Exam 2 - OB Flashcards
What is the minimum amount of weight a woman should gain during pregnancy? What is the breakdown?
12 kg
Uterus and amniotic fluid = 1 kg each
Fetal weight + placental weight = 4 kg
New fat and protein stores = 4 kg
Blood volume increase = 2 kg
If a mom has a pre-pregnancy BMI that is underweight or normal weight, how much weight do they need to gain per week and how much is their total weight gain?
1 lb/week
Underweight = 28 - 40 lbs
Normal weight = 25 - 35 lbs
If a mom has a pre-pregnancy BMI that is overweight or obese, how much weight do they need to gain per week and how much is their total weight gain?
0.5 lbs/week
Overweight = 15 - 25 lbs
Obese = 11 - 20 lbs
How much does blood volume increase during pregnancy (%) and when does it occur?
30 - 35 %
Between 8-32 weeks. Majority of the increase by 24 weeks.
What is the average blood loss that occurs during vaginal delivery? During C-section?
Vaginal = 500 ml
C-section = 800 ml
What is the approximate blood volume (ml/kg) of a non-pregnant woman? Of a pregnant woman?
Non pregnant = 65 ml/kg
Pregnant = 85 - 90 ml/kg
How much does cardiac output increase by term pregnancy?
40%
How much does uterine blood flow increase? What is baseline UBF? What is term gestation UBF?
10-20x increase
About 50 ml/min baseline
About 700 ml/min at term gestation
How much does skin blood flow increase? What does that mean for the patient?
3-4 x
Warmer skin temperature, fushing, and itching.
How much does SVR increase/decrease from pre-pregnancy values?
Decrease 20%
What 4 hormones are responsible for maternal vasodilation?
Progesterone, prostacyclin, relaxin, and estrogen
Normal pregnancy is ____ flow, ___ resistance state.
Blood volume _________ (increases/decreases).
Heart rate and stroke volume _________ (increases/decreases).
Systemic vascular resistance _________ (increases/decreases).
High, low
Increases - increased preload
Increases - increased cardiac output
Decreases - decreased afterload
How much does left ventricular mass increase by term and what kind of hypertrophy is this?
50%
Eccentric hypertrophy (vs. concentric)
How does the position of the heart change in pregnancy? How does this affect chest xray? How does this affect PMI?
Shifts anterior and to the left.
Heart may appear larger on chest xray.
PMI goes from the 5th ICS, left midclavicular line to the 4th ICS, left midclav line.
What EKG changes will we see with pregnancy?
- QRS axis shift (leftward)
- T wave inversions in lead 3
- PR interval is shortened due to increased sympathetic activity in 3rd trimester (accelerated AV)
- ST segment depression
- QT increased
What is the most common arrhythmia in pregnancy?
Tachydysrhythmias - S. Tach, PAC, PVC
What causes tachydysrhythmias in pregnancy?
- Change in cardiac ion channel conduction
- Increase in cardiac size
- Changes in autonomic tone
- Hormones: progesterone and estrogen
What valvular problem is seen in > 90% of pregnant patients?
Tricuspid and pulmonic regurgitation
What valvular problem is seen in ~ 25-30% of pregnant patients?
Mitral regurgitation
What heart sound is commonly heard in the 3rd trimester.
3rd heart sound/ventricular gallop.
Occurs when mitral valve opens allowing filling of LV. Sound is from large volume of blood rushes int a very compliant LV.
What heart sound goes away at term?
4th heart sound
Low pitch sound from late diastolic ventricular filling from late atrial contraction
What heart sound is due to cardiac enlargement?
Grade 2 systolic ejection murmur (SEM)
Where are SEMs best heard?
Right side of the heart near the L sternal border
How early can aortocaval compression cause fetal distress?
13-16 weeks gestation
What cardiovascular changes occur during the 1st stage of labor?
CO increases between and during contractions.
HR increases
How much blood is autotransfused from the uterus to the rest of the body during a contraction?
300 to 500 mls
How much does cardiac output increase during the 2nd stage of labor?
50%
Due to pushing efforts, stroke volume increase, and HR increase.
How does CO change immediately after delivery and in the hrs after?
CO increases 60-80% immediately after delivery due to relief of pressure on the vena cava and increased venous return.
This increase begins to decline 10 minutes after delivery and returns to normal 24 hours postpartum.
How does estrogen change respiratory function?
Increases the number and sensitivity of progesterone receptors in the respiratory center of the brain.
How does progesterone change respiratory function?
Increases respiratory center sensitivity to CO2.
Causes bronchodilation.
Hyperemia/edema of respiratory passages.
How does relaxin change respiratory function?
Causes ligamentous attachments to lower ribs to relax allowing the subcostal angle to increase.
How much does FRC decrease at term?
20% decrease.
Results from decreased RV and ERV caused by elevation of diaphragm.
With an elevated diaphragm, negative pleural pressure leads to what?
Earlier closure of small airways.
How does supine position change ventilation when pregnant?
FRC decrease is more profound (30%) causing increased alveolar atelectasis.
Closing capacity may exceed FRC leading to air trapping. The small airway closure leads to v/q mismatch & decreased SpO2.
What respiratory volumes increase during pregnancy?
Tidal volume and inspiratory capacity
What causes increased tidal volumes?
Increased metabolic CO2 production and respiratory driver related to high progesterone levels.
What respiratory volumes are unchanged in pregnancy?
Total lung capacity
Vital capacity
What are 2 methods of pre-oxygenation?
- 3-5 vital capacity breaths with a tight mask seal delivering 100% oxygen.
- 8 deep breaths at an oxygen flow rate of 10 L/min within A period of 60 seconds.
How much does oxygen consumption increase by term?
about 20%
What is the goal FeO2 (fraction of expired oxygen)?
0.9 or 90%
How much does Minute Ventilation increase by term?
RR increases 1-2 breaths per minute and tidal volume increases. (progesterone mediated)
How much does PaCO2 decrease during pregnancy?
~ 8-10 mmHg
How much does PaO2 increase during pregnancy?
~ 5 mmHg
What is the expected ABG state during pregnancy? What are the expected values of each component?
Respiratory Alkalosis
pH: ~7.41-7.44 (think partially corrected alkalotic)
PaO2: 100-105 mmHg (norm = 100)
PaCO2: 30-32 mmHg (norm = 40)
HCO3: ~20 (norm = 24-26)
BE: 2-3
With bicarb and BE, think it is trying to compensate for the respiratory alkalosis from a lower CO2
How much (%) does Vm increase during the 1st stage of labor?
up to 140%
How much (%) does Vm increase during the 2nd stage of labor?
up to 200%
CO2 will decrease further from 30-32 mmHg to 10-15 mmHg bc they are working so hard.
How much does Hgb/Hct drop from pre-pregnancy to 36 weeks gestation?
~ 2.4 g/dL for Hgb
~ 6.5% for Hct
What is an abnormally low maternal hemoglobin concentration?
less than 11 g/dl
What is an abnormally high maternal hemoglobin concentration? What might this mean?
13 g/dL
May indicate hemoconcentration which is a precursor to pre-eclampsia.
Why is platelet count and function important for pregnant patients?
Low or poor function platelets increase risk for epidural hematoma from neuraxial techniques.
At what platelet count should we transfuse platelets prior to major surgery and prior to an epidural?
major surgery: 10,000
epidural: 80,000 (this is a conservative number- most CRNAs practice at 65-75,000)
What platelet level tells us we need to cancel surgery?
10,000
What clotting factor has the most significant increase during pregnancy and what is the level at term?
Fibrinogen (Factor I)
> 400 mg/dL at term
List all clotting factors that are increased at term gestation.
1: Fibrinogen (I)
7: Proconvertin (VII)
8: Antihemophilic (VIII)
9: Christmas (IX)
10: Stuart Prower (X)
12: Hageman (XII)
What clotting factors are unchanged at term gestation?
2: Prothrombin (II)
5: Proaccelerin (V)W
What clotting factors are decreased at term gestation?
11: Thromboplastin antecedant (XI)
13: Fibrin-stabilizing factor (XIII)
PT & PTT decrease by 20%
Fibrinolytic activity decreases in 3rd trimester
How much does WBC increase during pregnancy and during labor?
Increase steadily to 9,000-11,000 during pregnancy
Increase up to 34,000 during labor
What type of leukocyte function is impaired during pregnancy and what does this cause?
Polymorphonuclear leukocyte
Cause potential improvement of autoimmune disease symptoms.
What 3 viruses are humoral antibody titers decreased to during pregnancy?
Measles, Flu A, and Herpes simplex
When is the Lower Esophageal Sphincter tone the lowest during pregnancy and when does it return to normal?
Lowest at term and returns to norm 4 weeks postpartum.
How long should we treat parturients as full stomach and why?
6 weeks postpartum
Uterus takes 6 weeks to go back to normal size and LES takes 4 weeks to go back to normal tone.
What is Mendelson’s syndrome?
Essentially aspiration pneumonitis.
Inflammatory response of the lung parynchema from perioperative aspiration of gastric contents
What is criteria for being high risk of Mendelson’s syndrome if a patient aspirates?
If their gastric pH is < 2.5 or they aspirate more than 25 mLs of gastric content.
What liver enzymes is it normal to be increased during pregnancy?
Serum aspartate aminotransferase
Lactic dehydrogenase
Alkaline Phosphatase
What causes colloid oncotic pressures to decrease during pregnancy and when do they return to normal?
Decreased total protein and decreased albumin to globulin ratio
Return to normal ~ 6 weeks postpartum
How much does pseudocholinesterase activity decrease during pregnancy, when does it return to normal, and why is that important?
Decreases 25% before delivery and 33% on 3rd postpartum day.
Returns to normal 2-6 weeks postpartum
Could prolong duration of succinylcholine (not common)
When does cholestasis occur during pregnancy?
3rd trimester
What are the symptoms of cholestasis?
PRURITUS
High serum bilirubin
Abnormal liver function tests
When does enlarged kidneys return to baseline postpartum?
~ 6 weeks
How much does renal blood flow increase during pregnancy?
~75%
What do normal kidney function labs look like at term gestation?
Cr ~ 0.5-0.6
BUN ~ 8-9 mg/dL
May have glucosuria and protenuria bc reabsorption cannot keep up with higher GFR but this is normal.
What urinalysis result is indicative of pre-eclampsia?
EXCESSIVE proteinuria
What labs suggest ABNORMAL renal function and require further evaluation in pregnant women near term?
BUN > 15 mg/dL
Cr > 1.0 mg/dL
CrCl < 100 mL/min
How much does the thyroid increase in size during pregnancy?
50-70%
How can hypothyroidism affect a developing fetus?
Increased incidence of fetal cognitive issues, spontaneous abortion, grown restriction, and placental abruption if not treated.
What causes insulin resistance in pregnant women?
human placental lactogen
How much does cortisol increase in pregnancy?
100% in 1st trimester
200% by term
How much does pituitary gland increase in size?
3x
What changes occur in the anterior pituitary gland during pregnancy?
Hyperplasia of lactotrophic cells causing increased prolactin secretion.
This is prep for breastfeeding but hyperprolactinemia can cause acne.
What changes occur in the posterior pituitary gland during pregnancy?
Oxytocin secretion increases by 30% by term to stimulate uterine contractions, breast milk letdown, and bonding
What musculoskeletal changes are caused by relaxin?
Increased joint mobility causing sacroiliac and knee pain
Overstretching of joints
What nerves are commonly susceptible to compression during pregnancy?
Sciatic nerve
Lateral femoral cutaneous nerve
What is caused by compression of the lateral femoral cutaneous nerve?
Meralgia Paresthetica
this is compression where the nerve exits the pelvis and it affects the outer side of the thigh causing:
Tingling
Numbness
Burning pain
What causes increased pain threshold for pregnant patients?
- Increased plasma endorphins
- Progesterone activating spinal cord kappa-opioid receptor analgesic mechanisms
How is the epidural space changed during pregnancy?
The volume of the venous plexus increases
* engorged epidural veins
* higher risk of venous puncture during epidural placement
CSF volume decreases in space
* greater spread of local anesthetic
What considerations are there for NMBD in the pregnant population?
Enhanced sensitivity to non-depolarizers like vecuronium and rocuronium
Decreased pseudocholinesterase activity for succ.
How much of maternal cardiac output is going to UBF at term?
About 12% (700 ml/min)
What is the primary source of uterine blood flow? Where does it branch from?
Uterine arteries, branching from internal iliac (hypogastric) arteries.
What is the secondary source of uterine blood flow? Where does it branch from?
Ovarian arteries, branching from the aorta at L4
What is the equation to calculate uterine blood flow?
(UAP - UVP) / UVR = UBF
What is the equation to calculate uterine perfusion pressure?
UAP - UVP
Where does the majority of uterine blood flow pass through to allow for gas exchange between mom and baby?
Intervillous space (70-90% of blood flow)
What causes decreased uterine blood flow in terms of UAP, UVP, and UVR?
↓UAP
↑ UVP
↑UVR
What causes ↓ uterine arterial pressure?
- Aortocaval compression
- Hypovolemia (dehydration, bleeding)
- Hypotension (neuraxial, blood loss, drug-induced)
What technique is used to prevent hypotension with neuraxial anesthesia sympathectomy?
Coloading fluid
What are pregnant patients typically given magnesium for?
Pre-eclampsia for neuro protection
If we have a decrease in maternal blood pressure, how does that affect uterine arterial pressure? Why?
Uterine arterial pressure will rise and fall with systemic blood pressure.
There is NO AUTOREGULATION for uterine arterial pressure.
What factors can increase uterine venous pressure?
- Aortocaval compression
- Contractions
- ## drug induced tachysystole
What drugs can induce tachysystole?
Oxytocin/Pitocin
Cocaine
Methamphetamine
What is tachysystole?
Increased uterine contraction strength and frequency
How does uterine contractions affect uterine blood flow?
It increases uterine venous pressure which decreases uterine blood flow. UBF is inversely related to contraction strength. The stronger the contraction, the more blood is being squeezed out of the uterine vessels and into systemic circulation.
Think of the uterus as a sponge that is being wrung out with each contraction
What factors increase Uterine Vascular Resistance?
- Endogenous vasoconstrictors (catecholamine) released in response to stress or hypotension.
*Exogenous catecholamines that we give (phenylephrine, ephedrine)
Why would you choose to give phenylephrine to a parturient over ephedrine?
Ephedrine crosses the placenta and increases fetal metabolic requirements.
Can cause decreased:
* fetal pH
* base excess
* umbilical O2 content
How do phenylephrine and ephedrine affect UBF?
Increased UVR through vasoconstriction
Decreased UBF
What is epinephrine’s effect on UBF?
No change with epi wash in neuraxial, no change with epidural test dose.
Decreased if administered IV - vasoconstriction - increased UVR - decreased UBF
How do clonidine and dexmedetomidine affect UBF?
If given neuraxial - no change in UBF
If given IV –> vasoconstriction –> increased UVR –> decreased UBF
How does neuraxial anesthesia affect UBF?
Decreased UAP if causes hypotension because there is no uterine autoregulation.
If hypotension is avoided, increased UBF because there is pain control and decreased circulating catecholamines
How does magnesium affect UBF?
This is DOSE DEPENDENT!
If the dose causes hypotension, it will decrease UBF.
It will increase UBF by relaxing smooth muscle and causing vasodilation provided there is no hypotension.
How does hydralazine affect UBF?
Decreased UVR leading to increased UBF from direct relaxation of arterioles
How do volatile agents affect UBF?
Decreased UAP d/t decreased CO and BP
This is only if we are using an increased MAC. This is DOSE DEPENDENT! If the MAC is 0.5-1.5, there will be minimal effect on UBF
What are the functions of the placenta?
*Production of proteins, hormones, and enzymes.
*Gas exchange
*Nutrient and waste exchange
How much maternal blood is accommodated by the intervillous space? What % of UBF is this?
about 350 ml
70-90% of UBF
What structure does the blood enter the intervillous space through (maternal side)?
spiral arteries
What kind of organ is the placenta considered to be?
Endocrine
What 3 things does the rate and amount of transfer of substances through the placenta depend on?
*Concentration gradient
*Permeability
*Restriction of movement
What 4 transfer mechanisms does the placenta use for nutrient/gas exchange?
- Passive diffusion
- Facilitated diffusion
- Active transport
- Pinocytosis
What is passive diffusion?
List 3 examples that use passive diffusion as a transport mechanism in the placenta.
Movement along a concentration gradient
- O2
- CO2
- Anesthetic drugs
What is facilitated diffusion?
Give one example of a substance that uses facilitated diffusion as a transport mechanism in the placenta.
Movement following the concentration gradient with the help of carrier proteins.
Ex: Glucose
What is active transport?
List three examples of substances that uses active transport as a transport mechanism in the placenta.
Movement agaisnt the concentration gradient requiring energy
- Sodium
- Potassium
- Calcium
What is pinocytosis?
Give one example of a substance that uses pinocytosis as a transport mechanism in the placenta.
Cellular engulfment to transfer large molecules utilizing energy
Ex: transfer of IgG from mother to fetus
What is “saturation kinetics” and which mechanisms of transport follow this?
When all available binding sites are saturated, the rate of transfer is maxed out. So you are only able to transfer the amount of substance that corresponds to the amount of binding sites available.
Facilitated diffusion and active transport.
Why does gestational age affect how drugs are transferred through the placenta?
The placental barrier changes throughout pregnancy.
What maternal factors affect how drugs are transferred through the placenta?
Hepatic and renal function.
How does blood flow determine how drugs are transferred through the placenta?
Rate of blood flow determines how much drug reaches the placenta since most anesthetic drugs are passively transferred.
How does lipid solubility determine how drugs are transferred through the placenta?
High lipid solubility of drugs allows for greater bilayer penetration.
Ex: Sufentanil
How does protein binding determine how drugs are transferred through the placenta?
Maternal and fetal plasma proteins can bind to highly protein bound drugs affecting the amount of free drug in the maternal and fetal circulation.
Ex: Bupivicaine and Ropivacaine are both highly protein bound and less likely to cross the placenta.
What type of compounds does albumin bind to?
ACIDIC & LIPOPHILIC compounds
What type of compounds does Alpha1-Acid Glycoprotein bind to?
BASIC compounds
How does pKa determine how drugs are transferred through the placenta?
Non-ionized drugs tend to cross the placenta more easily than ionized drugs
Refresh: What is the definition of pKa?
the pH at which 50% of a specific drug is ionized and 50% is non-ionized
What is the mechanism behind “ion trapping”?
Fetus usually has a lower pH than mom. When a non-ionized drug at maternal pH enters fetal circulation (encountering a lower pH), hydrogen ions bind to the non-ionized form of the drug - making it ionized - and trapping it in fetal circulation.
Remember: non-ionized drugs cross the placenta easily; ionized drugs do not
What molecular weight of drug in daltons can cross the placenta easily?
< 500 Da
What molecular weight of drug in daltons can NOT cross the placenta easily?
> 1000 Da
What are 3 drugs that we use regularly that are too big to cross the placenta?
- Non-depolarizing NMBD
- Heparin
- Protamine
Which anticholinergics readily cross the placenta and which do not?
Readily cross: atropine and scopalamine
Do not: glycopyrrolate
Which antihypertensives readily cross the placenta?
Beta blockers
Nitroprusside
Nitroglycerine
Which Anesthetics and Induction agents readily cross the placenta?
*Volatiles
*Benzos
*Opioids
*Propofol
*Ketamine
*Etomidate
*Dexmedetomidine
Which anticholinesterases readily cross the placenta?
Neostigmine and edrophonium
Which anticoagulants readily cross the placenta and which do not?
Crosses: Warfarin
Does not: Heparin/Protamine
Which hypOtension medications readily cross the placenta and which do not?
Crosses: Ephedrine
Does not: Phenylephrine
What drugs would we choose to reverse a NMBD in a pregnant pt and why?
Neostigmine and atropine.
Glyco cannot cross the placenta and Sugammadex is detrimental in the 1st trimester of pregnancy and has not been studied past that.
What is the definition of teratogen?
A substance that produces an increase in the incidence of a defect that cannot be attributed to chance.
How does a teratogen produce a defect?
It is administered in a sufficient dose at a critical point in development which is 15 - 60 days gestational age ( approximately )
What are the FDA classes of teratogens and what do they mean?
What is the teratogenicity of nitrous gas?
Thought to be harmful to DNA synthesis in high doses.
Has been found to be associated with congenital abnormalities in humans but it is not regulated by FDA (bc it is a medical gas) so it isn’t classified.
What is the teratogenicity of benzodiazepines?
GABA has been shown to cause cleft palate formation. Association between diazepam in first 6 weeks of pregnancy and cleft palate in retrospective human studies?
