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Advanced Principles of Anesthesia > Week 12 - OB Physiology and Anesthetic Considerations > Flashcards

Week 12 - OB Physiology and Anesthetic Considerations Flashcards

1
Q

What maternal cardiovascular changes are seen in pregnancy?

A
  • Increased intravascular fluid volume
  • Increased CO
  • Decreased SVR
  • Supine aortocaval compression (decreases uteroplacental circulation)
  • Systolic BP drop 0-5 mmHg, Diastolic BP drops 15%, MAP remains normal
  • Unchanged CVP
  • Distension of peripheral vessels (sluggish flow – increases risk of clots)
  • Delayed absorption of IM, SubQ drugs
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2
Q

How does maternal cardiac output change during pregnancy?

A
  • Increases 40% by 10 weeks and stays thru delivery
  • Increases from 4.5 lpm to 6,5 lpm
  • Stroke volume increases 30%
  • Heart rate increases 15-30%
  • Total peripheral resistance decreases 15% due to estrogen

*at delivery CO increases another 40-60% – rapidly declines within 1 hr of delivery and returns WNL about 2 weeks postpartum

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3
Q

What is supine hypotension syndrome in a pregnant woman?

A
  • Associated w/ pallor, sweating, N&V (symptoms are worse when combined with HoTN due to GA or RA)
  • Secondary to compression of the vena cava
  • Turn pt left side down or tilt (mandatory when pt is supine)

*uterine contractions relieve vena caval compression but worsen aortic compression

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4
Q

What causes the physiologic anemia of pregnancy?

A

Plasma volume increases by a greater amount than RBC volume

  • Plasma volume increases 30-40%
  • Red cell volume increases 20-30%
  • Blood viscosity decreases 12-20%
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5
Q

What changes to maternal blood volume occur during pregnancy?

A

Blood volume increases 1000-1500 mL
-allows for delivery without transfusion (vaginal EBL = 400-500, c-section EBL = 600-1000) – can lose ~20% w/o symptoms

  • increased volume is accommodated by uterine vasculature, maternal mammaries, renal, and muscular system, and cutaneous vascular system
  • increase is stimulated from fetal adrenals
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6
Q

How does maternal blood protein levels change during pregnancy?

A

Total protein decreases by 18%

Serum Albumin decreases by 15%

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7
Q

What cardiovascular effects does progesterone have?

A

Increases RAAS Activity: leading to increased blood volume and CO

Vascular Muscle Relaxation: leading to decreased SVR and PVR, increasing blood flow

Increases Minute Ventilation: leading to decreased PaCO2 and the kidneys eliminate HCO2 to preserve pH

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8
Q

What maternal respiratory changes are seen during pregnancy?

A
  • O2 consumption and minute ventilation increases progressively (TV 40%, RR 10%)
  • Oxyhgb dissociation curve shifts to the right (greater tissue extraction of O2)
  • PaCO2 decreases to about 28-31 mmHg (decreased HCO3 from increased renal excretion prevents resp acidosis)
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9
Q

How does pregnancy affect the maternal FRC?

A

FRC decreases up to 20% at term – returns to normal 48 hr postpartum

  • decreased FRC and increased O2 consumption leads to rapid desaturation (good pre oxygenation is mandatory)
  • closing volume likely to exceed FRC when supine (atelectasis and hypoxemia, usually wear O2 when supine)
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10
Q

What maternal airway changes are seen during pregnancy?

A
  • Engorged airway mucosa – gentle DL and intubation, use smaller ETT
  • Exacerbated signs and symptoms of URIs
  • Swollen nasal mucosa leads to mouth breathing – NO nasal intubations

*capillary engorgement of larynx, oral pharyngeal, and nasal mucosa begins in first trimester and increases throughout pregnancy

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11
Q

What hematologic changes are seen in pregnancy?

A

Pregnancy is hypercoagulable – most clotting factors increase

Cell mediated immunity is depressed – may be more susceptible to viral infections

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12
Q

What maternal renal changes are seen during pregnancy?

A
  • Renal blood flow and GFR increase 50% at 3 months until 3 months post partum
  • Sodium retention due to increased renin and aldosterone
  • Serum BUN and Cr decrease (increased clearance and increased protein excretion)
  • Mild glycosuria or proteinuria is common due to increased glucose
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13
Q

What maternal hepatic changes are seen during pregnancy?

A
  • Liver function and blood flow unchanged
  • Plasma cholinesterase levels decrease (not associated w/ clinically significant increase in duration of SUX)
  • Pregnancy resembles DM – insulin levels rise throughout
  • B cell hyperplasia due to increased insulin demand
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14
Q

What maternal GI changes are seen during pregnancy?

A
  • Decreased lower esophageal sphincter tone
  • pH decreases – increased acid and volume
  • Decreased gastric motility
  • Increased intra-gastric pressure
  • Increased gastric emptying time – during labor (intrathecal opioid delay gastric emptying)
  • Increased gastric residual volume

*ALL lead to increased risk of aspiration

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15
Q

How can you prevent aspiration in a pregnant woman?

A
  • Regional is best method
  • NPO
  • Non-particulate antacids (BiCitra)
  • H2 receptor antagonists (60-90 min)
  • Reglan (15-30 min)
  • Head up position
  • RSI
  • Cricoid pressure
  • ETT
  • Awake extubation
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16
Q

How is MAC affected during pregnancy?

A

MAC is decreased

  • decreases 40% at term
  • increased pain tolerance
  • related to high progesterone and endorphin levels
  • returns to normal about 3 days postpartum
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17
Q

Is sensitivity to local anesthesia increased or decreased in pregnancy?

A

Increased sensitivity

  • may reduce local dose by 30%
  • possibly resp acidosis which increases unionized drug
  • due to hormones, engorged epidural veins
18
Q

How does pregnancy effect an epidural?

A

Obstruction of the IVC engorges epidural veins and venous plexus:

  • increases the chances for venous puncture, venous injection, and venous “epidural” catheter
  • decreases volume of CSF in subarachnoid space
  • decreases epidural space which increases cephalad spread of injections for SAB and epidural
  • increases pressure in epidural space which increases the potential for dural puncture
19
Q

What is uterine blood flow directly proportional to?

A

Maternal SBP and Difference between uterine artery and venous BP
-uterine artery vasoconstriction decreases UBF, uterine contractions decrease UBF

*NO autoregulation – mom’s BP determine fetal blood flow

20
Q

How do you maintain uterine blood flow?

A

By maintaining MAP

UBF = uterine arterial BP - venous BP / uterine vascular resistance

21
Q

How can a fetus survive 10+ minutes without O2?

A
  • Redistribution to vital organs
  • Decreased O2 consumption
  • Anaerobic metabolism
  • fetal O2 consumption is 21 mL/min
  • fetal O2 stores about 42 mL
22
Q

How do the different anesthetics affect uteroplacental circulation?

A
  • Volatiles: decrease maternal BP and UBF (minimal at <1 MAC)
  • Propofol and Barbs: dose dependent decrease in maternal BP, beware low dose and maternal sympathetic response
  • Ketamine: <1.5 mg/kg has little effect on BP
  • Etomidate: assumed minimal effect
  • Local Anesthetics: high levels cause uterine artery vasoconstriction, appropriate levels can improve circulation in preeclampsia
23
Q

What does diffusion of substances across the placenta depend on?

A
  • Maternal fetal concentration gradient
  • Maternal protein binding
  • Molecular weight of the substance
  • Lipid solubility of the substance
  • Degree of ionization of the substance
24
Q

What principle describes the transfer of anesthetics across the placenta?

A

Fick’s Principle of Diffusion

25
Q

What anesthetic drugs transfer across the placenta?

A

ALL inhaled agents and MOST IV agents

-opioids, BZDs, propofol, barbs all transfer (low molecular weights, lipophilicity, neutral charges)

26
Q

What anesthetic drugs do not transfer across the placenta?

A

Paralytics (due to ionization and molecular weight)

Glycopyrrolate

Heparin/Anticoagulants

27
Q

What three things affect placental transfer of local anesthetics?

A

pKa of drug
Maternal and fetal pH
Degree of protein binding of drug

*fetal acidosis produces higher fetal/maternal drug ratios which leads to LA toxicity after birth (happens less with Bupivacaine and Ropivacaine – greater protein binding decreases placental transfer)

28
Q

How does maternal minute ventilation change during labor?

A

MV can increase 300% during contractions

-PaCO2 can drop below 20 mmHg – hypoventilation and maternal and fetal hypoxemia, hypocarbia reduces UBF and promotes fetal acidosis

29
Q

What are the stages of Labor?

A

First Stage (8-12+ hrs in primips, 5-10 in multips):

  • latent phase - slow, 2-4cm dilation
  • active phase - increased frequency of contraction, progressive cervical dilation to 10cm
  • need T10-11 dermatomal level for pain relief

Second Stage (15 min - 2 hrs):

  • complete dilation and effacement and delivery of fetus
  • need S2-4 dermatomal level for pain relief
Third Stage (15-30 min):
-delivery of the placenta
30
Q

What dermatome levels are needed for pain relief for each stage of labor?

A

Stage 1 = T10-11

Stage 2 = S2-4

Stage 3 = S2-4

31
Q

What are the neuraxial anesthesia options for labor?

A
  • Epidural
  • Combined spinal-epidural
  • Intrathecal narcotics
  • Continuous spinal anesthesia
  • Spinal anesthesia for delivery
  • Blocks: paracervical, pudendal, caudal, saddle
32
Q

What are the advantages of epidural anesthesia in L&D?

A
  • Ease of technique
  • Rapid onset of analgesia
  • Decreased dose of local anesthetic necessary
  • Ability to provide segmental analgesia
  • Avoidance of airway complications
  • Ability to titrate the level of analgesia depending on the level of maternal pain
  • An awake, pain free mother that can actively participate in the labor and birth process and bond with her newborn
33
Q

What are the disadvantages of epidural anesthesia in L&D?

A
  • Effect on labor and maternal hemodynamics (can slow 2nd stage if too dense – watch for HoTN)
  • Placental transfer and fetal absorption of the local anesthetic
  • Accidental dural puncture and PDPH
  • Accidental intravascular injection – seizures, fetal distress, or CV collapse
  • Backache
34
Q

What are the general anesthetic effects on labor?

A
  • Rapid induction of anesthesia (increased CO, decreased FRC, increased MV)
  • Inhaled agents cause dose-dependent uterine relaxation
  • Opioids decrease labor progression minimally
  • Regional anesthesia does NOT prolong labor
35
Q

What does APGAR score assess?

A 
Appearance
Pulse
Grimace
Activity
Respiration
36
Q

What are the different fetal heart tones?

A

Early Decels - follow with contractions, may be due to head compression-vagal response

Late Decels - some time after contractions and thought to be due to uteroplacental insufficiency

Variable Decels - inconsistent, possible cord compression

37
Q

What are the characteristics of Pre-eclampsia? (3)

A

HTN
Edema
Proteinuria

*after 20-24 weeks

38
Q

What medications are used for uterotonic therapy to treat uterine atony?

A
  • Oxytocin 20-40 units/L infucion
  • Ergot Alkaloids (Methergine) 0.2 mg IM
  • Prostaglandin (Carboprost) 0.25 mg IM - contraindicated in pt with asthma
  • Misoprostol 800-1000 mcg PR/PV/PO
  • Dinoprostone 20mg PO
39
Q

How does magnesium sulfate affect muscle relaxants?

A
  • Increased sensitivity to ALL muscle relaxants
  • No fasciculations with SUX
  • No defasciculating dose of NDMR with SUX
40
Q

What are some known teratogens?

A
  • Thalidomide
  • Diethylstibesterol (vaginal ca)
  • Synthetic Progestagens (masculinization)
  • Folic Acid Antagonists (growth retardation)
  • Tetracycline (dental staining/bone deform)
  • Warfarin (bone malform)
  • Iodides (thyroid dysfunction)
  • Alcohol (craiofacial abnormalities)

Advanced Principles of Anesthesia (31 decks)

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