Maternal Physiology Flashcards
1
Q
Generally speaking, how is maternal physiology different than normal physiology
A
- physiology different from baseline and continues to change through pregnancy
- differential diagnosis may be different
- lab value ranges may be different
- choice of radiologic studies may be affected
- 2nd patient to consider
2
Q
Total body water metabolism in pregnancy
A
- increase from 6.5-8L = 2 kg (expanded plasma by ~50%, more RBC by 20-30%, additional extravascular and intracellular fluid in uterus/breasts)
- chronic volume overload with active Na and water retention (changes in osmoregulation/RAAS)
- Total body water increases relate to weight gain, hemodilution, physiologic anemia of pregnancy, elevated cardiac output
- impaired volume expansion linked to increased risk of pre-eclampsia and impaired fetal growth/fetal growth restriction
3
Q
Osmoregulation in Pregnancy
A
- early alteration of arginine vasopressin secretion (plasma AVP unchanged due to placental inactivation)
- increased water retention > sodium retention. Additional 900 mEq Na retained but serum sodium drops 3-4mmol/l. Osmolarity decreases. These changes take place by 10 weeks gestation through 2-3 weeks post-partum
4
Q
RAAS system during pregnancy
A
(Renin-Angiotensin-Aldosterone system)
- Marked Increases in all components
- Early pregnancy changes cause decreased MAP, which triggers activation of plasma renin, angiotensinogen, angiotensin–all 4-5x higher than nonpregnant
- 2x inrease in aldosterone – increased Na retention and prevent loss
5
Q
Atrial Natriuretic Peptides/Brain Natriuretic peptides in pregnancy
A
- These are released by myocardium to maintain vascular hemostasis
- Both are elevated in physiologic/path stages of volume overload–can be used to screen for CHF outside pregnancy in symptomatic pts
- Many physiologic complaints of pregnancy mimic heart disease (i.e. dyspnea)
- ANP changes unclear–likely increases but still within nl range
- BNP increases mostly in 3rd trimester; highest in pregnancies with preeclampsia but to levels less than used to screen for CHF
6
Q
Cardiac changes
A
- increased plasma volume by 50%~ 1.2-1.3L, RBC mass by 20-30% –dilutional anemia
- BP progressively decreases until 22-24 weeks and returns to baseline at 36 weeks
- Decreased systemic vascular resistance– progesterone effect on smooth muscle and increased NO production
- Increased CO: mainly due to increase in stroke volume since HR only goes up 10-20 bpm in 3rd trimester
- Decreased Vascular resistance/BP: 2nd trimester. CO impacted by position. Greatest in left lateral position, avoid supine >20-24 weeks for IVC compression
- ventricular Hypertrophy/muscle mass
- increased preload due to increased venous return
- decreased afterload due to decreased vascular resistance
- Elevated: cardiac compliance, contractility, EDV (NO change in ESV),
7
Q
What is the association between pregant women who do prolonged standing work
A
Decreased birthweight–decreased CO while standing may be physiologic basis for this
8
Q
Regionalization of CO
A
increased CO not distributed evenly
- no change in brain/liver
- 50% increase in renal perfusion
- increased perfusion to: breasts, skin, uterus. flow to uterus about 740 ml/min at term (15% CO compared to 2%)
** increases in venous pressure and pressure on vena cava contribute to edema, varicose veins, hemorrhoids, and increased risk for DVT
9
Q
Cardiac assessment in pregnancy
A
PE:
- nl sinus rhythm; HR >100 may be abnl (mild tachy may not be path; 39% pregnant women tachy at rest vs 58% for obese)
- PMI displaced to left
- systolic ejection murmur on LSB in up to 96%
- Exaggerated aplit S1, less so with S2
- S3 common in ?; S4 rare
CXR:
- cardiothoracic ratio unchanged
- left heart border more straight
- heart position may be horizontal
- prominent pulmonary vasculature
EKG:
- mild left axis deviation
- non-specific ST-T wave changes; small Q and negative P in lead III
- increased premature atrial/ventricular contractions
10
Q
Clinical s/sx mimicking heart dz in pregnancy
A
Sxs:
- Dyspena
- Decreased exercise tolerance
- fatigue
- occasional orthopnea, syncope and chest discomfort
Signs:
- peripheral edema
- mild tachycardia
- JVD after midpregnancy
11
Q
Arrhythmias in pregnancy
A
- due to anatomic changes, heart closer to chest wall so more likely to notice palpitations
- increased premature atrial and ventricular beats
- if monitored in labor, almost all will have some type of arrhythmia (premature A/V/nodal complex, SA arrest, wandering atrial pacemaker, paroxysmal ventricular tachy, sinus tachy)
12
Q
Cardio changes during labor
A
- further increase in CO; highest 10-30 min after delivery
- due to pain (increased sympathetic stimmulation) and uterine autotransfusion (300-500 cc forced from uterus in each contraction, so increases venous return/preload/CO)
- valsalva in pushing creates wide fluctuation in BP and HR
- pts with significant cardiac dz should have careful hydration/fluid balance, early epidural to decrease pain and epi’s effects on BP/CO, assisted 2nd stage to shorten dangerous pd that can tip them into heart failure or arrhytmias
- For Cesarean delivery– major surgery, so significant fluid shifts and increased blood loss compared to vaginal delivery
13
Q
Postpartum CV changes
A
- acute increase in CO first hr due to decreased venocaval obstruction, autotransfusion from uterine circulation, mobilization of extra fluid
- acute loss of up to 500-1000 cc blood with nl delivery (Vaginal: nl EBL up to 500cc; Cesarean: nl EBL up to 1000 cc)
- anatomic/physiologic changes return to prepregnant baseline over weeks-months
14
Q
Considerations for valvular heart dz
A
- regurgitant lesions better tolerated than stenotic lesions during pregnancy
- many valvular dz pts will have deterioration in NYHA functional class, some will develop CHF, some will have adverse pregnancy outcomes like preterm birth/IUGR, stillbirth)
- women with AS- fixed SV and CO variation determined by HR. Bradycardia can cause hypotension, and excessive tachy can cause hypotension, syncope, and risk of MI due to decreased filling time. Severity defined by valve area and/or peak gradient (Mild: less than 36)
15
Q
Aortic stenosis in pregnancy
A
- at baseline keep preload adequate for CO
- in pregnancy, decreased afterload may lead to progression of disease
- avoid vasodilators
- 15-20% mortality in critical AS pts (CHF, syncope, cardiac arrest)
- If decompensation, consider early delivery
DURING LABOR:
- careful hydration/fluid balance
- early epidural
- assisted 2nd stage to shorten dangerous pd that can tip into HF or arrhythmia
