Physiologic Changes During Pregnancy Flashcards
Why does upper airway swelling occur during pregnancy?
Increased progesterone, estrogen and relaxin cause vascular engorgement and hyperemia.
Increased extracellular fluid volume
Change in Mallampati score during pregnancy
Increases
Risk of difficult/ failed intubation during pregnancy
Increases (up to 8x in full term pts)
Change in glottic opening during pregnancy
Narrowed
Change in airway equipment for pregnant patients
Short handled laryngoscope (Datta handle)
Downsized ETT (6.0 - 7.0)
Avoid nasal airways
How does lung/ diaphragmatic physiology change during pregnancy?
Ribs more horizontal d/t relaxin relaxing the ligaments of the ribcage
AP diameter of chest increases> lungs have more space
As uterus grows, diaphragm moves cephalad
How do lung volumes and capacities change during pregnancy?
Decrease in expiratory reserve volume and residual volume = decrease in functional residual capacity
FRC falls below closing capacity= airway closure during tidal breathing
No change in vital capacity and closing capacity
Total lung capacity decreases by 5%
How does progesterone affect breathing?
Respiratory stimulant
How does OxyHgb dissociation curve change in pregnancy?
Rightward shift (d/t increased P50)
Facilitates transfer to fetus
How do ABGs change during pregnancy?
Increased PaO2 (104-108 mmHg) d/t hyperventilation
Decreased PaCO2 (28-32 mmHg)
Decreased HCO3 (20 mmol/L)
No change in pH
How does minute ventilation change during pregnancy?
Increased (by 50%)
Vt increases by 40%
RR increases by 10%
How does oxygen consumption change in pregnancy?
Increases by 20% at term
Increases by 40% over prelabor value in the first stage of labor
Increases by 75% over prelabor value in the second stage of labor
When does cardiac output return to pre-labor values?
24-48 hours
When does cardiac output return to pre-pregnancy values?
~ 2 weeks
What percentage of cardiac output does the uterus recieve?
10%
By what percentage does cardiac output increase during pregnancy?
40%
How does SVR change during pregnancy?
Decreased d/t progesterone
Why does the MAP not change during pregnancy?
There is an increased blood volume but decreased SVR/ DBP = no net effect on MAP
By what mechanism does progesterone decrease SVR and PVR?
Increasing nitric oxide > vasodilation
Decreasing response to angiotensin and norepinephrine
How does pregnancy affect filling pressures?
There is no change in filling pressures in pregnancy until uterine contraction occurs > autotransfusion occurs > filling pressures increase
How does cardiac axis deviation change during pregnancy?
Diaphragm pushes cephalad > heart is pushed up and to the left > L axis deviation
What is the pathophysiology of aortocaval compression syndrome?
The gravid uterus compresses the vena cava and the aorta > decreased blood flow to the heart/ extremities/ uterus > fetal perfusion compromised/ mother loses consciousness
How is aortocaval compression prevented in pregnancy?
Elevate the mother’s right torso 15 degrees starting in the second trimester
How does intravascular volume change during pregnancy?
Increases by about 35%:
Plasma 45%
Erythrocyte 20%
What clotting factors increase during pregnancy?
1, 7, 8, 9, 10, 12
How does fibrin break down change during pregnancy?
Increases to compensate for the hypercoagulable state
Mother makes more clots, but breaks them down faster
How do PT/ PTT change during pregnancy?
They both decrease by up to 20%
Normal PT at term: 9.6-12.9 s
Normal PTT at term: 24.7- 35 s
What are causes of thrombocytopenia in pregnancy?
Gestational thrombocytopenia (hemodilutional and consumption) - most common
Hypertensive disorders
Idiopathic
How does MAC change during pregnancy?
Decreases by 30-40% beginning at 8-12 weeks d/t progesterone
How does response to local anesthetics change during pregnancy?
Increased sensitivity d/t progesterone
How do subarachnoid and epidural space volumes change during pregnancy?
Decrease d/t increase in volume of epidural vein and compression
How does gastrin change during pregnancy
Increase
How does the change in gastrin affect the pregnant patient?
Increase in gastric volume
Decrease in gastric pH
Why does lower esophageal sphincter tone decrease during pregnancy?
Increased progesterone
Increased estrogen
Cephalad displacement of the diaphragm
How does renal function change during pregnancy?
Increased cardiac output/ blood volume > GFR/ creatinine clearance/ glucose in urine all increase > creatinine and BUN/ renal absorption decrease
What is uterine blood flow in mL/min?
Up to 700-900 mL/min
How do changes in serum albumin affect anesthesia for pregnant patients?
Albumin decreases > increase in free fraction of highly protein- bound drugs
How does the change in pseudocholinesterase affect anesthesia for pregnant patients?
Pseudocholinesterase decreases in pregnancy, but there is not meaningful change in anesthesia approaches d/t this change
