Unit 2 Flashcards
1
Q
What is the cutoff point for gestation vs preterm?
A
37 weeks (if before, it’s preterm, if at or after, its gestation)
2
Q
What does G1P0 mean?
A
Pregnant but not yet given birth
3
Q
What does G3P2 indicate?
A
3 total pregnancies with 2 live births and currently pregnant
4
Q
Define “Para”
A
number of births/>20 weeks
5
Q
What is gravida?
A
The number of pregnancies
6
Q
What is the minimum expected weight gain in pregnancy?
A
~ 12 kg
7
Q
Describe how much uterus/amniotic fluid, fetal/placental weight, fat/protein stores and blood volume increase in weight throughout pregnancy
A
U/A fluid = 1 kg each (total of 2 kg)
Fetal/placental weight = 4 kg
Fat/protein = 4 kg
BV = 2 kg
8
Q
Why may a Parturient lose weight in the first trimester?
A
From food avulsion. Generally the avulsion goes away after the first trimester
9
Q
What is the rate of weight gain for underweight and normal weight Parturients?
A
1 pound per week
10
Q
What is the rate of weight gain for overweight and obese Parturients?
A
Overweight = 0.6 pounds / week
Obese = 0.5 pounds / week
11
Q
What is the relationship of body weight to weight gain during pregnancy?
A
Inverse; the lower you weight is, you more weight you can expect to gain. The higher your starting weight is, the less weight you should expect to gain
12
Q
How much does blood volume increase in pregnancy? When does the majority of the increase occur?
A
30 - 35% increase, occurs from 8 - 32 weeks but the majority occurs by 24 weeks
13
Q
Despite blood volume increasing in pregnancy, dilutional anemia is common. Why is this?
A
The plasma volume increases more than the RBCs
14
Q
How much blood loss should be expected for a vaginal vs a c-section?
A
V = 500 ml
CS = 800 ml
15
Q
When does blood volume return to normal after delivery?
A
6 weeks
16
Q
What is the simple math formula to estimate blood volume for a non-parturient vs a parturient?
A
NP = 65 ml/kg
P = 85 - 90 ml/kg
17
Q
How much does CO increase at term?
A
40%
18
Q
At what timeframe do changes to HR and SV begin to occur?
A
HR = 6 weeks
SV = increase at 8 - 10 weeks d/t reduction in SVR
19
Q
Describe how the RAAS system modulates hemodynamics in pregnancy
A
Increased plasma renin activity
Increased aldosterone concentration -> increase Na reabsorption -> increased water retention -> increased plasma volume -> increased preload = increased SV and CO
20
Q
What pregnancy related hormone causes upregulation in angiotensinogen and increases aldosterone release?
A
Estrogen
21
Q
How much does uterine blood flow increase in pregnancy?
A
10 - 20x
22
Q
What is the normal UBF (uterine blood flow)? Full term gestation rate?
A
Normal = 50 ml/min
Term = 700 ml/min
23
Q
Why is skin flushing, itching and warmer skin temperature common in pregnancy?
A
The skin gets 3 - 4x more blood flow
24
Q
How much does SVR decrease in pregnancy?
A
By 20%
25
What hormones cause maternal vasodilation?
Progesterone, Prostacyclin, Relaxin & Estrogen
26
Normal pregnancy is what kind of flow state?
High flow, low resistance
*D/t maternal vasodilation, low resistance placental circulation and decreased renal vasculature resistance*
27
What type of cardiac hypertrophy occurs in pregnancy?
Eccentric hypertrophy - increased LV mass with normal relative wall thickness. More of an "volume overload" state that is reversible after delivery.
*Concentric hypertrophy is more pressure overload, it also has increased LV mass but with increased wall thickness and is NOT reversible*
28
How does the heart position change in pregnancy?
Shifts anterior and left, there is also diaphragmatic elevation and the heart may be enlarged on xray
29
Where does PMI shift in pregnancy?
Up and to the left, now at the 4th ICS midclavicular line
30
What kind of axis shift occurs in pregnancy?
A left QRS shift
*T-wave inversions in lead II, ST-depression and shortened PR interval are also common*
31
In a left axis shift, what leads are + and -?
I and aVL are positive
II and aVF are negative
32
What are the most common EKG abnormalities in pregnancy?
Tachydysrhythmias (ST, PAC and PVCs
*Common d/t change in cardiac ion channel conduction, increase in cardiac size, changes in autonomic tone and hormones*
33
What valvular changes may occur in pregnancy (include occurrence rates)?
Tricuspid/pulmonic regurg in more than 90% of of patients
Mitral regurg in 25 - 30%
34
Why are valvular changes in pregnancy generally not a concerning finding?
They are normal responses to pregnancy (they are now in a volume overload state which is what allows regurg to occur) and the regurg goes away in the postpartum period
35
Why is supine position not ideal in pregnancy?
The gravid uterus can compress the IVC and aorta (aortocaval syndrome)
*can occur as early as 13 - 16 weeks*
36
Describe the sequelae of aortocaval syndrome
Aortocaval compression -> decreased venous return to the RA -> decreased CO -> hypotension -> decreased UBF = decreased perfusion to fetus
37
S/sx of aortocaval compression?
Tachycardia initially
Followed by bradycardia
N/V
Pallor
Loss of consciousness
Fetal distress
38
Describe what happens to HR during aortocaval compression?
Initial tachycardia to offset the loss of preload, followed by bradycardia if preload continues to be low
39
What maneuver can treat aortocaval compression?
Tilt patient to the left with LUD (left uterine displacement)
40
What CV changes occur in the first stage of labor? 2nd?
1st = increase CO/HR causing 300 - 500 ml of blood to leave the uterus and return to general circulation
2nd = 50% increase in CO causing a dramatic increase in SV and HR
41
What stage of labor has the greatest increase in CO?
Immediately after delivery -> 60 - 80% in CO
*begins to decline within 10 minutes*
42
When does CO return to baseline?
24 hours postpartum
43
What are 4 common respiratory anatomical changes in pregnancy?
Vascular engorgement of airway structures
Edema/friable tissue
Difficult airway possible
Nosebleeds/Rhinitis
44
What are some anesthetic implications in pregnancy r/t the hyperemia/edema of their airway?
May need smaller ETT (6.5, 6.0) — have available
Avoid nasal tube/nasal trumpet/NGT
Increased risk for airway obstruction
Mallampati class may worsen, even during labor — airway assessment very important!
Unanticipated airway difficulties may arise
45
How does estrogen affect the pulmonary system?
Increases number and sensitivity of progesterone receptors in respiratory center in brain
46
How does progesterone affect the pulmonary system?
Increases respiratory center sensitivity to CO2
Bronchodilation
Hyperemia/edema of respiratory passages
47
How does relaxin affect the pulmonary system?
Causes ligamentous attachments to lower ribs to relax
*this creates a barrel chest to compensate for the uterus pushing upwards on the lungs*
48
What chest wall changes would you expect with increased relaxin?
The subcostal angle increases and the A/P and transverse diameter of the chest wall increases
Chest height is shortened, but AP dimensions increase, aka, barrel chest
49
Why is the chest wall changes from relaxin so important to pulmonary function?
It preserves TLC
50
Schmidt refresher: what two volumes make up our FRC?
The RV and ERV
51
What changes to FRC occur at term?
20% decrease in FRC d/t decreased RV/ERV from elevation of the uterus and diaphragm
52
What mechanical changes occur from the elevated diaphragm in pregnancy?
Negative pleural pressure increases -> earlier closure of small airways (most important part to note) = decreased FRC/ERV/RV
53
How much does FRC decrease in the supine position?
30%
*diaphragm elevates even more and alveolar atelectasis is more likely*
54
How does the supine position affect CC?
The closing capacity may exceed FRC, causing small airway closure, V/Q mismatch = drop in O2 saturation
55
What lung volumes increase, decrease and stay the same in pregnancy?
Decrease = RV, FRC and ERV
Increase = Vt and IC
Same = TLC and VC
56
Why does Vt increase in pregnancy?
There is increased metabolic CO2 production and a higher respiratory drive d/t high progesterone
57
Why is TLC maintained in pregnancy despite the fact that the uterus/diaphragm shifts upwards?
Relaxin -> the ribs relax/expand to allow the lungs to expands laterally to maintain TLC
58
Why can parturients desat so fast?
The decreased FRC = decreased O2 reserves
59
Why is preoxygenation key for parturients?
Low oxygen levels can quickly cause fetal distress
60
What are the goals of pre-oxygenation?
Bring O2 sat as near as possible to 100%
Denitrogenate the residual lung capacity
Maximize the storage of oxygen in the lungs
Denitrogenate and oxygenate the bloodstream to a maximal level
61
What are 2 methods to quickly preoxygenate a patient?
3-5 vital capacity breaths with a tight face
mask seal delivering 100% O2
8 deep breaths at an oxygen flow rate of 10 L/min
within a time period of 60 seconds
62
What is the ideal expired fraction of oxygen?
0.90
63
What position may be helpful in pre-oxygenation?
20 degrees reverse t-burg
64
What factors make dyspnea common starting in the first trimester?
Increased respiratory drive
Increased O2 consumption
Decreased PaCo2
Larger pulmonary blood volume
Anemia
Nasal congestion
65
How much does RR increase in pregnancy?
About 1 - 2 breathes per minute (Vt also increases) -> alveolar ventilation increases
66
What kind of ABG would you expect from a pregnant patient?
Respiratory alkalosis
67
How much does PaCO2 and PaO2 increase or decrease in pregnancy?
PaCO2 decreases by 8 - 10 mmHg
PaO2 increases by 5 mmHg
*this is due to increased ventilation*
68
What changes to the ranges of ABG values would you expect to see in a pregnant patient?
pH partially corrected to ~7.41 – 7.44 (vs 7.40)
PaO2 ~100 – 105 mmHg (vs 100 mmHg)
PaCO2 ~30 – 32 mmHg (vs 40 mmHg)
HCO3 ~20 mEq (vs 24-26 mEq)
Base excess = 2 – 3 mEq/L
69
How much does minute ventilation increase in the first stage of labor? Second?
1st = 140% increase
2nd = 200% increase
70
What pulmonary changes occur during the 2nd stage of labor?
Minute ventilation increases up to 200%
Maternal CO2 decreases 10 – 15 mmHg
O2 consumption increases
Aerobic requirements increase
Maternal lactate level increases
May need supplemental O2
71
How much does Hgb decrease at 36 weeks gestation? How much does Hct decrease?
2.4 g/dL decrease in Hgb
6.5% decrease in Hct
72
What is considered an abnormally low Hgb in a parturient?
Less than 11 g/dL
73
What Hgb level in a parturient would indicate a need for further workup for pre-eclampsia concerns?
Greater than 13 g/dL -> hemoconcentration, HTN and proteinuria
74
Do platelets increase, decrease or stay the same in pregnancy?
Generally no change or a moderate decrease
*normal range is 165 - 415*
75
Thrombocytopenia in pregnancy can be idiopathic, what factors combined with thrombocytopenia may indicate that something is wrong and not idiopathic?
Gestational: <150k, no abnormal platelet function or bleeding seen -> a hint that something is wrong
76
In general, what is the rule of thumb before giving a patient neuraxial anesthesia?
You must have labs before poking the back (a CBC at LEAST, coags may be indicated too)
77
Pregnancy creates a hypercoagulable state by increasing what factors? Which has the most profound increase?
Factors I, VII, VIII, IX, X and XII all increase
Factor I, fibrinogen, has the most significant increase
78
Which factors do not increase in pregnancy?
II, V, XI and XIII
79
How much does fibrinogen increase in pregnancy?
Greater than 400 mg/dL at term
*Protects against hemorrhage but blood clot risk is greater*
80
What factors are increased at term gestation?
Factor I (fibrinogen)
Factor VII (proconvertin)
Factor VIII (antihemophilic factor)
Factor IX (Christmas factor)
Factor X (Stuart-Prower factor)
Factor XII (Hageman factor)
81
What factors are unchanged at term gestation?
Factor II (prothrombin)
Factor V (proaccelerin)
82
What factors are decreased at term gestation?
Factor XI (thromboplastin antecedent)
Factor XIII (fibrin-stabilizing factor)
*PT & PTT decreased by 20%, fibrinolytic activity decreases in the third trimester*
83
Put all together: what factors are increased, decreased and unchanged at term gestation?
Increased:
Factor I (fibrinogen)
Factor VII (proconvertin)
Factor VIII (antihemophilic factor)
Factor IX (Christmas factor)
Factor X (Stuart-Prower factor)
Factor XII (Hageman factor)
Decreased:
Factor II (prothrombin)
Factor V (proaccelerin)
Unchanged:
Factor XI (thromboplastin antecedent)
Factor XIII (fibrin-stabilizing factor)
84
How much do WBCs increase in pregnancy? In labor?
Preg = 9 - 11k
Labor = up to 34k
85
Why is there increased risk of infection in pregnancy?
Immune function is compromised d/t polymorphonuclear leukocyte function impairment
*This may actually cause autoimmune disease symptom improvement*
86
What humoral antibody titers decrease in pregnancy?
Measles, influenza A & herpes simplex
87
Why are all parturients considered full stomachs?
Enlarged gravid uterus displaces the stomach cephalad
Increased gastric pressure
Decreased competence of the lower esophageal sphincter (LES)
88
What occurs to LES tone during pregnancy?
Tone decreases throughout, lowest at term. Returns to normal ~4 weeks postpartum
*this is why heartburn/GERD is so common in pregnancy*
89
Is gastric emptying affected by pregnancy?
Generally no, though it becomes delayed during labor
90
Why do you continue to treat patients as full stomachs 4 - 6 weeks postpartum?
Uterus takes about 6 weeks to go back to normal size
LES tone returns to normal around 4 weeks
91
What factors put you at risk for Mendelson's syndrome (aspiration pneumonitis)?
A gastric pH of less than 2.5 and gastric volume of greater than 25
*Give bicitra to increase pH*
92
What hepatic changes occur in pregnancy?
Generally none, though splanchnic/portal/esophageal venous pressure is increased, so there is increased risk of esophageal varices
93
What liver enzymes are increased in pregnancy?
Serum aspartate aminotransferase
Lactic dehydrogenase
Alkaline phosphatase
*This is a normal finding, liver enzymes and cholesterol increase in pregnancy*
94
What changes occur to colloid oncotic pressure in pregnancy?
The colloid oncotic pressure decreases, total protein is decreased and the albumin/globulin ration decreases
95
How does colloid oncotic pressure change after delivery?
It decreases even further
*returns to normal after 6 weeks*
96
How does pseudocholinesterase activity change during pregnancy?
25% decrease before delivery and 33% decrease on postpartum day 3
*generally, this decrease is not enough to cause prolonged paralysis with Sux*
97
What are the s/sx of pregnancy related cholestasis?
Pruritus
High serum bilirubin
Abnormal liver function tests
*high chance of reoccurrence in subsequent pregnancies*
98
If cholestasis occurs, when would it manifest?
During the third trimester (may have to have gallbladder out)
99
How much does RBF increase in pregnancy?
75% increase
*kidneys also enlarge, returns to normal size at 6 weeks*
100
What renal lab changes would you expect to see in pregnancy?
Increased: GFR and creatinine clearance
Decreased: Creatinine and BUN
101
What would your creatinine and BUN be at term?
Cr: 0.5 - 0.6 mg/dL
BUN: 8 - 9 mg/dL
102
Why is glucosuria common in pregnancy?
Tubular glucose reabsorption may not keep up with increased GFR
103
What does excessive proteinuria indicate?
It may be indicative of pre-eclampsia
104
What lab values, for a parturient at/near term, indicate renal dysfunction?
a BUN greater than 15 mg/dL and/or a creatinine greater than 1.0 mg/dL
105
How much does the thyroid increase in pregnancy? Why is this of concern to anesthesia?
50 - 70% increase, it increases the potential for a difficult airway
106
Why is treatment of hypothyroidism (occurs ~10% of parturients) essential?
Increase incidence of fetal cognitive issues, spontaneous abortion, growth restriction, placental abruption if not treated
107
Why does insulin resistance occur in pregnancy?
It is due to human placental lactogen -> increases BG d/t insulin resistance
108
What adrenal function changes would you expect to see in pregnancy?
Increased cortisol and increased plasma endorphins
109
How much does cortisol increase in the 1st trimester? At term?
1st = 100% increase
Term = 200% increase
110
How much does the pituitary gland increase in size?
3x
111
What changes occur to the anterior pituitary gland in pregnancy?
Hyperplasia of lactotrophic cells -> increased prolactin secretion -> prep for breastfeeding and may cause acne
112
How much does oxytocin increase at term?
Increases by 30%
113
What does oxytocin do?
Stimulation of uterine contractions
Responsible for breast milk letdown
”Bonding hormone”
114
Other than rib/chest wall changes, what changes does relaxin cause in the body?
Increased joint mobility
Sacroiliac pain
Knee pain
Over-stretching of joints is possible
115
What is meralgia paresthetica?
Compression of lateral femoral cutaneous nerve
(where it exits the pelvis)
S/sx = tingling, numbness and burning pain
*Sciatic pain is also common*
116
Lumbar lordosis is caused by what in pregnancy?
Center of gravity changes
Anterior pelvic tilt
Narrowing of intervertebral spaces
*back/hip pain is common*
117
What CNS changes are common in pregnancy?
Increased Cerebral Blood Flow (CBF)
Increased permeability of Blood Brain Barrier (BBB)
Increased pain threshold
118
Why does the pain threshold increase in pregnancy?
Plasma endorphins increased
Progesterone activates spinal cord kappa-opioid receptor analgesic mechanisms
119
Why are parturients at higher risk of venous puncture during neuraxial anesthesia?
The venous plexus volume is increased, causing engorged epidural veins
120
Does CSF volume increase or decrease in pregnancy? How does this affect spread?
Decreases, and this causes greater spread
121
Do parturients require more or less LA for an epidural/spinal?
Less: smaller epidural space and decreased CSF
122
What paralytics do parturients display enhanced sensitivity to?
Non-depolarizers - primarily Roc and Vec
*While pseudocholinesterase activity is decreased it is rarely enough to be clinically significant with one dose of Sux*
123
What does IUGR stand for?
Intrauterine Growth Restriction
124
What is the UBF at term?
~ 700 ml/min
*claims ~ 12% of the maternal CO*
125
What is one of, if not the most, important determinant of maternal/fetal gas exchange?
UBF
126
What is the primary source of UBF? Where do they branch from?
The uterine arteries which branch from the internal iliac arteries (also known as the hypogastric arteries)
127
What is the secondary source of UBF? Where do they branch from?
The ovarian arteries which branch from the aorta at L4
128
Where does 70 - 90% of the UBF pass through?
The intervillous space
*This is a low resistance system for exchange of gas/nutrients*
129
What 2 factors determine UBF?
Uterine perfusion pressure / uterine vascular resistance
130
What 2 factors determine uterine perfusion pressure?
Uterine arterial pressure - uterine venous pressure
131
What is the combined formula to determine uterine perfusion pressure and UBF?
(uterine arterial pressure - uterine venous pressure) / uterine vascular resistance = UBF
132
Why is UBF so dependent on maternal BP?
There is no autoregulation of UBF, it is all dependent on pressure
*the ONLY backup mechanism to this is UBF exceeds the minimal demand for fetal oxygen, so small drops can be tolerated but in general must be quickly addressed*
133
What 3 vascular changes decrease UBF?
Decreased uterine arterial pressure
Increased uterine venous pressure
Increased uterine vascular resistance
134
Other than aortocaval compression, what are 2 common causes of decreased uterine arterial pressure?
Dehydration and bleeding
135
For neuraxial anesthesia, if hypotension occurs, what is the preferred first treatment?
Fluids first, then constrictors
*Giving them concurrently is also an acceptable option*
136
What pregnancy related condition is magnesium used to treat?
Pre-eclampsia for neuro protection
137
What is the relationship of UBF to contraction strength?
Inverse; if you are strongly contracting, UBF is decreased and vice versa
138
What is tachysystole?
Increased uterine contraction strength
139
What is hyperemia?
Excess blood going into or present in an organ
*For this section, this occurs during uterine relaxation after contraction*
140
What drugs can induce tachysystole?
Oxytocin, and street drugs like cocaine and meth
141
T/F: pushing effort can lower UBF
True: strong pushing effort can force blood out of the uterus
142
In general, why is Neo preferred over ephedrine to manage maternal BP (especially if multiple doses are needed)?
Because ephedrine crosses the placenta and increases fetal metabolic requirements (can decrease fetal pH, base excess and umbilical O2 content)
143
What is the primary effect of neo/ephedrine on UBF?
Increases UVR which decreases UBF
144
What effect does epi have on UBF when given via: subdural, epidural and IV routes?
Subdural: no change
Epidural: no change
IV: decreases UBF
145
In general, the common pharmacologics we use in neuraxial anesthesia have what effect on UBF/UVR?
No change in UBF/UVR when given neuraxially (either subdural/epidural), but if given IV, can increase/decrease (depends on the drug) UBF/UVR
*There are always exceptions to the rule, this just appears to be a common theme in the powerpoint*
146
If hypotension is avoided, what effect does neuraxial anesthesia have on UBF?
It increases it d/t decrease in catecholamines and reduction of pain
147
How does a spinal decrease UBF?
Via hypotension: Sympathectomy → peripheral vasodilation → hypotension → Decreased UBF
148
How does Mag affect UBF at low/normal dose? High dose?
Low/normal: decreased UVR which increases UBF
High: decreased UVR so much that hypotension occurs and UBF decreases
*this is a dose dependent effect*
149
What drug increases UBF by direct relaxation of arterioles?
Hydralazine
150
At what range of MAC do volatiles have no/minimal effect of UBF?
0.5 - 1.5 MAC, any higher and CO/BP decrease can occur which decreases UBF via a reduction in UAP
151
There are 2 sides to the placenta, fetal and maternal, what are these 2 sides called?
Fetal = chorionic plate
Maternal = basal plate
152
Describe what vessels are contained in the umbilical cord?
1 umbilical vein containing oxygenated blood going to the fetus and 2 umbilical arteries taking deoxygenated blood back to maternal circulation
153
Where would you find spiral arteries?
They located in the basal plate and is where blood comes in and pools
154
What are the basic functions of the placenta?
Production of proteins, hormones & enzymes
Gas exchange
Nutrient & Waste exchange
Drug/Toxin transfer can occur
155
How much blood is contained in the intervillous space?
~350 cc of maternal blood
*blood enters via the spiral arteries*
156
Why can the intervillous space accommodate so much blood?
Because it is a large sinus with multiple folds and is a low resistance area
157
In terms of two-way transfer, what protective mechanism can keep dangerous substances from getting to the fetus?
Restriction of movement - some substances can be bound to placental tissues to minimize fetal exposure/accumulation
158
Describe how O2/CO2 moves from maternal and fetal circulation?
O2 goes from maternal to fetal
CO2 goes from fetal to maternal
159
What substances generally move via passive diffusion?
O2, CO2 and most anesthetics
160
What method of diffusion follows saturation kinetics?
Facilitated diffusion, this involves carrier proteins. So if the proteins become saturated, you can't move further substances at a faster rate.
*Think glucose, this is why diabetics can't move glucose d/t insulin resistance, they have fewer carrier proteins to move glucose because they aren't responding to insulin which is responsible for moving these proteins to the cell membrane*
161
What substances rely on ATP to move against the concentration gradient?
E-lytes: Na, K and calcium
162
Describe how pinocytosis moves substances into the cell
It uses the transfer of large macromolecules, requires an energy source and uses membrane rearrangement and vesicle formation
163
What is an example of pinocytosis in the maternal/fetal relationship?
Transfer of Immunoglobulin G from mother to fetus
164
Review: What are the primary factors impacting drug transfer across the placenta?
Blood Flow
Lipid solubility
Protein binding
pKA & pH/Charge
Size of Molecule
165
What are the "other" factors that affect drug transfer across the placenta?
Gestational age (placental barrier changes throughout pregnancy)
Maternal factors (hepatic, renal function)
Drug metabolism in placenta
166
In terms of drug transfer, what is the most important factor that determines how much anesthetic crosses into the placenta?
Rate of blood flow: this is because most anesthetics passively transfer from high to low
167
In terms of solubility, what drugs tend to cross the bilayer? Why is this not ideal for a fetus?
Highly lipid soluble drugs -> they penetrate the bilayer and encourages the drug to be trapped in the placental tissue, especially if acted on by hydrogen ions to become ionized
168
What lipid soluble opioid should be avoided in pregnancy?
Sufentanil
*because it's lipid soluble it can be trapped in the placental tissue*
169
Why are highly protein bound drugs generally safe in pregnancy?
Because they are highly protein bound they are less likely to cross the placenta
170
What binds to acidic and lipophilic compounds? Basic compounds?
Acidic/lipophilic = Albumin
Basic = A-1 acid glycoprotein
171
What 2 LA's are commonly used in OB and why?
Bupivacaine & Ropivacaine – highly protein bound and less likely to cross placenta
172
Why are non-ionized drugs subject to placental trapping?
As they are non-ionized they can cross the membrane, once crossed, H+ ions can bind to them and make them ionized, and ionized drugs do not cross membranes
173
What are common non-ionized drugs that are subject to ion trapping?
Lidocaine and opioids
174
What is an example of a highly ionized drug that does not cross the placenta easily?
Sux
175
Why do drugs like Non-Depolarizing Muscle Relaxers, Heparin, Protamine not cross the placental membrane?
They are large molecules, making it harder to cross the placental barrier
176
What anticholinergics are able to cross the membrane?
Atropine and scopolamine
177
What anti-hypertensives are able to cross the membrane?
BBs, NTG and nitroprusside
178
What classes of drugs are able to easily cross the placenta?
Volatiles, BZDs, opioids, tylenol, anticoagulants (mainly warfarin), many of our induction agents and (not a class) ephedrine
179
What LA is notorious for it's ability to cross the placenta?
Lidocaine
180
What anti-cholinesterases are able to cross the placenta?
Neostigmine and edrophonium
181
What anti-cholinergic does not cross the placenta?
Glyco
182
What would be your reversal of choice in a parturient who received Roc?
Neostigmine and atropine
*Glyco does NOT cross the placenta, using neo/glyco would cause fetal bradycardia*
183
What anticoagulant would be an ideal choice as it does not cross the placenta?
Heparin
184
T/F: most muscle relaxants do not cross the membrane
T: Sux is too ionized and non-depolarizers are too big
185
T/F: Sugammadex is safe in pregnancy because it doesn't cross the placenta
F: more because it hasn't been proven to be safe. While it doesn't directly cross the placenta, there is conflicting evidence about it's safety, particularly in the first trimester (it encapsulates/neutralizes important hormones)
186
T/F: no anesthetic drug has been proven to be a teratogen
True
187
Define teratogen
A substance that produces an increase in the incidence of a defect that cannot be attributed to chance
188
List the classes of teratogenic substances
Category A: Safe during pregnancy, with no evidence of risk to the fetus
Category B: Animal studies show no risk, but human studies are lacking
Category C: Animal studies show adverse effects, but potential benefits may outweigh risks
Category D: Positive evidence of risk, but benefits may outweigh risks in life-threatening situations
Category X: High risk of causing birth defects and should not be used during pregnancy
189
Tylenol is what class of teratogenic substance?
Class B
*meaning considered safe but with animal studies only*
190
Why is N2O not regulated by the FDA?
Because it is classified as a medical gas, not a drug
191
Why is nitrous use in pregnancy a "grey" area?
In animal studies, a high does can be harmful to DNA synthesis, but there is no conclusion what constitutes a "high" dose. Furthermore, Despite these theoretical concerns, nitrous oxide has not been found to be associated with congenital abnormalities in humans
192
Why are BZDs generally avoided in pregnancy?
They have been shown to cause cleft palate formation
*However, this occurs with CHRONIC use, not acute/one time dose. Despite this, it is common practice to not use Versed for anxiolysis until AFTER the fetus has been delievered*
193
What teratogenic classification does Versed have?
Class D: positive evidence of risk
194
What effects can Demerol have on the fetus?
Neonatal CNS depression
Metabolite normeperidine can cause seizures if it accumulates
195
What effects can Morphine have on the fetus?
Decreased maternal respiration, can lead to deoxygenation in fetus
Fewer fetal heart rate accelerations
196
What 2 opioids are "safer" options for parturients?
Remi - causes maternal sedation w/o neonatal effects and the rapid metabolism means minimal fetal exposure
Butorphanol (Stadol) - commonly used for pain relief because it has very few s/e to the fetus
*In practice, you are far more likely to use Stadol than Remi*
197
What are the 2 limiting factors that dictate the passive diffusion of oxygen to the fetus?
UBF and the partial pressure of oxygen
198
At a PP of 19, how saturated would HbA and HbF be?
HbA (adult Hgb) = 25 - 30% saturated
HbF (fetal Hgb) = 50% saturated
199
Approximately what PP of O2 is HbF fully saturated?
~80 ish (purely based off an estimation of the graph on slide 55)
*Adult looks closer to 100 - 120 ish*
200
A right shift causes what change to Hgb O2 affinity?
Less affinity; more O2 comes off the Hgb or rather more O2 is released
201
What kind of shift does a high CO2 content cause?
A right shift
202
Fetal blood returning to the placenta would exhibit what kind of shift?
A right shift: it is high in CO2 content, causing a right shift
203
How does the double-bohr effect ensure the fetus gets oxygen?
There are 2 separate entities, each experiencing their own bohr effect
Maternal: They experience a right shift getting waste products (mainly CO2) from the fetus, making them have less affinity to oxygen, meaning there is more available in the blood for the fetus
Fetus: They are sending CO2 to the placenta via the umbilical arteries, causing a left shift making the fetal Hgb have a higher affinity to oxygen
Combined: The mother is setup up to donate oxygen and the fetus is setup to receive oxygen
204
What is MVU?
Montevideo units
*They are the measurement of the strength of uterine contractions*
205
Define TOCO and IUPC
TOCO = tocodynamometer
IUPC = intrauterine pressure catheter
206
Define FSE
Fetal scalp electrode
207
Define CPD
Cephalopelvic disproportion
208
Define BPP
Biophysical profile
209
Define DA, DV and FO
DA = Ductus arteriosus
DV = Ductus venosus
FO = Foramen ovale
210
Where does oxygen exchange occur for a fetus?
In the placenta
211
What is the basic difference between fetal and adult circulation?
Adult = circulation in series (goes from RA -> PA -> Lungs -> left heart)
Fetal = in parallel (they have several shunts that all direct blood to the left heart in different areas)
*SHOUTOUT TO THE MAN THE MYTH THE LEGEND DR. RICH, PHYSICS IS SHOWING UP IN ANESTHESIA TOPICS*
212
What are the 3 anatomic communications in fetal circulation?
Ductus Venosus
Foramen Ovale
Ductus Arteriosus
213
Why is PVR high in a fetus?
Fetal lungs are collapsed and filled with fluid
Very little pulmonary circulation
214
What circulation conditions favor shunting blood away from fetal lungs (not the actual shunts themselves like the DV, FO and DA)?
PVR is very high, and SVR is low, so it is easier for blood to go into the low resistance vascular bed of the placenta rather than the high resistance pulmonary circuit
215
Describe why this is a true statement: Both the right and left sides of the fetal heart provide systemic flow (whereas the adult is in series, right heart goes to the lungs, left goes systemic)?
Both the right and left sides of the fetal heart provide systemic flow because of shunts that divert blood into systemic circulation
216
What anatomic feature allows blood to bypass the fetal portal circulation and go to the vena cava?
The Ductus Venosus (DV)
217
What anatomic feature allows blood to go directly from the RA to the LA?
The Foramen Ovale (FO)
*The pressure gradient also favors blood going from the RA to LA as PVR is quite high*
218
What anatomic feature diverts blood that does reach the PA to go to the ascending aorta?
Ductus Arteriousus (DA)
219
Split the total blood going to the fetus by half; describe where each half goes
Half goes to the fetal portal circulation, the other half bypasses fetal portal circulation via the ductus venosus and goes to the vena cava
220
What is the relationship of gestational age and amount of blood directed to the liver/portal circulation in a fetus?
As gestational age increases, blood flow to the liver/portal circulation increases
221
What type of blood (have to keep this vague on purpose) enters the RA of a fetus?
Mixed; oxygenated blood from the placenta is mixing with deoxygenated blood coming from the lower/upper body
*There is a process to force more oxygenated blood to the LA, that discussion will be a different semester*
222
Most of the blood entering the RA goes where?
The LA via the Foramen Ovale (FO)
223
List where most of the blood goes in a fetus when it reaches the RA
RA -> FO -> LA -> LV -> AA -> Systemic circulation
224
What pressure is higher if a fetus: RA or LA?
RA (d/t high PVR from collapsed lungs that are filled with fluid)
*In adults it is reverse, the LA pressure is higher than RA*
225
Blood from where tends to perfuse the lower body of the fetus?
Blood from the PA that goes to systemic circulation via the ductus arteriosus (DA)
226
What nervous system develops first and is predominant in fetal life?
The PNS
227
Unlike our baroreceptors, what are fetal baroreceptors measuring?
BP changes from environmental factors (rather than own physiologic) such as maternal BP or stress
228
What organ systems undergo the most profound changes upon birth?
Pulmonary and CV
229
How does PVR drastically decrease upon birth?
First breath occurs (in 30 - 90 seconds) -> air enters lungs -> lung expands and PaO2 increases, PaCO2 decreases -> pH increases and alveolar O2 tension increases -> decreases PVR
230
Upon birth, PA flow increases because of what?
There is increased blood flow to the lungs because the RV output shifts to pulmonary circulation
231
When does surfactant production occur in a fetus?
~ 24 - 28 weeks
*If born prior, they are given a steroid (betamethasone) to help induce surfactant production*
232
What causes the DA to close?
Increased oxygen levels
233
What causes the FO to close?
Increased LAP that exceeds RAP
*Umbilical cord clamps -> increased SVR -> increases LAP -> decreases R to L shunt*
234
What causes the DV to close?
The clamping of the umbilical cord (d/t increased IVC pressure)
235
What can keep PVR elevated after delivery?
Hypoxia
Acidosis
Hypovolemia
Hypothermia
236
What can cause premature constriction of the DA?
Maternal NSAID use
Preterm births
Increased PA pressure, decreased pulmonary blood flow
Can lead to insufficient oxygenation and strain on heart
237
Why is premature constriction of the DA dangerous?
Worsens R -> L shunt which increases acidosis and hypoxia
*can quickly cascade to a downward spiral*
238
What is fetal oxygenation dependent on?
Maternal BP & oxygenation, and patency of umbilical cord
239
What occurs when fetal O2 demand exceeds supply?
Decreases endothelial release of NO → vasoconstriction → blood flow redistribution
Adenosine accumulation → vasodilation of cerebral vessels (Fetal protection of cerebral flow)
240
In fetal hypoxemia, what protective mechanism preserves fetal CBF?
Accumulation of adenosine which causes vasodilation
241
In general, what is the first sign of something being wrong with the fetus?
Bradycardia (this occurs from intense peripheral vasoconstriction to shunt blood to vital organs, this also shunts mores blood through the ductus venosus). This overall increases O2 delivery to heart/brain
*This mechanism is similar to neosynephrine, the intense vasoconstriction causes a reduction in HR*
242
What does fetal bradycardia responses designed to protect?
The brain and heart
243
What does fetal bradycardia usually result from?
Increased vagal activity
*Remember, the PNS is dominant in a fetus*
244
What is the initial fetal response to hypoxia? Prolonged response?
Initial = bradycardia to spare the brain/heart
Prolonged = SNS kicks in, catecholamines released and tachycardia occurs. Over time, leads to fetal demise
245
What occurs over time if fetal hypoxia is persistent?
Fetal growth restriction
Impaired brain and kidney function
Apoptosis of cardiomyocytes
Fetal demise
246
Electronic fetal monitoring combines what 2 measurements?
FHR interpretation with contraction monitoring
247
What measurement of FHR is external? Internal?
External = Doppler
Internal = Fetal scalp electrode (FSE)
248
What are 2 invasive methods to measure FHR and/or contractions?
FSE (fetal scalp monitor) and IUPC (intrauterine pressure catheter)
249
What is the difference between TOCO and IUPC in terms of what they measure?
TOCO = Only measures contraction frequency
IUPC = Measures contraction frequency and strength/pressure
250
Contractions force blood out of the placenta, why do normal contractions not make the fetus hypoxic?
Because the fetus has placental reserves that can last throughout the contraction
251
What are some placental causes of oxygenation impairment?
Abruption, infarction, too small and increased placental resistance
*most likely NOT reversible -> proceed to C-section*
252
What are some uterine causes of fetal oxygenation impairment?
Tachysystole or maternal causes such as hypotension/hypoxia
253
What is the normal contraction rate?
Less than or equal to 5 per 10 minutes
254
What contraction rate is considered tachysystole?
Greater than 5 contractions per 10 minutes
255
Tachysystole treatment?
Stop Pitocin, give Nitroglycerine (SL or IV) or give a beta-2 adrenergic receptor agonist (Terbutaline or Ritodrine)
256
What is a normal, tachycardic and bradycardic FHR?
Normal FHR = 110-160 bpm
Tachycardia > 160 bpm
Bradycardia < 110 bpm
257
What are fetal causes of tachycardia?
Chorio
Sepsis
Acute fetal hypoxia
Fetal heart failure
Anemia
258
What is Chorioamnionitis?
Chorioamnionitis is an infection of the membranes (chorion and amnion) that surround the fetus during pregnancy
259
What are maternal causes of fetal tachycardia?
Maternal hyperthyroidism
Maternal fever
Epinephrine / ephedrine
Beta-2 adrenergic agonists (such as Ritodrine or Terbutaline)
260
What are some common causes of fetal hypoxemia that causes bradycardia?
Initial response to:
Umbilical cord compression
Fetal head compression
261
What are some causes of fetal bradycardia?
Hypoxemia
Hypothermia
Maternal hypotension – can be caused by us!
Maternal hypoglycemia
Congenital heart block
262
Are fetal heart rate accelerations a cause for concern?
No, this is FHR variability and is a normal/healthy finding
263
What is the single most important indicator of an adequately oxygenated fetus?
FHR variability
264
What are the 4 categories of FHR variability?
Absent – amplitude range not detectable
Minimal – detectable range but 25 bpm
265
What is the ideal amplitude range of FHR variability?
A range of 6 - 25 bpm
266
What steroid would you give if a fetus was born prematurely?
An antenatal corticosteroid -> Betamethasone
267
What drugs can cause minimal/absent variability?
Dexamethasone
Benzodiazepines
Magnesium sulfate
Systemic opioid analgesia
Promethazine
268
What are some causes of increased FHR variability?
Fetal stimulation
Mild & transient hypoxemia (such as umbilical cord compression during the 2nd stage of labor)
Maternal illicit drugs/stimulations -> may also cause tachysystole
269
What are the 3 types of FHR decelerations?
Early, late and variable
*can also be categorized as prolonged or severe*
270
What are early decelerations usually associated with?
Uterine contractions and are usually benign
*note the nadir is at the peak of contraction*
271
What are common causes of early decelerations?
Vasovagal response to fetal head compression (pressure alters CBF along with vagal nerve stimulation)
Contraction pressure increases → HR decreases
Typically limited to active stage of labor
May be related to cephalopelvic disproportion if noted in early labor
272
What shape types are consistent with variable decelerations?
Typically jagged & irregular. U, V, or W shape
273
What changes in FHR are consistent with variable decelerations?
Abrupt decrease in FHR & abrupt return to baseline
Onset of decel to beginning of FHR nadir < 30 secs
FHR decreases 15 bpm or more
Lasts 15 seconds or longer, < 2-minute duration
*onset, depth and duration vary with contractions*
274
When are variable decels ok? When are they not?
If the variability/accelerations are also present, likely ok
If the decels are frequent and/or early in labor, it may indicate umbilical cord compression = emergency surgery
275
What are 3 causes of variable decelerations?
Umbilical cord compression, 2nd stage of labor (dural stimulation -> increased vagal discharge) or oligohydramnios (low amniotic fluid)
276
What conditions are consistent with late decels?
Symmetric gradual decrease in FHR with return to baseline
Begin after peak of contraction, or after contraction is over
Onset of decel to nadir of FHR = / > 30 seconds (smooth and shallow)
Associated with uterine contractions, can be benign as long as variability is present
277
Common causes of late decels?
Hypoxemia, myocardial decompensation/failure, chorio and post-term gestation, uterine hyperactivity, maternal hypotension/hypertensive disorders/cardiac disease, maternal smoking, maternal anemia and placental abruption/previa
278
What would continued hypoxia leading to lactic acidosis manifest on a TOCO monitor?
Late decels combined with fetal tachycardia with minimal variability
279
What is the "ominous" combination on a TOCO monitor?
Late decels combined with absent FHR variability
280
Common causes of prolonged decels?
Umbilical cord compression
Prolonged maternal hypotension/hypoxia
Tetanic uterine contractions
Prolonged head compression in 2nd stage of labor
281
What constitutes prolonged decels?
Decrease in FHR >/= 15 bpm lasting 2 minutes or more but < 10 minutes
If decel lasts > 10 minutes – baseline change
282
What CV changes occur if contractions last longer than 60 seconds?
Decreased umbilical blood flow
Impaired fetal cardiac output
283
What constitutes a severe deceleration?
FHR < 70 bpm
Decrease in FHR > 60 bpm from baseline
Contraction duration > 60 seconds
284
What constitutes a sinusoidal pattern?
Smooth, wave-like, undulating pattern
Cycle frequency of 3-5 cycles per minute
Amplitude range of 5-15 bpm
Persists > 20 minutes
Requires obstetrical intervention
285
Causes of a sinusoidal pattern?
Fetal anemia
Rh disease (incompatible blood)
Severe hypoxia
286
What is a category 1 FHR tracing?
Baseline FHR 110 - 160 bpm
Moderate baseline variability
No late or variable decelerations
Early decelerations present/absent
Accelerations present/absent
287
What can FHR tracing be predictive of?
Fetal acid-base balance
288
Category 1 is predictive of what acid-base balance?
Normal fetal acid/base balance
289
What is a category 2 FHR tracing?
Indeterminate:
Fetal tachycardia
Absence of induced accelerations after fetal stimulation
Prolonged decelerations > 2 mins < 10 mins
Recurrent late decels w/ moderate variability
Not predictive of abnormal fetal acid-base status
290
T/F: category II FHR tracing is predictive of abnormal fetal acid-base balance?
False
291
What is a category 3 FHR tracing?
Abnormal:
Sinusoidal FHR pattern
Absent FHR variability w/recurrent late decels
Recurrent variable decels
Sustained bradycardia
292
How do you manage category 3 tracings?
Maternal position change
Discontinue labor augmentation
Treatment of tachysystole
Surgical delivery
293
What are the 5 parameters of the APGAR score? What is the score range of each variable?
Heart rate
Respiratory effort
Muscle tone
Reflex irritability
Color
Scored from 0 - 2
*The higher the score the better*
294
What is normal, moderate impairment and immediate resuscitation APGAR scores?
8 -10 = normal
4 -7 = moderate impairment
0 -3 = immediate resuscitation required
295
What is the relationship of the 1-minute APGAR score to mortality?
Inverse: The higher the score, the lower the mortality risk, and vice versa
296
Determine APGAR score: HR is over 100, with regular crying, intermittent extremity flexion noted, active coughing with pink extremities
9
297
Determine APGAR score: HR less than 100, no respiratory effort, minimal flexion of extremities, no response to suction with blue fingers
3
298
Determine APGAR score: HR over 100, shallow crying, movement in all extremities, grimacing response to suction with pink extremities
8
299
Determine APGAR score: HR over 100, frequent crying, minimal extremity movement, active coughing with pink skin
9
300
Determine APGAR score: No pulse or respiratory effort, no response to suction, no extremity movement with a pink trunk but blue extremities
1
301
What blood vessels return deoxygenated blood from the fetus to the placenta?
Umbilical arteries
302
Variable decels occurring early in labor can indicate what?
Umbilical cord occlusion, emergent surgery required
303
What is the placental efflux transporter that helps regulate the transfer of unwanted drugs from fetal to maternal circulation?
Placental efflux transporter proteins, or P-glycoprotein
304
What is the critical development point range in which a teratogen is most likely to produce a defect?
15 - 60 days gestational age
305
