Lecture 14 - Renal Function during Pregnancy Flashcards
What abnormal lab values are actually normal during pregnancy?
- Hyponatremia
- Hypokalemia
- Low plasma [HCO3-] and PCO2
What normal lab values are actually abnormal during pregnancy?
- BUN => renal insufficiency
- Plasma creatinine => renal insufficiency
- Plasma urea => hyperuricemia
- BP => HT
What is preeclampsia?
Hypertensive disorder with proteinuria unique to human pregnancy
Changes in CO during pregnancy? Cause?
50% increase, peaks at midpregnancy and is sustained through delivery
Due to increase in both SV and HR
Describe volume retention during pregnancy. What does this cause? What to note?
- Weight gain averages 12.5 kg
- ~8-9L increase in TBW (4-7L increase in ECF)
- Cumulative retention of ~900mEq Na
- Plasma volume increased ~42% to 3.7L
Can cause edemas
Volume expansion sensed as normal
BP changes during pregnancy? What to note? Provide an explanation.
Falls by 10 mmHg (even more so in women with underlying HT) due to dramatic systemic vasodilation with increased arterial compliance and venous capacitance
This occurs despite increased CO, volume retention, and RAA system activation
Describe 3 renal structural changes during pregnancy.
- Kidney length increases ~1cm
- Dilated collecting system (mimics obstruction response)
- GFR and ERPF both increase ~35-85% (peak effect by late 1st, early 2nd trimester) and RVR decreases
Does GFR vary in normal women?
Yes, during the menstrual cycle
Changes in plasma creatinine during pregnancy?
Falls due to increased GFR and its clearance
Normal Pcr in pregnant woman?
0.5 mg %
Do the changes in GFR in pregnant women happen to pregnant women with renal disease?
YUP
What is the increase in GFR during pregnancy due to exactly?
Balanced vasodilation of the afferent and efferent arterioles to increase flow and keep glomerular hydrostatic pressure constant => increase in SNGFR
Due to increase in relaxin => it binds to the relaxin receptor on afferent and efferent arterioles => increases MMPs (matrix metalloproteases) activity => MMPs cleave endothelin precursor (normally a potent vasoconstrictor) => alternate form binds to endothelial tissue (B receptor) causing the release of NO in endothelial cells => vasodilation causing increase in GFR, increase in RPF, and decrease in myogenic reactivity
Major role of relaxin during pregnancy?
Hormone that relaxes the pelvic ligaments in preparation for delivery
Describe the 5 acid base and tubular adaptations during pregnancy.
- Minute ventilation increased ~50% due to progesterone, resulting in compensated primary respiratory alkalosis (pH ~7.44) => normal pCO2~30, normal HCO3~18-20
- Urine often alkaline due to bicarbonate leak
- Modest glucosuria and aminoaciduria due to increased filtered loads
- Decreased uric acid (~2.8-3.0), due to increased renal clearance
- Absorptive hypercalciuria due to increased calcitriol (i.e., active vitamin D)
Describe calcium balance in pregnant women. Timing?
Increased vitamin D is because the placenta has 1-alpha hydroxylase just like the kidney => increased Ca++ absorption in GIT (needed to build the fetal skeleton - 25g of calcium transferred to fetus over pregnancy) => total plasma calcium is actually low due to high volume (ionized is normal) => hypercalciruia
Happens during all 3 trimesters