Obstetric Anesthesia Flashcards
What is the leading cause of postpartum hemorrhage?
Uterine atony
It is also the most common indication for peripartum blood transfusion.
Some of its causes are: Polyhydramnios, multiple gestations, chorioamnionitis, use of tocolytic therapy (which relaxes the uterine muscle)
Define preeclampsia (and what defines the severe type)
It is hypertension occurring after 20 weeks gestation or in the early postpartum period and returning to normal within 3 months after delivery or onset after 20 weeks gestation.
Classic triad: hypertension, proteinuria, and edema
Severe form: SBP >/= 160 mmHg, DBP >/= 110 mmHg, urinary protein > 0.5 g/24 hr, and urine dipstick 3+ or 4+
Severe form symptoms: headaches, visual disturbances, epigastric pain, RUQ abdominal pain, pulmonary edema, HELLP syndrome, or cyanosis
What factors increase the risk for postural puncture headaches?
Thin patients
Age of late teens to early 20s
A low opening pressure at the time of lumbar puncture
A history of migraines or tension headaches
What cardiac signs/symptoms should warrant further investigation in a pregnant patient?
Syncope Chest pain Severe arrhythmias Systolic murmur > grade 3 Diastolic murmur
What are normal cardiac signs/symptoms in a pregnant patient?
Soft systolic murmur
A wide loud split first heart sound
Development of a S3 heart sound
SOB palpitations dizziness edema poor exercise tolerance
What happens to serum cholinesterase activity during pregnancy?
Serum cholinesterase activity DECREASES 30% during pregnancy and remains depressed during the postpartum period.
What happens to arterial carbon dioxide tension during pregnancy?
Due to the increase in minute ventilation, there is a compensatory respiratory alkalosis which is evident on arterial blood gases as a DECREASE in arterial carbon dioxide tension
What happens to tidal volume, minute ventilation, functional residual capacity (FRC), expiratory reserve volume (ERV), Inspiratory reserve volume (IRV), closing volume, and vital capacity (VC) during pregnancy?
Tidal volume - INCREASES
Minute ventilation - INCREASES due mostly to an increase in TV
FRC - DECREASES
ERV - DECREASES
IRV - INCREASED
Closing volume - NO CHANGE
VC- UNCHANGED
What effect does Ephedrine have on fetal beat-to-beat variability
Ephedrine increases fetal beat-to-beat variability
What factors may decrease fetal beat-to-beat variability?
Sleep
Fetal hypoxia
Acidosis
Narcotics (i.e. fentanyl and meperidine)
What happens to renal function during pregnancy?
GFR rises by almost 50% as a result of the increase in cardiac output
Creatinine clearance also increases substantially from 100 mL/min in the non pregnant state to 150 mL/min in the pregnant state
What level of anesthesia is necessary to achieve with an epidural for a routine vaginal delivery? For a c-section?
Vaginal delivery: T10
C-section: T4
What spinal levels are associated with the first stage of labor? Second stage?
First stage of labor, pain fibers originate from T10-L1 associated with progressive cervical dilation and stretching of the lower uterine segment.
Second stage of labor: pudendal nerve S2-4 associated with dissension of the vaginal vault and perineum as the baby is delivered.
What medical conditions increase the risk of placental abruption?
Chronic hypertension Pregnancy-induced hypertension Pre-eclampsia Maternal cocaine use Excessive alcohol intake Smoking Prior history of abruption
How does a patient with placental abruption present?
Vaginal bleeding and uterine tenderness
What medical problem presents as painless vaginal bleeding in a parturient?
Placenta previa
What level of anesthesia is necessary to achieve with regional anesthesia in a C-section?
T4 level, which provides analgesia for the mother and abdominal muscle relaxation which makes it easier for the delivery
What drugs can produce thrombocytopenia and lupus syndrome in neonates when used in preeclampsia?
Hydralazine
What effect does oxytocin have on the airway?
It worsens airway edema because of its antidiuretic effect
How does neuraxial anesthesia effect labor?
It is associated with a prolongation of the second stage of labor in nulliparous women possibly due to a decrease in expulsive forces or fetal malposition.
This prolongation can be minimized by using dilute local anesthetic solutions in combination with opioid or intravenous oxytocin
What is thought to be the cause of preeclampsia?
It is felt to be an imbalance between placental production of prostacyclin and thromboxane
How much is MAC decreased in parturients? At what point in pregnancy does this occur?
MAC is decreased 25% (most likely from progesterone) starting at 10-weeks’ gestation
Why is Hydralazine the most commonly used vasodilator used in the treatment of HTN in the setting of preeclampsia/eclampsia?
It increases uteroplacental perfusion and renal blood flow
What is the P50 of the term parturient?
Rightward shift = 30 mmHg
What factors and associated with an increase risk of placenta previa?
Multiparity Prior C-section Smoking Advanced maternal age Multiple gestation Cocaine abuse
What are common cardiovascular abnormalities found in pregnancy on CXR, ECG, and ECHO that are considered normal?
CXR: apparent cardiomegaly, straightening of the left heart border, and an enlarged left atrium
ECG: right axis deviation, RBBB, Q waves in lead III, a small decrease in the PR and QT interval, and t-wave inversion in leads III, V2, and V3
ECHO: trivial tricuspid regurgitation, pulmonary regurgitation, increased LA size, and increased LVED dimensions, mitral regurgitation, and pericardial effusion
What coagulation factors are increased/ decreased/unchanged in pregnancy?
Preganancy is generally a hypercoagulable state.
Increased factors: VIII, IX, X, and XII, fibrinogen, VII
Unchanged factors: II, platelets
Decreased factors: XI
Name a cutting needle (epidural)
Quincke
Name a non-cutting needle (epidural)
Whitacre or Sprotte
What is the typical/average blood loss for an uncomplicated vaginal delivery?
400-500 ml
How can meperidine affect a parturient?
Nausea/vomiting
Orthostatic hypotension
Maternal depression of ventilation and neonatal depression
Fetal tachycardia
What are some maternal risk factors associated with an increased risk for meconium stained amniotic fluid at birth?
Maternal drug abuse
Use of misoprostol for induction of labor
Chorioamnionitis or other intrauterine infection
Primiparity
Gestational cholestasis
Intrauterine growth retardation
In severe preeclampsia, if a patient’s platelet count is less than 100,000/ mm^3, what must be assessed?
Coagulation abnormalities may occur at platelet counts that are significantly less than 100,000/mm^3. Therefore, it is important to evaluate her coagulation profile (e.g. PT, PTT, and fibrinogen) before using neuraxial block.
What factors increase a parturient’s risk for postpartum hemorrhage?
- retained placenta
- failure to progress during the second stage of labor
- placenta accreta
- lacerations
- instrumental delivery
- large-for-gestational-age newborn
- hypertensive disorders
- induction of labor
- augmentation of labor with oxytocin
At what stage of labor is there the greatest change in the cardiac output in the pregnant patient?
The greatest increase in cardiac output occurs IMMEDIATELY after delivery of the placenta - 80%.
First stage of labor - 30% increase
Second stage of labor - 45% increase
Describe the use of the paracervical block
It can be used for relief of pain during the 1st stage of labor.
However, because it is associated with fetal asphyxia and uterine artery vasoconstriction, it has fallen out of favor over the years.
What are common side effects of magnesium toxicity in pregnancy?
Used to prevent seizures in a woman with moderate to severe preeclampsia, it can cause:
- muscle weakness
- lack of energy
- loss of DTRs
- blurry vision
- headache
- flushing
- slurred speech
- nausea/vomiting
- stuffy nose
Name and describe the stages of labor
1) Latent phase - the longest and least intense phase when mild contractions begin at 15-20 mins apart and last 60-90 seconds. The contractions become more regular until they are less than 5 minutes apart
2) Active phase - when the cervix dilates from 4-8 cms and contractions get more intense, ~ 3 mins apart, lasting ~ 45 seconds
3) Transition phase - when the cervix dilates from 8 to 10 cms, contractions are 2-3 mins apart and last ~ 1 min
4) Fetal descent - the baby’s head moves through the pelvis
5) Second stage - begins when the cervix is fully dilated at 10 cms, followed by crowning of the baby’s head
6) Neonatal delivery - the baby passes through the birth canal, vagina, and is born
7) Third stage - begins after the baby is born and ends when the placenta separates from the wall of the uterus
8) Placental delivery - placenta is passed through the vagina
How is vital capacity maintained during pregnancy?
Primarily by the expansion of the chest wall
What distinguishes preeclampsia from severe preeclampsia?
- Urine output < 500 mL/24 hrs
- Proteinuria > or = 5 g/ 24 hr
- Systolic BP > or = 160 mmHg
- Diastolic BP > or = 110 mmHg
- CNS disturbances
- Pulmonary edema
- Epigastric or RUQ pain
- Hepatic rupture
- Impaired liver function
- Thromboytopenia
- HELLP syndrome
How many umbilical arteries are there? How many veins?
There are 2 umbilical arteries and one umbilical vein
What is the pH, PaCO2, PaO2, and SaO2 of the uterine vein vs. the uterine artery?
Umbilical vein: pH 7.35/ PaCO2 40/ PaO2 30/ SaO2 70%
Umbilical artery: pH 7.28/ PaCO2 50/ PaO 20/ SaO2 40%
What is the path of arterial flow to and from the fetus?
2 uterine arteries —> placenta —–>umbilical vein —-> fetus —> 2 umbilical arteries —> placenta —-> uterine veins
How long does it take for cardiac output to return to 10% of pre-pregnant values in postpartum?
2 weeks
What factor conveys the highest risk of abnormal placentation (accreta, increta, percreta)?
Placenta previa carries the highest risk with an odds ratio of 51.42 (vs. 2.16 for 1 prior c-section, or 8.62 for >/= 1 prior c-sections, and 1.14 for advanced maternal age
(other risks are: advanced maternal age, prior c-section)
What is the one advantage of epidural analgesia alone over combined spinal-epidural analgesia?
A decreased risk of pruritis
What are the risk factors for amniotic fluid embolism?
Multiparity Placenta previa Placental abruption Cervical lacerations Uterine rupture Operative Vaginal Delivery
