Obstetrical And High Risk Ob Anesthesia- Chris

Front 1

During Labor, when does the largest increase in CO occur?

Back 1

Immediately after delivery....can increase up to 180% over baseline nonpregnant values.

Returns to baseline 10 -14 days later (HR & SV normalize)

Up to that point, CO increases 40% over nonpregnant values, beginning at wk 5, mostly due to increase in SV and less to increase in HR.

Front 2

What causes anemia during pregnancy?

Back 2

A relative (dilutional) anemia occurs b/c blood vol increases 45% during pregnancy, but RBC volume increases by only 30%.

avg H-H: 11.6g/dl & 35.5%

Front 3

Why is maternal HOTN a concern?

Back 3

Uterine blood flow and fetal oxygenation are reduced. (Remember, gas exchange at the placenta/fetus is PERFUSION limited). Risk of fethal hypoxia increases.

Maternal MAP is an indice of placental blood flow.

In a normal pregnancy you want an SBP equal to/> 100 to maintain fetal perfusion. The placenta lack the ability to autoregulate. Perfusion is determined by mom's MAP.

Maternal HOTN can be caused by aortocaval compression.

Front 4

Describe supine HOTN syndrome.

Back 4

Caused by compression of the vena cava by gravid uterus. Venous return to heart is restricted when parturient is supine. More severe with larger than normal uterus (poly hydramnios), tense abdomen or mult gest. ↓ venous return results in sig ↓ in SV and CO. Patient attempts to compensiate by ↑HR and vasoconstriction of lower extremities...during which uterine blood flow and fetal oxygenation are decreased.

May take up to 10 minutes to max out, or can occur immediately. Some parturienst can lose consciousness.

When aorta is compressed, the upper body BP remains normal, but BP distal to L3-L4 site of compression (uterus and LEs) may be sig ↓.

Tx: Left uterine displacement (rotate OR table 15 degrees L or put 15 cm high wedge under right hip and back), have parturient lying on side.

Left uterine displacement is important in face of Labor Epidural Analgesia induced sympatholysis, which impairs compensatory mechs.

In most pts, right uterine displacement does not increase SV over supine.

Front 5

In an event of supine HOTN syndrome, why is left uterine displacement or getting patient to lie on left side important?

Back 5

B/C even the compensatory mechs of tachycardia and peripheral vasoconstriction are not adequate to prevent decreased uterine blood flow and fetal hypoxia.

Front 6

What is more effective in treating supine HOTN syndrome...LUD or lying on left side?

Back 6

Lying on side.

Front 7

How does cardiac output change in the parturient?

Back 7

Heart rate increases 20% in the first trimester.

CO increases by 40% over nonpreg values.
The increase in CO begins by week 5 and is mostly due to increase in SV and to a lesser extent ↑ in HR.

CO ↑ until week 32 where it stabilizes until labor and delivery.

Imm post delivery, CO may increase further to as much as 180% above baseline s/t fluid autotransfusion from uterus.

CO remains elevated for approx 24 hours and returns to baseline 10 days later as HR & SV normalize.

Front 8

Describe the tx for supine HOTN and aortocaval compression.

Back 8

Compression of aorta & venacava can be accomplished by displacement of the uterus to the left (L uterine displacement) or by having patient lie on side (more effective).

If on OR table, can tilt table 15 degrees to the left or place a 15 CM high wedge under right hip & back.
Greater displacement may be necc in parturients with extra large uterus.

Though helps in a few women, R side displacement gen'ly does provide SV >supine position.

Front 9

How does Labor Epidural Anesthesia contribute to fetal hypoxia?

Back 9

LEA sympatholysis defeats compensatory LE vasoconstriction by blocking the sympathetic nervews responsible for vasoconstriction, resulting in even greater HOTN if supine HOTN Syndrome occurs.

Front 10

What happens to baroreceptor responsiveness in parturients?

Back 10

They have greater baroreceptor sensitivity at term than at 6-8 weeks. This leads to greater lability in HR changes in r/t changes ↑/↓ in BP.

Front 11

A parturients increase in CO immediately post-partum places her at increased risk of bleeding. How does the body compensate for this?

Back 11

Uterine contractions.
Hypercoagulability (↑ Factor VIII, PLT and fibrinogen - also places parturient at ↑ risk of DVT)

Front 12

What are some CV changes, other than CO, that occur in the parturient?

Back 12

A normal enlarging of the heart and thickening of ventricular walls & End-diastolic volume increases.
This leads to a loud split first heart sound, an S3 or a benign systolic murmur grade 1 or 2.
If systolic murmur is > grade 3 or accompnied by chest pain or syncope.

Normal CV changes include: SOB, exercise intolerance and edema.

Diastolic murmurs are always pathologic.

(Tab: How can we really discern grades 1or2 vs. grade 3or4. So when is it a concern? When it is sx-atic: when pt exhibits chest pain, syncope or dyspnea and fatigue beyond what you'd expect for a normal parturient.)

SVR decreases by as much as 21% by term s/t ↓ resistance in the uteroplacental, pulmonary, renal and cutaneous vascular beds. Venous capacitiance vessels lose tone and allow pooling of blood. ↓SVR does not mean big changes in BP overall, despite increases in Blood Volume.

↓ in DBP of up to 15 mmHG may occur, lowering overall MAP.

Baseline central sympathetic outflow is twice as high.

Tab says arterioles are dilated s/t placental hormones.

Front 13

How does the renin-angiotensin system work?

Back 13

It provides support for MAP in absence of SNS stimulation.

Front 14

Is sympathetic tone increased or decreased during pregnancy?

Back 14

↑ since patient is hyperdynamic.

Front 15

Describe the role of renin in the parturient.

Back 15

The parturient is very reliant on the renin-angiotensin system. Esp. important during admin of RA/NA.
Plasma levels of Renin and AngII are ↑ despite increase in bl. vol.
Renin activity in 3rd trimester is 12x that of nonpreg female.
Vascular sensitivity to AngII is diminished in 3rd trim & varies diurnally thru day, but sensitivity to NE is unchanged.

**If we give too much fluid (2-3L very rapidly), we shut down the Renin-Angiotensin mechanism

NOTE: Vasopressin is 3-4x normal in 36-38 week parturient. Helps maintain MAP.

Front 16

What are some ways to treat maternal HOTN, esp s/t aortocaval compression?

Back 16

Left uterine displacement
Turn on side (Left most likely)
Stand up early in pregnancy.
Semi-Fowler's position..

Front 17

Discuss typical upper airway findings in the parturient.

Back 17

Narrowing of the glottic opening.
Generalized edema s/t capillary engorgement.
Airway becomes friable and can result in a difficult intubation.
Take care when placing airway adjuncts to avoid bleeding.
Nasal intubation in parturient should generally be avoided.

Front 18

How is a parturients Ve affected by pregnancy.

Back 18

At term, Ve is increased by 50%, primarily d/t ↑ in TV (↑40%) whereas RR only ↑10%.

During labor, the Ve can ↑ up to 300% and can occ cause maternal PaCO2 to drop below 15 mmHg. This hyperventilation (<20 mmHG) may cause a decrease in uterine blood flow and prove harmful esp since combined with extreme stress of labor.

Front 19

When an anesthetized parturient hyperventilates during labor, the fetus is at risk of _______ & ________.

Back 19

When an anesthetized parturient hyperventilates during labor, the fetus is at risk of _acidosis_ & _hypoxia_.

Front 20

What happens to FRC during pregnancy?

Back 20

FRC is ↓ by 20%.
The FRC, expiratory reserve and residual volume are ↓ s/t upward displacement of diaphragm -->get a fx-al restrictive lung disease.
The ↓FRC and the increase oxygen consumption in pregnancy commonly result in rapid desat of apneic parturient.

Closing capacity is unchanged leading to ↓CC/FRC ratio meaning small airways close before TV is exhaled.

(But, O2 transport is maxed out by ↑ in CO & right shift of oxyhb curve)

Front 21

What can hapeen to PaO2 and PaCO2 during labor?

Back 21

↑PaO2 and ↓PaCO2 s/t Ve increase of up to 300%.

Alkalosis becomes a risk if pt hyperventilates (pain and stress of labor) which can lead to decreased fetal blood flow.

Front 22

What is the lowest PaCO2 that doesn't seem to harm the fetus?

Back 22

A PaCO2 of 20mmHg.

Front 23

Due to the upper airway changes associated with pregnancy what might you consider when choosing an ett or setting up for intubation?

Back 23

The glottic opening is narrowed and the upper airway tissues are edematous and friable s/t cap engorgement.

Pick an ETT a half size smaller than you would normally use.

Anticipate that the airway could more easily become bloody...be careful placing ANY airway adjuncts.

Patient is going to be at increased risk of aiway edema and stridor post op.

Front 24

If a patient is exhibiting stridor and sx of airway edema post extubation, what tx can you provide?

Back 24

Racemic epi nebulizer.

Front 25

Is inhalational agent uptake affected by pregnancy?

Back 25

Yes, parturients have an ↑ sensitivity to inhalational agents and their MAC is reduced. (This is, per Tab, s/t progesterone making the brain more sensitive to VAs)

Front 26

What happens to the oxyhb curve during pregnancy?

Back 26

It shifts to the right.

A rightward shift, by definition, causes a decrease in the affinity of hemoglobin for oxygen. This makes it harder for the hemoglobin to bind to oxygen (requiring a higher partial pressure to achieve the same oxygen saturation), but it makes it easier for the hemoglobin to release bound oxygen

Front 27

Why are parturients at risk of aspiration?

Back 27

D/T to anatomic and physiologic changes that occur during pregnancy.
A sig # of preg women & imm postpartum have gastric vol >25 ML & gastric pH <2.5.

Ultrasound has shown solid food in stomach of laboring women who had not eaten in 12-24 hours.

↑ gastrin levels during pregnancy mean greater gastric volume and lower pH.

Upward displacement of stomach by gravid uterus --> mech obstr of pyloric outflow, delayed emptying and increased intragastric pressure.

Elevated progesterone levels (smooth muscle relaxant) slow down gastric motility & reduce LES tone.

These GI changes do not normalize until several weeks postpartum.

Labor onset further reduces gastric emptying.

Front 28

What is a good pharm adjunct in aspiration prophylaxis?

Back 28

H2 blocker and reglan prior to anesthesia (GA or any airway mgmt.)

Raniditine ↓ gastric pH within 30 minutes of IV dose & does not inhibit drug metab like cimetidine.

Front 29

T/F: Labor pain delays gastric emptying and women can still have food in stomach 12-24 hours after being NPO.

Back 29

TRUE

Front 30

T/F: Aspiration is one of the biggest morbidity factors in C-sections.

Back 30

TRUE

Front 31

A woman returns to OR for postpartum bleeding and removal of placental fragments 2 days postpartum. What should be considered regarding her airway and why?

Back 31

Normalization of GI fx takes several weeks postpartum. This patient still has delayed gatric emptying and should be treated as a full stomach.
Implement aspiration prophylaxis and consider RSI.

Front 32

What is an immediate way to decrease gastric pH in a parturient/postpartum patient?

Back 32

Oral nonparticulate antacid.

Front 33

Is it safe to admin RA/LA after giving Reglan?

Back 33

Yes, Reglan does not inhibit LA metabolism and increase risk of LA toxicity.

Front 34

What is one situation during an OB case when you would always want to use nonparticulate antacid?

Back 34

In an emergency C-section (or similar type surgery).

Front 35

Are the required doses of LA agents for spinal and epidural anesthesia different in the parturient?

Back 35

Well, lessee, the spread of analgesia via an epidural catheter is primarily by volume.

In a subarachnoid block, the dos in mg, the baricity of the LA and the patient positino are chief determinants of the extent of the anesthesia.

Up to 100 mcg of fentanyl can be added to an initial epidural bolus allows anesthetist to decrease the amount of LA and presents no harm to the fetus, but smaller doses are freqly effective.

Routine use of epinephrine containing solutions is not recommended, esp in preeclamptic parturient d/t risk of umbilical artery constriction.

In all, less LA is used and more effective analgesia is achieed when analgesia is maintained with a continuous epidural infusion.

During labor, the MEC of an LA should be used. That is Ropivicaine or Bupivicaine in 0.0625% to 0.2% with an infusion rate of 10-15 ml/hr to maintain adequate sensory block.

So, in the end, I don't know if parturients need more or less LA in spinal and epidural. I do know it is best to use the least amt possible.

Front 36

Per Tab, what are good options for tx of maternal HOTN?

Back 36

1) Reposition
2) Fluids
3)Ephedrine

Front 37

What is an advantage of Ephedrine vs Neosynephrine in tx of HOTN in a parturient?

Back 37

Ephedrine does not have the reflex bradycardia that Neo has.

Neosynephrine's reflex bradycardia s/t baroreceptor response to ↑SVR can mean ↓ blood flow to baby.

If use Neo, use only in small doses to avoid fetal hypoxia. Practically, 2-3 intcremental doses in 5' max...40-80 mcg.

Front 38

What is the single most important determinant of fetal O2/CO2 exchange?

Back 38

Maternal MAP.

Front 39

T/F: Women in labor should not be allowed to reach 4-5 cm of cervical dilation before receiving analgesia.

Back 39

TRUE

Front 40

Why is the parturient at risk for DVT?

Back 40

Patients become hypercoagulable s/t ↑ levels of Factor VII, PLT (high as 400K) and fibrinogen (400-650 mg/dl at term).

The venous pooling s/t loss of tone in the venous capacitance system in addition to hypercoagulability place patient at increased risk of DVT, esp if sedentary.

NOTE: PLT and fibrinogen levels in the normal range for a term parturient may indicate a dip below baseline for the pt and has implications for bleeding if RA is considered.

Front 41

On what does the integrity of uteroplacental circ depend?

Back 41

UBF is 800 ml/min - about 10% of maternal CO.

"Anything that ↓ maternal blood pressure or uterine artery blood flow also dereases uteroplacental bloodflow. This results in fetal hypoxia and eventually acidosis".

Front 42

Do parturients have an increased or decreased need for LAs?

Back 42

Pregnant women have an increased sensitivity to LA and a decreased MAC for all GAs.

Front 43

How does progesterone affect the CNS?

Back 43

Parturients have an ↑ sensitivity to local and GAs from early in pregnancy.

Variable reduction in MAC.

Increased sensitivity of nerves to LA blockade during pregnancy.

Front 44

What are the major factors that decrease uterine blood flow during pregnancy?

Back 44

Drops in maternal PaCO2 <15 mmHg.

Hyperventilation (added stress can produce fetal acidosis & hypoxia).

HOTN s/t epidural analgesia esp in face of hypovolemia.

Anything that drops maternal BP.

Front 45

What is the most frequent complication in ob anesthesia?

Back 45

Hypotension.

Can cause dangerous ↓ in fetal oxygenation s/t ↓ uteroplacental blood Q.

fetal oxygenation is dep on intervillous blood flow which is dep on maternal MAP.

Maternal HOTN of suff magnitude and duration can lead to fetal hypoxia, fetal acidemia and fetal death.

In a healthy parturient, critical duration of HOTN is > 2 minutes.

Front 46

What is an appropriate drug to treat HOTN in a parturient?

Back 46

Ephedrine: synthetic nonsel/noncatecholamine sypathomimetic with direct Beta and indirect alpha effects. 5-25 mg IV to treat acute ↓ in BP. 5-10 mg dose lasts five minutes. Tachyphylaxis occurs with repeated small doses. Long thought to effect uterine artery flow less than other vasoactives, but know now this isn't true. Greater incidence of fetal acidosis vs phenyepherine.

Phenylephrine: shown to be safe for tx of maternal HOTN during RA. Now DoC for maternal HOTN and often used with ephdrine for HR mgmt.

Front 47

Do all C-sections for failed labor warrant a general anesthesia?

Back 47

Not all C-sections are as urgent as others. When possible, RA techniques are desirable b/c ofthe increased M&M of GA in this population. RA also offers ability for parturient ot participate in caesarian birthing process.

Front 48

What are the pain pathways during labor?

Back 48

Uterus & Cervix: T10-L1/L2 - pain carriend in visceral afferent type C fibers.

Perineum: S2, S3 and S4 - pain impulses carried by somatic nerve fibers; pudendal nerves.

Front 49

What are some hepatic changes that occur during pregnancy?

Back 49

Serum albumin ↓ & results in increased fractions of protein bound drugs.

Serum cholinesterase activity decreases by 30% in 1st & 2nd trimester & recovers some by term. Clincially relevant prolongation of duration of action of drugs that depend on cholinesterase for eliminatino is uncommon.

Front 50

What are some renal changes that occur during pregnancy?

Back 50

S/T ↑ CO, GFR and renal plasma flow increase.
Creatinine clearance rises to 140-160 ml.min. S/t that, BUN ↓ to 8 mg/dL & serum creatinine to 0.5 mg/dL.
Reduced renal absorption --> low levels of glucosuria and proteinuria.

Front 51

What sort of MS changes occur in pregnancy?

Back 51

Lumbar lordosis is exaggerated --> narrowing of interspinous space, potentially making for a difficult spinal or epidural placement. .
Hormone relaxin results in increased mobility of joints (sacroiliac, sacrococcygeal, and pubic joints) & widening of pelvis for birth --> difficulty with patient positioning for neuraxial techniques in the side-lying position.

Front 52

What are some uterine changes that occur during pregnancy?

Back 52

UBF increases to a max of 800 ml/min (around 700 ml/min normally) - about 10% of maternal CO.

The maximal vasodilation of the uterine vessels abolishes autoregulation - so exchange of O2/CO2 become perfusion-limited - transfer to the fetus is limited only by the perfusion of the placenta, not by rate of diffusion of the gases.

Autoregulation of intervillous blood does not occur.

Evidence of fetal embarassment occurs if maternal SBP drops below 100mmHg in awake, healthy parturients during epidural anesthesia. Patients with preeclampsia can experience this at SBPs >100mmHg.

Patients receiving inhalational anesthesia seem ot maintain adequate placental blood flow despite somewhat reduced BP.

Front 53

Placental transfer of free drug is dependent on what?

Back 53

Magnitude of concentration gradient (best way to keep a drug out of fetal circ is to minimize its level in maternal blood).

Lipid solubility - highly lipid soluble drugs cross readily.

Molecular weight - drugs with MW >1000 daltons cross placenta poorly; those <500 cross easily.

Drug ionization state - nonionized drugs cross easily (they are lipid soluble). Ionized drugs (water soluble) do not cross easily. ndNMBDs are large and unionized and do not cross placenta easily.

Front 54

What is the chief factor that minimizes effects of the drug on a fetus?

Back 54

DILUTION:
Before reaching the fetus the drug is diluted in intervillous blood, absorbed by the placenta and further diluted in placental blood. It is then circulated to the fetus.

Once in the fetus, the drub is distributed within the fetal intravascular volume & redistributed to fetal tissues.

1/5 of fetal CO returns directly to placenta b/c of shunt flow via foramen ovale & ductus arteriosus. This blood has no systemic effect on fetus.

Fetal liver takes up some of the drug.

Front 55

T/F: parturient CO increases mainly due to increases in HR.

Back 55

FALSE: Parturient CO increases mainly due to increase in SV, but also due to some increase in HR>

Front 56

T/F: The greatest demand on the parturient heart is immediately after delivery.

Back 56

TRUE: CO increases up to 180% immediately after delivery s/t autotransfusion of fluid from uterus into systemic circ.

This is when cardiac parturients are most at risk.

Front 57

T/F: The parturient is at increased risk of bleeding s/t hypovolemia and depleted coag factors.

Back 57

FALSE: Blood volume is markedly increased and preoares the parturient for blood lost assoc with delivery.

PLTs, Factor VII and fibrinogen are also increased.

Front 58

T/F: Parturients experience anemia s/t naturally occurring Fe deficiencies.

Back 58

FALSE: Red blood cell volume actually increases, but not as much as blood volume so the parturient experiences a dilutional (relative) anemia.

Front 59

T/F: Parturients experience an increase in minute ventilation that is mainly due to a large increase in tidal volume.

Back 59

TRUE

Front 60

T/F: In the parturient, O2 consumption is increased, but CO2 production remains stable and unchanged.

Back 60

FALSE: O2 consumption increases and CO2 is similarly increased.

Front 61

T/F: Parturients need an increased volume or concentration of LAs due progesterone mediated changes that diminish the bodies response to LAs.

Back 61

FALSE: Pregnant women have an increased sensitivity to LAs anda decreased MAC for all general anesthetics.

Front 62

Why to parturients often have heartburn in the last trimester?

Back 62

B/C intragastric pressure is increased in the last trimester, which in combination with increased acid vlume often results in heartburn.

Front 63

T/F: All pregnant women are at risk of aspiration due to physiologic changes to the GI system.

Back 63

TRUE: Pregant women should be treated as if they have a full stomach regardless of NPO status.

These physio changes can persist for several weeks postpartum and the parturient should be treated as such.

Front 64

T/F: Due to the relaxin hormone, interspinous spaces widen a small amount and make LEA easier.

Back 64

FALSE: MS changes can result in a challenging neuraxial block.

Front 65

What are some physiological responses to labor pain.?

Back 65

Without adequate anesthesia:
Serum catecholamine levels increase.
Whole body O2 demand increases an additional 60% during painful contractions.
S/t expulsion of blood from uterus to systemic circ during contractions, acutely ↑ venous return and SV, CO during first stages of labor increases 40-80% during contractions.
It returns to baseline between contractions.
Ve can increase up to 300% & cause maternal PaCO2 to drop to <15 mmHg.
Hyperventilation can cause a decrease in uterine blood flow...placing fetus at risk for hypoxia and acidosis.

Front 66

Describe the stages of labor

Back 66

Stage 1: begins with onset of contractions and continues until full dilation. Latent phase of stage 1 is the beginning b/c there is little dilation of the cervix.

Stage 2: NOT FINISHED CARD.