Anesthesia for Obstetrics Flashcards
Uterine blood flow increases progressively during pregnancy from approximately … in the nonpregnant state to between … ( … % of cardiac output) at term gestation
100 mL/min
700 and 900 mL/min
∼10
During pregnancy, the maternal oxyhemoglobin dissociation curve shifts to the … with pregnancy while the fetal oxyhemoglobin dissociation curve lies to the …
right
left
Fetal O2 saturation does not exceed 85% even with 100% O2 delivery to
the pregnant patient
T or F
F
Fetal O2 saturation does not exceed 60% even with 100% O2 delivery to
the pregnant patient
Neuraxial analgesia is the most reliable and effective method of reducing pain during labor. Adequate analgesia is achieved with blockade of … during the first stage of labor and requires extension to include … during the second stage of labor.
T10 to L1
S2 to S4
Neuraxial analgesia may prolong the first stage of labor in comparison to unmedicated birth or intravenous opioid analgesia and can increase the risk for cesarean delivery.
Epidural analgesia utilized early compared to late in labor increase the risk for cesarean delivery but doesn’t prolong the first stage of labor
T or F
F
Neuraxial analgesia may prolong the second stage of labor in comparison to unmedicated birth or intravenous opioid analgesia but does not increase the risk for cesarean delivery.
Epidural analgesia utilized early compared to late in labor does not increase the risk for cesarean delivery or prolong the first stage of labor
Describe the changes on the cardiovascular parameters during pregnancy
1) Intravascular fluid volume: Increased 35%-45%
2) Plasma volume Increased: 45%-55%
3) Erythrocyte volume Increased: 20%-30%
4) Cardiac output: Increased 40%-50%
5) Stroke volume Increased: 25%-30%
6) Heart rate Increased: 15%-25%
7) Systemic vascular resistance: Decreased 20%
8) Pulmonary vascular resistance: Decreased 35%
9) Central venous pressure: No change
10) Pulmonary capillary wedge pressure: No change
11) Femoral venous pressure: Increased 15%
12) Electrocardiography:
- Heart rate dependent decrease in PR and QT intervals
- Small QRS axis shift to right (first TM) or left (third TM)
- ST depression (1 mm) in left precordial and limb leads
- Isoelectric T-waves in left precordial and limb leads
- Small Q-wave and inverted T-wave in lead III
13) Echocardiography
- Heart is displaced anteriorly and leftward
- Right-sided chambers increase in size by 20%
- Left-sided chambers increase in size by 10%-12%
- Left ventricular eccentric hypertrophy
- Ejection fraction increases
- Mitral, tricuspid, and pulmonic valve annuli increase
- Aortic annulus not dilated
- Tricuspid and pulmonic valve regurgitation common
- Occasional mitral regurgitation (27%)
- Small insignificant pericardial effusions may be present
Describe changes in cardiac auscultation during pregnancy
An accentuated first heart sound (S1) can be heard on auscultation, with an increased splitting noted from dissociated closure of the tricuspid and mitral valves.
A third heart sound (S3) is often heard in the third trimester, and a fourth heart sound (S4) can also be heard in some pregnant patients because of increased volume and turbulent flow. Neither the S3 nor S4 heart sounds have clinical significance by themselves.
In addition, a benign systolic ejection murmur is typically heard over the left sternal border and is secondary to mild regurgitation at the tricuspid valve from the annular dilation associated with the increased cardiac volume
Maternal intravascular fluid volume begins to increase in the first trimester secondary to changes in the … promoting …
These changes are likely induced by … from the gestational sac
renin–angiotensin–aldosterone system
sodium absorption and water retention.
rising progesterone
Blood volume returns to prepregnancy values approximately … postpartum.
6 to 9 weeks
During pregnancy, the largest increase in cardiac output occurs …, when cardiac output can increase by …% more than prelabor values.
This increase is secondary to the …
immediately after delivery
80% to 100
autotransfusion of uteroplacental blood as the evacuated uterus contracts, reduced maternal vascular capacitance from loss of the intervillous space, and diminished lower extremity venous pressure from release of the aortocaval compression
Cardiac output returns toward prelabor values within … postpartum depending on the mode of delivery and degree of blood loss.
Cardiac output decreases substantially toward prepregnant values by … postpartum, with complete return to nonpregnant levels between … after delivery
24 hours
2 weeks
12 and 24 weeks
During pregnancy, systemic vascular resistance decreases as a result of the …
vasodilatory effects of progesterone and prostaglandins as well as the low resistance of the uteroplacental vascular bed
Although the inferior vena cava is compressed in nearly all term parturients,supine hypotension syndrome (also known as …) is experienced by only 8% to 10% of women.
Supine hypotension syndrome is defined as …, and is often associated with …
aortocaval compression syndrome
a decrease in mean arterial pressure of more than 15 mm Hg, with an increase in heart rate of more than 20 beats/min
diaphoresis, nausea, vomiting, and changes in mentation
How does neuraxial/general anesthesia affect the supine hypotension associated with pregnancy?
Most pregnant patients have compensatory adaptations that reduce supine hypotension symptoms despite aortocaval compression. One compensatory response is a reflexive increase in peripheral sympathetic nervous system activity.
The reduced sympathetic tone from neuraxial or general anesthetic techniques impairs the compensatory increase in vascular resistance and exacerbates the impact of hypotension from supine positioning
Reducing the compression of the inferior vena cava and abdominal aorta with left tilt may mitigate the degree of hypotension and help maintain uterine and fetal blood flow. This is accomplished by positioning the patient laterally, with a historical goal of 15-degree left tilt.
The practice of left uterine displacement has been challenged recently. In a magnetic resonance imaging (MRI) study of healthy pregnant volunteers, the volume of the inferior vena cava did not differ significantly between the supine position and the 15-degree left-tilt position but when the patients were tilted to the … left-tilt position, the inferior vena cava volume did increase
30-degree
Describe Changes in the Respiratory System at Term
Minute ventilation: Increased 45%-50%
Respiratory rate: Increased 0%-15%
Tidal volume: Increased 40%-45%
LUNG VOLUMES
Inspiratory reserve volume: Increased 0%-5%
Tidal volume Increased: 40%-45%
Expiratory reserve volume: Decreased 20%-25%
Residual volume Decreased: 15%-20%
LUNG CAPACITIES
Vital capacity: No change
Inspiratory capacity: Increased 5%-15%
Functional residual capacity: Decreased 20%
Total lung capacity: Decreased 0%-5%
OXYGEN CONSUMPTION
Term: Increased 20%-35%
Labor (first stage): Increased 40% above prelabor value
Labor (second stage): Increased 75% above prelabor value
RESPIRATORY MEASURES
FEV1: No change
FEV1/FVC: No change
Closing capacity: No change
Upper Airway changes during pregnancy
Capillary engorgement with increased tissue friability and edema of the mucosal lining of the oropharynx, larynx, and trachea begins early in the first trimester. As a result, an increased risk for bleeding exists during manipulation of the upper airway, in addition to an increased risk of difficult mask ventilation and intubation of the trachea. Suctioning of the airway and placement of devices should be performed gently to prevent bleeding and nasal instrumentation should be avoided. Furthermore, there is increased risk for airway obstruction during mask ventilation and both laryngoscopy and tracheal intubation are more difficult. Also, after extubation, the airway may be compromised because of edema, with subsequent risk for airway obstruction in the immediate recovery period
Gastrointestinal Changes during pregnancy
The stomach and pylorus are moved cephalad by the pregnant uterus, which repositions the intra-abdominal portion of the esophagus intrathoracically and decreases the competence of the lower esophageal sphincter muscle. Higher progesterone and estrogen levels of pregnancy further reduce lower esophageal sphincter tone.
Gastrin, secreted by the placenta, increases gastric hydrogen ion
secretion and lowers the gastric pH in pregnant people.
These changes in combination with the increased gastric pressure from the enlarged uterus increase the risk for acid reflux in pregnancy
Gastric emptying is not prolonged in pregnancy. Conversely, gastric emptying is decreased with the onset of labor, pain, anxiety, or administration of opioids. Increased gastric contents can further increase the risk for aspiration. Although gastric emptying after a light meal is delayed in parturients compared to nonpregnant
patients and term pregnant patients not in labor, epidural analgesia does not appear to worsen gastric emptying, and may facilitate it in parturients.
All patients in labor are considered to have a full stomach and are at increased risk for pulmonary aspiration of gastric contents during induction of anesthesia.
Hepatic changes during pregnancy
Blood flow to the liver does not change significantly with pregnancy.
The markers of liver function, including aspartate aminotransferase (AST), alanine aminotransferase (ALT), and bilirubin, increase to the upper limits of normal with pregnancy. Alkaline phosphatase levels more than double secondary to placental production.
Plasma protein concentrations are reduced during pregnancy, and the decreased
serum albumin levels can result in elevated free blood levels of highly protein-bound drugs. Plasma cholinesterase (pseudocholinesterase) activity is decreased approximately 25% to 30% from the 10th week of gestation up to 6 weeks postpartum. The clinical consequences of the reduced cholinesterase activity is unlikely to be associated with marked prolongation of the neuromuscular block
resulting from succinylcholine.
Biliary changes during pregnancy
The risk for gallbladder disease is increased during pregnancy with incomplete gallbladder emptying and changes in bile composition.
Acute cholecystitis is the second most common cause of acute abdomen in pregnancy and occurs between 1 in 1600 and 1 in 10,000 pregnancies
Renal changes during pregnancy
Renal blood flow and the glomerular filtration rate (GFR) increase during pregnancy. Renal blood flow rises 60% to 80% by midpregnancy and in the third trimester is 50% greater than nonpregnant values. GFR is increased 50% above baseline by the third month of pregnancy and remains elevated until 3 months postpartum.
Therefore the clearance of creatinine, urea, and uric acid are increased in pregnancy, and the upper laboratory limits for blood urea nitrogen and serum creatinine concentrations are decreased approximately 50% in pregnant patients.
Levels of urine protein and glucose are commonly increased because of decreased renal tubular resorption capacity. The upper limit of normal in pregnancy in a 24-hour urine collection is 300 mg protein
During pregnancy, the greater increase in plasma volume creates a physiologic anemia of pregnancy with a hemoglobin value normally around … g/dL. Hemoglobin values less than this at any time during pregnancy are concerning for anemia.
The additional intravascular fluid volume of approximately …mL at term helps compensate for the estimated blood loss of …mL typically associated with vaginal delivery and the estimated blood loss of …mL that accompanies a standard cesarean delivery
11.6
1000 to 1500
300 to 500
800 to 1000
Leukocytosis is defined as a white blood cell (WBC) count greater than 10,000 WBCs/mm3 of blood. In pregnancy, the normal range can extend to … WBCs/mm3.
13,000
Describe the Changes in Coagulation System at Term
Pregnancy is characterized by a hypercoagulable state with a marked increase in factor I (fibrinogen) and factor VII and lesser increases in other coagulation factors.
Factors XI and XIII are decreased, and factors II and V typically remain unchanged.
Antithrombin III and protein S are decreased during pregnancy and protein C levels remain unchanged
PRO-COAGULANT FACTORS
- Increased: I, VII, VIII, IX, X, XII von Willebrand factor
- Decreased: XI, XIII
- Unchanged: II, V
ANTI-COAGULANT FACTORS
Increased: None
Decreased: Antithrombin III, Protein S
Unchanged: Protein C
Platelets: Decreased 0%-10%
Describe the Thromboelastography (TEG) results during a healthy at term gestation
TEG analysis reflects a hypercoagulable state with:
- decreased time to start of clot formation (R);
- decreased time to specified clot strength (K);
- increased rate of clot formation (α);
- increased clot strength (MA).
How does pregnancy affect the effect of anesthetics?
Pregnant patients are considered more sensitive to both inhaled and local anesthetics.
They have a reduced minimum alveolar concentration (MAC) for inhaled anesthetics. The MAC of a volatile anesthetic is reduced by 28% in humans
during the first trimester of pregnancy. The underlying mechanism of reduced MAC in pregnancy remains unclear; it is likely multifactorial, and many postulate progesterone may have a role.
Pregnant patients are more sensitive to local anesthetics and neuraxial anesthetic requirements are decreased by 40% by term.
At term, the epidural veins are distended and the volume of epidural fat increases, which decreases the size of the epidural space and volume of cerebrospinal fluid (CSF) in the subarachnoid space
Uterine blood flow increases progressively during pregnancy from about …mL/min in the nonpregnant state to …mL/min (∼…% of cardiac output) at term gestation
100
700 to 900
10
In a pregnant ewe model, use of α-adrenergic vasopressors – methoxamine and metaraminol – increased uterine vascular resistance and decreased uterine blood flow, whereas administration of ephedrine did not reduce uterine blood flow despite drug-induced increases in maternal arterial blood pressure.
As a result, ephedrine was previously considered the vasopressor of choice for the treatment of hypotension caused by the administration of
neuraxial anesthesia to pregnant patients. In complete contrast, more recent human trials demonstrate the use of phenylephrine (α-adrenergic agonist) for prophylaxis or treatment of neuraxialinduced hypotension not only is effective in preventing hypotension but also is associated with less fetal acidosis and base deficit than the use of ephedrine.
Explain why ephedrine is more associated with fetal acidosis than phenylephrine
Possible explanation:
- Ephedrine crosses the placenta more than phenylephrine.
- Stimulating the fetus’s beta-adrenergic receptors increases its metabolic rate.
- This increased metabolic rate increases the fetus’s demand for oxygen.
- When the fetus doesn’t get enough oxygen, it switches to anaerobic metabolism.
- Anaerobic metabolism produces lactic acid.
- When the tissues’ buffering capacity is depleted, the pH decreases.
OBS.: in the study “Ephedrine versus phenylephrine as a vasopressor for spinal anaesthesia-induced hypotension in parturients undergoing high-risk caesarean section: meta-analysis, meta-regression and trial sequential analysis (International Journal of Obstetric Anesthesia - 2019)” Pooling six studies of patients with preeclampsia and other reasons for fetal
compromise, as well as subgroup analysis of the preeclampsia studies, revealed no significant differences in the incidence of fetal acidosis.
Fetal hemoglobin has a higher O2 affinity and lower partial pressure at which it is 50% saturated (P50: 18 mm Hg) compared to maternal hemoglobin (P50: 27 mm Hg). Fetal PaO2 is normally … mm Hg and never more than … mm Hg, even if the mother is breathing 100% O2.
40
60
Most drugs have molecular weights less than … and, therefore, cross the placenta by … if the drug is not …
1000 daltons
diffusion
ionized
Does NMBD administered on the mother, cause NMB in the fetus?
Nondepolarizing neuromuscular blocking drugs are ionized, have a high molecular weight, and poor lipid solubility, resulting in minimal placental transfer.
Succinylcholine has a low molecular weight but is highly ionized and therefore does not readily cross the placenta unless given in large nonclinical doses. Thus, during administration of a general anesthetic for cesarean delivery, the fetus or neonate is not paralyzed
Both heparin and glycopyrrolate have significant placental transfer because they are poorly charged
T or F
F
Both heparin and glycopyrrolate have minimal placental transfer because they are highly charged
Dexmedetomidine may cross the placental barrier but is stored within the placenta and transfer to the fetus is reduced
T or F
T
Placental transfer of volatile anesthetics, benzodiazepines, local anesthetics, and opioids is facilitated by the …
relatively low molecular weights of these drugs
Describe the labor stages
1) The first stage of labor begins with regular, painful uterine contractions and includes the change of the uterine cervix from a thick, closed tube to an opening of approximately 10 cm through which the fetus can be expelled. This stage is further divided into a latent phase and an active phase.
2) The second stage of labor begins when the cervix is fully dilated and ends with the birth of the newborn.
3) The third stage of labor is the delivery of the placenta.
To account for the contemporary obstetric population including an older maternal age and increased maternal and fetal body sizes, a new labor curve has been proposed after analysis of 62,415 parturients. The main difference of the newly proposed curve is when latent labor is considered to transition to active labor. Traditionally, this transition point was …-cm dilation. However, the new curve proposes active labor beginning at …-cm dilation in both multiparous and nulliparous parturients
4
6
Fetal Heart Rate Monitoring Pattern Definitions about the Baseline
- The mean FHR rounded to increments of 5 bpm during a 10-min segment, excluding:
a. Periodic or episodic changes
b. Periods of marked FHR variability
c. Segments of baseline that differ by more than 25 bpm - The baseline must be for a minimum of 2 min in any 10-min segment, or the baseline for that period is indeterminate. In this case, one may refer to the prior 10-min window for determination of baseline.
- Normal: FHR baseline rate is 110–160 bpm.
- Tachycardia: FHR baseline is greater than 160 bpm.
- Bradycardia: FHR baseline is less than 110 bpm.
Fetal Heart Rate Monitoring Pattern Definitions about the Baseline Variability
- Fluctuations occur in the baseline FHR that are irregular in amplitude and frequency.
- Variability is visually quantitated as the amplitude of peak-to-trough in beats per minute.
a. Absent: amplitude range is undetectable.
b. Minimal: amplitude range is detectable but 5 bpm or fewer.
c. Moderate (normal): amplitude range is 6–25 bpm.
d. Marked: amplitude range is greater than 25 bpm.
Fetal Heart Rate Monitoring Pattern Definitions about the Acceleration
- A visually apparent abrupt increase (onset to peak in <30 s) occurs in the FHR.
- At 32 weeks’ gestation and beyond, an acceleration has a peak of 15 or more bpm above baseline, with a duration of 15s or more but less than 2 min from onset to return.
- Before 32 weeks’ gestation, an acceleration has a peak of 10 or more bpm above baseline, with a duration of 10 s or more but less than 2 min from onset to return.
- Prolonged acceleration lasts 2 min or more but less than 10 min.
- If an acceleration lasts 10 min or longer, it is a baseline change.
Fetal Heart Rate Monitoring Pattern Definitions about the Sinusoidal Pattern
- Visually apparent, smooth, sine wave–like, undulating pattern occurring in FHR baseline, with a cycle frequency of 3–5 cycles/min that persists for 20 min or longer.
What is the Montevideo unit (MVU)? How to calculate?
The Montevideo unit (MVU) is a way to measure uterine contractions during labor. It’s calculated by adding up the peak uterine pressure of each contraction over a 10 minute period.
How to calculate MVUs:
Measure the peak uterine pressure of each contraction in mmHg
Subtract the resting tone of the contraction
Add up the numbers for each contraction in a 10-minute period
Normal uterine contractions are defined as …
Tachysystole is defined …
five or fewer contractions in 10 minutes, averaged over a 30-minute window.
uterine activity greater than five contractions in 10 minutes, averaged over a 30-minute window
Treatment of tachysystole during labor may differ depending on the clinical situation but may include …
sublingual or intravenous nitroglycerin to briefly relax the uterus, as well as the use of β2-adrenergic drugs such as terbutaline
Late fetal heart rate decelerations on cardiotocography are a result of …
A second type of late deceleration is from …
uteroplacental insufficiency causing relative fetal brain hypoxia during a contraction. The resulting sympathetic outflow elevates the fetal blood pressure and activates the fetal baroreceptors and an associated slowing in the FHR.
myocardial depression in the presence of increasing hypoxia
Early fetal heart rate decelerations on cardiotocography are considered benign and tend to mirror the …
uterine contraction and are believed to be in response to vagal stimuli, which are often the result of fetal head compression
Variable fetal heart rate decelerations on cardiotocography are associated with …
umbilical cord compression.
A sinusoidal FHR pattern is associated with … and is considered ominous
fetal anemia
In general, minimal to undetectable FHR variability in the presence of variable or late
decelerations is associated with …
fetal acidosis
Prolonged decelerations (<70 beats/min for >60 seconds) are associated with … and are extremely ominous, particularly with the absence of variability
fetal acidemia
Category I FHR tracings include all of the following:
- Baseline rate of 110–160 beats/min
- Moderate baseline FHR variability
- Late or variable decelerations are absent
- Accelerations and early decelerations may be present or absent
Category II FHR tracings include all FHR tracings not categorized as Category I or III. Category II FHR tracings may include any of the following:
- Baseline rate:
a. Bradycardia not accompanied by absent baseline variability
b. Tachycardia - Baseline FHR variability
a. Minimal baseline variability
b. Absent baseline variability with no recurrent decelerations
c. Marked baseline variability - Accelerations
a. Absence of induced accelerations after fetal stimulation - Periodic or episodic decelerations
a. Recurrent variable decelerations accompanied by minimal or moderate baseline variability
b. Prolonged deceleration ≥2 min but <10 min
c. Recurrent late decelerations with moderate baseline variability
d. Variable decelerations with slow return to baseline, “overshoots,” or “shoulders”
Category III FHR tracings include either:
- Absent baseline FHR variability plus any of the following:
a. Recurrent late decelerations
b. Recurrent variable decelerations
c. Bradycardia - Sinusoidal pattern
Category III FHR tracings are considered abnormal and are associated with an abnormal fetal acid–base state at the time of observation. These tracings require prompt patient evaluation and interventions to improve the fetal condition. This may include …
intrauterine resuscitation with change in maternal position, discontinuation of labor augmentation, treatment of maternal hypotension with fluids and/or vasopressor administration, use of supplemental O2, and/or administration of a tocolytic agent such as terbutaline. If the FHR tracing does not improve, expeditious
delivery should occur, which may involve an assisted vaginal (forceps or vacuum) delivery or a cesarean delivery.
The American Society of Anesthesiology (ASA) has recommended that moderate amounts of clear liquids be allowed during the administration of neuraxial analgesia and throughout labor. A period of abstention from solids before the placement of neuraxial analgesia is required.
T or F
F
The American Society of Anesthesiology (ASA) has recommended that moderate amounts of clear liquids be allowed during the administration of neuraxial analgesia and throughout labor. A period of abstention from solids before the placement of neuraxial analgesia is not required. However, the ASA does recommend the ingestion of solid foods be avoided in laboring patients
Why meperidine should be avoided for systemic analgesia during labor?
Maternal half-life of meperidine is 2.5 to 3 hours, whereas the halflife for its active metabolite normeperidine is 13 to 23 hours. The half-life of both is up to three times longer in the fetus and newborn. Normeperidine can accumulate with repeated doses and can be neurotoxic. With increased dosing and shorter intervals between doses and delivery, risk to the newborn is increased, including lower Apgar scores and prolonged time to sustained neonatal respiration
Why morphine is rarely used for labor pain?
Like meperidine it has an active metabolite (morphine-6-glucuronide) with a half-life that is longer in neonates than in adults, and it produces significant maternal sedation. Obstetricians may use intramuscular morphine for analgesia, sedation, and rest. This produces analgesia with an onset of 10 to 20 minutes and may be used in latent labor. Maternal side effects may include respiratory depression and histamine
release resulting in pruritus and rash.
Mixed agonist–antagonist opioid analgesics such as … are utilized to treat labor pain.
… has similar analgesic potency as morphine. It is given either intravenously, intramuscularly, or by subcutaneous injection at doses of 10 to 20 mg every 4 to 6 hours.
… is five times as potent as morphine and 40 times more potent than meperidine. A dose of 1 to 2 mg intravenously or intramuscularly is commonly used for labor analgesia.
Both drugs are often well tolerated by the parturient.
nalbuphine and butorphanol
Nalbuphine
Butorphanol
Can fentanyl be used for labor systemic analgesia?
Yes
Fentanyl is a synthetic opioid that is highly lipid-soluble and has a rapid onset
time (2–4 minutes), short duration of action (30–45 minutes), and no active metabolites. When given in intravenous doses of 50 to 100 mcg/h, no significant differences are seen in neonatal Apgar scores and respiratory effort compared with those in newborns of patients not receiving fentanyl.
High doses of systemic fentanyl especially immediately prior to birth, could result in neonatal depression
Can remifentanyl be used for labor systemic analgesia?
Remifentanil PCA may offer superior pain relief and lesser fetal effects than other intravenous opioid analgesics, but its analgesic effects are inferior to neuraxial analgesia and it requires careful maternal oxygenation and ventilation monitoring.
The metabolism of remifentanil depends completely on tissue and plasma esterases,
which are fully developed in the term fetus. Furthermore, it is more rapidly metabolized in the placenta (by placental esterases) than in the maternal plasma and thus the fetal-to-maternal ratio is small. In the pregnant ewe model, the maternal-to-fetal ratio of remifentanil is approximately 10-fold, and the ratio was similar in human studies. Because of these characteristics, more remifentanil can be administered to the pregnant patient at times close to delivery than would be considered safe for longer-acting opioids that rely on slower metabolism by the liver.
Can inhaleed anesthetics be used for labor analgesia?
While volatile anesthetics are no longer used for labor analgesia, nitrous oxide (N2O) is commonly used worldwide.
Typically, it is blended with O2 in a 50:50 ratio for patient-inhaled selfadministration
just before and during contractions. The benefits of N2O include its ability to decrease awareness of pain, relieve anxiety, improve satisfaction, and provide a sense of control through selfadministration.
Overall, although patients are less likely to report excellent pain control with N2O, they were as likely to express satisfaction with their anesthesia care. Therefore although it is less efficacious than neuraxial analgesia, it provides an alternative to patients who desire a less-invasive analgesic approach as well as those who have a
contraindication to neuraxial analgesia.
Importantly, nitrous oxide has a long and robust safety profile when used for labor analgesia. Without the co-administration of opioids, the use of 50% N2O in O2 is safe and does not result in hypoxia or unconsciousness
How does epidural analgesia afeect the duration of the labor stages?
Large prospective studies in which patients were randomly assigned to early or late neuraxial anesthesia have invariably concluded that earlier neuraxial labor analgesia does not affect the length of the first stage of labor or increase the risk for cesarean delivery.
In contrast, several prospective trials and a meta-analysis suggest that neuraxial anesthesia may cause a modest prolongation of the second stage of labor by approximately 15 minutes. Increase in the duration of the second stage may occur because dense motor blockade could impede coordinated pushing
Current ASA guidelines note that maternal request for labor pain relief is sufficient justification for epidural initiation if cervical dilation is 3 cm or more
T or F
F
Current ASA guidelines note that maternal request for labor pain relief is sufficient justification for epidural initiation and the timing should not depend on an arbitrary cervical dilation
Lumbar epidural analgesia offers a safe and effective method of pain relief during labor and is the mainstay of labor analgesia. Epidural analgesia is typically initiated after placement of a catheter into the epidural space between …
L2–3 and L4–5
Benefits of epidural analgesia during labor include …
decreased maternal catecholamines, effective pain relief, increased patient satisfaction, and the ability to quickly achieve surgical anesthesia for an emergency cesarean delivery.
Why the initial dosing of local anesthetic through the needle within the epidural space is not recommended?
Initial dosing of local anesthetic through the needle within the epidural space is not recommended because of potential unintended intravascular or intrathecal placement that would result in local anesthetic systemic toxicity or total spinal
A retrospective study of 428 parturients who received a single-injection spinal block for labor analgesia found that …% (n= 60) needed an additional anesthetic intervention for labor analgesia or a procedure. Patients who were … were at increased risk of requiring an additional anesthetic providing evidence that the single-injection spinal block for labor analgesia should be reserved for …
14
nulliparous, were undergoing induction of labor, and had low cervical dilation
parous women in spontaneous labor and advanced cervical dilation
Benefits of Combined Spinal–Epidural Analgesia for labor analgesia
- Faster onset of analgesia
- Less likely to need additional epidural boluses
- Lower risk of catheter failure, inadequate analgesia, and catheter replacement
compared to epidural
Disadvantages of CSE for labor analgesia
- Inability to assess the effectiveness of the epidural catheter until the spinal drug has subsided;
- There is an increased risk of fetal bradycardia and a higher incidence of pruritus
Describe the Dural Puncture Epidural for labor analgesia
After the epidural space is located with the epidural needle, a pencil-point spinal needle is inserted utilizing the “needle-through-needle” technique and the dura is punctured. A 25- or 26-gauge spinal needle is usually used because a DPE placed by a 27-gauge needle was shown to offer no benefit in a single study.128 No drug is directly introduced into the intrathecal space but the dural puncture may facilitate the intrathecal migration of drug administered into the epidural space.
Neuraxial Analgesic Drugs more commonly used for labor analgesia
Most commonly, bupivacaine (0.0625%–0.1%) and ropivacaine (0.0625%–0.17%) are used because the ratio of sensory to motor blockade is greater than that for lidocaine or 2-chloroprocaine.
The most troublesome complication that limits the dose of epidural fentanyl and sufentanil during neuraxial labor analgesia is …
pruritus
For a paracervical block, local anesthetic is injected …, taking care to avoid vascular structures.
It controls pain of the … stage of labor and is more effective than placebo or intramuscular meperidine
lateral to the cervix at 4 o’clock and 10 o’clock
first
The pudendal nerve is derived from … and can be blocked with local anesthetic using a … approach to treat pain during the … stage of labor and for episiotomy repair.
Although a pudendal nerve block provides some relief during … stage, it is not as effective as a subarachnoid block with fentanyl and bupivacaine and therefore very rarely utilized.
A pudendal block can impede the urge to push during the second stage of labor. Other complications include a high rate of block failure; systemic local anesthetic toxicity; ischiorectal or vaginal hematoma; and, rarely, fetal injection of local anesthetic
sacral nerve roots (S2–S4)
transvaginal or transperitoneal
second
second
An international consensus statement on managing hypotension during cesarean delivery recommends a prophylactic infusion of … combined with …
phenylephrine
intravenous crystalloid fluid co-loading, and left lateral uterine displacement
Although various local anesthetics can be used for spinal blockade during a cesarean delivery, … is frequently used to achieve an adequate (…) level block.
Neither patient height nor weight affect block extension, although dosing may require adjustment at extremes of the … spectrum
hyperbaric bupivacaine 10 to 12 mg
T4
height
During a cesarean delivery, lipid-soluble opioids (such as fentanyl or sufentanil) may be added to the spinal anesthesia to enhance neuraxial blockade by reducing local anesthetic dose and decreasing stimulation from …
surgical traction of the viscera
Propofol administration not affect neonatal Apgar scores with typical intravenous induction doses
T or F
F
Propofol administration does not affect neonatal Apgar scores with typical intravenous induction doses (2–2.5 mg/kg), but repeated or larger cumulative doses (9 mg/kg) are associated with significant newborn depression
At typical induction doses of etomidate (0.3 mg/kg), decreased neonatal cortisol production for … hours was noted with unclear clinical significance
less than 6
Small neonatal depression is observed with standard ketamine induction dosing and larger ketamines doses can increase uterine tone, reduce uterine arterial perfusion, and lower maternal seizure threshold.
T or F
F
No neonatal depression is observed with standard induction dosing
How the uterine muscle tone is affected by NMBDs?
Uterine muscle tone is not affected by skeletal muscle relaxants
Succinylcholine is undetectable in umbilical cord samples unless larger maternal doses are administered (…mg/kg), and exceedingly high maternal doses (…mg/kg) are needed to inadvertently create neonatal neuromuscular blockade
2–3
10
Why there are current recommendations to avoid sugammadex in pregnant
patients undergoing nonobstetric surgery?
Sugammadex can reduce unbound progesterone and could theoretically impact the maintenance of early pregnancy; however, there is insufficient
evidence in the literature regarding safety of sugammadex during pregnancy for nonobstetric surgery. With the long history of safe use of neostigmine and the limited evidence for sugammadex, there are current recommendations to avoid sugammadex in pregnant patients undergoing nonobstetric surgery
During a cesarean, use of only volatile anesthetics at higher concentrations is associated with increased blood loss secondary to …
uterine atony
- all volatile anesthetics negatively impact uterine muscle contraction
If there is evidence of … during a PDPH case, then an epidural blood patch should be performed immediately.
Note that the symptom of muffled hearing is common with PDPH and thought not to be a result of …, but instead, a decrease in … because …
cranial nerve involvement such as diplopia
cranial nerve involvement
middle ear pressure
the middle ear fluid is connected to the cranial CSF via the cochlear aqueduct
Risk factors associated with high neuraxial blockade include …
obesity, spinal technique after failed epidural anesthesia, short stature, epidural after an accidental dural puncture, and spinal deformity
Hypertensive disorders of pregnancy complicate …% of pregnancies worldwide and preeclampsia is diagnosed in …% of pregnancies
5% to 10
3
Gestational hypertension definition
Gestational hypertension is defined as the onset of hypertension (systolic blood pressure [SBP] >140 mm Hg or diastolic blood pressure [DBP] >90 mm Hg) after 20 weeks’ gestation in a previously normotensive parturient without proteinuria
Preeclampsia definition
New-onset hypertension (> 20 weeks) accompanied by other signs or symptoms of end-organ dysfunction such as proteinuria, thrombocytopenia, renal insufficiency, impaired liver function, pulmonary edema, or headache
Severe features of preeclampsia include …
an SBP of 160 mm Hg or greater or DBP of 110 mm Hg or greater on two separate occasions at least 4 hours apart while on bed rest; thrombocytopenia (platelet count less than 100,000/mm3); impaired liver function with twice normal concentrations of liver enzymes; right upper quadrant pain; progressive renal insufficiency with serum creatinine greater than 1.1 mg/dL or a doubling of serum creatinine without other known renal disease; pulmonary edema; and new-onset cerebral or visual abnormalities.
Thrombocytopenia complicates …% of pregnancies because of several etiologic factors. Thrombocytopenia may be preexisting or can develop as a result of pregnancy.
In a normal pregnancy, the platelet count is expected to decrease by approximately …%.
10
10
The SOAP interdisciplinary consensus statement on neuraxial procedures in patients with thrombocytopenia concluded the best available evidence indicates a very low risk of neuraxial hematoma was associated with a platelet count of ≥ …
70,000/mm3
Women with von Willebrand disease are at increased risk for bleeding intrapartum and postpartum.254 Prophylactic treatment is recommended for women with von Willebrand factor (vWF) less than …
50 international units/dL
Factor V Leiden is an abnormal variant of factor V that acts as a … .
The factor V Leiden variant cannot be easily degraded by … and thus leads to hypercoagulability
cofactor that allows activation of thrombin by factor Xa
activated protein C
Neurofibromatosis is an autosomal-… disorder that occurs in 1 in 3000 individuals, with variable manifestations. It is characterized by … lesions on the skin, cutaneous neurofibromas, … of the iris, bone abnormalities, and tumors of the …
The hormonal changes of pregnancy may cause …, and a knowledge of lesion location and current clinical symptoms is needed to avoid instrumentation of tumors and safely deliver neuraxial anesthesia
dominant
café-au-lait
Lisch nodules
spinal cord and cranial nerves
tumor growth
Placental abruption is defined as …
partial or complete separation of the placenta from the uterine wall after 20 weeks’ gestation but before delivery
Risk factors for uterine atony include …
chorioamnionitis, oxytocin use during labor, high parity, macrosomia, multiple births, prolonged labor, retained products of conception, and use of volatile anesthetics, magnesium sulfate, or terbutaline
If oxytocin is not sufficient in controlling postpartum hemorrhage, … can be given as second-line agents.
Misoprostol (which is a …) … mcg orally, sublingually, vaginally, may be effective in patients who have been desensitized to oxytocin or when oxytocin is not available
methylergonovine 0.2 mg intramuscularly or carboprost (which is prostaglandin F2α [PGF2α]) 0.25 mg intramuscularly
prostaglandin E1 analogue [PGE1]
600 to 800
Side effects of methylergonovine, an ergot derivative, include …, and it is relatively contraindicated in patients with …
nausea, hypertension (systemic and pulmonary), and coronary artery spasm
hypertension and those with cardiac disease.
Adverse effects of PGF2α include …, and should be used with caution in patients with …
pulmonary hypertension, bronchospasm, desaturation, nausea, and tachycardia
asthma
Tranexamic acid is an antifibrinolytic that is used in trauma, cardiac surgery, and multiple surgical populations to decrease blood loss. It is a … that binds to …, which results in …
Current evidence supports the notion that tranexamic acid should be used as a therapeutic adjunct to control postpartum hemorrhage, with administration once hemorrhage is recognized
lysine analogue
receptors on plasminogen and plasmin
inhibition of plasmin-mediated fibrin degradation
Why is better to wait for the chord to be clamped before administration of tranexamic acid?
Tranexamic acid can cross the placenta and into breastmilk and it is recommended to wait until the cord is clamped to administer the drug
There is currently no diagnostic test for amniotic fluid embolism (AFE). Accordingly, the Society for Maternal-Fetal Medicine collaborated with the Amniotic Fluid Embolism Foundation to try and develop uniform diagnostic criteria for AFE. These include … .
Initial signs and symptoms of AFE include altered mental status, hypotension, respiratory distress, hypoxia, disseminated intravascular coagulation (DIC), and hemodynamic collapse
sudden onset of cardiorespiratory compromise, documentation of
disseminated intravascular coagulation (DIC), and clinical onset
during labor or within 30 minutes of placenta delivery, without other
obvious diagnosis
The mechanism of AFE remains unclear, but it is no longer believed to be embolic. Instead, it appears to involve …
a complex sequence of events triggered in certain women by entrance into the maternal circulation of fetal material, resulting in an abnormal activation of proinflammatory mediator systems similar to the systemic inflammatory response syndrome
How to manage uterine inversion?
Treatment goals include relaxation of the uterus to aid replacement back through the cervix, fluid resuscitation, and subsequent optimization of uterine tone once the inversion is alleviated to reduce postpartum hemorrhage.
Initially, all uterotonic drugs should be immediately discontinued. Uterine relaxation can be quickly and reliably achieved using either intravenous nitroglycerin or volatile anesthetics.
The patient’s hemodynamic condition may guide the choice of therapy.
If the initial uterine intervention and replacement is not successful with nitroglycerin because of lack of relaxation, maternal pain, hemodynamic
instability, or other logistics, transfer to the operating room should occur.
A rapid-sequence intubation with standard obstetric precautions followed by volatile anesthetic administration will allow needed uterine relaxation, pain control, and procedural conditions for uterine replacement. Only on rare
occasions are vaginal maneuvers unsuccessful and laparotomy required.
After uterine replacement, the uterine cavity should be explored for perforation, laceration, or retained products. After the uterus has been replaced, uterotonic drugs can be started.
Describe Anesthetic Considerations for Nonobstetric Surgery in the Pregnant Patient
- Postpone elective surgeries until after delivery.
- Regional anesthesia should be utilized when possible.
- Consider aspiration prophylaxis.
- Left uterine displacement to relieve aortocaval compression after 18–20 weeks’ gestational age.
- Consider intraoperative fetal monitoring.
- General anesthesia
a. Maximize preoxygenation
b. Consider rapid-sequence induction and intubation
c. Goal ETCO2 28–34 mm Hg. Avoid hyperventilation as hypocarbia can decrease placental blood flow secondary to uterine vasoconstriction.
d. Extubate when awake - Laparoscopic techniques should be utilized when feasible, limiting pneumoperitoneal pressures to 15 mm Hg or less.
- Fetal heart rate and uterine tone should be monitored postoperatively.
- Provide multimodal postoperative analgesia.
All general anesthetic drugs cross the placenta; however, when standard dosing is used, no currently used anesthetic drug has been shown to be teratogenic in humans
T or F
T
In general, the second trimester is preferred for surgical intervention because …
this is a period after organogenesis with lower risk for miscarriage, but the risk for preterm labor is less than in the third trimester.
During fetal heart rate monitoring during general anesthesia, loss of fetal heart rate … is expected while fetal … is more concerning and can be affected by …
variability
bradycardia
hypothermia, maternal acidosis, or the maternal administration of drugs such as particular beta blockers that can cross the placenta and reduce FHR
NSAIDs are associated with an increased risk for … when used in repeated doses early in pregnancy and … when used after 30 weeks’ gestation
miscarriage and fetal malformation
premature closure of the ductus arteriosus and oligohydramnios
With increased abdominal pressure from insufflation, maternal cardiac output and uteroplacental perfusion may decrease. For this reason, low pneumoperitoneal pressure (…mm Hg) should be used
15
Reduction of mean arterial pressure below … Hg may significantly reduce uteroplacental perfusion
70 mm
In animal studies, mannitol may accumulate in the fetus, leading to …
hyperosmolarity, reduced renal blood flow, and increased plasma sodium
concentration
During pregnancy, extreme hyperventilation can cause … .
Hyperventilation also shifts the …, which decreases oxygen delivery to the fetus
uterine artery vasoconstriction and reduce uterine perfusion
maternal oxyhemoglobin dissociation curve to the left
