Pregnancy Flashcards
Dogs, Cats - gestation, placental types
Gestation ~60d - dogs 58-68d, cats 64-67d
Zonary placenta, endothelial Attachment
Horses - gestation, placental types
11mo - 335-342d
Diffuse/microcotylendonary placenta with epitheliochorial attachment
Sheep, Dogs - gestation, placenta type
~150d, cotyledonary, epitheliochorial attachment
Bovids - gestation, placenta type
280-290d
Cotyledonary, epithelial attachment
Pigs - gestation, placenta type
3mo, 3wk, 3d - ~115d
Diffuse, epitheliochorial
Epitheliochorial Placental Barrier
least invasive, three layers of tissue btw maternal and fetal blood
LA: pigs, cows, horses, SR
Endotheliochorial Placental Barrier
– partially invasive, only endothelial wall of mom’s blood vessels and interstitial tissue between maternal and fetal blood
Dogs, cats
Hemochorial Placental Barrier
– trophoblast cells line maternal vasculature in placenta, maternal blood in direct contact with placental chorion
Humans
Changes in Circulating Blood Volume, etc In Pregnancy
–Blood vol increases by ~40%, PCV drops DT increase in plasma volume
–Increase in HR, SV –> CO increases by 30-50%
–Progesterones: increase venous capacitance, decrease SVR; SAP, DAP normal DT increased CO
–BP decreases by 20% - increases to meet non-pregnant values to term
Effect of Pregnancy: PCV
–Decreases PCV DT 50% increase in plasma volume at gestation
–PCV nadir at second trimester - PCV in healthy dogs at term similar to non-pregnant dogs
Changes During Labor
–CO increases another 10-25%
–MOA: uterine contraction, increased SV; loss of uterus/decreased SVR, release of aortovenous compression
–SAP increases by 10-30mm Hg
–CVP increases slightly with labor (4-6mmHg), increases drastically during painful fetal extraction (up to 50cmH2O)
Perfusion to the Uterus
NO AUTOREGULATION, completely dependent on BP for perfusion
Compression of VC, aorta by uterus in dorsal recumbency
decreases VR, CO –> Subsequent decreases in uterine BF, RBF
Positional marked decrease in BP DT aortovenous compression
* At term: almost complete inferior VC compression (dorsal)
* Increased risk of thromboembolism
* Compensatory response: increased sympathetic tone – eliminated via LA epidural or GA
Other Cardiac Changes Associated with Pregnancy
Increased cardiac work, decreased cardiac reserves
Workload = ventricular pressure x volume *area within PV loop
* Increased cardiac oxygen demand DT increased cardiac workload
Decreased reserve – not able to compensate, hypotension fairly fluid responsive
* Patient with heart dz can become decompensated
Ecbolic Drugs
- Oxytocin: vasodilation, hypotension
- Ergot (to control uterine bleeding): VC, hypertension
How does the O2 Curve Shift in mom?
TO THE RIGHT
Increased 2,3 DPG - ensures oxygen has a lower affinity for hgb so will offload to fetus
What pulmonary factors generally decrease throughout pregnancy?
Residual Vol
FRC
TLC (LJ: no change)
High Affinity for Oxygen
What pulmonary factors generally increase throughout pregnancy?
VT
Minute ventilation: DT increased myocardial O2 consumption, causes respiratory alkalosis - pH normalized via renal compensation
Changes with PaCO2 During Pregnancy
Increased serum progesterone increases respiratory center CO2 sensitivity, minute ventilation increases (40-50%)
PaCO2 decreases during gestation (~30mmHg around parturition)
Renal compensation leads to normal pH
Oxygen consumption increases 20%
* Due to developing fetus, placenta, uterine muscle, mammary tissue
Capacities Changes During Pregnancy
–FRC reduced DT cranial displacement of diaphragm: normally, FRC»_space;> CC
–Closing capacity unchanged: FRC reduction matches closing capacity, leading to atelectasis = prone to hypoxemia, hypoventilation induces hypoxemia more easily
Airway Changes During Pregnancy
Airway conductance increased, pulmonary resistance decreased by progesterone induced bronchodilation
FRC Changes During Labor
FRC reduces further DT increased pulmonary blood volume
* Small airway closure develops at end exhalation in 1/3 of humans
* Normally: FRC»_space;> CC
* Closing capacity remains unchanged: FRC reduction matches closing capacity, leading to atelectasis = prone to hypoxemia
Which capacities are unaltered during pregnancy?
TLC, VC, PaO2
Consequence of inhalant induction in pregnant patients?
Induction with inhalation agent more rapid DT decreased FRC, progesterone and endorphin levels in CNS reduce MAC
* MAC of isoflurane by up to 40%
* Greater CO, more drug taken up by blood, slower rise in [alveolar]
Pregnancy GI Effects: Decreased function?
–Delayed gastric emptying (displacement of stomach by uterus)
–Decreased motility (progesterone)
–Decreased LES: progesterone
Pregnancy GI Effects: Increased?
–Intragastric pressure, altered stomach position DT gravid uterus
–Increased gastrin production, more gastric acid secretions - progesterone
Consequences of GI Effects in Pregnancy?
High risk for regurgitation, aspiration
May present to ER with full stomachs
Risk of vomiting increased by hypotension, hypoxia, toxic reactions to LAs
Antiemetics: metoclopramide, H2 blocker, cerenia
Rapid airway control, cuffed ETT
Hepatic Changes with Pregnancy
–Minor alterations to function - normal biotransformation of drugs
–Total plasma protein increased DT increased blood vol, even though plasma protein concentrations slightly decreased
–ALP, ALT mildly increased
–PChE decreased - prolonged DOA sux
–Increased HBF
Renal Changes with Pregnancy
–Increased GFR, RBF - 50-60% by third trimester, remains so until 3mo post partum
–BUN/creatinine may be lower than normal - can be more difficult to determine renal dz
–Na, H2O balance unchanged
–Elsewhere: activation of RAAS - significant water, Na retention; decreased plasma osmolality
Causes of Decreased Uterine Blood Flow?
Maternal hypovolemia, hypotension
Uterine ctx
Caval compression
Anesthesia induced CV depression
Sympathetic blockade (LAs), increased SNS tone
Hypocapnia
Result: placental hypoperfusion, fetal hypoxia, acidosis, fetal distress
Uterine Blood Flow
Directly proportional to systemic perfusion pressure, inversely proportional total vascular resistance
Uterine BF entirely dependent on maternal CO, uterine perfusion pressure
o Increases dramatically in pregnancy, up to 10% of CO at end of pregnancy
o Uterine vascular resistance increased by contractions
Coagulation Changes with Pregnancy
hypercoagulable state (progesterone)
Increased plasma levels of VII, VIII, IX, X, XII, fibrinogen, vWF
Blood Work Changes Assoc with Pregnancy
Thrombocytopenia: increased platelet turnover, hemodilution
Leukocytosis (neutrophilia)
Decreased plasma proteins including albumin – hemodilution
Increased ALP – placental production
Specific Drug Metabolism Changes with Pregnancy
● Barbiturate biotransformation reduced in pregnancy
● Succinylcholine, procaine metabolism reduced DT PChE decreases
● Increased RBF, GFR increase excretion
● MAC reduced
MOA transfer of drugs across placenta?
DIFFUSION
▪ Low MW(<500Da), low protein binding, high lipid solubility, non-ionized diffuse quickest
● Most anesthetics diffuse quickly
Placental thickness decreases as gestation progresses: increase drug diffusion into fetus
Weak Acids
less ionized as pH decreases (barbiturates)
Weak Bases
more highly ionized at pH values less than pKa (opioids, LAs)
Drug Concentrations in the Fetus
Drug concentrations in umbilical vein greater than in fetal organs
o Up to 85% of umbilical blood initially passes through fetal liver
Drugs may get metabolized, sequestered in liver
Umbilical venous blood mixes with inferior vena cava - buffering drug concentration changes initially
Fetus Drug Metabolism
o Fetal microsomal enzymes not as active (longer drug half-lives)
o Fetal drug toxicity enhanced by fetal or maternal metabolism into toxic metabolites
Dog fetal liver: no fetal liver
Risks Assoc with Ax during the first trimester?
fetal teratogenesis, spontaneous abortion, fetal death
Risks Assoc with Anesthesia During Middle Trimester?
generally considered safest; spontaneous abortion, fetal death reported
Risks Assoc Anesthesia during Third Trimester?
carries risk of premature labor, fetal death
Which species lack fetal hgb?
Pigs, guinea pigs, rats, chickens, horses, cats, dogs, rabbits
