.
Thiopental or benzo
Avoid propofol d/t CV instability
Maintain oxygenation - possibly intubate
Support BP
Give Ca to raise the cardiac threshold
Avoid: vasopressin, CCB, BB
20% Intralipid: 1.5 mL/kg over 1 min, repeat, then infusrion of 0.25 mL/kg/min (max 10 mL/kg over the first 30 min)
In multiple situations, even in the scenario of a high spinal, what position should the pregnant patient be placed in with hypotension?
T-burg and L uterine displacement to increase VR to the heart
What fetal pH indicates fetal acidosis?
Fetal pH < 7.20
- Type II decels w/ normal beat-to-beat variability
- Type II decels w/ diminished beat-to-beat variability
- Type II decels w/ absent beat-to-beat variability
- Acute insult like hypotension
- Prolonged fetal asphyxia
- Severe decompensation
What is the most common cause of anesthesia-related maternal mortality on the OBESE parturient?
Airway complications
What are 3 pathophysiological problems that are responsible for the presenting s/s seen in the patient with AFE?
- Acute PE
- DIC
- Uterine atony
What is the appropriate position for the parturient with AFE?
L uterine displacement
Slight head-up position
What is the appropriate position for the parturient with VAE?
L uterine displacement
Slight head-up position
What should you think of with polyhydramnios?
Tracheoesophageal fistula (TEF) Or possibly congenital diaphragmatic hernia
Risk for umbilical cord prolapse, possible breech or malpresentation, uterine atony
What nerve is most commonly injured in the patient undergoing an abdominal hysterectomy?
Femoral nerve
Damage to what nerve…inability to dorsiflex the foot?
Common peroneal nerve
What nerve injury is most commonly associated with vaginal delivery?
Lumbosacral nerve
A pregnant patient presents with thrombocytopenia…name the most likely cause?
Incidental, or gestational thrombocytopenia
Then pre-eclampsia/eclampsia
Which opioids produce a greater degree of segmental analgesia - lipophilic or hydrophilic?
Lipophilic such as Fentanyl
Which intrathecal opioid has the fastest onset?
Sufenta
D/t lipid solubility
